JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008 - 42

FEATURE “Automotive” More information Delta-Tech Spa is an independent company founded in 1999 with the mission of providing materials and services to the composite materials industry. Delta-Tech develops and manufactures resin matrices, while controlled company Delta-Preg produces prepregs using matrices supplied by Delta-Tech. The prepreg product range includes woven fabrics, multiaxial fabrics and unidirectional tapes fabricated by solvent coating or hot-melt technology. Most of the production is based on carbon fibre, but glass, aramid and special fibres are also used. Delta-Preg’s production mainly targets the automotive market, including competition and high-end GT cars. Other important market segments are motorcycles, sporting goods, boat building and industrial machinery. g…/… Cost-effective high-performance solutions for automotive body panels Austrian car manufacturer KTM-Sportcar Produktions GmbH. The edges of the carbon fibre bodywork panels for this modern and aggressive car design comply with the safety regulations thanks to a continuous 5 mm-thick edge made out of Kordo™. Edge cutting and trimming has been eliminated as well, for considerably reduced labour. As a further advantage, the thick edge surrounding all the body panels significantly contributes to part stiffness and dimensional stability. Fig. 2: KTM X-bow and body panel details. Semi-impregnated micro-sandwich (SIMS™)* PET fleece has been used as a core layer in micro-sandwich construction for many years. Whether the fleece was impregnated or used dry, all the past experiences aimed at achieving full impregnation by the matrix in the final laminate in order to obtain the desired stiffness. Delta-Tech studied micro-sandwich constructions with PET needle-punched fleece core, showing that exceptionally high toughness could be achieved in the presence of residual dry (therefore not bonded by the matrix) domains within the fleece thickness. An optimum sandwich configuration, with the appropriate resin content, was selected and tested to achieve the right balance of stiff bridging between the skins while maintaining the desired amount of dry fleece within the laminate thickness. Once the right resin content in the prepreg was set, it was demonstrated that the minor resin content fluctuation in commercial prepreg production does not affect the final properties of microsandwich structures. The typical section of SIMS™ laminates is reported in Figure 3, together with a microscope image of an actual panel section. The skin fabric can be made of carbon or glass fibre, with the latter representing an extremely cost-effective solution that can provide the required stiffness due to the thick sandwich configuration, low raw material cost and low weight afforded by the light, partially impregnated PET core. The dry fleece is pre-matched with a prepreg skin directly at the Delta-Preg factory. The micro-sandwich structure is then completed by adding a ply of woven prepreg. This means that Fig. 3: SIMS™ , schematics and microscope picture of cross-section. only two plies are laid-up to produce the laminate. As the SIMS™ laminate cross-section shows dry PET fibres, the component edges need to be sealed. This can be ideally accomplished using Kordo™ all around the perimeter of the part. Alternatively, the fleece-containing ply can be left short on the edge and overlapped by a woven prepreg strip. The resulting structures are characterized by extremely high toughness. In case of a strong impact, the panel retains good stiffness until the first failure occurs; then it keeps yielding in the same way as a thermoplastic material. This results in high energy dissipation while the maximum yield force remains low. This will reduce personal injuries in the event of an accident. The advantage of SIMS™ over conventional micro-sandwich structures with impregnated fleece core is well illustrated by comparing the results of drop ball impact tests carried out on SIMS™ laminates and an equivalent laminate where the fleece core is fully impregnated by the matrix. Figure 4 shows a typical force profile versus time during an impact test. The comparative results are reported in Table 1. Here “SIMS™A” and “SIMS™ B” stand for different degrees of fleece impregnation, “A” being lower jec composites magazine / No45 November-December 2008

JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008