La détermination des conditions de chargements limites qui produisent une localisation du matériau est toujours un enjeu important, notamment lorsqu'il s'agit d'optimiser les dimensions d'outillage lors d'opérations durant lesquelles le matériau est fortement sollicité. Différents travaux récents ont montré que l'hétérogénéité structurale intrinsèque à tout matériau métallique joue un rôle important dans les différents stades de déformation. Le rôle des hétérogénéités sur la localisation n'est cependant pas abordé. L'objectif de cette thèse est donc de déterminer si l'hétérogénéité structurale des matériaux a un impact sur la localisation des matériaux ductiles. Une action corollaire est alors de valider le recours à des modèles qui intègre cette hétérogénéité pour obtenir des meilleurs résultats.Cette étude comprend deux volets. Le premier volet expérimental a pour objectif de constituer un référentiel expérimental qui met en évidence l'impact du facteur hétérogénéité sur la localisation. Différentes éprouvettes de titane ont été préparées de façon à obtenir différents degrés d'hétérogénéités. Deux paramètres ont été utilisés à cette fin : l'épaisseur et la structure cristalline. Le titane permet en effet de disposer de matériaux à structure hexagonale et cubique centrée qui présentent des possibilités d'accommodation plastique très différentes. Des essais de traction et d'expansion ont ainsi été pratiqués sur des éprouvettes de titane de tôle fine et épaisse dans les structures α et β du titane de nuance T40. Trois tôles différentes : Tiα(tôle fine); Tiα(tôle épaisse) et Tiα+β(tôle épaisse) ont été utilisées lors des essais. Pour obtenir les tôles Tiα+β un traitement thermique a été optimisé et l’analyse des tôles a été effectuée à l’aide de plusieurs techniques comme le MEB, les rayons X et l'ATD. Un second volet numérique s'est appuyé sur deux modèles pour réaliser la simulation des essais expérimentaux. Un premier modèle de type phénoménologique "classique", sans facteur d'hétérogénéité a tout d'abord été utilisé pour simuler le comportement idéal d'un matériau homogène. Dans un second temps, le recours à un modèle qui intègre une dimension physique, l'hétérogénéité, a montré que cette dernière a une incidence notable et permet d'améliorer la prédiction du phénomène de localisation. / The determination of limit loading conditions producing the localization in the material is always an important subject, notably as it is about the optimization of tool dimension during operations during which material is strongly solicited. Different recent works have shown that intrinsic structural heterogeneity inside any metallic material plays an important role in the different stages of deformation. However, the role of heterogeneities in localization is not addressed.The objective of this PhD thesis is therefore to determine if the structural heterogeneity of materials has an impact on the localization of ductile materials. A corollary action is then to validate the use of models which integrate this heterogeneity for best results.This study has two parts.The first experimental part has for objective to constitute an experimental base which highlights the impact of the heterogeneity factor on localization. Different titanium specimens were prepared so as to obtain different degrees of heterogeneities.Two parameters were used for this purpose: thickness and crystal structure. Titanium makes it possible to have materials with hexagonal structure and cubic centered that present possibilities of very different plastic accommodation.Tensile and equi-axial tests have thus been carried out on titanium specimens for thin and thick metal sheet in the structures α and β for T40 grade Titanium.Three different sheets Tiα(thin); Tiα(thick) et Tiα+β(thick) were used during the tests. To obtain the sheets Tiα+β, a heat treatment has been optimized and sheets analysis was done using several techniques such as SEM, X Rays and ATD. A second numerical part was based on two models to realize numerical simulation of the experimental tests. A first classical phenomenological model without heterogeneity factor was firstly used to simulate the ideal behavior of a homogeneous material. In a second time, the use of a model that incorporates a physical dimension that is to say the heterogeneity, has shown that this latter has a significant impact and makes it possible to improve the prediction of localization phenomenon.

Dans ce travail de thèse, le comportement des composites stratifiés est étudié en utilisant des développements d'ordres élevés ou de type layer wise. Un modèle layer wise LS1 (et l'élément fini à huit nœuds qui lui est associé) a été développé en premier lieu pour l'analyse spécifique des contraintes entre les couches pour des problèmes de bords libres ou bien pour l'étude des liaisons entre les couches. Il est fondé sur un modèle de type layer wise qui considère le stratifié comme une superposition de plaques de Reissner couplées les unes aux autres par des efforts d'interfaces. Cet élément a 5n degrés de liberté par noeud (n étant le nombre de couches) et donne une prédiction des contraintes d'interface. Les travaux précédents se concentraient sur la précision et l'utilisation de l'estimation de ces contraintes d'interface. Mais le modèle permet aussi de calculer les déplacements et les déflexions ainsi que d'extraire les contraintes dans l'épaisseur avec ou sans post-traitement. Dans ce mémoire, la précision et la validité du calcul des déplacements et des contraintes ont été établies à partir d'un nombre important de benchmarks en flexion de composites et des plaques sandwich. Le but de cette étude est aussi de mieux positionner et de promouvoir cette approche en contraintes issue des travaux de Pagano peu utilisés et mal référencés. Ce modèle est ensuite développé et implémenté dans le code de calcul par éléments finis Abaqus via la routine utilisateur User-Element (UEL). Pour démontrer l'efficacité du modèle et du code de calcul, des exemples qui comprennent des plaques isotropes et anisotropes sont traités / In this document, the behaviour of laminated composite is investigated using several high order or layer wise finite element calculations. A layer wise model and its devoted finite element on C° eight-node layer wise finite element have been originally and specifically developed for an interlaminar stresses analysis in a free edge problem or for a bonding study. This model is the core of the present comparisons. It is based on a typical layer wise model that considers the laminate by a superposition of Reissner plates coupled by interfacial stresses. This element consists of 5n degrees of freedom per node (n is the layer number) and is able to predict interlaminar stresses. These out-of-plane stresses are deduced directly from constitutive equations without post-processing works. The previous papers dealt with the accuracy of these estimated interface stresses. However, the model not only permits to compute displacements and usual deflections but also to compute stresses through the layer thicknesses with or without postprocess. In the present paper, the accuracy and the validity of these computed displacements and stresses have also been established on a large number of important benchmarks of bending examples for composites and sandwich plates. The aim of this research is also to better positioning and promoting of this stress approach deriving from the works of Pagano, which was not generally studied in this way. This model has also been implemented into the ABAQUS finite-element program through a User-Element subroutine interface. To demonstrate the effectiveness of the model and the finite element code, examples which include isotropic and anisotropic plates, the problem of the perforated plate are calculated

[pt] Nesta tese são estudadas as vibrações não-lineares de membranas circulares inicialmente tracionadas sujeitas a deformações finitas. O material da membrana é modelado como um material hiperelástico neo-Hookeano, isotrópico e incompressível. Baseada na teoria de deformações finitas para membranas hiperelásticas, uma formulação variacional é desenvolvida. Primeiro a solução da membrana sob tração radial uniforme é obtida e então as equações de movimento da membrana são obtidas pelo princípio de Hamilton. A partir das equações linearizadas, as freqüências e os modos de vibração da membrana são obtidos analiticamente. Os modos naturais são usados para aproximar o campo de deformações não-linear usando o método de Galerkin e modelos de ordem reduzida são deduzidos através do método de Karhunen-Loève e de métodos analíticos. Além disso, estuda-se a influência da variação da massa específica e da espessura ao longo da direção radial da membrana nas vibrações. A seguir a mesma metodologia é utilizada para uma membrana anular. Por fim, estudam-se as vibrações não-lineares da membrana anular acoplada a uma inclusão rígida que insere tensões de tração na membrana, pois, devido ao seu peso próprio, provoca deslocamentos estáticos transversais e axissimétricos na membrana. Os mesmos problemas são analisados por elementos finitos utilizando o programa comercial Abaqus. / [en] This work presents an analysis of the nonlinear vibration response of a prestretched hyperelastic circular membrane subjected to finite deformations. The membrane material is assumed to be isotropic, homogeneous and neo-Hookean. Based on the theory of finite deformations for hyperelastic membranes, a variational formulation is developed. First the exact solution of the membrane under a uniform radial stretch is obtained and then the equations of motion of the pre-stretched membrane are derived using the Hamilton’s principle. From the linearized equations of motion, the natural frequencies and mode shapes of the membrane are obtained analytically. Then the natural modes are used to approximate the nonlinear deformation field using the Galerkin method. Several reduced order models are tested using the Karhunen-Loève method and analytical methods. Besides, the influence of the variation of the membrane thickness and material density along the radial direction of the membrane on the vibrations is investigated. The same methodology it is used for the annular membrane. Finally, the non-linear vibrations of the annular membrane coupled to a rigid inclusion are studied. The rigid inclusion inserts traction forces in the membrane and its own weight causes static transverse and radial displacements in the membrane. The same problems are analyzed by finite elements using the commercial program Abaqus®.

Proplate, a world leading company, is expert on volume-based cutting and machining of both ordinary steel as well as stainless steel. One of Proplate’s mayor products is tension bars, which is a component made to balance high forces and give stability to structures such as cranes, buildings, bridges and much more. Proplate builds their tension bars in different high strength steel materials, purchased from SSAB, and sells them worldwide. Proplate would like to market themselves better and wishes to produce a catalogue for the maximum load that can be applied to their tension bars, as competitors Pretec and Macalloy, already have for their tension bars. The purpose of the project has been to investigate the tension bars and the maximum load they can withstand before failure. The tension bars have been modeled in the CAD-program Creo Parametric, and then sent to the finite element method program ABAQUS to analyze their structural strength. Three different types of tension bars, and a fourth tension bar (called the walnut-strap) used as a connecting element between some of the tension bars, were investigated. They were modeled with sprints, to hold several tension bars together, and with a construction called loader, to simplify the model load application step. The three different types of tension bars have been analyzed as individual and also when connected to other tension bars. Some tension bars could be directly connected to each other with sprints, and some used the walnut-strap to connect other tension bars to each other. The project was limited to fatigue analyses, which is an important factor to control. This could instead be a great continuation of the project. The results from the strength analyses show that the stress is higher at the surfaces around the hole at the end of each tension bar, and the maximum load the tension bars can withstand depends on this area. The length, thickness and orientation of the tension bar has been varied, and the maximum load that each model can withstand has been listed. The length and direction of the tension bars did not influence the result for singular tension bars, but the thickness did. Both the length and the thickness of the tension bars did influence the result when multiple tension bars where connected to each other. Tables have been derived which shows the absolute maximum load that the tension bars can withstand. Proplate can use the tables in their catalogue, and they can also put a safety factor on the models to make them safer. Another part of the study was to investigate advantages and disadvantages with if the sprints, the connecting element between the tension bars, were replaced with screws instead. The result describes the yield strength needed for the screws and how the structures would behave compared to the current structure. A larger investigation into the effect of using screws may be one way to continue the work after this project, together with other investigations of, for instance, the use of compression bars. / Proplate är ett världsledande företag, som är experter på volymbaserad skärning och tillverkning i både vanligt stål såväl som rostfritt stål. En av Proplates huvudprodukter är deras dragstag, som är en komponent gjord för att balansera stora krafter och tillbringa stabilitet till strukturer, exempelvis lyftkranar, byggnader, broar med mera. Proplate bygger sina dragstag med hjälp av olika typer av höghållfasta stålsorter, köpta från SSAB, och säljer sedan produkterna över hela världen. Proplate skulle vilja marknadsföra sig bättre och önskar att ta fram en katalog över den maximala kraften som kan appliceras på dragstagen, vilket konkurrenter som Macalloy och Pretec redan har för sina dragstag. Syftet med projektet är att undersöka dragstagen och den maximala kraften som dragstagen klarar av innan de går sönder. Dragstagen har modellerats upp i CAD-programmet Creo Parametric, och sedan skickats till finita-elementmetodsprogrammet ABAQUS för hållfasthetsanalyser. Tre olika typer av dragstag, och en fjärde variant (kallad valnöts-staget) som använts som ett sammankopplande element mellan olika typer av dragstagen, har undersökts. De har modellerats tillsammans med sprintar, för att hålla samman flera dragstag, och en konstruktion vid namn loader, som ska förenkla kraftapplikationssteget i analyserna. De tre olika typerna av dragstag har analyserats individuellt och sammankopplade till andra dragstag samtidigt. Några av dragstagen kunde direkt sammankopplas till andra dragstag med hjälp av sprintar, men andra behövde valnöts-staget för att sammankoppla dragstagen till varandra. Projektet var avgränsat så att utmattningslaster, vilket är en mycket viktig faktor, inte analyserades. Resultatet från hållfasthetsanalyserna visar att spänningarna i ytan kring ett hål i kanterna av dragstagen blir som störst, och den maximala kraften som dragstagen kan klara av är beroende på denna yta. Dragstagens längd, tjocklek och orientering i rummet har varierat, och den maximala kraften som varje modell kan klara av har tabellerats. Dragstagens längd och riktning i rummet påverkade inte resultatet när individuella dragstag analyserades, men dess tjocklek gjorde det. Både längden och tjockleken av dragstagen påverkade resultatet när flera dragstag blivit sammankopplade till varandra. Tabellerna visar den absolut maximala kraften som dragstagen kan klara av. Proplate kan använda dessa tabeller till deras katalog, och de kan också lägga till en säkerhetsfaktor på modellerna för att göra dem säkrare. En annan del av analyserna var att undersöka fördelarna och nackdelarna om sprintarna, som är det sammankopplande elementet mellan de olika dragstagen, blivit utbytta mot skruvar istället. Resultatet beskriver vilken sträckgräns som skulle behövas för skruvarnas material och hur strukturen skulle bete sig i jämförelse till den nuvarande strukturen. En större undersökning angående effekten med skruvar kan vara en bra fortsättning på arbetet efter detta projekt, tillsammans med andra undersökningar som exempelvis angående användning av tryckstag.

There is a high dependency on accurate finite element models in the packaging industry for concept selection, design and virtual validation of packages. One of themost used materials for these packages is High-Density Polyethylene (HDPE). Thismaterial is highly anisotropic, strain rate dependent and has different behavior intension and compression.The objective of this thesis is to improve the existing constitutive model of HDPEthrough additional material characterization experiments and validate those models.For this purpose, strain rate dependencies of the material on elastic and hardeningresponse are included in the constitutive model. In addition to that, the compressivebehavior of HDPE was incorporated in the model as well. The anisotropy of HDPEwas modeled using the Hill48 yield criterion which was characterized by performingmultiple uniaxial tensile tests in the three directions: Machine Direction (MD), 45◦and Cross Direction (CD).Validation was done on the coupon test and compression test on the package.The result displayed that the results from the physical test are comparable with theresults obtained from the FE-models.From the tensile tests, the deformation of HDPE in MD and 45◦ was successfullycaptured and validated. While for the CD direction, the deformation could be captured but not validated against FE-model. Furthermore, the test results displayedthat the material HDPE exhibits a significant degree of anisotropy. In conclusion,the project contributed knowledge and understanding of how a Tetra Pak® packagebehaved during top load compression / Det finns ett stort behov av exakta finita element-modeller inom förpackningsindustrin för konceptval, design och virtuell validering av paket. Ett av de mest användamaterialen för dessa förpackningar är Högdensitetspolyeten (HDPE). Detta materialär mycket anisotropiskt, töjningshastighetsberoende och har olika beteende i dragoch tryckspänning.Syftet med detta projektet är att förbättra den befintliga konstitutiva modellenav HDPE genom ytterligare materialkaraktärisering för experimenten och valideradessa modeller. För detta ändamål ingår töjningshastighet hos materialet för elasticitet och spänning-töjningskurva i den konstitutiva modellen. Utöver det användsäven HDPE:s tryckbeteende i modellen. Anisotropin av HDPE modellerades medanvändning av Hill48 som kännetecknades av att utföra flera enaxliga dragtester itre riktningar: Machine Direction (MD), 45◦ och Cross Direction (CD).Validering gjordes på dragprovstestet och trycktestet på förpackningen. Resultatet visade att resultaten från det fysiska testet är jämförbara med resultaten frånFE-modellerna.Från dragprovstesterna fångades och validerades deformationen av HDPE i MDoch 45◦framgångsrikt. Medan för CD-riktningen kunde deformationen fångas meninte valideras mot FE-modellen. Testresultaten visade också att materialet HDPEuppvisar en betydande grad av anisotropi. Sammanfattningsvis bidrog projektet medkunskap och förståelse för hur ett Tetra Pak®-paket betedde sig under trycktest

Detta examensarbete använder ett systematiskt tillvägagångssätt för att omkonstruera ett växellådshus till ett elektriskt fordon med avsikt att förbättra prestanda med avseende på hållfasthet, livslängd och styvhet. I examensarbetet ges även en kort beskrivning av hur växellådan fungerar, vilken roll den spelar i de elektriska fordonen, samt grundläggande teori som används  vid konstruktion av liknande växellådor. Den huvudsakliga arbetsmetoden som använts för att nå målen är topologioptimering och olika lösningar har simulerats för att förenkla den framtida omkonstruktionen. Analyser av de olika resultaten har lett fram till ett grovt förslag på hur växellådshuset kan utformas. Det resultatet förkastades efter det att några extra simuleringar gjorts. Även om inget slutgiltigt förslag hittades, har detta examensarbete tagit fram en bra grund och vägvisning för att senare lyckas med uppdraget. / This thesis targets a systematic approach for redesign of the gearbox housing for an electrical vehicle, with an intention to improve its performance in terms of structural integrity, durability and compliance. Throughout the work, a brief overview of gearbox purpose, position and significance in context of electric vehicles has been presented, some theoretical background concerning design of similar gearboxes is presented and underlying theoretical fundamentals are reviewed. Topology optimization has been utilized as the main method for achieving the goals and various solving runs were performed in order to ease the subsequent redesign. Interpretations of multiple result sets led to a rough outline guess of a possible solution candidate. After supplementary studies, that solution was later discarded. In the end, although no final redesign was generated, clear and comprehensive directions for achieving the targeted goal have been formulated.

This thesis has taken place at ABB High Voltage Cables in Karlskrona and focuses on their reinforcement process (AR50) which reinforces the cable by application of reinforcement wires. The research is strictly limited to only the short period during the application of the wire on the cable and investigates stress differences in one reinforcing wire depending on cable - and wire dimensions as well as brake forces used in the production. The study follows a model - and theory development research process combined with a testing process to obtain the results. The study aims is to increase and expand ABB's knowledge about the reinforcing process that is used to strengthen and protect ABB’s all different high voltage cables together with a computational calculation model. The model is developed in the FEA (Finite Element Analysis) program ABAQUS through a dynamic explicit model. An explanation of how the calculation model has been built and the parameters used are described in this report. These parts then contribute to the outcome of the study which provides a sense that the brake force used in AR50’s reinforcement process does not need to be controlled with a high precision so long as it is large enough to hold the reinforcement wire stretched upon the application. The study also shows that different cable - and wire dimensions does not affect the stress levels somewhat significantly by reinforcing the process and that the nipple used in reinforcement process to press down the reinforcing wire on the cable is the main source that determines how the stress distribution looks like on the reinforcement wire. / Detta examensarbete har tagit plats på ABB High Voltage Cables i Karlskrona och fokuserar på deras armeringsprocess (AR50) som förstärker kabeln genom påläggning av armeringstrådar. Arbetet är starkt begränsat till enbart den korta perioden för själva påläggningen av tråden och undersöker spänningsskillnader i en armeringstråd beroende på olika kabel – och tråddimensioner samt bromskrafter som används i produktionen. Studien följer en modell – och teoriutvecklande forskningsprocess kombinerat med ett utprövande resultatbildande. Studiens syfte är att tillsammans med en beräkningsmodell öka och fördjupa ABBs kunskaper kring armeringstråden som idag används för att stärka och skydda ABBs alla olika högspänningskablar. Beräkningsmodellen tas fram i FEA (Finita Element Analys) prorammet ABAQUS genom en dynamisk explicit modell. En förklaring till hur beräkningsmodellen har byggts upp och vilka parametrar som används beskrivs i rapporten. Dessa delar bidrar sedan till resultatet i studien som ger en bild av att bromskraften som används i AR50s armeringsprocessen inte behöver kontrolleras med en hög precision så länge den är tillräckligt stor för att hålla armeringstråden sträckt vid påläggningen. Studien visar också att olika kabel – och tråddimensioner inte påverkar spänningsnivåerna något markant vid armeringsprocessen och att nippeln som används i armeringsprocesen för att trycka ner armeringstråden mot kabeln bestämmer hur spänningsbilden ser ut. / <p>This thesis is kept confidential</p>

This research investigated the fire performance of unprotected timber floors, focussing on composite joist floors, composite box floors and timber-concrete composite floors. The study of these floors was conducted using the finite element software ABAQUS using a thermo-stress analysis in three dimensions, and with experimental fire tests of floor assemblies. The major goal of this research was to develop a simplified design approach for timber floors, validated against the numerical and experimental work. Four furnace tests were conducted on unprotected timber floor systems in the full-scale furnace at the BRANZ facilities in New Zealand. The tested floors were one-way strip floors with pinned support conditions exposed to the ISO 834 standard fire for varying durations of 30 – 105 minutes. The floors were loaded under standard office loading conditions of 3.0kPa live and 1.0kPa superimposed dead loading. The charring rates of the LVL timber members were found to range from 0.66 – 0.86 mm/min across all specimens. When designed to resist a similar load level both the composite joist and box floor types had a similar response to the fire loads, however the joist floors exhibited increased upward burning through the beam members in the latter stages of testing which may contribute to earlier failure times for smaller floor geometries. A sequentially coupled thermal-stress analysis was conducted to determine the effects of a fire on floor assemblies under load. Firstly a thermal analysis was performed to determine the temperature profile of the floor assemblies for the duration of modelling, and then a stress analysis was performed using the temperature profile as input into the structural model. With regards to the thermal modelling, a proposed set of effective values was used to account for the mass transfer processes occurring in the timber. The thermal modelling predicted the charring damage of the floors tested in the experiments to within a few millimetres of precision, and the simplified assumptions made in relation to fire inputs, boundary conditions, mesh refinement and effective material parameters were accurate to the desired level of precision. A sensitivity study was conducted comparing different mesh sizes, time step sizes, material model approaches and software suites to determine any shortfalls which may be encountered in the analysis. It was found that a material model adopting a latent heat approach was the most adequate for modelling timber in fires using these effective values, and mesh sizes of up to 6 mm produced relatively precise results. The structural modelling predicted the displacement response and failure times of the floors to within 20% of the experimental data, and the simplified assumptions made in relation to fire inputs, boundary conditions, mesh refinement and effective material properties were once again accurate to the desired level of precision. A modification to the reduction in tension strength at elevated temperatures was proposed to better predict the observed behaviour. A sensitivity study concluded that the material model definition plays a vital role in the output of the modelling. Non-standard fire exposures were also modelled for completeness. A simplified design method to estimate the fire resistance of unprotected floor assemblies was also developed. The method uses a bi-linear charring rate the assumption of a zero strength layer in the timber. The method was compared to the experimental data from this research and others around the world. The results were also compared to other charring rate methodologies from around the world.

Packaging industries widely use Low-Density Polyethylene (LDPE) in manufacturing different types of containers to store the food products. They are difficult to model numerically in order to have similar experimental response. This research deals with the study of numerical material model parameters of continuum LDPE. It is carried out with the help of experiments along with the numerical simulation of LDPE. Study of stress-strain distribution at crack tip and elements close to the tip is carried out in the LDPE material with the pre-existing center crack with varying lengths. By implementing an optimization algorithm and automating the simulation with the help of python code, we obtain a set of parameters. This obtained data for the material can be used directly for numerical simulation in the future without carrying out additional experimental studies. After implementing the optimization algorithm is also validated, against the results that were close to the experimental response.

This thesis will present the experimental and numerical analysis of composite sandwich structures under monotonic and fatigue loading. The sandwich skins were made of fiberglass and the core used was a closed cell PVC foam. Initial delaminations were introduced into the sandwich structures during manufacturing to see the effect of delamination size on the ultimate strength and monotonic fracture. Fiberglass rods, called shear keys, added to the foam core to determine whether or not they increased the strength of the test specimens. Furthermore, shear key locations were also varied and their effects noted. The fixed rate static behavior for all of the above cases listed were determined. The fatigue life and behavior were determined for sandwich structures with no initial delamination, 0.5 inch initial delamination, and 0.5 inch initial delamination with a shear key 0 inch from the delamination depth. The fatigue specimens were tested at various percentages of the ultimate monotonic failure loads to determine the fatigue life. A static numerical analysis was performed using Abaqus/CAE 6.7.1 to observe at the monotonic behavior of the test specimens with no initial delamination and with 0.5 inch initial delamination. The sandwich structures with an initial delamination and/or a shear key in the foam core experienced over a 70% reduction in the ultimate monotonic failure load. The two delamination lengths had no significant effect on the ultimate monotonic failure load, but the presence of an initial delamination corresponded to a material response dominated by plastic behavior. The experimental testing also showed that the location of the shear key in the sandwich structure had little effect on the monotonic strength, but moving the shear keys further away from the back edge of the delamination caused a reduction in strength. The monotonic testing determined that composite sandwich structures containing shear keys had approximately a 7% reduction in the monotonic failure load of test specimens with an initial delamination. Numerical analysis results matched the ultimate failure loads within 5% for the test specimens with a 0.5 inch an initial delamination and within 15% for the test specimens with no initial delamination. The fatigue testing showed that sandwich structures containing shear keys had life reduction of approximately 33%. Preliminary experiments involved with rotating the shear keys 90° showed increased ultimate monotonic failure loads of the composite sandwich structures by as much as 30%. Future funding and research would be necessary to verify the increased structural performance of the newly oriented shear keys.