指数化的Hencky-对数应变能。第III部分:理想各向同性有限应变塑性耦合
The exponentiated Hencky-logarithmic strain energy. Part III: Coupling with idealized isotropic finite strain plasticity
摘要:
我们调查的各向同性体积等容解耦应变能\begin{align*} F\mapsto W_{_{\rm eH}}(F):=\hat{W}_{_{\rm eH}}(U):=\{\begin{array}{lll} \fracμ{k}\,e^{k\,\|{\rm dev}_n\log {U}\|^2}+\fracκ{\text{}{2\, {\hat{k}}}}\,e^{\hat{k}\,[{\rm tr}(\log U)]^2}&\text{if}& {\rm det}\, F>0,\\ +\infty &\text{if} &{\rm det} F\leq 0, \end{array}.\quad \end{align*}的基础上的Hencky对数(真的,自然)应变张量$\log U$家庭的有限应变乘法塑性的立即应用。这里,$μ>0$是无穷小剪切模量,$κ=\frac{2μ+3λ}{3}>0$是无穷小体积模量,$λ$是第一Lamé常数,$k,\hat{k}$是无量纲拟合参数,$F=\nabla φ$是变形梯度,$U=\sqrt{F^T F}$是右拉伸张量,${\rm dev}_n\log {U} =\log {U}-\frac{1}{n}\, {\rm tr}(\log {U})\cdot 1\!\!1$是应变张量$\log U$的偏量部分。基于乘法分解$F=F_e\, F_p$,我们将这些能量与定义在塑性变形$F_p$中的各向同性弹塑性流动规则$F_p\,\frac{\rm d}{{\rm d} t}[F_p^{-1}]\in-\partial χ({\rm dev}_3 Σ_{e})$耦合,其中$\partial χ$是凸弹性域$\mathcal{E}_{\rm e}(W_{\rm iso},{Σ_{e}},\frac{1}{3}{\boldsymbolσ}_{\!\mathbf{y}}^2)$的指示函数$χ$在混合变量$Σ_{e}$ -应力空间和$Σ_{e}=F_e^T D_{F_e} W_{\rm iso}(F_e)$中的次微分.虽然$W_{_{\rm eH}}$可能会松动的椭圆度,我们表明,椭圆度的损失是有效地防止耦合与塑性,因为椭圆度域的$W_{_{\rm eH}}$一方面,和弹性域的$Σ_{e}$ -应力空间的另一方面,是密切相关的。
英文摘要:
We investigate an immediate application in finite strain multiplicative plasticity of the family of isotropic volumetric-isochoric decoupled strain energies \begin{align*} F\mapsto W_{_{\rm eH}}(F):=\hat{W}_{_{\rm eH}}(U):=\{\begin{array}{lll} \fracμ{k}\,e^{k\,\|{\rm dev}_n\log {U}\|^2}+\fracκ{\text{}{2\, {\hat{k}}}}\,e^{\hat{k}\,[{\rm tr}(\log U)]^2}&\text{if}& {\rm det}\, F>0,\\ +\infty &\text{if} &{\rm det} F\leq 0, \end{array}.\quad \end{align*} based on the Hencky-logarithmic (true, natural) strain tensor $\log U$. Here, $μ>0$ is the infinitesimal shear modulus, $κ=\frac{2μ+3λ}{3}>0$ is the infinitesimal bulk modulus with $λ$ the first Lamé constant, $k,\hat{k}$ are dimensionless fitting parameters, $F=\nabla φ$ is the gradient of deformation, $U=\sqrt{F^T F}$ is the right stretch tensor and ${\rm dev}_n\log {U} =\log {U}-\frac{1}{n}\, {\rm tr}(\log {U})\cdot 1\!\!1$ is the deviatoric part of the strain tensor $\log U$. Based on the multiplicative decomposition $F=F_e\, F_p$, we couple these energies with some isotropic elasto-plastic flow rules $F_p\,\frac{\rm d}{{\rm d} t}[F_p^{-1}]\in-\partial χ({\rm dev}_3 Σ_{e})$ defined in the plastic distortion $F_p$, where $\partial χ$ is the subdifferential of the indicator function $χ$ of the convex elastic domain $\mathcal{E}_{\rm e}(W_{\rm iso},{Σ_{e}},\frac{1}{3}{\boldsymbolσ}_{\!\mathbf{y}}^2)$ in the mixed-variant $Σ_{e}$-stress space and $Σ_{e}=F_e^T D_{F_e} W_{\rm iso}(F_e)$. While $W_{_{\rm eH}}$ may loose ellipticity, we show that loss of ellipticity is effectively prevented by the coupling with plasticity, since the ellipticity domain of $W_{_{\rm eH}}$ on the one hand, and the elastic domain in $Σ_{e}$-stress space on the other hand, are closely related.
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