Papers by Author: Lian Chun Long

Abstract: This paper has investigated the effect of hole shape, hole size and hole position on elastic buckling of square perforated plates by using the finite element method. According to the effect law of these three geometric factors on buckling bearing capacity, buckling coefficient was obtained by data fitting. The results show that: The plate with circular perforation has the greatest buckling bearing capacity of the three perforation shape plate; When the center perforations have the same area, the relationship between buckling coefficient and perforation size is exponential for the plate with circular hole or square hole, the relationship between buckling coefficient and perforation size is biquadratic for the plate with triangular hole and the greater the perforation size is, the less the buckling bearing capacity will be; For the plate with uniform circular perforation size, The relationship of buckling coefficient and the spacing between perforation center and structure center is quadratic and the greater the spacing is, the less the buckling bearing capacity will be. The results in this paper provide reference for perforation design of plate.

Abstract: Bamboo is a fiber-reinforced bio-composite with superior structural behavior. For the purpose of analyzing the correlations between the mechanical properties of bamboo and fiber volume fraction, tensile tests were performed on bamboo test specimen, and the corresponding volume fractions of fiber and parenchymatous ground tissue were measured. Linear and curvilinear regressions were done from tested data of elastic modulus, tensile strength and volume fractions of fiber. The results display that there is an obvious correlation between bamboo tensile properties and fiber volume fraction. In order to analyze the effects of fiber gradient distribution on bamboo structural behavior, models composed of fiber and parenchymatous tissue were built based on different fiber distribution for comparative analysis. The analysis results show that the maximum deformation of 4 layers model is 3.86% less than 1 layer model, and the maximum deformation of 8 layers model is 8.87% less than 4 layers model. In the part of maximum axial stress, the maximum axial stress of 4 layers model is 3.27% less than 1 layer model, and the maximum axial stress of 8 layers model is 8.90% less than 4 layers model. Conclusion can be drawn from the comparison that the strength and stiffness of the model appear to be growing with the degree of fiber gradient distribution deepening from 1 layer model to 4 layers model, and 4 layers model to 8 layers model.It can be concluded that the mechanical properties of bamboo structure are significantly improved because of fiber gradient distribution.

Abstract: Grid-stiffened cylindrical shells are widely applied in aviation and aerospace engineering. Bearing capacities of grid-stiffened cylindrical shells will be reduced by local heating. In this study, numerical simulation method is applied to deduce the temperature distribution of the grid-stiffened cylindrical shells subjected to high power laser irradiation. Temperature dependent aluminum alloy properties are fully considered in the process of numerical simulation. Comparing to smooth thin-wall cylindrical shells, the effect of ribs size to temperature distribution is studied. As the material properties varying with temperature, the temperature rising rate is higher at the initial period when cylindrical shell is subjected to laser irradiation. The temperature rising rate gradually reduces with irradiation time increasing. Buckling analysis was performed to obtain the buckling bearing capacity and the effect of local heating on grid-stiffened cylindrical shells subjected to local heating.

Abstract: This paper predicts the effect of main parameters to the failure behavior of T300/AG80 composite plate under preload and laser irradiation by experimental testing and data fitting. The load holding device was used to give certain preload to composite plate specimens, and an Nd: YAG laser was used to give laser radiation simultaneously for testing the failure time of the specimens. By varying the magnitudes of preload and the laser power densities, the effect of preload and laser power density on the failure time is obtained. The reaction process was recorded with a high-speed camera. The experimental data were fitted to obtain the expression of the materials failure time with preload and laser power density. When the preload kept constant, the relationship between the failure time and laser power density was exponential function. When the laser power density kept constant, the relationship between the failure time and pre-tensile-loads was approximating linear, and pre-compress-load was quadratic. Fitting the empirical formula provides a reference to predict life for the composite structure applied both preload and the action of the laser irradiation.

Abstract: In order to predict the size and shape of the laser ablative hole, a 3D finite element model was developed to simulate the Nd:YAG laser ablation of carbon fiber epoxy composite. For given irradiation conditions, good agreement with experimental data relating to hole dimensions. The numerical results and experimental observations indicate that with the irradiation time increasing, the domain under investigation temperature raises rapidly and the further to the spot center, the smaller the temperature raises. After 0.093s the target surface temperature is higher than the critical temperature of composite, so the removal of the material on first composite layer occurs. It also can be observed that heat energy of the laser spread within the material and the isotherm ribbon, as well as crater border, is step-like.

Abstract: This paper investigates failure behavior tests of T300/AG80 composite laminated specimens under tensile and compressive preload using a load holding device and laser irradiation from an Nd: YAG laser. By changing the magnitudes of the preload and the power densities of the laser, the effects of preload and laser power density on the time-to-failure of the specimens were observed. The response process of specimens was synchronized taken in using high-speed camera in experiment. The experimental results showed that tensile mechanical properties of T300/AG80 composite laminated specimens were obviously superior to ones in compression test. The relational expressions between the time-to-failure of specimens and pre-loads as well as with laser power densities were acquired through fitting experiment data. The time-to-failure reduced with the pre-load increasing, the relationship is approximating linear when the laser power density kept invariable. When the pre-load kept unchanged, the time-to-failure reduced as the laser power density increased. The relationship is approximating exponential. A basis for life prediction of structure mechanically loaded in either tension or compression during the irradiation by laser is provided by fitting expression.

Abstract: In this paper, precise integration in a symplectic system is used to analyze the stop-band characteristic of the dielectric layer PBG structure in a waveguide. The transverse section is made discrete by using edge elements. The stiff matrices of a dielectric layer and an air layer can be calculated by precision integration based on Riccati equations in a Hamiltonian system. The export stiff matrices of a period can be obtained by a combination of substructures, and then the whole structure can be solved. The stop-band characteristic of a dielectric layer PBG structure in a waveguide is obtained and the effects of the size of period and the number of periods are discussed. The examples presented show that this method is precise and efficient.

Abstract: Thin cylindrical shells are widely used in modern structures. When the structures are under axial compression, inflectional destruction happens early. In order to design reasonable and reliable shell structures, stiffened cylindrical shells are applied in the dissertation, ANSYS, an valid finite element analysis software, is employed to redevelop and set up parameter calculation model, subjected to volume and variables value range restriction, the structure’s critical buckling load is the objective, and the serial linear programming optimization procedure is executed as well as the optimized thickness of shell and the size of stiffeners are gained accordingly. The critical buckling load of the structure is obviously increased after optimization, and the feasibility of this method is validated due to the comparison with the numerical and theoretical result.