An intelligent inverse method for characterization of textile reinforced thermoplastic composites using a hyperelastic constitutive model

Uncontrollable factors such as contact friction, misalignment, slip, variations in local fiber volume due to fiber spreading or bunching, and tow compaction are a few sources leading to scatter (noise) in the response (signal) of textile composites. Accordingly, characterization methods often have difficulty due to non-repeatability of test data. If variance of such response within the replication of tests is neglected, then the identification of model parameters can be far from describing the true material behavior. In order to confront this shortcoming, the main objective of this paper is to elaborate on characterization of textile composites using a new inverse method by means of the signal-to-noise ratio. It will also be shown that using an appropriate constitutive model and statistical framework, the engagement of a larger range of test replications is not only useful but also may be critical for better characterization of this class of material.     

Fibre reinforced thermoplastic composites for dentistry

Clinical implementation of fibre-reinforced composites (FRCs) for treatment of misaligned teeth requires a stability of the material under stress in a moist environment. The performance of the material is strongly dependent on its resistance to hydrolytic deterioration of the components. Of particular concern are the quality and durability of the interfaces between the fibres and the matrix. Scanning electron microscopy (SEM) was utilized to evaluate qualitatively the effect of water immersion on the interfaces between constituents in a variety of E-glass fibre-reinforced thermoplastics. A particular series of organosilane-coated fibres embedded in polycarbonate (PC) were chosen for further quantitative study of the residual shear strength of the interfaces using an embedded-single-fibre test. Annealed PC and maleated polypropylene (MPP) reinforced with bare E-glass fibres have an appropriate combination of mechanical properties and environmental stability for potential orthodontic applications. The usual sizing agents used for commercial E-glass fibres interfere with the bonding of the fibres to the matrix and the usual silane treatments used to promote bonding could lead to problems of hydrolytic stability under extreme conditions of stress and moisture.     

A novel processing technique for thermoplastic manufacturing of unidirectional composites reinforced with jute yarns

This paper primarily investigates the fabrication process of long-fibre reinforced unidirectional thermoplastic composites made using jute yarns (both untreated and treated). Tubular braiding technique was used to produce an intermediate material called “microbraid yarn” (MBY) with jute yarn as the straightly inserted axial reinforcement fibre and polymer matrix fibre being braided around the reinforcing jute yarns. Microbraid yarns were then wound in a parallel configuration onto a metallic frame and compression molded to fabricate unidirectional composite specimens. In this study, two types of polymeric materials (biodegradable poly(lactic) acid and non-biodegradable homo-polypropylene) were used as matrix fibres. Basic static mechanical properties were evaluated from tensile and 3 point bending tests. Test results were analyzed to investigate the effects of molding temperature and pressure on the mechanical and interfacial behaviour. For the unidirectional jute fibre/poly(lactic) acid (PLA) composites, the results indicated that the molding condition at 175 °C and 2.7 MPa pressure was more suitable to obtain optimized properties. Improved wettability due to proper matrix fusion facilitated thorough impregnation, which contributed positively to the fibre/matrix interfacial interactions leading to effective stress transfer from matrix to fibre and improved reinforcing effects of jute yarns. For the jute/PP unidirectional composites, specimens with only 20% of jute fibre content have shown remarkable improvement in tensile and bending properties when compared to those of the virgin PP specimens. The improvements in the mechanical properties are broadly related to various factors, such as the wettability of resin melts into fibre bundles, interfacial adhesion, orientation and uniform distribution of matrix-fibres and the lack of fibre attrition and attenuation during tubular braiding process.     

Determination of strain rate dependent through-thickness tensile properties of textile reinforced thermoplastic composites using L-shaped beam specimens

The presented work focuses on a methodology to characterise strain rate dependent strength and elastic properties of textile reinforced composites in laminate through-thickness direction. Here, for the characterisation L-shaped beam specimens are used. The investigated composite is a fabric reinforced thermoplast made of hybrid E-glass/polypropylene yarns. The analytical solution for the determination of the through-thickness tensile strength as proposed by Lekhnitskii and Shivakumar is verified by means of an optical deformation analysis and is extended for thew determination of the through-thickness elastic modulus. Finally, the possibility of the strain rate dependent characterisation is investigated and a Johnson-Cook based modelling approach is used to represent the apparent strain rate dependency of the through-thickness failure onset. The methodology is successfully used to capture the material strain rate effects with the according strength values and model parameters over a strain rate range of 10 ⁻⁴ s⁻¹ to 10 s⁻¹ as well as the elastic modulus.     

Simulation‐aided development of a robust thermoclinching joining process for hybrid structures with textile reinforced thermoplastic composites and metallic components

In order to take advantage of the specific structural and functional properties inside a multi‐material assembly, it is necessary to provide adapted joining technologies. Therefore, the new joining technology “thermoclinching” was developed to join endless fiber reinforced thermoplastic composites and metallic joining partners. Previous experimental and numerical studies demonstrated the potential of the novel joining technology. In experimental and numerical studies essential geometrical and material parameters influencing the forming behavior are identified and evaluated. Thereby, the inline‐thermoclinching technology is developed by integrating the pre‐processed steps of cutting and heating into the actual joining process. For structural analysis of the joining zone as well as for quality analysis and validation of the process simulations computer tomography (CT) is used. Furthermore, experimental characterizations of the failure behavior of thermoclinched joints and the development of simulation models as well as strategies for numerical strength analyses are carried out.     

Reactive processing of textile fiber-reinforced thermoplastic composites – An overview

Thermoplastic composites offer some interesting advantages over their thermoset counterparts like a higher toughness, faster manufacturing and their recyclable nature. Traditional melt processing, however, limits thermoplastic composite parts in size and thickness. As an alternative, reactive processing of textile fiber-reinforced thermoplastics is discussed in this paper: a low viscosity mono- or oligomeric precursor is used to impregnate the fibers, followed by in situ polymerization. Processes that are currently associated to manufacturing of thermoset composites like resin transfer molding, vacuum infusion and resin film infusion, might be used for manufacturing of thermoplastic composite parts in near future. This paper gives an overview of engineering and high-performance plastic materials that are suitable for reactive processing and discusses fundamental differences between reactive processing of thermoplastic and thermoset resins.     

Possibility of closed loop material recycling for fiber reinforced thermoplastic composites

It becomes significantly important to preserve ecological balance of the earth and protect the environment from getting worse. One of the urgent issues to be tackled will be to develop and establish recycling technology for polymeric composite materials. The expression of recycling technology in this case is that after the life of industrial products of fiber reinforced thermoplastic (FRTP) is completed, instead of being thrown away as wastes, they are reused as a raw material for new applications. An additional goal is that of saving valuable resources and not consuming further energy. This paper deals with a possibility of closed-loop recycling technologies for FRTP. The key factor is the fiber length which is expected to reduce in each recycling step. Materials tested here are continuous FRTPs, long FRTPs, short FRTPs, and powder reinforced plastics. The effect of fiber length on the reinforcing mechanism is first examined. The correlation between outdoor exposure test and accelerated weathering test is the second subject to covered. The third subject is to make clear the influence of crushing and heat history which are inevitable during each recycling stage. Throughout the above investigation, the concept of closed-loop recycling technologies has been established, although it is still in a preliminary stage.Abbreviations FRTP fiber reinforced thermoplastic - C-, L-, S-, P-FRTP continuous-, long-, short-FRTP, powder-RTP - FRP fiber reinforced thermosetting plastic - UD unidirectional - PP polypropylene - CF carbon fiber - GF glass fiber - V _f volume fraction of fiber     

Hot isostatic pressing of metal reinforced metal matrix composites

Metal reinforced Metal Matrix Composites (MMMCs) made by combining an aluminium alloy matrix with stainless steel reinforcing wires are potentially cheaper and tougher than continuous fibre ceramic reinforced Metal Matrix Composites (MMCs). Although they do not give as great enhancements in stiffness and strength, worthwhile gains are achieved. Such MMMCs can be produced by Hot Isostatic Pressing (HIPping), which reduces interfacial reactions in comparison with liquid metal routes. Here, stainless steel (316L) and commercial purity aluminium wires were used to make bundles which were inserted into mild steel cans for HIPping at 525 °C/120 min/100 MPa. Some stainless steel wires were pre-coated with A17Si, to examine the effect of coatings on mechanical properties. Specimens were evaluated in terms of their tensile and fatigue properties. During HIPping, cans collapsed anisotropically to give different cross-section shapes, and for larger diameter cans, there was also some longitudinal twisting. Wires tended to be better aligned after HIPping in the smaller diameter cans, which produced material having higher modulus and UTS. Higher volume fractions of reinforcement tend to give better fatigue properties. Composites with coated stainless steel wires gave higher composite elongation to failure than uncoated wires. Both uncoated and coated wires failed by fatigue during fatigue testing of the composite. This contrasts with ceramic reinforced MMCs where the fibres fracture at weak points and then pull out of the matrix.     

低配网率纤维编织网增强混凝土轴拉力学性能

通过单束纤维与纤维编织网增强混凝土(Textile reinforced concrete, TRC)薄板的单轴拉伸试验, 研究了纤维编织网增强混凝土这种新型材料的受力特征和影响其极限承载力的主要因素, 提出临界配网率的概念。以配网率为变化参数, 讨论了在低配网率(配网率小于1%)时材料的力学性能。当配网率大于临界配网率时, 纤维编织网增强混凝土薄板的极限承载力大于其开裂荷载, 加载过程中没有承载力突降; 随着配网率增加, 纤维的利用率随着配网率增加呈线性降低, 即纤维丝的强度并不能完全发挥。低配网率时, 随着配网率增加, 薄板的裂缝间距减小, 裂缝宽度下降。根据混合定律和ACK模型把TRC薄板的拉伸应力-应变曲线简化成三线型模型, 从宏观上提出了考虑配网率影响的极限承载力计算公式。      

Stochastic matrix-cracking model for textile reinforced cementitious composites under tensile loading

When cementitious composites are loaded in tension, cracks initiate and propagate at very low stress levels, leading to a non-linear constitutive behaviour. A first attempt to model this behaviour (the well-known ACK-model) was done by Aveston et al. [1] and Aveston and Kelly [2]. However, according to several authors [3–10], the main limitation of this model is the stochastic nature of the strength of the cementitious matrix, which is not included in the ACK-model. Based on the work of Curtin et al. [7, 10], presenting a statistical treatment of matrix crack evolution in unidirectionally reinforced ceramic micro-composites with single fibres; a two-parameter Weibull model is proposed in this paper to describe the matrix strength. It was shown by Curtin et al. [7, 10] that one can determine the Weibull parameters on pure matrix specimens and transfer them to the matrix behaviour in the composite, if single fibre ceramic composites are used. However, it has been determined that this is not the case when textile reinforcement is used in a cementitious matrix. As will be shown in this paper, this stochastic cracking model cannot be simply transferred from single fibre ceramic composites to cementitious matrices with fibre bundles. The necessary modifications to make it useful for textile-reinforced cements are discussed.     

Modelling the Young''s modulus of platelet reinforced thermoplastic sheet composites

Particulate reinforced polymers is a mature field and many models are available to predict the Young's modulus of such composites. However, most existing models have a common flaw; they all predict that the composite modulus equals that of the reinforcing agent when the polymer content approaches zero. This implies, in this limit, a monolithic reinforcement whereas, in fact, it is composed of discrete particles with very little interaction. This is a serious drawback and therefore this study focussed on deriving an improved model for the prediction of the Young's modulus. The porosity of the present samples was correlated with the volume fraction binder and the maximum packing density of the pure reinforcement. A theoretical model for Young's modulus was derived along the lines of the Padawer and Beecher modified Cox model. However, it includes the effect of composite porosity on the composite's mechanical properties. In contrast to other available models, it correctly predicts the loss of material stiffness and strength in the limit of zero binder content. Good agreement was found between the predictions of this model and experimental measurements.     

Quasi-static penetration resistance behavior of glass fiber reinforced thermoplastic composites

Quasi-static penetration resistance of a composite structure represents the energy dissipating capacity of the structure under transverse loading without dynamic and rate effects. In this paper, a comparative study of the quasi-static penetration resistance behavior of S-2 Glass/SC-15, S-2 Glass/HDPE and E-Glass/HDPE composite systems with varying thicknesses, i.e., 1.4–8.4-mm, is presented using the Quasi-Static Punch Shear Test (QS-PST) methodology developed earlier. The penetration resistance behavior is usually presented by a series of force–displacement graphs at different support conditions, the integral of which is the energy dissipated by the composite during the quasi-static penetration at corresponding support conditions. The penetration energy varies with the diameter of the support span which is usually higher than the punch diameter, and also with the thickness of the composite laminate. During QS-PST experiments, a flat punch of diameter 7.6-mm with a range of support spans 8.89–50.8-mm has been used to obtain varying support span to punch diameter ratios (i.e., SPR = D_S/D_P = 1.16, 1.33, 1.67, 2.00, 2.33, 2.67, etc.). In order to compare the penetration resistance behavior of three different material systems, the S-2 Glass/SC-15, S-2 Glass/HDPE and E-Glass/HDPE composites of identical layer counts are used and the S-2 Glass/SC15 composite system is considered as the baseline. Composite plate specimens are sectioned after the test and then dipped into an ink–alcohol solution to study the damage mechanisms at different SPRs. Non-linear penetration stiffness and an average penetration resistance force are defined to quantify the average penetration resistance of each material. S-2 Glass and E-Glass reinforced HDPE composite material showed lower stiffness, lower peak force, higher deflection, lower damage area, and lower energy dissipation as compared to the baseline. A detailed comparison of results is presented.     

Cost effective manufacturing process of thermoplastic matrix composites for the traditional industry: the example of a carbon-fiber reinforced thermoplastic flywheel

Composite materials were successfully introduced and are now widely used for aerospace applications. Due to their high specific strength and stiffness, polymer-based composite materials should also be attractive candidates for many products of the traditional industries such as gas turbines, oil industry, or water and gas piping. The introduction of composite materials in the traditional industry is however a very slow process. Many factors can be identified as possible reasons such as the lack of previous examples on which to assess the durability of such composite products or reparability issues. However, the major factor hindering a broader use of composite materials for traditional products remains cost. Unlike the case of the aerospace industry, the use of composite materials is often not an enabling technology for traditional products: steel designs can be modified in order to increase the current product limitations. Therefore, the price of the composite system should be competitive when compared to the price of the equivalent system based on traditional materials such as steel or aluminum. In order to illustrate this concept, the case of steel risers for deepwater oil production is shortly discussed in the introduction of the present paper. When trying to reduce the price of composite products, the challenge often lies in lowering the manufacturing cost. The present paper focuses on applied manufacturing methods for various parts and products aiming to reduce cost. The associated performance of hot pressing and winding of short fiber and continuous fiber reinforced thermoplastic (AS4/PEEK) are compared for a high-speed flywheel type of application. Based on the mechanical performance and ease of fabrication, conclusions are drawn on a promising area of further investigation.     

Micro-crack behavior of carbon fiber reinforced thermoplastic modified epoxy composites for cryogenic applications

Three different types of thermoplastics, poly(ether imide) (PEI), polycarbonate (PC), and poly(butylene terephthalate) (PBT) were used to modify epoxy for cryogenic applications. Carbon fiber reinforced thermoplastic modified epoxy composites were also prepared through vacuum-assisted resin transfer molding (RTM). Dynamic mechanical analysis (DMA) shows that the storage moduli of PEI, PC, and PBT modified epoxies are 30%, 21%, and 17% higher than that of the neat epoxy respectively. The impact strength of the modified epoxies at cryogenic temperature increases with increasing thermoplastic content up to 1.5 wt.% and then decreases for further loading (2.0 wt.%). The coefficient of thermal expansion (CTE) values of the PBT, PEI, and PC modified epoxies also decreased by 17.76%, 25.42%, and 30.15%, respectively, as compared with that of the neat epoxy. Optical microscopy image analysis suggests that the presence of PEI and PC in the carbon fiber reinforced epoxy composites can prevent the formation of micro-cracks. Therefore, both the PEI and PC were very effective in preventing micro-crack formation in the composites during thermal cycles at cryogenic condition due to their low CTE values and high impact strength.     

碳纤维机织物增强热塑性树脂复合材料热冲压叠层模型

针对碳纤维增强热塑性树脂复合材料(CFRTP)在热冲压成型过程中涉及到大变形、各向异性和多场耦合的现象,为了表征CFRTP在成型中的力学特征,基于有限元方法与连续介质力学理论提出了一种热塑性树脂基体与碳纤维机织物的叠层模型。与单独采用碳纤维机织物超弹性本构模型预测CFRTP成型性能的方法相比,提出的叠层模型能够表征成型温度、压边力和纤维取向对CFRTP成型缺陷的影响,并能优化热冲压成型工艺参数。这一叠层模型具有简单实用和材料参数容易确定的优点,为碳纤维机织物增强热塑性树脂复合材料成型的数值模拟和成型工艺优化奠定了理论基础。     

Mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane composites

A study on mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane (TPU) composites is presented in this paper. Kenaf bast fibre reinforced TPU composites were prepared via melt-mixing method using Haake Polydrive R600 internal mixer. The composites with 30% fibre loading were prepared based on some important parameters; i.e. 190 °C for reaction temperature, 11 min for reaction time and 400 rpm for rotating speed. The composites were subjected to soil burial tests where the purpose of these tests was to study the effect of moisture absorption on the mechanical properties of the composites. Tensile and flexural properties of the composites were determined before and after the soil burial tests for 20, 40, 60 and 80 days. The percentages of both moisture uptake and weight gain after soil burial tests were recorded. Tensile strength of kenaf fibre reinforced TPU composite dropped to ∼16.14 MPa after 80 days of soil burial test. It was also observed that there was no significant change in flexural properties of soil buried kenaf fibre reinforced TPU composite specimens.     

纳米改性连续纤维增强热塑性树脂复合材料及其力学性能研究进展

连续纤维增强热塑性树脂复合材料（CFRTP）具有易加工、可回收、力学性能优异等特点,在航空航天、汽车等领域的应用前景良好。随着纳米技术的发展,研究者发现利用纳米材料改性CFRTP可显著提升其性能。本文对纳米材料改性CFRTP领域的最新研究进展进行了综述,首先对CFRTP改性中常用的纳米材料（如碳纳米管、石墨烯以及无机纳米颗粒）和主要的改性方法（包括树脂基体中直接添加纳米填料和利用纳米材料对增强相纤维表面进行修饰）进行了介绍,在此基础上总结并讨论了纳米改性对CFRTP力学性能（包括界面结合性能、拉伸性能、动态力学性能以及冲击性能）的影响,最后对纳米材料改性CFRTP的发展方向进行了展望。      

Viscoelasticity of multi-layer textile reinforced polymer composites used in soccer balls

This paper gives details of a comprehensive dynamic mechanical analysis (DMA) material characterisation activity for all constituent layers of two modern-day thermoformed soccer balls. The resulting material data were used to define a series of viscoelastic finite element (FE) models of each ball design which incorporated the through-thickness composite material properties, including an internal latex bladder, woven fabric-based carcass and polymer based outer panels. The developed FE modelling methodology was found to accurately describe the viscoelastic kinetic energy loss characteristics apparent throughout a soccer ball impact at velocities which are typical of those experienced throughout play. The models have been validated by means of experimental impact testing under dynamic loading conditions. It was found that the viscoelastic material properties of the outer panels significantly affected ball impact characteristics, with outer panel materials exhibiting higher levels of viscous damping resulting in higher losses of kinetic energy.     

A rate-dependent non-orthogonal constitutive model for describing shear behaviour of woven reinforced thermoplastic composites

A rate dependent constitutive model for woven reinforced thermoplastic matrix composites at forming temperatures is proposed in this work. The model is formulated using a stress objective derivative based on the fibre rotation. Nonlinear shear behaviour is modelled as a polynomial function and the rate dependence is described using a Cowper–Symonds overstress law formulated in terms of shear angle rate. The model parameters are determined by means of bias extension tests. The applicability of the material model is validated through a forming experiment.