Pressure hull development using hybrid composite with metal liner concept

Transcription

1 Indian Journal of Geo-Marine Sciences Vol. 40(2), April 2011, pp Pressure hull development using hybrid composite with metal liner concept Khairul Izman Abdul Rahim 1, A R Othman 2 * & Mohd Rizal Arshad 1 1 USM Robotics Research Group, School of Electrical and Electronic Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia 2 School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia Received 23 March 2011; revised 28 April 2011 Conceptual design of hybrid composite with metal liner for underwater application is presented in this study. Main objective of this concept is to reduce the total weight of underwater vehicle, while improving its strength characteristic. In this design, polymer composite is used as load bearing structure and metal liner has been introduced to prevent leakage from occurring within the system and also acts as a heat emission component. The main application of this concept is a compartment of pressure hull for electronic component and power system, as well as heat emission agent. This paper comprehensively discussed the design parameters, material properties, pressure hull design and fabrication of the design concept. It was suggested that E-glass/DER331 system and stainless steel were the preferable materials. It is also proposed that the system should be able to operate up to 200m depth. [Keyword: Hybrid composites, metal liner, pressure hull] Introduction The concept of hybrid polymer composite-metal construction in pressurized application of cylindrical structure are widely used in various applications such as hybrid composite domestic gas cylinder 1, CNG composite vessel 2, cryogenic pressure vessel 3-4, aircraft fuselage 5-6, and compressed hydrogen storage 7-8. However, for underwater application, common materials that can withstand high external pressure are metallic alloys. The use of polymer composite or hybrid polymer-metal is still new in this field. Specific studies are required, especially with regards to the heat emission characteristic, structure behaviour and interfacial bonding interaction between polymer and metal materials. There are possibilities to implement thermoplastic composite cylinder for underwater application of oceanography, submarine, glider, AUV, ROV and sub-sea offshore structure. A number of studies have been performed by several researchers 9-12 as they examined the suitability of potential materials for underwater application. For instance, finite element *Corresponding author Tel.: ; Fax: merahim@eng.usm.my (A.R. Othman) model for analysis of the static and dynamic response and behaviour of this structure has been carried out by Tarfaoui et al 13. For ROV and AUV system, the most important structure is a pressure hull. It acts as housing for the electronic equipments and power units. Furthermore, it provides protection for equipments and the enclosure from high external pressure and preventing water from penetrating into the hull. For polymer composite material, the most common types that have been extensively studied were carbon and glass-fibre reinforced plastics (CFRPs and GFRPs). The development of CFRPs composite pressure hull for UAV Seaglider has been presented with regards to the material characteristic, design of lamination and test results 14. E-glass composite has also been studied in the design aspect, analysis, and tested for underwater application by Yousefpour 15. In this concept, the polymer composite system also serves as a component that can withstand the hydrostatic pressure whilst metal system is used to prevent leakage and to improve the heat emission process. This concept has been implemented to gain advantages from the material selection process, in which the composite system should be able to produce a lighter pressure hull that could maintain its

2 208 INDIAN J. MAR. SCI., VOL. 40, NO. 2, APRIL 2011 performance which leads to the total weight reduction of underwater vehicle. In other words, more space for other components can be included with less buoyancy material is needed to maintain buoyancy force of the structure. Due to the simplicity in fabrication technology of the system, time and cost of fabrication are significantly reduced in comparison to conventional methods. Several prime steps are discussed which include the design parameters, material selection and pressure vessel topology design. Other than that, details of the fabrication process have also been discussed in this paper. Materials and Methods Design Parameters The aim of this study is to develop a structural design that can be submersed down to 200 m depth. Figure 1 highlights the methodological framework that has been implemented in this study. For the development, several requirements need to be fulfilled, such as the material capability to withstand high hydrostatic pressure, good heat conduction, high strength-to-weight ratio, as well as the ability to protect interior electronic components from direct contact with water. Note that, the load from external pressure is very much different as compared to the load from internal pressure. The analysis involving loading of external pressure required biaxial loading consideration which known as hoop and axial stress, compare to those of internal pressure which only considered the hoop stress. Another aspect that should be taken into account is to prevent water penetration into the hull due to poor material characteristic or manufacturing deficiency. It was found that the pressure acting on the immersed structure depends on the depth which can be expressed as 9 : Fig. 1 Methodology framework

3 RAHIM et al.: PRESSURE HULL DEVELOPMENT USING HYBRID COMPOSITE WITH METAL LINER CONCEPT 209 P = C 1.H+C 2.H 2 (1) where P is the acting pressure (MPa); H is the immerse depth(m); C 1 is equal to 0.01(MPa/m) and C 2 is equal to (MPa/m 2 ). This indicated that the development of pressure hull should satisfy a certain design pressure that corresponding to the operation depth. Based on the above equation, for 200 m depth, a structure needs to withstand a hydrostatic pressure up to 2MPa. Nonetheless, as an engineering precaution measure, the safety factor has been established as 2, in which the structure was designed to withstand external pressure up to 4MPa. In designing an enclosure, among the first parameters that should be considered is the selection of the shape of enclosure. It was anticipated that the curvature shape is an effective design of an enclosure which could withstand high external pressure. These signify that the common selected shape design of pressure hull consists of shapes such as spheres, cones, cylinders, ellipsoids, and combination of these shapes; all of the shapes employ a round and curvature section. Even though sphere is the ideal shape in the design of pressure hull, the most common practice is to employ the cylindrical ones 16. As cylindrical structure is exposed to a uniform hydrostatic pressure, the structure will experience both axial and hoop stresses. From the author understanding, the force of axial stress is half of the hoop stress that the structure will experience. Due to that, hence the common practice in cylindrical composite fabrication is to apply twice as much fibres in the hoop direction compare to those of the axial direction. In the manufacturing process, one of the main advantages of using composite materials is the ability to tailor the fibres in any orientation that could significantly increase the strength of structure in certain direction with regards to the applied load. Thus, the fibre orientation has been oriented to achieve a quasi-isotropic configuration; the sequence was used in order to achieve a uniform strength distribution on the structure and to accommodate an unexpected loading. Material Properties In order to withstand the hazardous condition of underwater environment, the selected material should possess specific properties with as good resistance to corrosion, better strength-to-weight ratio, low weight capability, ability to withstand high external pressure, material availability and cost effective. Other than that, the material must have a good heat transfer properties as well as long operating life span. In pressure hull construction, the most common materials that have been typically used are high strength steel, aluminium alloy, titanium alloy, and glass/carbon-fibre composites 16. These materials have several advantages compared to other materials, but in true practice, the material system could also create problems related to galvanic corrosion and thermal stress. In addition, higher weight and thickness of the material to withstand the desired operational environment can lead to problem regarding fabrication complexity, required time and total cost of the project. This also includes the problem to attain the required shape and thickness. Study has been focussed on hybridizing the metallic and polymer composite materials to increase the structural performance of cylindrical pressure hull. Composite material has been selected due to several advantages that the material could offer compare to others, i.e. high strength-to-weight ratio, ease of fabrication, high corrosion resistance, flexibility of the fibres to be tailored in any direction, etc. As the definition of composite material suggests that, two or more materials could be physically combined, the material characteristic may be varied depends on its constituents properties. E-glass was employed as the reinforcing element whilst Epoxy DER331 as the matrix. On the other hand, stainless steel 304 has been used as a metal liner. Tables 1 and 2 shows the material properties of the materials 11. Composite material can easily fulfil the requirement that has been mentioned previously. An extra advantage of the composites in dealing with underwater environment is the polymer composites can be easily fabricated in any shape and dimension; i.e. any hydrodynamic form can be fabricated using composite material. The most common practice in fabricating composite pressure hull is using a filament winding technique. Table 1 The typical material properties for stainless steel 304 E(GPa) ν 12 α (10-6 /ºC) 139GPa

4 210 INDIAN J. MAR. SCI., VOL. 40, NO. 2, APRIL 2011 Polymer composite offers a good resistance to creep and fatigue. This benefit is important for underwater application in order to avoid strength lost after continuous hydrostatic loading. Note that, the initiation and propagation of failures sequence in composite cylinder is usually taking place as elastic micro buckling, follow by fibre crushing, matrix failure and then inelastic buckling. These sequences occurred as a result of the external pressure is applied to cylindrical composite structure. On the other hand, stainless steel also fulfils the prerequisite requirements for an underwater application. In comparison to titanium alloy, stainless steel is more cost effective and provides more simplicity in fabrication process. In addition, the material offers more resistance property to creep compare to aluminium, although it is a lot heavier. Usually, this problem is related to the bending process; the fact that make stainless steel is more suitable for rolling application, a common technique in making cylindrical types structure. Besides, stainless steel can easily be welded; this is important to ensure heat sink can be installed at any critical sections in pressure hull, in which at that sections, the electronic equipments within the enclosure can produce extra heat compare to other parts. Stainless steel also possesses higher thermal coefficient value compare to polymer composite, which helps increasing heat emission of the structure. Nonetheless, one disadvantage of using polymer composite in underwater environment is due to its porosity characteristic. It has tendency to allow water to penetrate into the structure. By introducing the stainless steel to the design as a metal liner, this problem could be well avoided. Pressure Hull Design The general design structure of hybrid compositemetal construction was a circular section of cylinder with inner diameter of 100 mm and 300 mm in length. The performance of cylindrical pressure hull structure could be improved by introducing wall architecture into the design. Three types of wall architecture have been introduced; including pure monocoque for metal liner design, filament winding mosaic pattern design in winding the E-glass and sandwich wall construction to represent the whole concept A finite element analysis has been carried out to study the behaviour of the structure as well as to estimate the required thickness, in which ANSYS has been utilized. Two types of solid element were required to represent both materials, where Solid Tet10 node 187 was used to represent the stainless steel, whilst the composite material was represented by Solid Brick20 node 95. Figure 2 shows the finite element model of the structure. At the outer layers, GFRPs was assumed to be orthotropic and elastic. In contrast, for the inner metal liner, the material was defined as an isotropic, elastic perfectly plastic material. The detailed material properties are shown in Table 3. During the analysis, the structure were clamped at both end caps with uniform pressure has been applied on external surfaces of the structure to simulate the effect of hydrostatic pressure. In the final design, the required thickness of pressure hull was 5 mm for the composite material. Through analytical formulation of the required thickness, the composite layers should be increased to achieve the quasi-isotropic configuration. Fig. 2 Model of cylindrical hybrid composite-metal liner Table 2 Elastic Properties of the E-glass (Roving and Fabric types)/der331 systems Properties E 11 (GPa) E 22 (GPa) G 12 (GPa) ν 12 ν 13 ν 23 σ 11c (MPa) σ 22c(MPa) τ 12# (MPa) σ 11c =longitudinal compressive strength and σ 22c=transverse compressive strength, τ 12# =in-plane shear strength

5 RAHIM et al.: PRESSURE HULL DEVELOPMENT USING HYBRID COMPOSITE WITH METAL LINER CONCEPT 211 Table 3 Results of stress and displacement analysis of the pressure hull from ANSYS software analysis Wall thickness (mm) Metal liner = 1.5 mm Composite layers = 5mm Pressure (MPa) Displaceme nt (mm) (Static case) Stress (Nm -2 ) E Results and Discussion As both end of cylinders were clamped and set to be zero to fulfil the boundary condition in finite element modelling, the effect of both ends were assumed to be at the minimum or discarded and thus, only result at the mid-length were considered. The analysis of the end effect has been neglected due to the consideration that the shape of the enclosure end caps will determine the output of the analysis, especially on the result of structural behaviours. Figures 3 and 4 shows the sum of displacement vector and von Mises stress distribution as computed by the numerical methods, respectively. A typical buckling mode shape of the pressure vessel is shown in Figure 5. Value of von Mises stress was employed to predict the yielding of the material, and based on the analysis, this value was found lower than the yield strength of the selected materials. While, the sum displacement vector indicated the maximum bending displacement subjected to the applied operational pressure. All values from the numerical analysis were well within the allowable values, signified that the elastic buckling was indeed the deformation mode as this type of structural deformation was the most common structural characteristics for underwater application. The analysis of both displacement vector sum and von Mises stress exhibited the weak region along the mid length. In addition, the stress analysis also indicated that the metallic structure has experienced higher stresses concentration than the composite counterparts. As a precautionary measure, the thickness of the mid-length section should be increased or reinforced. Other than increasing the thickness of the metal component, the structural efficiency can also be improved by introducing different wall architecture into the structure, such as employing stiffening ring or corrugated wall 16 in the structure. Fig. 3 Displacement vector sum Fig. 4 von Mises stress Fig. 5 Typical buckling mode shape of pressure hull

6 212 INDIAN J. MAR. SCI., VOL. 40, NO. 2, APRIL 2011 Fig. 6 Illustration of hybrid polymer composite-metal cylindrical structure Prototype Fabrication The motivation behind the prototype fabrication was to examine whether the conceptual design could be utilized and used as a prototype for the future test. Due to the small required diameter of the specimen, stainless steel was prepared in a circular cylindrical tube. The thickness of stainless steel has been determined as 1.5 mm. The most common technique in fabrication of cylindrical composite structure is using filament winding method. In this technique, glass fibre has been wound on the cylindrical stainless steel (i.e. component that acts as metal liner). The method offers an efficient way to fabricate composite material structure especially for cylindrical shape types. This is corresponded to the flexibility in the orientating the continuous fibre precisely in control condition. In this process, fibres were continuously wound on the rotating mandrel in a desired pattern until the mandrel was completely covered to the required thickness before curing at room temperature to solidify the resin. Concurrently, as the filament winding technique was employed, vacuum bagging process has been conclusively implemented three times and the E-glass fabrics were also introduced to the system to increase the performance of the product 14. Selected winding angle was crucial in order to achieve quasi-isotropic configuration. Due to that reason, the orientation of the E-glass material should be considered carefully. The sequence of fibre Layer Table 4 Fabrication configuration Winding angle Material Apply Vacuum Bagging 1-45 E-glass roving No E-glass roving No 3-45 E-glass roving Yes 4 0/90 E-glass fabric No 5 0/90 E-glass fabric No 6 0/90 E-glass fabric Yes 7-45 E-glass roving No E-glass roving No 9-45 E-glass roving Yes orientation and stacking lay-up can be seen in Table 4. In addition, the illustration of composite structure are shown in Figure 6 while Figure 7, indicating the prototypes of hybrid composite-metal liner cylindrical structure. Conclusion The final shape of the pressure hull was a cylindrical shape with a circular cross-section. Stainless steel and E-glass/epoxy have been chosen as the structural materials in this study. The selection of the materials was based on their characteristic and mechanical performances, environmental operation condition as well as ease in fabrication. Both analytical and FE analysis results indicated that the structure could withstand the desired pressure. Even though the result showed a convincing value, there is still a lot work need to be carried out especially to

7 RAHIM et al.: PRESSURE HULL DEVELOPMENT USING HYBRID COMPOSITE WITH METAL LINER CONCEPT 213 perform an experimental study to attain the comprehensive data and to systematically observe the behaviour of the structures subjected to high external pressure. The experimental results were crucial to verify the analysis, so that further improvement and development on the design could be carried out. In addition, detail in heat emission characteristic within the hybrid composite structure will be considered in the future. This is crucial especially for the specific arrangement of heat sink with the intention that the electronic components inside the enclosure could perform at their optimum condition. Acknowledgement This study was sponsored by the National Oceanography Department, Malaysia, under grants NOD-USM References Fig. 7 Hybrid composite with metal liner 1 Antunes P J, Dias G R, Nunes J P, Van Hattum F W J, Oliveira T. Finite Element Modelling of Thermoplastic Matrix Composite Gas Cylinders, Journal of Thermoplastic Composite Materials, 21(2008) Choi J C, Kim C, Jung S Y. Development of an automated design system of a CNG composite vessel using a steel liner manufactured using the DDI process, International Journal of Advanced Manufacturing Technology, 24 (2004) Kang S G, Kim M G, Kim C G, Lee J R, Kong C W. Thermo elastic analysis of a type 3 cryogenic tank considering curing temperature and autofrettage pressure, Journal of Reinforced Plastics and Composites, 27 (2008) Kim M G, Kang S G, Kim C G, Kong C W. Thermally induced stress analysis of composite/aluminum ring specimens at cryogenic temperature, Composites Science and Technology, 68 (2008) de Vries T J, Vlot A, Hashagen F. Delamination behavior of spliced Fiber Metal Laminates. Part 1. Experimental results, Composite Structures, 46 (1999) Wu G, Yang J. The mechanical behavior of GLARE laminates for aircraft structures. JOM Journal of the Minerals, Metals and Materials Society, 57 (2005) Hocine A, Chapelle D, Boubakar L M, Benamar A, Bezazi A. Analysis of intermetallic swelling on the behavior of a hybrid solution for compressed hydrogen storage - Part I: Analytical modeling, Materials & Design, 31 (2010) Hocine A, Chapelle D, Boubakar M L, Benamar A, Bezazi A., Experimental and analytical investigation of the cylindrical part of a metallic vessel reinforced by filament winding while submitted to internal pressure, International Journal of Pressure Vessels and Piping, 86 (2009) Davies P, Riou L, Mazeas F, Warnier P, Thermoplastic Composite Cylinders for Underwater Applications, Journal of Thermoplastic Composite Materials, 18 (2005) Hernández-Moreno H, Collombet F, Douchin B, Choqueuse D, Davies P., Entire Life Time Monitoring of Filament Wound Composite Cylinders Using Bragg Grating Sensors: III. In-Service External Pressure Loading, Applied Composite Materials, 16 (2009) Ng R K H, Yousefpour A, Uyema M, Nejhad M N G, Design, Analysis, Manufacture, and Test of Shallow Water Pressure Vessels Using E-Glass/Epoxy Woven Composite Material for a Semi-Autonomous Underwater Vehicle, Journal of Composite Materials, 36 (2002) Gning P B, Tarfaoui M, Collombet F, Riou L, Davies P, Damage development in thick composite tubes under impact loading and influence on implosion pressure: Experimental observations, Composites Part B: Engineering, 36 (2005) Tarfaoui M, Gning P B, Hamitouche L, Dynamic response and damage modeling of glass/epoxy tubular structures: Numerical investigation, Composites Part A: Applied Science and Manufacturing, 39 (2008) Osse T J, Lee T J, Composite pressure hulls for autonomous underwater vehicles, paper presented at the Oceans 2007 MTS/IEEE Conference, Vancouver, BC; Yousefpour A, Ghasemi Nejhad M N, Design, Analysis, Manufacture and Test of APC-2/AS4 Thermoplastic Composite Pressure Vessels for Deep Water Marine Applications, Journal of Composite Materials, 38 (2004) Khairul Izman Abdul Rahim, A R O, Mohd Rizal Arshad, Conceptual design of a pressure hull for an underwater pole inspection robot, Indian Journal of Marine Sciences, 38 (2009) Morozov E V, Theoretical and experimental analysis of the deformability of filament wound composite shells under axial compressive loading, Composite Structures, 54 (2001) Xia M, Kemmochi K, Takayanagi H, Analysis of filamentwound fiber-reinforced sandwich pipe under combined internal pressure and thermomechanical loading, Composite Structures, 51 (2001)