The toughness of composite materials is size dependent below a critical load transfer length (l_T). Fiber-reinforced viscoelastic polymers are uniquely suited to study the size-limited regime because the l_T of these soft composites can be as high as several centimeters, in contrast to traditional composites where l_T is extremely small, allowing a large window for macroscale characterization. In this work, we elucidate the parameters that influence the toughness of soft composites when failure is governed by a fiber pullout-induced matrix-fracture mechanism. We ultimately demonstrate three important points: (1) fiber-reinforced viscoelastic polymers can possess high toughness, even at dimensions well below l_T, (2) significant toughness amplification occurs due to the presence of fibers, even when the fracture process consists solely of matrix rupture, and (3) the composite toughness in the fiber pullout region can be predicted from easily attainable component parameters.

复合材料的韧性在临界载荷传递长度 ( l _T )以下取决于尺寸。纤维增强粘弹性聚合物特别适合于研究尺寸限制机制，因为这些软复合材料的l _T可以高达几厘米，与l _T极小的传统复合材料相比，为宏观表征提供了一个大窗口. 在这项工作中，我们阐明了当失效受纤维拉拔诱导的基体断裂机制控制时，影响软复合材料韧性的参数。我们最终证明了三个重点：（1）纤维增强粘弹性聚合物具有高韧性，即使尺寸远低于l_T，（2）由于纤维的存在，即使断裂过程仅由基体破裂组成，也会发生显着的韧性放大；（3）纤维拉出区域的复合材料韧性可以从容易获得的组件参数中预测。