Flow induced fiber orientation in compression molded glass mat thermoplastics

This study examines how the mechanical properties in GMT are affected by axisymmetric flow during compression molding. Two types of GMT with different architecture are used, swirled mat and short fiber GMT. Tree different grades are tested for each fiber architecture 20, 30, and 40% fiber content by weight. These are in principle the grades of GMT commercially available today. It is found that the flow reduced the tensile strength by 30 to 50% and the tensile modulus up to 30% in the flow direction. The reduction in mechanical properties, which is mainly caused by flow‐induced fiber orientation, is larger at high fiber contents. The study also showed that there is no major difference in behavior between swirled mat and short fiber GMT regarding flow induced fiber orientation.     

Stamping rheology of glass mat reinforced thermoplastic composites

Glass mat reinforced thermoplastics (GMTs) offer a useful combination of mechanical properties and formability. In principle, these composites may be based on any thermoplastic matrix. In practice, matrix selection is limited because of its impact on the manufacturing and compression molding processes. In this work an isothermal squeezing flow technique is used to determine the apparent biaxial extensional viscosities of polycarbonate, polybutylene terephthalate, and polypropylene-based GMTs. Experimental load-deformation data are interpreted by treating the GMTs as viscous, incompressible Newtonian fluids. Two primary effects are observed: (1) the composites appear to strain harden as they are deformed, and (2) GMT apparent biaxial extensional viscosities correlate with the high rate of deformation shear viscosities of the matrices. A mechanism that explains the second result is proposed.     

Extensional processing behavior of thermoplastics reinforced with a melt processable glass

This work was concerned with investigating the processing behavior of thermoplastics reinforced with a melt processable phosphate glass under extensional flows at temperatures used for forming and shaping operations. Injection molded blends consisting of polyetherimide (PEI) and polyphenylene sulfide (PPS) reinforced with 30‐60 wt% phosphate glass were exposed to uniaxial and planar deformation at temperatures above the T_g of the phosphate glass (234°C) to evaluate the effects on the morphology and mechanical properties of the composites. Tensile testing at elevated temperatures (250‐300°C) was used to evaluate the forming behavior and ascertain the conditions most suited for the deformation of the composite blends. A temperature approximately 35°C above the T_g of the P‐glass was found to offer conditions most conducive to the deformation of the PEI/P‐glass blends. The phosphate glass reinforced PEI was found to offer greater retention of properties and smoother surfaces than an E‐glass filled material when exposed to shearfree deformation similar to that seen in a process such as thermoforming. For PPS based composites, the application of planar shearfree deformation near the melting point of the PPS (≈︁ 283°C) resulted in the elongation of the phosphate glass phase which served to enhance the stiffness of the composite blends along the principal deformation direction.     

Fatigue of glass and carbon fiber reinforced engineering thermoplastics

Cyclic tension fatigue S-N curves are given for injection moleded Nylon 6/6, polycarbonate, polysulfone, polyphenylene sulfide, and poly(amide-imide) matrices with glass and carbon fibers as well as for unreinforced material. The S-N curves for most composites appear linear, with no evidence of a fatigue limit up to 10⁶ cycles. Some nonlinearity is evident with the Nylon 6/6 composities, and these appear to fail at a cumulative strain similar to the ultimate static strain. The remainder of the composites appear to fail by a crack propagation mechanism. The glass reinforced materials all degrade at a similar rate in fatigue, while the carbon reinforced materials with brittle matrices degrade more slowly than do those with ductile matrices. The latter effect may be due to greater integrity of the cracked regions for brittle matrix systems.     

加快发展玻璃纤维增强热塑性塑料

1、关于玻纤增强热塑性塑料 塑料作为现代四大工业基础材料之一,越来越广泛地在各行各业应用.2002年全世界的塑料总产量已达1.65亿吨.塑料按受热后形态性能表现,可分为热固性塑料和热塑性塑料.后者是指能够多次受热软化的聚合物--聚合物的分子链间不发生交联,而且每次加工后分子链几乎没有变化.     

世界热塑性玻璃钢发展概况

3玻璃/热塑性塑料复合纤维 3.1 Twintex(R)复合纤维 Twintex(R)是法国圣戈班Vetrotex公司于1988年开发的玻璃/热塑性塑料复合纤维的商品名.在拉制玻璃纤维时即用热塑性塑料与其共挤相间复合而成紧密结合的复合纤维.可用塑料种类有聚丙烯、聚乙烯、聚酰胺、PET、PBT等.     

世界热塑性玻璃钢发展概况

玻璃纤维增强热塑性塑料(简称热塑性玻璃钢,英文缩写GRTP)最早出现于20世纪50年代,比热固性玻璃钢问世更晚.经过多年的发展,现今国际上热塑性玻璃钢已占玻璃钢总产量的四分之一以上,而且增长速度很快.据资料报道,在过去几年中,热塑性玻璃钢市场增长稳定,平均年增率为5%～6%.从现在到2007年,美国等国家对热塑性玻璃钢需求量的增长率将超过热固性玻璃钢.     

Compression molding of glass reinforced thermoplastics: Modeling and experiments

The shearing and extensional behavior of glass mat‐thermoplastic (GMT) material under compression molding was investigated with a special model being developed for the case of non‐lubricated mold‐plate surfaces. Mathematical expressions for the radial and through‐thickness flow velocities were derived that enabled the derivation of extensional and shear strain rates. The GMT non‐lubricated (no‐slip wall conditions) compression molding was modeled as a combination of extensional and shearing flow and the two extensional and shear viscosities were determined. Scott's approach was used in this work to determine the radial velocit in the r‐direction, which depends on the shear power‐law expression. The velocity component in the z‐direction was then calculated using the continuity equation. The velocity profiles were used to calculate the shear and extensional strain rates. Scott's shear viscosity did not satisfy the constitutive equation for the extensional part, but a power‐law expression with new parameters depending on the deformation tensors was successfully used to calculate an independent extensional viscosity using the same non‐lubricated squeezing experiment. Lubricated squeezing flow was carried out for the same material to achieve a pure extensional flow, and the extensional viscosity calculated using this approach agreed with the extensional viscosity determined using the non‐lubricated experiment. GMT material used in this study is confirmed to have two layers of continuous long fibers orientated randomly inplane, separated by short chopped fibers in the middle, which suggests that the material can be treated as an isotropic material, and the fiber‐matrix separation is seen to be high at the extremities of the flow.     

Rheological characterization of commercial glass mat thermoplastics (GMTs) by squeeze flow testing

The flow behavior of commercial glass mat thermoplastics (GMTs) has been investigated by isothermal axisymmetric squeeze flow testing between parallel circular plates. Tests have been performed over a range of squeeze rates and the analysis is based on simple power law constitutive equations. A key part of the work is determining the relative contributions of shear and extensional flow to the overall squeezing force response. By developing a variational flow model, based on the upper bound theory, the behavior has been found to be predominantly extensional, with shear effects becoming important at very small plate separations. In addition, a predictive model for the radial pressure distribution during squeezing has been developed, based on fiber suspension rheology. Since fibers are generally long or continuous, treating the material as a statistically homogeneous fluid does not yield accurate results in this respect.     

Short fiber reinforced thermoplastics. I. Rheological properties of glass fiber reinforced Noryl

An experimental study on the flow behavior of glass fiber reinforced Noryl (a commercial poly(phenyleneoxide)/polystyrene blend) using a capillary rheometer is described. The effect of fiber concentration on shear viscosity and die swell was studied at various temperatures. Breakage of glass fibers during flow through the rheometer is discussed; it was found that the average fiber length (about 230 μm) was not significiantly altered, except at the highest shear rate (575 s⁻¹) studied. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity without changing the basic rheological character-shear rate dependency. No discernible viscosity changes were measured by incorporating 10 weight percent fibers, and upon further increase of fiber concentration from 20 to 30 weight percent no appreciable increase in viscosity was noted. It is shown that short glass fibers cause a large reduction in extrudate swell. The presence of voids and fiber orientation contribute to the decrease of the die swell, an effect greater than expected from volumetric considerations alone.     

Improvement in impact property of continuous glass mat reinforced polypropylene composites

The toughened polypropylene (PP) was obtained by the blending of PP with ethylene‐propylene diene monomer (EPDM). The impact property of continuous glass mat‐reinforced polypropylene was adjusted through three ways: different toughness PPs and their blends were used as matrices, the functionalized polypropylene was added into the matrix to control the interfacial adhesion; the ductile interlayer was introduced at the fiber/matrix interphase by the grafting and crosslinking of rubber chains on fiber surface. The effect of PP toughness, interfacial adhesion, and ductile interlayer on the mechanical properties of composite systems was studied. The impact toughness of GMT increased with increasing the matrix toughness, whereas the flexural strength and modulus decreased. The good interfacial adhesion resulted in the low impact toughness. However, GMT composite with high strength, modulus, and impact toughness could be obtained by the introduction of a ductile interlayer at fiber/matrix interphase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2680–2688, 2002     

Dynamic fracture mechanics of a RIM polyamide block copolymer reinforced with glass strand mat

The fracture behavior of a reaction injection molded (RIM) polyamide block copolymer reinforced with randomly arranged continuous glass fiber bundles (glass mats) was studied under dynamic loading conditions at T=RT and T=-40 °C. Dynamic fracture toughness, K_d, and fracture energy, G_d, values were derived from instrumented high-speed impact bending tests carried out on Charpy and Izod specimens of different size and notching direction, respectively. It was established that fracture mechanics data depend on the ligament width of the specimens. It was shown how the “inherent” flaws caused by machining and molding can be determined. Failure mode of the composites was characterized by fractography and possible failure events were summarized. Recommendations were given for further material improvements. Work presented at the ECCM-4 Conference (25.–28. Sept. 1990) in Stuttgart, FRG     

Pressure/temperature measurements during compression molding of glass mat reinforced thermoplastic composites

Cavity pressure transducer measurements are used to determine the effective viscosity of glass reinforced polypropylene composites during compression molding. Part solidification time during the cycle is determined from changes in pressure profiles at different locations in the tool. Higher pressing speeds and part thickness lead to significantly lower effective material viscosity during the compression cycle.     

Effect of glass fiber length on the creep and impact resistance of reinforced thermoplastics

Impact and flexural creep testing were conducted at temperatures between −22°F (−30°C) and 250°F (121°C) to evaluate and compare the end-use performance of continuous long glass fiber-reinforced thermoplastic sheet composites to that of short glass fiber-reinforced thermoplastics. The matrices studied consisted of amorphous (polycarbonate and acrylonitrile-butadiene-styrene) and semicrystalline (polypropylene) polymers. Data were obtained from both injection-molded specimens (short fibers), and from specimens machine-cut from compression-molded test panels (continuous long fibers). The creep results of this study demonstrated that continuous long fibers are more efficient than short fibers in reinforcing the thermoplastic matrices, resulting in enhanced load-bearing ability at elevated temperatures. The addition of continuous long glass fibers to the thermoplastic matrices led to a significant increase in the notched Izod impact strengths between the temperatures of −22°F (−30°C) and 77°F (25°C), and only slight improvement in the drop-weight impact strengths. The lack of correlation between notched Izod impact and drop-weight strengths is largely due to the difference in crack propagation and fracture initiation energies. Results of the Rheometrics instrumented impact test indicated a higher total fracture energy for the long glass-reinforced thermoplastic sheet composites than for the short glass-reinforced injection-molded thermoplastics. The decreased ease of crack propagation in thermoplastic sheet composites is associated with the high energy-absorbing mechanisms of fiber debonding and interply delamination. The results of this study point to the significant property improvement of continuous long fibers vs. short fibers. The creep strength of short fiber-reinforced thermoplastics are greatly affected by the nature of the stress transfer which in turn is influenced by the critical fiber length and temperature, which is not the case for the long fiber-reinforced thermoplastic sheet composites. Long fibers dramatically increase the impact resistance of thermoplastics. The retention of toughness at low temperatures coupled with elevated temperature performance greater than similar short glass fiber-reinforced thermoplastics effectively extends the capabilities of thermoplastic sheet composites at both temperature extremes.