Lab05_Cold_Work_DKSinha - San Francisco State University...

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San Francisco State University School of Engineering ENGR 200: Materials of Engineering Laboratory 5 Cold Work I. OBJECTIVES The purpose of this experiment is to familiarize students with cold working metals and determining the effect of cold work on the strength and hardness of metals. II. INTRODUCTION “Cold working” or strain hardening is one of the most important methods in strengthening some metals,  defined as the process in which the metal undergoes plastic deformation at a temperature specifically  below one half of its melting temperature. When metals such as brass, copper, aluminum, iron that have  been annealed are cold worked at room temperature, they strain-harden and as a result, their yield  strengths increase. At the microscopic level, strain hardening occurs due to the increase in dislocation  density, which prevents the movement of dislocation and hence preventing further plastic deformation.  Cold working is the only method used to strengthen some metals such as pure copper and aluminum. In  this experiment, we will investigate the relationship between the amount of cold working, hardness, and  compressive strength of brass and aluminum.  III. Theory The percentage of cold work (% CW) experienced by a metal is defined as follows: ( 29 ( 29 ) 1 ..( .......... .......... % 100 ) ( % ) 1 ( .......... .......... .......... % 100 ) ( % 0 0 0 0 b n Compressio x A A A CW a Tension x A A A CW f f - = - = Where A 0 and A f are the original and final cross-sectional areas of the specimen, as shown in Figure 1. During the experiment, the volume of the specimen is conserved:
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Lab05_Cold_Work_DKSinha - San Francisco State University...

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