Tensile test
Introduction
The tensile test of a material consists of subjecting a normalized specimen "Specimen (mechanical)") to an increasing axial tensile stress until it breaks. This test measures the resistance of a material to a static or slowly applied force. The strain rates in a tensile test are usually very small.
Data extracted from the trial
In a tensile test, various characteristics of elastic materials can be determined:
Once the yield limit has been exceeded, a point is reached where, together with the previous elastic reduction associated with the Poisson effect, the so-called necking occurs, which is a plasticity phenomenon "Plasticity (solid mechanics)").
Normally, the proportionality limit is not usually determined since it is of no interest for the calculations. Young's Modulus is not calculated either, since this is characteristic of the material; Thus, all steels have the same modulus of elasticity although their resistances may be very different. The data obtained in the test must be sufficient to determine these properties, and others that can be determined based on them. For example, ductility can be obtained from elongation and area reduction.
Stress-strain curve
In the test, the deformation (elongation) of the specimen is measured between two fixed points of the specimen as the applied load increases, and it is represented graphically as a function of the tension (applied load divided by the section of the specimen). In general, the stress-strain curve thus obtained presents four differentiated zones:
Other characteristics that can be characterized by the tensile test are resilience "Resilience (engineering)") and tenacity, which are, respectively, the elastic and total energies absorbed and which are represented by the area under the stress-strain curve up to the elastic limit in the first case and until reaching failure in the second.
Shape and dimensions of the test tube
The specimens used in the tensile test have a circular or rectangular cross section. The central part must be machined so that its section is constant. If the material is fragile, the surface will need to be polished.