Fracture process zone of soft network composites

The fracture process zone of soft network composites is studied in this paper. When a crack propagates in the composites, even though polymer chains rupture in a very thin layer, all the elastic energy stored in a large zone of the fiber network is dissipated and contributes to the fracture energy. This zone acts as an elastic dissipater and is defined as the fracture process zone. By quantifying the distribution of released elastic energy during crack propagation, we determine the fracture process zone size. It varies with the increase of sample size and finally approaches a material constant: the steady-state fracture process zone size (SFPZ), which is determined by the fiber network geometry and fiber-to-matrix modulus ratio synergistically. A three-region phase diagram of the normalized SFPZ is constructed to illustrate the different key parameters in different regions. For a composite with small modulus ratio and slender fiber network (region I), the SFPZ is confined within one layer of the fiber network and the size is determined by the fiber width and modulus ratio. For a composite with large modulus ratio and stubby fiber network (region III), the size of SFPZ is dominated by the fiber network geometry, the influence of the matrix can be neglected. In between (region II), it depends on both factors. This work provides an insight into the fracture mechanism of soft network composites, gives practical guidance for fracture testing, and paves the way for designing fracture-resistant soft network-based materials and machines.