Experimental study on crack initiation and propagation of wood with LT-type crack using digital image correlation (DIC) technique and acoustic emission (AE)

Monitoring the cracks initiation and propagation of construction materials, as well as determining the fracture process zone, constitute two key factors to understand the damage mechanism of materials in order to control the risk of material degradation and failure. This paper demonstrates the results of a laboratory static test designed to investigate the in situ monitoring of crack tip growth in wood. LT-type single-edge notched specimens made of Chinese fir with the seam height ratio of 0.1, 0.2 and 0.3 were tested by three-point bending experiment. In this paper, acoustic emission (AE) method and digital image correlation (DIC) method were used to study the damage process of Chinese fir under monotonic loading techniques simultaneously. The results show that analyzing AE signals by considering the acoustic emission event number and the cumulative events yields interesting information on crack initiation and propagation. Based on the displacement field obtained from the DIC, the cracking displacement (COD) and crack extension length during crack propagation can be converted to provide information about the evolution of the fracture process zone at the interface. Moreover, an additional analysis of DIC and AE data indicates good correlation (involving the crack extension length and the cumulative events). It opens the possibility to characterize the crack initiation and propagation of wood materials without visible wood cracks.