Nonlinear finite element analysis of mechanical characteristics on CFRP composite pressure vessels

Transcription

1 IOP Conference Series: Materials Science and Engineering Nonlinear finite element analysis of mechanical characteristics on CFRP composite vessels To cite this article: Dong-xia Liu et al 2010 IOP Conf. Ser.: Mater. Sci. Eng Related content - Finite element analysis of filament-wound composite vessel under internal S Sulaiman, S Borazjani and S H Tang - Bird impact at aircraft structure Damage analysis using Coupled Euler Lagrangian Approach I Smojver and D Ivancevic - Nonlinear finite element analyses of tee joints of laminated composites S K Panigrahi and Y X Zhang View the article online for updates and enhancements. This content was downloaded from IP address on 03/05/2018 at 17:45

2 Nonlinear Finite Element Analysis of Mechanical Characteristics on CFRP Composite Pressure Vessels Dong-xia Liu 1,2, Li Liang 1, Ming Li 1 1 College of Resources and Civil Engineering, North-eastern University, Shenyang, Liaoning, , P. R. China 2 College of Economics, Liaoning University, Shenyang, Liaoning, , P. R. China Longlive2001@163.com Key words: FEM; CFRP; Pressure vessel Abstract. CFRP(Carbon Fibre Reinforced Plastic) composite vessel was calculated using finite element program of ANSYS for their mechanical characteristics in this paper. The elastic-plastic model and elements of Solid95 were selected for aluminium alloys of gas cylinder. Also liner-elastic model and layer elements of Shell99 were adopted for carbon fibre/epoxy resin. The stress state of CFRP composite vessel was calculated under different internal s include pre-stressing s, working s, test hydraulic s, minimum destructive s etcetera to determine the size of gas cylinder and layer parameter of carbon fibre. The mechanical characteristics CFRP composite vessel could were using to design and test of gas cylinder. Numerical results showed that finite element model and calculating method were efficient for study of CFRP gas cylinder and useful for engineering design. 1. Introduction Composite vessels are being widely used in commercial, civil, aeronautics and astronautics industries, for example in rocket motor cases, fuel tanks, portable oxygen storage bottles, and so on. With the development of material manufacturing technology, they offer a high stiffness and strength combined with a low weight and an excellent corrosion resistance. Composite vessels are commonly constructed with a filament overwrap of fibreglass, carbon fibre, or Kevlar in customized resin systems. Various properties can be achieved through an appropriate selection of fibre type, fibre orientation, inner pot, and resin matrix of the composite structure required for the applications in question. The strong and stiff fibres carry the load imposed on the composite, while the resin matrix distributes the load across the fibres, the inner pot keep the vessel airtight and partake some loads [1]. Typical CFRP vessels are generally designed with a central cylindrical section and two spherical end caps with optional polar openings. In this paper the CFRP vessel with cylindrical shape was analyzed. CFRP composite vessels are a kind of complex composite structure, large deformation and complex nonlinear mechanical characteristics will be generated under inner. In this paper three dimensional finite element methods achieved better results. c 2010 Published under licence by Ltd 1

3 2. Elastic-plastic modelling of CFRP composite vessels 2.1. Engineering background In the vessel aluminum alloy inner pot exhibit considerable plastic behavior, the elastic-plastic model was adopted for inner pot. The fibre works under elastic limits, the anisotropic elastic model was adopted for fibre. The material parameters of inner pot and carbon fibre/epoxy resin are shown in Table 1. Table 1. The material parameters of inner pot and fibre Material name Elastic modulus(gpa) Poisson ratio yield limit(mpa) strength limit(mpa) elongation percentage Aluminum % alloy Carbon fibre % For the aluminium alloy inner pot the experimental parameters were adopted, the constitutive relationship is shown in Figure 1. The material parameters of carbon fibre/epoxy resin were shown in table 2. Table 2. The material parameters of carbon fibre/epoxy resin V E x (MPa) E y (MPa) E z (MPa) xy V yz V xz G xy G yz G xz (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) In this paper different thickness of inner pot and fibre layers were taken into account. Due to the wrapping technologies, the wrapping order and angle of fibre in cylinder part were fixed. In the dome the geodesic wrapping method was adopted, the wrapping angle was calculated according to the shape of inner pot. The wrapping order and parameters of fibre was shown in table 3. In order to find the optimized design four models were built and calculated. The detailed data is shown in Table 4. Table 3. The wrapping order and parameters of fibre Wrapping order Wrapping method Number of layer Wrapping angel(deg) 1 All wrapping 2 ± Cylinder wrapping 2 or 3 ± All wrapping 2 ± Cylinder wrapping 2 or 3 ± Thickness of per layer Table 4. The component parameters of the four models Model Thickness of inner pot Number of layer As the structure and loads were symmetric, theoretically one quarter model was feasible. In order to make verification the whole model and one quarter model were calculated in one mode, the results were very similar. So in order to save computing time one quarter model was built and calculated. Figure 2 illustrates the inner pot of CFRP composite vessel Finite element model building The finite element model was built by APDL language. The section of inner pot was built at first, and then the section was rotated 90 degrees. The elements of fibre/epoxy resin were built at the outer surface of aluminium inner pot. The angel of per element was modified according to winding angels by APDL. For fibre/epoxy resin only one layer of elements was built. But different fibre orientation of 2

4 per layer was included in the one layered elements. As shown in the figure 3. For the aluminum alloy inner pot the solid95 element was adopted, it can reflect aluminum s elastic-plastic property, for the CFRP the layered shell99 element was adopted. The shell99 element can contain maximum 125 layers with different orientation and thickness. For hoop fibre the elements in the edge were given different thickness, as shown in figure 4. The stress of per layer can be calculated and be extracted [2]. The finite element model and meshing are shown in Figure 4. Figure 1. The constitutive relationship of Al alloy Figure 3. The information of per layer of fibre 3. Mechanical characteristics analysis Figure 2. The inner pot of CFRP composite vessel 3.1. Engineering background The CFRP vessel must pass a series of test, which includes 5 modes. The first mode is selftight process. During this process the inner pot obtained plastic deformation, in the following 0 process the inner pot and the fibre gained residual stress of self-tight, they work synergistically. Under working the stress was under the level of pre-, and it was the main state of the vessel in use. Higher safety could be obtained using the testing hydraulic. The minimum destructive was 3.4 times of working. The detailed dada of modes was given in Table 5 [3]. The finite element model was calculated according to the five modes. The loads in every mode were applied by load step. The main results of every model were shown in Table 6. 3

5 Inner pot Carbon fibre Finite element model Meshing Pre-stressing Figure 4. The finite element model and meshing Table 5. The mode information of CFRP vessel Testing hydraulic 0 Working Specified minimum destructive MPa Unit model Modes (MPa) S eqv of inner pot (MPa) Table 6. The results of FEM analysis Ratio of S eqv and Ratio of S yield limit eqv S 1 of and yield limit fibre under under 0 (MPa) working S 2 of fibre (MPa) 0~ ~ ~ (<60%) (>60%,<95%) 20~ ~ ~ ~ ~ (<60%) (>60%,<95%) 20~ ~ ~ ~ ~ (<60%) ( 60%, 95%) 20~ ~ ~ ~ ~ (<60%) ( 60%, 95%) 20~ ~ Ratio of S 1 under working and minimum destructive

6 The FRP and aluminum alloy composite vessel is designed according to CFFC-7 criterion, whose main content is as follows [4]: ⑴ The maximum tensile stress of aluminum inner pot under working cannot exceed the yield limit of aluminum alloy. The compressive stress of cylinder part under 0 s cannot less than 60%, and cannot exceed 95% of yield limit of aluminum alloy. ⑵ The load bearing ability of the glass fibre for protecting vessel from erosion cannot exceed 15% of total load under minimum destructive. ⑶ The maximum stress of carbon fibre under working cannot exceed 30% of the fibre stress under specified minimum destructive. ⑷ Burst fracture must begin from the cylinder part of the vessel. Comparing the finite element results and the criterion, the first model (1.5 thickness and 8 layers) and the second model (1.65 thickness and 8 layers) are feasible. The cloud map of stress in the first model was shown in Figure 4. Meanwhile the S eqv of inner pot under 0 in the third model (2.5 thickness and 8 layers) and fourth model (2.5 thickness and 10 layers) is less than the specified value. So a conclusion could be made that as to CFRP composite vessel the security didn t decide by the large amount used of a certain material. High security could only be achieved by appropriate amount of materials and distribution. In order to solve the problem the pre-stressing should be increased [5]. Though the CFRP vessel bearing inner, the inner pot under 0 could be considered as external vessel after self-tight process. So buckling became a problem under 0. In the criterion the limitation of stress under 0 could avoid this problem [6]. S eqv of inner pot under 0 S eqv of inner pot under working S 1 of fibre under working S 1 of fibre under min destructive Figure 4. The finite element results of the first model 3.2. failure criterion and strength checking The forth strength theory was adopted for inner pot, the Tsai-Wu quadratic criterion was adopted for CFRP. For inner pot the S eqv could be get from postprocessor. The failure pattern of CFRP was that a single layer came to failure at first, and then the stress of the failed layer passed to other layers, till the 5

7 last layer came to failure. As to the first failure layer the Tsai-Wu quadratic criterion was selected. According to the results under given loads the material of the vessel didn t come to failure [7]. 4. Conclusions (1)Compared with measured value, a conclusion can be made that using finite element programme ANSYS for designing CFRP composite vessels was feasible. The glass fibre outside the carbon fibre was ignored; this would increase the safety of the structure. The one quarter model for the analysis could achieve better accuracy. Thus the simplified method was feasible. The analysis process in this paper can be used in designing and testing of composite vessels. (2)Among the four CFRP composite model the first and second model satisfied CFFC-7 criterion, they were feasible design. In the third and forth model the inner pot was thicker, but the criterion wasn t be satisfied. So distribution and combination of material needed discretion in the CFRP vessel designing. It was not the more, the safer. (3)For composite vessels the CFFC-7 criterion is more safety than Tsai-Wu quadratic failure criterion and the forth strength theory. In the CFFC-7 criterion the problems of fatigue and buckling have been considered. References [1] T-L Teng, C-M Yu, and Y-Y Wu, Optimal Design of Filament-Wound Composite Pressure Vessels. Mechanics of Composite Materials, Vol. 41, No. 4, 2005, (8) [2] YAN Fei, DAI De-hai, ZHU Zhi-chun, Finite Element Analysis Technology of Filament Wound Pressure Vessel Structures. No.6, 1992, 33-36(4) [3] CHEN Ru-xun, Structure analysis for filament-wound cylinder vessel. Journal of Solid Rocket Technology. Vol.27 No.2, 2004, (3) [4] WEI Xi-long, SUN Yin-bao, LI Yao, CHEN Yue-dong, ZHANG Xiao-bing, Geometrical Nonlinear Analysis of Filament-Winding Vessel. Fibre Composites. (2007)1: 24-26(3) [5] Pieter Samyn, Ludo Van Schepdael, Wim Van Paepegem, J.S. Leendertz, Eric Suister, Patrick De Baets, Joris Degrieck, Fracture Assessment of Carbon Fibre/Epoxy Reinforcing Rings through a Combination of Full-Scale Testing, Small-Scale Testing and Stress Modeling. Appl Compos Mater (2006)13: 57 85(29) [6] BERNARD SCHRAUWEN, TON PEIJS, Influence of Matrix Ductility and Fibre Architecture on the Repeated Impact Response of Glass-Fibre-Reinforced Laminated Composites. Applied Composite Materials (2002)9: (22) [7] Prasad R.C, Ramakrishnam P. (2000), "Composites Science and Technology. New Delhi, New Age International (P) Ltd. 6