The influence of consolidation force on the performance of AFP manufactured laminates

With the increasing use of carbon/glass fibre reinforced polymer composites for large components like wing skins, fuselages and fuel tanks in aircrafts and next generation of spacecraft, utilization of advanced automated manufacturing is critical for mass production. In-situ consolidation in automated fibre placement (AFP) technology through merging several manufacturing stages like cutting, curing and consolidation has opened up a wider range of applications as well as new markets for composite materials in several sectors including aerospace and automobile in large scale. Nevertheless, the quality and integrity of AFP manufactured composites is heavily dependent on large number of variables and parameters like lay-up speed, curing/melting temperature and consolidation force. In order to establish and understand a correlation between the key parameters in AFP and the mechanical properties, several parametric experiments were performed. This is done through manufacturing uni-directional carbon fibre reinforced polymer laminates and identifying some of their main mechanical properties at different location along the length of samples. It was found that, the strength of laminates at different locations is critically dependent on the effect of those parameters

Le micocoulier : de l'arbre au fouet

Cet article expose le procédé (peu connu) de fabrication des cravaches et fouets d'attelage à partir de micocoulier du Roussillon, patrimoine mis en valeur de façon traditionnell

Fabrication and characterization of a magnetized metal-encapsulated FBG sensor for structural health monitoring

A novel means of metal packaging of a fiber Bragg grating (FBG) sensor using stainless steel and tin, together with high temperature resistant samarium cobalt (SmCo) magnet is proposed in this paper. The inclusion of high temperaturecapable SmCo magnets enable the metal packaging of the FBG sensor with magnetic capabilities. This packaged sensor can be placed in direct contact with the substrate structures such as iron pipelines and other ferromagnetic components without any adhesives, making them easily detachable and reusable. This is a significant improvement compared with other commercial fiber optic sensors which are, surface attached using epoxies or welded to the substrate. The design parameters and characteristic properties such as load, temperature, and vibration sensitivity of the magnetic metal-packaged FBG sensor are studied numerically and validated experimentally to demonstrate the feasibility of using the encapsulated reusable FBGs for structural health monitoring of compatible structures

Online Monitoring and Prediction of Thermo-Mechanics of AFP Based Thermoplastic Composites

Precision sensing in the characterization of complex additive manufacturing processes such as the Automated Fibre Placement (AFP) technique is important since the process involves a significant level of uncertainty in terms of quality and integrity of the manufactured product. These uncertainties can be monitored by embedding optical fibre Bragg grating (FBGs) sensors which provide accurate and simultaneous measurement of strain and temperature during the AFP process. The embedded sensors have been shown to remain resilient in continuous health monitoring after manufacturing. The thermal history obtained from the FBG sensors demonstrates a reduction of temperature on the bottom ply by up to 25% when the plies are laid one above the other. A numerical tool is developed to identify the physical parameters which may be responsible for the rise/fall of the temperature during ply layup. The numerical findings agree well with the sensor data and is extended to capture a breadth of parametric studies through the layup simulation. The model provides a comprehensive insight to the characteristics of the laid and the laying ply from a thermo-mechanics perspective

Fibre Bragg grating sensing technology for the evaluation of physical properties of dental resin composites

The characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fibre Brag grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature. A miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. This study demonstrates how optical fibre technology can provide simple and reliable methods of measuring the critical physical properties of dental composites. In addition due to the embedding and preservation of the sensor within the samples multiple parameters can be tested for with the same sample

Prediction of low cycle fatigue life of short fibre composites at elevated temperatures using surrogate modelling

The performance of any approximation scheme is known to be largely dependent on the type of surrogate models and its corresponding input variables. Elastic modulus prediction of short fibre composites with polyester and vinylester is presented using the surrogate framework supported by multiple spatially distributed surrogate models of different types. Poisson’s ratio is included as an additional variable to predict low cycle fatigue damage of short-fibre composites at elevated temperatures. The validation of the surrogate model is established through a comparison with analytical results. Furthermore, the surrogate model is coupled with an optimization algorithm to solve a number of inverse problems which is of significant interest to the end users in practice

Molecular dynamics study on effects of aspect ratio of carbon nanotubes in thermosetting epoxy based nanocomposites including modeling of crosslinking process

A comprehensive modeling and simulation approach using molecular dynamics (MD) is presented in this paper. The influence of aspect ratio of carbon nanotubes (CNTs) in thermosetting epoxy is studied using MD. The thermo-mechanical properties of epoxy models reinforced by CNTs with various aspect ratios are extracted. CNTs with the higher aspect ratio increase stiffness of the epoxy resin with facilitating premature yield in tension while a noticeable degradation in thermal properties is evidenced. The evolution of internal energy during straining shows that CNTs prolong the constant transition rate of dihedral and van der Waals energy in the elastic region. This might delay conformational changes of epoxy molecules to the lower energy level. Free volume and pair distribution function studies of the molecular models with CNTs compared with the neat epoxy model provide the plausible conclusion that the steric hindrance of CNTs in the three-dimensional epoxy molecular domain may result in the less dense structure of the epoxy

Thermal sensitivity and relaxation of carbon fibre-foam sandwich composites with fibre optic sensors

The increasing use of sandwich composites for structural applications brings with it a need to establish a reliable inspection and monitoring method to ensure structural integrity and safe operation throughout the service life. Since optical fibre-based photonic sensing technologies are increasingly common for structural health monitoring of composite structures, selection of optical fibre Bragg grating sensors could be one possible choice for this purpose. In this paper, performance characterisation of sandwich composite with embedded silica fibre Bragg grating sensor is reported. Experimental tests were performed on a carbon fibre foam core sandwich composite embedded with a silica fibre Bragg grating sensor to extract the structural health monitoring parameters such as strain and temperature. The current study found that sandwich composite exhibits foam relaxation; however, its impact on strain measurement is negligible. Another important finding from the theoretical and the experimental thermal modelling was that although the constituent components of the sandwich composite have entirely different thermal expansion coefficients, its effect on the embedded fibre sensor can be minimal if the sensors are embedded between the face sheets. These results can initiate further research in this area and can lead to the development of state-of-the art structural health monitoring techniques for sandwich composite structures

Effect of the addition of multi-walled carbon nanotubes on the thermomechanical properties of epoxy resin

The influence of multi-walled carbon nanotubes (MWCNTs) on thermosetting epoxy is examined using dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry (DSC). Specimens are prepared with loadings of 0.1 and 1 wt% MWCNTs which are dispersed in the resin using two different dispersion methods. While the storage modulus of the specimens is improved, both the glass transition temperature and the thermal stability are reduced by the addition of MWCNTs with both effects being greater for the higher MWCNT loading, for both dispersion systems. The DSC results additionally indicate that the level of residual unreacted epoxy increases progressively with the addition of the nanotubes. This finding is considered as confirmation that the MWCNTs obstruct crosslinking of the epoxy resin