High Performance Composite Structures for high temperature loads

Background

Increasing requirements for fiber composites for high-temperature applications such as aircraft engine cladding suggest the choice of matrix systems with high glass transition temperatures of up to 400°C. However, this material characteristic is often coined with reduced fracture toughness, which is why a carbon fiber-based, thin-film prepreg with modified plastic was developed within the framework of the European-funded SuCoHS project, which has an optimised compromise of these two properties.

Goals

The SuCoHs project aims to introduce polymer-reinforced fiber composites in areas with high temperature loads, where most metals are currently used, with a series of measures. The above-mentioned measures include not only the development of materials adapted to high-temperature applications, but also new virtual analysis methods for manufacturing and monitoring systems for production and operation. Carbon fiber-reinforced cyanate ester composites are of high interest in this context due to their high strength, stiffness, high thermal resistance and low moisture absorption for structural aerospace applications. However, the outstanding thermal properties of these materials are only achieved if they are cured at high temperatures of up to 260°C. This leads to the two difficulties that the material becomes brittle due to the high glass transition temperature achieved and, on the other hand, the component already experiences high temperature differences through the production process. In order to address the first problem, a matrix system has therefore been modified, which has an optimized compromise between fracture toughness and high glass transition temperature by adding additives

Results

In cooperation with the company NTPT, this modified system was processed into a thin film prepreg (87gsm) which can be stored with automated fiber positioning (AFP). The advantages of these so-called thin ply prepregs lie in an improved injury tolerance. The ThinPly Prepreg was used to create a demonstrator, namely a curved panel, using AFP and integrated sensor systems.

In addition, the high curing conditions of up to 260°C required in the production of components from this material lead to process-related deformations and residual stresses, which can be noticeable in a reduced component performance. In order to analyze the residual stresses and process-related deformations, a holistic thermomechanically coupled material description was implemented in a transient simulation. For this purpose, a material model was used, which records the material properties during the curing process of carbon fiber / cyanate ester composite parts and depicts the curness-dependent behavior with a viscoelastic approach.

The developed model was demonstrated at an aerospace application by a representative curved and stiffened panel.