OPTIMAL DESIGN OF STRETCHERS POSITIONS OF MORTISE AND TENON JOINT CHAIR

The chair joined by oval mortise-and-tenon was taken as a case. Then influences of two adjacent sides (side A and side B) stretcher positions on mechanical properties of chairs, including ultimate loading capacity, stiffness and strain distributions, were investigated through using experimental and numerical methods. Firstly, two factors and three levels experiments were conducted and analyzed by Finite Element Method (FEM) . The results showed that ultimate loading capacity of chairs decreased firstly and then increased with the growth of the height of stretchers positions. In addition, the stress concentration occurred at middle of side rails and joints of side rails, especially at the side B, while the stress at the middle of the leg was minimum. Besides, the higher the stretcher position of the side A was, the more harmonious the stress distributions of chair was, and the higher ultimate loading capacity and stiffness were. Moreover, the results of FEM were well consistence with those of experiments, and the errors were within 10%. Secondly, two factors and five levels numerical analysis was conducted to optimize the stretcher positions of chair by the FEM, and the results showed more boadly that the best stretchers positions of chair owning the highest loading capacity was not the only one. Finally, the relationship between ultimate loading capacity and stretcher positions was generated by using the response surface method, and the correlation coefficient was nearly 88%.