共查询到18条相似文献,搜索用时 156 毫秒
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对国产P92钢开展了600℃蠕变试验,得到了蠕变变形曲线、蠕变指数和蠕变延性等,再在600℃进行蠕变裂纹扩展行为试验研究,得到了蠕变裂纹萌生时间和蠕变裂纹扩展速率与蠕变断裂力学参量C*的关系,将国产P92钢的性能与BS 7910数据进行比较,评估NSW模型的预测效果,计算得到材料的蠕变断裂韧性。结果表明,蠕变裂纹萌生时间和蠕变裂纹扩展速率与蠕变断裂力学参量C*之间有较好的双对数线性相关性。国产P92钢的蠕变裂纹扩展性能优于BS 7910中9%Cr钢的平均性能,NSW模型的平面应力预测结果与试验数据接近,材料的蠕变断裂韧性随着服役时间的增大逐渐降低。该研究结果可以用于评估长期服役高温结构的安全性。 相似文献
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裂纹的存在及其扩展严重限制着高温承压部件的使用寿命,而目前对结构三维蠕变裂纹扩展行为的认识及其预测仍比较有限。以典型耐热钢P91为例,在650℃下对其开展了不同应力和不同初始裂纹尺寸的表面裂纹蠕变扩展试验,通过断面观察获得了蠕变裂纹扩展形貌演化,并采用基于多轴蠕变损伤模型的有限元法、基于蠕变裂纹尖端参量C*的有限元法以及英国标准BS7910推荐的简化计算方法进行表面裂纹蠕变扩展分析。结果表明,基于多轴蠕变损伤模型的有限元法能够合理地描述裂纹最终轮廓并准确地预测裂纹扩展时间。相比之下,基于C*的有限元法和BS7910简化计算方法计算的裂纹形貌预测有明显偏差,并且较依赖于紧凑拉伸试样的蠕变裂纹扩展试验数据及其拟合的参数C和q,易导致过于保守的裂纹扩展时间预测。评估了不同计算方法对于表面裂纹蠕变扩展行为的预测能力。 相似文献
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主要研究剪切载荷作用下,胶接材料中弹性和粘弹性界面间Griffith裂纹尖端动态应力强度因子的时间响应.采用积分变换方法,得到Laplace域内弹性和粘弹性材料的应力和位移的含未知系数的表达式;引入位错密度函数,并通过边界条件和界面连接条件,导出反映裂纹尖端奇异性的奇异积分方程组,采用Gauss积分,并运用Gauss-Jacobi求积公式化奇异积分方程组为代数方程组,利用配点法进行求解;最后经过Laplace逆变换,求得动态应力强度因子的时间响应.得到Ⅱ型动应力强度因子随着粘弹性材料的剪切松弛参量的增加而增大,膨胀松弛参量的增加而减小;随着弹性材料的剪切模量和泊松比的增加而增大. 相似文献
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通过在1103~1163°K下测量HK40钢时辰变裂纹扩展速率,分析了温度对蠕变裂纹扩展速率的影响,求出的裂纹扩展激活能接近蠕变激活能,这表明裂纹扩展由蠕变的某种机制控制。在1144°K下,研究了铸态(NL),运行21000小时(YB2)和运行50000小时(DB1)三种材料的蠕变裂纹扩展行为。指出,铸态材料和蠕变损伤的材料的蠕变损伤的材料的蠕变裂纹扩展行为是不同的,DB 1蠕变空洞数量多是其裂纹扩展速率高于YB2的主要原因,细小二次碳化物使裂纹扩展速率增高。 相似文献
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通过对不同热处理后获得3种典型显微组织的粉末高温合金FGH96合金试样在650 进行保载90 s和5 s并恒载荷循环应力作用下的疲劳试验,研究组织特征对疲劳裂纹扩展速率的影响规律,确定不同载荷条件下孕育期、萌生期、扩展期及瞬断期所占的比率。结果表明,γ相特征显著影响疲劳裂纹扩展速率;疲劳行为对保载时间存在敏感性,随保载时间的延长,在疲劳-蠕变的交互作用下会明显加快合金疲劳裂纹扩展;在整个疲劳破坏过程中,萌生比率均高于扩展比率,说明该合金抗裂纹萌生的能力要高于抗裂纹扩展的能力;此外,该合金疲劳裂纹扩展四个阶段在整个断裂周次所占的比率分配上,孕育期比率一般较小,萌生期和扩展期比率较大,瞬断期的比率很小,表明该合金裂纹扩展一旦失稳将高速扩展并迅速断裂。 相似文献
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基于新裂纹扩展驱动力参量的焊接接头疲劳裂纹扩展的研究 总被引:1,自引:1,他引:0
传统上疲劳裂纹扩展速率以一个参量——应力强度因子幅(PARIS模型)或有效应力强度因子幅(ELBER模型)来表达。PARIS模型不能统计应力比效应和变幅加载历史。ELBER裂纹闭合模型虽被广泛应用,但确定其开闭口载荷的测量方法很多,且测量结果均存在主观性。最近研究表明,疲劳裂纹扩展不仅依赖于应力强度因子幅,还与最大应力强度因子有关。并且KUJAWSKI提出了两参量模型,该模型避开了有争议的裂纹闭合效应。基于一个载荷循环中柔度变化与裂纹尖端开闭口与弹塑性行为的关系,提出一个新的具有物理意义的两参量驱动力模型。针对Q345钢焊接接头各区域进行两种应力比R=0.1和0.5的疲劳裂纹扩展试验。使用该模型针对Q345钢焊接接头各区域的疲劳裂纹扩展数据进行验证。结果表明,提出的新模型在预测应力比对裂纹扩展速率的影响时比上述三个模型更有效。 相似文献
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D. J. Kim D. Y. Seo J. Tsang W. J. Yang J. H. Lee H. Saari C. S. Seok 《Journal of Mechanical Science and Technology》2012,26(7):2023-2027
Fatigue crack growth rate (FCGR) tests with different load ratios and dwell-fatigue crack growth rate (DFCGR) tests with different dwell times were conducted at 750°C for Incoloy 800H. As the load ratio increases from 0.1 to 0.5, the crack growth rate increased and the transition ??K value from region I to region II (Paris regime) shifted leftward. In DFCGR tests with dwell time of 10 and 30 seconds, the Paris regime started at relatively lower ??K level and the crack grew much faster than in FCGR tests. However, the crack growth rates between the 10 sec and 30 sec dwell times were relatively similar. The higher crack growth rates in the DFCGR tests compared to FCGR tests was associated with the reduction of the M23C6 precipitates in the vicinity of the advancing crack by the Cr depletion, suggesting the crack propagation in DFCGR conditions was environmentally assisted. The crack growth rate was controlled by trans-granular mode regardless of the dwell time because the dwell time was not enough to cause creep damage. 相似文献
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WANG Yan WANG Zhongmin ZHOU Yingfeng 《机械工程学报(英文版)》2008,21(6):36-40
Based on the two-dimensional viscoelastic differential constitutive relation and the thin plate theory, the differential equations of motion of the viscoelastic plate with an all-over part-through crack are established and the expression of additional rotation induced by the crack is derived. The complex eigenvalue equations of the viscoelastic plate with crack are derived by the differential quadrature method, and the 8method is used at the crack continuity conditions. Dimensionless complex frequencies of a crack viscoelastic plate with four edges simply supported, two opposite edges simply supported and other two edges clamped are calculated. The effects of the crack parameter, the aspect ratio and dimensionless delay time of the material on the transverse vibration of the viscoelastic plate are analyzed. 相似文献
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This study is concerned with the general solution of the field intensity factors and energy release rate for a Griffith crack
in a piezoelectric ceramic of finite radius under combined anti-plane mechanical and in-plane electrical loading. Both electrically
continuous and impermeable crack surface conditions are considered. Employing Mellin transforms and Fourier series, the problem
is reduced to dual integral forms. The solution to the resulting expressions is expressed in terms of Fredholm integral equation
of the second kind. The solutions are provided to study the influence of the crack length, the crack surface boundary conditions
on the intensity factors and the energy release rate. 相似文献