具有永久和瞬时交联的双交联凝胶的断裂
Fracture of dual crosslink gels with permanent and transient crosslinks
摘要：
我们已经进行了系统的断裂实验，在一个单一的边缘切口的几何形状在一个范围内的拉伸率的双交联水凝胶由聚乙烯醇链与戊二醛化学交联和物理交联与硼酸根离子。如果裂纹扩展所需的能量释放率按常规计算，通过使用所做的工作，使样品变形到裂纹扩展的拉伸$λ_c$的临界值，我们发现，断裂能$Γ$的峰值附近$λ\sim 0.001 s^{-1}$，然后急剧下降，随着拉伸速率的增加，在矛盾的裂纹速度的测量。结合模拟和实验观察，因此，我们在这里提出了一个通用的方法来分离的能量消耗在加载过程中裂纹扩展之前，从裂纹扩展过程中消耗。对于快速加载速率（特征应变速率仅略低于物理键的典型断裂时间的倒数），这种估计裂纹扩展开始时的局部能量释放速率$g_{local}$的改进方法给出了恒定的局部断裂能$Γ_{local}$的值，与实验测量的裂纹扩展速度的恒定值一致。使用这种改进的方法，我们也得到了非常有趣的结果，即双交联凝胶在低加载速率下比在高加载速率下具有更高的断裂能值，与经典化学交联弹性网络的情况相反。
英文摘要：
We have carried out systematic fracture experiments in a single edge notch geometry over a range of stretch rates on dual crosslink hydrogels made from polyvinyl alcohol chains chemically crosslinked with glutaraldehyde and physically crosslinked with borate ions. If the energy release rate necessary for crack propagation was calculated conventionally, by using the work done to deform the sample to the critical value of stretch $λ_c$ where the crack propagates, we found that the fracture energy $Γ$ peaks around $λ\sim 0.001 s^{-1}$ before decreasing sharply with increasing stretch rate, in contradiction with the measurements of crack velocity. Combining simulations and experimental observations, we propose therefore here a general method to separate the energy dissipated during loading before crack propagation, from that which is dissipated during crack propagation. For fast loading rates (with a characteristic strain rate only slightly lower than the inverse of the typical breaking time of physical bonds), this improved method to estimate a local energy release rate $g_{local}$ at the onset of crack propagation, gives a value of the local fracture energy $Γ_{local}$ which is constant, consistent with the constant value of the crack propagation velocity measured experimentally. Using this improved method we also obtain the very interesting result that the dual crosslink gels have a much higher value of fracture energy at low loading rates than at high loading rates, contrary to the situation in classical chemically crosslinked elastic networks.
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