Effects of cycle load amplitude and count on fatigue damage progression in wooden furniture mortise-and-tenon joints quantified using porosity, fit, friction coefficient, and direct withdrawal load resistance

Abstract

Failure of mortise-and-tenon (M-T) joints used in wooden furniture construction is primarily attributed to long-term cyclic loading. Therefore, understanding how cyclic load alters the physical and mechanical properties of M-T joint components and leads to fatigue damage is essential. This study examined the effects of four cyclic load amplitudes (CLA: 150, 200, 250, 300 N) and four cyclic load count ratios (CLCR: 0, 25%, 50%, 75%) on the fatigue damage progression (FDP) in non-glued beech M-T joints. The assessment was conducted by quantifying changes of M-T porosity, fit, friction coefficient and the joints’ direct withdrawal load resistance (DWLR). Experimental analysis revealed that the porosities at the end section (5 mm, 20% of the T length) and the middle section (8 mm, 30% of the T length) of fatigued Ts decline linearly as functions of CLCR and CLA, respectively. The end section exhibits lower porosity than the middle section, and its porosity decreases at a higher rate as CLCR increases from 0 to 75%. The damage factor of M-T joints increases with CLCR and CLA. Across all tested CLA levels (150, 200, 250, 300 N), the ends section of fatigued Ts consistently exhibited higher damage factors than the middle section. The friction coefficients of fatigued M-T joints were found to follow a power function relationship with CLCR. The M-T fit decreased significantly as CLCR increased from 25% to 75% and showed a further decline with increasing CLA from 150 to 300 N. The reduction of M-T fit also showed a power function relationship with CLCR. Within each of the four CLA levels, the DWLRs of fatigued M-T joints decreased linearly with CLCR, and the slopes of these linear relationships increased as CLA increased from 150 to 300 N. Furthermore, the DWLRs can be estimated using the derived regression model, which incorporates the friction coefficients of the M-T materials, the M-T fit, the CLA level, and the initial DWLR.