Influences of Thermal Loads on Nonlinear Response of Thin-Walled Structures in Thermo-Acoustic Environment

2011 ◽  
Vol 105-107 ◽  
pp. 220-226 ◽  
Author(s):  
Yun Dong Sha ◽  
Zhi Jun Gao ◽  
Fei Xu
Keyword(s):  
High Speed ◽  
Nonlinear Response ◽  
Large Deflection ◽  
Thermal Protection ◽  
Thermal Loads ◽  
Acoustic Response ◽  
Restoring Force ◽  
Acoustic Environment ◽  
Thin Walled Structures ◽  
Thin Walled

Thin-walled structures of future hypersonic flight vehicles will encounter complex loadings and exhibit obvious nonlinear responses. The thermal loads from high speed flow or engine jet flow can cause thermal buckling of thin-walled structures, such as Thermal Protection System (TPS). If the structures are loaded with intense acoustic loads simultaneously, large deflection nonlinear response, including snap-through, can be induced. Snap-through will give rise to large amplitude stress cycles and non-zero mean stress, which can lessen the fatigue life markedly. Starting from Hooker’s Law with thermal components, the large deflection governing equations of motion for simply-supported plate under thermo-acoustic loadings are derived. The partial differential equation (PDE) of motion which is difficult to solve is then transformed with Galerkin’s method to the system of ordinary differential equations (ODE) under modal coordinates. The displacement responses under different combinations of temperature increments and sound pressure levels are calculated by employing Runge-Kutta method. Typical thermo-acoustic responses are predicted: 1) random vibration around pre-buckled equilibrium position, 2) persistent snap-through between post-buckled positions, 3) intermittent snap-through, 4) vibration around one of the two post-buckled positions. By dividing the restoring force term in the equation into linear term and nonlinear one, the evolutions of each term are obtained to illustrate the mechanism of thermo-acoustic response and the contributions of each force, including shear force, thermal force and membrane force. Thus a further insight into thermo-acoustic response has been achieved.

Nonlinear Response of Carbon-Carbon Composite Panels Subjected to Thermal-Acoustic Loadings

2011 ◽  
Vol 117-119 ◽  
pp. 876-881 ◽  
Author(s):  
Yun Dong Sha ◽  
Fei Xu ◽  
Zhi Jun Gao
Keyword(s):  
High Speed ◽  
Random Vibration ◽  
Nonlinear Response ◽  
Elevated Temperatures ◽  
Thermal Protection ◽  
Random Noise ◽  
Carbon Composite ◽  
Dynamic Responses ◽  
Composite Panels ◽  
Thin Walled

Carbon-Carbon composite materials are widely used as the surface thermal protection systems (TPS) of advanced high-speed air-craft and spacecraft. The thin-walled structures with this kind of materials would exhibit large displacement response under high-level acoustic loads and possibly display buckling at elevated temperatures. Reliable experimental data are difficult to acquire because of the high costs and difficulties with instrumentation at high acoustic intensity and elevated temperatures. Thus, in the design process greater emphasis will likely be placed on improved mathematical and computational prediction methods. Among these researches, the simulation methods for nonlinear response of thin-walled composite panels under thermo-acoustic loadings are being developed emphatically .This paper presents a nonlinear finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels under the combined effects of thermal and random acoustic loads. The acoustic excitation is assumed to be a band-limited Gaussian random noise and uniformly distributed over the structural surface and the thermal load is assumed to be a steady-state with different predefined temperature distribution. Three types of motion: 1) linear random vibration about one of the two buckled positions, 2) snap-through motion between the two buckled positions, and 3) nonlinear random vibration over the two thermally buckled positions can be predicted. And the dynamic response behaviors of the structures are discussed. Based on this, the influences of sound pressure level (SPL) and elevated temperatures on the dynamic responses are analyzed emphatically.

Nonlinear Response and Fatigue Life Prediction of Thin-Walled Structures under Thermo-Acoustic Loadings

2012 ◽  
Vol 157-158 ◽  
pp. 1204-1211 ◽  
Author(s):  
Yun Dong Sha ◽  
Jing Wei ◽  
Zhi Jun Gao
Keyword(s):  
Fatigue Life ◽  
Nonlinear Response ◽  
Damage Model ◽  
Complex Stress ◽  
Acoustic Response ◽  
Thin Walled Structures ◽  
Flow Cycle ◽  
Nonzero Mean ◽  
Thin Walled ◽  
Stress Models

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.

scholarly journals Large deflection and post-buckling of thin-walled structures by finite elements with node-dependent kinematics

2020 ◽  
Author(s):  
E. Carrera ◽  
◽  
A. Pagani ◽  
R. Augello
Keyword(s):  
Finite Elements ◽  
Large Deflection ◽  
Nonlinear Problems ◽  
Structural Domain ◽  
Fe Model ◽  
Efficient Manner ◽  
Cross Sectional ◽  
Thin Walled Structures ◽  
Post Buckling ◽  
Thin Walled

AbstractIn the framework of finite elements (FEs) applications, this paper proposes the use of the node-dependent kinematics (NDK) concept to the large deflection and post-buckling analysis of thin-walled metallic one-dimensional (1D) structures. Thin-walled structures could easily exhibit local phenomena which would require refinement of the kinematics in parts of them. This fact is particularly true whenever these thin structures undergo large deflection and post-buckling. FEs with kinematics uniform in each node could prove inappropriate or computationally expensive to solve these locally dependent deformations. The concept of NDK allows kinematics to be independent in each element node; therefore, the theory of structures changes continuously over the structural domain. NDK has been successfully applied to solve linear problems by the authors in previous works. It is herein extended to analyze in a computationally efficient manner nonlinear problems of beam-like structures. The unified 1D FE model in the framework of the Carrera Unified Formulation (CUF) is referred to. CUF allows introducing, at the node level, any theory/kinematics for the evaluation of the cross-sectional deformations of the thin-walled beam. A total Lagrangian formulation along with full Green–Lagrange strains and 2nd Piola Kirchhoff stresses are used. The resulting geometrical nonlinear equations are solved with the Newton–Raphson linearization and the arc-length type constraint. Thin-walled metallic structures are analyzed, with symmetric and asymmetric C-sections, subjected to transverse and compression loadings. Results show how FE models with NDK behave as well as their convenience with respect to the classical FE analysis with the same kinematics for the whole nodes. In particular, zones which undergo remarkable deformations demand high-order theories of structures, whereas a lower-order theory can be employed if no local phenomena occur: this is easily accomplished by NDK analysis. Remarkable advantages are shown in the analysis of thin-walled structures with transverse stiffeners.

Investigation of the Impact Analysis of Microscale Thin-Walled Structures Manufactured by High-Speed Machining

2006 ◽  
Vol 326-328 ◽  
pp. 1599-1602
Author(s):  
Bo Sung Shin
Keyword(s):  
Finite Element ◽  
Cutting Force ◽  
High Speed ◽  
Impact Analysis ◽  
Thin Wall ◽  
High Speed Machining ◽  
High Speed Cutting ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
The Impact

High-speed machining (HSM) is very useful method as one of the most effective manufacturing processes because it has excellent quality and dimensional accuracy for precision machining. Recently micromachining technologies of various functional materials with very thin walls are needed in the field of electronics, mobile telecommunication and semiconductors. However, HSM is not suitable for microscale thin-walled structures because of the lack of their structure stiffness to resist high-speed cutting force. A microscale thin wall machined by HSM shows the characteristics of the impact behavior because the high-speed cutting force works very shortly on the machined surface. We propose impact analysis model in order to predict the limit thickness of a very thin-wall and investigate its limit thickness of thin-wall manufactured by HSM using finite element method. Also, in order to verify the usefulness of this method, we will compare finite element analyses with experimental results and demonstrate some applications.

scholarly journals Nonlinear Response of Graphite-Epoxy Composite Thin-Walled Structure under Elevated Thermal Environment

2011 ◽  
Vol 2-3 ◽  
pp. 865-869
Author(s):  
Yun Dong Sha ◽  
Fei Xu ◽  
Zhi Jun Gao
Keyword(s):  
Critical Temperature ◽  
Boundary Conditions ◽  
Nonlinear Response ◽  
Thermal Environment ◽  
Epoxy Composite ◽  
Complex Loading ◽  
Thin Walled Structures ◽  
Buckling Behavior ◽  
Post Buckling ◽  
Thin Walled

Composite materials thin-walled structures are widely used as skin panel in flight vehicles in recent years. These structures will encounter severe complex loading conditions, which may be a combination of mechanical, aerodynamic, thermal and acoustic loads. Thin-walled structures subjected to this kind of loadings will exhibit nonlinear response; as a result, fatigue failure will occur. High temperature may cause large thermal deflection and stress, for some special conditions, may cause thermal buckling. Once the thermal buckling appears, the stiffness will change correspondingly, it will cause significant influence on the dynamic response and fatigue failure. Accordingly, it is important to research the nonlinear response of this kind of structures under elevated thermal environment. Nonlinear response and thermal pre-buckling/post-buckling behavior of a Graphite-Epoxy composite plate subjected to server thermal loading is numerically investigated in this paper. A composite laminated plate with clamped-clamped boundary conditions is chosen as simulated body, nonlinear finite element model is developed using the first-order shear deformable plate theory, Von Karman strain-displacement relations, and the principle of virtual work. The thermal load is assumed to be a steady-state with different predefined temperature distribution. The thermal strain is stated as an integral quantity of the thermal expansion coefficient with respect to temperature. Then the modes of the plate are analyzed, the nature frequencies and modal shapes are obtained. The critical temperature of buckling is calculated. The static nonlinear equations of motions are solved by the Newton-Raphson iteration technique to obtain the thermal post-buckling deflection. The Riks method is used to analyze static post-buckling behavior. In the numerical examples, four types of situations are studied, which include i) the buckling behaviors for different initial imperfections, ii) the buckling behaviors for different thickness to width ratios, and iii) The buckling behaviors for different width to length ratios; The critical temperature, the static thermal post-buckling deflection and the load to displacement relation are presented respectively. The influences of different boundary conditions on the buckling behaviors of the plate are achieved as well. The simulation method and results presented in this paper can be valuable references for further analysis of the nonlinear responses of thin-walled structures under complex loading conditions.

A basic design for automotive crash boxes using an efficient corrugated conical tube

2021 ◽  
pp. 095440702199092
Author(s):  
Alireza Mortazavi Moghaddam ◽  
Atefeh Kheradpisheh ◽  
Masoud Asgari
Keyword(s):  
High Speed ◽  
General Procedure ◽  
Reaction Force ◽  
Passenger Cars ◽  
Detail Design ◽  
Thin Walled Structures ◽  
Wide Range ◽  
Vehicle Structure ◽  
Thin Walled ◽  
Guide Lines

Frontal vehicle structure is of high importance through crash energy managements and crash boxes are the fundamental structural component for vehicle safety as well as after sales issues. Similar to many other vehicle components, the detail design of crash box is usually part of manufacture knowhow. However, some guide lines are always available. In this article a general procedure is introduced for designing of crash box with the aid of novel thin walled structures and according to conventional crash scenarios. The problem is followed through some basic steps. Firstly, the crash box idea is selected through a wide range of previous investigated elements and is packaged in a real bench vehicle. Then thanks to the protection provided by the new crash box on the other more expensive components (e.g. headlamp, cooling pack, etc.), the effectiveness of this element are acknowledged through the low speed offset crash. Further on the robustness of new proposed crash box is approved by high speed crash simulations. The quasi-static simulations implemented during the analyses are carried out by finite element explicit code (Abaqus) and the FE modeling and dynamic simulation through the next steps are also performed in ANSA and PAM CRASH respectively. Finally in addition to the general crash box design proposed procedure, the achieved results demonstrated that the corrugated conical thin walled tubes deforms in regular and rather stable shape under both axial and oblique loadings. They also produced a reasonable reaction force versus deformations which leads to stiff and crashworthy energy absorber in comparison to traditional rectangular and even some special models like as origami shapes, and so they could be a valuable selection for crash box implementations in passenger cars.

Nonlinear Response of C/C Composite Laminated Panels with Temperature Gradients under Guassian Pressure Waves

2013 ◽  
Vol 470 ◽  
pp. 1062-1068 ◽  
Author(s):  
Yun Dong Sha ◽  
Xiao Bo Jie ◽  
Lin Zhu
Keyword(s):  
Thermal Protection ◽  
Element Model ◽  
Carbon Composite ◽  
Temperature Gradients ◽  
System Response ◽  
Equivalent Linearization ◽  
Total System ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
High Level

Carbon-Carbon composite material is widely used as the thermal protection systems (TPS) of hypersonic vehicles for its special mechanical and heat-proof capabilities. The thin-walled structures with this kind of materials would exhibit large displacement response under high-level acoustic loads. Usually, the external heating is non-uniform. In the paper, a finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels with temperature gradients under Guassian sound excitation is founded. The total system response is decomposed into the time-independent component and the time-dependent component, using the equivalent linearization technique. Numerical results include root mean square (RMS) values of maximum deflections, time histories and power spectrum densities (PSD) of the deflection response. The results obtained in this paper can contribute to the thorough understanding of thermo-acoustic response of composite thin-walled structures.

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