- The stress-strain diagram is generally accepted as the plotted results of a tensile test completed under carefully controlled conditions on a speciman of a metal. The stress-strain diagram important for design engineers in that it establishes the physical properties of the material under test including the yield strength, the ultimate strength, the elongation at fracture, the elastic limit etc.
- The test is carried out on a bar of uniform cross section, in a testing machine which indicates the tensile load being applied. The elongation of a calibrated length of the test piece (called the gauge length) is recorded by and extensometer or strain gauge.
- The load is gradually increased until the specimen breaks.
- The measured load results and the extension results are then converted to stress values (Load/specimen area) and strain values (extension / gauge length ) and the results are plotted on a graph. The stress levels resulting from this test are nominal or practical engineering values.
- The tensile test does not provide any information as to the strength of a material under highly cyclic loading, and does not identify the resistance of the material to shock loading. Other test procedures are required to test these factors.
- Different materials clearly result in different graphs. The notes that follow relate to these different graphs and the important data which is extracted from these graphs.
STRESS STRAIN DIAGRAM FOR MILD STEEL: