残余应力外文翻译.doc

外文资料和中文翻译 外文资料 Residual Stresses A residual stress is one that exists without external loading or internal temperature differences on a structure or machine. It is usually a result of manufacturing or assembling operations. Sometimes it is called initial stress, and the operation, pressures when the structure or machine is put into service, the service loads superimpose stresses. If the residual stresses add to the service-loads superimpose stresses, they are detrimental; if they subtract from the service-load stresses they are beneficial. Only a few examples of detrimental residual stresses will be given here. One , in the assembly of machinery, occurs when two shafts are not in line or are a few thousandths of an inch out of parallel, and they are forced into connection by rigid couplings. The resulting stresses in the shafts become reversing stresses when the shafts are rotated. The correction, when perfect alignment cannot be economically attained, as is frequently the case, is to use flexible couplings of a type necessary for the degree of misalignment. The preceding case occurs with elastic stresses only, and the residual stresses are maintained by bearing constraints. In application where mechanical work causes plastic yielding, stresses remain when the constraints are removed. For example, the forging of shafts and crankshafts and the cooling after forging may induce residual stresses, the equilibrium of which is changed in machining, causing some warping of the shafts. It is then common practice to straighten the shafts in a press before the final machining operation. Straightening requires a bending moment large enough to cause permanent set or yielding. Detrimental residual stresses commonly result from differential heating or cooling. A weld is a common example. The weld metal and the areas immediately adjacent are, after solidification, at a much higher temperature than the mail body of metal. The natural contraction of the metal along the