1. mechnical properties of metal

# 1. mechnical properties of metal - Chapter 6 Mechanical...

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Chapter 6 - 1 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: Mechanical Properties

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Chapter 6 - 2 Mechanical Properties of Metals Material when in service are subjected to forces or loads. Thus it is necessary to know the characteristics of the material and to design the member so that deformation will not be excessive and fracture will not occur . Mechanical properties of material reflects the relationship between its responds or deformation to an applied force. Key mechanical design properties are: Stiffness, Strength Hardness Ductility Toughness
Chapter 6 - 3 Elastic means reversible ! Elastic Deformation 2. Small load F bonds stretch 1. Initial 3. Unload return to initial F Linear- elastic Non-Linear- elastic

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Chapter 6 - 4 Plastic means permanent ! Plastic Deformation (Metals) F linear elastic linear elastic plastic 1. Initial 2. Small load 3. Unload planes still sheared F elastic + plastic bonds stretch & planes shear plastic
Chapter 6 - 5 Stress has units: N/m 2 Engineering Stress Shear stress, : Area, A o F t F t F s F F F s = F s A o Tensile stress, : original area before loading = F t A o 2 m N = Area, A o F t F t

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Chapter 6 - 6 Simple tension: cable Note: = M / A c R here. Common States of Stress o F A o F s A M M A o 2 R F s A c Torsion (a form of shear): drive shaft Ski lift (photo courtesy P.M. Anderson) A o = cross sectional area (when unloaded) F F
Chapter 6 - 7 (photo courtesy P.M. Anderson) Canyon Bridge, Los Alamos, NM o F A Simple compression: Note: compressive structure member ( < 0 here). (photo courtesy P.M. Anderson) OTHER COMMON STRESS STATES (i) A o Balanced Rock, Arches National Park

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Chapter 6 - 8 Bi-axial tension: Hydrostatic compression: Pressurized tank < 0 h (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) OTHER COMMON STRESS STATES (ii) Fish under water z > 0 > 0
Chapter 6 - 9 Tensile strain: Lateral strain: Strain is always dimensionless. Engineering Strain Shear strain: is the tangent of the strain angle 90º 90º - y x = x / y = tan   L o Adapted from Fig. 6.1(a) and (c), Callister & Rethwisch 8e. /2 L o w o L L w o L /2

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Chapter 6 - 10 Stress-Strain Testing • Typical tensile test machine Adapted from Fig. 6.3, Callister & Rethwisch 8e. (Fig. 6.3 is taken from H.W.
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• Spring '14
• Strain, Tensile strength

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