影響耐久性強度的因素機械設計及制造專業(yè)畢業(yè)設計外文翻譯-中英文對照-在線瀏覽
2025-03-05 15:23本頁面
【正文】 e stress concentration factors ,as found from the methods of Section,to the puted stresses,rather than to the allowable strengths. Flaws Internal flaws of the material,especially likely in cast parts,are places in which fatigue cracks parts can be inspected by xray techniques for internal flaws,If they are not inspected, a higherthanaverage design factor should be specified for cast parts,and a lower endurance strength should be used. Temperature Most materials have a lower endurances strength at high reported values are for room above 160176。F(72176。F（ 514176。R= ■ Partially reversed fluctuating stress with a tensile mean stress【 Figure 54(b)】 。R=0 ■ Fluctuating tensile stress【 Figure 54(a)】 。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 of load producing R greater than but less than have less of an effect on the endurance strength. This illustrates that using data from the reversed bending test is the most conservative. We will not use Figure 510 directly for problem in this book because our procedure for estimating the actual endurance strength starts with the use of Figure 59 which presents data from reversed bending tests .Therefore,the effect of stress ratio is already included. Section 59 of this chapter includes methods of analysis for loading cases in which the fluctuating stress produces a stress ratio different from R= Reliability The data for endurance strength for steel shown in Figure 59 represent average values derived from many tests of specimens having the appropriate ultimate strength and surface ,there is variation among the data points；that is, half are high
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