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制作高强钢特征试件,在压、弯应力共同作用下进行疲劳断裂试验;结合疲劳辉纹产生机理,采用降载勾线法在试件断面制造出“海滩状花纹”;利用CAD软件描绘断面形貌并测量裂纹长度,用Newman-Raju理论进一步研究表面裂纹扩展的规律,并与试验值比较。结果表明降载勾线法可以解决高强度钢表面裂纹不易测量及断面难以观测到疲劳辉纹的问题;采用Newman-Raju公式模拟压弯组合应力下表面裂纹扩展形貌是合适的,但由此计算的疲劳寿命偏于保守。另外,当压弯应力比值较小时,计算扩展形貌时压应力可以忽略,而计算疲劳寿命时压应力不可忽略。
The fatigue crack test was carried out under the joint action of pressure and bending stress. Combined with the generation mechanism of fatigue crest, the “beach-like pattern” was fabricated on the cross-section of the specimen by using the loading-down line method. Using CAD software The cross-sectional morphology was characterized and the crack length was measured. The rule of surface crack propagation was further studied by Newman-Raju theory and compared with the experimental data. The results show that the method of loading line can solve the problem of difficult to measure the surface crack of high-strength steel and difficult to observe the fatigue fringe. The Newman-Raju formula is suitable to simulate the surface crack growth under the stress of bending and bending, The calculated fatigue life is conservative. In addition, compressive stress can be neglected when calculating the extended morphology when compressive stress ratio is small, and compressive stress can not be ignored when calculating fatigue life.