Engineering Experimentation 2 Lab

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Howard University Washington, D.C. Department of Mechanical Engineering “Strain Hardening “ Lab 2 By Theron Lewis For Professor H.A. Whitworth October 3rd, 2011 Table of Contents ABSTRACT Work hardening (or strain hardening) is the strengthening of a metal by plastic deformation. This phenomenon occurs because of the altering of the material’s crystal structure through dislocation movements. Work hardening is used extensively in metalworking, where one intentionally induces plastic deformation to increase strength and change its shape. These processes are also known as cold working. In our lab, we showed how cold working will increase the strength of a metal material by inducing plastic deformation on a steel sample and an aluminum sample using an MTI tensile testing machine. INTRODUCTION Work Hardening Work hardening is defined as the phenomenon that occurs when a metal is strained beyond the yield point. Increasing stress is required to produce additional plastic deformation causing the metal to become stronger and more difficult to deform. If true stress is plotted against true strain, the rate of strain hardening tends to become almost uniform, that is, the curve becomes almost a straight line [2]. The strain hardening coefficient of work is defined as the gradient of the straight part of the line. This is closely related to the shear modulus [2]. Therefore, a metal with a high shear modulus will have a high strain or work hardening coefficient. Grain size will also influence strain hardening, and a material with small grain size will strain harden more rapidly than the same material with a larger grain size. This effect only

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