Chapter9

# Chapter9 - Mechanics &amp; 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.
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.
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
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.)
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 &amp; Materials I Chapter 9 Properties...

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