Abstract
This work had four primary objectives:1. Identify the influential parameters during epoxy curing.
2. Quantify the effect of measured process variability on curing.
3. Propose manufacturing concepts for cure gradients desirable for co-curing.
4. Demonstrate the influence of initial degree of cure on thermoplastic-thermoset co-curing.
The most influential sources of variability in composite processing were determined by sensitivity analyses using coupled heat transfer and cure kinetics models. The analyses showed, that in the standard aerospace case considered, cure temperature has the most influence and diffusion limiting cure kinetic effects become highly influential post vitrification.
To demonstrate the effect a source of process variability can have, calorimeter measurements from industrial scale ovens and autoclaves were used as inputs to a numerical model. It was shown that with the higher heat transfer coefficients in the autoclaves, spatial variability in thermal conditions was less influential. However, this effect was counteracted by the greater variability in the autoclaves, resulting in comparable repeatability between the two vessel types.
Combinations of tool material, tool thickness and heat transfer coefficient were explored for maximising part stiffness while retaining bonding surface reactivity for co-curing. A thick, thermally diffusive tool for the bonding surface and a thin, low diffusivity tool elsewhere, in an out-of-autoclave environment was proposed.
The effect of initial degree of cure on thermoplastic-thermoset co-curing was investigated at the laminate level. A diffusion model was derived from in-situ measurements of interdiffusion between polyetherimide and a model epoxy system. The model predicted that any increase in initial degree of cure decreased the interaction across the interface. This was supported by mechanical test results and interphase thickness measurements. The results indicated that unlike conventional co-curing, the manufacturing efficiency benefits from increasing the initial degree of cure cannot justify the significant decrease in bond strength.
| Date of Award | 5 Dec 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Arjun Radhakrishnan (Supervisor) & James Kratz (Supervisor) |