Soft materials have enabled diverse modern technologies, but their practical deployment is usually limited by their mechanical failures. Fracture and fatigue of polymer networks are two important causes of mechanical failures of soft materials. A soft material fails by fracture when a monotonic load reaches its fracture toughness or fails by fatigue when a cyclic load reaches its fatigue threshold. The fracture toughness is usually much higher than the fatigue threshold for randomly crosslinked elastomers and gels. While fracture and fatigue have been extensively studied in randomly crosslinked elastomers and gels, they have not been comparatively studied in polymer networks with well-controlled architectures and defects. This work systematically studies the fracture and fatigue of ideal polymer networks with controlled densities of dangling-chain defects. We show that the fracture toughness and fatigue threshold of an ideal polymer network almost without defects are the same. After introducing a low density of dangling-chain defects into the ideal polymer network, its fracture toughness and fatigue threshold still maintain approximately the same. The fracture toughness of the ideal polymer network is also independent of the loading rate. We further use the recently developed defect-network model to explain the fatigue threshold (i.e., intrinsic fracture energy) of ideal polymer networks with controlled densities of dangling-chain defects.

软材料使各种现代技术成为可能，但它们的实际部署通常受到机械故障的限制。聚合物网络的断裂和疲劳是软材料机械失效的两个重要原因。当单调载荷达到其断裂韧性时，软材料会因断裂而失效，或者当循环载荷达到其疲劳阈值时会因疲劳而失效。断裂韧性通常远高于随机交联弹性体和凝胶的疲劳阈值。虽然在随机交联的弹性体和凝胶中已经广泛研究了断裂和疲劳，但尚未在具有良好控制结构和缺陷的聚合物网络中进行比较研究。这项工作系统地研究了具有受控悬链缺陷密度的理想聚合物网络的断裂和疲劳。我们表明，几乎没有缺陷的理想聚合物网络的断裂韧性和疲劳阈值是相同的。在理想的聚合物网络中引入低密度的悬链缺陷后，其断裂韧性和疲劳阈值仍然保持大致相同。理想聚合物网络的断裂韧性也与加载速率无关。我们进一步使用最近开发的缺陷网络模型来解释疲劳阈值（其断裂韧性和疲劳阈值仍保持大致相同。理想聚合物网络的断裂韧性也与加载速率无关。我们进一步使用最近开发的缺陷网络模型来解释疲劳阈值（其断裂韧性和疲劳阈值仍保持大致相同。理想聚合物网络的断裂韧性也与加载速率无关。我们进一步使用最近开发的缺陷网络模型来解释疲劳阈值（即，具有控制的悬挂链缺陷密度的理想聚合物网络的固有断裂能。