Modelling of the degradation of mechanical properties of glass fiber reinforced composites (GFRP) due to environmental aging

• Κύριος συγγραφέας: Κελβερκλόγλου, Παναγιώτα
• Άλλοι συγγραφείς: Κωστόπουλος, Βασίλειος
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2018
• Θέματα: Composite materials; Environmental ageing; Σύνθετα υλικά; Περιβαλλοντική γήρανση; 629.134 42

The purpose of this Dissertation is to develop a methodology for estimating the lifetime of structures made out of glass fiber reinforced composite operating under conditions of hydrothermal ageing in the presence of mechanical loading and the application of this methodology to the air-conditioning system of modern civil aircrafts. Nowadays, the evolution of technology requires the detail study of the structural material used in a certain application as well as the detail structural analysis and the optimization of the component of interest, as part of the complete engineering system. This makes the analysis of the overall system a difficult but extremely interesting process that incorporates multi-functional applications that interact within the frame of life cycle analysis (LCA) of the full system. Aeronautic industry is pioneering in the direction of ‘Greening’ and the LCA approach has been incorporated in the design of modern aircrafts. The Environmental Control System (ECS) of civil aircraft is a vital subsystem for the safety and comfort of passengers. The ECS usually focuses on the inside part of the vehicle, whereas the environmental control of the outer side is usually named environmental protection system (EPS). ECS covers the cabin air conditioning (pressure, temperature, ventilation, humidity (e.g. windows defogging), and fire protection), the water and sanitation, the food, and solid waste, as well as others (such as fuel tank inertization, cabin furniture ergonomics, noise, lighting, entertainment). In the present dissertation, we will focus on the Air Conditioning Pack (ACP) of ECS, and more specifically on the plenum component of ACP. Plenum is a critical component of ACP, a diffuser-outflow chamber for the ram air and is heavily exposed to hydrothermal ageing in the presence of mechanical loading. The proposed methodology is based initially on the description and characterization of the materials from which the plenum is constructed, namely glass reinforced cyanate ester composite. Based on an extensive experimental work for the study of the hydrothermal ageing of glass reinforced cyanate ester composite at different temperature, the collected data was used for the development of an application, written in Python programming language, to predict/correlate the moisture absorption percentage, with property degradation, swelling and surface roughness development. This is a complete material model for the glass reinforced cyanate ester composite, and permits the calculation of hydrothermal stresses and eventually the prediction of failure of the plenum structure. This application, which in this thesis is focused on the air conditioning plenum component, can also be used in other structures made out of glass reinforced cyanate ester composite. The approach chosen for studying the hydrothermal ageing of composite materials involves degradation of mechanical properties and strengths as a function of temperature and exposure time and thus introduces a methodology of life prediction of the structure (Life Prediction Methodology). At the same time, however, because the absorbed moisture alters the geometry of the structure and the roughness of the surface of the composite material, the loads that are induced to the structure by the air flow within the plenum structure and the its supports, as well as the temperature profile change. Therefore, in the context of the present study, the hydrothermal ageing of the composite materials has been studied, but the problem solved in the application of the proposed methodology takes into account the change in mechanical and thermal loads to which the structure is exposed during its operation under hydrothermal ageing conditions. An integrated approach of the failure is proposed by applying the lifetime prediction methodology based on the stress analysis of the structure in the context of the changes described above.