Lecture+1b+-+Mechanical+Behavior

Lecture+1b+-+Mechanical+Behavior - Fundamentals of the...

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Fundamentals of the Mechanical Behavior of Materials Lecture 1.b ISE 2204 – Introduction to Manufacturing Processes Dr. Jaime Camelio January 21 st , 2010 1 Deformation Tension Test Engineering Strain – Stress True Strain/Stress Compression Torsion Bending Hardness Impact Residual Stresses Yield Criteria ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Outline 2
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Elastic vs. Plastic Deformation Elastic Deformation – Materials recover their original shape after removing an external force Plastic deformation - shaping materials by applying force Forging Rolling Extrusion Rod/wire drawing Stamping When does it happen? What happens to the material during these processes? ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Deformation How are its properties altered? 3 Force Requirements How big a press do we need? Formability of the Work Material Can the material be shaped as desired? Do we need to heat it up? Do we need a different material? Material Flow Pattern Are dies designed so that the workpiece can flow to fill the die cavity? Do we need more than one forming station? Surface Finish What are the finish requirements? The answer may determine whether we hot work (poor finish) or cold work (good finish). What lubricant do we select? Tool and Die Wear How can we slow down the die wear? Tooling is extremely expensive ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Relevant Factors in the Planning of a Forming Process High pressures accelerate die wear, as do high temperatures.
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Tension – material is pulled from both ends Compression – pushed from both ends Shear – forced from opposite directions at each end The degree of deformation is defined as strain Types of Strain The degree of deformation is defined as ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Basic Modes of Deformation (a) Tensile. (b) Compressive. (c) Shear. All deformation processes in manufacturing involve strains of these types. Tensile strains are involved in stretching sheet metal to make car bodies, compressive strains in forging metals to make turbine disks, and shear strains in making holes by punching. 5 Engineering Strain For tension (positive) or compression (negative) l = length after force is applied l 0 = length before force is applied Engineering Stress The ratio of the applied load (force) to the original area of the specimen (“original length”) Shear Strain A strain that acts parallel to the face of the material it is acting on 0 0 l l l e 0 A P ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Engineering Strain and Stress b a 6
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Provides the stress-strain curve Very simple test of material The determination of these forces as a function of strain is important Design the proper equipment to use
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Lecture+1b+-+Mechanical+Behavior - Fundamentals of the...

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