Barkatullah University Institute of Technology Presentation on …. Submitted to: Presented by MECH ENGG III Sem. 1
OUTLINEIntroduction Tensile Test- Basic Principles Terminology Objectives of the Lab Tensile 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.
COMPONENTSLoad 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.
Test Specimen: • The tensile test can be conducted with either a round bar or sheet specimen. Gauge • The round bar specimen used for the markings 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.
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 TEST Procedure (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 EXAMPLELoad vs. Elongation (Data obtained from the tensile test):Material Data: Load Vs. ElongationAl 6061 12000Y = 40 ksiTS = 49 ksi 10000 8000 Load (lb) 6000 4000 2000 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Elongation (in.)
TENSILE TEST EXAMPLEEngineering Stress vs. Strain (calculated from Load vs. Elongation data):Material Data: Engineering Stress vs. Engineering StrainAl 6061 60000Y = 40 ksiTS = 49 ksi 50000 Engineering Stress (psi) 40000 30000 20000 10000 0 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)
TENSILE TEST EXAMPLEEffect 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 = 0.33 Aluminum 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 EXAMPLEEffect of Strain Hardening: 180 Material 1 Material 2 160 140 True Stress (ksi) 120 100 80 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 True Strain (in/in)
TENSILE TESTING SIMULATIONAluminum 6111-T4 (σ=80.7ε0.23Ksi) Load-Elongation curve of Al 6111 10 9 8 7 Load (Klbs) 6 5 4 Load-Elongation curve 3 2 1 0 0 0.5 1 1.5 2 Elongation (in) Before the test