Experimental investigation on translaminar fracture behavior of cross-laminated bamboo

Cross-laminated bamboo (CLB) is a bamboo-based construction product with bamboo's advantages, which are green, environmentally protective, and sustainable. However, bamboo is easy to crack. Structural elements in bamboo constructions are assembled onsite, making splitting cracks easily form at joints and bolt connections. Therefore, it is essential to assess cracked structure safety with fracture mechanics. However, rare studies are addressed on fracture properties of bidirectional laminated bamboo, especially the translaminar fracture resistance, which represents the ability to arrest a catastrophic crack in structures. This paper studies the translaminar fracture properties of CLB composite using three-point bending beam tests. Load-displacement and load-CMOD curve characteristics, fracture process, and the failure modes of bidirectional laminated bamboo are analyzed. The R-curve expressed by the energy release rate is calculated by three methods. Results demonstrate that the R-curves obtained by the three different methods show similar results. The methods to determine R-curves employed in this study are simple and can describe the translaminar fracture toughness of laminated bamboo. The methods are validated by comparing the traction-separation relations calculated from the R-curves to those measured by double-edge notched tests (DENT). A comparison of the bidirectional laminated bamboo's energy release rate to the matrix-dominated energy release rate of unidirectional laminated bamboo reveals that bidirectional fiber arrangement has a remarkable improvement on the toughening of laminated bamboo at and after crack initiation. Moreover, the lay-up effects of CLB are analyzed by relating the energy release rate results to the failure pattern of fractured specimens. It is found that fiber pullout/bridging caused by 90°direction crack propagation around fiber bundles is the dominant toughening mechanism of CLB. The lay-up sequence of 0° and 90° plies also has an effect on 90°direction crack propagation; therefore, it will influence the toughness of CLB.