ISSN:0272-8397    

DOI:10.1002/pc.750160102

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe viscoelastic behavior of a series of vinyl ester resins and E‐glass fiber‐reinforced composites is discussed. It is shown that the temperature shift factors for these systems, and others, suggests a universal behavior. A similar observation is made for the aging shift rate. On the other hand, the temperature dependence of compliance components per se appear to differ from system to system. Finally, it is shown that the retardation spectra for the vinyl ester resin and composites systems are the same to within a multiplicative constant in the glassy and in the short time transition regions. This shows that the presence of fibers has no influence on the distribution of retardation times in those regi

ISSN:0272-8397    

DOI:10.1002/pc.750160103

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fracture performances of three short glass fiber‐reinforced polymer composite systems, PET with 30 wt% glass, nylon 6/6 with 33% glass fibers, and a nylon 6 and 6/6 copolymer with 33% glass, have been characterized using both standard mechanical characterization and fracture mechanics. These results have been compared to fracture tests of an experimental chair base. None of the characterizing techniques was successful in predicting the chair base fracture performances of the materials when the tests were conducted on standard 3‐mm‐thick test specimens. When larger specimens with comparable morphologies to the chair base were tested, the fracture mechanics tests compared favorably to the chair base fracture tests while the tensile test results were inconsistent in their predictive ability. The findings emphasize the importance of testing laboratory specimens that are similar in morphology to the final part and suggest that fracture mechanics methodologies can be used in materials selection of glass reinforced systems for structural applications. However, for quantitative design, it is necessary to address issues regarding the nature of the inherent flaw in the finished

ISSN:0272-8397    

DOI:10.1002/pc.750160104

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe aim of this study is to determine the fracture toughness of phenolic resin and its composite. Fracture tests on phenolic resin resulted in a fracture toughness close to values quoted for unmodified epoxy resins. Composite specimens of glass fiber reinforced phenolic were also tested. The interlaminar fracture toughness in both mode I and mode II failures was determined. The mode I initiation values were lower than the neat resin's toughness. Mode I propagation values were strongly influenced by fiber bridging. The mechanism of fiber bridging was found to be sensitive to specimen dimensions. The effect of fiber bridging on the mode I analysis is discussed. Fiber bridging was also evident in mode II failures. Two different geometries were used for the mode II tests (end loaded split and end notched flexure); a correlation between the results from the two geometries is made.

ISSN:0272-8397    

DOI:10.1002/pc.750160105

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractResults are reported of fatigue crack propagation experiments on an epoxy reinforced with long aligned glass fibers. The composite was prepared in such a way that fiber spacing was approximately the same in each specimen and the reinforcing fibers were sufficiently stronger than matrix. For a number of experiments with the same fiber spacing, fatigued under various stress levels, the crack speed as well as the rate of debonding reached steady values, i.e., independent of the crack length. In addition, the evolution of debonding followed a self‐similar growth pattern. The data implied that the applied load was a controlling parameter of the steady growth. Within the resolution of observations, no fiber fracture was observed in the bridging zone. Fiber debonding seemed to be the dominant mechanism of energy dissipation. Moreover, the crack front was not straight. Instead, it consisted of two branches growing on the specimen's surfaces first and then through the thickness of the specimen with a highly curved front. Stress intensity factor calculations showed that when the fibers in the bridging zone were under a uniform load, the total stress intensity factor was proportional to\documentclass{article}\pagestyle{empty}\begin{document}$ \sigma \sqrt \lambda $\end{document}(where σ is the applied stress and λ is the fiber spacing) and constant within the regime of steady crack growth. The steady values of crack growth and rate of debonding were correlated with the stress level, spacing, and fiber radius. The resulting power equations were found to have the same expon

ISSN:0272-8397    

DOI:10.1002/pc.750160106

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fatigue behavior of long fiber reinforced nylon 66 has been investigated by measuring fatigue crack propagation rates of injection molded samples. Plaques varying in thickness from 3 to 10 mm were employed for nylong 66 containing either glass, carbon or aramid fibers. Both conventional chopped, short fiber reinforcements and pultruded long fiber filled nylon 66 were examined. Long fiber reinforced nylon 66 exhibits improved fatigue resistance as shown by decreases in fatigue crack propagation rates compared to short fiber filled composites. Using a fracture mechanics analysis, it is shown that the improvements are due primarily to the higher moduli of the long fiber reinforced nylon 66, with only a slight increase in the calculated strain energy release rate associated with fatigue crack growth. For short or long glass fibers, and for short carbon fibers, the effects of fiber orientation on fatigue crack growth rates can be predicted from the fracture mechanics model. More significant effects of fiber length on fatigue fracture energies are noted for long aramid and long carbon reinforced nylon 66. It is also shown that thicker plaques can exhibit poorer fatigue fracture behavior owing to their inferior core sections.

ISSN:0272-8397    

DOI:10.1002/pc.750160107

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe response of the aramid reinforced aluminum‐epoxy‐laminate to uniaxial and biaxial fatigue loading has been investigated. The fracture process in the laminates propagates mainly in the form of cracks in aluminum layers, delaminations between the resin‐rich and fiber‐rich prepreg layers, splitting in prepreg layers and fiber fracture. Ultrasonic microscopy has been used to evaluate the shape and size of the damage zone. The ultrasonic images have been calibrated by means of SEM and optical microscopy of the laminates with sequential removal of the layers. Microscopic examination reveals a direct correlation between delamination, fiber fracture, and fatigue crack growth in the aluminum layer. The results of this investigation strongly suggest that the laminate resistance to tension‐tension biaxial fatigue is superior to that under uniaxial loading c

ISSN:0272-8397    

DOI:10.1002/pc.750160108

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractGreat efforts have been made in analyzing the strength of notched laminates under in‐plane loadings. However, no work has been reported on notched laminates under bending, because of the complexity of theoretical stress analysis. In this study, a simplified approach has been used to analyze the notched strength of laminated composites with an elliptical hole under bending. This approach combines notched sample experiments and finite element results. Based upon the consideration that not only the stress distribution at one ply, but also the stress variation across the laminate thickness, should be taken into account, two failure models are presented: a modified point stress model and a modified average stress model. Two characteristic parameters are presented to evaluate the notched strength of the laminated plate

ISSN:0272-8397    

DOI:10.1002/pc.750160109

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractBased on Barone and Caulk's model and a generalized variational functional, a finite element simulation was developed for the compression molding of thin and thick parts. For solving theu‐v‐ptype equations, an element‐based penalty method and a mixed formulation were implemented. Numerical results show that the new model gives better accuracy in velocity and velocity gradient than the Hele‐Shaw formulation for cases where both models are appropriate. Predictions of velocity and its gradient by the model are compared with other FEM results and BEM solutions. Using a fixed base mesh that covers the mold cavity, a new technique was developed for tracking the moving flow front. Temporary elements and nodes are generated for the filled part of elements intersected by the flow front. This method allows a smooth representation of the flow front and has exact boundary conditions on the flow front. The scheme is demonstrated for compression molding of an elliptical and an L‐shap

ISSN:0272-8397    

DOI:10.1002/pc.750160110

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA finite element simulation is proposed for the shaping of glass fiber fabric. The overall mechanical behavior of the fabric is obtained by combining the tensile behavior of a single thread and the current position of threads in the fabric. The constitutive model for a single thread in tension is based on a statistical approach and is identified using tensile tests. Shear and tensile tests have been carried out on fabric specimens to demonstrate that the behavior of the fabric mainly results from the contribution of each thread, the sliding between fiber threads having a small effect on the energy for the deformation mechanism of these fabrics. A numerical model for the shaping process is obtained based on a finite element approach using three‐ and four‐node membrane shell elements. The formulation accounts for the large displacements and large strains involved in the process as well as the mechanical behavior. A drawing simulation is presented in the case of an hemispherical punch. The comparison with experimental results obtained in this case shows good agreem

ISSN:0272-8397    

DOI:10.1002/pc.750160111

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY