关于钢管压弯仿真
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我做的是一个关于钢管压弯的有限元仿真。建模如图。
步骤就是给压头一个加载，使钢管在压头和支座间进行弯曲，完成弹塑性变形，然后撤去加载，它有个回弹，然后分析这加载和卸载后的应力变化。
我自己一开始做的步骤是：钢管和支座压头都是单元solid 45，钢管材料是双线性随动强化，压头和支座是线性各向同性。网格划分，所有实体默认的六面体扫射，接触是根据接触向导里刚柔接触的默认数值来做的（接触单元是contact174,target170), 加载及约束：压头只允许y向移动，施加y向载荷，支座全约束。打开几何大变形选项。载荷步选项采取默认值。
计算之后发现不收敛。错误:
*** WARNING *** CP = 13.416 TIME= 08:50:14
SOLID45 wedges are recommended only in regions of relatively low
stress gradients.
*** WARNING *** CP = 13.510 TIME= 08:50:32
The program chosen initial timestep/load-factor is arbitrary. It is
necessary for the user to supply a suitable initial
timestep/load-factor through the NSUB or DELTIM command for
convergence and overall efficiency.
*** WARNING *** CP = 18.112 TIME= 08:51:19
There are 14 small equation solver pivot terms.
*** WARNING *** CP = 23.790 TIME= 08:51:25
There are 148 small equation solver pivot terms.
*** WARNING *** CP = 25.709 TIME= 08:51:27
There are 305 small equation solver pivot terms.
.......
*** ERROR *** SUPPRESSED MESSAGE CP = 2059.775 TIME= 09:27:36
One or more elements have become highly distorted. Excessive
distortion of elements is usually a symptom indicating the need for
corrective action elsewhere. Try incrementing the load more slowly
(increase the number of substeps or decrease the time step size). You
may need to improve your mesh to obtain elements with better aspect
ratios. Also consider the behavior of materials, contact pairs,
and/or constraint equations. If this message appears in the first
iteration of first substep, be sure to perform element shape checking.
*** WARNING *** SUPPRESSED MESSAGE CP = 2059.775 TIME= 09:27:36
The unconverged solution (identified as time 1 substep 999999) is
output for analysis debug purposes. Results should not be used for
any other purpose.
我当时觉得不收敛的可能性是1.网格划分不好，压头支座的模型有尖角。2.选择单元不合理，因为根据接触理论，接触单元应该和下伏单元同阶，而solid45属于低阶，contact174属于高阶。3.约束加载不完全（对于这一点我不知道怎么改，而且我认为我的加载是正确的）4.接触设置参数采取默认值（这个我到现在也不知道怎么改）
鉴于上述的几点，我加以了改进。首先我选择单元为钢管solid95，支座压头为solid45.但是问题出现了，我发现划分钢管网格时出现了错误，有意思的是，我一开始对钢管使用扫射网格划分时可以，后来重新划分却出现了错误提示（错误提示有图）。还有就是压头支座的网格划分时老是出现警告（这个我认为还是模型问题）。学长学姐，我现在想问的就是1.这个模型的网格划分，怎么划分才好。如果我选择solid95的话2.约束加载有没有问题3.使用接触向导来设置接触对时接触设置哪些参数要改
建模图
solid95划分时的错误
用solid45时的加载图
其中一个接触对的图
求学长学姐指点一下，做了两个月了，不断的建模计算就是不收敛，心痛啊
步骤就是给压头一个加载，使钢管在压头和支座间进行弯曲，完成弹塑性变形，然后撤去加载，它有个回弹，然后分析这加载和卸载后的应力变化。
我自己一开始做的步骤是：钢管和支座压头都是单元solid 45，钢管材料是双线性随动强化，压头和支座是线性各向同性。网格划分，所有实体默认的六面体扫射，接触是根据接触向导里刚柔接触的默认数值来做的（接触单元是contact174,target170), 加载及约束：压头只允许y向移动，施加y向载荷，支座全约束。打开几何大变形选项。载荷步选项采取默认值。
计算之后发现不收敛。错误:
*** WARNING *** CP = 13.416 TIME= 08:50:14
SOLID45 wedges are recommended only in regions of relatively low
stress gradients.
*** WARNING *** CP = 13.510 TIME= 08:50:32
The program chosen initial timestep/load-factor is arbitrary. It is
necessary for the user to supply a suitable initial
timestep/load-factor through the NSUB or DELTIM command for
convergence and overall efficiency.
*** WARNING *** CP = 18.112 TIME= 08:51:19
There are 14 small equation solver pivot terms.
*** WARNING *** CP = 23.790 TIME= 08:51:25
There are 148 small equation solver pivot terms.
*** WARNING *** CP = 25.709 TIME= 08:51:27
There are 305 small equation solver pivot terms.
.......
*** ERROR *** SUPPRESSED MESSAGE CP = 2059.775 TIME= 09:27:36
One or more elements have become highly distorted. Excessive
distortion of elements is usually a symptom indicating the need for
corrective action elsewhere. Try incrementing the load more slowly
(increase the number of substeps or decrease the time step size). You
may need to improve your mesh to obtain elements with better aspect
ratios. Also consider the behavior of materials, contact pairs,
and/or constraint equations. If this message appears in the first
iteration of first substep, be sure to perform element shape checking.
*** WARNING *** SUPPRESSED MESSAGE CP = 2059.775 TIME= 09:27:36
The unconverged solution (identified as time 1 substep 999999) is
output for analysis debug purposes. Results should not be used for
any other purpose.
我当时觉得不收敛的可能性是1.网格划分不好，压头支座的模型有尖角。2.选择单元不合理，因为根据接触理论，接触单元应该和下伏单元同阶，而solid45属于低阶，contact174属于高阶。3.约束加载不完全（对于这一点我不知道怎么改，而且我认为我的加载是正确的）4.接触设置参数采取默认值（这个我到现在也不知道怎么改）
鉴于上述的几点，我加以了改进。首先我选择单元为钢管solid95，支座压头为solid45.但是问题出现了，我发现划分钢管网格时出现了错误，有意思的是，我一开始对钢管使用扫射网格划分时可以，后来重新划分却出现了错误提示（错误提示有图）。还有就是压头支座的网格划分时老是出现警告（这个我认为还是模型问题）。学长学姐，我现在想问的就是1.这个模型的网格划分，怎么划分才好。如果我选择solid95的话2.约束加载有没有问题3.使用接触向导来设置接触对时接触设置哪些参数要改
建模图
solid95划分时的错误
用solid45时的加载图
其中一个接触对的图
求学长学姐指点一下，做了两个月了，不断的建模计算就是不收敛，心痛啊
greatfang 
