Effects of Cyclic Load Amplitude and Count on the Roughness and Friction Coefficient of the Round-End Wood Mortise–Tenon Joint

The fatigue of wood mortise–tenon (M–T) joints commonly results from the looseness of the joints when subjected to long-term cyclic load. It is of critical importance to comprehensively understand the fatigue of M–T joints to know what occurs in M–T joints However, fatigue evolution progression (FEP) of M–T joints has been rarely studied. This study mainly aimed to investigate the FEP of the roughness of mortise (RM) and tenon (RT), and the friction coefficient of the non-glued round-end beech wood M–T joint when subjected to cyclic load to provide basic data for numerically modelling the FEP of the M–T joint. The effects of cyclic load amplitude (CLA) (150 N, 200 N, 250 N, and 300 N) and cyclic load count (CLC) (25%, 50%, 75%, and 100% fatigue life) on RM, RT, and the friction coefficient were investigated. The results demonstrate that the CLA and CLC have significant effects on RM, RT, and the friction coefficient of the M–T joint. The RM, RT, and friction coefficient of the M–T joint decrease non-linearly as the CLA and CLC increase, complying with the power law function. The RM, RT, and friction coefficient of M–T joints are reduced by a large margin within the CLC of the initial 25% fatigue life, and these reductions decelerate from a CLC of 75% to 100% for all CLAs. The relationships between the friction coefficient and RM and RT at each CLA can be well fitted by a quadratic model during FEP. This study provides a new insight to comprehensively understand the FEP of the round-end M–T joint and supplies basic data for numerically modelling the FEP of the M–T joint.