Chapter 6 Mechanical Properties of Materials PDF

Chapter 6: Mechanical Properties (Please follow my lecture too) ISSUES TO ADDRESS... Stress and strain: What are they and why are they used instead of load and deformation? Elastic behavior: When loads are small, how much deformation occurs? What materials deform l...

Chapter 6: Mechanical Properties (Please follow my lecture too) ISSUES TO ADDRESS... Stress and strain: What are they and why are they used instead of load and deformation? Elastic behavior: When loads are small, how much deformation occurs? What materials deform least? Plastic behavior: At what point does permanent deformation occur? What materials are most resistant to permanent deformation? Toughness and ductility: What are they and how do we measure them? Chapter 6 - 1 Chapter 6 - 2 Chapter 6 - 3 Chapter 6 - 4 Tensile test Chapter 6 - 5 Chapter 6 - 6 Chapter 6 - 7 Chapter 6 - 8 Chapter 6 - 9 Chapter 6 - 10 Chapter 6 - 11 Chapter 6 - 12 Chapter 6 - 13 Chapter 6 - 14 Chapter 6 - 15 Chapter 6 - 16 Chapter 6 - 17 Chapter 6 - 18 Chapter 6 - 19 Chapter 6 - 20 Chapter 6 - 21 Chapter 6 - 22 Chapter 6 - 23 Chapter 6 - 24 Chapter 6 - 25 Chapter 6 - 26 Chapter 6 - 27  Class problem (6.15,10e) A cylindrical specimen of aluminum having a diameter of 19 mm (0.75 in.) and length of 200 mm (8.0 in.) is deformed elastically in tension with a force of 48,800 N (11,000 lbf). Using the data contained in Table 6.1, determine the following: (a) The amount by which this specimen will elongate in the direction of the applied stress. (b) The change in diameter of the specimen. Will the diameter increase or decrease? Chapter 6 - 28  Class problem (6.28,10e) A bar of a steel alloy that exhibits the stress-strain behavior shown in Figure 6.22 is subjected to a tensile load; the specimen is 300 mm (12 in.) long, and of square cross section 4.5 mm (0.175 in.) on a side. (a) Compute the magnitude of the load necessary to produce an elongation of 0.45 mm (0.018 in.). (b) What will be the deformation after the load has been released? Chapter 6 - 29  Class problem (6.43,10e) For some metal alloy, a true stress of 415 MPa (60,175 psi) produces a plastic true strain of 0.475. How much does a specimen of this material elongate when a true stress of 325 MPa (46,125 psi) is applied if the original length is 300 mm (11.8 in.)? Assume a value of 0.25 for the strain-hardening exponent n. Chapter 6 - 30 Chapter 6 - 31 Chapter 6 - 32 Chapter 6 - 33 Chapter 6 - 34 Chapter 6 - 35 Chapter 6 - 36 Chapter 6 - 37  Hardness Hardness tests are performed more frequently than any other mechanical test for several reasons: 1. They are simple and inexpensive—ordinarily no special specimen need be prepared, and the testing apparatus is relatively inexpensive. 2. The test is nondestructive—the specimen is neither fractured nor excessively deformed; a small indentation is the only deformation. 3. Other mechanical properties often may be estimated from hardness data, such as tensile strength Chapter 6 - 38 Knoop (HK) and Vickers (HV) are referred to as microindentation-testing methods on the basis of indenter size. (using microscope) Knoop is used for testing brittle materials such as ceramics Chapter 6 - 39 Chapter 6 - 40  Summary Stress and strain: These are size-independent measures of load and displacement, respectively. Elastic behavior: This reversible behavior often shows a linear relation between stress and strain. To minimize deformation, select a material with a large elastic modulus (E or G). Plastic behavior: This permanent deformation behavior occurs when the tensile (or compressive) uniaxial stress reaches sy. Toughness: The energy needed to break a unit volume of material. Ductility: The plastic strain at failure. Chapter 6 - 41 Particular ways to increase strength are to: --decrease grain size --solid solution strengthening --precipitate strengthening --cold work Chapter 6 - 42 Chapter 6 - 43