Experimental study on Mode Ⅰ fracture characteristics of laminated flattened-bamboo lumber combined with VIC-3D system

Abstract

According to ASTM E399, Mode I fracture tests were conducted on compact tension (CT) specimens of laminated flattened-bamboo lumber (LFBL) loaded parallel to grain, in combination with the optical measurement system VIC-3D (video image correlate, 3D) to observe the evolution of strains and crack propagation. In the test results, the average fracture toughness of the specimen gradually decreased as the ratio of initial crack length to specimen width increased, and after the ratio reached 0.45, the fracture toughness value tended to be stable; the fracture toughness tests could only be considered valid if the thickness of the specimen was greater than or equal to 25 mm. Compared to large-thickness specimens, small-thickness specimens had a lower degree of brittleness; microscopic failure modes were classified as ground-tissue cracking and fiber damage. During the test, the tension-strain field was always concentrated at the tip of the extending crack. When the cracks extended to equal length, the specimens were in the same state, indicating that crack extension followed a self-consistent pattern. Furthermore, the compliance calibration method was used to develop the equation for the function of crack length-compliance.