Creep and fatigue analysis of furniture joints

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Absztrakt (kivonat)

Selection of joint type and its characteristics is one of the most important decisions in furniture design. In this study, the behaviour of Domino-type furniture joints under sustained as well as cyclic loading was investigated. Corner-joints and T-joints were prepared for loading in bending. Joints with two types of connectors, Domino wood dowel and dismountable Domino metallic connector were tested, both with two different sizes: 8x22x40 mm and 14x28x75 mm. Specimens were made of European beech wood and for glued samples a D3 grade PVAc adhesive was used. For a proper planning of the sustained and the cyclic loading, it was necessary to obtain information on the performance of the individual joint types in static loading. Because of the static bending tests, ranking of the joint types with respect to load carrying capacity and deformation was possible. The flexibility coefficient (rotation/moment ratio) of the studied joints were also determined taking into account their nonlinear behaviour. Cyclic loading tests were conducted on the principles of the standard EN 12512:200. The joints started to lose their original strength during the repetitions of the 75% amplitude level. At the end of the fatigue tests, it was possible to pull out the Domino wood dowels from the mortise, whilst this was not the case with the metallic Domino connectors. The load levels to be applied in sustained loading were determined not to exceed 50% of the maximum load obtained from the static load tests. The creep results were evaluated in terms of creep factor and the increase in joint flexibility. Considering creep factor the wood dowel fastened small size corner joints (LSWD) as well as T-joints (TSWD) performed best, while the big size T-joint with wood dowel (TBWD) proved to be the worst; the differences are quite important between the two ends of the rank (0.56 vs. 2.23). With the exception of T-joints with metallic connector, small-size samples performed 1.4 to 3.2 times better than their big-size counterparts did. Logarithmic functions were fitted on the creep factor data with high value of the coefficient of determination. The coefficient a in the equation as a measure of the initial creep rate is 1.4 to 2.8 times higher in the case of big-size specimens, as reflected in the creep curves; T-joints with metallic connector did not follow this trend. Increase of joint flexibility or loss of joint rigidity is 1.1 to 11.7 times higher in the case of big-size joint types. The increase of the rotation/moment ratio of joints with wood dowel is 1.5 to 2.8 times higher than that of similar joints with metal connector. The two main finding of the research were the superiority of small-size joints with respect to sustained loading attributable to the more advantageous positioning of the connecting elements, as well as the better performance of the dismountable joints both in sustained and cyclic loading.

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