Dynaform 难题

原帖由 dmdongmin 于 2005-10-4 09:59 发表
我看了一下是在K文件里的*Contact中的SST和MST两个参数可以控制，但是我也没有用过，试试吧！显示说当壳单元的厚度小于1Mm时就要增加它们的接触厚度，现在正在学习研究中

说的没错！

只要修改DYNAFORM里的接触参数就行了！那里的改变会修改到K文件的生成，里的SST就是　ＳＣＡＶＥ　ＳＵＲＦ。ＴＨＩＮＣＫＮＥＳＳ的参数，要CONTACT PARAMETERS里有的！很多，最好查一下LS_DYNA里的说明再修改，我没有全部查到每个参数的说明，还没有一个好的数值介绍给你，查到再说吧！

Yes, you are right. We could set up the parameters in Dynaform directly. In Dynaform, "Tools" ---> "Define Tools", we
could select select the particular tool and specify the contact type, for my case, "FORMING_ONE_WAY_SURFACE_TO_SURFACE". Then, under "Define Contact Parameters", there are several parameters could be specified. "SCALE FACTOR SLAVE" means SFS in Dyna; "SCALE FACTOR MASTER" means SFM; "SLAVE SURF. THICKNESS" means SST; and "MASTER SURF. THICKNESS" means MST. I am still trying. There are too many variables.
You could download all the manuals from the "Tutorials" under www.feainformation.com if needed.

谢谢！that is OK!

受教  谢谢

板材拉延的时候，有的地方变薄，有的地方变厚，变薄太厉害就会拉裂，变厚太厉害就会起皱。模具间隙一般为1.1t mm,t是板材厚度。dynaform里面可以定义板材和模具之间的穿透值，允许板材变厚比模具间隙大，如果没有穿透的话，接触计算就会报错。

"有的地方变薄，有的地方变厚，变薄太厉害就会拉裂，" You are right. "变厚太厉害就会起皱" I think it is only possible when the pressure pad (binder) force is not big enough and the wrinkle will happen only at the locations of the blank
between die and binder and can not happen between die and punch with good-designed production case since the
clearance between punch and die will iron the material. "模具间隙一般为1.1t mm,t是板材厚度。" This is the CONTACT
GAP set-up in Dynaform between tools and blank (e.g. contact gap between punch and blank), which can prevent initial
penetration. And normally, we can offset the tool from another tool (e.g. from punch to die) if and only if the geometry of
punch and die is the same. Unfortunately, this is not my case.
"dynaform里面可以定义板材和模具之间的穿透值", for shell element, the Max Distance of penetration is defined as
XPENE*(thickness of shell element) when SHLTHK=1.  but I am not quite sure how the contact algorithm works. (如果没有穿透的话，接触计算就会报错) Could you please explain a little more?
"允许板材变厚比模具间隙大", then neither the final results of thickness can not be trusted, nor the stress and strain
because it does not follow the reality.
Thanks a lot!

The progress is as following till now:
1. The problem may come from slave and master element/node penetration. Reason:
    1.1 The dimensions of the model are too small (least possibility);
    1.2 The thickness of the original blank is too small;
    1.3 Mass of the final product is increased a lot with mass scaling;
    1.4 Maximum penetration depth allowed is too big;
2. Methods to reduce the penetration but not to solve the problem:
    2.1 Make DT2MS = 0;
    2.2 SSF = 1; MSF = 1; make SLSFAC = 0.1 (or bigger enough without dynamic instability);
    2.3 Make XPENE smaller than default value 4.0, but can not be too small. (I am not sure).
    etc.
3. Conclusion:
    3.1 LS-Dyna can not really solve this kind of problem, especially when the thickness is too small, and it has limitations.
    3.2 Try to use other software. I am going to try MSC.Marc (preferred) or PAM STAMP for sheet metal forming.

楼主看来是个纯理论型,呵呵.
其实DYNAFORM的帮助中都说明过,但有的只是一句带过,
楼主还需要多多品一下.同时也需多到现场去看看调试过程.
这样对做分析有很大的好处.
结果出来了其实还是要看经验去分析其结果是否合理.
如果结果不合理说明你做的不对,在去调整参数.
有经验了,算一次基本就能得出定性的结果.

什么样的模拟结果才是最真实的？我也同意19楼的看法，要理论实际结合！呵呵