Compaction behavior of out-of-autoclave prepreg materials

The main challenges with composite parts manufacturing are related to the curing means, mainly autoclaves, the length of their cycles and their operating costs. In order to decrease this dependency, out of autoclave materials have been considered as a solution for high production rate parts such as spars, flaps, etc… However, most out-of-autoclave process do not possess the same maturity as their counterpart, especially concerning part quality1. Some pre-cure processes such as compaction and ply lay-up are usually less of a concern for autoclave manufacturing: the pressure applied during the cycle participates to reduce the potential defects (porosity caused by a poor quality lay-up, bad compaction, entrapped air or humidity…). For out-of-autoclave parts, those are crucial steps which may have many consequences on the final quality of the laminate2. In order to avoid this quality loss, those steps must be well understood

Enhancement of electrical conductivity of composite structures by integration of carbon nanotubes via bulk resin and/or buckypaper films

This study describes two approaches for the incorporation of carbon nanotubes (CNTs) in carbon fibre reinforced polymer (CFRP) composites, through the addition of the CNTs in the bulk resin and by the addition of CNT-based buckypaper (BP) in the CFRP structure. Several laminates were successfully manufactured integrating these two approaches, where a significant improvement of the electrical conductivity (EC) values was found. Additionally, in order to compare different surface preparations and testing methods, a cross check of EC test was carried out among different laboratories. This characterization was complemented with scanning electron microscopy (SEM) analyses, results of which were used to rule out a complete filtering effect of the CNTs. Furthermore, interlaminar shear strength (ILSS) tests were also performed, with the aim of assessing the mechanical behavior of the different configurations.We gratefully acknowledge the financial support from FP-7 EU project ELECTRICAL: Novel Aeronautical Multifunctional Composite Structures with Bulk Electrical Conductivity and Self-Sensing Capabilities (ACP8-GA-2010-265593), especially project partners CYTEC and ARKEMA for the material supply and technical support

Modélisation des cinétiques de polymérisation de résines destinées à la fabrication Hors Autoclave

The main challenges with composite parts manufacturing are related to the curing means, mainly autoclaves, the length of their cycles and their operating costs. In order to decrease this dependency, out of autoclave materials have been considered as a solution for high production rate parts such as spars, flaps, etc… However, most out-of-autoclave process do not possess the same maturity as their counterpart, especially concerning part quality 1. Three out-of-Autoclave prepreg materials were considered for this study, each one possessing different curing temperatures: A (180°C), B (125°C) and C (132°C). Those materials have also different chemical compositions, although all three have been designed for out-of-autoclave composite part manufacturing (primary and secondary structures). The interest of our study is to understand and compare polymerization mechanisms of each matrix, by defining each time a predictive model close to experimental values of the curing of those epoxy/amine systems 2

Une approche multi-physique du soudage en continu des composites à matrice thermoplastique : vers une modélisation multi-échelle

Le nouveau procédé de drapage de consolidation en continu de thermoplastiques permet de fabriquer des pièces composites par soudage de plis pré-imprégnés les uns sur les autres. L'adhésion des bandes de matériau entre elles, qui conditionnent les propriétés mécaniques de la pièce résulte principalement de la compétition de trois phénomènes physiques couplés : i) l'inter-diffusion des macromolécules à l'interface lorsque le polymère est fondu, ii) la cristallisation du polymère dont l'aspect cinétique peut conduire à des cristallisations partielles au niveau de l'interface, iii) la dégradation du polymère à haute température engendrant des réticulations dans le matériau. La prise en compte de ces phénomènes physiques couplés a demandé le développement d'un modèle thermique explicite 2D en différences finies permettant de prédire les évolutions locales de température au niveau de interface à souder à partir de l'identification par méthode inverse des échanges de chaleur entre le composite et l'air ambiant, l'azote chaud pulsé par les torches, les contacts avec l'outillage. La fenêtre de conditions de procédé a pu être déterminée

A more reliable DSC-based methodology to study crystallization kinetics: Application to poly(ether ketone ketone) (PEKK) copolymers

To quantify the isothermal crystallization kinetics of poly(ether ketone ketone) (PEKK), the integration of the crystallization peak measured using differential scanning calorimetry is rendered difficult due to the thermal transient effects at the start of enthalpy recording. The different attempts to extrapolate this peak beginning often lead to false values of the Avrami exponent. A new crystallization kinetic assessment method is established here based on the derivative of the Hillier crystallization kinetic model. This method consists of directly fitting the transformation rate to the heat flow of the experimental crystallization, thus avoiding the extrapolation of the crystallization peak beginning. This method is successfully applied to two different PEKK grades with different crystallization kinetics. The identified crystallization parameters are modelled as a function of the crystallization temperature, and based on these modeling results, time-temperature-transformation diagrams of crystallinity were built to provide a useful tool for PEKK processing

Development of miniaturized light endoscope-holder robot for laparoscopic surgery

PURPOSE: We have conducted experiments with an innovatively designed robot endoscope holder for laparoscopic surgery that is small and low cost. MATERIALS AND METHODS: A compact light endoscope robot (LER) that is placed on the patient's skin and can be used with the patient in the lateral or dorsal supine position was tested on cadavers and laboratory pigs in order to allow successive modifications. The current control system is based on voice recognition. The range of vision is 360 degrees with an angle of 160 degrees . Twenty-three procedures were performed. RESULTS: The tests made it possible to advance the prototype on a variety of aspects, including reliability, steadiness, ergonomics, and dimensions. The ease of installation of the robot, which takes only 5 minutes, and the easy handling made it possible for 21 of the 23 procedures to be performed without an assistant. CONCLUSION: The LER is a camera holder guided by the surgeon's voice that can eliminate the need for an assistant during laparoscopic surgery. The ease of installation and manufacture should make it an effective and inexpensive system for use on patients in the lateral and dorsal supine positions. Randomized clinical trials will soon validate a new version of this robot prior to marketing

Thermo-oxidation behaviour of composite materials at high temperatures: A review of research activities carried out within the COMEDI program

The present paper presents a review of the main activities carried out within the context of the COMEDI research program, a joint collaboration involving three research teams focusing on the thermo-oxidation behaviour of composite materials at high temperatures. The scientific aim of the COMEDI research program was to better identify the link between the physical mechanisms involved in thermo-oxidation phenomena: oxygen reaction-diffusion, chemical shrinkage strain/stress, degradation at different scales and to provide tools for predicting the thermo-oxidation behaviour of composite materials under thermo-oxidative environments including damage onset. This aim was accomplished by investigating experimentally the thermo-oxidation behaviour of pure resin samples - both industrial and "model" materials - and by interpreting the results by a coupled reaction-diffusion-mechanics multiphysics model. A dedicated numerical model tool has been developed and implemented into the ABAQUS® finite element commercial software. This tool was employed to simulate the thermo-oxidative behaviour of a fibre-matrix microscopic representative composite cell. Finally, the model predictions for the composite have been validated by comparing the experimental and the simulated local matrix shrinkage displacements and the mass loss of composite specimens

Isothermal crystallization kinetic modeling of poly(etherketoneketone) (PEKK) copolymer

Isothermal melt and cold crystallizations of a poly(etherketoneketone) (PEKK) copolymer prepared from diphenyl ether (DPE), terephthalic acid (T) and isophthalic acid (I) with a T/I ratio of 60/40 have been investigated by differential scanning calorimetry, wide-angle X-ray scattering and polarized optical microscopy. For the first time, the two-stage overall crystallization kinetics of PEKK taking into account effects of nucleation and crystal growth has been identified by using a modified Hillier type model. The primary crystallization stage is found to be an instantaneous two dimensional nucleation growth with an Avrami exponent of 2 whereas the secondary stage is found to be an instantaneous one dimensional nucleation growth with an Avrami exponent of 1. The evolution of the crystallization kinetic constants for two-stage crystallizations has been modeled according to the Hoffman and Lauritzen growth theory. Due to low crystallization kinetics, a crystallization induction time has been added to obtain a good fit with experimental data. Based on this modeling, Time-Temperature-Transformation (TTT) diagrams of the relative volume crystallinity have been established for the overall crystallization mechanism and also for the separated primary and secondary crystallization mechanisms providing an original crystallization mapping of the material

Influence of thermal history on the mechanical properties of poly(ether ketone ketone) copolymers

Since poly(ether ketone ketone) (PEKK) is a good candidate as a matrix for composite structural parts, the mechanical properties of PEKK copolymers prepared from diphenyl ether, terephthalic acid (T), and isophthalic acid (I) with different T/I ratios were assessed at room temperature and above their glass transition temperature depending on the thermal history during processing. The influence of cooling conditions and macromolecular modifications at high exposure temperatures was investigated. Results show that modulus and yield properties for a given testing temperature follow a master curve driven mainly by crystallinity regardless of the PEKK copolymers. By modifying PEKK during exposures at 400°C, which leads to branching mechanisms before crystallization, it is shown that modified PEKKs follow the master curve, thus confirming the predominant role of crystallinity in small deformation properties. However, for some morphologies, depending on the crystallization conditions such as cold or melt crystallization, a slight deviation is observed from the global master curve.The authors wish to thank the Arkema Company for providing the PEKK materials and the French National Research Agency (ANR IMPEKKABLE project

TER: A Robot for Remote Ultrasonic Examination: Experimental Evaluations

This chapter: o Motivates the clinical use of robotic tele-echography o Introduces the TER system o Describes technical and clinical evaluations performed with TE