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CIVE 1160 Ch03 - College of Engineering CIVE 1160 Summer 2011 Mechanical Properties of Materials The mechanical properties of materials enable

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Unformatted text preview: College of Engineering CIVE 1160 Summer 2011 Mechanical Properties of Materials The mechanical properties of materials enable engineers to: • determine the strength of materials ; • determine relationships between stress and strain; • develop theoretical equations that are used to compute stresses and deformations of loaded members, which is required for design. College of Engineering CIVE 1160 Summer 2011 Tension/Compression Test Test specimens are loaded incrementally in machines that are capable of applying high tensile or compressive loads, and deformations are measured. Fig 3-2 College of Engineering CIVE 1160 Summer 2011 Load Versus Deformation A plot of load versus deformation would be different depending on the size of the test specimen. College of Engineering CIVE 1160 Summer 2011 Load Versus Deformation (Q) Question: What would be a more general way to plot the results rather than load versus deformation? College of Engineering CIVE 1160 Summer 2011 Load Versus Deformation (A) Answer: Plot stress versus strain rather than load versus deformation. College of Engineering CIVE 1160 Summer 2011 Stress Versus Strain For a given material, a plot of stress, , versus strain, , would give virtually a unique curve for specimens of different sizes. = o A P σ = o L δ ε 100 200 300 400 500 600 700 800 0.05 0.1 0.15 0.2 Strain (L/L) Stress (F/L 2 ) 1 2 3 College of Engineering CIVE 1160 Summer 2011 Material Properties Conclusions: Since we get the same curves for different size specimens for a given material when plotting stress versus strain, plots of stress versus strain can be used to determine material properties . These material properties can be used for analysis and design purposes. College of Engineering CIVE 1160 Summer 2011 Engineering Versus True Stress and Strain Engineering stress and strain are computed using the original cross-sectional area and the original length. True stress and strain are computed using the actual cross-sectional area and the actual length at the instant the load is measured. Engineering stress and strain are used most often. College of Engineering CIVE 1160 Summer 2011 Material Behavior Fig. 3-4 Stress-Strain Diagram for Ductile Steel College of Engineering CIVE 1160 Summer 2011 Elastic Behavior Proportional Limit Stress is proportional to strain up to a proportional limit, σ pl . Material is linearly elastic. Elastic Limit At some value of stress above the proportional limit, the material will not return to its original shape after the load is removed. Very often this point is difficult to determine....
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This note was uploaded on 01/26/2012 for the course CIVE 1160 taught by Professor Pickett during the Spring '08 term at Toledo.

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CIVE 1160 Ch03 - College of Engineering CIVE 1160 Summer 2011 Mechanical Properties of Materials The mechanical properties of materials enable

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