04~chapter 04

04~chapter 04 - Materials: engineering, science, processing...

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Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
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Strength and Stiffness Stress is applied to a material by loading it Strain – a change of shape – is its response Stiffness is the resistance to change of shape that is elastic – the material will return to its original shape when unloaded Strength is the resistance to permanent distortion or total failure Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
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Material Properties Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon Stress and strain are not material properties – they describe a stimulus and a response Stiffness and strength are material properties which are measured by the elastic modulus (E), elastic limit (σ y ), and tensile strength (σ ts ) Stiffness, strength, and density are three material properties central to mechanical design
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Density Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon Figure 4.1 Mass per unit volume – kg/m 3 or lb/in 3 Double-weighing method for calculating density
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Modes of Loading (a) – axial tension (b) – compression (c) – axial tension on one side and compression on the opposite side (d) – torsion (e) – bi-axial tension or compression Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon Figure 4.2
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Stress Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon Figure 4.3 (a) Force applied normal to surface Positive F indicates tension Negative F indicates compression (b) Force applied parallel to surface Shaded plane carries the shear stress (c) Equally applied tensile and compressive forces on all six sides of a cubic element Hydrostatic pressure 1 N/m 2 = 1 Pascal (Pa) 10 3 Pa = 1 MPa 1 lb/in 2 = 1 psi 10 3 psi = 1 ksi
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Strain Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon Figure 4.3 (a) Tensile stress lengthens the element causing a tensile strain (+) Compressive stress shortens the element causing a compressive strain (-) Strain is the ratio of two lengths and is therefore dimensionless
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Stress-Strain Curves Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon Figure 4.4 Initial portion of curve is approximately linear and is elastic – the material returns to its original shape once the stress is removed Within the linear elastic region, strain is proportional to stress E: Young’s modulus G: shear modulus K: bulk modulus
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Stress-Strain Curve – Brittle Response Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
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This note was uploaded on 02/15/2012 for the course MASC 310 taught by Professor Nutt during the Fall '08 term at USC.

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04~chapter 04 - Materials: engineering, science, processing...

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