Applied Mechanics and Materials Vols. 477-478

Abstract: Energy absorbing component of bumper equipped at the front end of a car, is one of the most important automotive parts for crash energy absorption. It usually was made a mental thin walled tube. In the paper, automobile energy absorbing component at low-velocity impact was studied by using Finite Element Method. The FE model of the tube was builded by comparing the five cross section shape . Results show that the impact peak load and maximum energy absorption have certain effect to energy-absorbing component with different the cross section shape.

Abstract: Sonic boom suppression method is the key technology of next generation supersonic aircraft. Low boom mechanism of the off-body energy deposition is analyzed by using the thermal chocking model. The mass flux of energy deposition region is small than no energy deposition region, and off-body energy deposition will induce a bow shock wave. The mechanism of off body energy deposition is similar with quiet spike, so it can be regard as a virtual quiet spike. Off-body energy deposition analysis software is developed based on CFD, waveform parameter method and NSGA-II genetic algorithm. The location coordinate, value, shape and location number of energy deposition are the key parameters in low boom design. Initial pressure of optimized energy deposition decrease near about 54.65 than no energy deposition, and rise time increase 543.2%.

Abstract: Tests including the constant load tensile, three point bending and hydrogen induced cracking (HIC) are executed to evaluate the comprehensive properties of the 15CrMoR(H) with new smelting process in saturated hydrogen sulfide (H₂S) according to NACE and National Standard. By analyzing and fitting the results of constant load tensile test, the stress-life mathematical model of this material is given. Results show that the stress corrosion threshold of the constant load tensile is 0.7R_el (252MPa).The nominal stress of three point bending S_C is higher than 4.5 R_el (1620MPa). Results of HIC test show that the crack length rate CLR is 4.40%, the crack thickness rate CTR is 0.87% and the crack sensitive rate CSR is 0.04%. According to EFC standard, the safety margin is 3.4, 3.4 and 37.5 times respectively. All the experimental results show that the 15CrMoR(H) material has excellent H₂S stress corrosion cracking resistance properties.

Abstract: The contact between substrate and micro-cantilever simplified as an ideal flat substrate contact with a micro-cantilever rough surface. A three-dimensional adhesive contact model was established on isotropic rough surfaces exhibiting fractal behavior, and the equivalent plastic strain was discussed using the finite element analysis. The maximum equivalent plastic strain and its depth were presented with the different paths of rough solid when loading. The result show that the equivalent plastic strain versus different depth which at different locations showed different laws, in the top area of the asperities versus different depth, the maximum equivalent plastic strain occurs in the subsurface range about 0.5μm from the surface or on the surface. In addition, with different deformation characteristics, the degree of the equivalent plastic strain was different.. The contact model between micro-cantilever rough surface and flat substrate will lay a foundation to further research on the substance of the process of friction and wear.

Abstract: The scaled boundary finite element method (abbr. SBFEM) is a semi-analytical method developed by Wolf and Song. The analytical advantage of the solution in the radial direction allows SBFEM converge to the Williams expansion. The coefficients of the Williams expansion, including the stress intensity factor, the T-stress, and higher order terms can be calculated directly without further processing. In the paper the coefficients of higher order terms of the crack tip asymptotic field of typical wedge splitting specimens with two different loading arrangements are evaluated using SBFEM. Numerical results show the method has high accuracy and effectiveness. The results have certain significance on determining crack stability of the wedge-splitting specimen.

Abstract: In order to get a deep understanding of composite failure mechanisms, the new advanced signal processing methodologies are established for the analysis of acoustic emission (AE) data obtained from the quasi-static tension test of composite materials. Tensile test were carried out on twill-weave composite specimens, and acoustic emissions were recorded from these tests. AE signals were decomposed into a set of Intrinsic Mode Functions (IMF) components by means of Empirical Mode Decomposition (EMD) , the Hilbert-Huang Transform (HHT) of each IMF component was performed, it was shown that the frequency distribution of IMF component in time-scale could be directly related to composite materials failure mechanisms.

Abstract: The tearing mechanical properties and the deformation field distribution of 45 degree oblique direction of the crack tip was studied on the stratospheric airship envelope reinforced by plain woven Kevlar-fiber composite. Here, the material samples were prefabricated with the initial length of 20mm unilateral incision, and the digital speckle correlation experimental method was used to obtain the perpendicular crack tip displacement and strain fields with artificial spots under mono-axial tear test. The results show the deformation field changes with the characteristic of discrete step and the strain concentration phenomenon, and the strain concentration zone expands as increasing tensile load. The warp and weft step maximum displacement reaches 6.00mm and 1.7mm, and deformation in every step exhibits a diminishing step law, the warp deformation in the rear area of the crack tip are evenly, while the shear and weft strain volatile in a wide range

Abstract: The present work is devoted to the analysis of a buckling behavior of a cylindrical composite panel. The considered structure is subjected to the uniform axial compression. The wall of the panel consists of the 8 layers. In addition, in the geometrical center of the structure there is a square delamination located between the fourth and the fifth layer. The main goal is to determine the buckling and post - buckling behavior as well as the influence of the delamination on the stability of the structure. The nonlinear numerical analysis is carried out with aid of the FEM method. The experimental verification is also performed. The results obtained from numerical and experimental analysis show very similar behavior of the structure.

Abstract: The joint simulation of Virtual Prototype Technology and Finite Element Method was utilized to perform the analysis of both strength and fatigue life of the input axis in a six-speed vehicle transmission with three axes. Firstly, the software Pro/E was used to establish a 3-D model of the input axis and its gear engagement, and the model was then imported into a software ADMAS of the virtual prototype technology to perform a dynamic simulation analysis. Secondly, the gear contact forces obtained by above-mentioned analysis were used as the loading condition of finite element analysis of the input axis to check its strength. Finally, the fatigue of meshing teeth on the input axis was analyzed to determine the fatigue life of the input axis. The results show that the static strength of input axis can meet the requirement of safe use under the working condition of input torque T=1.5kN·m, and the minimum fatigue life on the place where the stress is maximum at flexural root of a tooth is about 2 million times.