【作者】 刘海波；

【导师】 薛启超；

【作者基本信息】 哈尔滨工程大学 ， 力学， 2022， 硕士

【摘要】 断裂力学的研究在实际工程中有着重要的意义,主要原因是目前工程很多事故是由于带裂纹的结构体在服役过程中裂纹逐渐扩展直至断裂导致的,如不加以预判和控制将会造成不可估量的损失。带裂纹的结构在承受准静态载荷时容易发生裂纹扩展,当承受冲击载荷时更容易发生断裂。本文主要针对含裂纹的管道结构,并在结构的上方加一块重物,对其施加冲击加速度的数值计算,获得结构的响应和裂纹扩展时程。基于J-A₂双参数方法,获得材料的动态断裂韧性,结合断裂约束理论,对管道结构I型裂纹的动态断裂韧性进行修正,与有限元分析结果对比,验证了断裂韧性转化公式在结构裂纹动态断裂分析的有效性,具体研究成果如下:1.介绍了断裂力学的分类与发展,并详细阐释了线弹性断裂力学的基本理论以及相应的断裂准则;阐释了线弹性断裂力学的基本理论以及主要的三种断裂韧性准则,即COD准则、J积分准则和J-A₂双参数法,基于J-A₂双参数法得到了断裂韧性转化方法。2.对于动态断裂力学的数值计算方法进行了介绍,主要介绍了有限元法。基于薄壁圆管结构的力学性能分析方法,获得了薄壁圆管冲击断裂的损伤本构模型。3.基于有限元法对于细长圆管与短粗圆管进行了数值计算,得到了不同裂纹尺寸的两种结构圆管在承受三种冲击载荷作用下的冲击响应。4.对圆管结构进行数值模拟,不断增加载荷通过二分法得到了薄壁圆管结构的极限载荷。并对圆管结构进行多次冲击载荷的数值计算,获得了半正弦波冲击载荷下的力学响应。5.分析了结构裂纹特性,得到了裂纹嘴张开位移（COD）时程曲线,裂纹扩展量Δa时程曲线,并研究了裂纹尖端主应力和应力场随时间的变化的曲线,以及裂纹扩展速率,并对裂纹尖端应力场做了分析。6.通过对不同裂纹尺寸下的J积分临界数值进行转化,并将转化结果与数值计算结果对比,再经过误差计算,验证对于较复杂带裂纹圆管结构在低速冲击条件下,J-A₂双参数法在动态断裂韧性转化方面的可实施性。更多还原

【Abstract】 The research of fracture mechanics is of great significance in practical presentation.The main reason is that many engineering accidents are caused by the gradual propagation of cracks to fracture in the service process of structures with cracks.Failure to predict and control it will cause immeasurable losses.The structure with crack is prone to crack propagation under quasi-static load,and it is more likely to break when the structure is subjected to an impact load.This article mainly focuses on the pipeline structure with a central crack,and adds a heavy object on the top of the structure and applies shock acceleration to it to obtain the response of the structure and the crack propagation time history.Based on the J-A₂ method,the dynamic fracture toughness of the material is obtained.Combined with the fracture constraint theory,the dynamic fracture toughness of I-shaped cracks of the pipeline structure is modified.Combined with the finite element results and the test results,the effectiveness of the J-A₂ method in the dynamic fracture analysis of structural cracks is verified.The specific results as follows:1.The classification and development of fracture mechanics,and explained in detail the basic theory of linear elastic fracture mechanics and the corresponding fracture criterion.The classification and development of fracture mechanics are introduced,and the basic theory of linear elastic fracture mechanics and the corresponding fracture criteria are explained in detail.The basic theory of linear elastic fracture mechanics and the three main fracture toughness criteria are explained,namely COD criterion,J integral criterion and J-A₂ method.Fracture toughness transformation method is obtained based on the J-A₂ method,makes difficult tests can be obtained through a simple standard specimen test and the corresponding fracture toughness can be obtained through the conversion formula.2.The numerical calculation method of dynamic fracture mechanics,mainly the finite element method is explained.The principles,advantages and application scope of various methods are compared and explained.Determine the mechanical performance analysis method for thin-walled round pipe structure,and determined the damage constitutive model for impact fracture of thin-walled pipe.Based on the mechanical property analysis method of thin-walled round pipe structure,the damage constitutive model of impact fracture of thin-walled round pipe is obtained.3.Numerical simulations are carried out for the slender pipes and the stubby pipes based on the finite element method.The mechanical response of two pipeline structures with different size of cracks under three types of impact is analyzed.4.Numerical simulation of pipeline structure,continuously increase the load,the ultimate load of the thin-walled pipeline structure is determined by the dichotomy.And carry out the numerical simulation of multiple impact loads for the pipeline structure,the mechanical response under the impact load of a half sine wave was carried out.5.The structural crack characteristics are analyzed,the crack mouth opening displacement（COD）time history curve and the time-history curve of crack growth（Δa）are obtained.The curves of the principal stress and the stress field at the crack tip were studied.And the crack growth rate was studied.The stress field at the crack tip was analyzed.6.Compared the transformation results with the numerical calculation results by converting the J-integral critical values for different crack sizes,after error calculation,what proved the feasibility of J-A₂ method in dynamic fracture toughness transformation,which in the conditions of the pipeline structure with crack under low-velocity impact.更多还原