universal testing machines
TRANSCRIPT
UNIVER
SAL TE
STING
MACHIN
ES
Barkatullah University Institute of Technology Presentation on ….
Submitted to: Presented byMECH ENGGIII Sem.
1
OUTLINE
IntroductionTensile Test- Basic PrinciplesTerminologyObjectives of the LabTensile Test (Material and Equipment)Tensile Test Example (Video , Material Properties and Simulation)
INTRODUCTION
A universal testing machine, also known as a universal tester, materials testing machine or materials test frame, is used to test the tensile stress and compressive strength of materials. It is named after the fact that it can perform many standard tensile and compression tests on materials, components, and structures.
COMPONENTS
Load frame - usually consisting of two strong supports for the machine. Some small machines have a single support.
Load cell - A force transducer or other means of measuring the load is required. Periodic calibration is usually called for.
Cross head - A movable cross head (crosshead) is controlled to move up or down. Usually this is at a constant speed: sometimes called a constant rate of extension (CRE) machine.
Output device - A means of providing the test result is needed. Some older machines have dial or digital displays and chart recorders. Many newer machines have a computer interface for analysis and printing.
Conditioning - Many tests require controlled conditioning . The machine can be in a controlled room or a special environmental chamber can be placed around the test specimen for the test.
Test fixtures, specimen holding jaws, and related sample making equipment are called for in many test methods.
The set-up and usage are detailed in a test method, often published by a standards organization. This specifies the sample preparation, fixturing, gauge length (the length which is under study or observation), analysis, etc.
The specimen is placed in the machine between the grips and an extensometer if required can automatically record the change in gauge length during the test. If an extensometer is not fitted, the machine itself can record the displacement between its cross heads on which the specimen is held.
However, this method not only records the change in length of the specimen but also all other extending / elastic components of the testing machine and its drive systems including any slipping of the specimen in the grips.
Once the machine is started it begins to apply an increasing load on specimen. Throughout the tests the control system and its associated software record the load and extension or compression of the specimen.
Machines range from very small table top systems to ones with over 53 MN (12 million lbf) capacity.
• The tensile test can be conducted with either a round bar or sheet specimen.
• The round bar specimen used for the current test complies with the ASTM standards.
• A 2 inch gage length is marked on the specimen prior to testing.
• The specimen is held in the clamps at either end. Load and movement are applied to the bottom clamp.
Test Specimen:
Gauge markingsGauge markings
TENSILE TEST
Extensometer: • The elongation during testing is measured with respect to the gauge length using an extensometer.
• As the specimen elongates, the extensometer reading (elongation of the specimen) is recorded, either real-time or at discrete time intervals.
• For the current test, an analog extensometer will be used.Analog Digital
TENSILE TEST
Procedure:
Mark a 2 inch gage length on the tensile test specimen using the dial calipers and marker.
Measure the diameter of the specimen using dial calipers.
Load specimen in the machine grips and remove most of the slack by moving the lower crosshead.
Attach and zero the extensometer; secure it with a lanyard so it will not fall and break if specimen fracture occurs before the extensometer can be removed.
Zero the load indicator and open the right side hydraulic valve about ½ turn.
TENSILE TESTProcedure (continued):
As the sample is loaded, close the valve and record the load and elongation at regular load intervals (e.g. every 1000 pounds) up to the yield point (when the load starts increasing more slowly and the strain starts increasing more rapidly).
Continue to load the sample until the extensometer range is exceeded, then remove the extensometer.
Continue to load the sample until it breaks; pay close attention to the load indicator and record the load at failure.
Observe and record the maximum load on the follower needle.
Using the dial calipers, measure the final gage length and gage diameter of the fractured specimen (note: when you calculate the fracture strength, use the fracture area calculated from the measured final diameter).
TENSILE TEST EXAMPLE
Load vs. Elongation (Data obtained from the tensile test):
Material Data:Al 6061Y = 40 ksiTS = 49 ksi
Load Vs. Elongation
0
2000
4000
6000
8000
10000
12000
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Elongation (in.)
Lo
ad (
lb)
TENSILE TEST EXAMPLEEngineering Stress vs. Strain (calculated from Load vs. Elongation
data):
Material Data:Al 6061Y = 40 ksiTS = 49 ksi
Engineering Stress vs. Engineering Strain
0
10000
20000
30000
40000
50000
60000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Engineering Strain (in/in)
En
gin
eeri
ng
Str
ess
(psi
)
TENSILE TEST EXAMPLE
Effect of Strain Hardening:The influence of work/strain hardening on
the load vs. elongation during the tensile test can be demonstrated using finite element (FE) analysis.
Consider two materials with the following flow stress data:
Stainless Steel: K = 188 ksi; n = 0.33Aluminum Alloy: K = 80 ksi ; n = 0.10.The tensile test simulations for these two
materials show the effect of strain hardening on the load required for deformation and the uniform elongation prior to the onset of necking.
TENSILE TEST EXAMPLE
Effect of Strain Hardening:
0
20
40
60
80
100
120
140
160
180
0 0.1 0.2 0.3 0.4 0.5 0.6
True Strain (in/in)
Tru
e S
tre
ss
(k
si)
Material 1 Material 2
TENSILE TESTING SIMULATION
Aluminum 6111-T4 (σ=80.7ε0.23Ksi)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60
1
2
3
4
5
6
7
8
9
10
Load-Elongation curve of Al 6111
Load-Elongation curve
Elongation (in)
Load (
Klb
s)
Before the test
TENSILE TESTING SIMULATION
Aluminum 6111-T4 (σ=80.7ε0.23Ksi)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60
1
2
3
4
5
6
7
8
9
10
Load-Elongation curve of Al 6111
Load-Elongation curve
Elongation (in)
Load (
Klb
s)
Uniform elongation
TENSILE TESTING SIMULATIONAluminum 6111-T4 (σ=80.7ε0.23Ksi)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60
1
2
3
4
5
6
7
8
9
10
Load-Elongation curve of Al 6111
Load-Elongation curve
Elongation (in)
Load (
Klb
s)
Neck formation
TENSILE TESTING SIMULATIONAluminum 6111-T4 (σ=80.7ε0.23Ksi)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60
1
2
3
4
5
6
7
8
9
10
Load-Elongation curve of Al 6111
Load-Elongation curve
Elongation (in)
Load (
Klb
s)
Post-uniform elongation Necked region
Fracture occurs after a certain amount of elongation that is influenced by the n-value
(a) n=0.2 (b) n =0.4 (c) n = 0.6
Simulation results- Fracture