Materials and Processes in Manufacturing

E. Paul Degarmo, J T. Black, Ronald A. Kohser

Chapter 2 Strain Hardening

Stress-Strain Behavior at Large Strain

The flow stress or flow strength of a material is the stress that has to be applied to cause continuing deformation of the material. A widely-used stress-strain relation for ductile materials deformed to large strain is
flow stress = ( a material constant ) ( strain )strain hardening exponent
s = K en
K is the strength factor and n is the strain hardening exponent for the material
- this is often called a "K e to the n" type of material
To clarify the meanings and importance of K and n in describing the flow stress of a ductile material, the following exercise is provided

Chapter 2 Tensile Instability

Instability in Tensile Deformation

Instability in work material deformation during manufacturing leads to nonuniform, uncontrollable local deformation. For example, locally nonuniform deformation during production of auto body panels and aluminum canns results in wavy, locally thin and thick regions of the product.

An exercise aimed at describing the factors determining when nonuniform deformation will start in tensile deformation is provided.