**Background**
Recent advances in fabrication of unidirectional prepreg materials have allowed for the realization of ultra-thin composite laminas with ply thicknesses of below 70 μm by using tow-spreading techniques. These in turn, can be used to design thin laminates for ultra-lightweight structures in aerospace applications or for morphing structures where the thin material allows for small bending radii and hence high deformations. In addition, the ultra-thin plies are ideal for adaptation to mould-less fabrication techniques, where complex shapes can be obtained from flat laminates due to thermal residual stresses during the cure of the composite. Such a technique has the potential to save significant processing costs as it eliminates the need for machining of expensive moulds. However, dimensional accuracy is often a strict requirement in aerospace applications and there are significant difficulties in accurately predicting the curvatures realized via residual stresses.
**Motivation**
Thermal residual stresses have been used as a technique in CMASLab for mould-free fabrication of corrugated structures and cylindrical shells. However, it has been found that many parameters in the composite cure, other than the thermal coefficient mismatch of the constituent materials, can significantly influence the final curved shape of the thin composites. To date, no systematic inves-tigation of the cure parameters has been carried out and no simulations exist for predicting the cured composite shapes.
**Background** Recent advances in fabrication of unidirectional prepreg materials have allowed for the realization of ultra-thin composite laminas with ply thicknesses of below 70 μm by using tow-spreading techniques. These in turn, can be used to design thin laminates for ultra-lightweight structures in aerospace applications or for morphing structures where the thin material allows for small bending radii and hence high deformations. In addition, the ultra-thin plies are ideal for adaptation to mould-less fabrication techniques, where complex shapes can be obtained from flat laminates due to thermal residual stresses during the cure of the composite. Such a technique has the potential to save significant processing costs as it eliminates the need for machining of expensive moulds. However, dimensional accuracy is often a strict requirement in aerospace applications and there are significant difficulties in accurately predicting the curvatures realized via residual stresses.
**Motivation** Thermal residual stresses have been used as a technique in CMASLab for mould-free fabrication of corrugated structures and cylindrical shells. However, it has been found that many parameters in the composite cure, other than the thermal coefficient mismatch of the constituent materials, can significantly influence the final curved shape of the thin composites. To date, no systematic inves-tigation of the cure parameters has been carried out and no simulations exist for predicting the cured composite shapes.
**Thesis Objectives**
This work shall provide a fundamental experimental and numerical analysis of how curing parameters influence the final shape of ultra-thin laminates. Initial observations have shown a strong influence of the release film and the specimen’s orientation within the autoclave. Therefore, the influence of the curing setup’s boundary conditions shall be investigated for a wide range of specimens in order to determine all relevant curing parameters and to quantify their effect. Based on the experimental analysis, a parametric Finite Element Model shall be created and validated to allow an accurate prediction of the cured shape for arbi-trary layups for future projects.
**Thesis Objectives** This work shall provide a fundamental experimental and numerical analysis of how curing parameters influence the final shape of ultra-thin laminates. Initial observations have shown a strong influence of the release film and the specimen’s orientation within the autoclave. Therefore, the influence of the curing setup’s boundary conditions shall be investigated for a wide range of specimens in order to determine all relevant curing parameters and to quantify their effect. Based on the experimental analysis, a parametric Finite Element Model shall be created and validated to allow an accurate prediction of the cured shape for arbi-trary layups for future projects.
ETH Zürich, Dr. Maria Sakovsky, LEE O 204, Leonhardstr. 21, 8092 Zürich
ETH Zürich, Michael Kölbl, CLA E 32.2, Tannenstr. 3, 8092 Zürich
ETH Zürich, Dr. Maria Sakovsky, LEE O 204, Leonhardstr. 21, 8092 Zürich
ETH Zürich, Michael Kölbl, CLA E 32.2, Tannenstr. 3, 8092 Zürich