Influence Of Glass Fibers Research Articles

Free and restrained early-age shrinkage of mortar: Influence of glass fiber, cellulose ether and EVA (ethylene-vinyl acetate)

The objective of this paper is to present a new testing method for investigating early-age (i.e. between 0 and 24 h after mixing) shrinkage of cement-based material. Whatever the free or restrained conditions, the plastic shrinkage is caused by the evaporation of water from the surface of fresh concrete. Free plastic shrinkage was investigated by optical instrumentation system. It can thus be measured the average shrinkage before and/or very early after the setting process. In addition to this value, the optical system provides a measurement of the deformation field to assess the degree of heterogeneity of shrinkage at the surface of the sample during the drying. The restrained shrinkage tests are performed using an active restrained system. The testing apparatus, based on a ring test, is presented with its own computer-controlled closed loop. This technique provides quantitative information about stress development that may be used to assess the potential for cracking in thin cement-based materials subjected to drying. As first results, the influence of the mix design (cellulose ether, EVA and glass fiber) has also been investigated: reducing of cellulose ether quantity in mix-design, modifies the kinetic and level of early-age shrinkage. The use of EVA decreases the overall shrinkage but does not reduce the heterogeneity of surface shrinkage. However we obtained with EVA, a decrease in the internal residual stress. The glass fiber reduces shrinkage and also reduces the heterogeneity of the surface shrinkage. However at a low rate of incorporation of glass fibers, no reduction of internal residual stress is obtained.

Properties of GF/PP Commingled Yarn Composites

The influence of glass-fiber (GF)/polypropylene (PP) commingled yarn structure on the impregnation quality of laminates is investigated by characterizing the microstructure and mechanical properties of the laminates. For this study, the degree of interlacing of the commingled yarns is taken as a measure of the structure of commingled yarns. Properties of laminates made by compression molding of commingled yarns are compared with those of laminates made with two other methods of composite manufacturing: film stacking and side-by-side (SBS) winding of glass roving and PP yarns. The results show that the degree of interlacing has a significant influence on the void content, fiber impregnation, and tensile behavior of composites made from commingled yarns. Laminates made from SBS and film stacking show more voids and dry fibers than those made from commingled yarns for the same consolidation conditions.

The influence of glass fiber on fracture behavior of isotactic polypropylene

Abstract This study is focused on the role of glass fiber on the fracture mechanism in PP/GF composites. Several composites with different amounts of glass fiber were examined. Three-point and four-point bending tests were carried out. The results of three-point bending tests show that the fracture toughness of PP increases with the increase of GF content. The results of four-point bending tests display a wide spread damage zone in front of the pre-crack while optical photographs appears that the damage zone including craze which is initiated from glass fibres. Also, the observation of the damage zone utilizing cross-polarized light illustrates that there is no evidence of shear yielding phenomenon. Looking at this in more detail via scanning electron microscopy shows that the craze propagation can be dictated by glass fiber. The crazes in PP/GF composite, studied in this work, are propagated by moving towards the interface followed by craze thickening and fiber breakage.

Fatigue fracture of nylon polymers

The influence of glass fibres on the fatigue crack propagation rates of injection-moulded nylons has been determined. In contrast to previous results for unreinforced nylons, the cracking kinetics are independent of the oscillating load frequency. The fact that the crack growth rate per cycle is constant, when expressed in terms of the time under load, demonstrates that the contribution of creep crack extension is minimized by the glass fibres. Thus a true fatigue process is suggested for the fatigue fracture of the reinforced system, even when the glass fibres are preferentially aligned parallel to the crack growth direction. A complicating factor in characterizing the fatigue resistance of the glass-reinforced nylons is the tremendous influence of fibre orientation on crack growth rate. It is shown that the anisotropy problem can be handled by simply expressing the crack growth rate data in terms of the strain energy release rate rather than the usual stress intensity factor representation. Results for four different glass-filled nylons show that the diverse crack growth rates for cracking parallel versus perpendicular to the glass-fibre axes collapse on to individual strain energy release rate curves. Each single relationship therefore characterizes the fatigue fracture of the filled material and furthermore permits a prediction of the cracking rates for any glass-fibre orientation based upon the expected change in modulus. Finally it is demonstrated that the increased stress dependence of fatigue crack propagation (slope of the Paris plot) in filled nylons can be duplicated in unfilled samples under certain conditions. It is concluded that the fatigue fracture mechanism is matrix dominated in these chopped glass-fibre reinforced materials.

Crystallization behaviour and mechanical properties of polypropylene-based composites

The influence of glass fibres on the primary nucleation process, isothermal radial growth rate of spherulites and overall kinetic rate constant of isotactic polypropylene (iPP) has been examined. The polypropylene was also modified by means of acrylic acid (iPP*) in order to improve the adhesion between the matrix and the fibres, and the relative properties were compared with those concerning the composites having as matrix plain MR Moreover the mechanical properties of injection-moulded composites containing iPP and iPP* have been studied. These properties improved on increasing the fibre content. It was found that for the same glass-fibre content better values of the elongation at break and creep are observed in the case of reinforced polypropylenes having as matrix acrylic acid modified polypropylene.

Influence of glass fibers on the extrusion and injection molding characteristics of polyethylene and polystyrene melts

AbstractA basic study is reported of extrusion and injection molding for melts of polyethylene and polystyrene filled with glass fibers. It is shown that glass fibers cause large increases in end pressure losses and decreases in extrudate swell. Flow visualization of injection molding studies indicates that polymer melts containing high loadings of glass fibers exhibit jetting in end gated molds. This is attributed to the reduction in extrudate swell. To avoid jetting, special care is required in design of gating.