Void formation model and measuring method of void formation condition during hot pressing process

Abstract

For resin matrix composites, voids are common defects that can seriously deteriorate the properties of the composite parts. Thus, the elimination of voids is a crucial element in controlling the manufacturing process of composite parts. This article focuses on void formation originating from hygroscopic water for resin matrix composite laminates prepared with hot pressing process. The Kardos void formation model was developed to analyze the critical resin pressure for the initiation of voids, and the influencing factors were investigated experimentally to validate the modified model. It is found that resin pressure and gel temperature are the two key parameters to control void defects and that entrapped air in prepreg stacks must be considered in the void formation model. Furthermore, a simple method was established to measure the relationship between porosity and the processing parameters, and the void formation conditions of the resin and the prepreg stack were also studied. The theoretically predicted void formation conditions and the experimental results were compatible for the studied cases. These results are valuable for eliminating void defects, optimizing processing parameters, and enhancing the performance of composite parts.

Voids formation and their effects on mechanical properties in thermoformed carbon fiber fabric‐reinforced composites

“…The voids formation mechanisms of carbon fiber‐reinforced composites have been intensively studied . Experimental results showed that small and spherical voids came from prepreg, either present before consolidation or generated by diffusion of water vapor during forming process, while large and elongated voids resulted from air entrapment and wrinkles created during lay‐up .…”

Methodology for Evaluating Manufacturability of Composite Materials

“…And the manufacturing knowledge applied to the quality manufacturability analysis should be exploited further based on guidelines, empirical data, statistical data and physical models. In addition, it is also necessary to develop a software tool to effectively support this methodology and provide a user interface to perform the manufacturability evaluation for the composite Table 3 Experimental results of glass fiber/epoxy 648 laminates [16] Sample no.…”

“…Gu et al [16] studied the effects of four quality indices such as relative humidity of prepreg, isothermal temperature T 2 and dwell time t 2 , as well as lay-up type of laminate and the applied pressure P 2 on the void formation based on the orthogonal experiment for epoxy 648 laminates. From the experiment results shown in Table 3, the applied pressure P 2 has the largest influence on void content.…”

“…Compared with the prohibitively expensive method of iterative testing, FEM simulations based on the physical model are now mature and increasingly accepted techniques for process simulation and optimization of composite structures. Recently, there are a number of studies developed to support the prediction of different quality issues in polymer composite processes such as stability of composite structures [12,13], porosity [14][15][16][17][18], un-uniform cure degree [19], delamination [20,21], residual strains [22], etc.…”

Role of Tool-Part Interaction in Consolidation of L-Shaped Laminates during Autoclave Process

“…Moreover, the resin pressure in the laminate increases with the improving slippage ability. This is helpful to eliminate the formation of voids in autoclave process [20].…”