Modelling component cost in compression moulding of thermoplastic composite and sandwich components

Thermoplastic composite and sandwich materials offer a potential of reducing component weight and improving recyclability while at the same time enhancing process economy through reduced manufacturing cycle time. The economical aspects of compression moulding of three different thermoplastic composite and sandwich material systems are modelled herein and are compared to compression moulding of a thermoset sheet moulding compound and stamping of sheet metal. A program has been developed which predicts component cost for different component sizes and complexities. It is found that raw material cost strongly dominates component cost for compression moulding of composite components, while in sheet metal stamping component cost is dominated by equipment costs.The model shows that thermoplastic composites are cost competitive for small to medium sized components and short production series of large components. The sandwich concepts offers a potential of further reducing component cost compared to composites, thus making the concept interesting for larger components, but still for short to intermediate production series, which is illustrated by calculating component cost for compression moulding of a sandwich tailgate.     

Modelling of composite sheet forming: a review

The use of composite materials in sheet forming applications is gaining popularity with the rise of consumer demands and specific mechanical properties. In addition to unidirectional (UD) fibres, the use of textile reinforcements such as woven fabric and knitted fabric has been shown to be feasible in recent years. This paper gives a survey on the modelling of composite sheet forming for both UD fibre and textile composites. Two broad approaches are reviewed here—the mapping approach and the mechanics approach. Mapping approaches for UD fibre composites, woven fabric composites and knitted fabric composites are elucidated on the basis of their fibre geometry. For the mechanics approach both the viscous fluid models and elastic solid models, as a means of describing the constitutive properties, are reviewed. Various updating methods for modelling large deformation found in sheet forming are then described. Finally, a guideline for the choice of modelling techniques for various types of fibre/fabric reinforcements and suggestions for future work are given.     

Impact damage in hybrid braided twill composites

Impact damage to composite plates is significantly reduced by replacing some of the high-strength fibres with more ductile glass or synthetic fibres. Hybrid composites reduce impact damage by distributing more widely the deformations and strain in the contact region. This investigation focussed only on hybrid textile composites with individual tows composed of either carbon or glass which are braided together in a twill textile. At a similar level of impact energy, low and high-speed impact tests resulted in different failure mechanisms dominated, respectively, by quasi-static and flexural wave deformations. The damage severity was evaluated in terms of damage area (C-scan) and absorbed energy.     

Textile composite double dome stamping simulation using a non-orthogonal constitutive model

Stamping is one of the most effective ways to form textile composites in industry for providing high-strength, low-weight and cost-effective products. This paper presents a fully continuum mechanics-based approach for stamping simulation of textile fiber reinforced composites by using finite element (FE) method. A previously developed non-orthogonal constitutive model is used to represent the anisotropic mechanical behavior of textile composites under large deformation during stamping. Simulation are performed on a balanced plain weave composite with 0°/90° and ±45° as initial yarn orientation over a benchmark double dome device. Simulation results show good agreement with experimental output in terms of a number of parameters selected for comparison. The effects of meshing and shear moduli obtained from bias extension test and picture frame test on forming simulation results are also investigated.     

Potentiality of utilising natural textile materials for engineering composites applications

This paper gives an overview of utilising natural textile materials as reinforcements for engineering composites applications. The definition and types of textile materials are addressed to provide readers a thoughtful view on the role of these materials in a structural composite system. Available material properties of natural textile and their composites are critically reviewed here. In general, these materials are categorised into fibre, yarn and fabric forms. The load bearing capacity of natural textile fibre reinforced polymer composites is governed by the quantity, alignment and dispersion properties of fibres. It has been found that the natural fibre reinforced composites are limited to use in low to medium load bearing applications. However, a limited research work has been performed to date and there is a significant gap between the high performance textile fabric and their use as reinforcement in fibre reinforced composite materials.     

The method of cells and the mechanical properties of textile composites

The method of cells has been gaining ground as a method for predicting the elastic properties of textile reinforced composite materials. This method deals away with the constant stress/strain assumption present in most analytical models allowing for a more accurate prediction of the elastic properties, with computational cost only a fraction in comparison with finite element analysis. A new implementation is presented here, which links this method to a mechanistic predictive geometry preprocessor allowing the presented model to deal with 2D and 3D textile reinforced composites. Numerical results for prediction of stiffness and strength of textile composites are generated and compared to other methods.     

Estimating mechanical properties of 2D triaxially braided textile composites based on microstructure properties

Textile composites manufactured using Resin Transfer Modeling (RTM) can offer advantages in some automotive applications including reduction in weight, while being relatively simpler to fabricate than standard laminated composites used for aerospace applications. However, one of the challenges that arise with these textile composite materials is that the mechanical properties are inherently dependent on the local and final (in-situ) architecture of the textile itself as a result of the molding and curing processes. While this provides additional latitude in the composite design process it also necessitates the development of analytical models that can estimate the mechanical properties of a textile composite based on the textile architecture and the properties of the manufactured component.In this paper, an analytical model is developed and its estimations are compared against experimental in-plane engineering properties for composites with various textile architectures. Results from the model are also compared against finite element (FE) based computational results. The microstructures of the 2D triaxially braided composite (2DTBC) studied were extensively characterized. The microstructure properties thus measured were used in the analytical model to estimate the mechanical properties. Uniaxial tension and V-notched rail shear tests were conducted on 2DTBC with different textile architectures. Good agreement between the analytical, computational, and experimental results were observed and are reported here. Furthermore, computational estimations of matrix mechanical properties are limited to the linear elastic range of a representative material volume (unit cell) and coupon data. Full mechanical response of larger 2DTBC structures, albeit of prime interest, is beyond the scope of this work and could be the focus of follow up studies.     

Predictive modelling for optimization of textile composite forming

Wrinkling often occurs during textile composite forming and is a major problem for manufacturers. The prediction of this defect is, therefore, of major importance for the design and optimization of textile composite structures. Numerical simulations of forming for textile composites over a hemisphere have been conducted using a rate/temperature-dependent hybrid FE model. The hybrid FE model incorporates a fully predictive multi-scale energy model which determines the shear resistance of the textile composite sheet. The effects of varying the normal force distribution across the edges of the blank and blank size, together with the effect of changes in forming temperature on the final fibre pattern and wrinkling behaviour, are investigated. Predictions are evaluated against press-formed components. The results from the simulation and the experiments have good correlation and show that wrinkling can be minimized by optimizing the force distribution around the edge of the manufacturing tool and by careful choice of forming temperature.     

Numerical study on thermo-stamping of woven fabric composites based on double-dome stretch forming

Through the international corporative benchmark works, the material characterization of the woven fabric composites has been examined to better understand their mechanical properties and to provide the process design information for numerical analysis. As the second stage of the benchmark work, the double-dome geometry has been used to illustrate the effect of numerical schemes on the forming behaviors of the woven composites parts. To account for the change of fiber orientation under the large deformation, the non-orthogonal constitutive model was utilized and nonlinear friction behavior was incorporated in the simulation. The equivalent material properties based on the contact status were used for the thermo-stamping process. Furthermore, we incorporated a recently developed non-orthogonal model which captures the dependency of shear behavior of woven fabric composites on the tensions in yarns. Simulation results showed the effect of coupling on the predicted forming behavior for the double-dome parts. As numerical results, blank draw-in, punch force history and fiber orientation after forming have been compared based on various numerical models and methods.     

碳纤维/聚醚醚酮(PEEK)复合材料拉拔制管工艺设计和模拟

从太空制造角度出发,设计了一种碳纤维/聚醚醚酮(PEEK)预浸复合板料拉拔连续制管工艺.综合考虑了预浸复合板料的供料放卷过程、冲压、拉拔成形工步和超声焊接工序,并创造性的提出了卷曲拉挤成型方式.利用Johnson-Cook和Holzapfel-Gasser-Ogden模型构建了一种以PEEK为基体,以碳纤维编织布为增强体相互叠加的材料模型,通过实验数据确定材料参数.采用商业软件ABAQUS对各工序分步进行了地面条件下的有限元数值模拟,分析了预浸复合材料板材在供料放卷、冲压拉拔成形过程中的应力分布,并采用蔡-希尔最大变形能理论证明了本文设计的放卷模具和卷曲成形模具可以进行连续制管.在焊接过程中,分析了预浸料基体PEEK在焊接区域产生的Mises应力分布,证明了超声波焊接方案对管材表面质量的影响较小.模拟结果表明,所设计的连续拉拔制管工艺能够快速有效地生产出表面良好的管材.仿真结果可为后续复合材料在轨拉拔连续制管的工艺设计和制造提供借鉴.     

高强度高导电性铜合金研究现状及展望

本文综述了高强度高导性铜合金的研究现状，并对其进一步发展作了展望，指出，自生复合材料由于充分利用了铜基体的高导电性和第二相的强化作用，同时又避免了人工复合材料中相界面处的润湿及化学反应等问题，因而在制备高强度高导电性铜材料方面具有广阔的应用前景。     

A dual homogenization and finite element approach for material characterization of textile composites

A novel procedure for predicting the effective nonlinear elastic moduli of textile composites through a combined approach of the homogenization method and the finite element formulation is presented. The homogenization method is first applied to investigate the meso-microscopic material behavior of a single fiber yarn based on the properties of the constituent phases. The obtained results are compared to existing analytical and experimental results to validate the homogenization method. Very good agreements have been obtained. A unit cell is then built to enclose the characteristic periodic pattern in the textile composites. Various numerical tests such as uni-axial and bi-axial extension and trellising tests are performed by 3D finite element analysis on the unit cell. Characteristic behaviors of force versus displacement are obtained. Meanwhile, trial mechanical elastic constants are imposed on a four-node shell element with the same outer size as the unit cell to match the force–displacement curves. The effective nonlinear mechanical stiffness tensor is thus obtained numerically as functions of elemental strains. The procedure is exemplified on a plain weave glass composite and is validated by comparing to experimental data. Using the proposed approach, the nonlinear behavior of textile composites can be anticipated accurately and efficiently.     

Finite element calculation of 4-step 3-dimensional braided composite under ballistic perforation

The ballistic perforation test results of 4-step 3-dimensional (3D) braided Twaron^®/epoxy composites, which were subjected to impact by conically cylindrical steel projectile, are presented. The residual velocities of projectile perforated composites target at various strike velocities were measured and also compared with that from finite element calculation. ‘Fiber inclination model’ for 3D textile composites was adopted to decompose the 3D braided composite at quasi-microstructure level for the geometrical modeling in preprocessor of FEM. The material modeling was also based on this simplified model. The finite element code of Ls-Dyna was used to simulate the impact interaction between projectile and inclined lamina. The residual velocity of projectile perforating the entire 3D braided composite can be calculated from the sum of kinetic energy loss of the projectile that obtained from FEM. From the simulation of ballistic penetration process and comparison between numerical results and experimental results, it proves that the analysis scheme of quasi-microstructure level in this paper is valid and reasonable. The simplified method in this paper could be extended to model other kinds of 3D textile composites under ballistic impact.     

Self-reinforced poly(ethylene terephthalate) composites by hot consolidation of Bi-component PET yarns

Self-reinforced polymer composites or all-polymer composites have been developed to replace traditional glass-fibre-reinforced plastics (GFRP) with good lightweight, mechanical and interfacial properties and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, unidirectional all-PET composites were prepared from skin–core structured bi-component PET multifilament yarns by a combined process of filament winding and hot-pressing. During hot-pressing, the thermoplastic copolyester skin or sheath layers were selectively melted to weld high-strength polyester cores together creating an all-PET composite. Physical properties of the resulting composites including thickness, density and void content were reported. The effect of processing parameters, i.e. consolidation temperature and pressure on mechanical properties and morphology was investigated in order to balance good interfacial adhesion with residual tensile properties of the composite.     

氧化石墨烯在纺织品领域的抗菌应用

目的总结归纳氧化石墨烯及其复合材料在抗菌纺织品类包装材料的应用现状,为氧化石墨烯及其复合材料在纺织领域的应用提供参考。方法总结氧化石墨烯的性能、结构特点以及抗菌机理,阐述氧化石墨复合材料、复合纤维材料和复合织物等纺织品类材料的抗菌性能应用,并简单讨论氧化石墨烯的抗菌影响因素和氧化石墨烯的生物安全性。结果氧化石墨烯具有二维纳米结构、优异的比表面积和水溶性,纺织品类包装材料通过与氧化石墨烯的复合应用可改善其抗菌性能。目前,氧化石墨烯抗菌性能的应用尚处于初级阶段,需要更深入的研究。结论随着对氧化石墨烯研究的不断深入,氧化石墨烯在抗菌纺织品类包装材料的应用会越来越广泛。     

In-plane Compressive Behaviors of 3-D Textile Composites at Various Strain Rates

The in-plane compressive behaviors of 3-D textile composites, which including 3-D woven composite, multi-axial multi-layer warp knitted (MMWK) composite and 3-D braided composite, were studied at quasi-static and high strain rate compression loading. The compression behaviors at high strain rates (600∼2,500/s) were tested with split Hopkinson pressure bar (SHPB). The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with the results at high strain rates. The comparisons indicate that the compression stiffness, failure stress and failure strain for the three kinds of 3-D textile composites are sensitive to strain rate. The MMWK composite has higher failure stress than the 3-D woven composite and 3-D braided composite at the same strain rate; however, the failure strain of the 3-D braided composites is higher than that of the 3-D woven composite and 3-D knitted composite at quasi-static compression because of the quasi-isotropic structure feature in the 3-D braided composite. The compressive failure modes of the 3-D woven composite, MMWK composite and 3-D braided composite are totally different because of the different preform structure.     

Tensile properties and meso-scale mechanism of weft knitted textile composites for energy absorption

The investigation on large deformation tensile properties and the relevant meso-scale mechanisms of weft knitted textile composites is presented. The correlation between fabric structure (e.g. loop height and width, number of wale or course per unit length, etc.), matrix damage and material properties are described. Weft knitted fabrics with 1×1 interlock structure were used as the preform for the composites. The materials studied include knitted nylon fabric/unsaturated polyester resin and co-knitted polyethylene terephthalate (PET)/polypropylene (PP) textile composites. The results show that all the nylon/polyester thermoset textile composites samples displayed an ideal bi-linear character in their tensile stress–strain curves, whilst the tensile curves of PET/PP co-knitted thermoplastic samples along the wale, course and 45° directions are all significantly non-linear. The tensile behavior is superior in the wale direction to those in the course and 45° directions. The deformation mechanisms in meso-scale were identified experimentally by in-situ observation of large deformation process for both thermoset matrix and thermoplastic matrix textile composites. For the nylon/polyester composite samples, the non-linear properties mainly come from the change in the configuration of the fabric structure during extension. For the PET/PP co-knitted textile composite samples, the inelastic properties are attributed to the damage evolution in the matrix, interface damage between fiber bundle and matrix, sliding between the wales of the knitted fabric, as well as the change in the configuration of the fabric structure during loading.     

Three-dimensional simulations of impact induced damage in composite structures using the parallelized SPH method

To address the strain-rate dependent behavior of unidirectional composites in Air Force and Navy military systems subjected to impact loading, a one-parameter visco-plasticity composite material model was developed and incorporated into the MAGI code which was parallelized for this study. This code is based on the smoothed particle hydrodynamics method. The strain-rate dependent composite model is applied here to investigate the high-velocity impact induced damage of armored composite plates which consisted of eight graphite/epoxy (Gr/Ep) layers with a lay-up of [±45/0/90]_s. The face sheets consisted of two different materials (either aluminum or boron carbide) of variable thickness. The effects of face sheet position, face sheet material types, and impact velocity on the detailed damage of the laminate are presented.     

不同秸秆增强环氧树脂复合材料的力学性能研究

秸秆具有生物降解、绿色环保等特性,且来源丰富,在绿色纺织复合材料领域受到广泛关注。本文采用真空辅助法制备了长芦苇秆、麦秆、高粱秆、稻草秆增强环氧树脂复合材料,研究了芦苇秸秆在整体和劈裂状态下复合材料的力学性能,并比较了在劈裂状态下芦苇秸秆和其他3种秸秆增强复合材料的力学性能及形态特征,分析了4种秸秆的红外光谱、表面润湿性、表面元素及微观结构。结果表明:4种秸秆均有相似的振动吸收峰位置,且它们表面微观结构差异较大,但其相同之处是表面均有硅元素、氧元素以及碳元素。同时4种秸秆都具有疏水性,芦苇秆、高粱秆、麦秆和稻草秆与水的接触角依次降低。在力学性能上,由于纤维素纤维在秸秆内合理有效分布使其出现结构物效应,秸秆增强复合材料的弯曲性能较拉伸性能具有明显的优势,同时芦苇秆劈材增强环氧树脂复合材料的拉伸强度和弯曲强度比芦苇秆复合材料高165.07%、55.72%。在4种秸秆劈材复合材料中,芦苇秆劈材复合材料的拉伸、弯曲性能最好,其次是稻草杆、高粱杆、麦秆复合材料。秸秆增强复合材料的开发有利于提高秸秆资源利用率,为复合材料的开发利用提供了新路径。