Chapter9

Chapter9 - Mechanics & Materials I Chapter 9 Properties...

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FAMU-FSU College of Engineering Department of Mechanical Engineering Chapter 9 Chapter 9 Properties of Materials Properties of Materials
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Properties of Materials Properties of Materials • The design of machines and structures so that they will function properly requires that we understand the mechanical behavior of the materials being used. • Ordinarily, the only way to determine how materials behave when they are subjected to loads is to perform experiments in the laboratory.
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Tensile Test Tensile Test • The tension test is commonly employed to determine such engineering properties as 1- Young’s modulus ,E 2- Yield strength σ y 3- Ultimate strength σ u 4- Percent elongation , and percent reduction of area. 5- Toughness 6- Modulus of Resilience 7- Ductile/brittle behavior
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Tensile Test Tensile Test • One of the most common tests of material is the tension test. • In the usual tension test the cross section of the specimen is round, square, or rectangular.
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Tensile Test Tensile Test • The tensile-test specimen is placed in a test machine called tensile-test machine. • The deformation is recorded by extensometer or strain gauge.
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Tensile Test: Stress Calculation Tensile Test: Stress Calculation Loads are gradually applied to the specimen and simultaneous readings of the load and deformation are taken at specified intervals. • Nominal, or engineering, stress σ is determined by the formula where A 0 is the original cross-sectional area in the gage section and P is the applied load. 0 A P = σ
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Tensile Test: Strain Calculation Tensile Test: Strain Calculation Corresponding values of strain are found by dividing the deformation by the gauge length. Where l o is the original length of an axial line element and l is the current current length of this element. The convention for strain is that it is positive when l is greater than l 0 . 0 0 0 l l l l l = - = ε
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Tensile Stress Tensile Stress Strain Curve Strain Curve
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Tensile Test: Curve Tensile Test: Curve The stress and strain values obtained can then be plotted in a stress- strain curve. The shape of the curve will depend on the kind of material tested. (The temperature and speed at which the test is performed also affect the results.)
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Stress Stress Strain Curve: Regions Strain Curve: Regions • Elastic behavior : The sample returns to its original shape/ length when the load is removed. Curve acts like straight line, the end of this region is the elastic limit.
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Chapter9 - Mechanics & Materials I Chapter 9 Properties...

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