Pre-existing flaws in highly stretchable elastomers trigger fracture under large deformations. For multifunctional materials, fracture mechanics may be influenced by additional physical phenomena. This work studies the implications of hard magnetics on the fracture behaviour of ultra-soft magnetorheological elastomers (MREs). We experimentally demonstrate that MREs with remanent magnetisation have up to a 50% higher fracture toughness than non pre-magnetised samples. Moreover, we report crack closure due to the magnetic field as a mechanism that delays the opening of cracks in pre-magnetised MREs. To overcome experimental limitations and provide further understanding, a phase-field model for the fracture of MREs is conceptualised. The numerical model incorporates magneto-mechanical coupling to demonstrate that the stress concentration at the crack tip is smaller when the MRE is pre-magnetised. Overall, this work unveils intriguing applications for functional actuators, with better fracture behaviour and potential better performance under cyclic loading.

高度可拉伸的弹性体中预先存在的缺陷会在大变形下引发断裂。对于多功能材料，断裂力学可能会受到其他物理现象的影响。这项工作研究了硬磁对超软磁流变弹性体 (MRE) 断裂行为的影响。我们通过实验证明，具有剩磁的 MRE 的断裂韧性比未预磁化的样品高 50%。此外，我们报告了由于磁场导致的裂纹闭合是一种延迟预磁化 MRE 裂纹打开的机制。为了克服实验限制并提供进一步的理解，MRE 断裂的相场模型被概念化。数值模型结合了磁力耦合，证明当 MRE 预磁化时，裂纹尖端的应力集中较小。总的来说，这项工作揭示了功能性致动器的有趣应用，具有更好的断裂行为和在循环载荷下可能更好的性能。