CIV2235—STRUCTURAL MATERIALS
Week 6 Practice Class
Mechanical Properties of Structural Material
Question 1 (5 marks)
For a bronze alloy, the stress at which plastic deformation occurs is 275 MPa and the modulus of elasticity is 115 GPa . What is the maximum load that can be applied to a specimen with a cross-sectional area on 325 mm2 without plastic deformation?
Question 2 (10 marks)
Consider a cylindrical specimen of steel alloy (see figure 1), 8.5 mm in diameter and 80 mm long that is pulled in tension . Determine its elongation when a load of 65250 N is applied.
Fig 1. (Source: W.D. Callister, Materials Science and Engineering An Introduction, 6th Ed.)
Question 3 (40 marks)
The results of a tensile test conducted using a metal specimen of 50 mm2 cross section and 30 cm gauge length is given in figure 2. Determine the yield stress, fracture stress, elastic modulus , ductility , modulus of resilience of the metal.
Fig 2. The load at the point starting the plastic regime is 13500 N and the corresponding extension is 0.3 mm .
Question 4 (20 marks)
Draw the approximate expected tensile stress-strain curve for a material that has a yield stress of 100 MPa, an ultimate tensile stress of 150 MPa, an elastic modulus of 10 GPa, a ductility of 20%, and a uniform. elongation of 10% and a fracture stress of 80 MPa. Label all known points e.g. (strain, stress)
Question 5 (5 marks)
For the following problems, state whether the statement is True or False .
1. The modulus of resilience is a measure of the area under the elastic portion of a stress-strain curve .
a . TRUE b. FALSE
2. The sound heard at fracture of a tension specimen is caused by the plastic energy stored in the bar .
a . FALSE b. TRUE
Question 6 (20 marks)
A steel rod (E=200 GPa) has a circular cross section and is 10 m long. Determine the minimum diameter if the rod must hold a 30 kN tensile force without deforming more than 5mm. Assume the steel stays in the elastic region. Note, 1 GPa = 10^9 Pa .
Question 7 (not marked, exercise)
A tensile specimen with a 12 mm initial diameter and 60 mm gage length reaches maximum load at 90 kN and fractures at 70 kN. The minimum diameter at fracture is 10 mm . Determine:
-- the engineering stress at maximum load (or the ultimate tensile strength)
-- the true fracture stress
-- true strain at fracture
-- engineering strain at fracture