222-227%20%20Mechanical%20Properties%2002

222-227%20%20Mechanical%20Properties%2002 - MECHANICAL...

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MECHANICAL PROPERTIES
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HARDNESS
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1. Resistance to permanent indentation; indentation hardness 2. Energy absorption under impact loads ; rebound hardness 3. Resistance to scratcing; scratch hardness 4. Resistance to abrasion; wear hardness 5. Resistance to cutting or drilling; machinability
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1. The surface to be tested should be clean and dry, smooth and free from oxide 2. The surface should be flat and perpendicular to the indenter 3. The thickness of the specimen should be at least 10 times the depth of indentation 4. The spacing between the indentations should be 3 to 5 times the diameter of indentation 5. Tests on cylindirical surfaces will give low readings, the error depending on curvature should be corrected.
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TENSION TEST
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Aims 1) To determine the stress strain diagrams; σ - e b Engineering stress strain σ T - ε b True stress strain (Flow curve) 2) To determine the tensile properties of a material.
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TENSILE PROPERTIES E Young’s Modulus σ Y , e Y Yield Strength and Strain σ TS (UTS) , e u Ultimate Tensile Strength and Strain σ F , e F Fracture Strength and Strain % L Percent Elongation %RA Percent Reduction Area STRENGTH DUCTILITY
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TENSILE PROPERTIES U R Resilience U T Toughness v Poisson’s Ratio n Strain Hardening Coefficient ENERGY
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PROCEDURE • A tensile test specimen is either loaded at a constant rate or elongated at a constant rate. Tensile Specimen P L 0 , D 0 : initial dimensions L F , D F : final dimensions P vs Δ L diagram (from recorder) EXPERIMENTAL DATA By the help of these data σ -e diagram is drawn.
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STANDARD TENSILE SPECIMEN TS 138 EN 10002-1 L 0 L C D 0 D 0 : Initial Diamater L 0 : Gague Length L c : Initial Length For Cylindrical Specimens:
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YIELD STRENGTH σ Y Yield strength is the minimum stress at which first plastic deformation begins. h Some materials (like low-C steel) exhibit definite yield point.
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Most of the materials exhibit a gardual change in the slope of σ -e curve during yielding APPLY: 0.2% OFF-SET TECHNIQUE
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h % RA is more accurate, because it is independent on the gage length! 100
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222-227%20%20Mechanical%20Properties%2002 - MECHANICAL...

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