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Because of the increasing use of polymer composites in a wide variety of industrial applications, the manufacturing of complex composite parts has become an important research topic. When a part is manufactured by liquid composite molding (LCM), the reinforcement undergoes a certain amount of deformation after closure and sealing of the mold. In the case of bidirectional woven fabrics, this deformation may significantly affect the resin flow and mold filling because of changes in the values of permeability. Among other considerations that govern the accuracy of numerical simulations of mold filling, it is important to predict the changes of permeability as a function of the local shearing angle of the preform. The resin flow through a fibrous reinforcement is governed by Darcy's law, which states that the fluid flow rate is proportional to the pressure gradient. The shape of the flow front in a point-wise injection through an anisotropic preform is an ellipse. Part I of this article describes a new methodology based on the ellipse equation to derive the in-plane permeability tensor from unidirectional injection experiments in deformed woven fabrics. Part II presents a mathematical model that predicts the principal permeabilities and their orientation for sheared fabrics from the permeability characterization of unsheared fabrics. Unidirectional flow experiments were conducted for a nonstitched, balanced, woven fabric for different shearing angles and fiber volume fractions. This article presents experimental results for deformed and undeformed fabrics obtained by unidirectional flow measurements. A comparison of the proposed characterization methodology with radial flow experiments is also included. POLYM. COMPOS., 28:797-811, 2007.

The production of polymer composites by resin injection has strongly increased in the recent years for a wide variety of industrial applications. Manufacturing techniques are continuously optimized for higher and faster production cycles and high performance composites are needed to meet industrial requirements. Actually, the reduction of cost and cycle time is the main motivation for liquid composite molding (LCM) process simulation. In this context, the characterization of preform permeability is a key issue in numerical flow analysis. This investigation concerns the experimental study and development of a predictive model for deformed fabric permeability. Such deformations occur when a fabric is draped on a complex surface. A local shear appears. In Part I, an experimental procedure has been described to measure the permeability of deformed fabrics, and a new methodology presented to characterize the in-plane permeability tensor. In order to implement experimental results in numerical simulation, a permeability model for deformed fabrics is required. Part II develops a predictive model of the principal permeabilities of deformed fabrics and of the orientation of the permeability tensor. Based on unsheared fabric measurements, the model takes into account the unit cell deformation during shear and the initial elliptic flow pattern orientation and anisotropy ratio of undeformed fabrics. Model predictions are corroborated with sheared fabric measurements. Finally, numerical simulations for an automotive body part are carried out to illustrate the effects of fabric shearing on the filling of the composite part. POLYM. COMPOS., 28: 812-827, 2007.

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In order to further advance the state of the art in the electron beam processing of polymers and composites, it is necessary to better understand the development of cure-induced residual stresses. In situ measurement of electron beam cure–induced stress development is challenging due to the bombardment of specimens with intense beams of very high-voltage electrons. In this study, a custom fixture was designed to measure the deformation of an electron beam–cured specimen during processing and thereby to assess specimen stress state during the curing process. The unbalanced composite specimen consisted of two cured unidirectional carbon–epoxy laminates separated by a thin woven fibreglass carrier, which was infused by a layer of electron beam curable epoxy resin systems (Tactix 123 and CAT B). The out-of-plane specimen deformations were monitored during various electron beam irradiation schedules and subsequent thermal post-cure. The preliminary results confirmed that the apparatus was not affected by the irradiation and was capable of accurately measuring the specimen warpage during the cure. It was also shown that the electron beam–cured specimens exhibit a reduced residual stress state compared to equivalent thermally cured specimens. It was observed that the irradiation dose rate applied to a specimen is the main factor in the difference in the way residual stresses develop during electron beam curing. Furthermore, the results suggest that there is a direct relation between the stress-free temperature (TSF) and the temperature of the specimen at gelation (TGEL).