Costanzo Bellini

To design the cure process of thick composite parts: experimental and numerical results

The cure degree must be as uniform as possible during the manufacture of polymer matrix composite components in order to have a product without defects. For thick composite components, this condition is not often respected; in fact, the cure degree trend between the core and the external surface is different causing structural and geometrical/dimensional unconformities. In most cases, these problems can be solved through a redesign of cure process in terms of thermal cycle, in fact that one recommended by furnisher is usually suitable for thin components. The optimization of cure thermal cycle should include several performance criteria for the production system such as the targeted cure degree, the targeted maximum temperature of the part and the duration of the cure cycle, as well as the production system limitations such as the maximum allowable heating rate, the maximum allowable cooling rate and so on. A previous work shows a method to optimize the cure degree of a thick composite component. The present work presents an indirect way to validate the proposed method: some experimental tests have been carried out by implementing the cure cycle identified by this method, the values of temperatures have been recorded by thermocouples and the obtained temperature trend has been compared with that due to numerical approach. Further considerations on the cure degree and the cure rate have been deduced. The experimental results show a good agreement with the numerical ones.

Compaction influence on spring-in of thin composite parts: Experimental and numerical results

Geometric unconformities may arise due to residual stresses during the manufacturing process of polymer matrix composite materials. Compaction of the laminate, due to resin squeeze, is another phenomenon that occurs and it influences the mechanical behaviour of the laminate itself. In the past, models for spring-in or for compaction were developed separately, whereas in the present work a new kind of analysis is developed to take into account both residual stresses and compaction that take place during cure simultaneously. This analysis is composed by two different steps: in the former the compaction is predicted, in the latter the cure state and the residual stress condition are determined. Finally, the relationship between different degrees of compaction and the corresponding values of spring-in is studied, and it was found that a higher value of thickness reduction produces the smallest residual stresses for the composite structures with angled cross sections.

Validation of a Methodology for Cure Process Optimization of Thick Composite Laminates

The cure degree must be as uniform as possible during the manufacture cycle of polymer–matrix composite laminate to obtain parts without defects. Thermal cycle recommended by technical sheet is usually suitable for thin components, so its redesign is necessary to solve unconformities for thick laminate parts, which usually show these problems. In this study, a methodology to optimize the cure cycle of a thick composite laminate, presented in previous studies, has been validated by a more reliable direct method based on dielectrical analysis through the use of an interdigital sensor capable to measure the local cure degree trend. GRAPHICAL ABSTRACT

New methodology to determine the compressibility curve in a RIFT process

In liquid resin infusion processes, the compression phase and the resin flow are important stages that influence the quality of the obtained parts. In this study, an experimental device is presented to measure thickness and pressure variations in order to obtain an experimental compressibility curve that can be implemented in a software dedicated to numerical simulations. To perform these experiments no typical compression testing machine is required and there is no test fluid. The aim of this work is to present a new methodology in order to obtain an empirical relation to determine the compressibility as a power law function. In order to evaluate the reliability of the proposed methodology, the obtained experimental curve is compared with another curve achieved performing standard compaction test.

Hard and soft computing models of composite curing process looking toward monitoring and control

The curing process of thermosetting resins plays a key role on the final quality of the composite material components. Soft computing techniques proved to be an efficient method to control and optimize the curing process, replacing the conventional experimental and numerical approaches. In this paper artificial neural network (ANN) and fuzzy logic control (FLC) were implemented together to predict and control the temperature and degree of cure profile during the autoclave curing process. The obtained outcomes proved the capability of ANNs and FLC with respect to the hard computing methods.

Neural-fuzzy optimization of thick composites curing process

ABSTRACT This article addresses the optimization of curing process for thick composite laminates. The proposed methodology aims at the evaluation of the thermal cycle promoting a desired evolution of the degree of cure inside the material. At the same time, temperature overshooting as well as excessive temperature and cure degree gradient through the thickness of the material are prevented. The developed approach is based on the integrated application of artificial neural networks and a fuzzy logic controller. The neural networks promptly predict the behavior of composite material during curing process, while the fuzzy logic controller continuously and opportunely adjusts the proper variations on the imposed thermal cycle. The results highlighted the efficiency of the method in comparison with the cure profiles dictated by the material suppliers. For thick laminates, a reduction of 35% of cure time and improvements of approximately 10% of temperature overshooting was obtained compared to conventional curing cycles. The method was validated by experimental tests.