Energy dissipation around a propagating crack is the primary mechanism for the enhanced fracture toughness in viscoelastic solids. Such dissipation is spatially non-uniform and is highly coupled to the crack propagation process due to the history-dependent nature of viscoelasticity. We present an experimental approach to map the dissipation field during crack propagation in soft viscoelastic solid. Specifically, we track randomly distributed tracer particles to measure the evolving deformation field. The measured deformation field is then put into a nonlinear constitutive model to determine the dissipation field. Our methodology was used to investigate the deformation and dissipation fields around a propagating crack in a Polyampholyte (PA) hydrogel. The deformation field measurements allowed us to assess whether the commonly assumed translational invariance in viscoelastic fracture theories holds true in practical experiments. Furthermore, by combining the obtained deformation fields with a nonlinear viscoelastic model, we captured the complete history of the dissipation field during crack propagation. We found that dissipation occurred even at material points that are a few millimeters away from the crack tip. The mapped dissipation field also enabled the separate determination of the intrinsic and dissipative components of fracture toughness for the viscoelastic hydrogel.

中文翻译：

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绘制软粘弹性固体断裂过程中的变形和耗散

扩展裂纹周围的能量耗散是粘弹性固体中断裂韧性增强的主要机制。由于粘弹性的历史依赖性，这种耗散在空间上是不均匀的，并且与裂纹扩展过程高度耦合。我们提出了一种实验方法来绘制软粘弹性固体中裂纹扩展过程中的耗散场。具体来说，我们跟踪随机分布的示踪粒子来测量不断变化的变形场。然后将测量的变形场放入非线性本构模型中以确定耗散场。我们的方法用于研究聚两性电解质 (PA) 水凝胶中传播裂纹周围的变形和耗散场。变形场测量使我们能够评估粘弹性断裂理论中普遍假设的平移不变性在实际实验中是否成立。此外，通过将获得的变形场与非线性粘弹性模型相结合，我们捕获了裂纹扩展过程中耗散场的完整历史。我们发现，即使在距裂纹尖端几毫米的材料点处也会发生耗散。绘制的耗散场还能够单独确定粘弹性水凝胶断裂韧性的固有分量和耗散分量。