Kinematic modelling of 3D woven fabric deformation for structural scale features

A multi-scale approach to modelling is optimal for computationally intensive problems of a hierarchical nature such as 3D woven composites. In this paper an approach capable of modelling feature/component scale fabric deformations and defects is proposed. The proposed technique starts with a meso-scale model for predicting the as-woven geometry of a single unit cell using a high fidelity digital element method. The unit cell geometry is then converted into a macro-scale fabric model by geometric reduction then tessellation. On the macro-scale, two and three dimensional approaches to yarn geometry representation are proposed, with an accompanying yarn mechanical model. Each approach is evaluated based on solution accuracy and computational efficiency. The proposed approach is then verified against experimental results on the meso- and macro-scales. The applicability of this modelling technique to larger scale compaction problems is then investigated. The proposed algorithm was found to be accurate and computationally efficient.     

Modelling deformation and damage characteristics of woven fabric under small projectile impact

Fabrics comprising highly oriented polymers possess high impact resistance and are often used in flexible armour applications. As these materials are viscoelastic, accurate modelling of their impact and perforation response requires formulation of constitutive equations representing such behaviour. This study incorporates viscoelasticity into the formulation of a model to analyse the impact of small spherical projectiles on plain-woven PPTA poly(p-phenylene-terephthalamide) fabric. The fabric is idealized as a network of viscoelastic fibre elements and a three-element viscoelastic constitutive model is used to represent polymer behaviour. Viscoelastic parameters are used to reflect intermolecular and intramolecular bond strengths as well as the static mechanical properties of fibres. Results of the theoretical analysis were compared with data from experimental tests on fabric specimens subjected to projectile impact ranging from 140 m/s to 420 m/s. Predictions of the threshold perforation velocity and energy absorbed by the fabric showed good agreement with experimental data. The proposed analysis is able to model deformation development and rupture of the fabric at the impact point. Fraying and unravelling of yarns are also accounted for. The study shows that a knowledge of static mechanical properties alone is insufficient and results in gross underestimation of impact resistance. An important parameter identified is the crimping of yarns. Yarns in woven fabric are not initially straightened out and hence part of the stretching in fabric is due to the straightening of yarns. The effect of crimping was found to be significant for high impact velocities.     

基于自由变形技术的二维机织物细观模型

为了避免理想化织物模型横截面恒定、纱线间相互渗透的问题,生成具有真实感的二维机织物三维细观模型,提出一种基于自由变形技术的几何变形方法。首先通过理想化的纱线中心线轨迹、横截面建立织物初始几何模型,然后应用自由变形技术对纱线进行变形。在变形过程中,所有纱线横截面在空间位置和参数的约束下进行自由变形,所有横截面变形后的控制网格组成纱线的控制网格,以驱动纱线的整体变形,最终生成具有真实感的织物细观模型。变形过程中纱线间的接触应用基于射线的碰撞检测技术处理。该方法可以扩展并应用于其他织物结构,且可以输出到其他软件中进行模拟计算。      

预浸织物剪切变形时树脂细观分析模型

为了更好地研究在发生剪切变形时预浸织物材料的力学性能,建立了在像框剪切试验时未固化的树脂对织物发生剪切变形时的阻碍作用的细观分析模型.通过对材料的单胞进行分析,得到了织物单胞变形前、后各质点间的运动学关系,进而得到了树脂材料对整个织物单胞的阻力矩,即树脂的阻尼作用.此阻尼作用较好地说明了树脂在预浸织物材料中的作用.此外,通过树脂的流变试验得到其粘性系数,该粘度系数确定,即该材料的阻尼作用确定.     

Through-thickness compressive strength of carbon–phenolic woven composites

Carbon–phenolic woven composites are increasingly employed as the material for the heavy-duty journal bearings. Since the through thickness compressive strength (TTCS) is important for the heavy-duty bearing, in this paper, the effects of lay-up angles and specimen thickness of woven composites on TTCS were investigated for the efficient design of carbon–phenolic woven composite bearings. From the experiments and FEM analysis, it was found that the TTCS of the carbon–phenolic woven composite is much dependent on the stacking sequence rather than composite thickness because different stacking sequence produced much different interlaminar stresses.     

Numerical prediction of in-plane permeability for multilayer woven fabrics with manufacture-induced deformation

A unit cell based Computational Fluid Dynamics model is presented for predicting permeability of multilayer fabric structures. In Liquid Composites Moulding processes, fabric lay-ups undergo significant manufacture-induced deformation, combining compression, shear, and inter-layer nesting. Starting from the configuration of un-deformed fabric, the deformation is simulated geometrically by accounting for self-imposed kinematic constraints of interweaving yarns. The geometrical modelling approach is implemented in the open-source software TexGen. The permeability tensor is retrieved from flow analysis in ANSYS/CFX, based on TexGen voxel models. Using only measured geometrical data for un-deformed fabrics, deformed plain weave fabric and twill weave fabric lay-ups were modelled and their permeability tensors predicted. Comparison with experimental data demonstrates the generally good accuracy of predictions derived from the proposed numerical method.     

Progressive failure modelling of woven carbon composite under impact

The design of composite structures or components, subject to extreme loading conditions, such as crash, blast, etc. requires a fundamental understanding of the deterioration mechanism within the composite meso-structure. Existing predictive techniques for the analysis of composite structures and components near and beyond their ultimate strength are either based on simple scalar stress functions, or use very complex damage formulations with many material constants, some of which may be difficult to characterise. This paper presents a simple damage mechanics based progressive failure model for thin woven carbon composites under impact loading. The approach is based on an unconventional thermodynamic maximum energy dissipation approach, which entails controlling damage evolution and hence energy dissipation per second, rather than damage. The method has been implemented into the explicit dynamic finite element code DYNA3D. Numerical simulation results using the proposed model are compared with two experimental impact tests.The analysis methodology proposed in this paper reflects a very simple, but effective technique that can be used to model a wide range of problems from extreme events, such as crash or blast, to birdstrike, when tearing and perforation are major failure mechanisms. As damage is cumulative, the technique allows initial or/and post-impact static loads to be applied to the composite structure or component, thus allowing a cradle-to-grave design methodology.     

In-plane and out-of-plane crack-tip constraint effects under biaxial nonlinear deformation

In-plane and out-of-plane constraint effects on crack-front stress fields under both elastic–plastic and creep conditions are studied by means of three-dimensional numerical analyses of finite thickness boundary layer models and plane strain reference solutions. This investigation is an extension of the plane strain solution obtained by Shlyannikov and Boychenko in 2008, with special attention on what constraint parameters existed in the nonlinear crack-tip fields in a finite thickness solid. Characterization of constraint effects is given by using the non-singular T-stress, the local triaxiality parameter, the factor of the stress-state in 3D cracked body and the second order term amplitude factor. The influence of nominal stress load biaxiality and creep time on the behavior of constraint factors is considered. Stresses and constraint factors from FEA at the crack-front on different planes in the thickness direction of the plate are compared with plane strain reference solutions. The results show that 3D-stress fields can be characterized in common with the local triaxiality parameter and factor of the stress-state in 3D solid by the three-term solution throughout the thickness even in the region near the free surface. It is found that there is a distinct relationship between the in-plane and the crack-front out-of-plane constraint factors which can be well captured using the relation between the second order term amplitude factor and remote boundary layer stress.     

织物形式对苎麻纤维渗透率及其复合材料力学性能的影响

采用树脂传递模塑工艺(RTM)研究了三种典型苎麻纤维织物结构(平纹、 斜纹和缎纹)对树脂流动性的影响, 并研究了三种苎麻纤维织物结构对其增强酚醛树脂复合材料的拉伸性能和层间剪切性能的影响。结果表明, 苎麻纤维织物树脂渗透率主要受纤维屈曲和流道面积的影响。斜纹和缎纹苎麻织物的纤维屈曲较小且流道面积较大, 其织物的树脂渗透率较大, 同时, 较小的纤维屈曲使其增强的复合材料拉伸性能也较优。然而, 不同织物形式对苎麻纤维织物/树脂复合材料的层间性能影响不大。     

Modelling microscopic flow in woven fabric reinforcements and its application in dual-scale resin infusion modelling

A physical unit cell impregnation model is proposed for the micro-scale flow in plain woven reinforcements. The modelling results show a characteristic relationship between tow impregnation speed, the surrounding local macro-scale resin pressure and the tow saturation within the unit cell. This relationship has been formulated into a mathematical algorithm which can be directly incorporated into a continuum dual-scale model to predict the ‘sink’ term. The results using the dual-scale model show a sharp resin front in inter-tow-pore spaces and a partially saturated front region in intra-tow-pore spaces. This demonstrates that the impregnation of fibre tows lags behind the resin front in the macro pore spaces. The modelling results are in agreement with two reported experimental observations. It has been shown that the unsaturated region at the flow front could increase or have a fixed length under different circumstances. These differences are due to the variation in tow impregnation speed (or the time required for the tow to become fully impregnated), the weave architecture and the nesting and packing of plies. The modelling results have also demonstrated the drooping of the inlet pressure when flow is carried out under constant injection rates. The implementation of the algorithm into a dual-scale model shows coherence with a single-scale unsaturated model, but demonstrates an advantage in flexibility, precision and convenience in application.     

Analysis on failure mechanisms of an interlock woven fabric under ballistic impact

In this paper, damage mechanisms of a 3D interlock woven fabric subjected to ballistic impact were analyzed using a numerical model. Two impact configurations were carried out in order to validate the numerical model with experimental observations: perforation (900 m/s) and no-perforation (90 m/s). Global deformation of the fabric during impact is determined continuously to detail fabric impact behavior. Also, in this study, the effects of boundary conditions on failure mechanisms have been investigated. Boundary conditions are divided into two cases: (1) only warp yarns fixed and (2) only weft yarns fixed. Basing on continuous evolutions of global deformation, projectile velocity, different energies and reaction force onto projectile, the influence of both these fixation conditions is investigated.     

织物形式对苎麻纤维渗透率及其复合材料力学性能的影响

采用树脂传递模塑工艺(RTM)研究了三种典型苎麻纤维织物结构(平纹、斜纹和缎纹)对树脂流动性的影响,并研究了三种苎麻纤维织物结构对其增强酚醛树脂复合材料的拉伸性能和层间剪切性能的影响.结果表明,苎麻纤维织物树脂渗透率主要受纤维屈曲和流道面积的影响.斜纹和缎纹苎麻织物的纤维屈曲较小且流道面积较大,其织物的树脂渗透率较大,同时,较小的纤维屈曲使其增强的复合材料拉伸性能也较优.然而,不同织物形式对苎麻纤维织物/树脂复合材料的层间性能影响不大.     

A three-dimensional modelling technique for predicting the linear elastic property of opened-packing woven fabric unit cells

Woven fabric has been recognized as one of the widely used materials in the aerospace industry. In order to effectively utilize this material, it is necessary to evaluate its mechanical properties. In this paper a three-dimensional multi-scaled modelling technique has been developed to investigate the linear elastic properties of single-ply opened-packing woven fabrics for pure tension and shear responses. This technique is accomplished by introducing a number of new three-dimensional macro- and micro-blocks. Thus, this technique can be considered as a full three-dimensional modelling technique. In order to verify the capability of this method, some theoretical and finite-element analysis (FEA) numerical studies were carried out for four types of opened-packing woven fabric unit cells. It was shown that there exists a good agreement between the theoretical results and those predicted using the FEA models. The trends of the stiffness and engineering elastic constants with n_g, which denotes a warp (or weft) yarn is interlaced with every n_gth weft (or warp) yarn, were also investigated. For the in-plane elastic properties, the present results correlate well with those available in the literature.     

Woven fabric permeability: From textile deformation to fluid flow mesoscale simulations

A two-step methodology is proposed in order to estimate from numerical simulations the permeability of deformed woven fabrics. Firstly, the shear deformation of a glass plain weave until the shear locking is studied from a mesoscale analysis achieved with a representative volume element (RVE) of the periodic plain weave. Simulations have been carried out within the scope of large transformations, accounting for yarn–yarn contacts, and assuming that yarns behave as hypoelastic materials with transverse isotropy. From the simulated deformed solid RVE, a complementary periodic fluid RVE is then built and the slow flow of an incompressible Newtonian fluid within it is investigated. This allows to compute, in a second step, the permeability of the deformed plain weave. The role of the shear deformation on the permeability of multi-layers or single layer preforms is discussed.     

Piezoelectric control of delamination response in woven fabric composites under mode I loading

This paper investigates the application of piezoelectric actuators to control the delamination response in woven fabric composites subjected to Mode I loading. Experiments were conducted on a double cantilever beam (DCB) specimen of woven glass fiber reinforced polymer (GFRP) composite laminates with piezoelectric ceramic actuators bonded on the surfaces, in order to evaluate the dependence of the delamination behavior on the applied electric fields. A finite element analysis of the DCB specimen with surface-bonded actuators was also performed, and a comparison was made between the finite element predictions and the test results. In addition, the effect of the actuator location on the effectiveness of the piezoelectric control was examined numerically.     

The shear properties of woven carbon fabric

This paper presents experimental and theoretical studies of the shearing properties of carbon plain weave fabrics and prepregs. The shearing characteristics of these materials are determined by the use of a picture frame shear rig which is loaded by a mechanical test machine. The shear force/angle curves are presented for the experiments conducted with the various test materials. A proposed shear model based on previous research which idealizes the fabric yarns as beam elements is presented. Using fabric geometric and material parameters, the model predicts the initial slip region of the fabric, as well as the more dominant elastic deformation range. Comparisons of the experimental and theoretical results were conducted to validate the model. A discussion of the findings from the analysis is also given, with particular focus relating to the accuracy, limitations and advantages offered by such a model. Results indicated that the slip model gives modestly accurate predictions, whilst the elastic modulus model showed very good correlation with experimental data.     

Multi-scale modeling of refractory woven fabric composites

Thermomechanical analysis of a refractory, woven fabric composite was conducted using a multi-scale analysis technique. The composite was made of carbons and ceramic materials. The fibers were made of carbons and the outer coating was made of a ceramic material. In order to reduce the thermal stress in the carbon fibers and the ceramic material caused by mismatch of coefficients of thermal expansion between the two materials, a graphitized carbon layer was introduced between the fiber and the ceramic coating. For the multi-scale analysis, a new analysis model was developed and used to bridge the micro-scale characteristics, i.e. the constituent material level such as carbon and ceramic materials, to the macro-scale behavior, i.e. the woven fabric composite level. Furthermore, finite element analyses were undertaken with discrete modeling of the representative fibers, coating, and the graphitized middle layers. Then, both multi-scale analytical and numerical results were compared. In this study, thermal stresses at the micro-level, i.e. in the fibers and coating materials, as well as effective thermomechanical properties of the refractory composites were computed using the multi-scale technique.