Fatigue and damage evolution in wood T-shaped mortise and tenon joints.

Mortise and tenon joint is a key connecting component in timber-framed architecture. Accurately assessing the damage to joints is crucial for the structural design of wooden buildings. This study conducted fatigue tests at three stress levels (70%, 100%, and 130%) based on the maximum stress from static bending tests to analyze the impact of different stress levels on the fatigue performance of mortise and tenon joints. The results showed that the deformation increased as the stress level increased. The energy loss per cycle de-creased and then increased at 130% stress level, and remained essentially constant at 70% and 100% levels. Then, micro-CT scanning was performed on the specimens after fatigue testing. The ambient occlusion algorithm was used to identify the outer boundaries of the tenon, which can distinguish internal cracks from outside air. The sphericity index was used to differentiate between pores and cracks. Three-dimensional visualization analysis was performed on the specimens, and the obtained information on pores and cracks was quantitatively analyzed. The results indicated that deformation and fracture of the tenon were the primary causes of joint damage. The layer-by-layer porosity of the undeformed portion of the tenon remained essentially constant and was lower than that of the fractured region and higher than that of the deformed region. This study analyzed the damage behavior of mortise and tenon joints under different stress levels, contributing to the design and protection of wooden structure buildings.