During a tensile test, the elongating sample leads to a reduction in the cross-sectional width and thickness. The shape of the engineering stress-strain curve showing a peak at the load maximum (Figure 1) results from the balance of the work hardening which occurs as...
Elastic Modulus (Young’s Modulus) When a punch initially contacts a sheet metal blank, the forces produced move the sheet metal atoms away from their neutral state and the blank begins to deform. At the atomic level, these forces are called elastic stresses and the...
M-Value, Strain Rate Sensitivity All metals strengthen as they are deformed through a process called work hardening. However, the degree of strengthening may change as a function of the speed at which they are tested. In these cases, when local necking starts, the...
Introduction to Mechanical Properties Tensile property characterization of mild and High Strength Low Alloy steel (HSLA) traditionally was tested only in the rolling direction and included only yield strength, tensile strength, and total elongation. Properties vary as...
R-Value, The Plastic Anisotropy Ratio The r-value, which is also called the Lankford coefficient or the plastic strain ratio, is the ratio of the true width strain to the true thickness strain at a particular value of length strain, indicated in Equation 1. Strains of...
N-Value, The Strain Hardening Exponent Metals get stronger with deformation through a process known as strain hardening or work hardening, resulting in the characteristic parabolic shape of a stress-strain curve between the yield strength at the start of plastic...
Necking: Diffuse Neck and Local Neck A tensile bar increases in length as it is pulled, with a concurrent reduction in width and thickness. The cross section is rectangular in shape through uniform elongation. After uniform elongation, however, strains concentrate in...
Total Elongation to Fracture Deformation continues in the local neck until fracture occurs. The amount of additional strain that can be accommodated in the necked region depends on the microstructure. Inclusions, particles, and grain boundary cracking can accelerate...
Forming forces need to exceed the yield strength for plastic deformation to occur and an engineered stamping to be produced. If a metal structure is loaded to a level below the yield strength, only elastic deformation occurs, and the load can be removed. With no...
Engineering stress-strain units are based on the starting dimensions of the tensile test sample: Engineering stress is the load divided by the starting cross-sectional area, and engineering strain is the change in length relative to the starting gauge length (2...