Tài liệu 03 mechanical and physical properties of materials

ADVANCED MANUFACTURING ENGINEERING 3: Review of Mechanics and Physical Properties of Materials December 2016 2 Introduction • Often materials are subject to forces (loads) when they are used. Mechanical engineers calculate those forces and material scientists see how materials deform (elongate, compress, twist) or break as a function of applied load, time, temperature, and other conditions. • Materials scientists learn about these mechanical properties by testing materials. Results from the tests depend on the size and shape of material to be tested (specimen), how it is held, and the way of performing the test. That is why we use common procedures, or standards, which are published by the ASTM. 3 Introduction 4 Introduction • Relative Mechanical Properties of Various Materials at Room Temperature (in Decreasing Order). Metals Are in Their Alloy Form 5 Mechanical Loading 6 Tensile testing 7 Stress–strain curve 8 Stress strain 9 Shear stress and strain 10 True stress- true strain 11 True stress- true strain 12 Mechanical properties & temperature • Effect of temperature on mechanical properties of a carbon steel 13 Bending test • Two bend-test methods for brittle materials: (a) three-point bending and (b) four-point bending. 14 Material Hardness • Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials (e.g. metals) are harder than others (e.g. plastics). Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behaviour of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness. • Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, and viscosity. • Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter. 15 Material Hardness A selection of hardness testers. (a) A Micro Vickers hardness tester, (b) Rockwell hardness tester (the support for the part has been removed for clarity), (c) Durometer, and (d) Leeb tester. 16 Material Hardness • Indentation geometry in Brinell hardness testing: • (a) annealed metal, • (b) work-hardened metal, and • (c) deformation of mild steel under a spherical indenter. Note that the 17 Material Hardness • General characteristics of hardness-testing methods and formulas for calculating hardness. 18 Ratio of maximum yield stress to density 19 Specific strength • Specific strength (tensile strength/density) and specific stiffness (elastic modulus/density) Fatigue • Fatigue is the progressive and localized structural damage that occurs when a material is subjected to repeated loading and unloading “repeated stress cycles ”.