The goal of this study is to design and analyze a sandwich composite panel with lightweight graphite foam core and carbon epoxy face sheets that can function as a radiator for the given payload in a satellite. This arrangement provides a lightweight, structurally efficient structure to dissipate the heat from the electronics box to the surroundings. Three-dimensional finite element analysis with MSC Visual Nastran is undertaken for modal, dynamic and heat transfer analysis to design a radiator panel that can sustain fundamental frequency greater than 100 Hz and dissipate 100 W/m2 and withstand launch loads of 10G. The primary focus of this research is to evaluate newly introduced graphite foam by Poco Graphite Inc. as a core in a sandwich structure that can satisfy structural and thermal design requirements. The panel is a rectangular plate with a cutout that can hold the antenna. The panel is fixed on all the sides. The objective is not only to select an optimum design configuration for the face sheets and core but also to explore the potential of the Poco foam core in its heat transfer capacity. Furthermore the effects of various parameters such as face sheet lay-up, orientation, thickness and material properties are studied through analytical models to validate the predictions of finite element analysis. The optimum dimensions of the sandwich panel are determined and structural and thermal response of the Poco foam is compared with existing aluminum honeycomb core.

The goal of this study is to design and analyze a sandwich composite panel with lightweight graphite foam core and carbon epoxy face sheets that can function as a radiator for the given payload in a satellite. This arrangement provides a lightweight, structurally efficient structure to dissipate the heat from the electronics box to the surroundings. Three-dimensional finite element analysis with MSC Visual Nastran is undertaken for modal, dynamic and heat transfer analysis to design a radiator panel that can sustain fundamental frequency greater than 100 Hz and dissipate 100 W/m2 and withstand launch loads of 10G. The primary focus of this research is to evaluate newly introduced graphite foam by Poco Graphite Inc. as a core in a sandwich structure that can satisfy structural and thermal design requirements. The panel is a rectangular plate with a cutout that can hold the antenna. The panel is fixed on all the sides. The objective is not only to select an optimum design configuration for the face sheets and core but also to explore the potential of the Poco foam core in its heat transfer capacity. Furthermore the effects of various parameters such as face sheet lay-up, orientation, thickness and material properties are studied through analytical models to validate the predictions of finite element analysis. The optimum dimensions of the sandwich panel are determined and structural and thermal response of the Poco foam is compared with existing aluminum honeycomb core.

This thesis presents the results of research on sandwich panel construction, with the aims of developing tools for modelling sandwich panel fire performance and hence to use the tools to aid the development of sandwich panel construction with improved fire resistance. The research focuses on sandwich panels made of thin steel sheeting and a polyisocyanurate (PIR) foam core. For non-loadbearing sandwich panel construction, fire resistance is measured in terms of thermal insulation and integrity only. However, these two parameters are affected by mechanical performance of sandwich panel construction due to the high distortion and large deformation nature of sandwich panel construction under fire attack. Therefore, it is necessary to consider both thermal and mechanical performances of sandwich panels under fire conditions. The work in this thesis includes development of a thermal conductivity model for PIR foam as this thermal property is one of the key values in determining heat transfer through sandwich panels; this thermal conductivity model is based on the effective thermal conductivity of porous foams proposed by Glicksman (1994) and includes the effects of polymer decomposition and increases in foam cell size. It is validated against fire tests carried out on PIR sandwich panels 80mm and 100mm thick with steel facings of thickness 0.5mm. A large 3D sequentially coupled thermal-stress model of a full scale fire test has been developed in the commercial finite element analysis (FEA) software ABAQUS to provide insight into the way sandwich panels behave in a fire resistance test and also to assess different modelling techniques. Aspects and stages of the simulation that agree well with test data are explained. Limitations of the ABAQUS software for simulating sandwich panel fire tests are highlighted; namely, it is not possible to simulate the correct radiation heat transfer through panel joints, as cavity radiation cannot be specified in a fully coupled thermal-stress analysis. Joints are key components of sandwich panel construction. In order to obtain temperature development data for modelling joints, a number of fire tests have been carried out. These fire tests were conducted with different joint configurations and panel thicknesses under realistic fire conditions using timber cribs. The joint fire tests revealed significant ablation of the foam core within the joints of sandwich panels at high temperatures. At the beginning of fire exposure, the joint temperature on the unexposed surface was lower than that on the panel due to the better insulation property of air compared to the foam. However, as the joint gap increased due to ablation of the foam, the joint temperatures became higher than in the panel. A numerical simulation model has been created to investigate this behaviour. Using the aforementioned thermal model, numerical simulations have been carried out to examine the influences of possible changes to sandwich panel design on sandwich panel construction fire performance. It was suggested that if the maximum gap in the joints can be limited to 5mm, for example, by applying intumescent coating strips within the sandwich panel joints to counter the increasing gap formed due to core ablation, then the joint temperature on the unexposed surface would not exceed that of the panel surface, hence the joint would cease to be the weak link. To increase the panel fire resistance, the use of graphite particles in the PIR foam formulation may be considered to lower the contribution of radiative heat transfer within the foam cells by reducing the transmissivity of the cell walls. Graphite particles may offer considerable increases in the thermal resistance of PIR foam at high temperatures by limiting the radiation contribution which dominates heat transfer above 300oC.

This thesis explores the use of lightweight composite materials in road freight trailer design as a means of reducing the emissions of the road freight industry. A comprehensive review of previous lightweight composite trailers and related projects was conducted; it concluded that the application of composites in trailers to-date has largely been limited by relatively high material and production costs. The review highlighted that the trailer industry could learn from the success of composites in the bridge construction industry. A statistical weight analysis of two road freight fleets and an energy consumption estimation, via a drive cycle analysis, were used to identify trailers that are particularly suited to lightweighting. Hardwood trailer decking was identified as a prime subcomponent for composite replacement. However, there is little literature on how conventional hardwood trailer decks react to in-service loadings. This problem was addressed through a comprehensive deck damage study, which was used to benchmark novel lightweight deck systems. Several lightweight replacement composite sandwich panels were designed, built and tested. Two different pultruded GFRP decks were also examined. While pultrusions do not offer the same level of weight savings as sandwich panels, the highly cost-driven nature of the trailer industry could dictate that their integration is the most reasonable first step to introducing composites into structural subcomponents. The final part of the thesis explores options for lightweighting the trailer chassis holistically. Trailer load cases were investigated through finite element modelling in Abaqus. A parametric model of a typical longitudinal trailer I-beam was developed using Python scripting and Abaqus. The model was expanded to analyse composite trailer structures. It showed that approximately 1,300 kg of weight could be saved by shape and material optimisation in a composite trailer. In summary, this research has shown that short-term trailer weight reductions can be effectively achieved through subcomponent replacement, while more significant reductions can be achieved in the long-term by a ‘clean slate’ composite redesign of the trailer chassis. The lightweighting strategies presented here are poised to have an increasingly important role in reducing the emissions of the road freight industry.

abstract: Honeycomb sandwich panels have been used in structural applications for several decades in various industries. While these panels are lightweight and rigid, their design has not evolved much due to constraints imposed by available manufacturing processes and remain primarily two-dimensional extrusions sandwiched between facings. With the growth in Additive Manufacturing, more complex geometries can now be produced, and advanced design techniques can be implemented into end use parts to obtain further reductions in weight, as well as enable greater multi-functionality. The question therefore is: how best to revisit the design of these honeycomb panels to obtain these benefits? In this work, a Bio-Inspired Design approach was taken to answer this question, primarily since the hexagonal lattice is so commonly found in wasp and bee nests, including the well-known bee’s honeycomb that inspired these panel designs to begin with. Whereas prior honeycomb panel design has primarily focused on the hexagonal shape of the unit cell, in this work we examine the relationship between the various parameters constituting the hexagonal cell itself, specifically the wall thickness and the corner radius, and also examine out-of-plane features that have not been previously translated into panel design. This work reports findings from a study of insect nests across 70 species using 2D and 3D measurements with optical microscopy and X-ray tomography, respectively. Data from these biological nests were used to identify design parameters of interest, which were then translated into design principles. These design principles were implemented in the design of honeycomb panels manufactured with the Selective Laser Sintering process and subjected to experimental testing to study their effects on the mechanical behavior of these panels. / Dissertation/Thesis / Masters Thesis Manufacturing Engineering 2020

The topic of this publication is a comparison of insulated sandwich panels and materials of organic origin - wood based materials. There were compared insulative properties, lifetime and finacial costs of these materials.

abstract: The main objective of this study is to develop an innovative system in the form of a sandwich panel type composite with textile reinforced skins and aerated concrete core. Existing theoretical concepts along with extensive experimental investigations were utilized to characterize the behavior of cement based systems in the presence of individual fibers and textile yarns. Part of this thesis is based on a material model developed here in Arizona State University to simulate experimental flexural response and back calculate tensile response. This concept is based on a constitutive law consisting of a tri-linear tension model with residual strength and a bilinear elastic perfectly plastic compression stress strain model. This parametric model was used to characterize Textile Reinforced Concrete (TRC) with aramid, carbon, alkali resistant glass, polypropylene TRC and hybrid systems of aramid and polypropylene. The same material model was also used to characterize long term durability issues with glass fiber reinforced concrete (GFRC). Historical data associated with effect of temperature dependency in aging of GFRC composites were used. An experimental study was conducted to understand the behavior of aerated concrete systems under high stain rate impact loading. Test setup was modeled on a free fall drop of an instrumented hammer using three point bending configuration. Two types of aerated concrete: autoclaved aerated concrete (AAC) and polymeric fiber-reinforced aerated concrete (FRAC) were tested and compared in terms of their impact behavior. The effect of impact energy on the mechanical properties was investigated for various drop heights and different specimen sizes. Both materials showed similar flexural load carrying capacity under impact, however, flexural toughness of fiber-reinforced aerated concrete was proved to be several degrees higher in magnitude than that provided by plain autoclaved aerated concrete. Effect of specimen size and drop height on the impact response of AAC and FRAC was studied and discussed. Results obtained were compared to the performance of sandwich beams with AR glass textile skins with aerated concrete core under similar impact conditions. After this extensive study it was concluded that this type of sandwich composite could be effectively used in low cost sustainable infrastructure projects. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2012

L’industrie aérospatiale doit faire face à de nouvelles exigences environnementales, tout particulièrement concernant la réduction des coûts de lancement. L’utilisation de matériaux sandwichs composites plus légers permet de répondre à ces besoins. Cependant, l’allégement des matériaux sandwichs favorise une transmission importante du bruit, d’où la nécessité de prendre en compte des critères vibroacoustiques dès la phase de préconception. Dans cette optique, le travail présenté dans ce mémoire a pour objectif de proposer une démarche d’optimisation vibroacoustique des panneaux sandwichs composites légers, sous contraintes de masse et rigidité. Une étude spécifique est consacrée à l’optimisation des variables géométriques de solides cellulaires à périodicité de type nid d’abeille. L’objectif principal est de minimiser la densité modale en s’appuyant sur des modèles homogénéisés fiables. Afin de calculer les propriétés mécaniques macroscopiques des panneaux sandwichs, une méthode numérique d’homogénéisation tridimensionnelle est développée. Cette méthode permet de calculer les propriétés mécaniques équivalentes en utilisant les déformations et contraintes moyennes sur le volume représentatif. Les résultats obtenus sont conformes à ceux calculés par des méthodes classiques basées sur des modèles analytiques. Dans le but d’identifier une fonction objectif riche en informations sur le comportement vibroacoustique de panneau sandwich, on choisit d’étudier la densité modale du panneau. Par la suite, la fréquence de transition, qui sépare la zone de comportement de flexion pure du panneau sandwich du comportement en cisaillement pur de l’âme, est utilisée pour définir la fonction objectif. Après une étude d’analyse de sensibilité sur les paramètres mécaniques et géométriques de la structure sandwich, une démarche globale d’optimisation mono-objectif est mise en oeuvre pour maximiser la fréquence de transition de la structure sandwich composite constituée d’une âme en nid d’abeille hexagonale. Enfin, cette démarche est étendue pour estimer les propriétés géométriques optimales de nouvelles âmes. / The aerospace industry has to adapt to new environmental requirements, especially concerning the reduction of the launch costs. The use of lighter composite sandwich materials can meet part of these requirements. However, their high stiffness-toweight ratio implies that they tend to increase noise transmission, which may be damageable to the payload. Vibroacoustic criterai should hence be taken into account from the early design stages. In this context, the work presented in this thesis aims to provide a vibroacoustic optimization approach of lightweight composite sandwich panels, under mass and stiffness constraints. A specific study is devoted to the optimization of geometric variables of periodic cellular solids such as honeycombs. The main objective is to minimize the modal density based on reliable homogenized models. In order to calculate the macroscopic mechanical properties of the sandwich panel, a numerical method of three-dimensional homogenization is developed. This method allows to calculate the equivalent mechanical properties by applying the average strains and stresses on a unit cell. The results obtained are consistent with those calculated by conventional methods based on analytical approaches. The modal density is chosen as an objective function for optimization, as it is closely related to the vibroacoustic behavior of the structure. The transition frequency, which separates the region of pure panel bending from the pure core shear zone, is further studied and considered as an alternative objective function. After a sensitivity analysis of the mechanical and geometric parameters of the sandwich structure, a mono-objective optimization approach is implemented to maximize the transition frequency of a composite sandwich structure with a hexagonal core. This approach is then extended to estimate the optimal geometric properties of new core shapes.

Incremental sheet forming (ISF) is a flexible process where an indenter moves over the surface of a sheet of metal to form a 3D shell incrementally by a progression of localised deformation. Despite extensive research into the process, the deformation mechanics is not fully understood. This thesis presents new insights into the mechanics of ISF applied to two groups of materials: sheet metals and sandwich panels. A new system for measuring tool forces in ISF is commissioned. The system uses six loadcells to measure reaction forces on the workpiece frame. Each force signal has an uncertainty of ±15 N. This is likely to be small in comparison to tool forces measured in ISF. The mechanics of ISF of sheet metals is researched. Through-thickness deformation and strains of copper plates are measured for single-point incremental forming (SPIF) and two-point incremental forming (TPIF). It is shown that the deformation mechanisms of SPIF and TPIF are shear parallel to the tool direction, with both shear and stretching perpendicular to the tool direction. Tool forces are measured and compared throughout the two processes. Tool forces follow similar trends to strains, suggesting that shear parallel to the tool direction is a result of friction between the tool and workpiece. The mechanics of ISF of sandwich panels is investigated. The mechanical viability of applying ISF to various sandwich panel designs is evaluated by observing failure modes and damage under two simple tool paths. ISF is applicable to metal/polymer/metal sandwich panels. This is because the cores and faceplates are ductile and largely incompressible, and therefore survive local indentation during ISF without collapse. Through-thickness deformation, tool forces and applicability of the sine law for prediction of wall thickness are measured and compared for a metal/polymer/metal sandwich panel and a monolithic sheet metal. The mechanical results for ISF of sheet metals transfer closely to sandwich panels. Hence, established knowledge and process implementation procedures derived for ISF of monolithic sheet metals may be used in the future for ISF of sandwich panels.

Present day composite sandwich panels provide incredible strength. Their largest problem, however, is early bonding failure between the core and the skin. This is due to the low bonding surface area of present cores like honeycomb. Corrugated structures could provide a remedy for this with their much larger bonding surface area. Corrugated structures have extreme mechanical properties deeming them particularly useful in aerospace and automotive applications. However, previous research has shown that the stiffness of carbon fiber causes debonding and drastic failure when used as both a core and a skin. Bio-composites have properties that could strengthen the corrugated sandwich panel against such debonding and increase the strength of the structure while making it cheaper and more environmentally friendly. This thesis presents the optimum design, manufacturing, and testing of corrugated sandwich panel structures with integrated bio-composites under edgewise compression loading. To do this, optimum corrugation geometry was identified using theoretical analysis of the moment and bonding area of the shape. Control tests with carbon fiber and hemp were conducted. The bio-composite was integrated in both the core and the skin individually in corrugated sandwich panels. The cases tested were all-carbon fiber, hemp skin with carbon fiber core, carbon fiber skin with hemp core, and all-hemp. These corrugated structures were analyzed by conducting compression loading tests on varying lengths of single-ligament panels utilizing trapezoidal corrugation as the core and a flat plate as the skin. The lengths tested were 1, 2, 3, and 4 inches. As many samples as possible were manufactured out of limited material with heavier focus on creating the shorter samples. The goal of this testing was, first, to determine if hemp fibers were viable as a substitute for certain sections of the traditional composite structure, and second, to see if integrating hemp fibers would solve the problems of debonding seen in the all-carbon fiber samples seen in previous research. To determine mechanical property viability, the ultimate load and stiffness were investigated for each sample, as well as investigation of the failure modes seen in the test. Secondary goals were to see at what length buckling behavior became an issue and to see if this corrugated structure and all its failure modes could be simulated in finite element analysis. At the 1-inch and 2-inch lengths where minimal buckling was encountered, the hemp core-carbon skin samples showed better results than both the all-carbon fiber and the all-hemp samples with a 4% and 6% increase in average ultimate load and a 11% and 47% increase in stiffness, respectively. From these results, it was concluded that hybrid bio-composite structures can have comparable mechanical properties to traditional composites and can solve bonding failure.