VUMAT基本知识

1、vumat基本知识vumat基本知识 编辑整理：尊敬的读者朋友们：这里是精品文档编辑中心，本文档内容是由我和我的同事精心编辑整理后发布的，发布之前我们对文中内容进行仔细校对，但是难免会有疏漏的地方，但是任然希望（vumat基本知识）的内容能够给您的工作和学习带来便利。同时也真诚的希望收到您的建议和反馈，这将是我们进步的源泉，前进的动力。本文可编辑可修改，如果觉得对您有帮助请收藏以便随时查阅，最后祝您生活愉快 业绩进步，以下为vumat基本知识的全部内容。nblock: 在调用vumat时需要用到的材料点的数量ndir：对称张量中直接应力的数量（sigma11,sigma22,sigma33）n

2、shr：对称张量中间接应力的数量(sigma12， sigma13， sigma23)nstatev：与材料类型相关联的用户定义的状态变量的数目nfieldv：用户定义的外场变量的个数nprops：用户自定义材料属性的个数lanneal：指示是否在退火过程中被调用例程的标志.lanneal=0，指示在常规力学性能增量,例程被调用。lanneal=1表示，这是退火过程,你应该重新初始化内部状态变量，steptime：步骤开始后的数值totaltime:总时间dt：时间增量值cmname：用户自定义的材料名称,左对齐。它是通过字符串传递的。一些内部材料模型是以“abq_”字符串开头给定的名称.为了

3、避免冲突，你不应该在“cmname”中使用“abq_”作为领先字符串。coordmp(nblock,）：材料点的坐标值。它是壳单元的中层面材料点，梁和管（pipe）单元的质心.charlength（nblock）：特征元素长度，是基于几何平均数的默认值或用户子程序vucharlength中定义的用户特征元长度.props(nprops)：用户使用的材料属性density(nblock)：中层结构的物质点的当前密度straininc (nblock， ndir+nshr)：每个物质点处的应变增量张量relspininc (nblock, nshr):在随转系统中定义的每个物质点处增加的相对旋转矢

4、量tempold（nblock）：物质点开始增加时的温度。defgradold （nblock,ndir+2nshr)：在增量开始时,每个物质点出的变形梯度张量，在3d中形为（f11, f22,f33，f12，f23，f31，f21,f32,f13),在2d中形为（f11，f22，f33，f12，f21)stretchold （nblock， ndir+nshr）fieldold (nblock, nfieldv)：在增量开始时，每个物质点处用户定义场变量的值stressold （nblock, ndir+nshr):在增量开始时，每个物质点处的应力张量:stateold （nblock， n

5、statev）：在增量开始时，每个物质点处的状态变量：tempnew（nblock）：在增量结束时，每个物质点处的温度defgradnew (nblock,ndir+2*nshr):在增量结束时，每个物质点出的变形梯度张量，在3d中形为（f11， f22，f33，f12，f23，f31，f21，f32，f13），在2d中形为(f11，f22，f33，f12，f21)fieldnew (nblock， nfieldv)：在增量开始时，每个物质点处用户定义长变量的值example：elastic/plastic material with kinematic hardeningas a simpl

6、e example of the coding of subroutine vumat, consider the generalized plane strain case for an elastic/plastic material with kinematic hardening. the basic assumptions and definitions of the model are as follows.let be the current value of the stress， and define to be the deviatoric part of the stre

7、ss. the center of the yield surface in deviatoric stress space is given by the tensor , which has initial values of zero。 the stress difference, ， is the stress measured from the center of the yield surface and is given by the von mises yield surface is defined as where is the uniaxial equivalent yi

8、eld stress. the von mises yield surface is a cylinder in deviatoric stress space with a radius of for the kinematic hardening model， r is a constant. the normal to the mises yield surface can be written as we decompose the strain rate into an elastic and plastic part using an additive decomposition:

9、 the plastic part of the strain rate is given by a normality condition where the scalar multiplier must be determined。 a scalar measure of equivalent plastic strain rate is defined by the stress rate is assumed to be purely due to the elastic part of the strain rate and is expressed in terms of hook

10、es law by where and are the lams constants for the material。the evolution law for is given as where h is the slope of the uniaxial yield stress versus plastic strain curve.during active plastic loading the stress must remain on the yield surface， so that the equivalent plastic strain rate is related

11、 to by the kinematic hardening constitutive model is integrated in a rate form as follows. a trial elastic stress is computed as where the subscripts and refer to the beginning and end of the increment， respectively. if the trial stress does not exceed the yield stress， the new stress is set equal t

12、o the trial stress。 if the yield stress is exceeded， plasticity occurs in the increment。 we then write the incremental analogs of the rate equations as where from the definition of the normal to the yield surface at the end of the increment， , this can be expanded using the incremental equations as

13、taking the tensor product of this equation with ， using the yield condition at the end of the increment， and solving for ： the value for is used in the incremental equations to determine ， ， and 。subroutine vumat（c read only - 1 nblock， ndir, nshr， nstatev， nfieldv， nprops, lanneal， 2 steptime, tota

14、ltime, dt, cmname, coordmp, charlength， 3 props， density， straininc， relspininc, 4 tempold, stretchold， defgradold， fieldold， 3 stressold， stateold， enerinternold， enerinelasold， 6 tempnew, stretchnew, defgradnew， fieldnew,c write only 5 stressnew， statenew， enerinternnew, enerinelasnew ）c include v

15、aba_param。inccc j2 mises plasticity with kinematic hardening for plane c strain case.c elastic predictor， radial corrector algorithm。cc the state variables are stored as:c state(*,1) = back stress component 11c state(*,2) = back stress component 22c state(，3) = back stress component 33c state（,4) =

16、back stress component 12c state(*,5) = equivalent plastic strainccc all arrays dimensioned by （*） are not used in this algorithm dimension props(nprops), density（nblock), 1 coordmp(nblock,*)， 2 charlength（), straininc(nblock,ndir+nshr), 3 relspininc（*), tempold(*), 4 stretchold(）, defgradold（*）, 5 f

17、ieldold（), stressold(nblock,ndir+nshr), 6 stateold（nblock,nstatev)， enerinternold(nblock）, 7 enerinelasold(nblock)， tempnew（)， 8 stretchnew()， defgradnew(*)， fieldnew（*), 9 stressnew(nblock，ndir+nshr）, statenew(nblock，nstatev）， 1 enerinternnew(nblock)， enerinelasnew(nblock)c character80 cmnamec para

18、meter( zero = 0。, one = 1。, two = 2。, three = 3。, 1 third = one/three, half = .5, twothirds = two/three, 2 threehalfs = 1。5 )c e = props（1) xnu = props（2) yield = props（3) hard = props(4）c twomu = e / ( one + xnu ） thremu = threehalfs twomu sixmu = three * twomu alamda = twomu ( e - twomu ） / ( sixm

19、u two e ) term = one / ( twomu ( one + hard/thremu ) ） con1 = sqrt( twothirds ）c do 100 i = 1,nblockcc trial stress trace = straininc(i,1) + straininc(i,2) + straininc（i，3） sig1 = stressold（i，1) + alamdatrace + twomu*straininc(i,1) sig2 = stressold（i，2) + alamda*trace + twomu*straininc(i，2） sig3 = s

20、tressold(i,3） + alamda*trace + twomustraininc(i,3) sig4 = stressold（i,4） + twomu*straininc(i，4）cc trial stress measured from the back stress s1 = sig1 stateold(i，1） s2 = sig2 - stateold(i，2) s3 = sig3 stateold（i，3) s4 = sig4 stateold（i，4)cc deviatoric part of trial stress measured from the back stre

21、ss smean = third * ( s1 + s2 + s3 ) ds1 = s1 - smean ds2 = s2 smean ds3 = s3 - smeancc magnitude of the deviatoric trial stress difference dsmag = sqrt( ds1*2 + ds2*2 + ds32 + 2.*s42 )cc check for yield by determining the factor for plasticity，c zero for elastic， one for yield radius = con1 * yield

22、facyld = zero if( dsmag radius 。ge. zero ） facyld = onecc add a protective addition factor to prevent a divide by zero c when dsmag is zero。 if dsmag is zero, we will not have exceededc the yield stress and facyld will be zero. dsmag = dsmag + ( one facyld ）cc calculated increment in gamma (this exp

23、licitly includes the c time step) diff = dsmag radius dgamma = facyld term diffcc update equivalent plastic strain deqps = con1 * dgamma statenew（i，5) = stateold（i,5） + deqpscc divide dgamma by dsmag so that the deviatoric stresses arec explicitly converted to tensors of unit magnitude in thec follo

24、wing calculations dgamma = dgamma / dsmagcc update back stress factor = hard dgamma * twothirds statenew（i,1） = stateold（i,1) + factor * ds1 statenew(i,2) = stateold（i,2） + factor * ds2 statenew(i，3) = stateold(i,3） + factor * ds3 statenew(i，4) = stateold(i,4) + factor * s4cc update the stress factor = twomu * dgamma stressnew（i，1） = sig