JF 302 –MATERIAL TECHNOLOGY 1

“MATERIAL TESTING”

PURPOSE AND TYPES OF MATERIAL TESTING DEFORMATION

PUPOSE OF MATERIAL TESTING:

Every materials shall be tested before using it in any construction works. Reasoning of testing construction materials as follows:

Required for any construction project at preliminary stage, on-going progress works, at completion stage, and during maintenance period.

To make sure the cost-effective in utilizing materials and factor of safety guaranteed upon test achievement.

Testing specification and guidelines are met as accordance to technical standards requirements; example technical manuals like British Standard or ASTM.

Testing of construction materials becomes one of project benchmark in terms of quality control assurance.

To make sure the durability and longevity of the constructed structures could be achieved and maintain.

To prevent any possible damage or defect to the structure at early stage before completion.

DEFINE MECHANICAL PROPERTIES IN MATERIALS TESTING

a) Strength:– Defines as the capacity of a material to withstand axially

directed pushing forces whereby the material will crushed when the limit of compressive strength is reached. The mechanical test measuring the maximum amount of compressive load a material can bear before fracturing. The test piece, usually in the form of a cube, prism, or cylinder, is compressed between the platen of a compression-testing machine by a gradually applied load. Materials used for testing are normally aggregate, cement, concrete, timber, brick, and etc.

b) Hardness: -Hardness is the resistance to plastic deformation (e.g., a local

dent or scratch). Thus, it is a measure of plastic deformation, as is the tensile strength, so they are well correlated. Historically, it was measured on an empirically scale, determined by the ability of a material to scratch another, diamond being the hardest and talc the softer. Now we use standard tests, where a ball, or point is pressed into a material and the size of the dent is measured. There are a few different hardness tests: Rockwell, Brinell, Vickers, etc. They are popular because they are easy and non-destructive (except for the small dent).

c) Elasticity:

- A material’s ability to return to its original shape after a load is removed.

d) Plasticity: -The ability of material to permanently deform but not break.

e) Ductility:– The ductility of a metal is the property that allows it to be

stretched or otherwise changed in shape without breaking and to retain the changed shape after the load has been removed. The ductility of a metal can be determined from the tensile test and it is done by determining the percent of

elongation.

f) Toughness: Toughness is measured using an impact test. Impact tests are

designed to test the ability of a notched sample to absorb sudden force. A striker is mounted on the end of a pendulum. When it is released, it breaks the sample. The height of the swinging pendulum after it breaks the sample is the amount of energy absorbed by the sample piece.

g) Brittleness: -A material is brittle if it is liable to fracture when subjected to

stress and has little tendency to deform (or strain) before fracture. This fracture would absorb relatively little energy, even in materials of high strength, and usually makes a snapping ‘pop’ sound especially tested against metal or steel.

DESTRUCTIVE TEST To find out how strong, resilient, flexible, or long-lived a material

is often requires the ultimate sacrifice: the destruction of the sample by equipment and instruments designed to precisely measure its performance in the face of an overwhelming force.

THE PRINCIPLE OF HARDNESS TESTa) Brinell Test In this test a hardened steel ball of 2.5, 5

or 10 mm in diameter is used as indenter.

The loading force is in the range of 300N to 30000N (300N for testing lead alloys, 5000N for testing aluminum alloys, 10000N for copper alloys, 30000N for testing steels). The Brinell Hardness Number (HB) is calculated by the formula:

HB = 2F/ (3.14D*(D-(D² - Di²)½)) Where F- applied load, kg D – indenter diameter, mm Di – indentation diameter, mm. In order to eliminate an influence of the

specimen supporting base, the specimen should be seven times (as minimum) thicker than indentation depth for hard alloys and fifteen times thicker than indentation depth for soft alloys.

b) Vickers Test The principle of the Vickers Hardness

method is similar to the Brinell method. The Vickers indenter is a 136 degrees

square-based diamond pyramid. The impression, produced by the

Vickers indenter is clearer, than the impression of Brinell indenter, therefore this method is more accurate.

The load, varying from 1kgf to 120 kgf, is usually applied for 30 seconds. The Vickers number (HV) is calculated by the formula:

HV = 1.854*F/ D² Where F-applied load, kg D – length of the impression diagonal,

mm The length of the impression diagonal is

measured by means of a microscope, which is usually an integral part of the Vickers Tester.

c) Rockwell Test Rockwell Superficial Test is

applied for thin strips, coatings, carburized surfaces.

Reduced loads (15 kgf, 30 kgf, and 30 kgf) as a major load and deduced preload (3kgf) are used in the superficial test.

Depending on the indenter, two scales of Rockwell Superficial method may be used: T (1/16” steel ball) or N (diamond cone).

62 R30T means 62 units, measured in the scale 30T (30 kgf, 1/16” steel ball indenter) by the Rockwell Superficial method (R).

d) Shore Test The Shore Scleroscope hardness is associated with the elasticity of the

material. The appliance consists of a diamond-tipped hammer, falling in a graduated

glass tube from a definite height. The tube is divided into 140 equal parts. The height of the first rebound is the hardness index of the material. The harder the material, the higher the rebound. The Shore method is widely used for measuring hardness of large machine

components like rolls, gears, dies, etc. The Shore scleroscope is not only small and mobile, it also leaves no

impressions on the tested surface.

PRINCIPLE AND RESULTS OF TOUGHNESS TESTSa) Izod Test: The Izod test is has become the

standard testing procedure for comparing the impact resistances of plastics. While being the standard for plastics it is also used on other materials.

The Izod test is most commonly used to evaluate the relative toughness or impact toughness of materials and as such is often used in quality control applications where it is a fast and economical test. It is used more as a comparative test rather than a definitive test. This is also in part due to the fact that the values do not relate accurately to the impact strength of moulded parts or actual components under actual operational conditions.

Schematic of the izod test

b) Carpy Test: -While most commonly used

on metals, it is also used on polymers, ceramics and composites. The Charpy test is most commonly used to evaluate the relative toughness or impact toughness of materials and as such is often used in quality control applications where it is a fast and economical test. It is used more as a comparative test rather than a definitive test.

Schematic of the Charpy impact test.

NON-DESTRUCTIVE TEST

By definition, Non-destructive Testing (NDT) is determination of a specimen’s quality without impairing its intended application. There are many types of Non-destructive Testing Methods available to the whole spectrum of industries. Generally these NDT techniques use a probing energy and a recording and/or display medium. Other terms for NDT are Non-destructive Evaluation (NDE), Non-destructive Examination (NDE) and Non-destructive Inspection (NDI).

METHODS FOR NON DESTTRUCTIVE TEST

a) Penetration Testing Defined There is a considerable amount of confusion in the industry

regarding the differences between vulnerability scanning and penetration testing as the two phrases are commonly interchanged. However, their meaning, and implications are very different. A vulnerability assessment simply identifies and reports noted vulnerabilities, whereas penetration testing attempts to exploit the vulnerabilities to determine whether unauthorized access or other malicious activity is possible. Penetration testing typically includes network penetration testing and application security testing as well as controls and processes around the networks and applications, and should occur from both outside the network trying to come in (external testing) and from inside the network.

b) Magnet Powder Test: -Magnetic testing is a method used to reveal defects

(discontinuities, voids, etc.) in the surface of ferromagnetic materials. IMA Dresden can provide this method as a mobile test using a portable electromagnet. In this way, welded joints in steel structures can be tested for production errors and defects resulting from loading or operation. IMA Dresden has been approved by the Federal Railway Office (Eisenbahnbundesamt - EBA) as a testing laboratory for typical railway tests and inspections on railway vehicles.

c) Ultrasound test:

-Ultrasound is used to create images of soft tissue structures, such as the gallbladder, liver, heart, kidneys, pancreas, bladder, thyroid gland, prostate, female reproductive organs, and even of babies in the uterus. Ultrasound can also measure the flow of blood in the arteries to detect blockages.

d) X-ray Test:-X Rays can be used for detection of internal flaws and faults in

most engineering materials. X ray testing is expensive due to the costly equipment, film and processing required. There is also the need for the implementation of specialised safety equipment and procedures.

Complex shapes require examination from two different angles.

X ray or Gamma radiation is passed through the test specimen and then recorded upon a photo-sensitive film. The flaws or defects are indicated as dark areas on the film because faults absorb less radiation than the material itself.

Due to its expense X ray detection is generally used during product development, or in laboratory testing.

Gamma radiation is suited to field or on site applications as less complex equipment is used.