Mechanical Testing and Properties of Materials

Abstract

This chapter first emphasizes the dependence of material processing on mechanical properties; then the classification chart of mechanical properties is presented. Shear deformation is discussed with particular reference to the shear modulus. Engineering stress and strain are quantitatively defined. Tensile testing of materials is explained with reference to tensile testing equipment; and the stress-strain curves are analyzed to determine the various strength and ductility properties. Hardness testing is qualitatively and quantitatively discussed with particular references to the various types of hardness tests. Impact testing is also explained, including the mathematical relationship to calculate the impact energy. Mechanical properties data are presented, wherever necessary. This chapter contains 12 diagrams, 14 worked examples/solved problems, 6 exercise problems, 8 MCQs, and 18 mathematical models/formulae.

Questions and Problems

• 3.1 (MCQs). Encircle the most appropriate answer for the following questions.

  • (a) Which of the following mechanical tests involves the highest strain rate?

    (i) tensile test, (ii) hardness test, (iii) impact test, (iv) shear test

  • (b) Which of the following mechanical tests involves indentation in the test material?

    (i) hardness test, (ii) shear test, (iii) impact test, (iv) tensile test.

  • (c) Which of the following mechanical tests is the best for determining the yield strength?

    (i) hardness test, (ii) impact test, (iii) shear test, (iv) tensile test

  • (d) Which of the following mechanical properties involves elastic energy absorption?

    (i) impact toughness, (ii) resilience, (iii) Young’s modulus, (iv) ductility

  • (e) Which of the following hardness tests involves the use of rhombic-based pyramidal diamond indenter?

    (i) Knoop test, (ii) Brinell test, (iii) Rockwell test, (iv) Vickers test.

  • (f) Which of the following terms describes the ratio of the lateral strain to the axial strain?

    (i) true strain, (ii) engineering strain, (iii) strain ratio, (iv) Poisson’s ratio

  • (g) Which of the following mechanical tests involves the angle of twist?

    (i) impact test, (ii) hardness test, (iii) tensile test, (iv) shear test

  • (h) Which hardness test allows us to use hardened steel ball indenter?

    (i) Brinell test, (ii) Vickers test, (iii) Rockwell test, (iv) Knoop test.

• 3.2 Does there exist a strong relationship between a material’s mechanical behavior and its processing? Support your answer by giving at least two example.

• 3.3 (a) Differentiate between elasticity and plasticity.

  (b) Draw the classification chart showing the various mechanical properties of materials.

• 3.4 (a) Draw the sketch of a tensile test specimen, and label it.

  (b) Briefly describe the tensile testing of materials.

  (c) List the various strength and ductility properties as obtained from a tensile test.

• 3.5 Describe the Vickers hardness test with the aid of sketch.

• 3.6 Which mechanical property must be high in mechanical springs? Explain.

• 3.7 A tensile force of 2 kN is applied to a 160-mm-long metal bar with a diameter of 2 mm. The final length of the bar is 175 mm. Calculate the: (a) engineering stress, and (b) engineering strain.

• 3.8 Table 3.6 shows the tensile test data for a ductile material; the original gage length of the tensile-test specimen was 50 mm. (a) Plot the stress-strain curve for the material. (b) Identify the proportional limit and hence calculate the Young’s modulus. (c) Calculate the percent elongation for the material. (d) What is the final gage length after fracture?

Table 3.6 Tensile Test data for the ductile material

• 3.9 By using the data in Table 3.6, determine the tensile strength and the breaking strength for the test material.

• 3.10 A load of 1000 kgf is applied by using a 10-mm-diameter steel ball that results in the indentation diameter of 9 mm in a test material. Calculate the BHN for the test material.

• 3.11 The indenter of a Vickers hardness tester is subjected to a load of 70 kgf for 15 s. The two diagonals of the indentation left on the surface of the test material are 0.7 mm and 0.8 mm, respectively. Calculate the Vickers hardness number of the material.

• 3.12 A Charpy impact test was conducted by using a heavy pendulum of 2.5 kgf that is released from a height of 15 cm. The pendulum struck the specimen on its downward swing thereby fracturing it. The height at the end of swing is 5 cm. Calculate the impact energy of the test material. Is the material brittle or ductile?