Abstract

Abstract

A general constitutive model adequate for analysis of the thermomechanical response of composite materials is presented. The model is based on the mixture of the basic substances of the composite and allows the evaluation of the interdependence between the constitutive behaviour of different compounding materials. The behaviour of the each compound is modelled by a general anisotropic thermo‐elasto‐plastic model, termed the ‘base model’. The different base models for each compound are combined using mixing theory to simulate the behaviour of the multiphase material.

Abstract

Abstract

In recent years many of the developments in the field of composite materials have focused on processes of dry carbon fiber, and efforts have been directed to achieve with these materials the same levels of industrialization as with pre-impregnated materials, since it is a technology of low cost and with a high productivity.

The objective of this project has been to develop dry carbon fiber manufacturing methods to obtain an automated, robust and efficient process for reaching manufacture the lower skin of a wing with stringers and integrated spars by automatic laying in Fiber Placement, posterior Hot forming and finally a process of resin infusion by "Vacuum Assisted Process".

To achieve this objective, the Fiber Placement machine has been set up to optimize the laying parameters for the processing of the material to be used (½” Hexcel Hi-Tape fiber).
On the other hand, several tests of hot forming of this laminates have been carried out by means of the previous process, modifying process variables, tooling details and forming bag configuration, in order to obtain the preforms of stringers and spars.

Finally, the integration of spars, stringers and skin was performed by a resin infusion process using the VAP technique "Vacuum Assisted Process".

Abstract

Today’s merchant and passenger vessels are complex structures that operate in harsh environments with respect to static and cyclic loads and corrosion. Depleting funds for fleet renewal and increasing through-life cost of maintenance and repair are the principal factors that lead to the need to implement new solutions that are easy to apply and low cost. All this added to the growing need for lightening in the transport sector turn the FRP materials into the main candidates as drivers for this change.

This present study within RAMSSES is focused on the compare a damage steel structures to repair composite patches. A representative structural detail of a cruise vessel was selected and designed as a demo case. The best patch solution was selected by FEM calculations, which have been fed from the mechanical test results of the composite material combinations, steel, surface treatments and adhesion joint of the one-shot dissimilar joints without adhesive.

Fatigue tests have been carried out and monitoring by strain gauges and FBGs positioning and distribution in the high stress areas along the demonstrator. Fatigue tests have been carried out in the six demos to compare crack evolution in cracked Patched and Un-Patched demonstrators.

As conclusion after the fatigue tests, composite patch works as crack arrested. Therefore, this behaviour represents an improvement of the 2.6 times of the fatigue life comparing UnPatched and Patched damaged steel.

Abstract

The deployment of composites for lightweight solutions in the automotive market is still emerging due to the production cost of these components and the limited production capacity of current manufacturing technologies.

The development of more reactive formulations for processes that allow to increase production rates and reduce process times to a few minutes are arousing great interest, such as the HP-RTM (high pressure RTM) and the HP-CRTM (RTM compression).

In the case of RTM resins, ultra-fast (2-5min) and low viscosity curing formulations are sought to optimize the curing and injection cycles to the maximum. The technology based on polyurethane resins (PUR) offers against other alternatives the advantage of having great tenacity and resistance to fatigue which makes it especially attractive for elements subject to impacts or cyclic loads such as suspension elements.

This work, based on simulations, has determined an optimal value of the PUR viscosity for RTM. In addition, a preliminary analysis of the curing kinetics of a commercial PUR resin has been carried out. The results indicate that the resin evaluated is not viable for the process due to its high reactivity at the beginning of curing, so that work will continue on the search for more latent PUR solutions for RTM.

Abstract

For years there has been a need to develop multifunctional composite materials, which in addition to the classical properties such as high strength and high stiffness, integrate different functionalities such as the ability to detect any deformation of the structure or the integration of lighting, in a trend towards lighter structures.

Abstract

This work deals with the revaluation of coffee bean residues from the coffee liquor industry with the aim of developing eco-efficient composite materials with a polymeric matrix of polylactic acid (PLA). The coffee residue is incorporated in a proportion of 20% to the PLA by extrusion. After a grinding process, they are processed by injection to obtain standardized test pieces for their characterization. In order to improve the mechanical properties, as well as the toughness and compatibility between the biopolyester and the lignocellulosic particles of the coffee residue, two oligomers of lactic acid (OLA2 and OLA2mal functionalized with maleic anhydride) are added, together with the particles of the coffee residue during the extrusion process. These "Green composites" show that the incorporation of coffee residue particles from the manufacture of coffee liquor considerably increases the ductility of the samples analyzed by practically 280% due to their high content of oils present in the lignocellulosic residue. In addition, the incorporation of the OLA2 and OLA2mal oligomers contribute to improve the tensile strength of the composite materials studied, by 35% and 60%, respectively. These interesting results show the wide possibilities of this eco-efficient and sustainable material made of PLA and coffee residue. These are biodegradable materials, respectful of the environment and that allow the revaluation of coffee bean residues from the agri-food industry such as coffee liquor.

Abstract

The main objective of this work was to show the technical viability of a traditional Sheet Moulding Compound process hybridized with Carbon fibre prepreg reinforcements, in a demonstrative car seat structure. The new reinforced seat is lighter, has better mechanical resistance to impact and the typical carbon fibre visual aspect in the reinforced areas. Currently, the seat structure is composed by the hybrid solution with the matrixes of both materials being epoxy, therefore compatible which promotes a good adhesion under the correct processing conditions. To ensure the viability of this hybridization, an extensive laboratorial test campaign was conducted in a laboratorial hot plate press to study the Sheet Moulding Compound flow dynamics during the moulding process and how it interacts with the prepreg preforms. The cure process of both materials was also analysed to establish the optimal temperature profiles. Finally, mechanical tests were performed according to ASTM D 5868-01 to evaluate the mechanical properties of the bonding between the two materials. The reinforced car seat prototype was validated according to the ECE-R17 and FMVSS202a impact tests on the head rest and a 25% reduction in overall weight was achieved. The life-cycle cost and the visual aspect benefits are expected to compensate the slightly higher manufacturing cost in relation to the original part due to the cost of the prepreg material. Further research will be needed to in terms of process automation to ensure the required process quality.