影響耐久性強(qiáng)度的因素機(jī)械設(shè)計(jì)及制造專(zhuān)業(yè)畢業(yè)設(shè)計(jì)外文翻譯-中英文對(duì)照-文庫(kù)吧資料
2025-01-22 15:23本頁(yè)面
【正文】 enter of the circular cross the actual loading is different from bending,a factor for the type of loading should be applied to the endurance strength. Axial Tension Under pure tension, all of the materialnot just the surface— is subjected to the maximum stress. A factor of is suggested to be the bending endurance strength to reflect this different behavior. Effect of Stress Ratio on Endurance Strength Figure 510 shows the general variation of endurancestrength data for a given material when the stress ratio R varies from to +,covering the range of cases including the following: ■ Repeated,reversed stress(Figure 53)。C) will reduce the endurance strength of most ductile materials. Nonuniform Material Properties Many materials have different material properties in different directions because of the manner in which the material was sheet or bar products are typically stronger in the direction of rolling than they are in the transverse 本科生畢業(yè)論文（設(shè)計(jì)） 第 4 頁(yè) 共 17 頁(yè) direction. Fatigue tests are likely have been run on test bars oriented in the stronger of such material in the transverse direction may result in lower endurance strength. Nonuniform properties are also likely to exist in the vicinity of welds because of inplete weld peration,slag inclusions,and variations in the geometry of the part at the weld. of heattreated materials may alter the strength of the material because of local annealing near the weld. Some welding processes may result in th production of residual tensile stresses that decrease the effective endurance strength of the material. Annealing or normalizing after welding is often used to relieve these stresses,but the effect of such treatments on the strength of the base material must be considered. 本科生畢業(yè)論文（設(shè)計(jì)） 第 5 頁(yè) 共 17 頁(yè) 本科生畢業(yè)論文（設(shè)計(jì)） 第 6 頁(yè) 共 17 頁(yè) 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
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