18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS OPTIMIZATION OF MECHANICAL PROPERTIES OF BASALT WOVEN/APA-6 COMPOSITE PARTS BY MEANS OF VELOCITY CONTROL R. Hoto 1 , J.Andrés 1 , B. Cabillic 2 , Ll. Gascón 1 , J.A. García 1 * 1 Universidad Politécnica de Valencia. Camino Vera s/n, 46022, Valencia (Spain). 2 Ecole Central de Nantes 1 rue de la Noë BP 92101 44 321 Nantes Cédex 3 * Corresponding author: (jugarcia@mcm.upv.es) Keywords : Balsalt fibers, LCM, Void content, Saturation, Anionic PA-6 reactants (Monomer ( Ɛ -caprolactam) + Activator + 1 General Introduction Initiator) are injected through the reinforcement, Nowadays the use of liquid composite molding being it a low energy consumption process. It is (LCM) processes for the development of composite followed by a catalyzed ring opening reaction, parts for both structural and non-structural which take place at temperatures between 130 and applications has become of increasing interest. 190 degrees and completed within 2 to 50 minutes, Carbon fiber has been traditionally used as depending on the amount and the type of activator reinforcement for its outstanding properties and initiator. The result is a high molecular weight (chemically inert and very stiff), but it has the linear polymer ( anionic PA-6, APA-6) [2]. In this disadvantage of its high cost. Glass fiber is process, it is also to remark that the void content, susceptible to undergo surface damage and to be together with the fiber volume fraction, the sensitive to alkaline environment. Additionally, the microstructure of the preform, will affect the current environmental requirements promote the use mechanical performance of LCM obtained parts. of natural fibers as reinforcement, in order to The main objective of this paper is to validate the achieve more sustainable GreenComposites . In this use of APA-6 as matrix material of basalt fibers. It context, basalt fibers are an alternative to current studies the dependency between injection flow rate reinforcements. They are obtained directly from the and void content, which affects final mechanicals molten single material, thus being biologically properties o the part. FEM simulation is suggested to inactive, non-toxic, good electric insulator, and optimize the filling process, opposed to commonly resistant to high temperature. Moreover they exhibit used trial and error methods at shop floor. mechanical properties comparable with those of E- glass [1]. 2 Overview on the anionic polymerization of ε - caprolactam These new Greencomposites also assume the use of a thermoplastic matrix ( Thermoplastic Composites , In the APA-6, the most important intermolecular TpC’s). The matr ix determines most of the force is hydrogen bonding. The nitrogen-bonded mechanical and chemical properties. Unlike hydrogens of one chain will bond very strongly with thermoset-based matrices, their thermoplastic the carbonyl oxygens of another chain, resulting in counterparts can be recycled or reprocessed. In great physical properties [2]. These interactions are addition, Tp C’s do also offer higher mechanical obtained via a classical ring-opening anionic properties [2]. polymerization. This reaction is a polyaddition reaction, that is, in ideal conditions (free-moisture Polyamide-6 (PA-6) currently used in industry is environment), no byproducts are produced. It hydrolytically polymerized and delivers pellets, requires an activator and an initiator that will ensure which are further thermoformed into parts. But the both initiation and propagation of the reaction. molten viscosity of thermoplastic resins is very high, Reactants are shown in Fig. 1. which makes it difficult to impregnate thermoplastic resin into fiber bundles. To overcome this problem, The initiator has to be a very strong base to break anionic reactive processing is used as an alternative the N-H bond of the ε -caprolactam, in order to form way to obtain PA-6: initial low viscosity raw a reactive amide. Introducing an activator will lead
original form, Darcy’s Law is not very useful us to have very reactive imides, allowing, after an induction time , a very fast chain growth because the permeability term (K h ) term is polymerization. This reaction time is due to the dependent on the properties of both the fluid and difference of reactivity between amides and imides. porous medium: This difference simply relies on the number of P reactive carbonyl carbons, two for the imides against (1) Q K ·A· h one for the initial amide. One can modify the x induction time (from 2 to 50 minutes [2]), using the where Q is the volumetric flow rate, A is cross different reactivity of the common activators and sectional area of the flow, dP/dx is the pressure initiators. The reaction will end when any proton gradient and K h is a constant of proportionality donating species neutralizes all anionically-charged known as the hydraulic permeability. In order to polymeric chains. separate the influences of the two constituents, K h was defined in terms of fluid viscosity μ and permeability K, which is dependent on the structure of the porous medium only : K K (2) h μ This concept was popularized by Wyckoff et al. in 1933 and has been validated by many successful determinations of permeability. The practice has converged on the use of the tensorial form of Darcy’s Law for anisotropic media: K ij (3) v · P i i μ Fig. 1. Up, reactants used; (a) monomer, (b) initiator, (c) activator; down, reaction mechanism for where K is the second order symmetric ij APA-6 polymerization permeability tensor (its value depends on the 3 Governing Equations v is the volume averaged direction of the flow), i 3.1 Darcy’s Law “Darcy velocity”, μ is the viscosity of the resin, and P Flow through porous media is usually treated as a is the pressure gradient. For non-isothermal i flow Newtonian governed by Darcy’s Law and the mold filling, the resin is a function of temperature continuity equation. In such considerations, the and degree-of-cure. process is modeled either as a flow through fully The continuity equation for the flow in RTM process saturated or as a flow through unsaturated porous of an incompressible resin through a porous medium media. Modeling and measurements through can be expressed as: saturated porous media is much easier since it practically involves only unidirectional Darcy’s v=0 (4) flows and corresponding simple theoretical models Inserting eq. (3) into (4) lead to the following [1]. However, in a wide range of application of simplified form: porous media such as in LCM processes, unsaturated permeability is more important for the analysis of K ij initial fabric wet out, which requires more · P 0 (5) μ i sophisticated models and an in-depth analysis of two or three-dimensional theoretical models. In its
Recommend
More recommend
