应变增量（strain· increment）

leo121888

各位前辈，后处理里的应变增量（strain· increment）是不是就是应变？？我想知道运算完具体的应变数值怎么做？？谢谢

leo121888

恳请得到大家的指教

sunston

应变增量不是应变，flac中概念同岩体力学。
应变量应根据模拟目的查看

mazhongyuan9049

就是应变 只不过FLAC是显式计算  得到的位移是由每一增量步计算的量值累加起来的 再将累加之后的位移计算应变，这个过程是通过增量实现的。所以strain increment就是想要求的应变。

FLAC手册中说的：
The computation of strain rate is identical to that performed by FLAC when it applies constitutive relations to a zone (see Section 1.3.3.1 in Theory and Background)—i.e., strain rates are based on gridpoint velocities and the current coordinates. “Strain increments” are computed with the same equations, but with displacements substituted for velocities. There are two potential problems with the latter calculation. First, gridpoint displacements may be reset or changed at any time by the user; they are not used in the calculation process. It is the user’s responsibility to ensure that displacements are accumulated over a meaningful interval. Second, the strain increments are based on the geometry at the time of measurement. If the geometry changes significantly during a large-strain simulation, the measured strain will depend on the assumption made about the reference state for geometry; there are many different formulations for strain to be found in the literature when large displacements are involved. The conscientious user may wish to use only the function fsr, and derive strain increments by accumulation, using some formula of choice.


具体数值就要用到FISH   FLAC(不是FLAC3D)手册中的FISH REFERENCE 2-48 有讲。

spwxxn

我觉得关键问题是楼主想要哪个应变？轴像位移也应该算应变吧！

leo121888

谢谢，几位楼上的赐教。

leo121888

怎么求某一节点的应变值？应变值的正负号怎么规定的？应变值在工程上的意义？恳请大家赐教

mazhongyuan9049

应变是对应单元而言的 节点只有位移，程序一般根据节点位移对单元进行积分求应变。FLAC采用中心差分方法及高斯积分公式由节点位移求单元应变（这点有些像FVM 计算流体力学中的有限体积法），FEM一般通过单元的高斯积分点来积分出应变值（节点位移是分片差值的）。
FLAC可以使用FISH输出指定单元的应变（比如exx exy eyy等应变分量），方向和弹性力学中规定应力及应变方向是一致的，一般认为应力和应变轴相重合（不发生旋转）。

fishermanhua

请问，体积应变增量就是我们需要的体积应变吗，望高手不吝赐教