math
pde
A Note on Elastic Deformation
Nguyen Minh Hieu
12/07/2023

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u(x,t)=[u1(x,t)u2(x,t)u3(x,t)] \begin{aligned} \mathbf{u}(\mathbf{x}, t) = \begin{bmatrix} u_1(\mathbf{x},t) \\ u_2(\mathbf{x},t) \\ u_3(\mathbf{x},t) \end{bmatrix} \end{aligned}

Stress denotes a force on surface ii in the direction jj

σij=σ(x,t)=[σ11σ12σ13σ21σ22σ23σ31σ32σ33] \begin{aligned} \sigma_{ij} = \bm{\sigma}(\mathbf{x}, t) = \begin{bmatrix} \sigma_{11} & \sigma_{12} & \sigma_{13} \\ \sigma_{21} & \sigma_{22} & \sigma_{23} \\ \sigma_{31} & \sigma_{32} & \sigma_{33} \end{bmatrix} \end{aligned}

Strain denotes the variation of the displacement under stress

ui(x+δx)ui(x)+ui(x)xjδxj=ui(x)translation+δui(x)rotation+deformation \begin{aligned} u_i(\mathbf{x} + \delta\mathbf{x}) \approx u_i(\mathbf{x}) + \frac{\partial u_i(\mathbf{x})}{\partial x_j} \delta x_j = \underbrace{u_i(\mathbf{x})}_{translation} + \underbrace{\delta u_i(\mathbf{x})}_{rotation + deformation} \end{aligned}

References

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