Large deformations of soft materials are customarily associated with strong constitutive and geometrical nonlinearities that originate new modes of fracture. Some isotropic materials can develop strong fracture anisotropy, which manifests as modifications of the crack path. Sideways cracking occurs when the crack deviates to propagate in the loading direction, rather than perpendicular to it. This fracture mode results from higher resistance to propagation perpendicular to the principal stretch direction. It has been argued that such fracture anisotropy is related to deformation-induced anisotropy resulting from the microstructural stretching of polymer chains and, in strain-crystallizing elastomers, strain-induced crystallization mechanisms. However, the precise variation of the fracture behavior with the degree of crosslinking remains to be understood. Leveraging experiments and computational simulations, here we show that the tendency of a crack to propagate sideways in the two component Elastosil P7670 increases with the degree of crosslinking. We explore the mixing ratio for the synthesis of the elastomer that establishes the transition from forward to sideways fracturing. To assist the investigations, we construct a novel phase-field model for fracture where the critical energy release rate is directly related to the crosslinking degree. Our results demonstrate that fracture anisotropy can be modulated during the synthesis of the polymer. Then, we propose a roadmap with composite soft structures with low and highly crosslinked phases that allow for control over fracture, arresting and/or directing the fracture. The smart combination of the phases enables soft structures with enhanced fracture tolerance and reduced stiffness. By extending our computational framework as a virtual testbed, we capture the fracture performance of the composite samples and enable predictions based on more intricate composite unit cells. Overall, our work offers promising avenues for enhancing the fracture toughness of soft polymers.

软材料的大变形通常与强本构和几何非线性相关联，从而产生新的断裂模式。一些各向同性材料可以产生强烈的断裂各向异性，表现为裂纹路径的改变。当裂纹偏离方向而不是垂直于载荷方向传播时，就会发生侧向裂纹。这种断裂模式是由于垂直于主拉伸方向的传播阻力较高所致。有人认为，这种断裂各向异性与聚合物链的微观结构拉伸引起的变形诱导的各向异性有关，并且在应变结晶弹性体中，与应变诱导的结晶机制有关。然而，断裂行为随交联程度的精确变化仍有待了解。利用实验和计算模拟，我们表明，双组分 Elastosil P7670 中裂纹横向扩展的趋势随着交联程度的增加而增加。我们探讨了合成弹性体的混合比，该混合比建立了从正向侧向压裂的过渡。为了协助研究，我们构建了一种新的断裂相场模型，其中临界能量释放速率与交联度直接相关。我们的结果表明，在聚合物的合成过程中可以调节断裂各向异性。然后，我们提出了一个路线图，其中复合软结构具有低交联相和高交联相，允许控制断裂、阻止和/或引导断裂。这些相的智能组合使软结构具有更高的抗断裂能力并降低了刚度。 通过将计算框架扩展为虚拟测试台，我们捕获了复合材料样品的断裂性能，并能够基于更复杂的复合材料晶胞进行预测。总体而言，我们的工作为提高软聚合物的断裂韧性提供了有前途的途径。