A class of isotropic and scale-invariant strain energy functions is given for which the corresponding spherically symmetric elastic motion includes bodies whose diameter becomes infinite with time or collapses to zero in finite time, depending on the sign of the residual pressure. The bodies are surrounded by vacuum so that the boundary surface forces vanish, while the density remains strictly positive. The body is subject only to internal elastic stress.

中文翻译：

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真空环境下球对称各向同性弹性体的膨胀和塌缩

给出了一类各向同性且尺度不变的应​​变能函数，其中相应的球对称弹性运动包括直径随时间变得无限或在有限时间内塌陷为零的物体，具体取决于残余压力的符号。这些物体被真空包围，因此边界面力消失，而密度仍然严格为正。身体仅承受内部弹性应力。