Evaluation of the crosslinking steps of an unsaturated polyester resin during the infusion process of polymer-matrix composites using embedded PZT transducer

Corentin Tuloup,Walid Harizi,Zoheir Aboura

doi:10.25518/esaform21.2693

Abstract

The originality of this study lies in the real-time monitoring of the crosslinking steps of the polyester resin during the Liquid Resin Infusion (LRI) process of polymer-matrix composites (PMC) by a simple measurement of the electrical capacitance variation of a PZT (Lead Zirconate Titanate) transducer embedded into the heart of the fibrous stack. Three mass rates of a Methyl Ethyl Ketone Peroxide (MEKP) hardener were tested (1wt%, 1.5wt% and 2.5wt%). The electrical capacitance showed a very sensitivity to the crosslinking kinetics while identifying the key steps of the physicochemical transitions of the thermosetting matrix. To identify the promising potential of the PZT transducer as a real-time curing assessment tool of the thermosetting resins, and understand its capacitance signature, the LRI device was multi-instrumented by various non-destructive testing (NDT) techniques such as acoustic emission (AE) and infrared thermography (IRT). The obtained NDT results are confronted with the ones conducted using the oscillatory rheology tests. The agreement between the two types of results (NDT and rheological) allows determining the gelation and vitrification phases of the polyester resin impregnating six plies of 2/2 twill glass fabrics.

Highlights

Nowadays, polymer-matrix composite (PMC) materials are invading the industrial domains by ensuring many structural applications
We propose to integrate, for each PMC plate, a PZT (Lead Zirconate Titanate) transducer within its reinforcement stack composed of six 2/2 twill glass fabrics, and follow the different stages of crosslinking of the polyester resin by a measurement of the electrical capacitance variation of the embedded PZT during the different phases of the Liquid Resin Infusion (LRI) process
All PMC plates are manufactured using the LRI process: a fiber stack is arranged on a mold previously coated with a release agent, covered with a vacuum bag, and impregnated by a degassed beforehand (-0.4 bar–4 minutes) liquid polyester resin until saturation of the preform, the resin flowing through the stack thanks to the vacuum created in the system (-0.65bar)

Summary

Introduction

Polymer-matrix composite (PMC) materials are invading the industrial domains by ensuring many structural applications. The Liquid Resin Infusion (LRI), part of the Liquid Composite Molding (LCM) techniques along with Resin Transfer Molding (RTM) and their variants, is significantly very used in wind and shipbuilding industries [1] due to its ability to produce parts with big dimensions and complex geometries in one shot, without need for further machining. Other techniques, such as RTM or autoclave, are limited by the size and complexity of the molds (for RTM), and by the size of the pressurized oven and the price (for autoclave). We propose to integrate, for each PMC plate, a PZT (Lead Zirconate Titanate) transducer within its reinforcement stack composed of six 2/2 twill glass fabrics, and follow the different stages of crosslinking of the polyester resin (gelation and vitrification) by a measurement of the electrical capacitance variation of the embedded PZT during the different phases of the LRI process

Manufacturing of PMC specimens

Oscillatory rheology

Multi-instrumented PM setup mutualizing several NDT techniques

Impact of MEKP hardener rates on the NDT signatures

Comparison between the LRI results and rheological measurements