【作者】 孙远韬；

【导师】 王少梅；

【作者基本信息】 武汉理工大学 ， 机械设计及理论， 2008， 博士

【摘要】 近年来,随着社会发展和科技进步,为满足生产发展的需要,机械设备正在向重型、高速、自动化方向发展,其金属结构的承载能力对生产安全的影响也愈来愈大。裂纹作为影响金属结构安全的主要隐患,长期以来一直是人们关注和研究的热点,因而对机械结构裂纹诊断方法的研究具有重要的理论意义和工程应用价值。本文以断裂力学理论为依据,通过有限元方法及其二次开发技术、声发射检测、无网格方法等技术对机械结构裂纹诊断方法及其应用进行了研究,完成了如下工作:(1)应力强度因子在断裂力学中是重要的参数,本文同时使用有限元和无网格方法对其进行了分析计算。由于无网格方法是以节点位移为基础求取应力强度因子的,本文提出了一种权函数自变量方程结合位移外推法来处理裂纹不连续线,从而较精确地求出裂纹尖端的应力强度因子,并且避免了目前处理方法中节点和计算点重合时所发生的数值溢出现象,从而为无网格方法应用于裂纹诊断提供一条新的途径。通过把有限元模型的计算结果与无网格方法所得的结果进行对比分析,说明两种方法的计算结果是合理的。(2)目前裂纹结构的剩余寿命预测往往是根据经验选取若干工况对Ⅰ型裂纹的剩余寿命进行分析的结果,理论上会给裂纹结构剩余寿命的预测带来误差。本文提出了移动载荷下的复合型裂纹结构剩余寿命预测方法,即在复合型裂纹扩展路径有限元仿真的基础上,利用Paris公式研究载荷变化过程中裂纹结构剩余寿命的变化规律,得到载荷位置—裂纹剩余寿命关系曲线,通过分析载荷位置对裂纹剩余寿命的影响可使裂纹诊断结果更直观,更符合工程实际。并通过裂纹试件的声发射实验,得到了裂纹处的声发射定位次数特征,从实验的角度验证了由上述预测方法所得的载荷位置变化对裂纹扩展速率的影响规律。(3)在裂纹扩展有限元分析模型中,结构整体相对其内部裂纹的几何尺寸差异悬殊,而分析裂纹扩展的动态过程中需不断地修改模型,其难度大,效率低,易出错,本文提出了参数化的子模型分析方法,利用Ansys中的APDL技术建立了参数化的动态修改模块,实现了整体结构的粗糙模型和裂纹结构的子模型分析数据文件的动态关联,提高了模型重建与分析的效率,并以龙门起重机裂纹为例验证了该方法的可行性。(4)基于上述研究成果,针对结构中裂纹部位的随机性和形状的复杂性给工程裂纹诊断所造成的难度,研制了复合型裂纹诊断模块,用户可利用原结构件有限元模型通过菜单引导输入裂纹的位置、长度等参数,模块便能自动修改并生成含裂纹缺陷的有限元模型并完成结构件的剩余寿命分析,并实例验证了该模块的有效性,为工程裂纹诊断提供了有效的工具。更多还原

【Abstract】 In recent years,with social development and progress of science and technology, many mechanisms are in trend of heavy,high speed,the automation to meet the needs of the transport industry,industry and agriculture.The metal structure’s load-bearing performance has affect on the safety in production more and more. Metal structure crack is considered as main hidden danger in production and has attracted various aspects personnel’s attention.So it has an important theory significance and practical application value to study on method of crack diagnose for mechanical structure.This description take fracture mechanics theory as the basis and study on method of crack diagnose for mechanical structure through some technologies such as FEM and its secondary development,AE,meshless method.The dissertation consist of the following new results:(1) The stress intensity factor(SIF) is key parameter in fracture mechanics,the description calculate the crack specimen’s SIF through FEM and EFGM.The results of both have little difference so the results calculated through two methods are valid. Because the meshless method calculates SIF based on node-displace,the description put forward a method that binary linear equation is used to the weitht function arguments to dispose of the crack’s non-continuous interface to get the value of SIF. And this function can avoid the value overflow phenomenon which the node and a computation superposition occurs in the present processing method,has provided the new mentality and the method for the present meshless method in crack analysis.(2) In current,the diagnosis result is got in condition to the crack is thought as I-mode and expirial decided work-conditons,that lead to error.The description put forward the crack propagation remain life forecast method in moving load.In the description,a crack specimen as an example is analyzed,its crack propagation remain life change rule is studied in the load change process and the load change influence on crack propagation remain life is analyzed,the crack propagation remain life relation curve with load position is obtained to determinate the load position and load circle number relatively make crack growth most rapidly,that the method make the diagnosis more comprehensive and closer to the actual situation.And the crack specimens AE experiment are carried on in the different load position.Then the AE localization number of times rule is analyzed.The rule is compared with the calculated result through FEM that the qualitative confirmed proposed the forecast technique rationality.(3) In view of the shortcomings of the static modify method in the submodel analysis,such as time cost is so much in the model modifition,the extraction, analysis and delivery of the parameters,error-prone,low efficiency,the description put forward the method on crack growth for mechanics structure based on paramater submodel,namely automatically modifies coarse model,crack structure submodel and the model analysis data file based on the sub-model analysis enhanced in the entire crack growth building and the analysis efficiency.At latst a gantry crane crack, as the example is carry on according to the method.(4) In the view of the complexity and the randomness for the structure of the crack location,shape,according to the above-mentioned research results,the description construction crack analysis module using software’s UIDL and the APDL technology,guide user input parameters and so on crack position,length to the procedure can produce automatically the crack finite element model and completes crack propagation remain life analysis.更多还原