Study Of Stiffness For Shell Plastic Parts Based On Experiment

The stiffness of the shell plastics is one of the difficult problems for manufacturers and consumers at all times. In the paper, after presently synthetically researching the stiffness of the thin-wall plastic both domestic and international, and adequately studying difficulty, the author use numerical optimization combining experimental modal analysis(EMA) to fabricate the main body of the paper. The paper adopts the method of optimization to optimize the bending stiffness of the structure,EMA can examine the structural dynamic characteristic and the weak stiffness locations.First, depending on the theory of sniffness distortion of shell plastics,the author optimize and design the board which has strengthening ribs. Based on the theory, the paper brings up the relationship between bending stiffness and warpage,discusses the infection of bell structure to the warpage. The author list the number of the strengthening rib—n, corresponding each n, define the thinckness of the board—t ,the thickness of the strengthening rib—b and the height of the strengthening rib—h etc as the variable to build the math-model of bending stiffness of the board, and optimize the objective function by programming on the microsoft visual basic plateform. The optimized results assist the analysis and optimization of the cross section parameter of the board whose bending stiffness is weak.Then, depended on the theory of the experimental modal analysis, a modal analysis experimentation of hugely structural dynamic characteristic for the rear shell of a computer display—mode hammer attacking experiment is projected, the auther analyse its structural dynamic characteristic and the weak stiffness locations, mode shapes from 11# to 20# in low frequencies are analyzed, weak stiffness locations are found, and structure optimum is conducted. The stiffness optimization of the strengthening rib board can make the bending stiffness reach the maximum by altering the width—d and the area of the cross section—K₁, then with the direction of the shell plastics distortion theory to improve the structural design such as strengthening ribs and so on. In another words, to choose the cross section of the board which bear the weight and is obviously weak stiffness, then optimize the cross section parameters to re-design the parameters of the cross section, which you want to optimize.The research shows that warpage of a shell plastic structure is reason of weak stiffness. The results of the numerical optimization reveal that when the area of the cross section is fixed, the height of the strengthening rib make the biggish infection to stiffness of the shell plastics. If allowable, we can augment the height of the strengthening rib to improve its stiffness, and the EMA has proved this point. Using EMA to investigate structural dynamic characteristic of shell plastics can obtain more credible mode shapes and analyse its weak stiffness locations to optimize the structure, what'more, we also can numerical optimize the parameters of the cross section of the bearing weight board whose stiffness is weak to make the stiffness reach the maximum under satisfying arts and crafts and assembly conditions.