Thermo-oxidation behaviour of organic matrix composite materials at high temperatures

The present paper is a review of the main activities carried out within the context of the COMPTINN‟ program, a joint research project founded by a FUI program (Fonds Unifiés Interministériels) in which four research teams focused on the thermo-oxidation behaviour of HTS-TACTIX carbon-epoxy composite at „high‟ temperatures (120°C-180°C). The scientific aim of the COMPTINN‟ program was to better identify, with a multi-scale approach, the link between the physico-chemical mechanisms involved in thermo-oxidation phenomena, and to provide theoretical and numerical tools for predicting the mechanical behaviour of aged composite materials including damage onset and development

Effets de la thermo-oxydation sur le comportement mécanique de matériaux composites pour applications aéronautiques

It has been previously shown that, at medium temperatures, carbon fibres -epoxy matrix composites can be affected by thermo-oxidation that is a coupled phenomenonof oxygen diffusion and chemical reaction taking place in the oxidation sites present in themolecular structure of the organic matrix. Thermo-oxidation can lead to damage thecomposite surface, without any applied external load.This work has been conducted within the framework of the COMPTINN' project, aiming tostudy the effects of thermal oxidation on the mechanical behaviour of two polymers (an epoxyresin and a polyimide resin) and of the corresponding composites (carbon fibre), and tocharacterize the matrix damages promoted by isothermal ageing. This study is composed ofthree parts: development of a new numerical/experimental technique for characterizing theeffects of thermal oxidation on the local mechanical behaviour of the studied polymers andidentification of a constitutive law; development of a new numerical/experimental approachfor calculating the matrix shrinkage field on the unidirectional composite surfaces, whichleads, during ageing, to the onset of fibre/matrix debonding phenomenon; development of anovel experimental technique for studying the interaction between the mechanicalsolicitations and the oxidation degradation mechanisms through fatigue tests.L’oxydation conduit à une modification des propriétés mécaniques de la matricepolymère, associée à sa fragilisation, et à la création de déformations résiduelles (retrait) quiinduisent l'amorçage et le développement d'endommagements.Avec l’objectif de prévoir l’amorçage de ces endommagements, il est nécessaire de calculerl’état des contraintes à différentes échelles du matériau vieilli. Il faut donc disposer demodèles de comportement du polymère et du composite dépendant du niveau d’oxydation.Deux types de difficultés se présentent : l’une associée à la nature locale de ce phénomène,difficilement captée par des essais classiques (traction, compression…) et l’autre de parl’aspect visqueux du comportement mécanique, qui doit être identifié sur les temps courts etles temps longs. Ce travail – conduit dans le cadre du programme COMPTINN' – est consacréà l'étude des effets de la thermo oxydation sur le comportement mécanique de deux polymères(une résine Epoxy et une résine Polyimide) et des composites associés (à fibres de carbone),ainsi qu'à la caractérisation de l'amorçage des endommagements induits par la thermooxydation de la matrice. Cette étude se compose de trois parties : mise en place d'une nouvelleméthodologie numérique/expérimentale pour l'analyse des effets de la thermo oxydation sur lecomportement mécanique local du polymère et le développement d'une loi constitutiveappropriée ; mise en place d'une nouvelle approche numérique/expérimentale pour le calculdu champ des retraits matriciels sur la surface des composites UD, conduisant, au cours duvieillissement, à l’amorçage des décohésions fibre/matrice ; développement d'une techniqueexpérimentale pour l'étude de l'interaction mécanique/oxydation au cours d'essais de fatiguede composites stratifiés

Study of the effects of thermal oxidation on the mechanical behaviour of aeronautical composite materials

L’oxydation conduit à une modification des propriétés mécaniques de la matricepolymère, associée à sa fragilisation, et à la création de déformations résiduelles (retrait) quiinduisent l'amorçage et le développement d'endommagements.Avec l’objectif de prévoir l’amorçage de ces endommagements, il est nécessaire de calculerl’état des contraintes à différentes échelles du matériau vieilli. Il faut donc disposer demodèles de comportement du polymère et du composite dépendant du niveau d’oxydation.Deux types de difficultés se présentent : l’une associée à la nature locale de ce phénomène,difficilement captée par des essais classiques (traction, compression…) et l’autre de parl’aspect visqueux du comportement mécanique, qui doit être identifié sur les temps courts etles temps longs. Ce travail – conduit dans le cadre du programme COMPTINN' – est consacréà l'étude des effets de la thermo oxydation sur le comportement mécanique de deux polymères(une résine Epoxy et une résine Polyimide) et des composites associés (à fibres de carbone),ainsi qu'à la caractérisation de l'amorçage des endommagements induits par la thermooxydation de la matrice. Cette étude se compose de trois parties : mise en place d'une nouvelleméthodologie numérique/expérimentale pour l'analyse des effets de la thermo oxydation sur lecomportement mécanique local du polymère et le développement d'une loi constitutiveappropriée ; mise en place d'une nouvelle approche numérique/expérimentale pour le calculdu champ des retraits matriciels sur la surface des composites UD, conduisant, au cours duvieillissement, à l’amorçage des décohésions fibre/matrice ; développement d'une techniqueexpérimentale pour l'étude de l'interaction mécanique/oxydation au cours d'essais de fatiguede composites stratifiés.It has been previously shown that, at medium temperatures, carbon fibres -epoxy matrix composites can be affected by thermo-oxidation that is a coupled phenomenonof oxygen diffusion and chemical reaction taking place in the oxidation sites present in themolecular structure of the organic matrix. Thermo-oxidation can lead to damage thecomposite surface, without any applied external load.This work has been conducted within the framework of the COMPTINN' project, aiming tostudy the effects of thermal oxidation on the mechanical behaviour of two polymers (an epoxyresin and a polyimide resin) and of the corresponding composites (carbon fibre), and tocharacterize the matrix damages promoted by isothermal ageing. This study is composed ofthree parts: development of a new numerical/experimental technique for characterizing theeffects of thermal oxidation on the local mechanical behaviour of the studied polymers andidentification of a constitutive law; development of a new numerical/experimental approachfor calculating the matrix shrinkage field on the unidirectional composite surfaces, whichleads, during ageing, to the onset of fibre/matrix debonding phenomenon; development of anovel experimental technique for studying the interaction between the mechanicalsolicitations and the oxidation degradation mechanisms through fatigue tests

Effets de la thermo-oxydation sur le comportement mécanique de matériaux composites pour applications aéronautiques

L oxydation conduit à une modification des propriétés mécaniques de la matricepolymère, associée à sa fragilisation, et à la création de déformations résiduelles (retrait) quiinduisent l'amorçage et le développement d'endommagements.Avec l objectif de prévoir l amorçage de ces endommagements, il est nécessaire de calculerl état des contraintes à différentes échelles du matériau vieilli. Il faut donc disposer demodèles de comportement du polymère et du composite dépendant du niveau d oxydation.Deux types de difficultés se présentent : l une associée à la nature locale de ce phénomène,difficilement captée par des essais classiques (traction, compression ) et l autre de parl aspect visqueux du comportement mécanique, qui doit être identifié sur les temps courts etles temps longs. Ce travail conduit dans le cadre du programme COMPTINN' est consacréà l'étude des effets de la thermo oxydation sur le comportement mécanique de deux polymères(une résine Epoxy et une résine Polyimide) et des composites associés (à fibres de carbone),ainsi qu'à la caractérisation de l'amorçage des endommagements induits par la thermooxydation de la matrice. Cette étude se compose de trois parties : mise en place d'une nouvelleméthodologie numérique/expérimentale pour l'analyse des effets de la thermo oxydation sur lecomportement mécanique local du polymère et le développement d'une loi constitutiveappropriée ; mise en place d'une nouvelle approche numérique/expérimentale pour le calculdu champ des retraits matriciels sur la surface des composites UD, conduisant, au cours duvieillissement, à l amorçage des décohésions fibre/matrice ; développement d'une techniqueexpérimentale pour l'étude de l'interaction mécanique/oxydation au cours d'essais de fatiguede composites stratifiés.It has been previously shown that, at medium temperatures, carbon fibres -epoxy matrix composites can be affected by thermo-oxidation that is a coupled phenomenonof oxygen diffusion and chemical reaction taking place in the oxidation sites present in themolecular structure of the organic matrix. Thermo-oxidation can lead to damage thecomposite surface, without any applied external load.This work has been conducted within the framework of the COMPTINN' project, aiming tostudy the effects of thermal oxidation on the mechanical behaviour of two polymers (an epoxyresin and a polyimide resin) and of the corresponding composites (carbon fibre), and tocharacterize the matrix damages promoted by isothermal ageing. This study is composed ofthree parts: development of a new numerical/experimental technique for characterizing theeffects of thermal oxidation on the local mechanical behaviour of the studied polymers andidentification of a constitutive law; development of a new numerical/experimental approachfor calculating the matrix shrinkage field on the unidirectional composite surfaces, whichleads, during ageing, to the onset of fibre/matrix debonding phenomenon; development of anovel experimental technique for studying the interaction between the mechanicalsolicitations and the oxidation degradation mechanisms through fatigue tests.POITIERS-ENS Mécanique Aérot (860622301) / SudocSudocFranceF

Durability and thermo-oxidation behaviour of organic matrix composite materials at high temperatures

International audienceThis paper introduces a review of the main activities carried out within the context of the ‘COMPTINN’ research program, for the activities focusing on the durability and thermo-oxidation behaviour of organic matrix composite materials at ‘high’ temperatures (120°C-180°C). The scientific aim of ‘COMPTINN’ research program was to better identify, with a multi-scale approach, the link between durability, accelerating ageing factors and physical mechanisms involved in thermo-oxidation phenomena, and to provide theoretical and numerical tools for predicting the mechanical behaviour of aged composite materials including damage onset and development. Work has been carried out on continuous carbon fibre composite with epoxy matrix. The influence of thermo oxidation on the mechanical behaviour of the matrix, the creep properties and durability of the composite, has been identified with ultra-micro indentation (UMI). Based on the evolution of the elastic indentation modulus of the resin in the thickness of a sample exposed to oxidative environment at 150°C for different durations, we have clearly validated that the thickness of the oxidised layer is linked with the exposed time. Another innovative experimental technique has also been used: a climbing drum peel test has been modified to investigate the influence of oxygen on mode I delamination propagation in a composite laminate. In this test, crack propagation is driven by oxidation under constant mechanical energy and the delamination propagation speed can be linked with the oxidation level. This enables one to identify the critical strain energy release rate associated with an oxidized interface and to predict the interaction between mechanical and environmental loadings. Thermo-oxidation is identified as the result of oxygen diffusion and oxygen reaction with the molecular structure of the resin. The predominance of chain scissions over crosslinking leads to a decrease in the glass transition temperature combined with an increase in the Young’s modulus at room temperature (called “antiplasticization” effect). This process is also at the origin of matrix shrinkage, weight loss and cracks initiation

Poor sleep quality may contribute to dysfunctional illness perception, physical and emotional distress in hospitalised patients: results of a national survey of the Italian Society of Consultation‐Liaison Psychiatry

Distress associated with physical illness is a well-known risk factor for adverse illness course in general hospitals. Understanding the factors contributing to it should be a priority and among them dysfunctional illness perception and poor sleep quality may contribute to it. As poor sleep quality is recognised as a major risk factor for health problems, we aimed to study its association with illness perception and levels of distress during hospitalisation. This cross-sectional study included a consecutive series of 409 individuals who were hospitalised in medical and surgical units of different hospitals located throughout the Italian national territory and required an assessment for psychopathological conditions. Sleep quality was assessed with the Pittsburgh (Sleep Quality Index), emotional and physical distress with the Edmonton Symptom Assessment System (ESAS), and illness perception with the Brief Illness Perception Questionnaire (BIPQ). Differences between groups, correlations and mediations analyses were computed. Patients with poor sleep quality were more frequently females, with psychiatric comorbidity, with higher scores in the ESAS and BIPQ. Poor sleep quality was related to dysfunctional illness perception, and to both emotional and physical distress. In particular, by affecting cognitive components of illness perception, poor sleep quality may, directly and indirectly, predict high levels of distress during hospitalisation. Poor sleep quality may affect >70% of hospitalised patients and may favour dysfunctional illness perception and emotional/physical distress.Assessing and treating sleep problems in hospitalised patients should be included in the routine of hospitalised patients

Changes of consultation-liaison psychiatry practice in Italian general hospitals: A comparative 20-year multicenter study

Conducted under the auspices of the Italian Society of Consultation Liaison Psychiatry (SIPC) the aim of this study was to describe the characteristics of Consultation Liaison Psychiatry (CLP) activity in Italy (SIPC-2-2018) over the past 20 years by comparing with data from the first Italian nation-wide study (SIPC-1-1998)