Abstract

Abstract

In this work the development of a profile manufactured by pultrusion and thereafter curved by thermoforming is presented. The pultrusion profile is based on a new thermostable epoxy resin with dynamic bonds capable of being reprocessed, repaired and recycled thanks to the incorporation of reversible links within its reticulated structure (3R Technology). Being a resin that contains dynamic bonds, the cured composite shows unexpected properties for thermosetting materials.

In a first phase, a new resin/hardener formulation processable by pultrusion with a viscosity, adhesion to the fibre and speed of curing similar to a conventional formulation have been developed and in a second phase, taking into account the properties of the new composite material, the parameters of the thermoforming process (pressure, temperature or speed of thermoforming) have been analysed and optimized.

Thanks to the combination of pultrusion and thermoforming processes, longitudinal 3R composite profiles acquire a new curved geometry defined by the design of a mould. In this way, the thermoforming of the straight profiles will allow manufacturing curved parts from profiles of thermostable composites with high mechanical performance manufactured by pultrusion in medium-high rates, typical of the automotive sector. Additionally, it will be shown that the profiles manufactured using these composites can be recycled, reducing the amount of waste generated and offering these materials a second useful life.

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

Composite profiles processed by pultrusion are replacing metallic profiles in sectors like building or automotive, due to two interested properties: lightweight (the gas consumtion of the vehicle will be reduced) and corrosion resistance. However, if the profile needs to be covered in order to achieve aesthetic properties or new functionalities, several drawbacks arise (high labour content and VOCs and small particles emissions), limitating its competitivness versus profile metals. In this work the results of COALINE project are described; pultrusion process has been enhanced achieving a coated profile inside the mould (with a gelcoat or a primer) thanks to the development and integration of a sensor system (needed to adjust the curing degree of the resin in each stage of the process), a MW technology curing (to faster the curing time of the resin and shorten the lenght mould) and a modular advanced die design. Two moulds have been manufactured and a covered profiled obained in-line has been achieved for the building sector. For the automotive sector a case study cargo bed has been manufactured using profiles covered with the primer and joined with an adhesive with debonding capability to provide a simple repair or recycling at the end life-cycle.

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

Simulation of composite structures through Finite Elements Method (FEM) is widely used in the aeronautics sector to reliably predict its performance. The incorporation of new materials with enhanced properties, and also new manufacturing processes usually require the use of such tools for validation.

This work has been focussed on studying an emerging technology such as Pultrusion for stiffeners manufacturing. For this, it has been used a demonstrator based on a common airframe structure, panels stiffened with profiles. This time, the classic stiffener manufactured using prepreg and autoclave cured has been replaced by stiffeners manufactured by Pultrusion. For that purpose, it was manufactured flat panels using prepegs and autoclave curing, for subsequently bond L shaped high resistance carbon fibre profiles manufactured by Pultrusion.

Furthermore, FEM simulations were conducted over these coupons for three different mechanical testing conditions, tensile, compression and shear, aiming to determine the capability of these methods for simulating reliably the mechanical performance of pultruded materials on such above-mentioned structures.

The results obtained in this work have been used for model parameter adjustments to obtain reasonable correlation levels, enabling the future usage of Pultrusion technology in the stiffener profiles manufacturing.

Abstract

The manufacture by means of a pultrusion process allows to obtain structural profiles of composite materials, avoiding discontinuous processes that need the use of an autoclave to cure the material. This process usually uses fiberglass as reinforcement, not reaching the necessary qualities in structural aeronautical applications. The present work develops a numerical simulation of the pultrusion with composite materials reinforced with carbon fiber for aeronautical structural applications. In order to obtain high quality materials, a product development is required where the process parameters are studied. In this sense, a complete study of the pultrusion process has been carried out through the development of numerical simulations using the software ABAQUS and NASTRAN / PATRAN from the point of view of the material manufactured and the pultrusion mold used.

These two approaches have been developed by generating finite element models. In the first place, models that simulate and predict the physical-chemical properties of the material, such as the glass transition temperature and the degree of final curing of the material before processes with different temperature settings, draft speeds and geometries. Second, the pultrusion mold was simulated to obtain the expansions and loads applied to the fabricated profile to evaluate the influence of this on the pultrusion process and the quality of the obtained profile.

The results obtained have been correlated by mechanical and physical-chemical tests as well as manufacturing tests that obtained the simulated profiles in order to introduce the technology and the parts manufactured in future aeronautical structures.

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

Currently, most of the composite ship manufacturing is performed using highly manual processes. This implies the need for skilled labour, a low productivity, and a poor control of quality. The Robtrusion concept solves this issue as the manufactured profiles can be directly bonded onto the ship's structure. Furthermore, these profiles have high mechanical properties, reducing the amount of fibre and matrix used. As a result, processes and vessels are more sustainable, although addressing challenges such as the use of bio-based polymeric matrices would further reduce the environmental impact. Despite efforts to develop new sustainable formulations, most commercial formulations still incorporate reduced amounts of bio-based raw materials and generally have lower mechanical properties than their non-sustainable counterparts.

Therefore, the aim of this work is to develop advanced photocurable formulations with a sustainable origin for the manufacturing of structural profiles for ships. For this purpose, bio-based raw materials that offer the best performance and adaptability to the ultraviolet (UV) pultrusion process have been selected. After photocalorimetric and spectrometric analysis, the best formulations were validated in the UV pultrusion line. It is concluded that the quality of the bio-based profiles manufactured is similar to that of the reference profiles, with a void percentage of less than 2% and equivalent mechanical properties.

This work has been conducted within the scope of the ARRAUN project (PNA-020100-2023-48), funded as part of the Strategic Project for Economic Recovery and Transformation for the modernization and diversification of the Spanish naval ecosystem (PERTE NAVAL – PNA-010000-2023-03).

Abstract

Thermosetting matrix composites are by far the most use composite solutions in the market. Thermosetting matrices are not currently possible to recycle by convenient means, which makes them a poor sustainable solution. In environmental terms, these matrices materials are also more harmful due to gas emissions during the curing process that can be considered harmful to the workers. Thermoset composites also have some disadvantages from the point of view of mechanical behaviour, being less ductile and resistant when compared to thermoplastic matrix composites. Despite the very high viscosity of thermoplastic materials that is a main problem regarding composite processing, they have advantages such as being recyclable, cleaner workspaces and greater availability, as well as a longer shelf life. This paper aims to be a contribution to increase use of thermoplastic matrix composites as alternative to the more traditional thermosetting based composites. First, thermoplastic matrix prepregs were produced in tape form by dipping the fibres into a molten polymer bath. Carbon and glass fibres are used as reinforcement material, testing their combination with thermoplastic polymers and recycled polymers. The use of prepregs is more attractive on the market as the process of mixing and selecting the raw materials is carried out prior to their application in a consolidation process. The prepregs were then processed by pultrusion, which is characterised by its continuous nature, allowing the manufacturing of constant cross section profiles for structural applications. The pultrusion of thermoplastic composites is still a novelty and therefore presents challenges. The determination of the best combination of operational parameters was also conducted in this study. Finally, the produced profiles were subjected to mechanical tests as a way of assessing the quality of the processed composites. The mechanical properties obtained will be compared to those predicted by the application of micromechanical models using experimentally obtained mass fibre fraction content.