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Pulling force modeling and analysis in conventional pultrusion and Resin Injection Pultrusion (RIP) of vinylester resin were carried out in this study. Based on the friction coefficient value of the liquid resin, an analytical model was developed to predict the resistance force in the injection die. A thermal expansion– polymerization shrinkage model and a friction coefficient model, combined with the temperature and resin conversion profiles along the die, were used to predict the resistance stress in the heating die, and to determine the composite separation point from the die wall. The simulation results were verified by the experimental data in the conventional pultrusion and RIP processes. The comparison shows that the models and the simulation tool developed in this study are capable of predicting the pulling force in the entire die with good agreement.

Pulling force is the summation of resistance forces along a pultrusion die. Its mechanism is complicated because the impregnated resin inside the compressed fiber reinforcement changes from a liquid to a gel, and finally to a solid in the die. Two methods, a ‘mat tracer’method and a ‘short die length’ method, were used to determine the pulling force distribution. Results show that the downstream part of the die contributes little to the pulling force. In order to predict the resistance force in both the injection die and the heating die, two models were developed in this study. A friction measurement device was designed to measure the friction coefficient between the composite and the mold surface. The effect of process variables, such as temperature, resin conversion, normal force, and line speed, on the friction coefficient was investigated and a friction coefficient model was proposed based on the experimental results. A volume change model of vinylester resin was also developed to predict the thermal expansion–polymerization shrinkage during curing. The parameters of the model were determined by dilatometry, thermomechanical analysis (TMA) and differential scanning calorimetry (DSC).

Gas diffusion is important in composite manufacturing, while moisture diffusion is important for composite performance. In this study, analytical models are developed to predict the mass diffusivity of both square and hexagonal arrays of cylindrical cylinders. These models are able to bridge the gap between continuum calculations via finite differencing of finite element analysis and simple/trivial models. By breaking the liquid region into zones and making some general assumptions about the diffusion in those zones, simplified models have been developed, which rely solely on the geometry and fiber volume fraction. The models are fairly accurate for a broad porosity range, but specially at low porosity values. A single weight factor is proposed to compensate for the error introduced by the model assumptions. When the weight factor is incorporated, the modified models agree extremely well with the experimental data for the whole porosity range.

This work investigates the preforming process of composite ducts made of biaxial braided fabrics. Two models based on the geometric modeling were developed to predict the fiber orientation and surface density. It is found that fabrics tend to slip during preforming in the case of curved ducts. A slip coefficient was introduced in the model to take this into account. A series of experiments were conducted to validate the models. The results show good agreement between model prediction and experiments.

This paper investigates the manufacturing method and mechanical properties of composite tubes made from braided fiber preforms. The tubes molded by Vacuum-Assisted Resin Transfer Molding (VARTM) process with different resins, fiber reinforcements and braiding architecture were tested for weeping and burst strength. Both biaxial and triaxial braided fiber preforms were used. The failure modes of tubes made from these two braiding architectures were different. For biaxially reinforced tubes, the initial cracks are aligned along the direction of the fiber tows, while for triaxially reinforced tubes, the initial cracks along the longitudinal direction appear first. Tubes with and without flanges were also fabricated. The strength tests indicated that the tube with flanges is much stronger than the one without flanges. Two theoretical models based upon mechanics of material were employed to predict the mechanical properties. The pressure vs. deformation curves from the weep/burst tests are consistent with the theoretical predictions in the elastic region.