Technical ReportElasticity modulus of cabinet furniture joints
Introduction
Furniture strength assessment should be initiated at the stage of their design process. Conformity certification of a given piece of furniture prototype always entails the need to bear considerably higher costs of eliminating the identified defects and mistakes [1], [2], [3]. One of the major quality evaluation criteria of cabinet furniture is their stiffness [4], [5], [6], [7], [8], [9]. This stiffness depends, primarily, on the stiffness of the applied joints [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Studies on analytical models of cabinet furniture stiffness have been conducted since 1957 [4], [5], [6], [7], [8], [26]. The results of those experiments revealed that for physical models connected with the assistance of various couplings, furniture deflections were lower in comparison with the calculated values. The main reason of the discrepancies was disregarding the influence of furniture joint stiffness on the rigidity of the entire construction. Therefore, many researchers focused their attention on the issue of stiffness and strength of furniture joints and their impact on the rigidity of the entire construction [10], [11], [21], [22], [23], [24], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38]. The main assessment criterion of joint strength was the value of the breaking force or bending moment. On the other hand, stiffness was evaluated on the basis of the deflection value along the direction of load application or on the basis of the value change of the angle between the arms of the joint. These results, albeit very important from the cognitive point of view, fail to make easier work for designing offices of furniture factories which employ the CAE (computer aided engineering) tool for rapid prototyping. Numerical modelling requires determination of joint stiffness coefficients or realistic modelling of elastic bodies which remain in contact with one another [39], [40], [41], [42], [43]. This kind of modelling is very accurate but also labour-consuming and impractical from the point of view of application by designing offices. For this reason, an attempt was made to elaborate a method of simplified modelling of furniture joint stiffness for the needs of numerical calculations [44]. In the proposed method, joint stiffness was expressed by means of a modulus of elasticity in the form of a load and deflection function.
The main goal of this study was determination of elasticity moduli of furniture L-type joints, numerical calculation of furniture stiffness with joints which were assigned elasticity moduli as well as verification of the results of these calculations employing for this purpose experimental investigations.
Section snippets
Kinds of L-type joints
For experiments, standard connectors were selected ensuring possibilities of self-assembly by the user (Fig. 1). These were beech dowels Ø 8 × 35 mm (D), “konfirmat” screws Ø 7 × 50 mm (C), eccentric couplings with threaded mandrels Ø 5 mm (E1) and eccentric couplings with expanding mandrels Ø 8 mm (E2). Fig. 1 also gives characteristics of the provided holes. Shapes and dimensions of joints are presented in Fig. 2 and described in Table 1. Three kinds of 500 mm long (L) and two kinds of 150 mm long (S)
Stiffness of joints
Fig. 7 illustrates stiffness of joints in the form of dependences between the load and deflection, whereas Table 3 presents load values, deflections corresponding them, joint stiffness coefficients Kj as well as elasticity moduli Es. It is evident from Fig. 7 that LCD joints were characterised by high load-carrying ability and considerable deflections. In comparison with the carrying capacities of LE1D, LE2D, SE1 and SE1D joints, it was, respectively, by 97.6%, 87.1%, 171.4% and 102.2% higher.
Conclusions
On the basis of the obtained research results and their analysis, the following conclusions and remarks were arrived at: the correctness of the developed model of joint elasticity modulus was verified positively by experimental investigations. The model makes it possible to compare objectively stiffness of joints and, on this basis, to select the most advantageous solutions. The application of joint elasticity moduli simplifies numerical analysis of cabinet furniture construction. The highest
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