Deformation - Orthopaedic Biomaterials in Research and Practice - page 25

1000

Load
(N)

c−d

c d

500

b

e

a

0.5 1.0

Elongation (cm)

1.5

FIGUre 2.2 load-elongation curve (tensile deformation).

obtained by plotting any force or moment as a function of some measure
of the deformation.
If we connect the points a - e with a smooth curve, we find that the
force apparently reached a maximum (= 750 N) when the bar had an
elongation of 1.0 cm ( L = 5.0 cm), somewhere between points c and d .
This point, c - d , is the point of maximum load and coincides, observa-
tionally, with the onset of necking.

Types of load-deformation curves There are two types of load-
deformation curves. The first type is produced by forces alone and
records changes in linear dimensions of objects without change in shape.
The two types of forces that produce linear dimensional changes are ten-
sion and compression. These can be seen in Figure 2.3. The bar has been
ruled with ghost rectangles; after either tensile or compressive deforma-
tion, the sides of these rectangles have different lengths but the rectan-
gular shape is retained.
The second type of load-deformation curve is produced by moments
and records changes in shape. Since the change in shape is frequently

F'

∆ L /2

F'

∆ L /2

L

F

Undeformed

Compressive
deformation

F

Tensile
deformation

FIGUre 2.3 tensile and compressive deformation.