# Topic 7

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Topic 7
Seminar Sheet 7.1
Problem 1: A brass rod (E = 110GPa) is 1.5m long and 3cm in diameter. A force of 70kN is applied. What is the extension?
Problem 2: Distinguish between the terms strength, toughness, ductility, and hardness as used to describe the mechanical properties of materials. What material property defines each of these characteristics?
Problem 3:

In the diagram above, identify the elastic and plastic regions, estimate the Modulus of
Elasticity, the Ultimate Tensile Strength, the Yield Strength and the fracture strain.
Problem 4: A student reads that the Young’s modulus of elasticity for cast iron is 2.1x1011
Pa and that the cast iron fails abruptly when a strain of 0.0005 is reached. From this information, what would be the stress needed to break the specimen of this material in a tensile test? What assumption is being made here.
Problem 5: The UTS of a grade of aluminium is 1x108 Pa. What is the maximum tension that is possible in a wire of this material with a cross sectional area of 2.5 x 10-7 m2. What assumption is made here?
Problem 6: On a graph, sketch an approximate stress-strain curve for mild steel, which has a Young’s Modulus of 210 MPa, a Yield Strength of 220 MPa and an Ultimate Tensile
Strength of 430 MPa.
Problem 7: A table which has three aluminium alloy legs carries an evenly distributed mass of 225 kg. Each leg is a circular tube of length 90cm, inside diameter 4.6cm and outside diameter 5cm. Neglecting the mass of the table and assuming that the legs compress elastically, find the compressive stress in one leg.
If the alloy has a modulus of elasticity of 70GPa, what will be the shortening of the leg?

Problem 8: Sketch a load vs. extension graph for mild-steel. Clearly identify where the load is at the yield point and where the maximum load occurs.
Problem 9: A steel bar has a diameter of 16.00mm. A tensile force of 30kN is applied to the ends of the bar causing it to have a final length of 80.06mm. Calculate the modulus E of the
steel

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