Reducing the weight of the truck vehicle conveys more cargo to be carried by thetrailer. This has a significant impact on the efficiency of the transport lowering both the total cost of cargo moved and the total carbon dioxide emitted. Half of the body in-white weight of a truck is comprised out of panels made out of thin mild forming steel which cannot be made thinner to reduce weight due to the lowered stiffness it would entail. Sandwich materials have a high stiffness to weight ratio and would for the same panel thickness as regular forming steel have a comparable bending stiffness but lowered weight. This master thesis is intended to be a preliminary study for Scania CV AB on sandwich materials and its potential use as lightweight panels in their trucks. With the intention of investigating whether a commercial sandwich material is capable of filling the role as outer panels of a truck, comparative tests regarding significant matters such as forming and painting was made on identically manufactured demonstrators comparing a sandwich material and a regular forming steel material. The tests identified weaknesses in the current manufacturing process for parts of a sandwich material. Such limitations are problems with painting and joining due to isolated cover sheets, forming problems revealing sink marks likely due to different spring back of the material and hemming flaws due to inadequately optimized hemming technique and anisotropy. Now that more knowledge of sandwich materials has been gained, counter measures for these findings can be made in order to take another step towards lowering the weight of the truck and a more efficient way of transporting goods. / Genom att minska vikten på lastbilen frigörs mer last att bäras av släpvagnen. Detta har en betydande inverkan på effektiviteten hos transporten som sänker både den totala kostnaden för transporterad last och de totala koldioxidutsläppen. Hälften aven lastbils rena karossvikt består av paneler gjorda av tunt mjukt formningsstål vilke tinte kan bli tunnare för att minska vikten på grund av den sänkta styvheten som detskulle medföra. Sandwichmaterial har en hög styvhet till viktförhållande och skulle församma paneltjocklek som vanligt formningsstål ha en jämförbar böjstyvhet men sänkt vikt. Denna uppsats är avsedd att vara en preliminär studie för Scania CV AB om sandwichmaterial och dess potentiella användning av lättvitkspaneler i lastbilar.Med avsikt att undersöka huruvida ett kommersiellt sandwichmaterial kan fylla rollen som lastbilens ytterpaneler utfördes jämförande tester med avseende på signifikanta frågor såsom formning och målning på identiskt tillverkade demonstratorer som jämförde ett sandwichmaterial och ett vanligt formningsstål. Testerna identifierade svagheter med materialet samt hur processen behöver anpassas för att kunna använda sandwichmaterialet i rådande tillverkningsprocess. Identifierade problem var bland annat problem med målning och sammanfogning på grund av isolerade ytterskickt i sandwichmaterialet, problem med formning som gav upphov till limdragningar som troligen beror på materialets olika återfjädring samt falsningsfel på grund av otillräckligt optimerad falsteknik och anisotropi. Nu när mer kunskap om sandwichmaterial erhållits kan motåtgärder för de funna resultaten undersökas för att ta ytterligare ett steg mot att sänka lastbilens vikt och därmed få ett effektivare transportmedel.

The use of sandwich structures in automobile body panels is investigated in this thesis. The applications on vehicles such as trains, aeroplanes and automobiles, advantages, isadvantages and modelling of sandwich structures are discussed and studies about static, vibrational and acoustic benefits of sandwich structures by several authors are presented. The floor, luggage, firewall and rear wheel panels in sheet metal form is replaced with panel made from sandwich materials in order to reduce the weight obtained by a trial and error based optimization method by keeping the same bending stiffness performance. In addition to these, the use of sandwich structures over free layer surface damping treatments glued on floor panel to decrease the vibration levels and air-borne noise inside the cabin is investigated. It has been proven that, the same vibration performance of both flat beam and floor panel can be obtained using sandwich structures instead of free layer surface damping treatments with a less weight addition. Furthermore, the damping effect of sandwich structures on sound transmission loss of complex shaped panels like floor panel is investigated. A 2D flat and curved panel representing the floor panel of FIAT Car model are analysed in a very large frequency range. Four different loss factors are applied on these panels and it is seen that, until it reaches damping controlled region, damping has a very little effect on TL of flat panels but has an obvious damping effect on TL of curved panels. However in that region, damping has an increasing effect on TL of both flat and curved panels.

Afin de réduire les déchets et les émissions de CO2, la demande des constructeurs automobiles a évolué vers l'utilisation de nouveaux matériaux biosourcés permettant d'alléger les véhicules et diminuer leur consommation en carburant. Dans ce contexte, la thèse a eu pour objectif de réaliser un panneau sandwich léger et résistant renforcé par des fibres longues de lin pour des applications semistructurelles automobiles. Outre la recherche bibliographique, le travail est réparti en trois volets : la mise en œuvre, la caractérisation et la modélisation du comportement mécanique du panneau sandwich. Les peaux composites sont renforcées par un nouveau renfort « Flaxtape », qui est un voile de fibres longues de lin unidirectionnelles et ne contenant aucune filature en trame. La matrice est une résine thermodurcissable aqueuse permettant un temps de réticulation très court et une bonne processabilité. Les peaux composites et les panneaux sandwichs dérivés sont élaborés à l'aide d'un procédé de thermocompression respectant des cycles de fabrication industriels. La compréhension et l'optimisation des paramètres entrant en jeu dans leur élaboration et leur mise en œuvre (cycle de cuisson, température, séchage, densification, fraction volumique de fibres, taux de réticulation et séquence d'empilement) passent par une série de caractérisations thermomécaniques et physicochimiques. Les résultats obtenus montrent les bonnes propriétés mécaniques spécifiques du panneau sandwich à différentes températures. D'autre part, le panneau sandwich en Flaxpreg est destiné à la réalisation d'un plancher de coffre de véhicule. La modélisation numérique du comportement mécanique du panneau sandwich a permis de prédire sa réponse mécanique lorsqu'il est mis en service à différentes positions dans le coffre. Afin de simplifier la géométrie du panneau sandwich et de réduire le temps de calcul, un modèle d'homogénéisation analytique de l'âme en nid d'abeille a été utilisé pour réaliser cette étude. / To reduce waste and CO2 emissions, car manufacturers use more and more new bio-sourced materials to lighten vehicles and reduce fuel consumption. In this context, this thesis aimed at processing a lightweight sandwich panel reinforced by long flax fibers for automotive semi-structural applications.In addition to the literature state of the art, the work is divided into three parts: the material processing, characterization and modeling of the mechanical behavior of the sandwich panel. The composite skins are reinforced by a new reinforcing material "Flaxtape", which is a veil of long unidirectional flaxfibers withouth any weft spinning. The matrix is an aqueous thermosetting resin with a very short cure time and good processability. The composite skins and derived sandwich panels are processed by a thermocompression technique respecting industrial production cycles. Thermomechanical and physicochemical characterizations are used to understand and optimize the parameters involved in their development (cooking cycle, temperature, drying, densification, fiber volume fraction, degree of crosslinking and stacking sequence). Our results highlight good specific mechanical properties of the sandwich panels at different temperatures.Furthermore, the Flaxpreg sandwich panel has been used for the achievement of a vehicle compartment floor. Numerical modeling of the mechanical behavior of the sandwich panel was used to predict the sandwich panel mechanical response at different positions in the trunk. To simplify the geometry of the sandwich panel and reduce the computation time, an analytical model of the homogenized honeycomb was used in this study.