Properties of Engineering Materials - Structural and Stress Analysis - page 207

8.8 M ATERIAL P ROPERTIES

Table 8.1 lists some typical properties of the more common engineering materials.

PROBLEMS

P.8.1 Describe a simple tensile test and show, with the aid of sketches, how mea-
sures of the ductility of the material of the specimen may be obtained. Sketch typical
stress-strain curves for mild steel and an aluminium alloy showing their important
features.

P.8.2 A bar of metal 25mm in diameter is tested on a length of 250mm. In tension
the following results were recorded:

T ABLE P.8.2(a)

Load (kN) 10.4 31.2 52.0 72.8

Extension (mm) 0.036 0.089 0.140 0.191

A torsion test gave the following results:

T ABLE P.8.2(b)

Torque (kN m) 0.051 0.152 0.253 0.354

Angle of twist (degrees) 0.24 0.71 1.175 1.642

Represent these results in graphical form and hence determine Young's modulus,
E , the modulus of rigidity, G , Poisson's ratio, ν , and the bulk modulus, K , for the
metal.

(Note: see Chapter 11 for torque-angle of twist relationship).

205 000N/mm 2 , G 80 700N/mm 2 , ν 148 500N/mm 2 . Ans . E 0.27, K

C ε n where
C is a constant. Assuming that the material suffers no change in volume during plastic
deformation, derive an expression for the nominal stress-strain curve and show that
this has a maximum value when ε

P.8.3 The actual stress-strain curve for a particular material is given by σ =

= n / (1 − n ).

C ε n / (1

Ans. σ (nominal) = + ε ).

P.8.4 A structural member is to be subjected to a series of cyclic loads which produce
different levels of alternating stress as shown below. Determine whether or not a
fatigue failure is probable.

Ans. Not probable ( n 1 / N 1 + n 2 / N 2 +··· = 0 . 39).