The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping tec...The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping technique, the general periodic solutions for collinear cracks are obtained. The stress intensity factors and the size of saturation strips are derived analytically, and their dependencies on the ratio of the periodicity on the half-length of the crack are analyzed in detail. Numerical results show the following two facts. （1） When h/l 〉 4.0, the stress intensity factors become almost identical to those of a single crack in an infinite piezoelectric body. This indicates that the interaction between cracks can be ignored in establishing the criterion for the crack initiation in this case. （2） The speed of the saturation strip size of periodic cracks approaching that of a single crack depends on the electric load applied at infinity. In general, a large electric load at infinity is associated with a slow approaching speed.展开更多
本文根据10CrNiMo高强钢的材料常数C、m,按照Cycle by Cycle方法的计算流程,采用Newman-Raju公式和Paris公式,分别计算了悬臂弯曲加载方式下表面裂纹扩展沿长度和深度方向上的应力强度因子范围△K,得到了裂纹扩展长度与深度的关系及其...本文根据10CrNiMo高强钢的材料常数C、m,按照Cycle by Cycle方法的计算流程,采用Newman-Raju公式和Paris公式,分别计算了悬臂弯曲加载方式下表面裂纹扩展沿长度和深度方向上的应力强度因子范围△K,得到了裂纹扩展长度与深度的关系及其裂纹扩展速率。通过与试验结果的对比,分析了理论计算可能出现的误差,并对Newman-Raju公式进行了修正。结果表明,公式计算所得表面裂纹扩展趋势和裂纹扩展速率趋势与试验结果是一致的,且修正后的Newman-Raju公式在裂纹扩展形貌和扩展速率方面与试验数据拟合曲线都可以较好吻合。采用修正后的Newman-Raju公式,还可以很好地对具有不同初始裂纹形状试样的表面裂纹扩展情况进行预测。展开更多
因四点弯曲梁跨中裂缝截面附近处于纯弯段,故其从理论上更符合Ι型断裂模式。基于此,该文通过开展跨中带缝的四点弯曲梁试验,将荷载作用下的四点弯曲梁纯弯曲段等效为纯弯曲梁,基于线性叠加原理给出了计算混凝土四点弯曲梁双K断裂参数...因四点弯曲梁跨中裂缝截面附近处于纯弯段,故其从理论上更符合Ι型断裂模式。基于此,该文通过开展跨中带缝的四点弯曲梁试验,将荷载作用下的四点弯曲梁纯弯曲段等效为纯弯曲梁,基于线性叠加原理给出了计算混凝土四点弯曲梁双K断裂参数的计算公式,并研究了不同初始缝高比(0.2、0.3、0.4、0.5及0.6)对四点弯曲梁双K断裂参数的影响,结果表明:随着初始缝高比的增大,试件起裂荷载Pini,最大荷载Pmax及相对临界有效裂缝扩展长度(ac-a0)/H均逐渐减小;起裂断裂韧度ini IC K和失稳断裂韧度un IC K基本保持不变。可见,四点弯曲梁可以用于研究混凝土的双K断裂参数。展开更多
基金Project supported by the Postdoctoral Science Foundation of China (No.20070410944)
文摘The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping technique, the general periodic solutions for collinear cracks are obtained. The stress intensity factors and the size of saturation strips are derived analytically, and their dependencies on the ratio of the periodicity on the half-length of the crack are analyzed in detail. Numerical results show the following two facts. （1） When h/l 〉 4.0, the stress intensity factors become almost identical to those of a single crack in an infinite piezoelectric body. This indicates that the interaction between cracks can be ignored in establishing the criterion for the crack initiation in this case. （2） The speed of the saturation strip size of periodic cracks approaching that of a single crack depends on the electric load applied at infinity. In general, a large electric load at infinity is associated with a slow approaching speed.
文摘本文根据10CrNiMo高强钢的材料常数C、m,按照Cycle by Cycle方法的计算流程,采用Newman-Raju公式和Paris公式,分别计算了悬臂弯曲加载方式下表面裂纹扩展沿长度和深度方向上的应力强度因子范围△K,得到了裂纹扩展长度与深度的关系及其裂纹扩展速率。通过与试验结果的对比,分析了理论计算可能出现的误差,并对Newman-Raju公式进行了修正。结果表明,公式计算所得表面裂纹扩展趋势和裂纹扩展速率趋势与试验结果是一致的,且修正后的Newman-Raju公式在裂纹扩展形貌和扩展速率方面与试验数据拟合曲线都可以较好吻合。采用修正后的Newman-Raju公式,还可以很好地对具有不同初始裂纹形状试样的表面裂纹扩展情况进行预测。
文摘因四点弯曲梁跨中裂缝截面附近处于纯弯段,故其从理论上更符合Ι型断裂模式。基于此,该文通过开展跨中带缝的四点弯曲梁试验,将荷载作用下的四点弯曲梁纯弯曲段等效为纯弯曲梁,基于线性叠加原理给出了计算混凝土四点弯曲梁双K断裂参数的计算公式,并研究了不同初始缝高比(0.2、0.3、0.4、0.5及0.6)对四点弯曲梁双K断裂参数的影响,结果表明:随着初始缝高比的增大,试件起裂荷载Pini,最大荷载Pmax及相对临界有效裂缝扩展长度(ac-a0)/H均逐渐减小;起裂断裂韧度ini IC K和失稳断裂韧度un IC K基本保持不变。可见,四点弯曲梁可以用于研究混凝土的双K断裂参数。
