Littérature scientifique sur le sujet « Nonlinear thermomechanical properties »
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Articles de revues sur le sujet "Nonlinear thermomechanical properties"
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RAHMAN, S. M. MUJIBUR, et SAMIRA SALEK. « THERMOMECHANICAL PROPERTIES OF CERTAIN ELEMENTAL CRYSTALS ». International Journal of Modern Physics B 06, no 18 (20 septembre 1992) : 3069–77. http://dx.doi.org/10.1142/s0217979292002371.
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We have investigated the temperature variation of the Einstein temperatures and elastic constants of various metallic crystals. In this respect we have employed the interatomic pair potential involving pseudopotential and an appropriate exchange and correlation function. The temperature dependence of the properties concerned is taken into account through changes in the number densities. The systematic compilation of these thermomechanical properties may prove to be useful for various metallurgical purposes.
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KARAOGLU, B., et S. M. MUJIBUR RAHMAN. « THERMOMECHANICAL PROPERTIES OF 3d TRANSITION METALS ». International Journal of Modern Physics B 08, no 11n12 (30 mai 1994) : 1639–54. http://dx.doi.org/10.1142/s0217979294000701.
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We have investigated the density variation of the Einstein temperatures and elastic constants of the 3d transition metals. In this respect we have employed the transition metal (TM) pair potentials involving the sp contribution with an appropriate exchange and correlation function, the d-band broadening contribution and the d-band hybridization term. These calculations are aimed at testing the TM pair potentials in generating the aforesaid quasilocal and local thermomechanical properties.
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Zhang, Zhong, Wenjie Zhao, Ying Sun, Zhenyuan Gu, Wangping Qian et Hai Gong. « Thermoelastic Behaviors of Temperature-Dependent Multilayer Arches under Thermomechanical Loadings ». Buildings 13, no 10 (16 octobre 2023) : 2607. http://dx.doi.org/10.3390/buildings13102607.
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This work presents analytical solutions for thermoelastic behaviors of multilayer arches with temperature-dependent (TD) thermomechanical properties under thermomechanical loadings. The temperature is varied across the thickness of the arch. Firstly, an arched-slice model is developed, which divides every layer of the arch into numerous hypothetical arched slices with uniform thermomechanical properties. Based on the model, the nonlinear heat conduction equations across the thickness of the arch are solved using the iteration approach, and then the thermoelastic equations obtained from the two-dimensional thermoelasticity theory are solved using the state-space approach and transfer-matrix approach. The present solutions are compared with those obtained using the finite element method and the Euler–Bernoulli theory (EBT). It is found that the error of the EBT increases when the angle of the arch increases or the length-to-thickness ratio decreases. Finally, numerical examples are conducted to analyze the effects of surface temperature and TD thermomechanical properties on the temperature, displacement, and stress distributions of a sandwich arch. The results show that the temperature dependency of thermomechanical properties is a key parameter in predicting the thermoelastic behaviors of the arch in a high-temperature environment.
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Zhang, Tao, Qiang Li, Jia-Jia Mao et Chunqing Zha. « Nonlinear Thermomechanical Low-Velocity Impact Behaviors of Geometrically Imperfect GRC Beams ». Materials 17, no 24 (11 décembre 2024) : 6062. https://doi.org/10.3390/ma17246062.
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This paper studies the thermomechanical low-velocity impact behaviors of geometrically imperfect nanoplatelet-reinforced composite (GRC) beams considering the von Kármán nonlinear geometric relationship. The graphene nanoplatelets (GPLs) are assumed to have a functionally graded (FG) distribution in the matrix beam along its thickness, following the X-pattern. The Halpin–Tsai model and the rule of mixture are employed to predict the effective Young modulus and other material properties. Dividing the impact process into two stages, the corresponding impact forces are calculated using the modified nonlinear Hertz contact law. The nonlinear governing equations are obtained by introducing the von Kármán nonlinear displacement–strain relationship into the first-order shear deformation theory and dispersed via the differential quadrature (DQ) method. Combining the governing equation of the impactor’s motion, they are further parametrically solved by the Newmark-β method associated with the Newton–Raphson iterative process. The influence of different types of geometrical imperfections on the nonlinear thermomechanical low-velocity impact behaviors of GRC beams with varying weight fractions of GPLs, subjected to different initial impact velocities, are studied in detail.
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LIM, SHEAU HOOI, KAIYANG ZENG et CHAOBIN HE. « PREPARATION, MORPHOLOGY AND MECHANICAL PROPERTIES OF EPOXY NANOCOMPOSITES WITH ALUMINA FILLERS ». International Journal of Modern Physics B 24, no 01n02 (20 janvier 2010) : 136–47. http://dx.doi.org/10.1142/s021797921006406x.
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This paper presents recent studies on the processing and characterization of epoxy-alumina nanocomposites. Nano-sized alumina particles are incorporated into epoxy resin via solvent-assisted method, so that the particles are dispersed homogeneously in the epoxy matrix. The morphologies, mechanical and thermomechanical properties of the resulting nanocomposites are studied using transmission electron microscope (TEM), conventional tensile testing and thermomechanical testing methods. TEM results show that the alumina nano-particles with a higher specific surface area tend to agglomerate. Furthermore platelet shape particles shows a better dispersion homogeneity as well as better improvement in the mechanical properties of the composites compared to the rod shape particles.
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Hadi, Abbas, Hamid Reza Ovesy, Saeed Shakhesi et Jamshid Fazilati. « Large Amplitude Dynamic Analysis of FGM Cylindrical Shells on Nonlinear Elastic Foundation Under Thermomechanical Loads ». International Journal of Applied Mechanics 09, no 07 (octobre 2017) : 1750105. http://dx.doi.org/10.1142/s1758825117501058.
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Nonlinear dynamic characteristics of functionally graded material (FGM) cylindrical shells surrounded by nonlinear elastic foundation under axial static and lateral dynamic loads in thermal environment are investigated in the current paper. The main emphasis is on the simulation of the elastic foundation model and thermal loads. Nonlinear tri-parametric elastic foundation including linear and nonlinear parameters is used to model the reaction of the elastic foundation on the cylindrical shell. Different thermal loading scenarios are applied to the system to study the effects of thermal environment, including uniform, linear and nonlinear temperature distribution across the shell thickness. Governing equations are derived based on the Donnell’s thin shell theory. Material properties of the FGM are assumed to be variable through the shell thickness according to a power law function. Discretization of the obtained governing equations is performed using the Galerkin’s method. An averaging method and the Runge–Kutta method are applied to obtain the frequency–amplitude relation and time–deflection relation, respectively. Comprehensive numerical results are given for investigating the effects of thermo-mechanical loads, material and geometrical properties and nonlinear elastic foundation parameters on nonlinear dynamic characteristics of the functionally graded cylindrical shells (FGCSs). Present formulations are validated by comparing the results with the published data for some specific cases.
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Khorshidvand, A. R., et M. Jabbari. « Thermomechanical Analysis in FG Rotating Hollow Disk ». Applied Mechanics and Materials 110-116 (octobre 2011) : 148–54. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.148.
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In this paper, mechanical and thermal stresses of rotating hollow disks composed of functionally graded materials (FGMs) is presented. The material properties for FG are expressed as nonlinear exponential functions through the radius of disk and Poisson’s ratio is taken to be constant. The temperature distribution is derived from first law thermodynamics by solving energy equation, general thermal and mechanical boundary conditions are assumed on the inside and outside surfaces of the disk. Heat conduction and Navier equations of a FGM disk are expressed in elliptic cylinder coordinates system and solved analytically. The results are shown for displacement and stresses components along the radial direction.
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Dasgupta, A., et S. M. Bhandarkar. « Effective Thermomechanical Behavior of Plain-Weave Fabric-Reinforced Composites Using Homogenization Theory ». Journal of Engineering Materials and Technology 116, no 1 (1 janvier 1994) : 99–105. http://dx.doi.org/10.1115/1.2904262.
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A micromechanical analysis is presented to obtain the effective macroscale orthotropic thermomechanical behavior of plain-weave fabric reinforced laminated composites based on a two-scale asymptotic homogenization theory. The model is based on the properties of the constituents and an accurate, three-dimensional simulation of the weave microarchitecture, and is used for predicting the thermomechanical behavior of glass-epoxy (FR-4) woven-fabric laminates typically used by the electronics industry in Multilayered Printed Wiring Boards (MLBs). Parametric studies are conducted to examine the effect of varying fiber volume fractions on constitutive properties. Nonlinear constitutive behavior due to matrix nonlinearity and post-damage behavior due to transverse yarn failure under in-plane uniaxial loads is then investigated. Numerical results obtained from the model show good agreement with experimental values and with data from the literature. This model may be utilized by material designers to design and manufacture fabric reinforced composites with tailored effective properties such as elastic moduli, shear moduli, Poisson’s ratio, and coefficients of thermal expansion.
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Tabouret, V., B. Viana et J. Petit. « ZnGa2Se4, a nonlinear material with wide mid infrared transparency and good thermomechanical properties ». Optical Materials : X 1 (janvier 2019) : 100007. http://dx.doi.org/10.1016/j.omx.2019.100007.
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Chamis, C. C., P. L. N. Murthy, S. N. Singhal et J. J. Lackney. « HITCAN for Actively Cooled Hot-Composite Thermostructural Analysis ». Journal of Engineering for Gas Turbines and Power 114, no 2 (1 avril 1992) : 315–20. http://dx.doi.org/10.1115/1.2906589.
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A computer code, HITCAN (High Temperature Composite Analyzer) has been developed to analyze/design hot metal matrix composite structures. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structure level and including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters, including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model, i.e., the material properties are expressed in terms of a product of several factors that affect the properties. HITCAN structural analysis capabilities (static, load stepping—a multistep static analysis with material properties updated at each step, modal, and buckling) for cooled hot structures are demonstrated through a specific example problem.
Thèses sur le sujet "Nonlinear thermomechanical properties"
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Mouiya, Mossaab. « Thermomechanical properties of refractory materials, influence of the diffuse microcracking ». Electronic Thesis or Diss., Limoges, 2024. http://www.theses.fr/2024LIMO0066.
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Les matériaux réfractaires sont largement utilisés dans les applications à haute température mais ne sont pas toujours enclins à résister aux chocs thermiques sévères. Pour résoudre ce problème, une microstructure incorporant des microfissures préexistantes est une solution bien connue pour améliorer la résistance aux chocs thermiques. Néanmoins, une telle microstructure endommagée nécessite une meilleure compréhension pour optimiser son design sans compromettre l'intégrité du matériau. Dans un tel contexte, le Titanate d'Aluminium (Al₂TiO₅, AT) présentant une forte anisotropie de dilatation thermique, constitue un système modèle idéal pour créer un réseau de microfissures adapté afin d'améliorer la flexibilité et le comportement à la rupture. Cette thèse étudie les propriétés thermomécaniques des matériaux réfractaires développés à base d'AT, comprenant des céramiques polycristallines et des composites alumine/AT, en mettant l'accent sur les relations entre la microstructure et les propriétés macroscopiques. Dans le cas de ces deux matériaux, les microfissures préexistantes jouent un rôle clé sur le module de Young, le comportement de dilatation thermique, la réponse contrainte-déformation en traction, l'énergie de rupture et donc la résistance aux chocs thermiques. Un effet d’hystérésis significatif sur le module de Young et l’expansion thermique en fonction de la température témoigne des mécanismes de fermeture-réouverture de microfissures. Des essais de traction uniaxiale ont mis en évidence des lois de comportement non linéaires, impactant l'énergie de rupture et la résistance aux chocs thermiques. En particulier, des essais de traction incrémentale à 850 °C ont montré des comportements antagonistes à la montée ou à la descente en température du fait de l’histoire thermique. Les composites (alumine/AT) avec des 0 à 10 % d’inclusions présentent des microfissures diffuses dues à un différentiel d’expansion thermique. Ils présentent un module de Young réduit, des lois de comportement fortement non linéaires et une déformation à la rupture plus élevée à température ambiante. Les essais de choc thermique effectués par le dispositif innovant ATHORNA pour tous les matériaux à base d'AT étudiés ont confirmé leur résilience sous gradient thermique élevé. Ces résultats fournissent des informations précieuses pour le design de futurs matériaux réfractaires avancés présentant une résistance aux chocs thermiques amélioréeRefractory materials are widely used in high-temperature applications but are not always prone to resist severe thermal shock. To address this problem, microstructure incorporating pre-existing microcracks are already well known to improve thermal shock resistance. Nevertheless, such damaged microstructure needs a better understanding to optimize their design without compromising material integrity. In such context, Aluminum Titanate (Al₂TiO₅, AT) exhibiting a great thermal expansion anisotropy, constitutes an ideal model system for creating a tailored microcracks network in order to improve flexibility and fracture behavior. This thesis investigates the thermomechanical properties of developed AT-based refractory materials, including polycrystalline AT and alumina/AT composites, with emphasis on the relationship between microstructure and macroscopic properties. In both materials, pre-existing microcracks play a key role on Young's modulus, thermal expansion behavior, tensile stress-strain response, fracture energy, and thus thermal shock resistance. A significant hysteretic effect on Young's modulus and thermal expansion as a function of temperature indicates microcracks closure-reopening mechanisms. Uniaxial tensile tests revealed nonlinear stress-strain laws, impacting fracture energy and thermal shock resistance. In particular, incremental tensile tests at 850 °C showed contrasting behaviors during heating and cooling, attributed to thermal history. Composite materials with AT inclusions (0 - 10 wt.%) embedded in an alumina matrix exhibit diffuse microcracking due to thermal expansion mismatch. These composites exhibited reduced Young's modulus, highly nonlinear stress-strain laws, and higher strain to rupture at room temperature. Thermal shock tests performed by the innovative ATHORNA device for all studied AT-based materials confirmed their resilience under high thermal gradients. These findings provide valuable insights for the design of future advanced refractory materials with improved thermal shock resistance
Livres sur le sujet "Nonlinear thermomechanical properties"
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Kleiber, Michał, et Piotr Kowalczyk. Introduction to Nonlinear Thermomechanics of Solids. Springer, 2018.
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Kleiber, Michał, et Piotr Kowalczyk. Introduction to Nonlinear Thermomechanics of Solids. Springer, 2016.
Trouver le texte intégralChapitres de livres sur le sujet "Nonlinear thermomechanical properties"
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Lenk, Claudia, Kalpan Ved, Steve Durstewitz, Tzvetan Ivanov, Martin Ziegler et Philipp Hövel. « Bio-inspired, Neuromorphic Acoustic Sensing ». Dans Springer Series on Bio- and Neurosystems, 287–315. Cham : Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-36705-2_12.
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AbstractWe present an overview of recent developments in the area of acoustic sensing that is inspired by biology and realized by micro-electromechanical systems (MEMS). To support understanding, an overview of the principles of human hearing is presented first. After the review of bio-inspired sensing systems, we continue with an outline of an adaptable acoustic MEMS-based sensor that offers adaptable sensing properties due to a simple, real-time feedback. The transducer itself is based on an active cantilever, which offers the advantage of an integrated deflection sensing based on piezoresistive elements and an integrated actuation using thermomechanical effects. We use a feedback loop, which is realized via a field-programmable gate array or analog circuits, to tune the dynamics of the sensor system. Thereby, the transfer characteristics can be switched between active, linear mode, for which the sensitivity and minimal detectable sound pressure level can be set by the feedback strength (similar to control of the quality factor), and an active nonlinear mode with compressive characteristics. The presented sensing system, which is discussed both from an experimental and theoretical point of view, offers real-time control for adaptation to different environments and application-specific sound detection with either linear or nonlinear characteristics.
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Scott, N. H. « Linear dynamical stability in constrained thermoelasticity II. Deformation-entropy constraints ». Dans Nonlinear Elasticity and Theoretical Mechanics, 135–46. Oxford University PressOxford, 1994. http://dx.doi.org/10.1093/oso/9780198534860.003.0012.
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Abstract The theory of infinitesimal disturbances of a uniform reference configuration Be of a constrained heat-conducting elastic body, developed in part I, is adapted here to the situation in which the constraint links the deformation and the entropy. There are now only three modes of plane-harmonic-wave propagation and, in contrast to the findings of part I, they all turn out to be linearly stable under conditions of a conventional kind on the material constants in Be. An a priori case is thereby established for the acceptability in thermomechanics of this type of constraint. The properties of the modes are investigated in some detail and compared with the corresponding solutions in the absence of a constraint. A limiting procedure is formulated which yields, as extreme cases, the secular equations for the constrained and unconstrained bodies.
Actes de conférences sur le sujet "Nonlinear thermomechanical properties"
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Chamis, C. C., P. L. N. Murthy, S. N. Singhal et J. J. Lackney. « Hitcan for Actively Cooled Hot-Composite Thermostructural Analysis ». Dans ASME 1991 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1991. http://dx.doi.org/10.1115/91-gt-116.
Texte intégralRésumé :
A computer code, HITCAN (HIgh Temperature Composite ANalyzer) has been developed to analyze/design hot metal matrix composite structures. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structure level and including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model, i.e., the material properties are expressed in terms of a product of several factors that affect the properties. HITCAN structural analysis capabilities (static, load stepping - a multistep static analysis with material properties updated at each step-modal, and buckling) for cooled hot structures are demonstrated through a specific example problem.
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Wu, Tong, Kai Liu et Andres Tovar. « Multiphase Thermomechanical Topology Optimization of Functionally Graded Lattice Injection Molds ». Dans ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-60538.
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This work presents a design methodology of lightweight, thermally efficient injection molds with functionally graded lattice structure using multiphase thermomechanical topology optimization. The aim of this methodology is to increase or maintain thermal and mechanical performance as well as to lower the cost of thermomechanical components such as injection molds when these are fabricated using additive manufacturing technologies. The proposed design approach makes use of thermal and mechanical finite element analyses to evaluate the components stiffness and heat conduction in two length scales: mesoscale and macroscale. The mesoscale contains the structural features of the lattice unit cell. Mesoscale homogenized properties are implemented in the macroscale model, which contains the components boundary conditions including the external mechanical loads as well as the heat sources and heat sinks. The macroscale design problem addressed in this work is to find the optimal distribution of given number of lattice unit cell phases within the component so its mass is minimized, while satisfying stiffness and heat conduction constraints of the overall component and the specific regions. This problem is solved through two steps: conceptual design generation and multiphase material distribution. In the first step, the mass is minimized subject to constraints of mechanical compliance and thermal cost function. In the second step, a given number of lattice material are optimally distributed subjected to nonlinear thermal and mechanical constraints, e.g., maximum nodal temperature, maximum nodal displacement. The proposed design approach is demonstrated through 2D and 3D examples including the optimal design of the core of an injection mold. The results demonstrate that a small reduction in mechanical and thermal performance allows for significant mass savings: the second example shows that 3.5% heat conduction reduction and 8.7% stiffness reduction results in 30.3% mass reduction.
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Birman, Victor, et George J. Simitses. « Theory of Box-Type Sandwich Shells With Dissimilar Facings Subjected to Thermomechanical Loads ». Dans ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0374.
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Abstract The present paper outlines a theory of sandwich box-type composite shells designed to withstand a combination of thermal loading, internal pressure, torsional and axial loads. A cross section of the shell represents a rectangular box with curved cylindrical sections at the corners. The facings of the shell are dissimilar to maximize their efficiency, according to the loads acting on each facing. This approach enables a designer to optimize the structure by maximizing the load-carrying capacity or minimizing the weight. The formulation includes the following developments: 1. Global theory of a sandwich shell composed of rectangular and cylindrical sections. Equations of motion are formulated based on a first-order shear deformable version of Sanders’ shell theory. 2. Theory for local deformations and stresses in the facings. The facing is treated as a thin geometrically nonlinear plate or shell on an elastic foundation using von Karman’s approach. The elastic foundation represents a support provided by the opposite facing. 3. An outline of an enhanced micromechanical constitutive formulation based on the incorporation of the effect of the thermomechanical coupling on the material properties and temperature.
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Gajjar, Margi, et Himanshu Pathak. « XFEM Fracture Analysis of 2-D Plastically Graded Domain With Thermo-Mechanical J-Integral ». Dans ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23355.
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Abstract Many engineering components fail in the presence of service loads like thermal residual stresses and thermomechanical loading. An accurate evaluation of the fracture parameter (J-integral) at the crack tip is essential for the safe design of structures. In this work, a novel computational method called the Extended Finite Element Method (XFEM) has been implemented to analyze the plastically graded material (PGM) subjected to thermal and thermo-mechanical loading. For crack discontinuity modeling, a partition of unity enrichment concept can be employed with additional mathematical functions like Heaviside and branch enrichment for crack discontinuity and stress field gradient, respectively. The modeling of the stressstrain relationship of material has been done using the Ramberg-Osgood material model. The isotropic hardening and Von-Mises yield criteria have been considered to check the plasticity condition. The variation in plasticity properties for PGM has been modeled by exponential law. Further, the nonlinear discrete equation has been numerically solved using a Newton-Rhapson iterative scheme.
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Rauer, Georg, Arnold Kühhorn et Marcel Springmann. « Residual Stress Modelling and Inverse Heat Transfer Coefficients Estimation of a Nickel-Based Superalloy Disc Forging ». Dans ASME Turbo Expo 2014 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25827.
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Aero engine disc forgings are subjected to heat treatment operations, i.e., solution treatment followed by quenching and artificial aging, with the aim of achieving improved mechanical material properties. During heat treatment high inhomogeneous temperature gradients and long loading times at elevated temperatures occur and lead to the development and partial relaxation of bulk residual stresses. The intention of this paper is to describe the residual stress modelling of a nickel-based ATI 718Plus® superalloy disc forging. For this purpose, an uncoupled thermomechanical finite element problem is solved consisting of a thermal model based on transient, spatially varying heat transfer coefficients (HTCs) and a stress model incorporating the nonlinear material behaviour to account for thermal induced inelastic deformations. A graphical user interface based application has been created for the automatic estimation of the a priori unknown HTCs by using a serial solution procedure for the two dimensional inverse heat conduction problem (IHCP) based on the function specification method. The estimated temperature fields have been compared at the thermocouple positions with the corresponding measurement data and confirm the suitability of the inverse algorithm to this problem. A rate-independent elasto-plastic constitutive model is used to simulate the residual stress formation while quenching the disc forging. Two creep models have been adjusted to uniaxial tensile test data and applied to simulate the stress relaxation during aging. Finally, this paper presents the numerical results of the stress analysis.
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Farley, Daniel, Abhijit Dasgupta et J. F. J. M. Caers. « Characterization of Non-Conductive Adhesives ». Dans ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems collocated with the ASME 2005 Heat Transfer Summer Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/ipack2005-73021.
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This study aims to establish a global-local modeling methodology for determining the residual contact stress developed during fabrication of flip-chip-on-flex (FCOF) microelectronics systems. The assembly consists of a silicon die with gold bumps bonded with a non-conductive adhesive (NCA) on to gold-plated copper bumps on a flex substrate. Manufacturing variabilities cause a nonuniformity in the bump heights, leading to some bumps that are “tall” and some that are “short.” The fabrication process needs to achieve a significant amount of compressive initial contact stress in all the bumps, to achieve an acceptable level of electrical contact resistance. Furthermore, this stress level forms the initial condition for cyclic relaxation of the stress (and corresponding progressive loss of contact resistance) due to temperature cycling throughout the life cycle of the assembly. A key issue to be investigated is the nonuniformity of the contact stresses due to the variabilities in the height of the metal contact bumps. The method is demonstrated for a selected NCA. The fabrication process consists of mechanical compression to bring all the bumps into contact, thermal curing of the adhesive during which it undergoes chemical shrinkage, removal of the mechanical compressive force and cool-down to room temperature. The modeling complexities include the geometric complexity, as well as nonlinearities due to elastic-plastic properties and large deformations of the metal bumps, evolution of contact surfaces between the two bumps, and nonlinear thermomechanical properties of the adhesive as it cures. Modeling strategies used to capture the nonlinearities include “contact elements” to prevent interpenetration at the contact surfaces, elastic-plastic models to account for metal plasticity, “element birth and death” to account for the solidification of the polymer NCA. The entire bonding process is modeled with a global-local model to reduce the computational complexity. The results of the global model serve as the input for the local model. Key findings include: the accuracy of the simulation is very sensitive to the accuracy of the gold and flex constitutive models used; the inclusion of viscoelastic properties for the epoxy has a significant effect on simulations; and better stress development comes from a higher concentration of short bumps than tall bumps.
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Donato, Gustavo Henrique B., et Fábio Gonçalves Cavalcante. « Influence of Plastic Prestrain on the Fatigue Crack Growth Resistance (da/dN vs. ΔK) of ASTM A36 Structural Steel ». Dans ASME 2015 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/pvp2015-45933.
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High responsibility components operating under cyclic loading can have their resistance against initiation and growth of fatigue cracks highly influenced by previous thermomechanical processing. Within the interest of the present work, different manufacturing processes and installation techniques incorporate cold plastic straining to engineering structures; two typical examples on the oil and gas fields are: i) the offshore pipelines installation method called reeling; ii) the fabrication of pipes using the UOE method and pressure vessels through calendering. Within this scenario, this work investigates the effects of plastic prestrain on the fatigue crack growth rates (da/dN vs. ΔK) of a hot-rolled ASTM A36 steel. Different from previous results from the literature, in which prestrains were applied directly to machined samples, in this work uniform prestraining was imposed to steel strips (1/2” thick) and specimens were then extracted to avoid (or minimize) residual stress effects. Prestrain levels were around 4, 8 and 14% and C(T) specimens were machined from original and prestrained materials according to ASTM E647 standard. Fatigue crack growth tests were carried out under load control in an MTS 810 (250 kN) equipment using R = 0.1. Results revealed that plastic prestraining considerably reduced crack growth rates for the studied material, which was expected based on the literature and hardening behavior of the studied material. However, results also revealed two interesting trends: i) the larger is the imposed prestrain, the greater is the growth rate reduction in a nonlinear asymptotic relationship; ii) the larger is imposed ΔK, the more pronounced is the effect of prestraining. Crack closure effects were also investigated, but revealed no influence on the obtained mechanical properties. Consequently, results could be critically discussed based on effective crack driving forces and elastic-plastic mechanical properties, in special those related to flow and hardening. The conclusions and success of the employed methods encourage further efforts to incorporate plastic prestrain effects on structural integrity assessments.