Analytical model for delamination growth during small mass impact on plates

AbstractAn analytical model is presented for delamination initiation and growth and the resulting response during small mass impact on orthotropic laminated composite plates, which typically is caused by runway debris and other small objects. The solution is obtained by a fast stepwise numerical solution of a single integral equation. Delamination size, load and deflection history are predicted by extension of an earlier elastic impact model by the author. Good agreement is demonstrated in comparisons with finite element simulations and experiments

Simplified theory for contact indentation of sandwich panels

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1994.Includes bibliographical references (leaves 159-164).by Robin Olsson.M.S

A micromechanics based model for rate dependent compression loaded unidirectional composites

Strain-rate effects in a unidirectional non-crimp fabric carbon/epoxy composite are addressed.\ua0To allow for kink-band formation including strain-rate\ua0 effects and damage in such composites, the paper advances a recent model focused on compression loading at small off-axis angles.\ua0The model is based on computational \textit{homogenization} with a subscale represented by matrix and fibre constituents at finite deformation.\ua0The fibre constituent is assumed to be elastic transversely isotropic and the matrix is viscoelastic--viscoplastic with damage degradation.\ua0Novel model improvements of special importance to small off-axis loading relate to the \textit{isostress} formulation of the homogenized response in transverse shear.\ua0In this context, an enhanced homogenized elastic response is proposed based on Halpin--Tsai corrections to account for the nonuniform stress distribution on the microscale.\ua0The model captures the strongly rate sensitive kink-band formation due to localized matrix shearing and fibre rotation, confirming the experimentally observed increase in compressive strength for high strain rates

A micromechanically based model for dynamic damage evolution in unidirectional composites

This article addresses the micromechanically motivated, quasistatic to dynamic, failure response of fibre reinforced unidirectional composites at finite deformation. The model draws from computational homogenization, with a subscale represented by matrix and fibre constituents. Undamaged matrix response assumes isotropic viscoelasticity–viscoplasticity, whereas the fibre is transversely isotropic hyperelastic. Major novelties involve damage degradation of the matrix response, due to shear in compression based on a rate dependent damage evolution model, and the large deformation homogenization approach. The homogenized quasi-brittle damage induced failure is described by elastically stored isochoric energy and plastic work of the undamaged polymer, driving the evolution of damage. The developed model is implemented in ABAQUS/Explicit. Finite element validation is carried out for a set of off-axis experimental compression tests in the literature. Considering the unidirectional carbon–epoxy (IM7/8552) composite at different strain rates, it appears that the homogenized damage degraded response can represent the expected ductile failure of the composite at compressive loading with different off-axes. Favourable comparisons are made for the strain and fibre rotation distribution involving localized shear and fibre kinking

A micromechanically based model for strain rate effects in unidirectional composites

This article addresses dynamic behaviour of fibre reinforced polymer composites in terms of a transversely isotropic viscoelastic-viscoplastic constitutive model established at the unidirectional ply level. The model captures the prelocalized response of the ply in terms of rate dependent elasticity and strength without damage. A major novelty is that the model draws from computational homogenization, with matrix and fibre materials as subscale constituents for a representative volume element of the ply. The micromechanics of the strain rate dependent polymer matrix is represented by an isotropic pressure sensitive viscoelastic-viscoplastic prototype model. For the fibre material, transverse elasticity is assumed. The constituents are homogenized via the fluctuating strain of the subscale, where a simple ansatz is applied to allow for constant stress in the plane transverse to the fibre orientation. Despite the relatively simple modelling assumptions for the constituents, the homogenized model compares favourably to experimental data for an epoxy/carbon fibre based composite, subjected to a variety of challenging uniaxial off-axis tests. The model response clearly reflects observed strain rate dependencies under both tensile and compressive loadings

Screening of hydrogen bonds in modified cellulose acetates with alkyl chain substitutions

This study aimed to elucidate how the glass transition temperature and water interactions in cellulose esters are affected by the structures of their side chains. Cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate with three fractions of butyrates, all having the same total degree of substitution, were selected, and hot-melt pressed. The degree of substitution, structural properties, and water interactions were determined. The Hansen solubility parameters were calculated and showed that the dispersive energy dominates the total cohesive energy, followed by hydrogen bonding and polar energy. The glass transition temperature (Tg) decreased, counter-intuitively, with an increased total cohesive energy, which can be explained by the short-range hydrogen bonds being screened by the increased length of the substituents. The solubility and penetration of water in the cellulose esters decreased with increased side chain length, although the hydrogen bonding energies for all the esters were approximately constant

Förfinad metod för användning av BIM-modeller för strukturanalys och dimensionering av betongkonstruktioner

Det ökande användandet av BIM leder naturligt till att programvaror behöver utvecklade funktioner och nya möjligheter. Fördelen med BIM är att en konstruktions alla egenskaper kan samlas i en och samma modell. Rimligtvis bör modellens geometriska information även enkelt kunna användas vid en strukturanalys. Däremot innehåller en beräkningsmodell i regel en rad förenklingar av geometrin, för att på ett rimligt sätt spegla den verkliga strukturens beteende. Många anläggningskonstruktioner, exempelvis broar, innehåller oftast en betydande del armerad betong, för vilken dimensioneringen utgår från snittkrafter. Då anläggningskonstruktioner ofta är stora och komplexa krävs det att beräkningsmodellen anpassas efter tillgänglig datorkraft och behov av resultat. För att beräkna snittkrafter ur en beräkningsmodell finns det klara fördelar att modellera med skal- och balkelement, vilka ger önskvärda resultat samtidigt som erforderlig datorkraft kraftigt minskas. Scanscot Technologys strukturanalysprogram BRIGADE/Plus kan importera BIM-modeller sparade i det standardiserade och öppna filformatet IFC. Beräkningsmodellen kommer då att bestå av tredimensionella solida objekt. En förenkling av beräkningsmodellen till att bestå av balkar och skal innebär att den måste rekonstrueras från grunden. Inom ramen för detta arbete har en metod tagits fram där en BIM-modell som importeras via IFC-fil till stor del automatiskt genereras till en modell bestående av skal- och balkelement. Metoden bygger vidare på befintlig funktion för import av IFC-filer i BRIGADE/Plus. När en IFC-fil är inläst kontrolleras byggnadselementens objektdefinitioner. Definierade balkar och pelare importeras som balkelement, medan plattor och bjälklag importeras som skalelement. Resterande element och de element som inte uppfyller vissa villkor importeras som solidelement precis som tidigare. Generering av balkelement görs efter given information om längd, orientering och tvärsnittsprofil lagrad i IFC-filen. Förenkling till skalelement sker efter två villkor; om de två största ytorna är lika stora och parallella. Resultatet är skalelement i tyngdpunktsplanet mellan de två största ytorna. Den framtagna metodens villkor för bedömning av vilka objekt som kan importeras som skalelement har vid tester visat sig ge goda resultat. Vissa balkprofiler definieras inte på samma sätt i IFC som i BRIGADE/Plus, vilket gör att information kan gå förlorad. De element som importeras som skal- och balkelement representerar inte alltid den riktiga geometrin exakt, dock tillräckligt bra. En del avancerade geometrier genererar dock skalelement som inte är korrekta. Ofta används BIM för att få en bra visuell byggnadsprototyp, där objektdefintionen för byggnadselementen är av mindre vikt. Denna definition är dock viktig för att ge rätt förutsättningar för metodens importering i BRIGADE/Plus. En modell med lämpliga definitioner kan spara beräkningsingenjören mycket tid medan en modell med blandad kvalitet kan ta längre tid att bygga om än en modell som importerats med enbart solidelement.IFC is key enabler for data interoperability of BIM models. This enables reusing the geometry for structural analysis, thus saving modeling time. BIM models and the IFC format consists of solid elements, therefor the imported geometry will generate solid elements when meshed. When performing structural analysis with the finite element method on concrete structures the use of shell and beam elements is preferred. A method has been developed to import BIM models into BRIGADE/Plus generating shell and beam elements when useful. The method works quite well importing most elements in an efficient way, given that definitions in the BIM model are sufficient. The result is that the user will have to spend less time rebuilding the geometry. Often the design engineer has not given parts definitions suitable for the structural analysis. The import will then not suffice and the geometry in the structural analysis has to be reconstructed. When importing a BIM model for structural analysis, a feature that would be beneficial is the opportunity to choose simplification for geometrical objects

銀ナノ粒子の腫瘍壊死因子αが誘導する細胞応答に与える影響

早大学位記番号:新8280早稲田大

Klädbranschens nya spelplan – en kvalitativ studie om vad som driver lojalitet inom e-handeln av kläder

Uppsatsens syfte är att undersöka vad som får konsumenter inom klädbranschen att bli tillfredsställda och vad som driver e-lojalitet och således återköp inom detta verksamhetsområde.The purpose of this study is to investigate the reasons behind what gets consumers in the clothing industry satisfied and what drives e-loyalty and consequently repurchases in this scope of practice

Interaction of Delaminations and Matrix Cracks in a CFRP Plate, Part I: A Test Method for Model Validation

Isolating and observing the damage mechanisms associated with low-velocity impact in composites using traditional experiments can be challenging, due to damage process complexity and high strain rates. In this work, a new test method is presented that provides a means to study, in detail, the interaction of common impact damage mechanisms, namely delamination, matrix cracking, and delamination-migration, in a context less challenging than a real impact event. Carbon fiber reinforced polymer specimens containing a thin insert in one region were loaded in a biaxial-bending state of deformation. As a result, three-dimensional damage processes, involving delaminations at no more than three different interfaces that interact with one another via transverse matrix cracks, were observed and documented using ultrasonic testing and X-ray computed tomography. The data generated by the test is intended for use in numerical model validation. Simulations of this test are included in Part II of this paper