fall, 2014 crn 71168 instructors: p. aderhold - rdarke -...
TRANSCRIPT
FALL, 2014
CRN 71168
Instructors: P. Aderhold
Bakersfield College
1801 Panorama Drive
Bakersfield, CA 93305
Engineering B45 Shear of Rubber Experiment
Lab Report
Introduction: Rubber has always been an interesting engineering material. Its elasticity is remarkable, while its use in vehicle tires requires other properties. Although originally a natural product, rubber became so important and in such demand that synthetic rubber was developed with the possibility of having special properties to suit the application. An important loading condition when deforming a material such as rubber is called shear. The strain associated with the tangential loading of shear deforms a body from a square cross-section to a parallelogram. If the body is homogeneous, isotropic, linear and elastic, there will be a constant proportionality between the magnitude of the applied shear stress and the associated shear strain. The shear stress, τ, is defined by force and area
τ =fA
where f = shearing load, and A = cross sectional area upon which the load acts. Below is an illustration of the geometric relationship between force and area. Shear strain, γ, is defined by the angular shape change of the body. Expressed in radians, the quantity is unitless. For a linear elastic solid, the relationship between shear stress and shear strain is
τ γ= G
where G = shear modulus (modulus of rigidity).
Material G (ksi) G (Pa) Material G (ksi) G (Pa) brass 6000 4.14 X 1010 epoxy 150 - 175 1.03 X 109 to
1.21 X 109 aluminum 3900 2.69 X 1010 nylon 100 - 150 6.90 X 108 to
1.03 X 109 steel 11500 7.93 X 1010 concrete 1500 1.03 X 1010
polyethylene 5 - 6.5 3.45 X 107 to 4.48 X 107
SiC 23000 1.59 X 1011
This experiment concentrates on the shear characteristics of rubber, which is used in anti-vibration mountings for machinery and the spring suspension of railway carriages. Rubber can withstand large shear deformation, especially in medium and soft grades of the material, which helps to absorb shock loading. Another condition examined in this experiment is creep. Creep is an increased tendency toward more strain and plastic deformation with no change in stress. Unlike metals or ceramics, over time in polymers, the force and stress do not change although the shape of the part continuously deforms. When unloaded, there is a remaining deformation. It can occur at room temperature, but the rate of creep increases with higher stresses and temperatures. Procedure: 1. The rubber shear apparatus consists of a block of medium grade rubber 150 x 75 x 25 mm size which has aluminum alloy strips bonded to the two long edges. One strip has two fixing holes enabling the assembly to be fixed to a rigid vertical surface. The bottom end of the other strip is drilled for a load hanger while the position of the top end is indicated by a small dial gauge. 2. Place the load hanger in position and zero the dial gauge. Add load to the hanger in 10 N increments reading the dial gauge at each load until the travel of the gauge is exceeded. When placing a new load on the hanger, allow 5 minutes for the dial to stabilize. 3. After each load is removed the rubber will not completely recover and the dial reading will not return to the initial value. Allow 2 minutes for the dial to stabilize. Measure the difference in the initial and “recovered” dial readings and record this as creep.1
Questions to be addressed in the lab report: 1. Record the load and deflection in a table. 2. In Excel (or other graphing software) plot a graph of deflection (y) versus load (x) and draw a best fit regression
line through the points. (You may use a calculator, Excel, or some other statistical software. Be sure to include the equation of the line and the coefficient of determination (R2) on the graph.) This implies a linear load-deformation relationship in the vertical plane.
3. Calculate the shear stress (in Pascals), shear strain (in mm/mm), and the modulus of rigidity (or shear modulus)
for each measurement using the following relationships:
G =τγ
where τ = loadarea
and
width block
deflection=γ
In your report, represent these values in a table with load, deflection, strain, stress, and modulus of rigidity. Be sure to show sample calculations. 4. Construct a graph of stress (y) versus strain (x) and draw a best fit regression line through the points. Include
the equation of the line and the coefficient of determination (R2) on the graph. 5. In order to obtain a single value of the shear modulus, you may average the shear modulus values for each
measurement. Compare this observed value to the accepted values for other materials in the table on the previous page.
1 Askeland, The Science of Engineering of Materials, 3rd Ed., pp. 489 – 490.
6. Were the results in #2 and #4 linear? Justify your answer.
7. What is the relationship between the regression model and the shear modulus found in #5?
8. Predict the deflection for a 130 N load. What would be the corresponding τ and γ? Show all calculations. Explain how you can predict this. 9. Construct a graph of creep (y) versus load (x) and comment on any linear relationship observed. Discuss any observations.
Engineering B45 Sand Sieve Analysis
Lab Report
Introduction:
A great many materials used by the engineer are comprised of an agglomeration of smaller units. Probably the most obvious example is that of concrete in which gravel, sand and cement are mixed together to form a monolithic (literally, one-stone) engineering material. The principle qualifications of aggregates for concrete are specified (ASTM C 33-55 T) as being clean, hard, tough, strong, durable and of the proper gradation. In general, a desirable gradation of aggregates is considered to be that combination of coarse and fine materials which produces maximum density, and thereby minimum voids, consistent with good workability of concrete and minimum cement requirement for the concrete of a given consistency. A uniformly sized material cannot be packed into a large container without considerable porosity. The largest packing factor possible for spheres is about 74%. This is to say that only 74% of the total space can be occupied by the spheres and the rest of the space exists as voids. For a uniformly sized material the packing factor is independent of the size. Packing factors can be increased by two methods. One is to use non-spherical particles. The packing factor for a pile of bricks, for example, can be nearly 100%. A second method for increasing the packing factor is to mix particle size. A mixture of sand and gravel has a greater packing factor than either one alone. The sand can fill the pore spaces between the gravel. The more space the engineer fills in concrete with sand and gravel, the less cement is required. This results in a decrease in the cost of the concrete.
If all the particles which are used in agglomerated materials were perfect spheres, the determination of the particle size would be a relatively simple matter. We would simply make a measurement of the diameter. In practice most particles vary considerably from perfect sphericity. However, the engineer still finds it desirable to have a measure of the particle size of sand and gravel. The gradation of an aggregate is determined by the method of sieve analysis by shaking a given quantity of the material through a series of sieves with standardized mesh openings. The mesh number is approximately the number of openings per lineal inch. Any aggregate mixture will be comprised of a range of mesh sizes. As a result, it is generally difficult to use one number to indicate the average size of an aggregate. This is illustrated in the following figure which shows the
percent of the aggregate which has been retained by each successively finer screen. In one case the particles are very closely graded (narrowly graded) and are essentially of one size. In the other case there is a wide variation in sizes (broadly graded). As a result, the engineer generally specifies the size distribution by listing the percentages retained on more than one screen.
The Bureau of Reclamation suggests the following gradation for sand to be used in mixing concrete.
Mesh # Cumulative % Retained 5 0 to 5 8 10 to 20 16 20 to 40 30 40 to 70 50 70 to 88 100 92 to 98
The percent retained in mesh 50 and 100 affects the workability of the concrete and the finish and surface texture of the concrete. For thin walls and smooth surfaces mesh 50 should retain at least 15% and mesh 100 should retain at least 3%.
Another measure used to grade aggregate is the fineness modulus, an index of the fineness or coarseness of the aggregate.
100percents cumulative of sum = Modulus Fineness
A fineness modulus equal to 6 would indicate that none of the aggregate fell to the pan and thus is very coarse. If the fineness modulus is less than one, then it follows that most of the aggregate fell to the pan and consequently is very fine. The Bureau of Reclamation requires a fineness modulus between 2.50 and 3.00 for the sand used in the construction of concrete.
Narrowly graded
Broadly graded
Procedure: 1. Weigh each sieve. 2. Weigh a dried sample of aggregate and record the weight (500 g + 25 g). 3. Arrange the sieves in order, with the sieve having the least number of mesh holes per inch (largest diameter openings) at the top and the pan at the bottom. 4. Pour the aggregate sample in the top sieve and cover. 5. Place the nest of sieves in a sieve shaker and shake for approximately 9 minutes. 6. Weigh each sieve and record the weight of the aggregate retained on each. 7. Repeat with remaining samples.
Questions to be addressed in the lab report:
1. Organize your data in the Sand Sieve Analysis Table stored in the Word document on Moodle. Discuss the data and calculations.
2. Calculate the fineness modulus for each sample--be sure to show a sample calculation. 3. For each sample, construct (a) a bar graph of percent retained aggregate weight for each mesh number and
(b) a plot of cumulative percent retained aggregate versus opening size in inches. Examples are shown below.
4. In your lab report be sure to discuss the physical characteristics of each aggregate sample, but specifically the sand that will be used for your concrete construction.
5. Address the following questions for each sample: Is the sample broadly or narrowly graded? Compare the fineness modulus to the Bureau of Reclamation standards. Compare the graphs to the ideal sand grading suggested by the Bureau of Reclamation.
0 5
10 15 20 25 30 35 40
14 20 28 35 48 65 100
Perc
ent
Wei
ght
Reta
ined
Mesh Number
Concrete Sand Aggregate Distribution
0 20 40 60 80
100 120
0 0.05
Cumulat
ive
Perc
ent
Weigh
t Re
tained
Opening Size (in)
Concrete Sand Cumulative Distribution
Concrete Sand I
Concrete Sand II
Engineering B45 Sand Sieve Analysis Table
Collected Data: (Note: Cumulative percent aggregate is the percent of total aggregate at and above the specified sieve number.)
Aggregate sample: Weight of aggregate =
Mesh No.
Opening Size in inches
Empty weight of
sieve
Weight of sieve after shaking
Aggregate weight
Percent aggregate
weight
Cumulative percent
aggregate #5 #8 #16 #30 #48 #100
Sum
Fineness Modulus =
Aggregate sample: Weight of aggregate =
Mesh No.
Opening Size in inches
Empty weight of
sieve
Weight of sieve after shaking
Aggregate weight
Percent aggregate
weight
Cumulative percent
aggregate #5 #8 #16 #30 #48 #100
Sum
Fineness Modulus =
Aggregate sample: Weight of aggregate =
Mesh No.
Opening Size in inches
Empty weight of
sieve
Weight of sieve after shaking
Aggregate weight
Percent aggregate
weight
Cumulative percent
aggregate #5 #8 #16 #30 #48 #100
Sum
Fineness Modulus =
Aggregate sample: Weight of aggregate =
Mesh No.
Opening Size in inches
Empty weight of
sieve
Weight of sieve after shaking
Aggregate weight
Percent aggregate
weight
Cumulative percent
aggregate #5 #8 #16 #30 #48 #100
Sum
Fineness Modulus =
Engineering B45 Identifying Plastics
General Instructions:
Listed below is a procedure and discussion for identifying unknown plastic samples using an opacity test, flexibility test, surface test, and burn test. Using the two KNOWN samples from the Resin Kit, fill out the flowchart and report your findings in the SA handout. Then repeat these procedures for the UNKNOWN plastic specimen provided by the lab instructor. Be sure to attach all three flow charts to your SA handout.
Procedure: Identifying an Unknown Plastic Specimen
Identifying Natural, Uncolored or Identifying a Colored Specimen Transparent Specimens
Special Considerations
Engineering B45 Identifying Plastics
Short Answer
Name: Date:
1. Carefully describe your observations for each of the four tests for the first known specimen chosen from the
Resin Kit. Be sure to identify the specimen and justify each outcome of the test. Known Specimen: Observations
Opacity Test
Flexibility Test
Surface Test
Burn Test
2. Carefully describe your observations for each of the four tests for the second known specimen chosen from the Resin Kit. Be sure to identify the specimen and justify each outcome of the test.
Known Specimen: Observations
Opacity Test
Flexibility Test
Surface Test
Burn Test
3. Carefully describe your observations for each of the four tests for the unknown specimen chosen from the Resin Kit. Be sure to justify each outcome of the test.
Unknown Specimen Observations
Opacity Test
Flexibility Test
Surface Test
Burn Test
4. Identify the Unknown Specimen below and describe the physical properties of this specimen. List items that
are made of this particular resin. This information can be found in the Resin Kit.
Identification
Unknown Specimen
Mechanical Properties
Items
Engineering B45 Corrosion in Metals
Introduction:
Corrosion may be defined as the deterioration of a material resulting from chemical attack by its environment. Most metals that we use in society were taken from the earth as an oxide, sulfide, carbonate, or silicate and went through a series of steps to reduce the metal. Corrosion can be thought of as the reverse of the extraction and production process, returning the metal back to its original state. Corrosion usually results in both a loss of metal by its dissolving and in the formation of a nonmetallic scale or film. It has been estimated that approximately 5% of an industrialized nation’s income is spent on corrosion prevention and the maintenance or replacement of products lost or weakened as a result of corrosion. This cost was estimated to be $150 billion in the United States alone. Corrosion also results in the loss of life and productivity due to car and airplane crashes and bridge and building repair.
Corrosion is nothing more than a bunch of chemical reactions—interactions of atoms involving an exchange of electrons. In one location, you see neutral metal atoms leave a few of their electrons behind and jump into the solution:
Fe(s) Fe2+ (aq) + 2e- (anode half reaction)
This type of chemical reaction, where something becomes more positive is called oxidation. You look to another location; there you may see groups of chemicals in the surrounding medium combining to take on extra electrons: ½ O2(aq) + H2O + 2e- 2OH- (aq) (cathode half reaction)
This is called reduction and it happens at the cathode. Both oxidation and reduction take place during corrosion. The oxidized material is the one that is corroded. Where both of these types of reactions take place we have a galvanic cell or galvanic corrosion. Fe2+
(aq) + 2OH- (aq) Fe(OH)2(s) (one component of rust)
As you can see, the oxidized electrode, or anode, dissolves. It is usually undesirable to have your engineering product dissolve in service so engineers go through great pains to prevent these chemical reactions. In order to prevent corrosion, we must first understand why it happens. The simplest answer to why corrosion takes place is that it wants to. The corroded state is more favorable in an energy sense. In fact, most materials have a “desire” to corrode. This desire is so great that you will usually find metals or elements in their “corroded” state, like iron oxide or copper oxide. On the next page in Figure 1 you’ll see that the electrons can flow from the anode through the wire to the cathode where they will be handed off to, in this case, the O2 + 2H2O.
If we were to sever the path for the electrons as shown in Figure 2, we could not continue our exchange of electrons and in fact, we would stop the corrosion process. Instead, we would measure an electrical potential across the severed path. The size of this potential would depend on the cathode and anode materials. A material that has a slight preference to lose its electrons will have a small negative potential and those with a strong tendency to shed its electrons will have a large negative potential (measured relative to the cathode material). In fact, it’s possible to measure a series of materials relative to a single cathode material and make a listing of their relative tendency to corrode. The cell shown below has a metal A attached to a voltmeter through the black, ground connection and metal B attached to the HI, red side. The surrounding solution is a 3-wt. % NaCl solution that is similar to saltwater.
A positive voltage will be displayed if the metal A is more likely to be oxidized than B. Little or no reaction should take place while the voltmeter is attached because the voltmeter measures voltage by having an infinite resistance, meaning no electrons can flow through the wires connecting the two metals. By connecting a resistor between the HI and LOW connections (i.e., the resistor is in parallel to the corrosion cell), current can flow and the corrosion reaction starts. The resistor lets electrons flow through the circuit. We can measure the current using Ohm’s law: I = V/R, where I is the current in amperes (A), V is the voltage in volts (V) and R is the resistance in ohms (). We
will be using 100-ohm resistors. So in this example the current would be .010 A or 10 mA.
To measure the corrosion rate we use the following equation, which is derived from Faraday’s equation:
Here m is the change in mass per second per square centimeter, I is the current in amperes, M is the molar mass in g/mole, n is the number of electrons in the half reaction (e.g., 2 for Zn → Zn+2 + 2e-), F is Faraday’s constant (96,500 C) and A is the electrode area in cm2.
nFAIMm =
Engineering B45 Corrosion in Metals
Short Answer
Name: Date:
Some chemical facts needed: Phenolphthalein is colorless in an acidic solution and pink in a basic solution. Potassium hexacyanoferrate (III) forms a dark colored (blue to green to red-brown) precipitate where iron has
been oxidized. The oxidation product for zinc is a white precipitate while the copper product is either black or green.
Mechanical stress (such as bending or cutting metal) will cause the volume affected to be more anodic than non-stressed regions. The stressed regions typically have smaller grains (metal crystals) and can absorb impurities that contribute to corrosion.
Procedure and Results:
Part I:
1. Prepare the following mixture and observe after several days. Place 40 ml of water into a beaker. Add 0.5 g of agar agar, 0.5 g of NaCl, 0.5 ml of phenolphthalein, and 0.5 ml of potassium hexacyanoferrate (III) (0.1 M K3Fe(CN)6) and stir with a stirring rod. Heat on a hot plate until the solution boils and the entire agar agar dissolves.
2. Prepare five nails as follows: leave first nail as is; bend the second nail in the center with pliers; nick the third
nail in the middle with a file; wrap a piece of copper wire tightly around the middle of the fourth nail; wrap a small piece of zinc tightly around the middle of the fifth nail. Place the five nails into a Petri dish with one inch between each nail.
3. Pour the hot solution over the nails, until they are completely submerged in the agar. If a nail shifts, adjust the
nail position with a stirring rod so you maintain their 1-inch separation. 4. Dispose of the leftover agar solution while it is still a liquid by pouring it into the proper container for agar
waste. 5. After several days, draw a diagram or take a picture of each nail. Identify the position of the cathode and anode
on the diagram for each nail: “As is” Nail; “Bent” Nail; “Nicked” Nail; “Copper-wrapped” Nail; “Zinc-wrapped” Nail.
Part II:
1. You will need to prepare about 1000 ml of a 3-wt. % NaCl solution in a large beaker. A 3-wt. % solution would have 30 g of solute and 970 g of solvent (or 970 ml of water). Please use the rock salt. You will also need a DVM, 2 red wires, 2 black wires, 4 alligator clips and the following electrodes; Graphite (fragile, like a pencil lead), Al foil, Ag, Cu, Fe, Mg, Sn, and Zn.
2. Clean each electrode sample with steel wool (skip cleaning the Al foil). 3. The graphite will be our reference electrode. It is connected with a red wire and alligator clip to the “HI” side
of the DVM. The test metal will be connected with a black wire and alligator clip to the “LOW” side. A
positive voltage means the metal is more likely to be oxidized in the salt water than the graphite electrode. Try and keep the same amount of graphite submerged for each metal and try and have the submerged surface area of each metal the same.
4. Wait at least 30 seconds after submerging the electrodes before recording the voltage for each metal. In the
table below list the name of each metal and the potential in Volts, listing the metal with the largest voltage (i.e., the greatest tendency to be oxidized) first and the metal with the smallest voltage last. Use your references (Askeland) to list the accepted rank of oxidation for each metal.
Metal Potential (V) Accepted Rank (List by name)
Part III:
This part of the experiment demonstrates the importance of the relative sizes of the anode and cathode areas in galvanic corrosion. Two metal strips of Zn and Cu will be used with the Zn connected to the black (anode) side. LARGE refers to an exposed area of 30 cm2 and SMALL refers to an exposed area of 0.5 cm2.
1. Suspend the LARGE Zn electrode and the SMALL Cu electrode in the 3-wt. % solution and measure the
voltage after 15 seconds. No galvanic corrosion should be occurring because the voltmeter is not allowing any current to flow.
2. Attach a 100-ohm resistor in parallel across the galvanic cell using a second set of red and black wires/alligator
clips plugged into the wires in the DVM and connected to the two sides of a resistor. In the table on the next
page, record the voltage versus time every 30 seconds until you get to a constant voltage (this should take 1 to 5 minutes).
Large Zn, Small Cu:
Time (s) Voltage (V)
3. Step 1 and 2 should be repeated using a LARGE Cu electrode and a SMALL Zn electrode. Small Zn, Large Cu:
Time (s) Voltage (V)
4. Using the values for the equilibrium current, molar mass of Zn, and anode area, calculate the mass loss/(s.cm2) for each sized anode. Current is calculated using I = V/R.
Potential without resistor
(V)
Equilibrium Potential (V)
Equilibrium Current (A)
Mass Loss/(area
time)
0.50 cm2 anode (Zn)
30 cm2 anode (Zn)
Ratio of Small Anode to Large
Anode Mass Loss
Sample Calculations:
5. Construct a plot of the corrosion current (y) versus time (x) for the LARGE Zn, SMALL Cu electrodes and for the LARGE Cu, SMALL Zn electrodes. (Please note: One plot with two curves.) Why do you observe different corrosion rates for the two cases?
Engineering B45 Recrystallization of Brass
Lab Report
Introduction: The usefulness of solid materials in engineering structures depends primarily on two mechanical properties of high strength and enough ductility to allow relaxation of stress concentrations without fracture. In specific cases, of course, factors such as dimensional stability, abrasion resistance, corrosion resistance, high impact strength, electrical or heat conductivity, or many other factors may assume primary importance. Hardness is a measure of the resistance of a material to permanent (plastic) deformation. Since tensile strength and hardness are both indicators of a metal’s resistance to deformation, they are roughly proportional. Conversions from one property to another have been found to be dependent on material type. A hardness measurement is much easier to perform than tensile strength and can be nondestructive (i.e., the small indentation may not reduce the use of an object). Because of this, hardness testing has found extensive application in industry as a tool for quality control of metal products. Hardness is not a simple property; it depends on a complex set of properties of the material. Furthermore, different kinds of hardness tests measure different properties. For example, one type of hardness test yields the same value for rubber and steel. Therefore the information gathered from hardness tests on any given material must be interpreted in the light of data gained from other more quantitative measures of mechanical properties, such as the tensile test. In the Rockwell test the depth of penetration of an indenter under an applied load is recorded automatically on a micrometer scale. The scale reads from 0 to 100, one unit corresponding to a penetration of 0.002 mm. To minimize the effect of surface irregularities the zero setting of the scale is made after a minor load of 10 kg is applied to set the indenter into the specimen. The increase in penetration due to application of a major load is then determined. The load and the design of the penetrator used depend on the kind of material under study. For hard materials a diamond (brale) indenter and a 150 kg major load are ordinarily used (Rockwell C scale). For softer materials a 1/16 “ steel ball penetrator and a 100 kg major load is commonly used (Rockwell B scale). A number of other scales are used for special purposes. For testing surface hardened materials or thin samples a superficial hardness tester that employs smaller loads is used. During cold-working processes, the grain of the metal becomes distorted and internal stresses are introduced into the metal. If the temperature of the cold-worked metal is now raised sufficiently, nucleation occurs and “seed” crystals form at the grain boundaries at points of maximum internal stress. This is called nucleation. The more severe the cold working and the greater the internal stress, the lower will be the temperature at which nucleation occurs for a given metal. The minimum temperature at which the reformation of the grain occurs is called the recrystallization temperature. At temperatures above the recrystallization temperature, the kinetic energy of the atoms on the edges of the distorted grains increases. This allows these edge atoms to move away and attach themselves to the newly formed nuclei which will then begin to grow into grains. This process continues until all the atoms of the original, distorted crystals have been transferred. Since, after severe cold working, more nuclei form than the number of original grains, the grain structure after recrystallization is usually finer than the original grain structure before cold working. Thus a degree of grain refinement occurs. In this experiment you will use hardness as a measure of strength to examine temperature effects on cartridge brass.
Procedure: 1. Prior to starting the lab today, you should have already removed the burrs by grinding from 5 brass specimens.
You should have also annealed four of the brass samples at different temperatures between 150 and 550°C in the lab furnace.
2. Determine the Rockwell B hardness for the five annealed brass samples and the untreated brass sample.
Average 3 trial measurements. Suppose the average hardness measurement is 51, you would record it as RB 51 since it is measured on the B scale. Record all these measurements with an appropriate error in the data table for this lab.
3. Plot the Rockwell B hardness (y) versus temperature (x) for the brass samples. Attach this graph to the back
of your lab. The temperature where there is a significant drop in hardness is the recrystallization temperature as shown in figure 6-29 below.
3. Two of the heat-treated brass samples (150o and 550o) are to be mounted, polished, etched, and examined with
the microscope. Grind each specimen and mount following the instructions shown in the metallographic room. After the final polishing step, examine the specimens using the metallurgical microscopes and note the presence of scratches, inclusions, pits, voids, etc. Focus with the lowest magnification first; then it will be easier to focus at higher magnification. Please be careful not to collide the microscope objective (the lens nearest the specimen) into the specimen. Repolish if large scratches or numerous scratches exist. Now etch the specimen using the appropriate etchant and etching time. Be careful not to etch the specimen too long. Examine the etched specimen under the microscope and note the changes that have occurred as a result of the etching. Include digital pictures of the specimens in your report.
Questions to be addressed in the lab report:
1. Include the data table, graph, and the digital pictures. Notate the accepted recrystallization temperature on the graph. Discuss the effect temperature has on hardness. How will this affect tensile strength?
2. Do you observe any important features, such as twinning? Describe. 3. Why was there a great change in the hardness of your brass samples? 4. Draw and describe the grains of a material for the recovery, recrystallization, and grain growth phases. 5. What are the main factors affecting the recrystallization temperature of a pure metal?
6. Why was etching needed to bring out the grain boundaries?
Engineering B45 Concrete
Lab Report
Introduction: Concrete is a mixture of sand and rock or similar inert material (aggregates) held together by a cementing material. Usually the cementing material is Portland cement, but sometimes binders such as asphalt or gypsum are used, in which case the concrete may be called asphaltic concrete or gypsum concrete. Properties of concrete are governed not only by the properties of its ingredients (cement, water, sand, and coarse aggregate) but also, to a great extent, by the relative proportions of these ingredients. The proportions must be so selected as to produce a concrete mixture of desired workability, strength, durability, and economy. The most common aggregates are gravel and crushed stone, although cinders, blast-furnace slag, burned shale, crushed brick, or other materials may be used because of availability, or to alter such characteristics of the concrete such as workability, density, appearance, or conductivity of heat or sound. Usually aggregate which passes a sieve with 0.187-inch openings (No. 4 sieve) is called fine aggregate, but that retained by a No. 4 sieve is coarse aggregate, although the division is purely arbitrary. If all the particles of aggregate are of the same size, or if too many fine particles are present, an excessive amount of cement paste will be required to produce a workable mixture; a range of sizes aids in the production of an economical mixture. The best concrete for a given use is usually the one which will provide the necessary strength and the desired workability at the lowest cost. Unless otherwise indicated, strength, as applied to concrete, refers to the ultimate compressive strength of the moist-cured concrete at the age of 28 days. Most concretes are batched to provide an ultimate compressive strength of 2500 to 4000 psi after 28 days. The figure below shows a typical strength curve of concrete with the passage of time.
The modulus of elasticity of concrete is about 1000 times the ultimate compressive strength. The strength of concrete depends chiefly on the water-cement ratio, with a low ratio producing a strong concrete. While only a small amount of water is required to complete the chemical reactions of setting concrete, more than this is used to make the concrete more workable. The workability of concrete is usually measured by its slump. The standard method of measuring slump consists of placing the freshly-mixed concrete in a mold in the form of a truncated cone, 12 inches high, 8 inches in diameter at the bottom, and 4 inches in diameter at the top. The concrete is placed in the slump cone in three layers, each layer rodded thoroughly to compact it. When filled, the mold is immediately withdrawn by lifting it gently, and the slump of the concrete is measured at the vertical distance from the top of the mass to its original 12 inch height. An increase in the amount of mixing water will increase the slump, but it will also decrease the strength and increase the tendency of the ingredients of the concrete to segregate unless more cement is added. Increasing the amount of cement paste increases the cost, so all three factors-strength, workability, and cost-are interrelated in a complex way.
Procedure: 1. Concrete mixtures are commonly given as volume ratios as cement: sand: gravel. You will make two concrete
mixtures at ratios given to you by the instructor. Calculate the volume of the mold and determine the volume of cement, fine aggregate (sand) and coarse aggregate (gravel) for your mix ratio. Make one mixture and fill the mold, then mix the second mixture.
2. From the density of the materials, determine the weight of the required materials. Verify your calculations with
the instructor. Show all calculations in your report. 3. Weigh out and mix the materials (Refer to ASTM C192). The mass of water used should be about 50 – 60% of
the cement mass. Record the mass of the cement, sand, gravel, and water (the mass of water used is approximately equal to the volume).
4. Record the type of cement of used: 5. Mix the dry ingredients and gradually add the water. You may not need to add the full amount of water
calculated. Be sure to use the gloves provided as you mix your concrete. When adding the water note the concrete’s cohesiveness – whether the concrete tends to hang together well or whether it tends to crumble readily – and the troweling workability – if the concrete works smoothly and with little effort when using a trowel. Continue to add water until you have a desirable consistency.
6. Perform the slump test (Refer to ASTM C143). Fill the slump mold 1/3 full and tamp with the tamping rod 25
times; add more concrete until 2/3 full and tamp an additional 25 times; fill completely, tamp 25 times and then top off. Do not tamp more than 25 times. Measure the height of the concrete after removing the slump mold. The slump is 12” (the height of the mold) minus the height of the concrete after removal of the mold. The greater the slump usually means the greater the workability. Your slump should be about 2 inches.
7. Be sure to measure and record the temperature of the concrete and the outside temperature. 8. Fill the molds, tamp 25 times, top off, and cover with a plastic bag to setup. 9. After a day or two, cut off the mold. Note any cracking or pores in the test samples. Put the concrete samples
in a bucket, spray the concrete with water, and cover the bucket tightly with plastic. 10. On the designated “concrete crush lab day,” perform the compression test according to ASTM C39. Questions to be addressed in the lab report: 1. Fill in the group data sheet posted in the lab and include this table in your report. 2. Your report should include all data related to the preparation of your concrete, the group data sheet, and any calculations
pertaining to these items. 3. Plot compressive strength (y) versus cure time (x) for the two mixtures (on one plot). Add a polynomial trend line for
both mixtures. 4. From the class results, comment on how the mix ratio, weight % water, curing time, water/cement ratio, temperature,
type of cement used and slump affect concrete’s compressive strength. What was the percent gain in strength between the 7 day and 28 day samples? What causes the difference? In addition, you need to note the fineness modulus of the concrete sand from the sand sieve analysis in rotation A.
5. Be sure to include your observations of the physical properties of the concrete mixtures.
6. How does the compressive strength of the samples compare to the expected compressive strength of cured concrete? If
different, explain why.
Engineering B45 Impact Testing of Polymers
Introduction: Materials sometimes display brittleness which precludes their use in a given design. Brittleness is a property characterized by fracturing with low energy under impact. Ductility is the property which allows a reduction in cross sectional area without fracture (allows plastic deformation). “The energy required to break a material during impact testing (i.e. impact toughness) is not always related to the tensile toughness (i.e. the area contained under the true stress-true strain curve).”1 A tough steel is generally ductile and requires 100 ft-lbs of energy to cause failure. A brittle steel does not deform very much during failure and requires less than 15 ft-lbs energy to cause failure. Characterizing the toughness of a material is done in several ways. The most common method is the notched-bar impact test for which two types of specimens prevail, Charpy and Izod. By subjecting a specimen to an impact load, it will fail if the load exceeds the breaking strength of the material. By using a swinging pendulum to impart the load, the energy required to fracture the specimen can be calculated by observing the height the pendulum swings after fracture.
This test has been used almost exclusively with BCC crystalline materials. These materials show a transition from ductile to brittle with temperature as shown in the diagram on the following page. This means that at low temperatures the fracture energy is low. Very often BCC materials are ductile until they are heat treated.
As with metals, polymers may exhibit ductile or brittle behavior under impact loading conditions, depending on the temperature, specimen size, strain rate (The rate at which a material is deformed.), and mode of loading. Both crystalline and amorphous (noncrystalline) polymers are brittle at low temperatures, and both have relatively low impact strengths. However, they experience a ductile-to-brittle transition over a relatively narrow temperature range. Of course, impact strength undergoes a gradual decrease at still higher temperatures as the polymer begins to soften. Ordinarily, the two impact characteristics most sought after are a high impact strength at the ambient temperature and a ductile-to-brittle transition temperature (DBTT) that lies below room temperature. “In polymeric materials, the DBTT is related closely to the glass-transition temperature (GTT) and for all practical purposes is treated as the same.” 1 The transition temperature for a polymer is noted in the following illustration.
______________________________________________________________________________________
1Askeland, The Science of Engineering of Materials, 6th Ed., p.228-229.
Materials: Charpy notched specimens of the four polymers described below.
Acrylic Nylon Polyethylene HD PVC Major Application
Characteristics Outstanding light transmission and
resistance to weathering; only fair mechanical
properties
Good mechanical strength, abrasion
resistance, and toughness; low coefficient of
friction; absorbs water and some
other liquids
Chemically resistant, and
electrically insulating; tough and relatively low
coefficient of friction; low
strength and poor resistance to weathering
Typical Applications Lenses, transparent aircraft enclosures,
drafting equipment,
outdoor signs
Bearings, gears, cams, bushings,
handles, and jacketing for wires
and cables
Flexible bottles, toys, tumblers,
battery parts, ice trays, film
wrapping materials
Pipe, valves, fittings, floor tile, wire insulation,
vinyl automobile roofs
Tensile Strength (psi) 12000 12000 5500 9000 % Elongation 5 300 130 100
Elastic Modulus (psi) 450000 500000 180000 600000 Impact Energy (Izod)
(ft.lb)
0.5 1
1-12
1
Rockwell Hardness (R) 130 121 40 110 Glass Transition
Temperature (oC)
90-105
50
-120
87
Note: The glass transition temperature (GTT) is the temperature below which the amorphous polymer assumes a rigid glassy structure and the failure mode changes from ductile to brittle. We expect to see a sudden drop in impact strength at the GTT.
Engineering B45 Impact Testing of Polymers
Short Answer
Name: Date: Safety Precautions: 1. Wear safety goggles. 2. Make sure the area is clear before allowing the pendulum on the Impact Tester to swing. Pieces can fly a
fair distance. 3. Be careful inserting and removing specimens from the boiling water. Procedure: 1. Turn on the Tinius-Olsen Impact Testing machine by flipping the switch at the back of the Impact Display. 2. When beginning a set of tests, always calibrate the machine following the instructions provided under the
calibration menu. 3. Select 5 PVC specimens, measure the width of each, and record the measurements on the data sheet. 4. Latch the pendulum. 5. Place the specimen on the striking tups with the notch facing away from the hammer strike. Center the
specimen using the setting gage. 6. Follow the instructions outlined in the test menu. 7. Before releasing the pendulum, make sure the area around the Impact Tester is clear and team members are
wearing safety glasses. 8. Record the breaking energy (BE), impact strength (S1), and the type of break on your data sheet. Label the
specimen with a pen. Draw an outline of the break on a piece of paper for your lab report or take a picture with the digital camera. The objective is to clearly identify/describe the type of break and texture of the surfaces.
9. Repeat steps 4 - 8 with specimens of the same polymer at four additional temperatures: ice water mixture approx 0 oC room temperature approx 20 oC (already did this one) hot water bath approx 45-50 oC hot water bath approx 90 oC boiling water approx 100 oC
Soak your specimens 20 minutes in the appropriate baths. If the specimens are transferred rapidly to the machine, it can be assumed that the temperatures at which they are broken are those of the baths in which they have been held.
10. Use two Nylon 101 specimens and choose two temperatures at which to impact test. Make your choice in
such a way that you may be able to bracket the glass transition temperature. Follow the procedure outlined above in steps 4 - 8 and complete the data sheet.
Data Sheet Material: PVC
Width
Temperature
Impact Energy (ft.lb)
Impact Strength (ft.lb/in)
Break Type
Surface
Material: Nylon 101
Width
Temperature
Impact Energy (ft.lb)
Impact Strength (ft.lb/in)
Break Type
Surface
1. Plot the impact strength (y) of the PVC polymeric material vs. its temperature (x). Mark the GTT as a
vertical line on the graph. Attach this graph to the back of this report. 2. Compare the impact strengths of the two materials. Do the materials react (ductile/brittle) as expected
based on the expected GTT? Explain. 3. Describe the surfaces of each break and the break type of each specimen. How does each break indicate the
brittleness/ductility?
4. Using the graph below, discuss the yield strength, ductility, and brittleness of material A and material B. 5. Using the figure shown below, discuss how the temperature affects the impact strength and the ductile to
brittle transition of each of the three materials.
Engineering B45 Compression Anisotropy Test for Wood
Introduction: Wood is the most widely used construction material in the United States and it is probably the oldest. Our forests are full of wood. Figure 1 shows how its annual production exceeds all other engineering materials used in the US. Wood is used for the construction of furniture, houses, buildings, bridges, airplanes, etc. and it is also used to make composite materials such as plywood, particleboard, and paper. Figure 1. Competition of six major materials produced in the United States.i While relatively weak compared to other materials, Table 1 shows that on a per unit weight basis, wood has similar strength. With the exceptions of woods used for expensive furniture or decoration, wood has the advantage of being considerably cheaper than other materials and it has a pleasant, “organic” appearance. It has the disadvantages of being subject to fire and various forms of biological attack such as mold and termites. Wood may be considered to be a composite material consisting of strong, flexible cellulose fibers surrounded by a stiffer, shorter polymer called lignin. Because it is a naturally occurring material, wood contains flaws (such as knots and cracks) which limit its strength to less than that expected for a “perfect” piece of wood. Because of the way trees grow; wood is remarkably anisotropic (different properties in different directions). The bulk mechanical properties of most materials are independent of specimen orientation, (i.e., they are isotropic). Wood’s mechanical properties may vary by over a factor of 20 when measured in different directions. Your textbook defines the different directions in wood. In this experiment we will be measuring the compressive strength of two types of wood in two directions. One compression test will have the platens parallel to the wood grain. This will measure the compressive strength in the radial direction. The second compression test will measure the compressive strength in the longitudinal direction by having the platens perpendicular to the wood grain. The Tinius-Olsen H50K-5 Universal Testing machine (UTM) configured with the 50 kN Load Cell and two compression platens will be used. With digital calipers, you will measure the thickness and width (in) on the specimen. The product of this gives you the initial cross-sectional area, A0, of the sample before the test. You will need to measure the initial length, L0, of the specimen as well. The UTM will provide a plot of crosshead distance on the x-axis and load (or F for force) in lbf on the y-axis. You can convert these load-deflection points to stress-strain points by determining the Engineering stress and Engineering strain as shown on the next page. i Smith, W. F., Foundations of Materials Science and Engineering, 2nd Edition, McGraw-Hill Inc., 1993, p. 11.
Engineering Stress: Engineering Strain:
The following is a typical stress-strain curve for a wood specimen that is produced by a compression test. The stress corresponding to the maximum load sustained by the specimen prior to failure is the compressive strength. The modulus of compressibility is the slope of the initial linear incline on the graph.
0 100 200 300 400 500 600 700
0 0.05 0.1 0.15
Stre
ss (p
si)
Strain (in/in)
Wood Compression on California Pine
0AF
=σ0
f0
L
LL −=ε
Engineering B45 Compression Anisotropy Test for Wood
Short Answer
Name: Date: Procedure & Results:
1. Obtain two wood samples from instructor. You should note the type of wood.
2. Weigh to the nearest milligram and convert to pounds, measure the three dimensions in inches using the Vernier Caliper, and count the rings/inch on both specimens. To count the number of rings per inch, draw a line perpendicular to the rings and count. Calculate the density--Show all work in the table below.
Radial Specimen Longitudinal Specimen
Dimensions (in)
Number of rings/inch
Mass (lbs)
Density (lbs/in3)
Length after Compression
(in)
3. While the UTM and printer are turned off, attach the printer to the UTM.
4. If needed, adjust the position stops along the left rail, up or down so the top tool will not collide with the
bottom tool.
5. Turn the UTM on. Review the menu selection flow chart.
6. Before testing the first sample, use option 7 and then 3 to clear previous results. This is the only time you will clear results.
7. Select option 5 in the main menu to enter the identifiers for your group.
8. In option 7, enter 2 (Program) and then set 1 to Stress. In option 9, enter sample thickness and width.
9. Select option 3 to set the auto return setup to off.
10. Place your wood sample on the bottom platen. Adjust the position of the top platen using the up and down buttons. You might want to use an intermediate speed, (option 1) of say 0.1 inches/min. to get the platens just touching the wood sample. Move the top platen down until the display has just started registering a load. Using a slow speed, you can raise the platen until you have approximately a zero load. Using the F keys at the top, zero the force, extension, and auxiliary values and then press 6 to toggle to the graphic display. Use option 1 to set the test speed (0.01 inches/min.).
11. Now look at your panel display to check your previous selections by selecting option 6 from the main menu.
This is a toggle switch that toggles between the panel and graphic display. On the panel display, check the test speed (0.01 in/min.), thickness, width and auto return. You must be in the graphic display in order to get a printout of your results.
12. Select test mode, put on your safety goggles, and begin the test by depressing the down arrow.
13. Once the wood sample breaks, press the stop button (between the up and down arrows). Use option 1 to
reset to a faster speed and move the top platen using the up arrow. Remove the wood.
14. Include a photograph of the failed wood sample (labeled as radial or longitudinal) and use the ASTM D143 standard to describe the type of failure.
15. Print copies of the graph by pressing F4. You should print one copy per lab partner. Be sure to attach the
graph to your report.
16. Repeat this test with the other wood sample.
17. From your load-deflection curve, calculate the modulus of compressibility, compressive strength (psi), and percent compression for each test. Label points used for the modulus of compressibility. Show all equations used and calculations in the table below.
Radial Longitudinal
Modulus of Compressibility (psi)
Compressive Strength (psi)
% Compression
18. How do the radial and longitudinal compressive strengths compare (ratio or percent difference)? Why do they differ?
19. Using your references, calculate the percent error in your observed compressive strength and the accepted compressive strength of the wood specimens.
20. Using your resulting compressive strength, compute the maximum load in pounds that could be supported by a 4” X 4” post of each wood type. Show all equations used and calculations.
Radial: Longitudinal:
Engineering B45 The Tensile and Three-Point Flexure Test for Materials
Lab Report Introduction: When external forces act on a solid member, deformation of the member occurs until internal forces are built up within it, which are just sufficient to balance the external load. The deformation may be almost undetectable or it may be large resulting in marked changes in shape of the member; it may reach a constant value for a given applied load or it may continue to increase under a constant load. If the load is removed the deformation may be completely recovered, the member returning to its original shape or it may occur over a period of time. Elastic deformations are those that recover completely and almost instantaneously upon removal of the force producing them. Non-recoverable deformations are referred to as plastic deformations and slowly recoverable deformations are anelastic. The stress and strain properties of a material are generally used in engineering design rather than using load and elongation. By using stress and strain properties of materials, it is possible to design parts and predict their response to loads without having to actually test the part. Plastic and elastic properties of a material are often determined by means of a tensile (pulling) test. From a tensile test a stress versus strain curve may be obtained for a particular material. In this experiment, we will be measuring some mechanical properties of aluminum and soda-lime glass. We will be performing a tensile test of the aluminum and a three-point flexure test of the glass. The Tinius-Olsen H50K-5 Universal Testing machine (UTM) will be used for both tests on the two materials. This machine has a maximum load capacity of 50 kN or 11,250 lbf, which is plenty for pulling apart our metal samples and for breaking a glass rod. The tensile test and the three-point flexure test use different tools for the test. Whichever tool is on the UTM will be the first test performed. It is strongly emphasized that you will need the instructors' help to guide you on changing tools and on the setup of the UTM. This is a new and expensive piece of equipment and we need it to last a long time. Tensile Test: In our tensile test, a metal specimen is held in grips attached to the bottom and the crosshead of the machine. The crosshead slowly moves up, putting a tensile stress on the sample. The instrument measures the load versus elongation in the sample. The specimen will be stretched until it fractures. With digital calipers, we will measure the thickness and width (in.) on the specimen. The product of this gives you the initial cross-sectional area, (A0) of the sample before the test. You will need to measure and mark the length of the inner part of the specimen. This is L0, the original gage distance between gage marks. The instrument will provide a plot of crosshead distance on the x-axis and load (or F for force) in lbf on the y-axis. You can convert and graph a stress-strain curve by determining the Engineering stress and Engineering strain.
Engineering Stress: Engineering Strain:
0AF
=σ
o
of
LLL −
=ε
The following is a typical stress-strain curve for a hot-rolled, low carbon steel specimen that is produced by a tensile test.
Indicated on the figure are a number of important parameters: The yield point indicates the onset of plastic deformation. The yield strength is the stress corresponding to the onset of plastic deformation. Some steels exhibit an upper and lower yield strength. The stress corresponding to the maximum load sustained by the specimen prior to fracture is the tensile strength. The fracture point is where the material fractures. Once the yield point has been exceeded, the total strain at any point along the curve is partly elastic and partly plastic. For metals other than hot rolled, low carbon steels, the following stress-strain curve is typical.
Note that this curve does not have the pronounced yield point indicated on the previous curve. For curves such as this the yield point is generally taken as the point of intersection of the curve and a line drawn parallel to the initial portion of the curve and intersecting the strain axis at 0.2% strain. The straight-line segment of the stress-strain curve is the elastic region where stress is proportional to strain. The slope of this line is called the Modulus of Elasticity, E. The larger the modulus of elasticity, the less deflection or strain for a given stress in the material. The modulus of elasticity is found by taking any value on the straight-line segment of the stress-strain curve and dividing it by the corresponding value of the strain. (Note the point must be chosen in the elastic region.) The amount of strain that a material can withstand before failure is one indication of the ductility, or deformability,
of a material. Ductility is a measure of a material’s ability to be easily formed into useful shapes. With a tensile specimen the ductility is measured from the material elongation and its reduction in area. Elongation is the average plastic strain at the time of fracture and is calculated as: Reduction in area is calculated as: Flexure Test: When a material is brittle, tensile testing can be difficult and yield poor results. Therefore, a three-point flexure (or bend) test can be used to obtain values that correlate to the tensile strength of the specimen. Two points support the material, while one point applies a load to the top of the specimen at a distance halfway from either support. At the point of loading, the top of the specimen is placed in a state of compression, whereas the bottom surface is in tension. Stress is computed from the specimen thickness, the bending moment, and the moment of inertia of the cross section. The maximum tensile stress exists at the bottom surface of the specimen directly below the point of load application. The stress at fracture using this flexure test is known as the flexural strength or modulus of rupture. The stress-strain graph below describes the fracture behavior for aluminum oxide and glass, while the accompanying table compares flexural strength to the modulus of elasticity for several brittle materials. In this experiment, you will determine the flexural strength of a glass rod. The flexural strength that corresponds to a circular cross-section is where F = applied load L = distance between the supports R = radius of the circular cross-section
3RFLπ
=σ
( )100L
LLElongation %
0
0f
−=
( )100A
AA Areain Reduction %
0
f0
−=
Procedure: 1. The instructor will tell you, based on the tools attached to the UTM, which test you will do first. Changing
tools requires the UTM be turned off. (The UTM will not recognize a new load cell unless it is turned off.) The printer should also be attached while the UTM is off.
2. The tensile test uses the 50 kN (10k lbf) Load Cell and the wedge grips. The flexure test uses the 5 kN Load Cell and the three-point flexure tools.
3. Adjust the position stop along the left rail, up or down, to prevent the top tool from colliding with the bottom tool.
Tensile Test: 4. Turn the UTM on. A menu selections flow chart is posted next to the UTM. 5. From the main menu, select option 1 to change the speed. If you need to move the crosshead a large distance,
(several inches), you will want a fast speed (5 in/min.). Otherwise, the actual testing speed selected will depend on the type of test conducted.
6. Select option 5 in the main menu to enter the identifiers for your group. 7. Measure the thickness, width, and length of the specimen with a digital caliper. This will be entered in option 9
of the main menu. Draw two marks across the length of the narrow part of the specimen about 2 inches apart and measure this length, (L0). After fracture this new, longer length will be Lf.
8. Place your specimen in the Wedge Grips. Adjust the position of the wedge grips using the up and down buttons. Hand-tighten the wedge grips.
9. In option 7, change Results to Stress. In option 9, enter sample thickness and width. In option 1, set the speed to 0.08 in/min.
10. Select option 3 to set the auto return setup to off. 11. Now look at your panel display to check your previous selections by selecting option 6 from the main menu.
This is a toggle switch that toggles between the panel and graphic display. On the panel display, check the test speed (0.08 in/min.), thickness, width and auto return.
12. Using the F function keys at the top of the panel, zero the force and extension values and then press 6 to toggle to the graphic display.
13. Select test mode, put the Plexiglas shield up, put on your safety goggles, and begin the test by depressing the up arrow.
14. Once the specimen breaks, press the stop button (between the up and down arrows). Remove the specimen from the grips. Piece together the two parts of the sample and measure the distance between the gage marks (Lf), and the thickness and width at the fracture point.
15. Print copies of the graph by pressing F4. You should print one copy per lab partner. Flexure Test: 16. Turn the UTM on. 17. Measure the diameter of the glass rod with digital calipers and record. 18. In option 7, change Results to Force. 19. Select option 3 to set the auto return setup to stop. 20. Now look at your panel display to check your previous selections by selecting option 6 from the main menu.
This is a toggle switch that toggles between the panel and graphic display. 21. With digital calipers, measure the distance in inches between the top of each support. Then place the specimen
on the flexure supports. 22. Depress the down button to move the load tool close to the specimen. Be sure your speed is set at 0.002
in/min. You may want to continue until a force registers in the panel display and then back it off to a value close to zero force.
23. Zero the force and extension values and then toggle to the graphic display. 24. Select the test mode, put the Plexiglas shield up, and begin the test by depressing the down arrow. 25. Once the glass rod breaks, the UTM should stop deflection. Print copies of the graph by pressing F4. You
should print one copy per lab partner.
Questions to be addressed in the lab report: Tensile: 1. Include a table with all initial and final measurements.
2. Include a copy of the load vs. deflection curve with the report. On the load curve for the tensile test, clearly
label the 0.2% offset yield point, tensile strength, and fracture point.
3. Using data from the load curve for the tensile test, calculate the yield strength and Young’s Modulus. Label the points used for calculating Young’s Modulus. Include equations used and sample calculations. Tabulate your results (i.e., list in a table.).
4. Using the load at the time of failure and the final cross sectional area, calculate the “true stress” for this sample
at the time of failure. 5. From the distance between the gage marks and the thickness and width at fracture, calculate the percent
elongation and percent reduction in area. 6. Discuss the reaction of the metal to tensile stress (physical changes during the test). Did the sample appear to
be more ductile or brittle? Explain. Describe the type of fracture. 7. Photograph the fracture zone and include in your report as further evidence of the type of fracture. 8. Compare the tensile strength and Young’s modulus with accepted values (be sure to list the accepted values).
Calculate percent error. Flexure: 1. Comment on any observations about physical changes in the glass rod during this test. Did the sample appear to
be more ductile or brittle? Explain. Describe the type of fracture. 2. Calculate the flexural strength and compare to the tabulated value for glass. Find the percent error. Include
equations used and sample calculations. 3. Include a copy of the load vs. deflection graph in your report. 4. Explain when and why flexure tests are used rather than tensile tests?
Engineering B45 Hardenability of Steel
Lab Report
Introduction: When steel is austenized (heated at a high enough temperature so that the steel is homogenous austenite) and then water-quenched quickly, martensite is easily formed. The alloy composition of a steel alloy will affect the ability of the alloy to transform to martensite for a given quenching treatment. Generally, most alloying elements delay the formation of softer microstructures and allow the higher hardness structures to form at lower temperatures. The measure of this ability of an alloy to be hardened by the formation of martensite as a result of a given heat treatment is called "hardenability." Hardenability should not be confused with hardness, which is a measure of the resistance to indentation. In contrast, hardenability is a qualitative measure of the rate at which hardness diminishes with distance into the interior of a specimen. A steel alloy that has a high hardenability is one that hardens (or forms martensite), not only at the surface, but throughout the interior of the specimen. In steel designations, the first two digits identify the alloy elements and the last two or three give the carbon content. A 1045 steel is a plain carbon steel with 0.45% C and a 4140 steel is an alloy steel with Chromium and Molybdenum added and 0.40% C. The Jominy Test is a standard quenching procedure used to determine the hardenability of steel. In this procedure all factors that may affect the depth of hardening, except for alloy composition, are maintained constant. A cylindrical specimen is heated at an austenizing temperature for sufficient time for the austenite phase to form. Upon removal from the furnace, the bottom of the specimen is quenched by a jet of water at a specified flow rate and temperature (see figure below).
Consequently, the cooling rate is a maximum at the quenched end and decreases with distance from the quenched end. After the specimen has cooled to room temperature, a shallow flat is ground and Rockwell hardness measurements are made every sixteenth of an inch for a set distance along the ground flat. The graph of the RC measurements versus the distance from the quenched end is called a hardenability curve. The following graph is an example of experimental hardness measurements for 1045 and 4140 steels.
The quenched end is cooled most rapidly and exhibits the maximum hardness, with 100% martensite formed for most steels. Not only does the cooling rate decrease with distance, but the hardness also decreases. A steel that is highly hardenable will retain large hardness values for relatively long distances, whereas a low hardenable steel will not. Each steel alloy has its own unique hardenability curve. Procedure: 1. Turn the furnace on and set at a temperature of 927 oC. When the furnace reaches the desired temperature,
place two jominy specimens, one plain carbon steel and one alloy, in the furnace. Be sure to place the specimens where they are standing up. Heat for at least 45 minutes.
2. While the specimens are heating, set up the jominy tank by attaching the hose to the faucet and directing the
outlet above the sink. Adjust the flow rate so that the stream of water rises to a free height of 2 1/2" above the 1/2" orifice.
3. When ready to remove the first specimen, very carefully grab the upper portion of the specimen with the
tips of the tongs, walk slowly to the jominy tank, and drop the specimen into the fixture. Quench the end of this specimen for 15 minutes.
4. After the quenching time is complete, remove the specimen from the jominy fixture and quench in a bucket
of water. 5. Repeat steps 3 & 4 for the second specimen. 6. Grind a flat line along one edge of the bar approximately 0.015" deep and 0.282" wide. 7. Calibrate the Rockwell tester using the steel testing block. Remove the flat anvil and install the jominy
fixture. Place your specimen in this fixture and measure the Rockwell hardness. Record your results on the attached data sheet. Measure only one measurement per distance increment. You should have 32 measurements for both specimens.
8. Repeat steps 6 & 7 for the second specimen.
0
10
20
30
40
50
60
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Roc
kwel
l C H
ardn
ess
Distance (1/16 in.)
Hardenability of Steel
1045 Steel
Questions to be addressed in the Lab Report: 1. Be sure to type your table of measurements in the “findings” section of your report. 2. Construct one graph of both hardenability curves for each specimen. 3. Discuss and compare the hardenability of the two specimens. 4. Discuss the difference between hardenability and hardness? 5. What influence does the presence of alloying elements (other than carbon) have on the shape of the
hardenability curve? Explain this effect including a complete description of the composition of the alloy specimen (including percentages).
References: 1. The Science and Engineering of Materials, 3rd Ed., by Donald R. Askeland, pp. 353-356. 2. ASTM A255
Engineering B45 Hardenability of Steel
Data Sheet
Steel Designation: Steel Designation: Sixteenths of an inch RC RC
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Engineering B45 Thermistors
Introduction: A thermistor is a thermally sensitive resistor, an electronic component that exhibits a large change in resistance as temperature changes. PTC thermistors are typically manufactured from barium titanate and have a large positive temperature coefficient of resistance, i.e., as temperature increases, resistance increases. This type of thermistor is best used in applications where a drastic change in resistance is required over a narrow temperature range. Some typical applications include over temperature protection, over current protectors, self-regulating heaters, and single phase motor starting. NTC thermistors are manufactured from metal oxides such as manganese, nickel, cobalt, copper, nickel and titanium and have a large negative temperature coefficient of resistance, i.e., as temperature increases, resistance decreases. This type of thermistor is best used in applications where a continuous change of resistance is required over a wide temperature range. Because NTC thermistors have a high degree of sensitivity along with mechanical, thermal and electrical stability they are extensively used in temperature measurement and control, temperature compensation, surge suppression and fluid flow measurement. The fabrication of NTC thermistors begins with a mixture of two or more metal oxide powders combined with suitable binders. This mixture is formed to a desired geometry, dried, and sintered at elevated temperatures. Commercial NTC thermistors can be classified into two major groups—bead type thermistors and metallized surface contact thermistors. All of the bead type thermistors have platinum alloy lead wires which are directly sintered into the ceramic body. Bead type thermistors include bare beads, glass-coated beads, ruggedized beads, and glass probes. The metallized surface contact thermistors are available with radial or axial leads as well as without leads. Metallized surface contact thermistors include disks, chips, rods, and washers. The most stable and accurate thermistors available are those which are hermetically sealed in glass.
Engineering B45 Thermistors Short Answer
Name: Date:
Procedure: 1. Attach the digital multimeter to each of the leads of the KNOWN (20 k) thermistor. Set up a stand and
clamp in which to hold the thermistor. Use an appropriate scale on the digital multimeter to read about 1 - 2 k. (check with instructor)
2. Measure the resistance and temperature beginning at room temperature and for each 5oC temperature rise to
about 85oC. Record these measurements on the following data sheet.
KNOWN Thermistor UNKNOWN Thermistor Temp (oC) Resistance (k) Temp (oC) Resistance (k)
3. Graph resistance (y) vs. temperature (oC) (x) for this thermistor. 4. Fit an exponential model to the data using Trendline in Excel. Print this regression equation along with the R2
value on your graph. Attach this graph to your report. 5. Repeat steps 1-5 with the UNKNOWN thermistor. 6. Set up circuits using two digital multimeters and both the KNOWN and UNKNOWN thermistors. Immerse
both thermistors in a beaker of boiling water and measure the resistance of each thermistor. Record below.
Resistance (k) of KN OWN Thermistor for Boiling Water
Resistance (k) of UN KN OWN Thermistor for Boiling Water
Questions to be addressed: 1. Base resistance is the resistance value of a thermistor at a specified temperature with negligible electrical power
to avoid self-heating. Usually base resistance will be defined at 25oC. What is the accepted base resistance of your KNOWN thermistor?
2. Classify each thermistor as either PTC or NTC.
KNOWN Thermistor UNKNOWN Thermistor
3. List the regression equation for each thermistor. KNOWN Thermistor UNKNOWN Thermistor
4. Using the regression equation, find the base resistance of the UNKNOWN thermistor. Show work in box. 5. Estimate the temperature of the boiling water using the resistance values measured and the regression
equations recorded in (3).
KNOWN Thermistor UNKNOWN Thermistor
6. Find the percent discrepancy between the two estimates in (5). Show work in box. 7. What are some applications of thermistors?
