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, SEⅠC. 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 SEⅠC calculated by the compliance method is 1.5 ± 0.5 kJ/m2.