A design approach for the mechanical properties of polypropylene discontinuous fiber reinforced cementitious composites by extrusion molding

Polypropylene discontinuous fiber reinforced cementitious composites were prepared by extrusion molding and tested in uniaxial tension to determine the mechanical properties such as ultimate composite strength and strain, and the critical volume fraction for multiple cracking. It was shown that the experimentally determined critical fiber volume fraction reasonably agreed with the theoretical value predicted by a micromechanics model. The extruded fiber composites yielded the ultimate composite strength of 9.0 MPa and composite strain of 0.55% at the fiber volume fraction of 7.4%. Our experimental results suggest that there is an optimal fiber aspect ratio and fiber volume fraction for enhancing the fracture properties.     

A non-local void filling model to describe its dynamics during processing thermoplastic composites

A model is developed to describe the void dynamics within thermoplastic composite tape during the tape placement process. The model relates the volatile pressure in voids, the applied compaction load, fiber bed response and the resin pressure due to squeeze-flow of resin from resin-rich regions to fill void regions. This model relies on some geometric simplifications, but incorporates the relevant physical phenomena.This void consolidation model was implemented in a numerical code which predicts the void development during the process. The initial void geometry can be introduced either manually, using a random generation algorithm or from actual processed tape micrographs.The model predicts that the final void content depends on the original void content but also on the initial void distribution. Presented results analyze the influence of void distribution on tape consolidation. Limitations of the consolidation process rate by the resin squeeze flow pressures are clearly demonstrated.     

Compaction and Transverse Permeability of Glass Rovings

Continuous reinforcements such as glass rovings are used in a variety of polymer processes such as filament winding and compression molding. In all these processes, impregnation of the roving fiber bundle by the liquid polymer is essential. Modeling polymer impregnation requires an estimate of the void fraction-compressive stress relationship and the transverse Darcy permeability. The void fraction of 2400 tex glass rovings of different glass fiber diameters and roving thicknesses was assessed as a function of the applied compressive stress. The results indicate that existing void fraction-compressive stress models can be used to adequately fit the experimental data. The transverse permeability of these rovings was also measured as a function of applied compressive stress, fiber diameter, roving thickness, fluid velocity and viscosity using two different permeameters developed for this research. The permeability was observed to depend strongly on the compressive stress, and hence void fraction. As expected, the permeability was independent of the roving thickness, fluid velocity and viscosity. A Kozeny constant value of 7 was found to reasonably fit the data from both permeameters. Scatter of the experimental data was observed. It is hypothesized that this may be due to variations in the roving void fraction resulting from twists, cross-overs and waviness among the fibers.     

钢-聚丙烯纤维增强人造花岗岩复合材料的制备与性能

为深入研究钢-聚丙烯纤维增强人造花岗岩复合材料（钢-聚丙烯纤维/人造花岗岩）抗压、抗弯强度的影响因素,通过排水法实验研究了骨料堆积的空隙率,确定了骨料级配和实验指数q并对大量试件进行了抗压、抗弯强度测试,分析了钢-聚丙烯纤维/人造花岗岩复合材料各组分质量分数、骨料堆积空隙率等因素对钢-聚丙烯纤维/人造花岗岩复合材料抗压、抗弯强度的影响。实验结果表明:钢纤维与聚丙烯纤维能够明显增大钢-聚丙烯纤维/人造花岗岩复合材料的抗弯强度,随着钢-聚丙烯纤维质量分数的增加,钢-聚丙烯纤维/人造花岗岩复合材料试件的抗压和抗弯强度都逐渐增大;当钢纤维与聚丙烯纤维质量比为30∶1、钢-聚丙烯纤维质量分数为1.7wt%时,钢-聚丙烯纤维/人造花岗岩复合材料试件的抗压强度达到最大,当钢-聚丙烯纤维质量分数为1.9wt%时,钢-聚丙烯纤维/人造花岗岩试件的抗弯强度达到最大;黏结剂质量分数越接近骨料堆积空隙率,钢-聚丙烯纤维/人造花岗岩复合材料试件的抗压和抗弯强度越大,当骨料质量分数为80wt%、黏结剂质量分数为11wt%时,钢-聚丙烯纤维/人造花岗岩复合材料试件的抗压、抗弯强度同时达到最大。      

CF/PA12 composite femoral stems: Manufacturing and properties

The fabrication process for a novel carbon fiber-reinforced polymer (polyamide 12) composite femoral stem using inflatable bladder molding was studied. Effect of processing temperature, holding time and applied internal pressure on the consolidation quality of the composite was investigated. Consolidation quality was evaluated by density and void content measurements and scanning electron microscope analysis. As expected, void content (porosities) and presence of large resin pockets were found to increase for lower processing temperature, holding time and applied pressure. Crystallinity as well as melting temperatures measured using differential scanning calorimetry could be related to molding conditions. A progressive reduction of the previous thermal history (crystalline peak of neat composite) and an increase in crystallinity were obtained for higher molding temperature. Static compression testing with void content analysis of molded specimens was used to determine optimal molding conditions. The composite structure molded showed compressive modulus close to cortical bone’s. Compression load at failure of composites molded in optimal conditions were found to be three times higher than those of femoral bone for jumping on one leg or 10 times those for normal gait. The molded composite structure appears to be an excellent candidate for femoral stems used in total hip arthroplasty.     

Correlation of void distribution to VARTM manufacturing techniques

Vacuum assisted resin transfer molding (VARTM) is a liquid composite molding (LCM) technique used to manufacture large scale composite structures. Fiber preforms are placed on a tool surface and covered by a flow enhancement layer and a plastic bag. A vacuum is drawn on the system to infuse the resin. When the resin does not fully saturate the empty regions in between the fibers, voids are created. The fiber tows in woven and stitched preforms have a much lower permeability as compared to the bulk permeability of the fabric. Hence, fiber tows saturate with resin later than the pores between fiber tows and are more prone to voids.This study explores the impact of extended resin bleeding time and additional flow resistance at the vent on the void content within fiber tows both experimentally and by numerical simulation. Samples were machined from each of the manufactured panels and analyzed using image analysis techniques to obtain a relative void content. The experimental results were compared to results obtained by numerical simulation.The experimental void distribution showed that if resin is not allowed to bleed or if no external resistance is attached at the vent, the void content over the length of the part is not uniform. All void levels reduced when resistance was added or bleeding was allowed. The discrepancy between experimental and numerical results was addressed by including deformable distribution media in numerical model to capture the continuation of resin flow after the injection gate is closed.     

Mechanical behavior of carbon fiber reinforced polyamide composites

The purpose of this work is to compare tensile, compressive and interlaminar shear properties of different carbon reinforcement/polyamide composites obtained by interfacial polymerization and hot compression molding techniques. Two types of composite matrices were studied: polyamide 6 and polyamide 6/6, both reinforced by fabric and unidirectional carbon fibers. The effects of the fiber volume fraction and the matrix on mechanical properties were analyzed through tensile, interlaminar shear and compressive tests. In general, the results have shown a slight increase of the composite elastic modulus, tensile and compressive strength with the increase of carbon fiber content. The microscopic damage development within selected composites during the loading has been observed through optical and scanning electron microscope techniques and has shown that shear failure at the fiber/matrix interface has been mostly responsible for damage development, initiated at relatively low stress.     

Effect of curing cycle on void distribution and interlaminar shear strength in polymer-matrix composites

The effect of temperature cycle on the void volume fraction, shape and spatial distribution was determined by means of X-ray microtomography in [0]₁₀ AS4/8552 composite laminates manufactured by compression molding. Cure temperatures were designed to obtain different processing windows while the overall degree of cure was equivalent, leading to laminates with average porosities in the range 0.4% and 2.9%. Regardless of the final porosity, voids were elongated, oriented parallel to the fibers and concentrated in channels along the width of the laminate as a result of the inhomogeneous process of consolidation and resin flow along the fibers. The interlaminar shear strength was found to be controlled by the void volume fraction in panels with porosity above 1%.     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.     

Non-isothermal forming of glass fiber/polypropylene commingled yarn fabric composites

The commingled glass fiber/polypropylene (GF/PP) composites were fabricated using a double-belt press and the influence of temperature and velocity on the consolidation quality and mechanical performance of the composites were investigated. The contents and distribution of the voids in the composites were changed with varying the level of the processing parameters, and the composite tensile and flexural properties were dramatically decreased when the void contents were beyond 3.6%. Reducing the viscosity of the matrix or increasing the uniformity of fibers in the commingled yarns was important to improve the consolidation quality. But the production efficiency was not improved as hoped by increasing the velocity at higher temperatures because of the weakened interfacial bonding. The crystal form and crystallinity degree had no obvious changes under different processing conditions, but the composite mechanical performance was enhanced when the degree of order in the crystal structures was decreased, which might be caused by more effective stress transferring or less initial cracks.     

Permeability of natural fiber reinforcement for liquid composite molding processes

We investigate the influence of liquid type on the saturated permeability of natural fabrics in liquid composite molding processes. The permeability of flax woven fabric was characterized with two different liquids which have different viscosity, wettability, and sorption characteristics with flax fiber. From the experimental data, it was observed that the saturated permeability values were different for the liquid type. The fiber swell during the mold filling process and the corresponding change of fabric microstructure were assumed to be the main reason for this dependency of saturated permeability on the liquid type. The fiber swell due to the liquid sorption was characterized as a function of time, and the corresponding change of fiber diameter was investigated. The effective fiber volume fraction of wet natural fabric was defined in terms of fiber swelling ratio. The predictions by the classical Kozeny–Carman model and by the modified Kozeny–Carman model with two model constants were compared with the experimental data. It was shown that the modified Kozeny–Carman equation considering fiber swell could predict very well the saturated permeability of natural fabrics regardless of liquid type.     

液体模塑成型工艺用纤维织物厚度方向饱和渗透率的预测模型液体模塑成型工艺用纤维织物厚度方向饱和渗透率的预测模型

树脂在复合材料预成型体厚度方向的渗透能力对复合材料液体模塑成型工艺（LCM）的成功实施至关重要。本文采用连续加载的方式,研究了玻璃纤维增强树脂基复合材料液体成型过程中多轴向无屈曲织物（NCF）和斜纹织物（WF）的压缩响应行为,并建立描述该行为的数学模型。采用自制测试装置对预成型体在重力等不同注射压力驱动下的厚度方向渗透率进行测试,考察了预成型体纤维体积分数、测试流体注射压力等对预成型体厚度方向渗透率K_z的影响。基于预成型体压缩响应数学模型和厚度方向渗透率与注射压力的关系,对Kozeny-Carman公式进行修正,提出了变注射压力条件下的厚度方向渗透率预测模型。结果表明:预成型体厚度方向渗透率随着纤维体积分数的增大而减小,与Kozeny-Carman方程结果相符合。当纤维体积分数为0.42≤V_f≤0.58时,注射压力对厚度方向渗透率影响较大,实验结果验证了本文提出的预测模型;当纤维体积分数V_f≥0.58时,注射压力对厚度方向渗透率影响较小,厚度方向渗透率趋于恒定。      

UHMWPE纤维增强LDPE复合材料的界面形态研究

为实现聚乙烯单聚合物复合材料(PE SPC)的嵌件注射成型,研究基体与增强体间的界面非常关键.本文采用超高分子量聚乙烯(UHMWPE)纤维增强低密度聚乙烯(LDPE)基体,对纤维和基体进行了差示扫描量热仪测试,在偏光显微镜下模拟了基体与纤维的复合过程,研究不同因素对复合材料界面结晶形态的影响.根据DSC确定了UHMWPE和LDPE复合的温度范围在110.98~147.14℃;合适的温度和剪切作用都有利于界面横晶的产生,从而使基体和纤维产生更好的粘结,提高复合材料的力学性能;温度比剪切的影响更大,注射温度设置在125~135℃可在保证纤维与基体复合的情况下不破坏纤维的增强作用;纤维丝之间会相互影响界面结晶形态,部分界面有横晶产生,说明在实际注射成型过程中纤维束或纤维布的结构对基体渗透和界面形成有较大影响.     

三维编织超高分子量聚乙烯纤维-碳纤维混杂增强环氧树脂复合材料摩擦磨损性能

以超高分子量聚乙烯纤维(UHMWPE)-碳纤维(CF)三维混杂编织体为增强体,环氧树脂(ER)为基体,通过树脂传递模塑(RTM)工艺制备了三维编织混杂复合材料,研究了其摩擦磨损性能了,并采用混合正压力模型对摩擦系数进行了预测。结果表明,在纤维总体积含量一定的情况下,随着CF体积含量的增加,复合材料的摩擦系数增大,而其比磨损率降低。UH_3D/ER复合材料的磨损机制以粘着磨损为主,CF_3D/ER复合材料则以磨粒磨损为主,混杂复合材料的磨损机制主要取决于CF与UHMWPE纤维的相对含量 ,通过调节UHMWPE纤维和CF的体积比例可实现对复合材料摩擦磨损性能的有效调控。采用的计算模型可较好地预测UH_3D/ER的摩擦系数。     

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%V_f). The short beam strength increased up to %V_f of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component.     

废旧线路板粉料/玻璃纤维增强复合材料研制

以废旧线路板回收处理过程中得到的塑料粉料与玻璃纤维作为增强材料,采用模压成型的方法制备成不饱和聚酯复合材料。研究了模压工艺参数以及废弃物粉末填料配比等对复合材料力学性能的影响规律,并初步展望了废弃物复合材料的应用。结果表明,随着模压温度、压强、模压时间和填料含量的增加,复合材料的弯曲强度先升高后降低;在优化的模压工艺参数条件下,用废弃粉体与短切玻璃纤维作为组合增强体,制得的不饱和聚酯复合材料的力学性能远大于仅用废弃粉体作为增强体的力学性能,其弯曲强度和冲击强度可达150MPa、18kJ/m2。     

Processing of PLA/sisal fiber biocomposites using direct- and extrusion-injection molding

The processing strategy adopted to develop biocomposites plays a significant role in determining their characteristics. The present experimental investigation explores the feasibility of using direct-injection molding (D-IM) process for processing of sisal fiber (3?mm and 8?mm) reinforced poly-lactic acid biocomposites with a fiber weight fraction of 30%. For a comparative analysis, mechanical and morphological behavior of biocomposites developed using D-IM process is compared with biocomposites developed using extrusion-injection molding (E-IM) process. The mechanical behavior in terms of tensile, flexural and impact properties is compared and discussed in relation to extracted fiber morphology and fiber orientation as well as dispersion within the developed biocomposites. Morphological investigation of extracted fibers revealed severe fiber attrition and fiber length variation during E-IM process as compared with D-IM process. However, short sisal fiber (3?mm) reinforced biocomposites developed using both the processes exhibit uniform fiber dispersion and orientation, resulting in comparable mechanical properties. The tensile and flexural strength of D-IM-SF biocomposites increased remarkably by 34.7% and 15.9%, respectively, as compared with D-IM-LF biocomposites. Similarly, the tensile and flexural modulus of D-IM-SF biocomposites increased significantly by 92.5% and 56.7%, respectively, as compared with D-IM-LF biocomposites. However, D-IM process incorporating long fibers exhibit better impact properties.     

On the recyclability of a cyclic thermoplastic composite material

The recyclability of a novel cyclic thermoplastic composite material has been investigated. The virgin composite was prepared by liquid molding the cyclic thermoplastic resin and a knitted glass fabric. The resultant high fiber content composite (58.7% fiber weight fraction) was recycled by grinding/compounding/injection molding process. A variety of physical and mechanical tests were then conducted on the blended cyclic composite and a baseline, commercially available short fiber reinforced thermoplastic composite. In general, the recycled cyclic composite demonstrated comparable properties to the baseline material. The only exception being the ultimate tensile elongation of the recyclate, which was almost 25% lower than that of the baseline.     

Experimental investigation of carbon fiber reinforced poly(phenylene sulfide) composites prepared using a double-belt press

The high-performance carbon fiber reinforced poly(phenylene sulfide) composites were continuously fabricated using thermoplastic prepregs in a double-belt press. The effects of process velocity on the composite consolidation quality and mechanical properties were investigated. It is found that the tensile and interlaminar shear properties of composites prepared using the double-belt press are comparable to that of compression-molded composites when the process velocity is no more than 0.20 m·min⁻¹. The composite fracture morphologies also show different failure mechanisms between different samples and indicate that the interfacial adhesion strength may play a vital role in the mechanical properties of CF/PPS composites. Furthermore, experimental results show that the heating time above 330 °C should be over 440 s and the void content should be lower than 2.38% in order to obtain high performance CF/PPS composites.     

碳纤维复合材料层合板压缩性能的相关影响因素

碳纤维作为一种新型的增强材料,具有优良的理化性能,已在多个领域广泛应用.由于单向碳纤维复合材料层合板的压缩强度较低,其在结构复合材料方面的应用受到限制,提高其压缩性能成为关键.本文综述了影响碳纤维复合材料层合板压缩性能的相关因素,详细介绍了纤维弯曲、孔隙率、纤维体积分数、树脂性能等影响因素对碳纤维复合材料层合板的重要性,以及各影响因素之间的关系等,为提高碳纤维复合材料层合板压缩性能的研究提供了参考.