Material Testing and Experimental Methods

Abstract

The behaviour of a ductile material, such as mild steel, when subjected to a simple tensile test, was described in Para. 1.7. It was shown that, up to a certain value of stress, strain is proportional to stress, and if the load is removed within this range there will be no permanent strain (i.e. the material is stressed in the “elastic” range). If the load is increased the material “yields,” undergoing a large “plastic” strain at a constant stress value. As the load is further increased appreciable strain (mostly plastic) occurs up to the “ ultimate ” stress value. At this stage the specimen begins to “neck” at some position along its length, the load falling off until fracture occurs. Most engineering materials show these features to a varying degree, and definitions of the principal values will be found in Para. 1.7. It is proposed to discuss some particular aspects of the tensile test and the significance of the results obtained.