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961.
Multiaxial fatigue damage parameter and life prediction for medium-carbon steel based on the critical plane approach 总被引:3,自引:0,他引:3
De-Guang Shang Guo-Qin Sun Jing Deng Chu-Liang Yan 《International Journal of Fatigue》2007,29(12):2200-2207
The tension–torsion fatigue characteristics were investigated under proportional and non-proportional loading in this paper. The fatigue cracks on the surface of multiaxial fatigue specimens were observed and analyzed by a scan electron microscope. On the basis of the investigation on the Kindil–Brown–Miller and Fatemi–Socie’s critical plane approaches, a shear strain based multiaxial fatigue damage parameter was proposed by von Mises criterion based on combining the maximum shear strain and the normal strain excursion between adjacent turning points of the maximum shear strain on the critical plane. The proposed multiaxial fatigue damage parameter does not include the weight constants. According to the proposed multiaxial fatigue damage parameter, the multiaxial fatigue life prediction model was established with the Coffin–Manson equation, which is used to predict the multiaxial fatigue life of medium-carbon steel. The results showed that the proposed multiaxial fatigue damage parameter could be used under either multiaxial proportional or non-proportional loading. 相似文献
962.
Tensile Strength Characteristics of Unsaturated Sands 总被引:5,自引:0,他引:5
Tensile strength characteristics of unsaturated sands are examined through a combined theoretical and experimental study. The characteristics of tensile strength in all three water retention regimes of pendular, funicular, and capillary are examined. A simple direct tensile strength apparatus is employed to determine tensile strength for sands with a broad range of particle sizes from silty sand to fine sand and medium sand over a full range of degree of saturation. Tensile strength characteristic curves (TSCC) are established experimentally for these sands and are used to validate the existing theories for tensile strength in the pendular regime. The TSCC for sand characteristically exhibits two zeros at 0 and near 100% saturation, and two peak values occurring in the pendular and capillary regimes, respectively. A minimum tensile strength is observed in the dense fine sand, indicating that either water bridges or pore pressure contributes exclusively to the tensile strength in the funicular regime of this sand. The maximum tensile strength for the silty sand is 1,448?Pa, the fine sand is 1,416?Pa, and the medium sand is 890?Pa. Comparison between the soil–water characteristic curves obtained for these sands indicates that the peak tensile strength in the capillary regime is highly correlated to the air-entry pressure. Photographs of the failure surfaces clearly delineate distinct geometric characteristics for different water retention regimes. Analysis of the patterns of failure surfaces in different water retention regimes indicates that the effective stress principle is valid for tensile stress failure in unsaturated sands. 相似文献
963.
基于有限元方法的1 000 kV级特高压交流线路耐张串均压环优化设计 总被引:3,自引:0,他引:3
特高压输电线路绝缘子串电压分布极不均匀,均压环的优化设计对于改善绝缘子端部场强和改变电压分布具有重要意义。应用三维有限元法分别对1000kV特高压交流线路两联、三联和六联耐张串进行了电场计算,计算中考虑了杆塔、导线对电场分布的影响。通过不同屏蔽深度的均压环对电压分布影响的讨论和4种不同形式均压环的对比,建议1000kV特高压交流线路耐张串采用管径为120mm的跑道环,圆形部分中心径为1000mm,联接距根据绝缘子串中心间距决定,放置在第3、4片绝缘子之间。 相似文献
964.
超(超)临界汽轮机汽缸以镍基超高温合金作为紧固件材料,螺栓蠕变损伤的研究对超(超)临界机组的安全运行及维修具有重要意义。对镍基合金Nimonic 80 A进行了550 ℃不同应力下单轴及空心螺栓的蠕变实验,引入应变阈值,结合Norton-Bailey-Kachanov蠕变方程,改进了蠕变损伤模型,模型能更准确描述蠕变全过程;修改有限元软件ABAQUS子程序,模拟了空心螺栓的蠕变过程。结果表明,空心螺栓蠕变断裂并不是在应力集中的螺纹处,而是在螺杆处,有限元计算结果与实验结果吻合较好。 相似文献
965.
966.
967.
968.
Thermal contact conductance at continuous roll-casting interface 总被引:1,自引:0,他引:1
The effects of surface roughness, strain rate, friction coefficient and pressure on real contact area were analyzed based on the research of Stupkiewicz. The real contact area model taking account of the effect of friction and deformation of material was obtained. The model of contact conductance at the rolling interface was obtained by integrating the specific feature of heat transfer through the interface of continuous roll-casting. The results indicate that the real contact area increases obviously when the material is under yield, and the real contact area varies inversely with surface roughness, whereas it varies exponentially with friction coefficient, strain rate and pressure, and the power factor depends on strain rate. 相似文献
969.
Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer (FLIP) laminates in reinforced concrete (RC) beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%. 相似文献
970.
讨论了带脉冲免疫和传染年龄的SEIJV传染病模型,这类传染病有病原体I和J,其中病原体I可发展为病原体J,并且两种病原体对其他人口的传染及病原体I的恢复率均与染病者的年龄有关。运用脉冲微分方程和积分方程的理论和方法,得到染病再生数的表达式,证明了当染病再生数小于某一个小于1的数时,得到了无病周期解的全局吸引性。提出了带脉冲免疫和传染年龄的传染病模型需要解决的问题。 相似文献