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Material Behavior (material + behavior)
Selected AbstractsStress Concentration Factors and Weight Functions in Thin Notched Structures of Equibiaxial Anisotropic Materials,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Michael Heinzelmann In notched structures, the influence of the notch on the structural strength of the component can be described by a stress concentration factor or,in the presence of cracks,a weight function. Numerous stress concentration factor and weight function solutions are available to the engineer, but regrettably almost exclusively for isotropic materials. In the present study, stress concentration factors and weight functions are calculated for equibiaxial anisotropic materials. The geometry under investigation is a flat plate in tension containing a central hole. The calculated results show that the elastic anisotropic material behavior can significantly influence the magnitude of both stress concentration factors and weight functions. [source] Advanced Homogenization Strategies in Material Modeling of Thermally Sprayed TBCs,ADVANCED ENGINEERING MATERIALS, Issue 7 2006K. Bobzin Thermal barrier coatings (TBC), obtained by atmospheric plasma spraying (APS), have a complex microstructure (lamellar, porous, micro-cracked). Process parameters take an influence on this microstructure. Two methods based on the homogenization for periodic structures are presented in this article. The methods are used to calculate the effective material behavior of APS-TBCs made of partially yttria stabilized zirconia (PYSZ) depending on the microstructure. [source] A model for pore-fluid-sensitive rock behavior using a weathering state parameterINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 16 2008R. J. Hickman Abstract Chalk and other porous rocks are known to behave differently when saturated with different pore fluids. The behavior of these rocks varies with different pore fluids and additional deformation occurs when the pore fluid composition changes. In this article, we review the evidence that behavior in porous rocks is pore-fluid-dependent, present a constitutive model for pore-fluid-dependent porous rocks, and present a compilation of previously published data to develop quantitative relationships between various pore fluids and mechanical behavior. The model proposed here is based on a state parameter approach for weathering and has similarities to models previously proposed for weathering-sensitive rocks in that the values for parameters that characterize material behavior vary as a function of weathering. Comparisons with published experimental data indicate that the model is capable of reproducing observed behavior of chalk under a variety of loading conditions and changes in pore fluid composition. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimization of multicomponent photopolymer formulations using high-throughput analysis and kinetic modelingAICHE JOURNAL, Issue 5 2010Peter M. Johnson Abstract While high throughput and combinatorial techniques have played an instrumental role in materials development and implementation, numerous problems in materials science and engineering are too complex and necessitate a prohibitive number of experiments, even when considering high throughput and combinatorial approaches, for a comprehensive approach to materials design. Here, we propose a unique combination of high throughput experiments focused on binary formulations that, in combination with advanced modeling, has the potential to facilitate true materials design and optimization in ternary and more complex systems for which experiments are never required. Extensive research on the development of photopolymerizable monomer formulations has produced a vast array of potential monomer/comonomer, initiator and additive combinations. This array dramatically expands the range of material properties that are achievable; however, the vast number of potential formulations has eliminated any possibility of comprehensive materials design or optimization. This limitation is addressed by maximizing the benefits and unique capabilities of high throughput experimentation coupled with predictive models for material behavior and properties. The high throughput experimentation-model combination is useful to collect a limited amount of data from as few as 11 experiments on binary combinations of 10 analyzed monomers, and then use this limited data set to predict and optimize formulation properties in ternary resins that would have necessitated at least 1000 high throughput experiments and several orders of magnitude greater numbers of traditional experiments. A data analysis approach is demonstrated, and the model development and implementation for one model application in which a range of material properties are prescribed, and an optimal formulation that meets those properties is predicted and evaluated. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Effect of crosslinking, remelting, and aging on UHMWPE damage in a linear experimental wear modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 7 2007Suzanne A. Maher Abstract The objective of this study was to establish the effect of postirradiation melting as a function of irradiation dose on the wear behavior and material characteristics of ultrahigh molecular weight polyethylene. Our hypothesis was that a low dose of irradiation followed by melting would have the same improved wear performance as is found with higher doses of irradiation, but without the disadvantages associated with reduced fracture toughness. The hypothesis was tested by measuring the wear performance (wear track area, incidence of pitting and delamination) in a linear doubly curved-on-flat cyclic test, material behavior (elastic modulus, fracture toughness), and aging response (density changes through the thickness) of the following materials: elevated crosslinked groups,radiated at 25, 65, and 120 kGy, melted, sterilized and aged; a melted group,melted, sterilized, and aged; and a control group,sterilized and aged. Our findings suggest that postirradiation melting, not the irradiation dose, dominates the material property changes and wear response. Melting ensured reduced modulus and therefore decreased contact stresses, superior wear performance, and good resistance to aging, even after low levels of irradiation (25 kGy). The low modulus of the 25 kGy elevated crosslinked group, coupled with increased fracture toughness compared to samples irradiated at higher doses and a resistance to aging not found in the melted group, support our hypothesis. A low dose of irradiation followed by heat treatment has the same beneficial effects in terms of improved wear performance, but without the disadvantages of reduced fracture toughness found with higher doses of irradiation. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:849,857, 2007 [source] Influence of polyethylene creep behavior on wear in total hip arthroplastyJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2006Janaki R. Penmetsa Abstract After total hip arthroplasty (THA), polyethylene acetabular liner creep occurs quickly and serves to increases head,liner contact area and decrease contact pressures. What effect these early changes in contact mechanics will have on the wear behavior of the articulation remains unclear, and hence, selection or modification of polyethylene materials for optimal creep and wear performance is impossible. The objective of this study was to determine the influence of polyethylene creep behavior on volumetric wear and linear creep and wear penetration during simulated gait loading conditions. A finite element model of THA articulation was developed, and simultaneous numerical creep and wear simulation was performed to 10 million gait cycles with three levels of polyethylene creep behavior. Long-term volumetric wear and penetration were surprisingly unaffected by the polyethylene creep behavior due to the competing decrease in contact pressures coupled with increased contact area. In addition, variation in contact mechanics with the creep levels studied was only noteworthy in the initial postoperative period; after 1 million gait cycles, peak contact pressures and areas were within 13% regardless of the creep material behavior selected. Femoral head size had considerable impact on wear and penetration, while liner thickness primarily affected only early penetration. These results suggest that polyethylene creep behavior plays a major role in early penetration, but has little influence on the more important long-term volumetric wear. © 2005 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:422,427, 2006 [source] Effects of Matrix Cracks on the Thermal Diffusivity of a Fiber-Reinforced Ceramic CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Kathleen R. McDonald Effects of matrix cracks and the attendant interface debonding and sliding on both the longitudinal and the transverse thermal diffusivities of a unidirectional Nicalon/MAS composite are investigated. The diffusivity measurements are made in situ during tensile testing using a phase-sensitive photothermal technique. The contribution to the longitudinal thermal resistance from each of the cracks is determined from the longitudinal diffusivity along with measurements of crack density. By combining the transverse measurements with the predictions of an effective medium model, the thermal conductance of the interface (characterized by a Biot number) is determined and found to decrease with increasing crack opening displacement, from an initial value of ,1 to ,0.3. This degradation is attributed to the deleterious effects of interface sliding on the thermal conductance. Corroborating evidence of degradation in the interface conductance is obtained from the inferred crack conductances coupled with a unit cell model for a fiber composite containing a periodic array of matrix cracks. Additional notable features of the material behavior include: (i) reductions of ,20% in both the longitudinal and the transverse diffusivities at stresses near the ultimate strength, (ii) almost complete recovery of the longitudinal diffusivity following unloading, and (iii) essentially no change in the transverse diffusivity following unloading. The recovery of the longitudinal diffusivity is attributed to closure of the matrix cracks. By contrast, the degradation in the interface conductance is permanent, as manifest in the lack of recovery of the transverse diffusivity. [source] AB-polymer Networks with Cooligoester and Poly(n -butyl acrylate) Segments as a Multifunctional Matrix for Controlled Drug ReleaseMACROMOLECULAR BIOSCIENCE, Issue 9 2010Christian Wischke Abstract Semi-crystalline AB-copolymer networks from oligo[(, -caprolactone)- co -glycolide]dimethacrylates and n -butylacrylate have recently been shown to exhibit a shape-memory functionality, which may be used for self-deploying and anchoring of implants. In this study, a family of such materials differing in their molar glycolide contents ,G was investigated to determine structure,property functional relationships of unloaded and drug loaded specimens. Drug loading and release were evaluated, as well as their degradation behavior in vitro and in vivo. Higher ,G resulted in higher loading levels by swelling and a faster release of ethacridine lactate, lower melting temperature of polymer crystallites, and a decrease in shape fixity ratio of the programmed temporary shape. For unloaded networks, the material behavior in vivo was independent of the mechanical load associated with different implantation sites and agreed well with data from in vitro degradation studies. Thus, AB networks could be used as novel matrices for biofunctional implants, e.g., for urogenital applications, which can self-anchor in vivo and provide mechanical support, release drugs, and finally degrade in the body to excretable fragments. [source] Elastic-plastic stress analysis of cracked structures using the boundary element methodPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Wilhelm Weber The application of the boundary element method (BEM) for the 3D-stress analysis of cracked structures considering elastic-plastic material behavior is presented. For separating the coincident crack surfaces the DUAL-BEM is utilized. The relevant boundary integral equations (BIE) , the strongly singular displacement BIE and the hypersingular traction BIE , are evaluated in the framework of a collocation procedure. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the calculation of crack face opening displacements in fiber reinforced composites under plane loadingPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Mike Richter This paper concerns with the calculation of the crack face opening displacement in fiber reinforced composites using analytical, semi-analytical and numerical approaches. Crack bridging is one of the most characteristic effects of fibers on the material behavior of the composite. Knowing the crack face opening displacement the additional strain due to cracks can be calculated and used in homogenization procedures. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Experimental and theoretical investigation on the microstructure of aluminum alloys during extrusionPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Tobias Kayser The purpose of this work is the investigation of the material behavior of aluminum alloys during extrusion and cooling. In particular, the alloys of the 6000 series (Al,Mg,Si) and 7000 series (Al,Zn,Mg) are relevant here. Under the corresponding conditions, their behavior is controlled mainly by dynamic recovery during the extrusion and static recrystallization during cooling. For the development of a suitable material model EBSD measurements are done on different parts of an extruded Al6060 specimen. For this sample a microstructure picture is generated and a statistical analysis is performed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effective Dynamic Material Properties of Foam-like MicrostructuresPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005S. Alvermann The effective material parameters of a microstructured material can be found using homogenization procedures based on calculations of a Representative Volume Element (RVE) of the material. In our approach the RVE is calculated in frequency domain and inertia is taken into account, leading to a frequency dependent behavior of the RVE. With the frequency response of the RVE, effective dynamic properties of the material are calculated using an optimization procedure. Due to the frequency dependent material behavior on the microscale a viscoelastic constitutive equation is applied on the macroscale. An example calculation is presented for an auxetic 2-D foam-like microstructure which is modelled as a plane frame structure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modelling of Shape Memory Alloys and Experimental VerificationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003M. Schleich Prestrained shape memory alloys change their length when heated above their transformation temperature. This effect can be used to generate high forces in a small workspace, which has particular advantages in actuator design. The optimization and control of the shape memory actuator requires a comprehensive simulation of the material behavior. However, many of the existing models are limited to specific load cases or offer rough approximations only. A material model for shape memory alloys from Seelecke [1] is examined in this paper. This model describes the behavior of a shape memory wire, which is heated by electric current. It is implemented in a simulation program to investigate the actuator output and to improve the performance. Finally, the parameters of the simulation are adapted to experimental results. [source] Kombiniertes Verfahren zur wirklichkeitsnahen Berechnung schlanker StahlbetonstabtragwerkeBETON- UND STAHLBETONBAU, Issue 10 2006Uwe Starossek Univ.-Prof. Der wirklichkeitsnahen und damit nichtlinearen Berechnung von allgemeinen Stahlbetontragwerken kommt eine wachsende Bedeutung zu. Eine Kombination des allgemeinen Weggrößenverfahrens, des Übertragungsverfahrens und eines Querschnittsmoduls führt zu einem effektiven Berechnungsverfahren für allgemeine Stabtragwerke aus Stahl- und Spannbeton. Neben der stofflichen Nichtlinearität berücksichtigt das Verfahren auch geometrische Nichtlinearität mit großen Verformungen. Die übergeordnete Berechnung des Systems erfolgt inkrementell und iterativ mit dem allgemeinen Weggrößenverfahren. Auf Stabebene wird ein erweitertes Übertragungsverfahren zur Bestimmung der Stabendschnittgrößen und der Steifigkeitsmatrix eingesetzt. Die Formulierung des Übertragungsverfahrens erfolgt in einem rekursiven Schema für einen verformten Stab, der in Abhängigkeit vom Steifigkeitsgradienten in einzelne Abschnitte diskretisiert wird. Das nichtlineare Materialverhalten einschließlich Rißbildung, Entfestigung und Fließen der Bewehrung wird im Querschnittsmodul über eine Querschnittsintegration erfaßt. Combined method for a realistic analysis of slender reinforced concrete frames A more realistic and, hence, nonlinear analysis of reinforced concrete structures is becoming increasingly important. A combination of the displacement method, the transfer matrix method, and a cross section module is suggested which leads to an effective analysis method for general reinforced and prestressed concrete frames. The combined method considers both material and geometrical nonlinearities including large deformations. The first level computation of the system is incrementally and iteratively carried out by the displacement method. At element level, an extended transfer matrix method is used for determining both the internal forces at the element end nodes and the stiffness matrix. The transfer matrix method is recursively applied to the deformed element, which is discretized into individual segments whose number and lengths depend on the stiffness gradient. The cross section module is based on cross-sectional integration. It takes into account nonlinear material behavior including cracking, softening, and yielding of reinforcement. [source] Effect of stoichiometry on liquid crystalline supramolecular polymers formed with complementary nucleobase pair interactionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006Kelly A. Burke Abstract We report herein studies on the liquid crystalline behavior of a series of supramolecular materials that contain different ratios of two complementary symmetrically-substituted alkoxy-bis(phenylethynyl)benzene AA- and BB-type monomers. One monomer has thymine units placed at either end of the rigid mesogenic core, while the other has N6 -(4-methoxybenzoyl)-adenine units placed on the ends. Differential scanning calorimetric and polarized optical microscopy studies have been carried out on these systems. These studies show that the material's behavior is strongly dependent on its thermal history. As a result, the materials can exhibit, on heating, either a liquid crystalline phase, a crystalline phase, or the coexistence of crystalline and liquid crystalline regions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5049,5059, 2006 [source] Bulk Nanoporous Metal for ActuationADVANCED ENGINEERING MATERIALS, Issue 8 2010Hai-Jun Jin Abstract Nanoporous metals prepared by controlled chemical or electrochemical corrosion of alloys can provide prototypical manifestations of bulk nanostructured material. Samples are readily prepared with dimensions at the millimeter or centimeter scale, while at the same time the microstructure is a homogeneous array of interpenetrating solid skeleton phase and pore channels with a characteristic size that can reach down to below 5,nm. The interest in nanoporous metals as functional materials derives from recent observations of unique materials behavior resulting from their extremely small structure size and their open porosity with large volume-specific surface area. As an example, this article discusses the possible use of nanoporous metal for actuation. [source] | |||||||||||||