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This study investigates the low-cycle fatigue behavior of mooring chains high-strength steel grade R4 under different strain amplitudes and strain ratios at room temperature. A fatigue test program has been carried out on small low cycle fatigue specimens cut from large mooring chains. The experimental results characterize the cyclic stress-strain relationship, the mean stress relaxation behavior, and the cyclic plasticity parameters of the material. Strain energy density is correlated with fatigue life through a simple power-law expression and very well represented by Basquin-Coffin-Mansion relationship. Further, a non-linear elastic-plastic material model is calibrated to the experimental stress-strain curves and used for the estimation of energy dissipation in the specimens under applied cyclic loads. The predicted fatigue life using the calibrated material parameters demonstrates a close agreement with the experimental fatigue life. Numerical simulations are carried out to analyze local plastic straining and assess crack initiation at the pit site of corroded mooring chains considering the multiaxial stress state. An energy-based approach is employed to estimate the number of cycles needed for a crack to initiate from an existing corrosion pit. 相似文献
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Grouted connections (GCs) are widely used to connect superstructures and driven piles in offshore wind turbine structures. They resist fatigue loading in marine splash zones and even submerged environments. In this paper, six GC segment specimens were designed and tested under fatigue loading in both the air and water ingression conditions. The results in the air condition showed that for the specimens with lower loading ranges, the strain distributions and residual displacements stabilized after 20 thousand load cycles. These conditions persisted until the end of the test with two million cycles, with only a few tiny cracks appearing on the grout material surface. Meanwhile, wide cracks and grout material exfoliation were found in specimens with higher loading ranges. The residual displacement accumulated gradually, which eventually caused the termination of the test when it reached 5 mm after 1.3 million cycles. The results in the water ingression condition showed that the water had entered into the micro-cracks of the grout material, which severely degraded the fatigue behavior of the GC specimens. Even in lower loading ranges, specimens W-1 and W-2 only endured 0.264 million and 64 thousand load cycles before the displacement of the top clamp reached −10 mm. Compared with two specimens tested in the air, with a total displacement of less than −0.7 mm after two million load cycles, the severe deteriorating effect of water ingression on the fatigue behavior of GCs was apparent. 相似文献
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介绍了2万Hz超声波振动疲劳试验机对两种铁的高周(大于10^6周)摩擦疲劳强度进行研究。结果发现,这两种材料在高周到超高周区间,疲劳强度随材料寿命的加大呈明显减小,即S-N曲线呈明显下降趋势,这一结果与传统的假说完全不同,高周疲劳强度曲线使用低周疲劳强度的延长线比水平线假设更为恰当,借助于电子显微镜对试件断面作了观察及对引起疲劳破坏起始处进行了化学分析,对高强度钢的高周摩擦疲劳损坏机理作了探讨。 相似文献
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基于修正CS模型的船用低碳钢动态力学性能研究 总被引:1,自引:0,他引:1
为了得到船用低碳钢的动态力学性能及本构关系,运用静态试验机及分离式Hopkinson压杆加载装置,在应变率为0.000 2~3 900 s-1范围内得到了准静态拉伸及动态压缩条件下的应力应变曲线,对Cowper-Symonds材料模型进行了修正,得到了两种形式的本构关系,并讨论了模型的适用性。结果表明:船用低碳钢具有明显的应变率强化效应和非线性应变硬化效应;两种动态本构关系可以描述材料在冲击荷载下的力学性能;模型在高应变率(2 000 s-1)下的使用应慎重。 相似文献
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采用万能试验机和霍普金森压杆(SHPB)系统,对火灾爆炸下921A钢高温力学性能及动态力学性能进行研究。基于试验数据,分别拟合Johnson-Cook本构模型、Cowper-Symonds本构模型,修正Cowper-Symonds模型应变硬化项,并通过试验验证了有效性。参考Johnson-Cook本构模型温度项耦合方法,建立综合考虑温度软化效应和应变率强化效应的921A钢本构模型。 相似文献
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《Marine Structures》2002,15(3):233-250
Reliability-based design analysis of the fatigue life of the connectors of the five sections of the 2-km long US Mobile Offshore Base (MOB) is demonstrated. A performance function is defined in terms of the nominal stress range, inherent defect or starter crack, and appropriate material properties, which are considered random variables. The reliability analysis is performed for a sea state 1–8 (SS1–8) random loading having a Gumbel distribution. Where possible, uncertainty data for random variables are obtained from published data relating to the fatigue of metal and metal alloys. Otherwise, judgmental coefficients of variation are prescribed for purposes of demonstration. The fatigue life is assumed to follow the Weibull distribution. The reliability function is defined in terms of the mean life and the total uncertainty in the fatigue life. Preliminary reliability calculations suggest that current design stress levels be reduced to meet the current fatigue life target reliability level for the MOB connectors. An illustrative design is demonstrated and the metal selected for a fatigue design of the connectors for 10 million cycles with a reliability of 0.99 at a nominal stress of 203 MPa is HY-130 steel. 相似文献
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内陆港口砂岩地基在水的循环作用下,岩石力学性能劣化,威胁港口地基的长期稳定性。为探究砂岩在干湿循环作用下的力学特性及能量损伤,开展不同干湿循环次数下的三轴压缩试验。结果表明:随着干湿循环作用的增强,砂岩力学性能指标逐渐衰减,当循环次数达到15次时,衰减幅度基本收敛;砂岩峰值强度、残余强度、弹性模量和变形模量的劣化度累积具有相似规律,干湿循环0~8次时累积速率较快,循环次数达到15次时累积速率放缓;在应力作用下,岩石吸收总能量随着应变增长而逐渐递增,耗散能累积主要集中在岩石破坏阶段。能量耗散导致损伤发展,损伤变量与耗散能走势较为一致。 相似文献
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采用不同焊接工艺对2205双相不锈钢进行焊接,分析不同焊接工艺对焊接接头力学性能、微观组织及耐腐蚀性能的影响。结果显示:在晶粒无明显长大时,焊缝及热影响区冲击韧性随奥氏体质量分数的增加而升高;采用熔化极气体保护焊(Gas Metal Arc Welding,GMAW)时,保护气体中加入N2可有效提高焊接接头各区域奥氏体质量分数,从而提高焊接接头力学性能及耐腐蚀性能;2205双相不锈钢母材及焊缝腐蚀速率均明显随腐蚀液质量分数的升高而增加。优化双相不锈钢焊接工艺参数,保证其焊接接头具有良好的综合性能,对于该类材料构件及产品的制造、推广及使用意义重大。 相似文献
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This paper presents experimental assessment of crack growth rates of S355J2+N steel in a corrosion fatigue environment similar to what is experienced on offshore wind farm monopile structures under various cyclic load frequencies in order to assess the effect of cyclic frequency of the applied loading within a frequency range pertinent to the structure. Fatigue crack propagation behaviour in this test programme is evaluated through fatigue tests on six compact tension test specimens in air and in laboratory simulated seawater under free corrosion condition. Fatigue crack lengths were monitored by back face strain (BFS), DCPD and ACPD. A regression model was derived through the BFS method to express strain values as a function of crack length to width ratio. The effectiveness of BFS method is particularly demonstrated in the simulated marine environment. Within the range of test frequencies, crack growth rates in simulated seawater when compared to the equivalent air test revealed environmental reduction factors of 2 and 4 at lower and higher values of stress intensity factors respectively. Significant difference in the results of the seawater test frequencies is discussed. 相似文献
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为研究不同钢管桩基础与砂土界面剪切特性,研制一种新型桩土界面环剪仪,并基于此设备开展不同围压下钢管桩与均质细砂、福建砂、美国戴维斯砂的界面剪切试验.试验设计压力为200~800 kPa,通过测试分析桩土界面环形剪切时的扭力特征,探究不同桩土界面条件下的剪切应力应变关系.研究结果表明:界面剪切应力随剪切位移增大而增大并趋向稳定,但是在大应变的情况下,界面剪切应力有一定的波动.桩土界面剪切应力拐点对应的剪切位移及界面摩擦角随着法向应力的增加而增加,呈近似线性关系. 相似文献
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潜艇在潜浮过程中,由于静水外压引起的工作应力与焊接残余应力叠加,形成拉压循环应力,导致耐压船体的局部结构可能出现低周疲劳裂纹.一般情况下,高强度钢在抗拉强度提高的同时往往伴随着材料塑性储备和断裂韧性的下降,因此分析高强度钢潜艇结构的低周疲劳寿命非常重要.本文基于断裂力学和Paris公式建立了潜艇耐压结构低周疲劳寿命的工程估算方法,根据裂纹无损检测的概率统计和含裂纹圆柱壳极限应力分析,给出了初始裂纹和裂纹临界状态的建议值.应用本文的简化方法分析了某潜艇结构和锥柱结合壳模型的低周疲劳寿命,锥柱结合壳模型的数值算例表明本文的计算结果与试验测试结果相吻合. 相似文献
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