General definition of 3D warp interlock fabric architecture

3D warp interlock fabric can be used as a fibrous reinforcement for composite material. Despite of the numerous research papers dealing with this specific woven structure, few researches were conducted to clearly define this multi-layer fabric. Moreover, in many research papers, unskilled scientists of weaving technology have some difficulty to describe the different components of the 3D warp interlock fabric and sometimes make some confusion between the different architecture. Then, with a lack of a clear definition of these 3D multi-layer fabrics, most of the research papers are conducted on a very limited number of structures such as orthogonal, angle and layer to layer interlock.Thus, based on different definitions proposed by skilled scientists, a new general definition of a 3D warp interlock fabric has been proposed to better describe the position of the several yarns located inside the 3D woven structure. Thanks to this improved definition, we hope that the scientific community will use it in order to better design new architectures and conduct finer research based on these product parameters.     

Characterising the loading direction sensitivity of 3D woven composites: Effect of z-binder architecture

Three different architectures of 3D carbon fibre woven composites (orthogonal, ORT; layer-to-layer, LTL; angle interlock, AI) were tested in quasi-static uniaxial tension. Mechanical tests (tensile in on-axis of warp and weft directions as well as 45° off-axis) were carried out with the aim to study the loading direction sensitivity of these 3D woven composites. The z-binder architecture (the through-thickness reinforcement) has an effect on void content, directional fibre volume fraction, mechanical properties (on-axis and off-axis), failure mechanisms, energy absorption and fibre rotation angle in off-axis tested specimens. Out of all the examined architectures, 3D orthogonal woven composites (ORT) demonstrated a superior behaviour, especially when they were tested in 45° off-axis direction, indicated by high strain to failure (∼23%) and high translaminar energy absorption (∼40 MJ/m³). The z-binder yarns in ORT architecture suppress the localised damage and allow larger fibre rotation during the fibre “scissoring motion” that enables further strain to be sustained by the in-plane fabric layers during off-axis loading.     

Evaluation of the integrity of 3D orthogonal woven composites with embedded polymer optical fibers

Due to their high flexibility, high tensile strain and high fracture toughness, polymer optical fibers (POF) are excellent candidates to be utilized as embedded sensors for structure health monitoring of fiber reinforced composites. In 3D orthogonal woven structures yarns are laid straight and polymer optical fiber can be easily inserted during preform formation either as a replacement of constituents or between them. The results of the previous paper indicated how an optic fiber sensor can be integrated into 3D orthogonal woven preforms with no signal loss. This paper addresses whether incorporating POF into 3D orthogonal woven composites affects their structure integrity and performance characteristics. Range of 3D orthogonal woven composites with different number of layers and different weft densities was fabricated. The samples were manufactured with and without POF to determine the effect of embedding POF on composite structure integrity. Bending, tensile strength tests, and cross section analysis were conducted on the composite samples. Results revealed that integrity of 3D orthogonal woven composite was not affected by the presence of POF. Due to its high strain, embedded POF was able to withstand the stresses without failure as a result of conducting destructive tests of the composite samples. Micrograph of cross-section of composite samples showed that minimum distortion of the yarn cross-section in vicinity of POF and no presence of air pocked around the embedded POF which indicates that 3D woven preform provided a good host for embedded POF.     

A comparative study of tensile properties of non-crimp 3D orthogonal weave and multi-layer plain weave E-glass composites. Part 2: Comprehensive experimental results

This Part 2 paper presents results of comparative experimental study of progressive damage in 2D and 3D woven glass/epoxy composites under in-plane tensile loading. As Part 1, this Part 2 work is focused on the comparison of in-plane tensile properties of two non-crimp single-ply 3D orthogonal weave E-glass fibre composites on one side and a laminate reinforced with four plies of E-glass plain weave on the other. The damage investigation methodology combines mechanical testing with acoustic emission registration (that provides damage initiation thresholds), progressive cracks observation on transparent samples, full-field surface strain mapping and cracks observation on micrographs, altogether enabling for a thorough characterisation of the local micro- and meso-damage modes of the studied composites. The obtained results demonstrate that the non-crimp 3D orthogonal woven composites have significantly higher in-plane strengths, failure strains and damage initiation thresholds than their 2D woven laminated counterpart. The growth of transverse cracks in the yarns of 3D composites is delayed, and they are less prone to a yarn–matrix interfacial crack formation and propagation. Delaminations developing between the plies of plain weave fabric in the laminate at certain load level never appear in the 3D woven single-ply composites.     

Effect of ground granulate blast-furnace slag on corrosion performance of steel embedded in concrete

Corrosion of steel in concrete is one of the major causes of premature deterioration of reinforced concrete structures, leading to structural failure. To prevent the failure of concrete structures because of corrosion, impermeable and high performance concretes should be produced various mineral admixtures. In this study, plain and reinforced concrete members are produced with mineral admixtures replacing cement. Ground granulated blast-furnace slag (GGBFS) has replaced cement as mineral admixture at the ratios of 0%, 25% and 50%. The related tests have been conducted at the ages of 28 and 90, after exposing these produced plain and reinforced concrete members to two different curing conditions. The unit weight, ultrasonic pulse velocity, splitting tensile and compressive strength tests are conducted on plain concrete members. Half-cell potential and accelerated corrosion tests are also conducted on reinforced concrete members. According to the test results, it is concluded that the curing age and type are important and corrosion resistant concrete can be produced by using GGBFS mineral admixture at the ratio of 25%.     

Analytical elastic stiffness model for 3D woven orthogonal interlock composites

This research presents the development of an analytical model to predict the elastic stiffness performance of orthogonal interlock bound 3D woven composites as a consequence of altering the weaving parameters and constituent material types.     

Experimental investigation of three-dimensional woven composites

This paper summarizes an extensive experimental study of composites reinforced with three-dimensional woven preforms subjected to tensile, compressive and in-plane shear loading. Three innovative three-dimensional woven architectures were examined that utilize large 12 K and 24 K IM7 carbon tows, including two ply to ply angle interlock architectures and one orthogonal architecture. Additionally, a two-dimensional quasi-isotropic woven material was evaluated for comparison. Loads were applied in both the warp and the weft directions for tensile and compressive loading. Digital image correlation was used to investigate full field strains leading up to quasi-static failure. Experimental results including ultimate strengths and moduli are analyzed alongside representative failure modes. The orthogonal woven material was found to have both greater strength and modulus in tension and compression, though a ply to ply woven architecture was found to outperform the remaining three-dimensional architectures. Recommendations are made for improving the manufacturing processes of certain three-dimensional woven architectures.     

Meshfree modeling and homogenization of 3D orthogonal woven composites

In this paper, evaluation of 3D orthogonal woven fabric composite elastic moduli is achieved by applying meshfree methods on the micromechanical model of the woven composites. A new, realistic and smooth fabric unit cell model of 3D orthogonal woven composite is presented. As an alternative to finite element method, meshfree methods show a notable advantage, which is the simplicity in meshing while modeling the matrix and different yarns. Radial basis function and moving kriging interpolation are used for the shape function constructions. The Galerkin method is employed in formulating the discretized system equations. The numerical results are compared with the finite element and the experimental results.     

钢筋增强超高韧性水泥基复合材料(RUHTCC)梁弯曲性能影响的几何参数分析

具有超高韧性新型随机PVA短纤维增强的水泥基复合材料(UHTCC)代替传统的具有准脆性应力软化特征的混凝土或纤维混凝土材料制作的钢筋(RUHTCC)受弯梁,可提高承载力,改善构件的延性,并具有良好的损伤演变能力,被认为是一种抗震性能较好的新型构件形式。除了配筋率和UHTCC拉压材料性能外,截面几何尺寸是影响其弯曲性能的一个重要因素。基于受弯理论分析和试验验证,采用该理论公式对截面几何尺寸(截面高度、宽度以及面积)的影响规律进行了系列分析。结果发现:对承载力,梁高度比宽度影响明显,而对承载力提高幅度和变形而言,随梁高的增加而减小,梁宽没有影响;对裂缝控制来说,只要梁下边缘的极限拉应变小于UHTCC材料的极限拉应变,截面尺寸的变化几乎不影响裂缝宽度的大小。并进一步针对RUHTCC梁的受弯设计提出了一些设计建议。     

Fabrication and mechanical behaviors of cementitious composites reinforced by 3D woven lattice sandwich fabrics

Glass fibers were firstly woven to form three-dimensional (3D) woven lattice sandwich fabrics (WLSFs) which then were applied to reinforce cementitious foams and mortars to fabricate novel ductile cementitious composites. Failure behaviors of WLSF reinforced cementitious composite structures were studied through compression and three-point bending experiments. The WLSF greatly enhances the strength of cementitious foams at a level of four times. For cementitious mortars, compression strength of WLSF reinforced blocks is a little greater for the fraction of the textile is small as well as the compression strength of the textile pillars is not strong. But in flexure, excellent stretching ability of the glass fiber textiles greatly improves the flexural behavior of WLSF reinforced cementitious composite panels. Load capacity and ultimate deflection of these composite panels were greatly enhanced. Flexural capacity of the WLSF reinforced beam is four times greater. Reinforced by WLSF, failure of the cementitious composite is ductile.     

Influence of fibre architecture on the tensile,compressive and flexural behaviour of 3D woven composites

This paper presents a comprehensive study on the tensile, compressive, and flexural performance of six types of 3D woven carbon-fibre/epoxy composites which were manufactured using a traditional narrow fabric weaving loom and resin transfer moulding. Four orthogonal and two angle-interlock weaves were tested with the primary loading direction parallel to the warp direction. The mechanical performance was found to be affected by the distribution of resin rich regions and the waviness of the load-carrying fibres, which were determined by the fibre architectures. The binding points within the resin rich regions were found to be the damage initiation sites in all weave types under all loading conditions, which were confirmed with both visual observation and digital image correlation strain maps. Among all weave types, the angle interlock weave W-3 exhibited the highest properties under all loading conditions.     

Crack profile in RC,R/FRCC and R/HPFRCC members in tension

The theoretical approaches used for the evaluation of crack width in reinforced concrete (RC) structures, are generally based on the hypothesis of parallel crack surfaces. In this way, crack width measured on the concrete cover should be equal to that on the bar surface. The results of several experimental analyses, developed during the past years in many Research Institutes, do not justify this assumption. On the contrary, even in RC members under tensile actions, crack width appears wider on external surface than on rebar–concrete interface. To better define the effective crack profile of RC structures, a new model, able to analyze the whole structural response of RC ties, is here presented. In the proposed approach, all the physical phenomena involved in the cracking process are taken into account: the bond-slip behavior between steel rebar and tensile concrete, the nonlinear fracture mechanics of concrete in tension, and the mechanism of aggregate interlock. Crack profiles computed with this model seem to be in accordance with those experimentally measured in RC elements in tension. A good agreement between numerical results and experimental data is also found both in case of steel rebar and ordinary fiber reinforced cementitious composites (R/FRCC), and in case of steel rebar and high?performance fiber reinforced cementitious composites (R/HPFRCC).     

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。     

三维机织结构的几何模型

根据三维机织结构中纱线系统的组成和相应纱线的几何形态,建立了具有普适意义的几何模型,获得了组成三维机织结构各纱线系统在一个结构单元内的纱线长度和取向角,进而计算出纤维体积分数。随后,选择了基于11种不同接结组织的三维机织复合材料试样,测试了试样的纤维体积分数,所得的测试结果与模型输出的预测值有很好的一致性。利用所建立的模型还定量讨论了接结组织对纤维体积分数和取向角的影响。结果表明:分层接结可以提供比正交接结高的纤维体积分数;而正交接结中接结经具有较大的取向,有利于增强三维机织复合材料在厚度方向上的力学性能。     

Tensile properties and failure mechanisms of 3D woven GRP composites

Tensile tests were performed on glass reinforced polymer (GRP) composites with three-dimensional (3D) orthogonal, normal layered interlock, and offset layered interlock woven fibre architectures. The mechanical properties and failure mechanisms under tensile loading were similar for the three composites. Cracks formed at low strains within the resin-rich channels between the fibre tows and around the through-thickness binder yarns in the composites, although this damage did not alter the tensile properties. At higher applied tensile stresses the elastic modulus was reduced by 20–30% due to inelastic tow straightening and cracking around the most heavily crimped in-plane tows. Further softening occurred at higher strains by inelastic straightening of all the tows. Composite failure occurred within a localised region and the discrete tow rupture events that have caused tow lock-up and pullout mechanisms in other 3D woven composites were not observed.     

Transverse impact damage and energy absorption of 3-D multi-structured knitted composite

Knitted composites have higher failure deformation and energy absorption capacity under impact than other textile structural composites because of the yarn loop structures in knitted performs. Here we report the transverse impact behavior of a new kind of 3-D multi-structured knitted composite both in experimental and finite element simulation. The knitted composite is composed of two knitted fabrics: biaxial warp knitted fabric and interlock knitted fabric. The transverse impact behaviors of the 3-D knitted composite were tested with a modified split Hopkinson pressure bar (SHPB) apparatus. The load–displacement curves and damage morphologies were obtained to analyze the energy absorptions and impact damage mechanisms of the composite under different impact velocities. A unit-cell model based on the microstructure of the 3-D knitted composite was established to determine the composite deformation and damage when the composite impacted by a hemisphere-ended steel rod. Incorporated with the unit-cell model, a elasto-plastic constitute equation of the 3-D knitted composite and the critical damage area (CDA) failure theory of composites have been implemented as a vectorized user defined material law (VUMAT) for ABAQUS/Explicit. The load–displacement curves, impact deformations and damages obtained from FEM are compared with those in experimental. The good agreements of the comparisons prove the validity of the unit-cell model and user-defined subroutine VUMAT. This manifests the applicability of the VUMAT to characterization and design of the 3-D multi-structured knitted composite structures under other impulsive loading conditions.     

About the influence of temperature and matrix ductility on the behavior of carbon woven-ply PPS or epoxy laminates: Notched and unnotched laminates

Could thermoplastic-based composites be used to replace thermosetting-based composites in high-temperature secondary aircraft structures? The purpose of this work is to establish the ability of a material system to be used in aircraft engine nacelles when subjected to static loadings, with a key upper temperature of 120 °C. In order to provide answers to this question, the thermo-mechanical behaviors of carbon fiber fabric reinforced PPS or epoxy laminates have been compared specifically within the temperature change with 120 °C at the upper bound. The temperature-dependent ductile behavior of laminates is more or less exacerbated, depending on polymers glass transition temperature, and laminates stacking sequence. For both materials, the degree of retention of tensile mechanical properties is quite high in notched and unnotched quasi-isotropic laminates. A Digital Image Correlation technique has been used in order to understand the influence of temperature and matrix ductility on the mechanisms of overstresses accommodation near the hole. In fabric reinforced laminates, the high-temperature results suggest a competition between the mechanisms of damage, and the mechanism of plasticization, enhanced in angle-ply lay-ups. Thus, the highly ductile behavior of TP-based laminates, at temperatures higher than their T_g, is very effective to accommodate the overstresses near the hole.     

Longitudinal and transverse damage taxonomy in woven composite components

This work addresses the issue of micro-structural damage in the longitudinal direction of the woven during a deformation process, primarily in the tensile mode. This paper extends the insight into self-inflicted damage in dimensional multilayer woven composites subjected to uniaxial tensile and shear loading. Two composites made of multilayer woven architectures, hereby named: orthogonal and normal layer interlock forms the basis of this study. It identifies the physical characteristics which initiate the various damage modes, what these modes are and when they occur. This work complements the work already reported on the transverse direction in woven composites.