Investigation of a critical separation criterion for mode I-Governed fracture of basalt fiber/polypropylene rods via a modified double cantilever beam test

A new approach using a modified double cantilever beam test was proposed for evaluating the mode Ⅰ-governed critical energy release rate representative of unidirectional composite rods, defined here as the mode Ⅰ critical separation energy, 〖SE〗_IC. This approach was used to characterize basalt fiber reinforced polypropylene rods. The relation between load and displacement is obtained from loading-holding-unloading tests, where apparent crack length—defined as the straight-line distance between the loading axis and crack tip—is measured at the end of holding time of each cycle; the start of crack propagation is confirmed by in-situ digital microscope observation. Scanning electron microscope observation of fracture surface reveals matrix crack growth and fiber-matrix interfacial debonding. The linear relation between apparent crack length and cube root of compliance is obtained, and the 〖SE〗_IC calculated by the compliance method is 1.5 ± 0.5 kJ/m2.