摘要:

AbstractThe influence of impact velocity, between 1 and 8.7 meters per second (m/s) (2.2 to 19.5 mph), on the impact behavior of polypropylene, reinforced with 20 volume percent continuous glass fibers, was investigated in a 3‐point bend test at 21 °C. The ratio of specimen span to thickness, which has a profound effect on the observed results, was varied between 5.3 and 26. An attempt to apply simple beam theory for the analysis of the initial specimen response to the high loading rate was successful, except for the lower than expected values of shear modulus. The stress to break and the tensile and shear moduli were found to increase along with velocity. The dependence of impact energy on velocity was observed to be affected by the span to thickness ratio: a positive dependency was observed at low ratios and none at high ratios. This is different from the negative dependency reported for polypropylene reinforced with short fibers, and is attributed to the influence of the continuous glass fibers on the impact behavior of the composi

ISSN:0272-8397    

DOI:10.1002/pc.750070602

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe dynamics of solid state extrusion of polypropylene, high density polyethylene, and poly(tetrafluorethylene) have been investigated at various extrusion temperatures and piston velocities. A model of solid state extrusion of semicrystalline polymers is proposed. The formulae are obtained relating the value of the extrusion pressure with the parameters of the process and polymer properties. It has been found that for certain values of the parameters, defects of two main types emerge. A mechanism of defect formation is suggested.

ISSN:0272-8397    

DOI:10.1002/pc.750070603

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractInterphasial toughness was evaluated for polyester and epoxy unidirectional glass fiber reinforced composites using single edge‐notched specimens. This was accomplished via a calculation of an energy term based onJ‐integral which accounted for the energy required to form a longitudinal split crack ahead of the original notch. It was found that the fiber‐matrix interphasial fracture resistance of the epoxy composite is substantially greater than that of the polyester composite. This technique may be an excellent way of evaluating the interphasial quality in unidirectional composite lami

ISSN:0272-8397    

DOI:10.1002/pc.750070604

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA thermal conductivity measuring apparatus that uses heat flow sensors to measure the heat flux through samples was constructed of inexpensive materials. This device was used to measure the thermal conductivity (k) of two composites used in the space program that consist of fibrous or granular components embedded in a resin matrix. Thek‐values that were determined ranged from 0.035 to 0.059 Btu/h‐ft2‐°F/ft (−163 to 553°F) and 0.029 to 0.035 Btu/h‐ft2‐°F/ft (77 to 212°F). Thermal conductivity values of the composites conformed to the rule of mixture. The accuracy of the system was found to be comparable to the guarded hotplate and it requires neither a skilled operator nor extens

ISSN:0272-8397    

DOI:10.1002/pc.750070605

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractEntrapped air can commonly lead to large delaminations in thick walled sheet molding compound (SMC) products. In this work different sources of air entrapment in SMC are investigated. The critical process is shown to be the impregnation of the fibers. If no surface active additives are used, large volumes of air may be entrapped in this process, unless the viscosity of the compound is very low. In this situation of poor wetting, the viscosity of the compound during fiber impregnation will critically determine the interlaminar, tensile strength of the product. However, if surface active additives are used, the air escapes entrapment even at relatively high viscosities. The lowering of the viscosity, which is a side effect of the additives, has practically no importance under these conditions of good wetting. Large numbers of small air bubbles are also entrapped during the mixing of the components, but it is shown that these bubbles have very little effect on the mechanical properties of the finished part.

ISSN:0272-8397    

DOI:10.1002/pc.750070606

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractTensile, flexural, and shear tests on glass fiber‐polyester pultrusions containing glass spheres show that the spheres reduce the tensile strengths when both rigid and flexible polyesters are used, but some increase in flexural strength is obtained with the flexible resins. Small additions of spheres increased the shear strengths, but for sphere volume fractions greater than about 0.2, the shear strength declined. A silane coupling agent on the spheres increased the strength of the rigid resin composites, but had little effect with the flexible resin. Some of the results could be due to the lack of straightness of the fibers caused by the presence of spheres having diameters greater than the fiber diameter. However, when the fibers were not present, the sphere filled matrices showed very diverse behavior. The results presented here indicate that even in the absence of fibers, simple models are unlikely to be successful in explaining the propertie

ISSN:0272-8397    

DOI:10.1002/pc.750070607

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractMica and polystyrene in four ratios were sheared for three different times, each at three speeds, and at two temperatures in the viscoelastic region, in a screw mixer. From precise density measurements on the resulting composites, void volume fractions were calculated and found to be proportional to mica concentration and independent of total screw rotations. Experimental void/mica ratios were represented by a kinetic model; they decreased from a single value common to all conditions to a steady‐state value proportional to the square root of the screw speed. Void formation and elimination occur simultaneously. The goodness of the fit to the data is insensitive to the details of the kinetic model. The characteristic rate constant depends only on temperature, increasing at the same rate as the reciprocal of the low‐frequency dynamic viscosity. Cavitation in regions of diverging flow of the mixer may inhibit void eliminat

ISSN:0272-8397    

DOI:10.1002/pc.750070608

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA series of composites based on low and high density polyethylene blend matrices with unmodified and previously organophylized sepiolite as filler have been prepared. In the latter case, isopropyl‐methacryl‐diisostearoyl titanate (KR‐6) was used as coupling agent. The Box‐Hunter Statistical Method was used to obtain the maximum information through a wide matrix composition and filler content range from a small number of experiments. The organophylization of the filler has hardly shown any improvement on the tensile, flexural, and impact properties of the composite. A morphological study carried out by means of scanning electron microscopy has shown that the organophylization tends to modify the surface textural characteristics of the sepiolite, compensating the effect of the coupling agent on the pro

ISSN:0272-8397    

DOI:10.1002/pc.750070609

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effects of tension on the absorbance of water at 60°C into neat and glass‐bead‐filled, cross‐linked polyester are reported. Experimental apparatus and procedure to determine water uptake for these materials subjected to three tensile stresses in the range of 0 to 30 percent of the breaking stress of the neat dry polyester are described. It was found, for bead‐filled samples, that a load of approximately 4.9 × 106N/m2caused the absorption level to increase by 30 percent over that of an unloaded sample. Tensile load was found to have no effect on the absorption characteristics of neat polyester. However, breaking stress was reduced to less than 15 percent of that in the dry neat material. Optical microscope examinations of damage at the fracture surfaces and at the sample cores indicate that the excess moisture uptake in bead‐filled samples was not due to microcrac

ISSN:0272-8397    

DOI:10.1002/pc.750070610

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe dynamic mechanical behavior of the binary blends high‐density polyethylene/EPDM rubber (ethylene‐propylene‐diene terpolymer) and isotactic polypropylene/EPDM rubber was investigated by means of a free‐oscillating torsional pendulum. Comparison of the moduli of the systems studied and predictions drawn from several models show that phase inversion in the polyethylene/EPDM blends takes place at the volume fractionvPE= 0.5, while polypropylene preserves a certain phase continuity also as the minor component (0.5>vPP>0.2) in blends with EPDM. Because of faster shrinkage in the course of cooling, inclusions are exposed to negative hydrostatic pressure, which accounts for a drop in the glass‐transition temperature of the rubber. The strength of the relaxation associated with the glass transition of inclusions and tensile impact strength increase proportionately to the rubber content in polypropylene (0

ISSN:0272-8397    

DOI:10.1002/pc.750070611

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY