Characterization of thermoplastic natural fibre composites made from woven hybrid yarn prepregs with different weave pattern

This paper focuses on the effect of weave structure on mechanical behaviour and moisture absorption of the PLA/hemp woven fabric composites made by compression moulding. The unidirectional woven fabric prepregs were made from PLA (warp) and PLA/hemp wrapped-spun hybrid yarn (weft) with two different weave patterns; 8-harness satin and basket. Unidirectional composites with 30 mass% hemp content were fabricated from these prepregs, and compared to winded PLA/hemp hybrid yarn laminates with same composition. The composite from the satin fabric had significantly lowest porosities and best mechanical properties compared to the composite made from the winded hybrid yarn and basket fabric. The tensile, flexural, and impact strength were 88 MPa, 113.64 MPa, and 24.24 kJ/m², respectively. The effect of weave pattern on water absorption is significant. Although the composite from hybrid yarn laminate has larger water absorption than that of the pure PLA, it exhibits lower moisture absorption than both weaves.     

Mechanical and sliding wear properties of multi-layered laminates from glass fabric/graphite/epoxy composites

Multi-layered laminates of bi-directionally woven E-glass fabric/epoxy with different loading of graphite particles were made by hand layup followed by compression molding. Tensile and flexural behaviors, impact strength, hardness and density of these laminates were determined. Wear behaviors of these composites were investigated by a pin-on-disc wear test apparatus. Specific wear rates of these composites strongly depend on their filler content and applied normal loads. The hybrid composite containing 3 wt% of graphite exhibits the optimum mechanical and wear performances. A further increase in the graphite content increases the specific wear rate and deteriorates the mechanical behavior. The lowest (σ e)⁻¹ factor (the reciprocal of the product of tensile strength and elongation at break) signifies the lowest specific wear rate. The results of the morphology study of the wear test specimens support the results of the wear test.     

Polyamide single polymer composites prepared via in situ anionic polymerization of ε-caprolactam

In order to prepare the polyamide single polymer composites (SPC_PA) comprised of polyamide 6 (PA6) fiber and PA6 matrix, a novel method based on the in situ anionic polymerization of ε-caprolactam was developed. The influence of a critical process parameter, molding temperature, on the structure of SPC_PA was investigated by thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Mechanical properties of SPC_PA prepared at 140, 160, 180, and 200 °C were appraised by three-point bending and tensile test. An optimum molding temperature (160 °C) at which both the tensile and flexural strength reached a peak value was found in the studied molding temperature range. High reaction degree (>93%), low void fraction (<2.5%) and strong and stable fiber/matrix interface contributed to the obvious reinforcing effect of PA6 fibers on PA6 matrix.     

Commingled yarn composites for rapid processing of complex shapes

Commingled yarns of reinforcing and thermoplastic fibres offer a potential for low-cost manufacturing of complex-shaped composite parts, due to reduced impregnation times and applied pressures during processing. In order to benefit from this competitive advantage, the process parameters governing consolidation must be controlled. In this study, a consolidation model, previously validated for unidirectional commingled yarn fabrics processed isothermally in a flat matched-die mould, is applied to three other processing techniques capable of producing complex-shaped composites. Tubes of braided commingled yarns were manufactured by bladder inflation moulding. Selectively reinforced polymeric parts were processed by compression–injection moulding. Stamp forming was also used to allow high-speed processing of commingled yarn-based laminates. Besides particular stamp forming cases, for which part deconsolidation occurred, the model predictions were in good agreement with the void content values obtained from specimens consolidated under different processing conditions. This suggests that the consolidation model can be successfully applied to a wide range of yarn architectures and processing techniques.     

Mechanical properties of woven glass fabric reinforced in situ polymerized poly(butylene terephthalate) composites

Cyclic butylene terephthalate (CBT) has been polymerized in situ at T = 190 °C in the presence and absence of woven glass fabric (WGF). The thermal properties of the in situ polymerized poly(butylene terephthalate) (ISP-PBT) were compared with those of a commercial injection molded PBT (IM-PBT). It was found that the crystallinity of IM-PBT is markedly lower than that of ISP-PBT rendering the latter more brittle. WGF-reinforced (ca. 50 vol.%) ISP-PBT composites were fabricated by compression molding at T = 190 °C using displacement and pressure-controls. Effects of the molding condition were investigated in tensile, three-point bending, short beam shear and dynamic mechanical thermal analysis tests. Both tensile and flexural properties (stiffness and strength), as well as inter-laminar shear strength, were enhanced when the molding occurred under pressure-controlled instead of displacement-controlled conditions. Scanning electron microscopic (SEM) inspection revealed excellent wet-out of the fibers and good interfacial bonding between the fibers and ISP-PBT.     

Modeling formability of multiaxial warp knitted fabrics on a hemisphere

The aim of this paper is to describe a model for the prediction of the formability of a multiaxial warp knitted (MWK) fabric to a 3D surface. For this purpose, we first characterized in detail the forming behavior of MWK fabrics containing two bias inserting yarns (TBMWK fabric). Through experimental observation, it was found that the two bias inserting yarns always tend to gather along the weft direction. The angle between the two bias yarns has a linear relationship with the perpendicular distance from the measured points to the longitudinal axis of the hemisphere during forming process. The slope of this linear relationship is also linear with the magnitude of radius of the pressing hemisphere provided that the radius is larger than 7 cm.Based on the above finding, a mathematical model is established for predicting the deformations of TBMWK fabrics during the hemisphere-forming process. The shape of flat TBMWK fabric that can yield the corresponding hemisphere during the forming process as well as local deformations can be calculated through this model. The hemisphere-forming experiments show that the present model is workable and accurate. The results from both the model and experiments suggest that the shape of flat TBMWK fabric that can yield the corresponding hemisphere which is close to a rectangular, not to a square as presented by woven fabric.The method developed in the paper has laid a foundation for further modeling of the forming behavior of MWK fabrics onto other 3D surfaces. More importantly, it is of great value to find that the two bias inserting yarns always tend to gather along the weft direction of the fabric which is a starting point for modeling of the forming behavior of MWK fabrics.     

Study on the interface modification of bagasse fibre and the mechanical properties of its composite with PVC

The surface treatments of bagasse fibre (BF) with benzoic acid as a surface/interface modifier and the mechanical properties of BF-polyvinyl chloride (PVC) composite were studied. A typical process for the preparation of the composite was as follows: A mixture of PVC, BF, benzoic acid, and other processing additives were dry-blended in a two-roll mill followed by compression molding. The experimental results indicated that the ratio of PVC/BF, the content of benzoic acid, and processing temperature had a significant effect on the mechanical properties of the composite, which was examined by the orthogonal optimal method. The interface modifier improved significantly on the tensile strength and little on the impact strength of the composite, for example, the tensile strength changed between 42 and 52 MPa comparing to the tensile strength of untreated BF/PVC composite (38 MPa), and the impact strength changed between 8.3 and 9.2 kJ/m² comparing to the impact strength of untreated BF/PVC composite (7.5 kJ/m²) when the content of benzoic acid changed between 3 and 10%.     

Microcellular polypropylene single-polymer composites prepared by insert-microcellular injection molding

An insert-microcellular injection molding process was performed on an injection molding machine equipped with a supercritical fluid system. The prepared microcellular polypropylene (PP) single-polymer composites (SPCs) combine the advantages of SPCs with benefits of microcellular plastics, they hold the promise for further reduced weight, improved fiber-matrix interface and enhanced recyclability. In comparison with the solid PP, the weight reductions of the tensile and impact microcellular PP SPCs (MPPSPCs) could be up to 12.9% and 3.3% respectively, the tensile and impact strengths of the MPPSPCs were improved by 59% and 1799% respectively. Based on the tensile properties, the injection temperature of 220 °C and injection speed of 70 mm/s were the optimum processing for the tensile MPPSPC samples. The typical morphology structure of the MPPSPC sample includes five different layers: sandwiched fabric layer, transition layer between fabric and core, center core layer, transition layer between skin and center core, skin layer.     

连续玻璃纤维/聚丙烯热塑性复合材料拉挤成型中的工艺参数

采用复合纱拉挤方法制备连续玻璃纤维/聚丙烯(GF/PP)热塑性复合材料,研究了复合纱拉挤成型过程中模具温度及拉挤速度对GF/PP复合材料截面中心温度的影响。以傅里叶定律为理论基础,分析了拉挤过程中模腔内的瞬态传热过程;建立了工艺参数矩阵,通过有限元数值计算,预测了不同模具温度、拉挤速度下GF/PP复合材料截面中心的温度变化,优选了工艺参数组合。通过实验制备不同温度、不同拉挤速度的GF/PP复合材料,并进行弯曲模量测试及截面形貌观察。结果表明:在GF/PP复合纱拉挤过程中,拉挤速度不宜超过350 mm/min,模具熔融区温度设定应高于180℃;GF/PP复合材料在150℃-230℃-50℃成型温度、100 mm/min拉挤速度的工艺参数设定下获得最优的制品力学性能;在设定拉挤参数时,拉挤速度相较于熔融区温度更重要。      

Thermal and mechanical behaviour of sisal/phenolic composites

This research proposes the development of polymeric composites reinforced with natural fibres to become stronger the damaged timber structures and proposes thermal and mechanical characterization of these composites. Fibres with larger structural applications are glass and carbon fibres but the use of natural fibres is an economical alternative and possesses many advantages such as biodegradability, low cost and is a renewable source. Woven sisal fabric was submitted to heat treatment before moulding and the influence of moisture content of fibres on the composites behaviour was observed. The paper presents mechanical characterization by tensile and flexural strength of woven sisal fabric composites, with and without thermal treatment (at 60 °C for 72 h) on the fabric, thermal characterization by TGA and the manufacturing process by compression moulding. Experimental results show to sisal/phenolic composites a tensile strength and a flexural strength value of 25.0 MPa and 11.0 MPa, respectively, independent to the use of sisal fibres with or without thermal treatment.     

Hybrid composites based on aramid and basalt woven fabrics: Impact damage modes and residual flexural properties

The low-velocity impact behaviour of hybrid laminates reinforced with woven aramid and basalt fabrics and manufactured by resin transfer moulding was studied. Specimens with different stacking sequences were tested at three different energies, namely 5, 12.5 and 25 J. Residual post-impact properties of the different configurations of aramid/basalt hybrid laminates were characterized by quasi static four point bending tests. Post-impact flexural tests have been monitored using acoustic emission in order to get further information on failure mechanisms. Results indicate that hybrid laminates with intercalated configuration (alternating sequence of basalt and aramid fabrics) have better impact energy absorption capability and enhanced damage tolerance with respect to the all-aramid laminates, while basalt and hybrid laminates with sandwich-like configuration (seven basalt fabric layers at the centre of the laminate as core and three aramid fabric layers for each side of the composite as skins) present the most favourable flexural behaviour.     

The effect of heterogeneous deformation on the hot deformation of WE54 magnesium alloy

The high temperature forming behavior of WE54 magnesium alloy is studied by means of compression and tension tests. Metallographic investigation was performed to evaluate the heterogeneous deformation of the compression samples at high temperature. Dynamic recrystallization was found to be related to the amount of deformation in the various regions of the compression sample. The compression data allowed determination of the Garofalo equation describing the hot deformation behavior. The parameters n and Q, stress exponent and activation energy, of this equation were 4.4 and 237 kJ/mol respectively. This equation was used to predict the formability behavior for the hot rolling process and also to determine the maximum forming efficiency and stability of the alloy. The optimum rolling temperature was found to be 520 °C.     

Limits in growing TlGaAs/GaAs quantum-well structures by low-temperature molecular-beam epitaxy

TlGaAs/GaAs multiple-quantum-well (MQW) structures were grown on GaAs substrates at a substrate temperature of 190 °C by molecular-beam epitaxy. The MQW structures were intended to consist of four identical TlGaAs wells, each of which is sandwiched by GaAs barrier layers. X-ray diffraction was used to investigate the limits to Tl content and thickness of the TlGaAs well layer for forming the MQW structures. Successful growth of TlGaAs/GaAs MQW structures having nominal Tl contents of 6, 8, and 9% was confirmed for the three different well thicknesses of about 15, 10, and 5 nm, respectively, while further increase in Tl content resulted in failure in forming MQW structures. The bounds for forming the MQW structures are discussed in terms of the epitaxial thickness of TlGaAs. The effect of the MQW structures on retarding the formation of Tl droplets is pointed out.     

Environmental effects on the mechanical and thermomechanical properties of aspen fiber–polypropylene composites

The mechanical properties of newly developed aspen fiber–polypropylene composites (APC) were experimentally explored and numerically predicted at the temperatures and humidity that are typical for domestic housing applications. The mechanical properties of APCs with five different fiber-loadings were evaluated at the room temperature, 4 °C, and 40 °C. Environmental effects on the mechanical properties of APCS were experimentally quantified after conditioning the APCs with two different fiber-loadings in the following temperature and humidity for over 7000 h: (1) hot/dry at 40 °C and 30% relative humidity (RH), (2) hot/wet at 40 °C and 82% RH, (3) cold/dry at 4 °C and 30% RH, and (4) cold/wet at 4 °C and 82% RH. The tensile moduli, flexural moduli, and the flexural strength increased as the woodfiber content increased in the composites. However, the tensile strength decreased as the fiber content increased. The tensile strength was shown to slightly improve with an addition of a coupling agent between the aspen fibers and polypropylene. The simple empirical micromechanics Halpin–Tsai model for randomly distributed short fiber reinforced composites was employed to predict the homogenized elastic moduli of APC, by optimizing the interfacial model parameter. Scanning electron microscopy (SEM) micrographs confirmed that an addition of the adhesion promoter maleated anhydride polypropylene (MAPP) between the aspen fibers and polymeric matrix improved the interfacial bonding.     

The potential of harakeke fibre as reinforcement in polymer matrix composites including modelling of long harakeke fibre composite strength

Mechanical properties of aligned long harakeke fibre reinforced epoxy with different fibre contents were evaluated. Addition of fibre was found to enhance tensile properties of epoxy; tensile strength and Young’s modulus increased with increasing content of harakeke fibre up to 223 MPa at a fibre content of 55 wt% and 17 GPa at a fibre content of 63 wt%, respectively. The flexural strength and flexural modulus increased to a maximum of 223 MPa and 14 GPa, respectively, as the fibre content increased up to 49 wt% with no further increase with increased fibre content. The Rule of Mixtures based model for estimating tensile strength of aligned long fibre composites was also developed assuming composite failure occurred as a consequence of the fracture of the lowest failure strain fibres taking account porosity of composites. The model was shown to have good accuracy for predicting the strength of aligned long natural fibre composites.     

Compression moulding of glass and polypropylene composites for optimised macro- and micro- mechanical properties-1 commingled glass and polypropylene

The continuing desire in the automotive industry to reduce cost and weight while increasing safety requires innovative materials and processing routes. Glass-mat-reinforced thermoplastics have been used to produce semi-structural components but a higher and aligned glass fibre content is required in moulding materials for structural applications. Experimental design was used to investigate the non-isothermal processing of commingled fabrics which were woven from yarns of intimately mingled glass and polypropylene fibres. Processing models were generated by regression techniques to predict laminate properties over a range of processing conditions. Void contents were measured by image analysis techniques. Preheat temperature had the greatest effect on laminate flexural properties and porosity. A compaction time of 54 s was required to consolidate, cool and reduce the void content in laminates. A two-fold increase in stiffness was found compared with equivalent glass-mat-reinforced thermoplastic laminates. The intimate distribution of matrix and reinforcement reduced moulding pressures by a factor of 10.     

Stamp forming of locally heated thermoplastic composites

Generally, an entire blank is heated in the stamp forming process. Since it will cause difficulty in the transferring process and errors in dimensions and waste more energy, a stamp forming process with locally heated specimen is proposed in this work. Three stamping parameters including working temperature, heated range, and holding time are considered. To evaluate the quality of stamp formed parts, they are macroscopically characterized for part angle actually formed and microscopically examined for delamination and fiber buckling. In addition, the maximum load that the deformed part can suffer is measured. The results indicate that locally heated part is competitive to entirely heated part in maximum load and final angle, even though wrinkles are still observed in locally heated part. Also, 260 °C working temperature, 20 mm heated range, and 1 s holding time are recommended for stamp forming process with locally heated specimen.     

Experimental Investigation About Stamping Behaviour of 3D Warp Interlock Composite Preforms

Forming of continuous fibre reinforcements and thermoplastic resin commingled prepregs can be performed at room temperature due to its similar textile structure. The “cool” forming stage is better controlled and more economical. The increase of temperature and the resin consolidation phases after the forming can be carried out under the isothermal condition thanks to a closed system. It can avoid the manufacturing defects easily experienced in the non-isothermal thermoforming, in particular the wrinkling [1]. Glass/Polypropylene commingled yarns have been woven inside different three-dimensional (3D) warp interlock fabrics and then formed using a double-curved shape stamping tool. The present study investigates the in-plane and through-thickness behaviour of the 3D warp interlock fibrous reinforcements during forming with a hemispherical punch. Experimental data allow analysing the forming behaviour in the warp and weft directions and on the influence of warp interlock architectures. The results point out that the layer to layer warp interlock preform has a better stamping behaviour, in particular no forming defects and good homogeneity in thickness.     

Robotic tow placement for local reinforcement of glass mat thermoplastics (GMTs)

A process has been developed where multiple yarns of commingled glass and polypropylene are heated and placed to a desired geometry. The placed unidirectional (UD) tow is then encapsulated by over-moulding with glass mat thermoplastics (GMTs). The effects of both force (20–80 N), with an equivalent pressure range of 8–46 bar, and the displacement rate (20–100 mm/s) during tow placement on void content and flexural modulus were investigated for nine placement conditions. Placement rate affected the tow quality measured before over-moulding. Void contents were reduced after over-moulding. The volume fraction of UD tow (vol. O° composite/vol. total composite) in the manufactured multi-material structure was 21.5%. Corresponding tensile tests showed a factor of 2 increase in modulus and a factor of 3 increase in strength relative to GMT. Tow placement rate had no significant effect on tensile properties after over-moulding. Tensile behaviour as a function of the UD tow volume fraction was modelled and predicted values agreed with the experimental results. Additionally, the predicted tensile performance of UD tow reinforced GMT has been compared with possible competitive materials using merit indices.     

Consolidation of GF/PP commingled yarn composites

Consolidation quality and corresponding mechanical properties of GF/PP thermoplastic composites manufactured from a commingled yarn system have been investigated. A small compression mould with a laboratory hot press was used to apply the different processing variables (i.e. pressure, holding time and processing temperature). The consolidation quality of finished samples was characterized mainly through (a) microscopic studies of the material's microstructure, (b) density measurements, and (c) evaluations of mechanical properties using a small transverse flexure testing facility. A model for qualitatively describing the impregnation and consolidation processes in commingled yarn based thermoplastic composites was applied to predict variations of void content during consolidation and the time, temperature and pressure required to reach full consolidation. Based on a desired, minimum level of void content (X _v =2.0%), optimum processing windows for manufacturing of GF/PP commingled yarn composites are suggested.