Rolling shear failure damage evolution process of CLT based on AE technology and DIC method

This paper proposed a methodology for monitoring the rolling shear (RS) failure of cross-laminated timber (CLT) via acoustic emission (AE) technique combined with digital image correlation (DIC) method. The RS strength of 3-layer CLT with different transverse layers (SPF dimension lumber, Douglas fir and Scots pine lumber) were measured using a modified approach. AE parameter analysis and cluster analysis were mainly focused on qualitative research on the relationship between wood RS failure evolution and AE events, while DIC method was used to characterize the shear strain distribution and development of specimens. Results showed that the tested group with Douglas fir lumber as transverse layer had the most AE events. The cumulative energy curve and cumulative counts curve of all tested groups had the same trend over time. The cluster analysis of AE signs indicated there were two kinds of AE events in CLT specimens during RS failure process, (a) the main AE events with low amplitude, originated from the initiation of micro-cracks in the transverse layer, and (b) the secondary AE events with all high-amplitude, attributed to the extension of cracks. A correlation between AE signal features and internal damage evolution of RS failure in the transverse layer was found in the experiments. DIC method could effectively and intuitively measure the surface shear strain of CLT, and predict the location of crack initiation in advance according to the evolution of the strain concentration area. The combination of AE technique and DIC method could correlate the RS damage modes with AE characteristics.