final review - 31 Chapter 3 (Mechanical Properties) 3 Types...

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31 Chapter 3 ( Mechanical Properties) 3 Types of Static Stresses Compression – squeezes material Tensile – stretches material Shear – tearing material Engineering stress - σ ε = F/ A o where A o Engineering strain e = (L- L o ) / L o where L o is original length, L is whatever length during elongation True Stress σ = F/ A σ = σ ε (1+e) where A instantaneous area True Strain ε = ln (1+e) Strain Hardening Work material has entered the plastic region stresses increase continuously until necking starts Metal gets stronger as strain increases Plasticity / Elasticity Perfect elastic – material is defined completely by stiffness Indicated by modulus of elasticity Brittle materials – ceramics, caste irons, thermosetting polymers fall into this category Elastic and Perfectly Plastic – stiffness defined by E Once material reaches yield point it deforms plastically at same stress level The flow curve is given by K=Y and n=0 Heat treated metals, lead act this way Effect of temperature on properties At elevated temperatures, materials are lower in strength and higher in ductility Chapter 5 ( Dimensions, Tolerances, and Surfaces) Dimensions Linear or angular sizes of a component specified on the part drawing Tolerances It is nearly impossible and very costly to make part of exact dimensions A tolerance is a limited variation from the dimension Surface – exterior boundary of an object
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31 Encloses objects bulk mechanical and physical properties Bilateral tolerance Variation is permitted in both positive and negative direction Surface technology Define characteristic of a surface Define surface texture Define surface integrity Surface Substrate – bulk of part; (grain structure built from previous processing) Altered layer – layer where grain structure does not resemble substrate Surface texture – topography of the exterior of the part Roughness – finely spaced derivations from nominal surface Chapter 6 (Metals) Properties of Metal High stiffness and strength (structural framework for most eng products.) Toughness (absorbs energy better than other materials) Good electrical conductivity Good thermal conductivity Alloys Metal composed of two or more elements, one which is metallic Solid solution: one alloying element is dissolved in another to form a single phase structure. The solvent is metallic, and the dissolved element is metallic or non metal. Substitutional solid solution: atoms of solvent are replaced by the dissolved element. Interstitial solid solution: atoms of dissolving element fit into vacant spaces in the lattice structure. The alloy structure is stronger and harder than either of the components.
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This note was uploaded on 10/22/2010 for the course ECON 201 taught by Professor Baker during the Spring '07 term at University of Tennessee.

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final review - 31 Chapter 3 (Mechanical Properties) 3 Types...

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