Papers by Keyword: Thin-Walled Structure

Abstract: Stress-strain analysis of a solid-propellant rocket engine is the subject of this study. A chosen material is selected in order to ensure its maximum strength at minimum weight of the engine. The airframe of the rocket engine is a thin-walled structure, which consists of cylindrical and spherical parts. The dynamic behaviour analysis of this thin-walled structure under the action of impact loads is performed. The anisotropic material model and dynamic properties of the shell material are taken into consideration to solve the underlying problem.

Abstract: In this paper, an analytical prediction and numerical simulation of the behavior of square crash box structures having hole at corners on dynamic axial crushing are studied. The focus of the present theoretical prediction is to calculate the mean crushing force and maximum crushing force during the folding process subjected to axial impact loading. Then, the effect of hole size to the crushing response of square crash box structures was also evaluated. For validation, an explicit non-linear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical method and theoretical prediction were in good agreement. The results showed that, by inserting holes at corners, the folding can be controlled to be always started from the hole, and peak crush load on the first fold can be reduced significantly. Meanwhile, the decreasing of mean crushing force is insignificant compared to the one without holes. Hence, the characteristic of impact energy absorption in a progressive buckling can be improved, the damage in passenger compartment can be minimized, and the deceleration level can be kept in safe level to prevent injury of the passenger.

Abstract: This paper reports a new way to conduct fracture mechanics experiments of welded thin-walled structure for aircraft fuselage applications made of the Al 6156 ally using lock-in infrared thermography. The heat wave, generated by both the themo-mechanical coupling and intrinsic energy dissipation was detected by an infrared camera. The crack growth rate measured by the lock-in infrared thermography is found to be consistent with that measured by conventional method. It is observed that the crack can either grow underneath the stiffener or grow into the stiffener web with the crack length measured at the same time. In addition, the crack tip plastic zone was observed before the specimen was about to be destroyed.

Abstract: Recent advancement in manufacturing technology has initiated a new phase of buckling structures analysis and structural design research development. As the ability to manufacture stiffeners in complex shapes has become increasingly more sophisticated, researchers are able to further enhance the design of thin-walled stiffeners. This paper presents an attempt to discover a structural design which employs the use of sub-stiffeners and the ability to retain maximal buckling load. FEM analysis was performed on compression loaded rectangular stiffened panels clamped on all sides to determine optimal attributes of two panel concepts: (1) stiffeners height changes according to sinusoidal law across the panel width, (2) stiffeners area changes according to sinusoidal law across the panel width. In both cases, total volume of the material was held constant. Non-dimensional parameters of the optimal panels were obtained. It was found that there was a positive correlation between the amount of change in buckling patterns caused by a sub-stiffener, and the amount of initial buckling load which could be obtained.

Abstract: Numerical and experimental study of the effects of center holes located at opposite sides on dynamic axial crushing of thin-walled square aluminum extrusions column are presented in this paper. The results showed that, by inserting the holes, the impact energy absorption characteristic in a progressive buckling can be improved as the starting location of the plastic deformation is always from holes and peak crush force can be decrease, so that the deceleration does not exceed the limit that can injure the passenger when frontal impact occurs. Here, the results of numerical simulations, conducted using an explicit finite element code, are compared with experimental results for various hole diameter. The results shows that the peak crushing force is decrease, while the mean crushing force is relatively constant.

Abstract: When the blasting method is used to demolish the underground thin-walled structure, the safety misadventure occurs possibly due to the small burden, the heavy workload of the drilling and excavation as well as the long construction time, thus, its demolition is more difficult than that of the foundation. This paper describes the new underground thin-walled structure blasting demolition method - the wall-outside blasting charge method and the primary discussion about the blasting mechanism of the wall-outside blasting charge method, which is used in engineering practice. The demolition practice has proved that the wall-outside blasting charge method is a safe, simple and efficient and economic method to demolish the thin-walled structure such as underground sinking well and the pool, its blasting fragmentation is uniform, the fly-rock is easily controlled, and this method has the good economic benefit and the application prospect.

Abstract: The paper presents the numerical studies of two different tubes under axial impact loading structures. The cylindrical tubes filled with closed-cell polymeric foam. The deformation and failure mechanism of this new structure were observed and analyzed numerically using the finite element method. It is revealed that the stress distribution and fracture of the foam-filled tube structure are different from those of foam-filled tube. In comparison with double cell foam-filled tubes, the load-carrying capacity of this new structure is much steadier, the collapse behavior resistance is enhanced, and the weight efficiency of energy absorption is higher. Parameters affecting the performance of the foam-filled tube structures are also studied. Comparison were carried out with load versus displacement curve and also dynamic mean load as well as dynamic absorbed energy versus deformation of tubular collapse modeling failure mode using finite element analysis.

Abstract: Thin-walled structure absorbs most impact kinetic energy during collision accident,and they are widely used as energy-absorbing element. In order to improve crashworthiness of them, regular pyramidal ripple is added on the thin-walled square tube’s surface. Explicit finite element technology is applied to simulate the behavior of the tube under axial impact load. Simulation data was delt with by Response Surface Method to form a function of variables and response,and the new structure was optimized. Research results show that, the thin-walled square tube with pyramidal ripples can improve controllable of structure deformation obviously and Optimized structure can absorb and dissipate much more impact kinetic energy.

Abstract: Thin-walled structures exhibit complex nonlinear response under thermo-acoustic loadings. Complex stress-strain states decrease the fatigue life of structures seriously. Based on the thermo-acoustic response obtained, the rain flow cycle counting scheme is used to calculate the number of fatigue cycles. Then the Miner accumulative damage model is employed to predict high cycle fatigue life, combined with various nonzero mean stress models, including Morrow TFS, SWT. The nonlinear response and fatigue life of 2024-T3 aluminum plate are obtained under different combinations of thermo-acoustic loadings. Results show that the fatigue life of pre-buckled plate decreases with the increase of temperature. For post-buckled plate, as the temperature increases, the fatigue life of plate undergoing persistent snap-through keeps going down till the lowest, and then increases after entering intermittent snap-through regime. At high temperatures, the influence of high temperature on the S-N curve must be considered, the results may be erroneous otherwise.

Abstract: Future flight vehicle structures will encounter severe loading conditions, a combination of aerodynamic, thermal, acoustic and mechanical loads. Although the analysis methods for responses of structures under acoustic loads have been developed to some extent, but with thermal loads considered, the responses show fundamental differences, which complicate the analysis immensely. It was reported that hypersonic flight may give rise to surface temperature as high as and intense noise whose overall sound pressure level (OSPL) may reach 180dB. Thin-walled structures subjected to such loadings will exhibit nonlinear responses. Large temperature increments may cause thermal buckling, large thermal deflections and large thermal stresses superimposed on dynamic stresses, coupled with changes in material properties. Both the geometry change by thermal buckling and stiffness change by thermal stress account for the changes of natural frequencies and mode shapes. When the acoustic loading increases to a high enough level, the post-buckled structures will exhibit snap-through motion, a large amplitude nonlinear vibration between different equilibrium positions, which will introduce extra large mean stress. As a result, thermo-acoustic fatigue may be caused, which will reduce the structure's fatigue life dramatically. Therefore it is an urgent need to estimate the influences of thermal loads on the nonlinear response of structures. A numerical investigation of the influences of thermal loads on the dynamic response of thin-walled structure under thermo-acoustic loadings is implemented. With clamped-clamped thin flat plate selected, the response characteristics related to temperature are investigated by changing thermal loads. The thermal load is considered as constant both on the surface and across the thickness. The acoustic load is simulated using stationary Gaussian white noise. Firstly, a thermal buckling analysis is proceeded to obtain critical buckling temperatures, followed by modal analysis under different thermal loads. The pre-buckled and post-buckled mode frequencies and shapes are obtained. Then three types of snap-though motions are predicted: i) vibration around one post-buckled equilibrium position, ii) intermittent snap-through, and iii) persistent snap-through. The relations between thermal loads and the occurrence of snap-though is obtained together with results about the statistics characteristic of dynamic response and their relations with thermal loads, which include critical thermal buckling loads, natural frequencies and mode shapes, RMS response and snap-through frequency. Good agreements have been achieved with previous analytical solutions, which demonstrate the effectiveness and reliability of the method employed.