Basic Materials Properties for Materials Selection - Medical Device Design: Innovation from Concept to Market - page 340

stress

elastic plastic

ultimate stress

region region

proof stress

yield stress

Young's
modulus

permanent
deformation

strain

Figure E.2
Example graph of stress versus strain.

The flexibility of the material is related to Young's modulus. Its symbol is E and its units
are also N/m 2 . This is the slope of the stress-strain graph in the elastic region. It is relatively
constant for a specific material. Materials with a high Young's modulus are stiff; those with
low values are flexible ( Table E.2 ).

CASE STUDY E.1
An orthopedic wire of diameter 2 mm is to be made from 316 L stainless steel annealed rod. If a
safety factor of 2 is to be applied, determine the maximum tensile load.
Using matweb.com the material properties are

2

380MN/m

σ y

Using a safety factor of 2, this reduces to

2

38 /2 0 19 MN/m 0

σ max