Influence of flow restriction on the microstructure and mechanical properties of long glass fiber-reinforced polyamide 6.6 composites for automotive applications

In this study, polyamide 6.6 with 40 wt% of long glass fibers was processed by injection molding into a mold with the ability to simulate controlled flow restriction. The mechanical properties of the molded test specimens were evaluated to verify the application of the composites as substitutes for metallic materials in automotive applications and the influence of flow restriction on these properties. Mathematical models were used to calculate the tensile strength of the composites in order to validate the experimental results. It was found that the presence of the controlled flow restriction affects fiber length as well fiber orientation, both of which influence the final mechanical properties of the composite. Moreover, a high degree of anisotropy in the mechanical properties was observed.     

Fracture behavior of injection-molded short and long glass fiber—polyamide 6.6 composites

Relationships between the fracture toughness, K_Q, and microstructure of chopped short (SGF) and long glass fiber (LGF) reinforced injection-molded polyamide 6.6 composites have been studied. K_Q and elastic modulus, E, of the composites were determined on compact tension specimens as a function of temperature, T, and crosshead speed, v. The microstructure of the composites was characterized by the dimensionless reinforcing effectiveness parameter, R, which was extended in this work for LGF reinforcement. R takes into account not only the processing-induced fiber layer structure, the fiber alignment and the fiber volume fraction but also the aspect ratio and aspect ratio distribution of the reinforcement. The semi-empirical linear relationship between fracture toughness of the composite, K_Q,C, and that of the matrix, K_Q,C, established for SGF-reinforced plastics, i.e. K_Q,C = MK_Q,M = (a + nR)K_Q,M still exists if the newly defined modified R is used. Both the matrix stress condition factor, a, and the energy absorption coefficient, n, have been determined under different testing conditions and tabulated together with K_Q,M. This allows an estimate of K_Q,C for any given R. Normalized fracture maps in form K_Q vs (E,T) have been constructed. Failure mechanisms of both the matrix and the composites which have been revealed by scanning electron microscopy are discussed and summarized in failure maps indicating changes of breakdown processes as a function of T and v.     

Influence of filler/reinforcing agent and post-curing on the flexural properties of woven and unidirectional glass fiber-reinforced composites

The aim of this study is to investigate the reinforcing effect of woven and unidirectional glass fibers and the effect of post-curing on the flexural strength and flexural modulus of glass fiber-reinforced composites. A series of composites containing 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane and triethyleneglycol dimethacrylate matrices and different reinforcements of unidirectional or woven glass fibers were prepared. The samples, 25 × 2 × 2 mm, were cured with a halogen curing lamp, followed by additional curing by thermal treatment at 135 ± 5 °C temperature and 60 psi pressure. Samples were tested before and after post-curing in order to determine the flexural strength and flexural modulus. The degree of reinforcement with glass fibers was varied between 14 and 57 wt% or 7.64 and 38.44 vol% by changing the number of unidirectional bundles or woven glass fiber bands in the composites, respectively. The obtained flexural strength values were in the range of 95.20–552.31 Mpa; the flexural modulus ranged between 2.17 and 14.7 GPa. The highest flexural strength and flexural modulus values were recorded for samples with unidirectional glass fibers. The mechanical qualities of the glass fibers-reinforced composites increased after post-curing treatment. Increasing of the glass fiber amount in the experimental composites improves both flexural strength and modulus. SEM micrographs of fractured composites indicate a strong interfacial interaction between the glass fibers and the polymer matrix.     

玻璃纤维增强复合材料的机械切割性能研究

从手糊成型层合板玻璃纤维增强复合材料的切割加工入手,利用单因素法测试切削参数对切削力的影响,观察试件加工表面状况,得到切削参数之间的关系式。首次提出切削参数关系因子R的概念,并对R在低速切割时的临界值RL进行了设定,为玻璃纤维增强复合材料的加工工艺参数取值提供了参考。     

Assessment of factors influencing surface roughness on the machining of glass fiber-reinforced polymer composites

In recent years, the utilization of glass fiber-reinforced polymers (GFRP) composite materials in many different engineering fields has undergone a tremendous increase. Accordingly, the need for accurate machining of composites has increased enormously. In the present work, an attempt has been made to assess the influence of machining parameters on the machining of GFRP composites. Design of experiments (full factorial design) concept has been used for experimentation. The machining experiments were conducted on all geared lathe using coated cermet tool inserts with two level of factors. The factors considered were cutting speed, work piece fiber orientation angle, depth of cut and feed rate. A procedure has been developed to assess and optimize the chosen factors to attain minimum surface roughness by incorporating: (i) response table and response graph; (ii) normal probability plot; (iii) interaction graphs; (iv) analysis of variance (ANOVA) technique.     

Assessment of flexural toughness and impact resistance of bundle-type polyamide fiber-reinforced concrete

This study compares the fiber/matrix bonding strength and flexural properties of bundle-type polyamide fibers to those of hooked-end steel fibers. Their fracture behavior upon impact with a high-velocity projectile is also assessed in terms of penetration depth, crater diameter and rear-side scabbing. The results obtained demonstrate that the bundle-type polyamide fibers undergo fracture without fiber pullout because of the increased interfiber gap and specific surface area for bonding, but exhibit poorer flexural fracture behavior with a lower flexural strength and fracture energy when compared to hooked-end steel fibers. Yet despite this, concrete reinforced with bundle-type fibers is shown to more effectively suppress scabbing during high-velocity impact, which is attributed to a more efficacious dispersion of shock stress due to the increased number of individual fibers.     

Influence of surface oxidation on thermal shock resistance and flexural strength of SiC/Al2O3 composites

It is known that SiC whisker/Al₂O₃ matrix composites can oxidize in air at high temperature and then form oxidation layers on their surfaces. Oxidation treatment has been experimentally performed in air at 1450 °C for a pre-determined time. The results show that the surface layer is in a state of compressive residual stress. The oxidized specimens have better resistance to thermal shock damage than the non-oxidized specimens. However, the surface oxidation can degrade the room-temperature flexural strength.     

Influence of fillers on abrasive wear of short glass fibre reinforced polyamide composites

Various composites of polyamide 6 filled with short glass fibre, polytetrafluoroethylene and metal powders viz. copper and bronze were formulated in the laboratory and characterised for their various mechanical properties such as tensile strength, tensile elongation, flexural strength, hardness and impact strength. Compositional analysis was done with gravimetry, solvent extraction and differential scanning calorimetry (DSC) techniques followed by tribo-performance evaluation in abrasive wear mode by abrading a sample against silicon carbide (SiC) abrasive paper in a single pass condition under various loads. It was observed that the fibre reinforcement deteriorated the abrasive wear resistance of virgin polymer. Combination of fibre and particulate filler was more detrimental in this respect. Efforts were made to correlate the wear performance with the appropriate mechanical properties. Under selected loading condition, wear as a function of product of hardness, elongation to break (e) and ultimate tensile strength (S) showed better correlation than Ranter-Lancaster plot. Scanning electron microscopy (SEM) was used to analyse the worn surfaces of the samples.     

超声振动对玻纤增强聚丙烯复合材料注射成型特性的影响

为了研究超声振动对纤维增强复合材料注射成型特性的影响,利用自行开发的超声辅助可视化注射成型实验装置对不同玻纤(GF)含量的GF增强聚丙烯(PP)复合材料进行了超声外场作用下的可视化实验,观测分析了超声功率对复合熔体充填流动行为的影响。此外,通过对试样不同部位的金相观察,分析了超声功率对复合材料纤维取向的影响。结果表明:超声功率会对复合材料注射成型的充填流动行为及制品的纤维取向产生影响,而复合材料纤维含量对超声振动的效果也有直接影响。在纤维含量较低时,超声振动对基体材料微观形态的作用为影响复合材料充填流动性及纤维取向的主因;在纤维含量较高时,超声振动对纤维的作用为影响复合材料充填流动性及纤维取向的主因。研究结果为复合材料超声辅助成型技术的发展提供了依据。     

A Study on flexural properties of wildcane grass fiber-reinforced polyester composites

The main objective of this study is to introduce a new natural fiber as reinforcement in polymers for making composites. Wildcane grass stalk fibers were extracted from its stem using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were intentionally reinforced in a polyester matrix unidirectionally, and the flexural properties of the composite were determined. The fibers extracted by retting process have a tensile strength of 159 MPa, modulus of 11.84 GPa, and an effective density of 0.844 g/cm³. The composites were formulated up to a maximum fiber volume fraction of 0.39, resulting in a flexural strength of 99.17 MPa and flexural modulus of 3.96 GPa for wildcane grass fibers extracted by retting. The flexural strength and the modulus of chemically extracted wildcane grass fiber composites have increased by approximately, 7 and 17%, respectively compared to those of composites made from fibers extracted by retting process. The flexural strength and the modulus of KMnO₄-treated fiber composites have increased by 12 and 76% over those of composites made from fibers extracted by retting process and decreased by 3 and 48% over those of composites made from fibers extracted by chemical process, respectively. The results of this study indicate that wildcane grass fibers have potential as reinforcing fillers in plastics in order to produce inexpensive materials with high toughness.     

Enhanced thermomechanical properties of long and short glass fiber-reinforced polyamide 6,6/polypropylene mixtures by tuning the processing procedures

Long and short glass fibers (GF) were incorporated into the polyamide 6,6 (PA66)/polypropylene (PP) mixtures in order to enhance the thermomechanical properties. The effect of fiber length and processing procedures on tensile strength, flexural modulus, impact strength, and heat deflection temperature has been investigated. Miscibility behavior of the PA66/PP mixtures has been examined by performing differential scanning calorimetry analysis and theoretical calculation. The mixtures exhibiting broad coexistent regions such as crystal + crystal (Cr₁ + Cr₂), crystal + liquid (Cr₁ + L₂), and liquid + crystal (L₁ + Cr₂) revealed a significant improvement in thermal and mechanical properties by the addition of GF. Especially, long fiber-reinforced thermoplastics showed better performances compared to short fiber-reinforced thermoplastics at the same filler loading. From the morphological observation of the fractured surface, it was realized that the incorporation of long GF after the melt blending of PA66 and PP was very effective to attain high thermomechanical properties due to the better homogeneity and compatibility.     

Influence of prepreg conditions on the void occurrence and tensile properties of woven glass fiber-reinforced polyimide composites

The influence of prepreg solvent content on void occurrence in woven glass fiber-reinforced polyimide composites and their tensile properties was studied. A precursor solution of SKYBOND 703 was diluted in an additional solvent (n-methyl pyrrolidone) and the glass woven fabric was immersed in about 40 wt.% polyamic acid, in solvent. Prepregs were dried at 373 K for different time intervals, ranging from 2 to 24 h. Prepregs with varying residual solvent content under each condition were laid up, and their [(0/90)]₄ composite laminates were formed by autoclaving at a hydrostatic pressure of 0.7 MPa. The relationship of drying time with the amount of residual prepreg solvent, as well as with the volume fractions of fiber and voids was investigated. The void geography and content for each composite laminate, and the tensile strength and modulus at room temperature were also evaluated. The results clearly indicated that, depending on the altering residual solvent content in the prepreg, the void geometry and location influenced reduction of the tensile properties of woven fabric composite laminate. An appropriate prepreg resin viscosity during curing, which avoids reduction of the tensile properties, was revealed.     

Compressive and flexural behavior of carbon fiber-reinforced PPS composites at elevated temperature

ABSTRACT

The effect of temperature on the mechanical behavior of carbon fiber reinforced polyphenylenesulfide (PPS) composites was investigated by compressive and flexural tests from ambient temperature up to 150°C. The failure morphologies of the C/PPS composites were analyzed to identify the variation of failure modes. Related results showed that the mechanical behavior of C/PPS composites decreased severely with the increase of temperature due to the softening of matrix. The PPS resin film tensile test was carried out and the PPS matrix behavior was recognized as the main factor to dominate the mechanical behavior of composites under compressive/flexural loading at elevated temperatures. It can be found that there was an approximate linear relationship between the compression properties of C/PPS composites and the PPS matrix. The dependence of failure modes of composites on temperatures was closely related to the mechanical behavior of PPS matrix.     

An experimental study of the water-assisted injection molding of glass fiber filled poly-butylene-terephthalate (PBT) composites

The purpose of this report was to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate (PBT) composites. Experiments were carried out on an 80-ton injection-molding machine equipped with a lab scale water injection system, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The materials included virgin PBT and a 15% glass fiber filled PBT composite, and a plate cavity with a rib across center was used. Various processing variables were examined in terms of their influence on the length of water penetration in molded parts, and mechanical property tests were performed on these parts. X-ray diffraction (XRD) was also used to identify the material and structural parameters. Finally, a comparison was made between water-assisted and gas-assisted injection molded parts. It was found that the melt fill pressure, melt temperature, and short shot size were the dominant parameters affecting water penetration behavior. Material at the mold-side exhibited a higher degree of crystallinity than that at the water-side. Parts molded by gas also showed a higher degree of crystallinity than those molded by water. Furthermore, the glass fibers near the surface of molded parts were found to be oriented mostly in the flow direction, but oriented substantially more perpendicular to the flow direction with increasing distance from the skin surface.     

Tension and flexural strength of silicon carbide fibre-reinforced glass ceramics

The use of silicon carbide-type fibres to reinforce lithium aluminosilicate glass ceramics results in composites with exceptional levels of strength and toughness. It is demonstrated that composite strength and stress-strain behaviour depend onin situ fibre strength, matrix composition, test technique and atmosphere of test. Both linear and non-linear tensile stress-strain curves are obtained with ultimate strengths at 22° C approaching 700 MPa and failure strains of 1%. Flexure tests performed at up to 1000° C in air are compared with data obtained in argon to demonstrate a significant dependence of strength and failure mode on test atmosphere. Finally, glass ceramic matrix composite performance is compared with a silicon carbide fibre-reinforced epoxy system to demonstrate the importance of matrix failure strain on strength and stress-strain behaviour.     

注塑级聚烯烃塑木复合材料性能研究

制备了注塑级塑木复合材料,研究了木粉添加量对塑木注塑成型复合材料流变性能、弯曲性能和熔融结晶性能的影响。结果表明:随木粉添加量的增加,塑木注塑成型复合材料弯曲强度、弯曲模量和熔融峰温度均出现先增加再降低的现象,当木粉添加量在30份时,复合材料弯曲强度达到30.85MPa,弯曲模量达到3065.21MPa,熔融峰温度也达到最高。     

Effects of surface roughness on the flexural strength of a hardmetal

A detailed study to assess the effect of surface roughness on three-point flexural strength of a WC-Co hardmetal was undertaken. Eight different types of surface finish were investigated;R-parameters were determined and Weibull statistics were applied to analyse the fracture strength results. It was concluded that the highest values of rupture stress and Weibull modulus are obtained when the surfaces and the edges of the specimens are submitted to careful and gradual, step-by-step, surface-finishing operations and a 1 m diamond paste is used as the final abrasive. Only when very fine finish is attained may the results of rupture stress then represent the intrinsic behaviour of the material.     

Isothermal crystallization kinetics of glass fiber and mineral-filled polyamide 6 composites

In this study, isothermal crystallization kinetics of polyamide 6 (PA6) composites reinforced with surface-treated glass fiber (GF) and natural, clay-type mineral (MN) were investigated by differential scanning calorimetry method in the presence and absence of a nucleating agent (NA). Microstructural features of the composites and interfacial interactions between filler and polyamide phases were also quantified by rheological measurements. The kinetic parameters for the isothermal melt-crystallization process of the samples were determined with the Avrami and Lauritzen–Hoffman models. The crystallization activation energies were determined by the Arrhenius method. It was found that the both fillers yielded a significant increase in the storage modulus of PA6. Kinetic calculations showed that the MN has a more pronounced acceleration effect on the crystallization rate of PA6 than the GF. Introduction of a small amount of NA significantly favored the isothermal crystallization rate of GF-reinforced PA6 but did not accelerate that of MN-reinforced one. Based on the results, it has been highlighted that PA6 composites reinforced with surface-treated GFs and including a small amount of clay-like mineral as a cheap and easy-accessible minor filler could yield the best performance for the injection-molded PA6 parts because the GF enhances the mechanical properties and the clay-like mineral accelerates the crystallization rate.