Abstract

The present work presents a preliminary study on the development of a tubular chassis design for automotive industry manufactured with ultraviolet (UV) 3D pultrusion. The use of straight profiles for energy absorption elements and the advantages and feasibility of using curved profiles in other structural areas have been analysed. For the straight profiles, the energy absorption cabability of the material (specific energy absorption, SEA) has been evaluated performing quasi-static compression tests, showing high energy dissipation values, over 50 kJ / kg. On the other hand, the manufacturing of curved profiles by UV pultrusion have been analysed, evaluating the influence of the processing parameters (emitting intensity and pulling speed) and the influence of the reinforcement type on the geometry of the profile. It has been observed that the roving reinforcement allows an easier manipulation and allows to obtain curves without wrinkles with complex sections, due to the free movement between yarns; while the tape reinforcement may present wrinkles during the curving stage. In addition, based on a design with straight profiles, it has been shown that using non-rectilinear profiles, a significant reduction of the necessary connection nodes can be achieved, reducing up to 75% the number of connection nodes based on the analyed design.

Abstract

In the present paper a resins comparative study has been carried out, focused in out of die ultraviolet (UV) cured pultrusion process. In this new approach of the traditional pultrusion, the profile is cured outside the die with UV radiation. This fact implies th necessity of working with resins that present fast curing kinetics at the first stage of conversion in order to avoid the expansion of the profile at the exit of the die. Thus, with the aim of developing new photocurable resin formulations, it has been analysed the curing kinetics of an unsaturated polyester, epoxy-acrilate and a mixture of both resins (50%) with the photocalorimetry technique. Moreover, physical properties test and quasi-static compression test have been performed of profiles manufactured by UV pultrusion. The results prove that the mixture of both resins increase the conversion rate of unsaturated polyester, due to the faster curing kinetics of epoxy-acrylate. However, this fact has not been reflected in the percentage of voids, more elevated in the profiles manufactured by epoxy-acrilate. Nevertheless, the mixture presents higher energy absortion (SEA) values, about 22% higher than the unsaturated polyester and approximately 15% higher than epoxy-acrilate.

Abstract

The stress redistribution around a broken fibre is a substantial issue in longitudinal strength analysis of unidirectional (UD) composites. Most investigated models are based on a regular fibre packings and classical shear lag theory (static failure) that considers pre-broken fibers, where the dynamic aspects of brittle fiber failure are not considered. In the present work, Representative Volume Elements with random fibre packings were modeled by means of 3D finite element analysis, and simulated considering the event of dynamic fibre failure. Significant effects were observed on the stress concentration factor (SCF) and ineffective load length which are related to the fibre debonding length and the volume of matrix damage-plasticity zones. Hence, it can be concluded that an accurate representation of the stress redistribution after a fibre breakage event requires consideration of dynamic effects.

Abstract

Composites are on the strategic agendas of all manufacturers of transport sector (automobile, industrial vehicle, bus, train ...) and civil infrastructure. The development of new manufacturing processes such as out of die ultraviolet (UV) cured pultrusion can realise many concepts that are currently unfeasible. Therefore, it is essential that composites for automotive, transport or civil infraestructure present excellent fire resistance properties, particularly for structural applications. There are multiple strategies to improve the fire resistance of composites, but the peculiarities of the UV pultrusion process require the use of systems that allow the transmission of UV light through the material, and ensure a fast curing of the profile at the exit of the die to prevent expansion problems. Hence, different ignifugant strategies have been studied in this work: fillers or additives (alumina tri-hydrate, ATH), reactive compounds (ammonium polyphosphate, APP) and intumescent coatings. After analysing the different flame retardant strategies, it has been concluded that all the strategies improve the fire resistance capacity with respect to the base formulation, being the ATH and the intumescent coating the ones that present greater fireproof capacity.

Abstract

Fast and eco-friendly composite curing technologies are highly sought after, and ultraviolet (UV) curing offers both features. UV curing can be applied as a bulk curing technology as long as light arrives at all the points in the material with enough intensity. Additionally, the outer layer cures almost instantaneously, reducing the emission of volatile organic compounds. Despite its benefits, the implementation of UV curing technology in composites manufacturing is still in an early stage, and more basic knowledge about its principles needs to be generated. For instance, when curing considerably thick laminates, the light arriving at the points in the material further from the exposed surface is insufficient for a one shot consolidation, requiring a layer-by-layer curing strategy.

In the present paper, we explore several approaches for the layer-by-layer curing of a glass fibre reinforced unsaturated polyester composite. We assessed the impact properties of the manufactured laminates through drop weight low velocity impact tests to quantitatively evaluate the different approaches. We found that the laminate cured in three steps, applying four plies by shot, had the best impact performance, followed by the composite cured in two steps. On the other hand, the laminate cured in one shot had the worst impact properties, dissipating 20% less energy than the best performing laminate. Therefore, we conclude that the bonding of the UV cured laminates is tough and that the residual stresses induced during manufacturing are lessened the thinner the layers cured in each step are.