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.     

The mechanical performance of 3D woven sandwich composites

Composite sandwich structures were manufactured from a 3D woven fabric consisting of two face fabrics interconnected by pile yarns (Distance Fabric). Specimens were produced from Distance Fabric (DF) consolidated with vinyl ester resin with and without a polyurethane foam core and compared to specimens produced from a precast polyurethane foam core with composite skins added separately. Flatwise compression, edgewise compression, climbing drum peel and flexure tests were conducted and all demonstrated a dramatic improvement in properties from the combination of DF and foam core. These improvements are postulated to arise from the mutual reinforcement of the pile yarns and foam core.     

三维机织复合材料多尺度黏弹性分析

建立了一种三维机织复合材料多尺度的黏弹性分析模型。首先构造了微观尺度纱线束胞元和细观尺度复合材料周期结构胞元两级有限元模型, 由微观尺度胞元分析得到纱线束的弹性常数, 再代入细观尺度胞元计算出复合材料的平均弹性常数。两级胞元模型均施加周期边界条件, 保证了胞元边界上位移和应力满足周期性和连续性。随后分别建立了树脂基体和浸润树脂纱线束的蠕变模型, 用实验标定树脂的蠕变参数, 代入微观尺度胞元进行蠕变计算来修正纱线束蠕变模型的参数。最后将树脂和纱线束的蠕变本构关系应用于细观尺度胞元, 得到材料宏观平均的应力-应变响应, 模拟了三维机织复合材料的蠕变实验曲线。本文模型对于该种复合材料弹性常数和蠕变性能的预测, 均与实验吻合。      

Micromechanics models for mechanical and thermomechanical properties of 3D through-the-thickness angle interlock woven composites

In this paper, a laminate block modeling approach for three-dimensional (3D) through-the-thickness angle interlock woven composites is used to develop one finite element analysis (FEA) model and two analytical models, namely the “ZXY model” and the “ZYX model”. These models can be used to determine the mechanical properties and the coefficients of thermal expansion for 3D through-the-thickness angle interlock woven composites. A parametric study shows that there is good agreement between these FEA and analytical models. The parametric study also demonstrates the effects of the fiber volume fraction of the warp weaver (i.e., z yarn) and the space between two adjacent filler yarns on the mechanical properties and the coefficients of thermal expansion. Finally, the present models are found to correlate reasonably well with the predicted and measured results available in the literature.     

Assessment of the mechanical properties of a new 3D woven fibre composite material

Fully interlaced 3D fabric is produced by a new weaving technology, and it is here utilised to produce woven carbon fibre preforms, which are then used as reinforcement in composite materials. The purpose of this study is to assess the mechanical performance of this new type of composite material. A prototype loom was used to weave preforms with a rectangular cross-section where all warp and weft yarns were fully interlaced in plain weave. Tensile, compressive, out-of-plane, shear and flexural properties of the composite flat beam specimens were tested. The in-plane stiffness and strength were found to be lower, while the out-of-plane properties were higher compared to conventional 2D laminates. In terms of strength, it was not possible to quantify the difference, since the specimens with 3D woven material exhibited other failure modes than those tested for.     

Fabrication and characterization of three-dimensional cellular-matrix composites reinforced with woven carbon fabric

A low-density three-dimensional cellular-matrix composite reinforced with woven carbon fabric (3DCMC), was fabricated by means of a pressure-quenching molding technique with nitrogen gas as the blowing agent. Epoxy resins in the interstices of yarns in the 3DCMC samples were vacated during the foaming process and needle shaped voids were also generated between fibers in yarns. The average density of the 3DCMC samples was about 10³ kg/m³, and their density reduction was 28–37% compared with a regular matrix composite with the same preform. The 3DCMC has 32–42% higher specific tensile strength, 14–37% greater specific tensile modulus, a lower specific flexure strength but 35% higher specific tangent modulus in 3-point bending, a 30–40% higher specific impact energy absorption at an impact velocity around 120 m/s and a similar specific energy absorption at about 220 m/s. Meanwhile, the 3-point bending and impact test results of 3DCMC showed that they have different fracture mechanisms from that of 3DRMC.     

Fabrication of 3D carbon nanotube/porous carbon hybrid materials

Three dimensional hybrid carbon materials have been prepared using different biomass-derived porous carbons as catalyst supports for growing multi-walled carbon nanotubes (MWCNTs) via a chemical vapor deposition method. The nickel catalyst-loaded supports before and after growing MWCNTs were characterized by scanning and transmission electron microscopy, Fourier transform infrared spectroscopy spectra, and mercury porosimetry. The results show that the grown MWCNTs microstructures are closely related to the porous structures and surface conditions of the carbon supports. By using bamboo as template, a porous carbon support with a large total pore volume, appropriate pore size, and abundant favorable surface functional groups is obtained, which is found to be an ideal support for growing the MWCNTs. Investigation of growth mechanism demonstrated that the combination of appropriate porous structures and surface conditions plays an essential role in catalyst distribution and MWCNTs growth.     

Fabrication and characterization of three-dimensional PMR polyimide composites reinforced with woven basalt fabric

A PMR polyimide composite reinforced with three-dimensional (3D) woven basalt fabric is fabricated for medium high temperature applications. The PMR polyimide matrix resin is derived from 4,4′-methylenediamine (MDA), diethyl ester of 3,3′,4,4′-oxydiphthalic (ODPE) and monoethyl ester of Cis-5-norbornene-endo-2,3-dicarboxylic acid (NE). The rheological properties of the PMR polyimide matrix resin are investigated. Based on the curing reaction of the PMR type polyimide and the rheological properties, an optimum two-step fabrication method is proposed. The three dimensional fabric preforms are impregnated with the polyimide resin in a vacuum oven at 70 °C for 1 h followed by removing the solvent and pre-imidization. The composites are then consolidated by an optimized molding procedure. Scanning electron microscopy analysis shows that needle shaped voids are generated in yarns and the void volume fraction is 4.27%. The decomposition temperature and the temperature at 5% weight loss of the composite post-cured at 320 °C for 24 h are 440 °C and 577 °C, respectively. The dielectric constant and the dielectric loss of the composite are measured by circular cavity method at 7–12 GHz. The tensile strength and the modulus in the warp direction of the composite are 436 MPa and 22.7 GPa. The composite shows a layer-by-layer fracture mode in three-point bending test. The flexure strength and modulus in the warp direction of the composite are 673 MPa and 27.1 GPa, respectively.     

2D and 3D imaging of fatigue failure mechanisms of 3D woven composites

A detailed investigation of the failure mechanisms for angle-interlocked (AI) and modified layer-to-layer (MLL) three dimensional (3D) woven composites under tension–tension (T–T) fatigue loading has been conducted using surface optical microscopy, cross-sectional SEM imaging, and non-destructive X-ray computed tomography (CT). X-ray microCT has revealed how cracks including surface matrix cracks, transverse matrix cracks, fibre/matrix interfacial debonding or delamination develop, and has delineated the complex 3D morphology of these cracks in relation to fibre architecture. For both weaves examined, transverse cracks soon become uniformly distributed in the weft yarns. A higher crack density was found in the AI composite than the MLL composite. Transverse cracking initiates in the fibre rich regions of weft yarns rather than the resin rich regions. Delaminations in the failed MLL specimen were more extensive than the AI specimen. It is suggested that for the MLL composite that debonding between the binder yarns and surrounding material is the predominant damage mechanism.     

Fabrication and characterization of RF nanoantenna on a nanoliter-scale 3D microcontainer

We report the design and fabrication of a nanoantenna structure on the surface of a 3D nanoliter-scale container for the development of communicable nanoliter-scale chemical delivery systems. The porous container was self-assembled, after which the nanoantenna was fabricated on the top of the microcontainer using focused ion beam (FIB) ion-induced metal deposition. The nanoantenna was structured as a rectangular metal coil composed of platinum (Pt) nanowires (70?nm in width). The response of the nanoantenna structure was simulated using finite element software and showed a strong resonant feature at 10.8?GHz, which was confirmed by high frequency measurements.     

Review: 3D woven honeycomb composites

Journal of Materials Science - Honeycomb is considered an excellent structural material because of its high strength and shear rigidity, excellent energy absorbing property, high impact strength,...     

Fabrication and characterization of three dimensional woven carbon fiber/silica ceramic matrix composites

Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO₂ CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO₂ CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO₂ and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO₂ CMC was 96.9 kJ/m², almost 4 times as much as those for typical other carbon fiber reinforced CMCs.     

Preparation and characterization of gypsum-based materials used for 3D robocasting

In this study, gypsum-based materials (GM) comprising mainly α-hemihydrate gypsum, polycarboxylate, hydroxypropyl methyl cellulose and starch ether were prepared and used for 3D robocasting (3DR). The setting time and rheological properties of the GM slurry and the physical properties of the GM sample, including bulk density, porosity and mechanical strength, were investigated. The results indicate that the GM slurry exhibits an obvious shear thinning behavior and a good shape fidelity. The measured dynamic yield stress, final viscosity and initial storage modulus of the GM slurry are as high as 420.73 Pa, 7.29 Pa s and 273.86 kPa, respectively. Meanwhile, the GM slurry presents an adequate initial setting time of 68 min compared with a printing time of 14 min. In addition, the GM sample prepared by 3DR has a high compressive strength of 64.96?±?5.98 MPa and a bending strength of 15.24?±?1.58 MPa. These mechanical strengths are comparable with those of the GM and pure gypsum plaster sample prepared by traditional molding. Generally, the 3DR of GM is a promising method to improve the mechanical strength of printed gypsum products and presents great application prospects in the building of complex large-scale structures.     

Fabrication and mechanical evaluation of hydroxyapatite/oxide nano-composite materials

In the current study, the semiconducting metal oxides such as nano-ZnO and SiO₂ powders were prepared via sol–gel technique and conducted on nano-hydroxyapatite (nHA) which was synthesized by chemical precipitation. The properties of fabricated nano-structured composites containing different ratios of HA, ZnO and SiO₂ were examined using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The effect of the variation of ratios between the three components on mechanical, microstructure and in-vitro properties was assessed to explore the possibility of enhancing these properties. The results proved that the mechanical properties exhibited an increment with increasing the ZnO content at the extent of HA. In-vitro study proved the formation and nucleation of apatite onto the surface of the fabricated composites after one week of immersion. It is concluded that HA composites containing SiO₂ or SiO₂/ZnO content had a suitable mechanical properties and ability to form apatite particles onto the composite surface. Based on bioactivity behavior, Si-HA is more bioactive than pure hydroxyapatite and nano-arrangements will provide an interface for better bone formation. Therefore, these nano-composites will be promising as bone substitutes especially in load bearing sites.     

Fabrication and characterization of rare earth hexaboride single-crystal materials

Oriented single crystals of LaB₆, CeB₆ and PrB₆ have been prepared by the arc float-zone refining technique, which is described. A critique of the various possible preparation techniques is given. Wet chemical methods were used to determine bulk stoichiometries of samples prepared from starting materials of various R/B compositions (where R = rare earth). It was found that LaB_6,09, a desired composition, could be grown in single-crystal form from LaB_6.2 starting material, the excess boron compensating for preferential boron vaporization. Starting materials with B/La < 6.2 produce a B/La gradient in two-pass zone-refined specimens. The level of metallic impurities in arc zone-refined LaB₆ is lower than that reported elsewhere for laser zone-refined LaB₆. Residual oxygen present in the zone-refined specimens was found to produce second-phase inclusions, which were studied in detail. The effect of contamination of LaB₆ surfaces by evaporated refractory metals has also been investigated.     

A mechanistic interpretation of the comparative in-plane mechanical properties of 3D woven,stitched and pinned composites

A comparison of substantial published data for 3D woven, stitched and pinned composites quantifies the advantages and disadvantages of these different types of through-thickness reinforcement for in-plane mechanical properties. Stitching or 3D weaving can either improve or degrade the tension, compression, flexure and interlaminar shear properties, usually by less than 20%. Furthermore, the property changes are not strongly influenced by the volume content or diameter of the through-thickness reinforcement for these two processes. One implication of this result is that high levels of through-thickness reinforcement can be incorporated where needed to achieve high impact damage resistance. In contrast, pinning always degrades in-plane properties and fatigue performance, to a degree that increases monotonically with the volume content and diameter of the pins. Property trends are interpreted where possible in terms of known failure mechanisms and expectations from modelling. Some major gaps in data and mechanistic understanding are identified, with specific suggestions for new standards for recording data and new types of experiments.     

Finite element simulation and experimental study on mechanical behavior of 3D woven glass fiber composite sandwich panels

The results of finite element simulation followed by an experimental study are presented in order to investigate the mechanical behavior of three-dimensional woven glass-fiber sandwich composites using FE method. Experimental load–displacement curves were obtained for flatwise compressive, edgewise compressive, shear, three-point bending and four-point bending loads on the specimens with three different core thicknesses in two principal directions of the sandwich panels, called warp and weft. A 3D finite element model is employed consisting of glass fabric and surrounding epoxy resin matrix in order to predict the mechanical behavior of such complex structures. Comparison between the finite element predictions and experimental data showed good agreement which implies that the FE simulation can be used instead of time-consuming experimental procedures to study the effect of different parameters on mechanical properties of the 3D woven sandwich composites.     

Fabrication of nano-scale Cu bond pads with seal design in 3D integration applications

A method to fabricate nano-scale Cu bond pads for improving bonding quality in 3D integration applications is reported. The effect of Cu bonding quality on inter-level via structural reliability for 3D integration applications is investigated. We developed a Cu nano-scale-height bond pad structure and fabrication process for improved bonding quality by recessing oxides using a combination of SiO2 CMP process and dilute HF wet etching. In addition, in order to achieve improved wafer-level bonding, we introduced a seal design concept that prevents corrosion and provides extra mechanical support. Demonstrations of these concepts and processes provide the feasibility of reliable nano-scale 3D integration applications.     

三维机织复合材料结构表征与实体造型

利用经纱脉络描述法解决了任意三维机织复合材料的结构表征问题;提出了单胞分解法与亚胞向量概念,实现了三维结构的二维化、数字化,根据数字表征结果和经典截面假设构造了初始断裂模型;使用一种迭代算法对初始断裂模型进行优化,使纱线束逐步逼近真实形态,进而实现三维实体造型,在此基础上进行网格剖分。研究结果表明,迭代算法能够使纱线形态趋于自然,使造型结果接近实际。数值分析结果表明,迭代算法中的经纬纱退让系数介于0.6～0.7之间时,迭代收敛速度最快。     

一种微尺度有序增强复合材料的制备及其力学性能表征

选择聚氨酯改性环氧树脂作为基体,利用微加工工艺制备了一种以电镀镍丝作为增强体的微尺寸有序增强聚合物基体复合材料。ANSYS有限元仿真结果表明基体完全包裹增强体能够很好地缓解应力集中,当增强体的排布角度为45°,体积含量为62.5%时,复合材料变形过程中应力集中程度相对最弱。对制备的微尺寸复合材料进行了DMA拉伸测试,结果表明相比单一的聚合物基体材料,有序增强复合结构材料的抗拉强度和弹性模量分别约提高了4倍和3倍,最后,通过扫描电镜观察了试样断口,对其拉伸断裂过程进行了合理分析。