MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 47

1.18 Draw a sketch of the Maxwell model and label all components.
Draw a graph showing displacement versus time when the model is
subjected to a constant force for a time period t and then released.
Comment on why the model responds this way.
1.19 Derive the response relation for each of the models shown in
Figure P1.19, assuming that the force F is constant and instanta-
neously applied.

b

d M d

F O F O

F F

(a) (b)

FIGURE P1.19

1.20 State four failure modes of materials. Describe typical examples of
each mode.
1.21 A metal rod having a diameter of 10 mm is subjected to a repeated
tensile load. The material of the rod has a tensile strength of 290 MPa
and a fatigue failure behavior as shown in Figure 1.14. How many
load repetitions can be applied to this rod before it fails if the magni-
tude of the load is (a) 5 kN, and (b) 11 kN?
1.22 What is the factor of safety? On what basis is its value selected?
1.23 State the typical values of the specific gravity of three materials
commonly used in construction.
1.24 Define the coefficient of thermal expansion. What is the relation
between the linear and the volumetric coefficients of thermal
expansion?
1.25 A steel rod, which is free to move, has a length of 200 mm and di-
ameter of 20 mm at a temperature of 15°C. If the rod is heated uni-
formly to 115°C, determine the length and the diameter of this rod
to the nearest micron at the new temperature if the coefficient of
thermal expansion of steel is 10 -6 m/m/°C.

12.5 * Is there a stress

on the rod at 115°C?
1.26 In Problem 1.25, if the rod is snugly fitted against two immovable
nonconducting walls at a temperature of 15°C and then heated uni-
formly to 115°C, what is its length at 115°C? If the modulus of elas-
ticity of steel is 207 GPa, what is the stress induced in the bar? Is
this stress tension or compression?
1.27 A 4-meter-long steel plate with a rectangular cross section
is resting on a frictionless surface under the sun.
The plate temperature is measured to be at 40°C. The plate is then
moved into a cold room and is left to rest on a frictionless surface.
After several hours, the plate temperature is measured to be at 5°C.

1 10 mm * 50 mm 2