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[探讨]问题6:在摩尔-库仑 模型中 是怎么判定 何时会有塑性变形?何时破坏? [复制链接]

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离线mano
 

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只看楼主 倒序阅读 使用道具 楼主  发表于: 2007-08-31
塑性点和破坏点是怎么判别的? 8:TX9`,  
如何计算塑性变形? s 4`-mIa  
欢迎大家讨论!
离线geofem

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只看该作者 1楼 发表于: 2007-08-31
翻看可一下Plaxis 的手册
ZSOIL2D/3D QQ群:68722113
岩土工程数值分析开发平台,共享、开放、合作、提高。
技术博客:http://blog.sina.com.cn/u/2650713094
离线mano

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只看该作者 2楼 发表于: 2007-08-31
Thanks, l4RqQ+[KA;  
qK'mF#n0#  
Some points you may concern: n~0wq(8M  
`O7vPE  
1) M-C model, undrained condition, effective stress analysis: V_ 6K?~j  
    In this case, the plasticity can be predicted as usual; 4<s;xSCL  
<);j5)/  
2)M-C model, undrained condition, total stress analysis: `)O9 '568  
S:!5 |o|  
    In this case, there is not effective stress calculation due to no pore pressure generated. OG#^d5(  
E zcch1  
    The total stress analysis plasticity occurs as soon as the total stresses reach the failure 7Ydqg&  
i<S \x  
criterium while with an effective stresses analysis plasticity occurs when the effective stresses Dml?.-Uv<  
kg Bkwp  
reach the failure criterium. U,b80%k:  
1<9d[N*  
The latter is of course more realistic; only the effective stresses determine plasticity, not the water pressures. 3~`\FuHHe  
l4kqz.Z-g  
In other words, using total stress analysis is only correct when the calculation is elastic. But this case is not very often in reality. .;?ha'  
4"PA7 e  
Suggestion: Try to use effective stress analysis when it is undrained condition (typically, there is  option for this in PLAXIS).
[ 此贴被mano在2007-08-31 16:34重新编辑 ]
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geofem 鲜花 +1 - 2007-08-31
离线mano

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只看该作者 3楼 发表于: 2007-08-31
Actually, in "geofem" 's post, there is no TOTAL STRESS FAILURE (YIELD) function and PLASTIC Potential Function; ++2a xRl  
}Bh\N 5G%  
They should be written by total stress terms in all the equations and without "phi" (friction angle) in Yield (failure) equation (3.8a-3.8f) and without dilatancy term in plastic strain calculation equation (3.3).
离线geofem

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只看该作者 4楼 发表于: 2007-08-31
Actually, our constitutive models are often based on CD experiments. So the effective stress and effective parameters are used to discribe our models. 6#d+BBKIc  
 0Ns Po  
For example,Plaxis is based on effective stress. If no pore pressure generated in the initial state or the phretic line is below the bottom of the fem mesh, the total stress equals to the effective stress.
[ 此贴被geofem在2007-08-31 15:07重新编辑 ]
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离线geofem

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只看该作者 5楼 发表于: 2007-08-31
When comes to Undrianed simulation, the phi is usually very small. So the MC model is not suitble for this condition, for MC is based on frictional material.
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离线mano

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只看该作者 6楼 发表于: 2007-08-31
In real condition, the water table is the big issue. The layer is always clay with low permeability. .9bP8u2B{  
5#? HL  
So the undrained condition is always the critical condition for analysis. fl9J  
5|[\Se#  
The good news is some softwares can specify effective stress for Undrained condition. .=b)Ae c  
ErMA$UkJ  
Correct for "geofem", MC model can be used in this condition, but specifying the effective l< |)LD q~  
Ps MCs|*  
Young's modulus and effective poisson's ratio (effective stress analysis)  is better way, not 7+p=4i^@Zs  
0SLn0vD!  
total stress analysis.
离线daniellb1023

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只看该作者 7楼 发表于: 2007-08-31
想问几个问题。 n.xW"omN  
1。plaxis 里面的plastic point 应该就是你说塑性点。我想问,这些点是不是就是接近fail的点?如果run construction sequence的时候,如果不能运行下去,出现错误,是不是说明是这些点fail了?那么请问应该怎么做才可以让你的程序继续运行。或者应该做些什么improvement 工作? 谢谢。 t7DT5SrR  
2。你的帖子里面说,如果是undrain conditioin的soil,从塑性和弹性来说,你建议用effective stress的方法来算。不过一般undrain condition的土都是clay / clayey soil.那么按经验+理论来说,不是一般都作total stress analysis的吗?这样不就是有矛盾之处了吗? 6d3-GMUQ  
3。在plaxis运行中,如果你想对改土进行total stress analysis,是不是就是把这个土的parameter都输入undrain的?gama wet 约=gama dry, 输入c/phi? 如果你要对改土进行effective stress analysis,就输入drain的condition? 输入c', phi', gama wet>> gama dry?  rOy-6og  
pEE.%U  
Looking forward your good explaination.... &P{[22dQ  
[& &9F};  
thanks a lot....
离线daniellb1023

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只看该作者 8楼 发表于: 2007-08-31
还有一个问题,土一般是考虑为PLASTIC?还是粘塑性? %9A6c(L  
为什么说TOTAL STRESS是只适用于ELASTIC ?从哪里可以看出来啊? >{^&;$G+*  
谢谢
离线ggbbggb

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只看该作者 9楼 发表于: 2007-09-01
"When comes to Undrianed simulation, the phi is usually very small. So the MC model is not suitble for this condition, for MC is based on frictional material." mRw &^7r  
fKMbOqU_  
1 Why phi is usually very small in undrained simulation? MGd 7Ont  
h`OX()N  
2 You say MC model is not suitble for this condition, FOR MC is based on frictional material. TEHN you are telling us that the frictional material is not suitable for undrained condition. I am very confused by this.
GGbbGGb
离线ggbbggb

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只看该作者 10楼 发表于: 2007-09-01
" T<"Hh.h  
Some points you may concern: s('<ms  
j^}p'w Tu{  
1) M-C model, undrained condition, effective stress analysis: ,mR$Y T8  
    In this case, the plasticity can be predicted as usual; q/[)Z @&(  
i w<2|]>l  
2)M-C model, undrained condition, total stress analysis: b/='M`D}#G  
]?p&sI4  
    In this case, there is not effective stress calculation due to no pore pressure generated. /AX1LYlr  
.V9/0  
    The total stress analysis plasticity occurs as soon as the total stresses reach the failure GpV"KVJJ/  
Gk0f#;  
criterium while with an effective stresses analysis plasticity occurs when the effective stresses }u0t i"V  
y{ReQn3> y  
reach the failure criterium. \-Mzs 0R  
^b=9{.5  
The latter is of course more realistic; only the effective stresses determine plasticity, not the water pressures. 3zU!5t g  
[!B($c|\  
In other words, using total stress analysis is only correct when the calculation is elastic. But this case is not very often in reality. 8|uFW7Q  
vkWh2z  
Suggestion: Try to use effective stress analysis when it is undrained condition (typically, there is  option for this in PLAXIS)." ORhe?E]  
y~CK&[H  
"1) M-C model, undrained condition, effective stress analysis: dHV3d'.P  
    In this case, the plasticity can be predicted as usual;"  Mvq5s+.  
  2)M-C model, undrained condition, total stress analysis: ]p/f@j?LU  
SR@yG:~  
    In this case, there is not effective stress calculation due to no pore pressure generate Sdl1k+u  
FMCX->}$  
THESE STATEMENT DO NOT MAKE SENSE TO ME.
GGbbGGb
离线mano

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只看该作者 11楼 发表于: 2007-09-01
引用第7楼daniellb1023于2007-08-31 20:20发表的  : >05_#{up  
想问几个问题。 {k.Dy92  
1。plaxis 里面的plastic point 应该就是你说塑性点。我想问,这些点是不是就是接近fail的点?如果run construction sequence的时候,如果不能运行下去,出现错误,是不是说明是这些点fail了?那么请问应该怎么做才可以让你的程序继续运行。或者应该做些什么improvement 工作? 谢谢。
In M-C Model, the plastic start from the failure point (these two start point is the same point). When the soil yield, it failure. But the plastic strain can still be calculated.  Normally, the program still can continue to proceed untill the big strain occur (big crack in some where).
2。你的帖子里面说,如果是undrain conditioin的soil,从塑性和弹性来说,你建议用effective stress的方法来算。不过一般undrain condition的土都是clay / clayey soil.那么按经验+理论来说,不是一般都作total stress analysis的吗?这样不就是有矛盾之处了吗?
You may read my previous posts.  For undrained condition, there are three options in PLAXIS:
A) analysis in terms of effective stresses (undrained material with E', v', x8H%88!j*  
c', phi' and psi')
B) analysis in terms of effective stresses with undrained strength n3w(zB  
parameters (undrained material with E', v', but with c_u, phi=0)
C) analysis in terms of total stresses (material is drained and dry, or non x2gnB@t  
porous, E_u, v_u, c_u and phi = 0)
3。在plaxis运行中,如果你想对改土进行total stress analysis,是不是就是把这个土的parameter都输入undrain的?gama wet 约=gama dry, 输入c/phi? 如果你要对改土进行effective stress analysis,就输入drain的condition? 输入c', phi', gama wet>> gama dry? 
A),B),C) can answer this question two!
.......
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