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

There is currently an interest in optimizing the structural design to improve materials' strength to weight ratio or improve stiffness for energy absorption. As such, cellular structures are continuously studied and improved. However, it is a well-known fact in the literature that one primary mechanism of failure of a honeycomb is the formation of shear bands. The impacts of these shear bands bring many questions and unknowns, especially when the cellular structures are created with the increasingly popular manufacturing technique of 3D printing. Therefore, understanding the deformations in 3D printed honeycomb structures is necessary to explain the behavior of materials generated through new additive manufacturing techniques and further the knowledge of the deformation localization and, consequently, formations of shear bands in the deformation process of cellular structures.In the first phase of this work, samples with a unit cell regular hexagonal honeycomb format were designed and manufactured using masked-stereolithography (M-SLA). After the curing process, the samples were prepared with a paint application in the format of speckle, and DIC was realized in a compression experiment to identify and analyze the presence of high strain regions indicating the presence of shear bands. A second phase was then conducted, aiming to consider the control and manipulation of the shear band through the utilization of relief holes. The results demonstrated that adding incisions in specific parts of the polymeric honeycomb makes it possible to change its strain spread through the shear band and change its toughness.

This work deals with the design of chassis for race car category E2 made from aluminium honeycomb sandwich, design of roll cage and conception of engine mount. In the text are FEM analysis, which are focused on torsional rigidity of chassis and strength properties of roll cage.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19913号 / 理博第4213号 / 新制||理||1605(附属図書館) / 32999 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 前野 悦輝, 教授 石田 憲二, 教授 川上 則雄 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This study will present the Experimental, numerical and analytical characterizations of composite sandwich structures needed to optimize structure design. In this study, the effects of varying honeycomb core ribbon orientation and varying face sheet thickness’s have on the flexural behavior of honeycomb sandwich structures was investigated. Honeycomb sandwich panels were constructed using Hexcel 6367 A250-5H carbon fiber face sheets and Hexcel Nomex HRH-10-1/8-5 honeycomb cores. The mechanical properties of the constituent materials were discovered experimentally using ASTM standards and theoretical models using honeycomb mechanics and classical beam and plate theory are described. A failure mode map for loading under three point bending is developed from previous works by Triantafillou and Gibson26, showing the dependence of failure mode on face sheet to core thickness and honeycomb core ribbon orientation. Beam specimens are tested with the effects of Honeycomb core ribbon orientation and unequal face sheet thickness’s examined. Experimental data sufficiently agrees with theoretical predictions. A finite element model was developed in ABAQUS/CAE to validate experimental and analytical analysis and produced agreeable results. Optimal bending stiffness and strength with respect to minimum weight was analyzed. The results reveal an important role core ribbon orientation has in a sandwich beam’s bending behavior, and design of unequal ply count face sheets can produce higher stiffness to weight ratios than conventional symmetric sandwich structures of similar weight when subjected to a single static load.

No description available.

The ability to quantify leakage flow and windage heating for labyrinth seals with honeycomb lands is critical in understanding gas turbine engine system performance and predicting its component lifes. Variety of labyrinth seal configurations (number of teeth, stepped or straight, honeycomb cell size) are in use in gas turbines, and for each configuration, there are many additional geometric factors that can impact a seal’s leakage and windage characteristics. To achieve high performance in modern gas turbine engines, the labyrinth seals operate at low clearances and high rotational speed which are generally deployed with honeycomb lands on the stator. During the transient operation of aircraft engines, the stator and rotor mechanical and thermal growths differ from one another and can often result in the rotor’s incursion into the stator honeycomb structure. The incursions create rub-grooves in the honeycomb lands that can subsequently enlarge as the engine undergoes various manoeuvres. However, the effects of different honeycomb cell size, rotation and presence of rub-groove have not been thoroughly investigated in previously published work. The objective of the present research is to numerically investigate the influence of the above three factors on seal leakage and windage heating. The present work focuses the development of a numerical methodology aimed at studying above effects. Specifically, a three-dimensional CFD model is developed utilizing commercial finite volume-based software incorporating the RNG k-ε turbulence model. Detail validation of the numerical model is performed by comparing the leakage and windage heating measurements of several rig tests. The turbulent Schmidt number is found to be an important parameter governing the leakage prediction. It depends on honeycomb cell size and clearance for honeycomb seals, and Reynolds number in the presence smooth lands. The present numerical model with the modified RNG k- turbulence model predicts seal leakage and windage heating within 3-10% with available experimental data. Using the validated numerical model, a broad parametric study is conducted by varying honeycomb cell size, radial clearance, pressure ratio and rotational speed for a four-tooth straight-through labyrinth seal with and without rub-grooves. They further indicate that presence of rub-grooves increases seal leakage and reduce windage heating, specifically at smaller clearance and for larger honeycomb cell size. Rotation significantly reduces leakage with smooth stator land and smaller honeycomb cells whereas the effect is minimal for larger (3.2mm) honeycomb cells. However, at very high rotational speed seal flow reduces in all seal configurations due to high temperature rise and Rayleigh line effects. At no rub condition and lower clearance, the larger honeycomb cells leak more flow due to high bypass flow through the honeycomb cells. This results into lower pocket swirl and higher windage. When the seal clearance increases the larger honeycomb cells offers more drag to the seal flow, therefore they leak less. At higher clearances the flow travels like a strong wall jet and isolates the pocket air from honeycomb cells. Hence, at open clearances labyrinth seals with any honeycomb cell size essentially produce the same pocket swirl and windage heating.

Stark formbare Wabenkerne als Kernschicht geformter Sandwichbauteile finden in vorteilhafter Ausführung bisher lediglich Verwendung in kostenintensiven Anwendungen mit hoher Leistungsklasse. Für eine weite Verbreitung der kombinierten Leichtbauweise fehlen bisher kostengünstige Wabenkerne, die die Formung schadlos überstehen und so ihre Verbundeigenschaften auch im geformten Bauteil aufweisen. Die vorliegende Arbeit befasst sich zunächst mit der Entwicklung eines Verfahrens zur Herstellung eines formbaren Papierwabenkerns mit vorgegebener Zellstruktur. Nach dem Funktionsnachweis erfolgt ein Anforderungsabgleich, welcher zeigt, dass eine kostengünstige Herstellung nicht realisierbar ist. Nach Diskussion folgt der Entschluss, den größtmöglichen iterativen Schritt beim Konstruktiven Entwicklungsprozess zu gehen und das gesamte Verfahren als nicht anforderungsgerecht einzustufen. Zugleich wird die vorgegebene Zellstruktur hinterfragt. Darauf basierend erfolgt eine umfangreiche Recherche zu Wabenkernherstellungsverfahren und formbaren Wabenkernen. Aus Letzterem werden sieben Gestaltungselemente abgeleitet, die zur Formbarkeit führen. Mit dieser Kenntnis wird der Entwicklungsprozess erneut durchlaufen. Die Zellstruktur ist dabei nicht definiert, sondern lediglich die zu erzielenden Eigenschaften, wodurch eine möglichst geeignete Produkt-Verfahrenskombination ermittelt werden soll. U. a. resultiert ein Flexibilisierungsverfahren, bei dem gängige Hexagonalwabenkerne aus Papier in einem zusätzlichen Schritt umgeformt werden und so die geforderte Formbarkeit erlangen. Nach der Entwicklung und dem Funktionsnachweis mit einer Prototypenmaschine erfolgt die Weiterentwicklung des Verfahrens. Mit einer Laborversuchsmaschine werden wesentliche Steuergrößen ermittelt, das Wirkprinzip diskutiert, ein erstes Verarbeitungsspektrum erprobt sowie ein Verfahren zur optischen Erfassung von Wabenkernzellstrukturen entwickelt. Letzteres dient der Charakterisierung von Wabenkernen und, speziell beim flexibilisierten Wabenkern, der Vorhersage des Formänderungsvermögens. Abschließend werden wesentliche Verbundeigenschaften eines flexibilisierten Referenzwabenkerns seiner gängigen hexagonalen Form gegenübergestellt und exemplarisch erste Musterformteile gefertigt. Im Rahmen der Arbeit werden entwicklungsübergreifende Forschungsfragen aufgestellt, die anhand gewonnener Erkenntnisse diskutiert werden.:1Einleitung 2 Stand der Wissenschaft und Technik 2.1 Wabenbauweise 2.2 Schalenbauweise 2.3 Wabenformteile 2.4 Geschichte der Waben- und Schalenbauweise 2.5 Wabenkerne - Kategorisierung, Aufbau und Terminologie 2.6 Wabenwerkstoffe - insbesondere Papier 2.7 Ausgewählte Einflüsse auf Wabenkerneigenschaften 2.8 Herstellung von Wabenkernen 2.8.1 Wellprinzip 2.8.2 Reckprinzip 2.8.3 Zellgrundformen sowie Anwendbarkeit des Well- und Reckprinzips 2.9 Formbare Wabenkerne 2.9.1 Papierwabenkerne in Wabenformteilen 2.9.2 Gestaltung und Klassifizierung formbarer Wabenkerne 2.9.3 Herstellung zellstrukturbedingt formbarer Wabenkerne 2.10 Herstellungsaufwand, Leistungsfähigkeit und Kosten 3 Präzisierte Zielstellung und Vorgehensweise 4 Verfahrensentwicklung – Herstellung einer geometrisch definierten Zellstruktur 4.1 Ausgangssituation 4.2 Weiterentwicklung des Herstellungsverfahrens 4.2.1 Vervollständigung des Herstellungsverfahrens 4.2.2 Neuentwicklung Formvorrichtung 4.2.3 Entwicklung Formbaugruppe 4.2.3.1 Fertigung und Erprobung von Formschienen und -baugruppen 4.2.3.2 Entwicklung vorteilhafter Formschienenkonturen 4.2.3.3 Potentiell vorteilhafte Formbaugruppe 4.2.4 Entwicklung Trenn- und Fügemaschine 4.3 Bewertung der Entwicklung und Diskussion 5 Verfahrensentwicklung – Flexibilisierung zum formbaren Wabenkern 5.1 Angepasste Zielstellung und Vorgehensweise 5.2 Ermittlung eines Vorzugsprinzips 5.2.1 Ermittlung geeigneter Lösungsräume 5.2.2 Ermittlung geeigneter Verfahrensprinzipe 5.2.3 Bewertung der Verfahrensprinzipe 5.3 Entwicklung des FlexCore-Verfahrens 5.3.1 Entwicklung FlexCore-Prototyp 5.3.2 Funktionsnachweis 5.3.3 Weitergehende Erprobung 5.4 Bewertung des Flexibilisierungsverfahrens FlexCore 6 Ausarbeitung FlexCore-Verfahren 6.1 Identifizieren verbleibender Entwicklungsschwerpunkte 6.2 Entwicklung einer Methode zur Charakterisierung von Wabenkern-Zellstrukturen 6.2.1 Konkretisierung der Entwicklungsaufgabe 6.2.2 Ermittlung einer Methode zur Zellstrukturerfassung 6.2.3 Entwicklung eines mobilen Prüfstandes zur Zellstrukturerfassung 6.2.4 Erarbeitung und Erfassung potentiell charakteristischer Kenngrößen 6.3 Maschine für wissenschaftliche Untersuchungen 6.3.1 Maschinenentwicklung 6.3.2 Maschinenerprobung 6.4 Identifizierung charakteristischer Kenngrößen flexibilisierter Zellstrukturen sowie wesentlicher Verfahrenssteuergrößen 6.4.1 Versuchsplanung und -durchführung 6.4.2 Prüfung des Formänderungsvermögens formbarer Wabenkerne 6.4.3 Bestimmung charakteristischer Kenngrößen 6.4.4 Bestimmung wesentlicher Steuergrößen des FlexCore-Verfahrens 6.5 Rückschlüsse zur Funktionsweise des Wirkprinzips 6.6 Erste Erprobung des Verarbeitungsspektrums 6.7 Stützstoffeigenschaften flexibilisierter Wabenkerne 6.7.1 Geometrie- und Masseeigenschaften 6.7.2 Druckeigenschaften - unstabilisiert 6.7.3 Druckeigenschaften - stabilisiert 6.7.4 Schubeigenschaften 6.8 Exemplarische Musterfertigung von Wabenformteilen 7 Zusammenfassung und Ausblick Abbildungsverzeichnis Tabellenverzeichnis Quellen Anlagen

Edgewise crushing responses of composite aluminum honeycomb sandwich structures were predicted using finite element analysis (FEA) software LS-DYNA by modeling the honeycomb as a material with anisotropic properties. The goal of the project was to develop a process for modeling the sandwich structure to rapidly iterate possible solutions for a safer workstation train table. Current workstation tables are too rigid and may cause injury or death in a head-on collision. Experimental compression tests were used to calibrate the aluminum honeycomb core with material type 26 (MAT 26, honeycomb). A published composite tensile test was used to validate the use of material type 22 (MAT 22, composite damage) for laminates. Finally, a model was made to recreate the results of a published compression test of an aluminum honeycomb sandwich structure with aluminum sheet metal face sheets to confirm contact types. With each component of the model verified separately, three plain weave composite aluminum honeycomb sandwich structures were modeled, one with [0/90] composite sheets completely bonded to the core, one with [0/90] composite sheets partially bonded to the core, and one with [±45] composite sheets partially bonded to the core. The failure modes for each sandwich structure were previously shown through research and the elastic region of the response was checked for accuracy using a simple beam theory. The analysis suggests that incorporating unbonded zones into the sandwich structure will change the failure mode from general buckling to face wrinkling, which effectively lowers the failure strength while not sacrificing energy absorption throughout loading. The analysis also indicates that using an angled ply orientation will lower the initial stiffness and the failure load. Future work is recommended such as performing compression tests with composite aluminum honeycomb sandwich structures and integrating delamination failure modes into the model using cohesive elements.

Finite element analysis with explicit time integration is widely used in commercial crash solvers to accurately simulate transient structural problems involving large-deformation and nonlinearity. Technological advances in computer software and hardware have expanded the boundaries of computational expense, allowing designers to analyse increasingly complex structures on desktop computers. This dissertation is a review of the use of finite element analysis for crash simulation, the principles of crashworthy design and a practical application of these methods and principles in the development of a concept energy absorber for a sailplane. Explicit nonlinear finite element analysis was used to do crash simulations of the glass, carbon and aramid fibre cockpit during the development of concept absorbers. The SOL700 solution sequence in MSC Nastran, which invokes the LS-Dyna solver for structural solution, was used. Single finite elements with Hughes-Liu shell formulation were loaded to failure in pure tension and compression and validated against material properties. Further, a simple composite crash box in a mass drop experiment was simulated and compared to experimental results. FEA was used for various crash simulations of the JS1 sailplane cockpit to determine its crashworthiness. Then, variants of a concept energy absorber with cellular aluminium sandwich construction were simulated. Two more variants constructed only of fibre-laminate materials were modelled for comparison. Energy absorption and specific energy absorption were analysed over the first 515 mm of crushing. Simulation results indicate that the existing JS1 cockpit is able to absorb energy through progressive crushing of the frontal structure without collapse of the main cockpit volume. Simulated energy absorption over the first 515 mm was improved from 2232 J for the existing structure, to 9 363 J by the addition of an energy absorber. Specific energy absorption during the simulation was increased from 1063 J/kg to 2035 J/kg. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015