No abstract

As new developments are brought to the group of manufacturing processes for composite parts known as liquid composites molding (LCM), the compaction behavior of the textile reinforcements is increasingly seen as an important parameter of the definition of these processes. The evolution of the permeability tensor of the reinforcements with time, the general kinetics of the manufacturing operations, and the modelization of these processes depend on a large extent on the compaction behavior of the reinforcements used, especially in flexible‐wall RTM and autoclave molding. Also, more research efforts are devoted toward the development of a complete analytical model of the properties of heterogeneous textile reinforcements. In this paper the published experimental data related to the compaction and relaxation of random mats and woven reinforcements are gathered. Observed parameters are defined, which allow numerical comparisons of the experimental curves to be made, as well as the identification of general trends seen with most tested reinforcements. The effects of various processing parameters are identified, and relations to published analytical models of the mechanical properties of fibrous assemblies are discussed.

No abstract

The objectives of this series of papers are to describe the mechanical behavior of textile reinforcements under normal load and to quantify the effects of diverse processing parameters on that behavior. In the first and second papers of the series, experimental compaction and relaxation results were reported; general trends were identified and the effects of changes in the processing parameters were analyzed. In this paper, the results of sequences of successive compaction cycles applied to dry textiles and to textiles saturated in distilled H2O and silicone oil are presented. The reinforcements investigated are produced by assembling tows or rovings following different patterns; it is shown that the resulting heterogeneity, or regular variation of the local fiber volume fraction, can be associated to some particular elements of the mechanical behavior of the reinforcements. The reorganization of the fiber network and the effect of friction at the fiber contacts are demonstrated. Different stages in the reorganization process are identified; each stage is controlled by different parameters and corresponds to a precise behavior. Successive compaction cycles applied to a preform can reduce the void content of the final part.

Previous analysis of published experimental results on compaction and relaxation of textile reinforcements allowed the effects of some processing parameters on the mechanical behavior of the reinforcements to be identified. However, a limited number of relaxation results are available; also, the effect of some parameters on compaction received limited attention, and the behavior observed with fluid-saturated reinforcements has not been investigated. In this paper, the results of a structured experimental program of compaction and relaxation performed on three woven reinforcements are reported. In half the trials, a relaxation period was imposed on the samples. In the other half, samples saturated with distilled H, O were compacted. The selection of the processing parameters was found to be as important as the selection of the reinforcement itself for the definition of a manufacturing operation. The processing parameters governing the compaction and relaxation were seen not to be the same, and the fiber reorganization that occurs during the compaction phase was found to have a different effect on successive compaction cycles than the reorganization occuring during the relaxation. (1)Darcy's empirical law was generalized for the case of high speed flows (2, 3) to be known as Forchheimer's (Lv K -VPJ = -*Corresponding author.