专业英语AskelandPhuleNotesCH6.MechanicalPropertiesofMetals

1,The Science and Engineering of Materials, 4th ed Donald R. Askeland Pradeep P. Phulé,Chapter 6 Mechanical Properties and Behavior,2,Objectives of Chapter 6,Introduce the basic concepts associated with mechanical properties of materials. Evaluate factors that affect the mechanical properties of materials. Review some of the basic testing procedures that engineers use to evaluate many of these properties.,3,Chapter Outline,6.1 Technological Significance 6.2 Terminology for Mechanical Properties 6.3 The Tensile Test: Use of the Stress-Strain Diagram 6.4 Properties Obtained from the Tensile Test 6.5 True Stress and True Strain 6.6 The Bend Test for Brittle Materials 6.7 Hardness of Materials 6.8 Strain Rate Effects and Impact Behavior 6.9 Properties Obtained from the Impact Test 6.10 Fracture Mechanics 6.11 The Importance of Fracture Mechanics,4,6.12 Microstructural Features of Fracture in Metallic Materials 6.13 Microstructural Features of Fracture in Ceramics, Glasses, and Composites 6.14 Weibull Statistics for Failure Strength Analysis 6.15 Fatigue 6.16 Results of the Fatigue Test 6.17 Application of Fatigue Testing 6.18 Creep, Stress Rupture, and Stress Corrosion 6.19 Evaluation of Creep Behavior 6.20 Use of Creep Data 6.21 Superplasticity,Chapter Outline(Continued),5,Section 6.1 Technological Significance,Figure 6.2 The materials used in sports equipment must be lightweight, stiff, tough, and impact resistant. (Courtesy of Getty Images.),Figure 6.1 Aircraft, such as the one shown here, makes use of aluminum alloys and carbon-fiber-reinforced composites. (Courtesy of Getty Images.),6,Section 6.2 Terminology for Mechanical Properties,Stress - Force or load per unit area of cross-section over which the force or load is acting. Strain - Elongation change in dimension per unit length. Youngs modulus - The slope of the linear part of the stress-strain curve in the elastic region, same as modulus of elasticity. Shear modulus (G) - The slope of the linear part of the shear stress-shear strain curve. Viscosity ( ) - Measure of resistance to flow, defined as the ratio of shear stress to shear strain rate (units Poise or Pa-s). Thixotropic behavior - Materials that show shear thinning and also an apparent viscosity that at a constant rate of shear decreases with time.,7,Figure 6.3 (a) Tensile, compressive, shear and bending stresses. (b) Illustration showing how Youngs modulus is defined for elastic material. (c) For nonlinear materials, we use the slope of a tangent as a variable quantity that replaces the Youngs modulus constant,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,8,Figure 6.4 (a) Various types of strain response to an imposed stress. (Source: Reprinted from Materials Principles and Practice, by C. Newey and G. Weaver (Eds.), 1991 p. 300, Fig. 6-9. Copyright © 1991 Butterworth-Heinemann. Reprinted with permission from Elsevier Science.),9,Figure 6.4 (Continued) (a) Various types of strain response to an imposed stress. (Source: Reprinted from Materials Principles and Practice, by C. Newey and G. Weaver (Eds.), 1991 p. 300, Fig. 6-9. Copyright © 1991 Butterworth-Heinemann. Reprinted with permission from Elsevier Science.) (b) Stress relaxation in a viscoelastic material. Note the y-axis is stress. Strain is constant.,10,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,Figure 6.5 Shear stress strain rate relationships for Newtonian and non-Newtonian materials,11,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,12,Section 6.3 The Tensile Test: Use of the Stress-Strain Diagram,Load - The force applied to a material during testing. Strain gage or Extensometer - A device used for measuring change in length and hence strain. Glass temperature (Tg ) - A temperature below which an otherwise ductile material behaves as if it is brittle. Engineering stress - The applied load, or force, divided by the original cross-sectional area of the material. Engineering strain - The amount that a material deforms per unit length in a tensile test.,13,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,Figure 6.7 A unidirectional force is applied to a specimen in the tensile test by means of the moveable crosshead. The cross-head movement can be performed using screws or a hydraulic mechanism,14,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,Figure 6.9 Tensile stress-strain curves for different materials. Note that these are qualitative,15,16,(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.,Figure 6.10 The stress-strain curve for an aluminum alloy from Table 6-1,17,Example 6.1 Tensile Testing o