Thin–Walled Structures 199 (2024) 111858 Contents lists available at ScienceDirect Thin-Walled Structures journal homepage: www.elsevier.com/locate/tws Full length article A three-dimensional progressive failure analysis of filament-wound composite pressure vessels with void defects Lei Ge a, b, Jikang Zhao a, Hefeng Li a, Jingxuan Dong a, Hongbo Geng c, Lei Zu d, Song Lin e, Xiaolong Jia a, b, *, Xiaoping Yang a, b a State Key Laboratory of Organic-Inorganic Composites, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China Key Laboratory of Carbon Fiber and Functional Polymer, Ministry of Education, Beijing University of Chemical Technology, Beijing, 100029, China Inner Mongolia Aerospace Hong Gang Machinery Corporation Limited, Inner Mongolia, 010076, China d School of Mechanical Engineering, Hefei University of Technology, Hefei, 230000, China e Department of Material Engineering, North China Institute of Aerospace Engineering, Hebei, 065000, China b c A R T I C L E I N F O A B S T R A C T Keywords: Composite pressure vessel Void defects Damage behavior Burst pressure Composite pressure vessels are promising solution for storing compressed gas with the high strength/stiffness to weight ratio, but the accurate modeling of mechanical behavior under high pressure remains a huge challenge considering manufacturing-induced void defects. The void generating method is developed to construct the finite element model with voids explicitly constructed. A three-dimensional(3D) progressive damage model complied with the user-defined material subroutine (UMAT) is performed to predict the void defect introduced damage behavior and burst pressure of composite pressure vessels. It indicates that the predicted burst strength agrees well with experimental value, and with the pressure increasing, the damage of composite layers initially appears in the matrix of middle cylinder section and region near the equator. The matrix damage is dominant at the outset, then achieves a balance with the fiber damage, and finally comes in second until the burst failure of the composite pressure vessels. The void defects will result in the damage initiation, evolution and final failure of composite layers, and the clustered voids will deteriorate the local damage status, but will not change the general damage trend. The present damage failure analysis scheme can provide theoretical guidance for reliability evaluation of composite pressure vessels with void defects. 1. Introduction Hydrogen energy is regarded as the most promising new energy with the advantage of zero release. A high focus has been placed on the hydrogen storage technology with the development of hydrogen energy. Now, the use of filament-wound thin-walled composite pressure vessel to store hydrogen represents the most mature technology, and has been applied in various fields of aerospace, aviation and automotive, etc. [1]. The internal pressure generates high stresses, which lead to the massive use of composite materials and therefore the high cost. The design optimization performed by an appreciate numerical method can improve the structural efficiency of composite pressure vessels and achieve balance of economic efficiency and performance. The composite pressure vessels are intertwined by yarns with different winding angles, and then thickened by the composite lay-up. The manufacturing process results in high heterogeneous characteristics of wound composites, and the reliability evaluation under high pressure remains a huge challenge due to their structural complexity. Furthermore, void defects inevitably produce in the manufacturing process, and highly influence the strength and damage mechanism of composites [2,3], adding another layer of difficulty in accurately capture the mechanical behavior of composite pressure vessels. Current numerical simulations of mechanical behavior are related to different structural and damage models for composite pressure vessels. The composite pressure vessel commonly consists of the cylindrical section and dome zone of which the thickness and winding angle constantly change due to the radius reduction. Consequently, variations of winding angle and material properties pose threats to the finite element modeling of pressure vessels [4,5]. A commercial plugin for ABAQUS, known as Wound Composite Modeler (WCM), is regarded as * Corresponding author at: State Key Laboratory of Organic-Inorganic Composites, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China. E-mail address: jiaxl@mail.buct.edu.cn (X. Jia). https://doi.org/10.1016/j.tws.2024.111858 Received 21 January 2024; Received in revised form 16 March 2024; Accepted 2 April 2024 Available online 3 April 2024 0263-8231/© 2024 Elsevier Ltd. All rights reserved. L. Ge et al. Thin-Walled Structures 199 (2024) 111858 an efficient way to the design and mechanical analyses of composite vessels. Due to the rotating symmetry and thin-walled structural fea­ tures, the axisymmetric [6–10] and shell [11–16] elements are suitable for modeling the composite layers, and the three-dimensional (3D) solid element are commonly selected for the liner of vessels [6,15]. Shell el­ ements show advantages over the computational efficiency whereas solid elements [16–22] are more appropriate for the accurate calcula­ tion and capturing the damage behavior across composite layers in spite of their more complex modeling procedures. The efficiency drawbacks of solid elements can be well relieved by reducing simulation structural models (i.e. 1/4 [6],1/12 [18] and 1/72 [17] of the whole vessel) coupling with periodical boundary conditions or symmetric constraints on the relative deformation of opposite sides. Another focus is the damage model which is equally critical to describe the damage failure mechanism of layers of winding composites. Numerous damage failure models for composites are built to simulate the constituent failures such as the fiber rupture, matrix cracking and in-plane shear damage, including the frequently-used progressive damage model with Hashin criterion [7,8,13], Puck failure criteria with sudden material degrada­ tion model [11], ABAQUS built-in failure model [12,15], Hashin–Rottem failure criterion based on progressive damage model [16], and the linking of principle stress with failure criterion of Maximum stress criterion, Hoffman, Tsai–Hill and Tsai–Wu criteria [18, 19]. Besides, some special damage models are also developed such as a specific continuum damage mechanics modeled by the concept of fixed damage directions [6,20], intra-laminar damage law model [9,10], discrete ply model [14], maximum stress criterion with temperature-dependent material strengths [17], and so on. Based on above finite element models and damage models, the mechanical behavior of filament-wound composite pressure vessels has been fully investigated including the burst pressure [6–8,11,13,15,16,18], optimal design [9,12], thermal effect on burst behavior [10], non-linear buck­ ling analysis [14], safety evaluation due to temperature rise [17], the structural integrity under low-velocity car-to-car collision [19], tensile or compression damage behavior of wound composite laminates [20] and the design optimization by suitable fibers [21]. On the whole, most of above literatures are based on the simplified 2D shell model or axisymmetric model without considering out-plane mechanical prop­ erties of composites, which cannot effectively capture damage charac­ teristics in the lay-up direction and therefore lead to the poor predicting accuracy [22]. Additionally, finite element analysis method can also be achieved by coupling the ANSYS Mechanical with the ANSYS Composite PrepPost (ACP) module to predict mechanical behavior of composite pressure vessels under the internal pressure [23–25]. On the whole, the more accurate 3D solid element model coupled with progressive damage method has been rarely adopted to simulate the damage and failure behavior of wound composite vessels under internal pressure. In the winding process, the fiber bands are wound on the mandrel, and there are still a lot of impregnant residing or process induced unsoaked region. The manufacturing defects will be inevitably gener­ ated during the curing step, which has been attracting special attention due to the detrimental threat to the strength and damage of composites [26]. Some literatures have been conducted to figure out the defect existence [27–29], defect grown [30] and defect effects [31–38] on properties of wound composite vessels. Lin et al. [27] found micro-cracks and defects by SEM images of the dome section under hydraulic and atmospheric fatigue cycling tests of filament wound CFRP vessels. Behera et al. [28] discussed the insight of various defects of filament wound composite pressure vessel arising from the parameter variation during the manufacturing process through the transmission ultrasonic technique. Guillon et al. [29] carried out a global tomography at the end of the tank prototyping, and examined the existence of numerous small size voids near the nozzle of thermoplastic composite overwrap pressure vessel. Wang et al. [30] developed a comprehensive prediction model to figure out the relationships between the final void size and time-dependent manufacturing characteristics in the filament winding process. The effects of void defects on the mechanical behavior of composite pressure vessels can be achieved by the experimental [31–33], analytical [34,35] and the most promising numerical [36–38] methods. Özaslan et al. [31] conducted a comprehensive experimental study to understand how manufacturing defects affect bursting behavior of pressure vessels with various stress ratios. Also, Arikan [32] con­ ducted a static internal pressure test to reveal the failure mechanism with an inclined surface crack in the filament wound pipes. Blanc-Vannet [33] confirmed the reduction of burst pressure due to the impact damage to composite cylinders by impact tests. Farukoglu and Korkut [34] introduced the void-inducted errors by an analytical method to investigate effects of the void-introduced defects on stresses and pressure of tubes. Kang et al. [35] proposed the analytical model of composite riser with void defect based on the Flügge model and Galerkin method, and the strong impact of void defects on the buckling resistance has been fully discussed. Moskvichev et al. [36] assessed the fracture of composite overwrapped pressure vessel with a constructed semi-elliptical crack defect on the internal surface of liner. Ellul and Camilleri [37] investigated the failure progression and response of filament wound pressure vessels, which was highly dependent on the developed two types of manufacturing defects. Wen et al. [38] intro­ duced random wrinkle defects by elements to study the mechanical re­ sponses, and a strong correlation existed between the defects and circumferential displacement distortion of composite overwrapped pressure vessels. To sum up, the existence of manufacturing defects has been studied and verified, but how the defects influence the damage and failure of composite pressure vessels has not been revealed. In this paper, a 3D progressive damage method coupled with the 3D finite element model is adopted to investigate the damage behavior across layers of composite pressure vessels with void defects. A void generation method is developed in order to introduce void defects in the 3D solid model, and therefore reveal the damage evolution and failure mechanism of wound composite pressure vessels considering void de­ fects. The influences of void position are discussed by explicitly con­ structing three different void-models with real void data from experiments. 2. 3D model and material system of composite pressure vessel 2.1. The geometry and finite element model To compare with the experimental data of the literature [7], the finite element model of the composite pressure vessel will be established with the cylinder section and elliptical domes according to following specific geometry sizes, as shown in Fig. 1: the diameter and length of the cylinder section are 380 mm and 540 mm, respectively, and the total length is 800 mm. The liner mainly plays the role of sealing hydrogen gas of wound pressure vessel. The composite layers are the main load-bearing structure, and ensure the service safety of the pressure vessel. The 3D solid model is advantageous over other shell or axisym­ metric models, but will cost more computing time. Due to the circum­ ferential symmetry of pressure vessels, to improve the computing efficiency, the 1/36 periodical symmetric model is adopted and con­ structed layer by layer, as shown in Fig. 1. Based on the geometry characteristics, the solid composite layers are modeled by the WCM plug-in of ABAQUS software 2017. Each layer is automatically generated from the new constructed surface with the layer winding angle and layer thickness. The winding angle along the cylin­ drical section remains constant, but the helical winding angle over the dome is described using the following Eq. (1) [39]. With regards to the dome structure, the winding angle of fiber band varies in a layer from the initial value in the cylindrical section to 90◦ (i.e. perpendicular to the vessel axis) at the layer end point. Then, the fiber band turns around the pole and goes back to the cylindrical section. This winding process of layers repeats until the whole vessel is completed. The netting theory is well-suited and applied commonly to calculate the variation of winding 2 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 Fig. 1. 3D structural model of composite pressure vessel. angle and layer thickness. (r ) 0 θ(r) = sin− 1 r cylinder section; BW is the helical band width. The filament winding can be divided into two types including the hoop winding (i.e. fibers wound in the hoop style can provide the circumferential strength) and helical winding (i.e. fibers wound in the helical style with a defined angle can resist both axial and circumfer­ ential loads). The winding initial angles and composite layers of the literature [7] are adopted to model wound composite pressure vessels so as to compare the finite element solution with the experimental one, as shown in Fig. 3a. The composite pressure vessel consists of three parts including the boss, liner and composite layers. The different parts of the 3D solid model are assembled together by assuming a perfect junction, and the tie connection is imposed on the contact surfaces of the liner, composite layer and boss to avoid the possible relative slippage. The boss, liner and composites layers are all meshed with 3D hexahedron elements (C3D8R). To facilitate the application of periodical boundary conditions, the symmetric nodes should be generated in opposite sides, and then periodical elements can be meshed, as shown in Fig. 3b. (1) where, r denotes the radial distance from the center axis to the current point in the layer; r0 is the radial distance from the center axis to the turnaround point. For the helical layers in the dome section, the layer thickness in­ creases gradually and then sharply near the polar openings, as described in Eq. (2) [39]. And, the calculation diagram of geometrical variables of the angle and thickness is depicted in Fig. 2. t(r) = ttl ⋅cos(θtl ) rtl ⋅ ( )4 cos(θr ) r + 2⋅BW⋅ rrtltl−− rr0 (2) where, ttl and θtl are the thickness and winding angle in the tangent line, respectively; rtl stands for the radius in the tangent line of the dome or 2.2. The finite element model with void defects To introduce void defects in the 3D finite element model, the following method is developed: Firstly, the elements of composite pressure vessel are meshed completely, as depicted in Fig. 3b. Secondly, a Python script is written to randomly choose elements in the specified region by ABAQUS software 2017. The following steps are required: first, define the specified region using the element set. Next, implement the strategy using Python’s random.sample function from the random module to obtain random non-repeating elements from a sequence. Finally, determine the random positions of the voids using the new void set. The chosen elements are marked in brown, and should satisfy the given void volume fraction of about 5 % in this literature [7], as depicted in Fig. 4. The void defects with the same void volume fraction are established in different positions, which are labeled as the MP-1(i.e. random voids, Fig. 4a), MP-2 (i.e. clustered voids in the middle, Fig. 4b) and MP-3 (i.e. clustered voids around the side, Fig. 4c). Finally, the material properties of chosen elements are weakened and assigned to simulate void defects and guarantee the satisfactory convergence. Spe­ cifically, based on the chosen void element set by the Python script, their mechanical parameters are highly reduced by 99.99 % in the ABAQUS software according to some other works [40,41]. In this case, these pore defects will not bear the loading in the simulation steps. Fig. 2. The calculation diagram of geometrical variables of the angle and thickness. 3 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 Fig. 3. Finite element model of composite pressure vessels [7]: winding layout (a) and element meshing (b). Fig. 4. Wound composites with voids in different positions [7]: MP-1 (a), MP-2(b) and MP-3 (c), location distribution of void(d), and finite element models(e). 2.3. The property of constitutes and stress–strain curves are shown in Fig. 5. The reinforced composite layers are wound by carbon fiber-epoxy bands, and the material model of composite bands is regarded as anisotropic. Assuming the composite bands are free from void defects, and the mechanical properties of the comparative literature are adopted, as listed in Table 2. The metal boss and liner of pressure vessel are made of the aluminum alloy and nylon, respectively, and both materials are assumed to be isotropic. The corresponding material parameters are shown in Table 1, 3. Progressive damage analyses of composite pressure vessel Table 1 Properties of constituents: aluminum alloy 6061-T6 and nylon PA6 [7]. Constitutes E (GPa) Υ σs (MPa) σb (MPa) δ ρ (g.cm− 3) 6061-T6 PA6 74.12 1.88 0.28 0.4 280 47 368 55 12 % – – 1.06 3.1. Boundary conditions The composite pressure vessels show periodical characteristics in the circumferential direction, and therefore, periodical boundary conditions 4 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 convenient to be applied in the finite element method. uleft − uright = νleft − νright = π Rj γ 18 tr (8) π Rj (9) 18 εt wleft − wright = 0 (10) where, Rj is the radius of the nodes on the periodic surfaces perpen­ dicular to the circumference; μ, υ, ω are the radial, circumferential and longitudinal displacements, respectively. 3.2. Progressive damage model The wound composites exhibit the inhomogeneity, and the failure of heterogeneous composites occurs when the damage accumulates to a certain extent. The composite layers of wound pressure vessel can be regarded as transversely isotropic, and a 3D Hashin’s criterion is adopted to describe damage initiation of composite layers in different failure modes, such as longitudinal breakage (1-direcion), transverse cracking (2, 3-direction) and shear failure (12, 13, 23-direction). The damage criterions of different failure modes are listed as follows: Tensile failure in 1-direcion (σ1 ≥ 0): ( )2 ( )2 ( )2 σ1 σ12 σ 31 f1t = + α + α ≥1 (11) X1t S12 S31 Fig. 5. The stress–strain curves of aluminum alloy and nylon PA6 [7]. Table 2 Mechanical properties of composite bands [7]. E1(GPa) E2/ E3(GPa) G12/ G31(GPa) G23(GPa) ν12/ν31 ν23 160 Xt (MPa) 7.42 Xc (MPa) 3.71 Yt/Zt (MPa) 1250 74 0.28 τ12/τ13 (MPa) 50 0.3 2500 4.79 Yc/Zc (MPa) 180 Compressive failure in 1-direcion (σ 1 < 0): ( )2 σ1 f1c = ≥1 X1c τ23 (MPa) 90 Tensile and shear failure in 2 and 3-direction (σ2 + σ3 ≥ 0): ( 2 ) ( )2 ( )2 ( ) σ23 − σ 2 σ3 σ2 + σ3 2 σ 12 σ 31 t f2(3) = + + + ≥1 X2t S12 S31 (S23 )2 (PBCs) are necessary to use the 1/36 model for numerical simulations. The opposite faces in the circumferential direction should satisfy the displacement and force continuities [42,43] in the following equation: ui = εik xk + ui ∗ (3) (4) uj−i (5) =ε j− ik xk + u∗i ( j+ ) j− j− = εik Δxjk uj+ i − ui = εik xk − xk ≥1 (14) When the material damage initiates, the composite material will gradually fail with the further increasing load. A damage evolvement model is necessary to describe the degeneration of the material prop­ erties. Therefore, a progressive damage model is adopted to describe the stiffness degradation of composite components [44]. The damage law of each damage mode is defined with the following equivalent displacements: ( ) I I0 δI1 eq δeq − δeq ); I ∈ {1t, 1c, 2t, 2c, 3t, 3c, mt, mc} dI = ( (15) I0 δIeq δI1 eq − δeq (6) where, the superscript “j+” and “j− ” represent the opposite and negative directions, respectively; xk is the node coordinate, and the difference j Δxk is constant for paired boundaries. The right side of Eq. (6) is invariant with a specified εik . A cylindrical-coordinate system is defined and PBCs in the circum­ ferential direction can be expressed as follows: i i Uleft − Uright = εh (13) Compressive and shear failure in 2 and 3-direction (σ2 + σ 3 < 0): [( ] ( 2 ) ( )2 )2 ) ( σ − σ2 σ3 1 X2c σ2 + σ3 2 σ12 c f2(3) = c − 1 (σ2 + σ3 ) + + 23 + X2 2S23 2S23 S12 (S23 )2 ( )2 σ 31 + S31 where, ui represents the displacement field; εik is the average strain tensor; ui* is the periodic part of displacement components on boundary surfaces. Due to the unknown ui ∗ in Eq. (3), it is hard to be directly imposed on symmetry boundaries. A transformed form is given in Eq. (4)–(6): j+ ∗ uj+ i = εik xk + ui (12) (7) I1 Here, δI0 eq and δeq denote equivalent displacements of the initiation and full damage of each damage mode I, respectively; δIeq is the equiva­ lent displacement of each mode I, as described in the literature [44]. The equivalent displacements of the initiation and full damage are described by Eqs. (16)–(18): where, Uileft and Uiright represent the displacements of corresponding nodes on a pair of periodic surfaces in circumferential directions, respectively. Under the six strain loadings (i.e. εr, εt, εz, γzr, γ zt, γ tr) on the opposite surfaces, the periodical boundary condition of the opposite surfaces perpendicular to the circumference can be realized by the following Eqs. (8)–(10). Then, the nodal displacement constraint equations are δIeq δI0 eq = √̅̅̅ fI 5 (16) L. Ge et al. δI1 eq = Thin-Walled Structures 199 (2024) 111858 2GI (17) σ I0 eq σ Ieq σ I0 eq = √̅̅̅ v ḊI = here, fI is the damage initiation value of each damage mode I; GI is the fraction energy density; σI0 eq denotes the equivalent initiation stress of each damage mode I. The voids are embedded in the composite layers of the finite element model, and the chosen elements simulating void defects own the same damage constitutive model as the composites. Differently, the material properties of chosen elements are greatly weakened to simulate void defects. The damage of constitutes can be described by Murakami–Ohno damage model [45]. When the material damage initiates, the stiffness matrix will be updated accordingly with the changing damage degree. The material constitutive relation is described with the damage vari­ ables, as shown in Eq. (19): bIJ = 4b2I b2J (bI + bJ )2 , IJ ∈ {12, 23, 31} (23) According to the periodical meshing on paired surfaces, the PBCs can be imposed by a Python script in ABAQUS software 2017, as shown in Fig. 6. The proposed progressive damage model will be achieved by writing the user subroutine “UMAT” with the Fortran Code and imple­ mented in the ABAQUS Software 2017. On the basis of the developed 3D finite element model and material system in Section 2, the established boundary conditions and damage model are applied to conduct nu­ merical analyses on the damage and failure behavior of composite pressure vessels, and the flowchart of finite element method with UMAT subroutine is shown in Fig. 7. The internal pressure loading is gradually added to the inside of the liner until the final burst failure of the com­ posite pressure vessel. here, the damage stiffness matrix C(D) is expressed by the following equation: ⎧ ⎫ ⎪ ⎪ ⎪ ⎪ ⎪ b2 C ⎪ ⎪ ⎪ b b C b b C 0 0 0 1 2 12 1 3 13 ⎪ ⎪ 1 11 ⎪ ⎪ ⎪ ⎪ 2 ⎪ ⎪ ⎪ ⎪ b C b b C 0 0 0 2 3 23 ⎪ ⎪ 2 22 ⎪ ⎪ ⎪ ⎪ ⎨ b23 C33 0 0 0 ⎬ C(D) = (20) ⎪ sym b12 C44 0 0 ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ b31 C55 0 ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ b ⎪ 23 C66 ⎪ ⎩ ⎭ bI = 1 − DI , I ∈ {1, 2, 3} ) DI − DvI , I ∈ {1, 2, 3} 3.3. Numerical implementation (19) σ = C(D)ε η where, η is the viscosity coefficient representing the relaxation time; DvI andDvm represent the regularized damage variables of mode I for com­ posite layers. (18) fI 1( 4. Results and discussion 4.1. The stress analysis of composite layers of wound pressure vessels The on-axis stresses in the fiber longitudinal direction (σ11) and transverse direction (σ 22) of pressure vessels are plotted under the in­ ternal pressure before the damage initiation. The stress values of first ten composite layers (i.e. Layer 1–10) are extracted as a representative including hoop and helix layers with the winding angle ranging from ◦ ◦ 20 to 89.5 . As shown in Fig. 8, in general, the stresses σ 11 of helical layers are obviously higher than the hoop layers. In addition, for the helical layers in the cylinder section, the higher winding angle means the higher ultimate stresses. However, in the dome section, the opposite trend has been found. From the dome section to the cylinder section, there is a sharp stress fluctuation in the transition region, which may cause a stress concentration. The stress variation of hoop layers is more stable than helical layers in the ‘W’ shape, and only a small fluctuation is observed. The stresses σ 11 of the random voids are about zero, but the existences of the void defects may lead to the stress fluctuation in the fiber-direction, as shown in Fig. 8. The voids show more effects on the stress σ11 in the hoop layers than the helical layers. The results of stress σ22 are shown in Fig. 9. On the whole, similar as that in σ11, there is a sharp fluctuation in the helical layers, which may (21) (22) where, Cij (i, j = 1, 2, 3) represents the component of the undamaged stiffness tensor. Severe convergence deficiencies may come with the material soft­ ening behavior and stiffness degradation in the implicit analysis pro­ grams. Duvaut and Lions regularization model is introduced to alleviate the deficiencies in Eq. (23) [46]: Fig. 6. Boundary conditions of the finite element model. 6 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 Fig. 7. The flowchart of finite element method with UMAT subroutine. cause a stress concentration in the transition region. The stress decreases with the increasing of winding angles of helical layers in the cylinder section. However, the stresses σ22 of hoop and helical layers are almost the same and vary with the distance along the axis direction in the ‘C’ shape. The hoop and helical layers in the cylindrical region are all critical factors in tolerating the internal pressure of the vessel. Similar as that of σ 11, the stresses σ 22 of the random voids are about zero, which has verified the effectiveness of the simulation method of void defects in Section 2.2. Also, the void defects have brought about the stress fluc­ tuation of stress σ 22 in the helical and hoop layers. 4.2. The defect induced damage behavior of composite pressure vessels Based on the finite element models coupling with the damage model, the progressive damage analysis is conducted to predict the pore defect induced progressive damage behavior and burst pressure by the UMAT subroutine in ABAQUS software 2017. The burst pressure of composite pressure vessel is predicted to be 133 MPa, with an error of about 3 % between the predicted value and experimental one in the literature [7]. Besides, compared to the numerical result in this cited literature, the prediction accuracy has been highly improved due to the 3D finite element model with void defects and the progressive damage model. As can be seen, the present 3D model has been demonstrated the reliability to predict the burst strength of composite pressure vessels. The damage results of the composite layers are shown in Fig. 10. The initial damage of composite pressure vessel is the matrix damage which appears in the middle of the cylinder section and the region near the equator under the pressure of 44 MPa. With the internal pressure increasing to 54 MPa, the matrix damage of the cylinder and dome region gradually evolves to a greater degree, and expands to each other. Meanwhile, under the pres­ sure of 54 MPa, the fiber damage emerges in the dome and cylinder section. When the internal pressure increases to 95 MPa, the matrix damage further deteriorates and has almost reached the full damage state compared to the damage state under the pressure of 120 MPa. Numerous fibers fractures under the pressure of 95 MPa, and almost all the fibers fractures under the pressure of 120 MPa. When the fiber failure of composite layers further deteriorates to the critical failure extent, the wound pressure vessel loses the load-bearing ability. It Fig. 8. The stress in the fiber longitudinal direction of helical(a) and hoop (b) layers. 7 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 Fig. 9. The stresses in the fiber transverse direction of helical(a) and hoop(b) layers. Fig. 10. Damage evolution of composite pressure vessels under pressure loading. 8 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 concludes that the burst of composite pressure is mostly determined by the fiber failure, even if the matrix failure produces earlier. Therefore, the fiber damage is the dominating regulation factor on the mechanical strength of composite layers, and the matrix damage shows lesser ef­ fects. The composite pressure vessels finally burst under the internal pressure of 130 MPa, which agrees well the experimental data in the literature [7]. To sum up, before the 54 MPa internal pressure, the matrix damage is the main damage mode. In the pressure scope of 54 MPa to 95 MPa, the matrix damage and fiber damage play the almost same important role. After the pressure reaches 95 MPa, the fiber damage has dominated the damage process until the burst failure of composite pressure vessels. To deeply figure out influences of the local void defect and layer type on the damage behavior of composite pressure vessels, the damage process under the internal pressure is investigated detailedly including the dome and cylinder section, as shown in Figs. 11 and 12. On the whole, the cylinder section shows more higher matrix damage range and damage rate than those of the dome section. And, more fiber damage produces in the cylinder section rather than the dome section, which is consistent with the failure mechanism of the experimental results [7]. For the fiber damage evolution in Fig. 11, the fiber damage initials firstly around the void defects in the cylinder section and the dome section near the equator. The fiber damage in the dome section tends to evolve from the middle region to fiber direction and then the sides, but in the cylinder section, the damage evolution process is that the fiber damage firstly starts at the inside helical winding layers, then extends to the outside helical winding layers and finally reaches the hoop winding layers. As shown in Fig. 12, for the matrix damage, the void defects induce the damage initiation around the edges of one side of the dome region, then extend almost in parallel to the other side, and further to­ ward the fiber direction. This damage evolution mechanism is different from that of the fiber damage in the dome section. As for the matrix damage in the cylinder section, similarly, the damage initials around the void defects of both edge regions, then rapidly extends to transverse regions, and in turn evolve along the fiber direction. As can be seen, the void defects will contribute to the damage initiation, evolution and final failure of composite layers of pressure vessels. As a conclusion, the present 3D finite element model with void defects is effective in pre­ dicting the damage failure mechanism and burst pressure of the com­ posite pressure vessels. The present damage failure analysis scheme can provide theoretical guidance for reliability evaluation of composite pressure vessels with void defects under the internal pressure. 4.3. Comparative analysis of defect models of composite pressure vessels The void distribution may influence the strength and damage behavior of the composite pressure vessels, and to compare with the experimental data [7], the average void volume fracture of 5 % is assigned for three different finite element models in Section 2.2 with the abbreviation of MP-1(i.e. random voids), MP-2 (i.e. clustered voids in the middle) and MP-3(i.e. clustered voids around the side). That is to say on the basis of the same void volume fraction, three different void types own randomly distributed or clustered void defects are generated to investigate the effects of large void defects on the mechanical properties of composite pressure vessels. Three type void models are simulated under the same internal pressure, and almost no stresses are generated in the void defects due to their weakened material properties. However, the void defects have changed the stress distribution and deteriorate concentrated stresses in the partial region. The burst strengths of MP-2 and MP-3 are predicted to be 131 MPa and 127 MPa, respectively. And, the burst strength of MP-2 is closer to the burst pressure value 133 MPa of MP-1. That is to say the void type Fig. 11. Fiber damage evolution of composite pressure vessels under pressure loading. 9 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 Fig. 12. Matrix damage evolution of composite pressure vessels under pressure loading. with clustered void defects shows stronger influences than random void defects on the burst pressure, and the clustered void defects in the edges show the greatest adverse effects on the strength of composite pressure vessels. Taking MP-1 as the reference, Fig. 13 shows the damage evo­ lution process of the same region of different models under the internal pressure loading. The region around the clustered voids of MP-2 expe­ riences almost no damage, but more damage initiates around the small defects in the neighbor layers (i.e. the region of Layer 18–21). And, the damage status is similar to that of MP-1 in the same region. However, more serious damage produces in the same layers of MP-3 compared to MP-1(i.e. the region of Layer 35–38). As a conclusion, the clustered voids will result in the damage deterioration of the basic extent brought by small void defects, but will not change the general damage trend of specific composite layers. This has explained why the predicted burst pressure of MP-3 is the lowest of these three models. 5. Conclusions In this paper, the WCM plugin coupled with a void generation method is employed in the ABAQUS software to accurately model the 3D composite pressure vessel with void defects. A 3D progressive damage model compiled in UMAT subroutine is developed to predict the damage evolution and failure modes of composite layers under the internal pressure, and therefore determine the burst pressure considering void defects which has been verified by the experimental data. To further explore the effects of void characteristics on the damage behavior and composite strength, three different finite element models have been constructed basing on the experimental data and clearly discussed. Based on the above research, the following conclusions have been drawn. (1) The 3D finite element model and progressive damage model are effective in predicting the burst pressure of composite pressure vessels with void defects, and the error of less than 3 % between the predicted value and experimental data has demonstrated the reliability of the present model. (2) With the internal pressure increasing, the matrix damage of composite layers initially appears in the middle of cylinder sec­ tion and the region near equator. Before the pressure of 54 MPa, the matrix damage is the main damage mode. In the pressure scope of 54–95 MPa, the matrix damage and fiber damage play almost the same important role. After the pressure reaches 95 MPa, the fiber damage has dominated the damage process until the final burst failure of composite pressure vessels. Fig. 13. Damage evolution of different models under pressure loading. 10 Thin-Walled Structures 199 (2024) 111858 L. Ge et al. (3) The void defects will result in the deterioration of damage initi­ ation, evolution and final failure of composite layers, but the clustered voids will not change the general damage evolution trend of composite layers. (4) The present damage failure analysis scheme can provide the theoretical guidance for reliability evaluation of composite pressure vessels with void defects under the internal pressure. damage and dome multi-sequencing, Int. J. Hydrogen Energy 40 (2015) 13215–13230. [10] B. Magneville, B. Gentilleau, S. Villalonga, F. Nony, H. Galiano, Modeling, parameters identification and experimental validation of composite materials behavior law used in 700 bar type IV hydrogen high pressure storage vessel, Int. J. Hydrogen Energy 40 (2015) 13193–13205. [11] M. Ahmadi Jebeli, M Heidari-Rarani, Development of Abaqus WCM plugin for progressive failure analysis of type IV composite pressure vessels based on Puck failure criterion, Eng. Fail. Anal. 131 (2022) 105851. [12] S. Alam, G.R. Yandek, R.C. Lee, J.M. Mabry, Design and development of a filament wound composite overwrapped pressure vessel, Compos. Part C: Open Access 2 (2020) 100045. [13] L. Wang, C. Zheng, H. Luo, S. Wei, Z. Wei, Continuum damage modeling and progressive failure analysis of carbon fiber/epoxy composite pressure vessel, Compos. Struct. 134 (2015) 475–482. [14] P. Sharma, A.K. Burolia, N.C. Adak, J. Daiya, H.H. Sardar, S. Neogi, Effect of tension on liner buckling and performance of a type-4 cylinder for storage of compressed gases with experimental validation, Thin-Walled Struct. 189 (2023) 110928. [15] Q.G. Wu, X.D. Chen, Z.C. Fan, D.F. Nie, Stress and damage analyses of composite overwrapped pressure vessel, Procedia Eng. 130 (2015) 32–40. [16] D. Leh, P. Saffre, P. Francescato, R. Arrieux, S. Villalonga, A progressive failure analysis of a 700-bar type IV hydrogen composite pressure vessel, Int. J. Hydrogen Energy 40 (2015) 13206–13214. [17] J.H. Hong, M.G. Han, S.H. Chang, Safety evaluation of 70MPa-capacity type III hydrogen pressure vessel considering material degradation of composites due to temperature rise, Compos. Struct. 113 (2014) 127–133. [18] P. Xu, J.Y. Zheng, P.F. Liu, Finite element analysis of burst pressure of composite hydrogen storage vessels, Mater. Des. 30 (2009) 2295–2301. [19] M.G. Han, S.H. Chang, Evaluation of structural integrity of type-III hydrogen pressure vessel under low-velocity car-to-car collision using finite element analysis, Compos. Struct. 148 (2016) 198–206. [20] J.P. Berro Ramirez, D. Halm, J.C. Grandidier, S. Villalonga, A fixed directions damage model for composite materials dedicated to hyperbaric type IV hydrogen storage vessel – part II: validation on notched structures, Int. J. Hydrogen Energy 40 (2015) 13174–13182. [21] M. Bouvier, V. Guiheneuf, A Jean-marie, Modeling and simulation of a composite high-pressure vessel made of sustainable and renewable alternative fibers, Int. J. Hydrogen Energy 44 (2019) 11970–11978. [22] B.B. Liao, L.Y. Jia, Finite element analysis of dynamic responses of composite pressure vessels under low velocity impact by using a three-dimensional laminated media model, Thin-Walled Struct. 129 (2018) 488–501. [23] A. Air, E. Oromiehie, B.G. Prusty, Design and manufacture of a Type V composite pressure vessel using automated fibre placement, Compos. Part B: Eng. 266 (2023) 111027. [24] V.G. Belardi, M. Ottaviano, F. Vivio, Bending theory of composite pressure vessels: a closed-form analytical approach, Compos. Struct. 329 (2024) 117799. [25] J. Lin, C. Zheng, Y. Dai, Z. Wang, J. Lu, Prediction of composite pressure vessel dome contour and strength analysis based on a new fiber thickness calculation method, Compos. Struct. 306 (2023) 116590. [26] M. Mehdikhani, L. Gorbatikh, I. Verpoest, S.V. Lomov, Voids in fiber-reinforced polymer composites: a review on their formation, characteristics, and effects on mechanical performance, J. Compos. Mater. 53 (2019) 1579–1669. [27] S. Lin, X. Jia, H. Sun, H. Sun, D. Hui, X. Yang, Thermo-mechanical properties of filament wound CFRP vessel under hydraulic and atmospheric fatigue cycling, Compos. Part B: Eng. 46 (2013) 227–233. [28] S. Behera, S.K. Sahoo, L. Srivastava, A.S Srinivasa Gopal, Structural integrity assessment of filament wound composite pressure vessel using through transmission technique, Procedia Struct. Integr. 14 (2019) 112–118. [29] D. Guillon, D. Espinassou, P. Pichon, J.J. Rojas Carrillo, C. Landry, D. Clainchard, et al., Manufacturing, burst test and modeling of high pressure thermoplastic composite overwrap pressure vessel, Compos. Struct. 316 (2023) 116965. [30] Q. Wang, T. Li, B. Wang, C. Liu, Q. Huang, M. Ren, Prediction of void growth and fiber volume fraction based on filament winding process mechanics, Compos. Struct. 246 (2020) 112432. [31] E. Ozaslan, K. Yurdakul, C. Talebi, Investigation of effects of manufacturing defects on bursting behavior of composite pressure vessels with various stress ratios, Int. J. Press. Vessels Pip. 199 (2022) 104689. [32] H. Arikan, Failure analysis of (±55◦ )3 filament wound composite pipes with an inclined surface crack under static internal pressure, Compos. Struct. 92 (2010) 182–187. [33] P. Blanc-Vannet, Burst pressure reduction of various thermoset composite pressure vessels after impact on the cylindrical part, Compos. Struct. 160 (2017) 706–711. [34] O.C. Farukoglu, I. Korkut, An analytical evaluation method to estimate effects of void induced errors on the stresses of pressurized fiber reinforced composite tube, Mater. Today Commun. 31 (2022) 103486. [35] C. Kang, S. Ye, H. Zhou, Z. Liu, B. Deng, J. Liu, et al., Multi-parametric analysis on buckling of nano-reinforced prepreg wound riser considering void shape and distribution, Ocean Eng. 258 (2022) 111753. [36] E. Moskvichev, Numerical modeling of stress-strain behavior of composite overwrapped pressure vessel, Procedia Struct. Integr. 2 (2016) 2512–2518. [37] B. Ellul, D. Camilleri, The influence of manufacturing variances on the progressive failure of filament wound cylindrical pressure vessels, Compos. Struct. 133 (2015) 853–862. CRediT authorship contribution statement Lei Ge: Writing – original draft, Software, Methodology, Investiga­ tion, Funding acquisition. Jikang Zhao: Validation, Resources, Inves­ tigation. Hefeng Li: Resources, Conceptualization. Jingxuan Dong: Software, Resources. Hongbo Geng: Resources, Data curation. Lei Zu: Software, Resources, Methodology. Song Lin: Resources, Conceptuali­ zation. Xiaolong Jia: Writing – review & editing, Project administra­ tion, Funding acquisition. Xiaoping Yang: Project administration, Methodology. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability No data was used for the research described in the article. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (Grant No. 52303071), China Postdoctoral Science Foundation (Grant No. 2022M720373), Beijing Natural Science Foun­ dation (Grant No. 2192044), Fundamental Research Funds for the Central Universities (Grant No. XK1802-2, BH2314), BUCT Youth Talent Plan, 2020–2023 Open Project of State Key Laboratory of OrganicInorganic Composites (Grant No. Oic-202001008, Oic-202101008, Oic-202201007, Oic-202301003), Consulting Research Project of Chi­ nese Academy of Engineering (No. 2020-XY-81). References [1] A. Air, M. Shamsuddoha, B Gangadhara Prusty, A review of Type V composite pressure vessels and automated fibre placement based manufacturing, Compos. Part B: Eng. 253 (2023) 110573. [2] A.E. Scott, I. Sinclair, S.M. Spearing, M.N. Mavrogordato, W. Hepples, Influence of voids on damage mechanisms in carbon/epoxy composites determined via high resolution computed tomography, Compos. Sci. Technol. 90 (2014) 147–153. [3] P. Journoud, C. Bouvet, B. Castanie, L. Ratsifandrihana, Effect of defects combined with impact damage on compressive residual strength in curved CFRP specimen, Thin-Walled Struct. 184 (2023) 110484. [4] O. Vallmajo, A. Arteiro, J.M. Guerrero, A.R. Melro, A. Pupurs, A. Turon, Micromechanical analysis of composite materials considering material variability and microvoids, Int. J. Mech. Sci. 263 (2024) 108781. [5] S. Ilangovan, S. Senthil Kumaran, K. Naresh, K. Shankar, R. Velmurugan, Studies on glass/epoxy and basalt/epoxy thin-walled pressure vessels subjected to internal pressure using ultrasonic ‘C’ scan technique, Thin-Walled Struct. 182 (2023) 110160. [6] J.P. Berro Ramirez, D. Halm, J.C. Grandidier, S. Villalonga, F. Nony, 700 bar type IV high pressure hydrogen storage vessel burst – simulation and experimental validation, Int. J. Hydrogen Energy 40 (2015) 13183–13192. [7] Z. Hu, M. Chen, L. Zu, X. Jia, A. Shen, A. Yang, et al., Investigation on failure behaviors of 70 MPa Type IV carbon fiber overwound hydrogen storage vessels, Compos. Struct. 259 (2021) 113387. [8] Z. Hu, M. Chen, B. Pan, Simulation and burst validation of 70 MPa type IV hydrogen storage vessel with dome reinforcement, Int. J. Hydrogen Energy 16 (2021) 23779–23794. [9] D. Leh, B. Magneville, P. Saffre, P. Francescato, R. Arrieux, S. Villalonga, Optimisation of 700 bar type IV hydrogen pressure vessel considering composite 11 L. Ge et al. Thin-Walled Structures 199 (2024) 111858 [38] A. Wen, L. Ma, J. Zheng, A novel modeling and virtual testing method of hydrogen storage COPV considering stochastic wrinkle defects, Int. J. Hydrogen Energy 48 (2023) 33656–33668. [39] Simulia Inc... Wound composite modeler for ABAQUS user; 2016. [40] J. Dong, Y. Gong, Influence of void defects on progressive tensile damage of threedimensional braided composites, J. Compos. Mater. 52 (2018) 2033–2045. [41] T. Liu, W. Fan, X. Wu, Comparisons of influence of random defects on the impact compressive behavior of three different textile structural composites, Mater. Des. 181 (2019) 108073. [42] Z. Xia, Y. Zhang, F. Ellyin, A unified periodical boundary conditions for representative volume elements of composites and applications, Int. J. Solids Struct. 40 (2003) 1907–1921. [43] Z. Xia, C. Zhou, Q. Yong, X. Wang, On selection of repeated unit cell model and application of unified periodic boundary conditions in micro-mechanical analysis of composites, Int. J. Solids Struct. 43 (2006) 266–278. [44] I. Lapczyk, J.A. Hurtado, Progressive damage modeling in fiber-reinforced materials, Compos. Part A: Appl. Sci. Manuf. 38 (2007) 2333–2341. [45] S. Murakami, Mechanical modeling of material damage, J. Appl. Mech. 55 (1988) 280–286. [46] G. Duvaut, J.L. Lions, Inequalities in Mechanics and Physics, Springer, Berlin, 1976. 12