影響耐久性強度的因素外文翻譯-全文預(yù)覽
【正文】 e base material must be considered. 本科生畢業(yè)論文（設(shè)計） 第 5 頁 共 17 頁 本科生畢業(yè)論文（設(shè)計） 第 6 頁 共 17 頁 Residual Stresses Fatigue failures typically initiate at locations of relatively high tensile and machining,especially with high material removal rates,also cause undesirable residual tensile has already been mentioned as a process that may produce residual tensile stress. Any manufacturing process that tends to produce residual stress will decrease the endurance strength of the ponent. Critical areas of cyclically loaded ponents should be machined or ground in a gentle that produce residual pressive stresses can prove to be blasting and peening are two such blasting is performed by directing a highvelocity stream of hardened balls or pellets at the surface to be uses a series of hammer blows on the ,springs,and other cyclically loaded machine parts can benefit from these methods. Corrosion and Environmental Factors Endurance strength data are typically measured with the specimen in conditions that expose a ponent to water,salt solutions,or other corrosive environments can significantly reduce the effective endurance may cause harmful local surface roughness and may also alter the internal grain structure and chemistry of ehe exposed to hydrogen are especially affected adversely. 本科生畢業(yè)論文（設(shè)計） 第 7 頁 共 17 頁 Nitriding Nitriding is a surfacehardening process for alloy steels in which the material is heated to 950176。F(72176。R= ■ Partially reversed fluctuating stress with a tensile mean stress【 Figure 54(b)】 。R=1 Note that Figure 510 is only an example,and it should not be used to determine actual data such data are desired for a particular material,specific data for that material must be found either experimentally or published literature. The most damaging kind of stress among those listed is the repeated,reversed stress with R=1.(See Reference 27.)Recall that the rotating shaft in bending as shown in Figure 52 is an example of a loadcarrying member subjected to a stress ratio R=1. Fluctuating stresses with a pressive mean stress as shown in Parts(c) and (d) of Figure 54 do not significantly affect the endurance strength of the material 本科生畢業(yè)論文（設(shè)計） 第 10 頁 共 17 頁 because fatigue failures tend to originate in regions of tensile stress. Note that the curves of Figure 510 show estimate of the endurance strength, Sn ,as a function of the ultimate tensile strength for data apply to ideal polished specimens and do not include any of ethe other factors discussed in this section. For example,the curve for R=(reversed bending)shows that the endurance strength for steel is approximately times the ultimate strength(Sn)for large numbers of cycles of loading(approximately 10 or higher).This is a good general estimate for steels. The chart also shows that types
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