Period: 09/2023 – 08/2026 (36 months)
Project Investigators of AMADE:
Emilio Vicente González Juan emilio.gonzalez@udg.edu (IP1)
Joan Andreu Mayugo Majó (IP2)
Project manager: Emilio Vicente González Juan
Other AMADE people involved in the project: Norbert Blanco, Lluis Ripoll, Jose Manuel Guerrero
Grant agreement number: MICIU/AEI/10.13039/501100011033 y por FEDER, UE
Grant PID2022-137979OB-I00 funded by MICIU/AEI/10.13039/501100011033 and by FEDER-European Union
Funded by: » Agencia Estatal de Investigación” (AEI), “Ministerio de Ciencia e Innovación” (MCIN) and by FEDER – European Union under reference PID2022-137979OB-I00 MICIU/AEI/10.13039/501100011033
Carbon Fiber Reinforced Polymers (CFRP) have been drawing great attention due to their unprecedented mechanical properties that can enable to make light but strong vehicle bodies and parts. Polymer-based composites are largely divided into thermoplastic and thermosetting polymers. Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied. On the other hand, thermoplastics soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be recovered without negatively affecting the material’s physical properties.
So far, thermoset-based composites have been extensively used in the aeronautical industry during the last 30 years and this trend is far away from being stopped. Indeed, global demand for carbon fibres is expected to increase where in the case of the aviation sector is expected to generate about 450,000 tons of accumulated thermoset-based CFRP waste from the production and end-of-life phase [1]. Existing EU regulations drive the aviation industries to make efforts in carefully dealing with production and end-of-life waste materials, e.g. the European Waste Framework Directive (2008/98/EC) requires the adoption of the waste management hierarchy (3R strategy): Reduce, Reuse, Recycling and Disposal. Current thermoset-based CFRP recycling techniques are based on either, mechanical recycling processes, in which the waste is reduced in size to produce fibrous or powdered materials, or thermal processes, in which the polymer is removed to yield a “clean” fibre. However, so far, there have been almost no cases where recycled carbon fibres have been used for mass production. On the other hand, thermoplastics have shown better recyclability/remoulding, long storage time, better chemical and environmental resistance, and reduced moisture absorption compared to thermosets. Therefore, the use of thermoplastics as a matrix material in CFRP has been growing steadily, especially in automotive and aerospace applications, largely due to their cost-effective production, the ability to be easily joined using heat welding techniques allowing easy repairing, and thermoforming. Moreover, they also offer improved fracture toughness over thermosets, potentially improving the behaviour under specific loading conditions such as in impacts.
Accordingly, the use of new high-performance thermoplastic composites (TPC) as an alternative for manufacturing primary structures with optimized weight is currently a topic of special interest. As a recent example, Airbus Atlantic manufactured an innovative TPC sized fuselage for A350 aircraft. The outcomes of such structure were: less energy consumption compared to autoclave or thermosets, consolidation time reduced by 50% vs thermoset curing process, reduced investment without autoclave, and use of self-heated tooling to maximize energy efficiency.
However, the implementation of TPC depends on breaking through some key difficulties: a good description of the mechanical behaviour at the material level, and the development of advanced analysis models capable to predict all dissipative mechanisms, specially under dynamic loading.
The use of Finite Element Analysis (FEA) tools is one of the main design methodologies for these structures. The accuracy of FEA predictions relies mostly on the material properties and the implemented constitutive laws. Generally, the material properties required for the numerical analysis are characterised under quasi-static loading conditions, however, these properties are usually used to feed constitutive models for the dynamic simulation of a given structure. In part, this is due to the fact that there are no standards for the characterization of the dynamic properties of CFRPs, and moreover, the literature is very scarce without a clear consensus between authors for a given property. Therefore, it is necessary to develop suitable test methods to obtain reliable input data for the material models used for dynamic loading, especially for TPC on properties governed by the matrix’s behaviour, such as the interlaminar crack propagation properties.
For all that has been described, the CRAPYREC project aims to increase the knowledge of the behaviour of TPC materials subjected to different loading rate conditions, from the quasistatic to the dynamic regime, for the particular case of the interlaminar crack propagation properties. The contribution will help to the application of TPC in primary transport structures, as an alternative to thermoset-based composites, promoting the circular economy of structures made with lightweight advanced composites materials through the use of recoverable polymers, and therefore reducing the associated carbon footprint.
Technical description
CAPRYREC focuses on the determination of the properties associated to the propagation of interlaminar cracks in Mode I, Mode II and Mixed Mode I/II. The methodology of the proposal is based on an initial determination of the best manufacturing parameters of the material. For this, different manufacturing tests will be carried out and physical properties of the resulting material, such as the degree of crystallization of the matrix, glass transition temperature or its corresponding melting temperature, will be verified. On the other hand, the corresponding mechanical properties of the manufactured panels will be determined by means of an experimental campaign to guarantee that they are within the acceptance range determined by the manufacturer. In parallel, reliable test methods will be developed with which to determine the interlaminar toughness of this type of materials under different load application speed rates, both in Mode II and in Mixed Mode I/II. For this, we have the experience of having already developed a test method to determine this property in Mode I. Special attention will be paid to ensure that the inertial effects in the test tools are minimized and that the speed of load application is constant during the crack propagation phase.
For the analysis of the experimental results, it will be necessary to have a clear criterion to determine when the inertial effects can be ignored in a dynamic load application, thus allowing the simplification of the determination of the experimental properties. This criterion will be developed through finite element analysis of the test methods developed in combination with a dimensionless analysis to determine the determining test parameters and establish a time-based criterion from which a quasi-static scheme can be used.
For the correct design of structural elements based on TPCs, it is necessary to have design and simulation tools that include the effect of the load application speed on the material properties. For this, it is intended to make use of finite elements and to formulate and implement the variation of interlaminar toughness with strain rate in the constitutive model of cohesive elements.
It is expected that at the end of the project a procedure will be achieved allowing the characterization and simulation of the propagation of interlaminar cracks in thermoplastic matrix composite materials in a reliable way. Therefore, a higher use of TPC for transport applications will be promoted, thus reducing fuel consumption and associated pollution while allowing greater recycling of the material at the end of its useful life with the consequent reduction of the carbon footprint
A total of 9 Work Packages (WP) have been defined in CRAPYREC: WPs 1-7 cover the scientific activities, while WPs 8 and 9 are devoted to the management/coordination and dissemination of the project (see Figure).
