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1. Read and translate the text. Stress and Strength The survival of many products depends on how the designer adjusts the maximum stresses in a component to ...

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1. Read and translate the text.

Stress and Strength

The survival of many products depends on how the designer adjusts the maximum stresses in a component to be less than the components strength at critical locations. The designer must allow the maximum stress to be less than the strength by a sufcient margin so that despite the uncertainties, failure is rare. In focusing on the stress-strength comparison at a critical (controlling) location, we often look for strength in the geometry and condition of use. Strengths are the magnitudes of stresses at which something of interest occurs, such as the proportional limit, 0.2 percent-offset yielding, or fracture (see Sec. 21). In many cases, such events represent the stress level at which loss of function occurs.

Strength is a property of a material or of a mechanical element. The strength of an element depends on the choice, the treatment, and the processing of the material. Consider, for example, a shipment of springs. We can associate a strength with a spe-cic spring. When this spring is incorporated into a machine, external forces are applied that result in load-induced stresses in the spring, the magnitudes of which depend on its geometry and are independent of the material and its processing. If the spring is removed from the machine unharmed, the stress due to the external forces will return to zero. But the strength remains as one of the properties of the spring. Remember, then, that strength is an inherent property of a part, a property built into the part because of the use of a particular material and process. Various metalworking and heat-treating processes, such as forging, rolling, and cold forming, cause variations in the strength from point to point throughout a part.

Available: http://www.academia.edu/6860372/Shigleys_mechanical_engineering_design_9th_edition

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