Introduction

Abstract

This introductory chapter first introduces readers to the definition, scope, and the areas of study in the field of mechanical behavior of materials. The study of this field requires adequate knowledge of materials in engineering, including the influence of microstructure on mechanical properties and behavior. It is also important to study the response of a material to applied load through stress-strain relationships. The main topics in this chapter cover deformation behaviors (elastic, plastic, and creep deformations); material fracture and failure, historical disaster caused by material failure, the classification of fracture, ductile and brittle fractures, DBT failure, fatigue, materials selection in design, and the factor of safety (FoS) in design. This chapter incudes 6 diagrams, and 2 calculations/worked examples, and 10 MCQs with answers.

Questions and Problems

• 1.1 Define the term mechanical behavior of materials. Why is the study of mechanical behavior of materials important in engineering?

• 1.2 (a) Classify various types of deformation and define each type of deformation.

  (b) Is plastic deformation always undesirable? Justify your answer.

• 1.3 (a) Distinguish between the terms fracture and failure.

  (b) Classify the various types of material fracture.

  (c) Differentiate between ductile fracture and brittle fracture with the aid of sketches.

  (d) What is meant by ductile-brittle transition (DBT) failure of a material? Explain with the aid of a sketch. How can DBT failure be avoided in steels?

• 1.4 Explain fatigue failure indicating the three stages involved in the failure.

• 1.5 (a) Define the terms design and materials selection.

  (b) What factor must be considered in materials selection in design? Briefly explain them.

• 1.6 A truck will have a mass of 7000 kg, and there will be four shock absorbers, each 20-in. long, to work with. Calculate the spring constant of the shock absorber.

• 1.7 A machine component has a diameter of 0.8 mm. The breaking strength of the material is 1800 MPa. Is it safe to use the component under a tensile load of 2 kN?

• 1.8 (MCQs). Encircle the most appropriate answers for the following statements/questions.

  • (a) Which failure results due to time-dependent deformation of a material?

    (i) fatigue, (ii) creep deformation , (iii) elastic deformation, (iv) plastic deformation

  • (b) Which failure results due to cyclic loading of a material?

    (i) fatigue failure, (ii) creep failure, (iii) ductile failure, (iv) brittle failure

  • (c) Which failure involves gross plastic deformation of a material?

    (i) DBT failure, (ii) creep failure, (iii) brittle failure, (iv) ductile failure

  • (d) Which failure occurs at high temperatures?

    (i) DBT failure, (ii) creep, (iii) brittle failure, (iv) ductile failure

  • (e) Which failure is associated with a low impact energy of a material?

    (i) fatigue failure, (ii) creep failure, (iii) brittle failure, (iv) ductile failure

  • (f) Which failure occurs at very low temperatures in BCC metals?

    (i) DBT failure, (ii) creep, (iii) brittle failure, (iv) ductile failure

  • (g) Which failure generally occurs in rotating shafts?

    (i) DBT failure, (ii) creep, (iii) brittle failure, (iv) fatigue failure

  • (h) Which failure is catastrophic?

    (i) ductile failure, (ii) creep, (iii) brittle failure, (iv) fatigue failure

  • (i) What was the cause of Titanic ship failure?

    (i) ductile failure, (ii) creep, (iii) DBT failure, (iv) fatigue failure

  • (j) Which failure is indicated by inter-granular fracture as observed under a microscope?

  • (k) ductile failure, (ii) creep, (iii) fatigue failure, (iv) brittle failure