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Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781723553493 Category : Languages : en Pages : 294
Book Description
A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed. Milligan, Walter W. and Antolovich, Stephen D. Unspecified Center NASA-CR-4215, E-4543, NAS 1.26:4215 NAG3-503; RTOP 505-63-1B...
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781723553493 Category : Languages : en Pages : 294
Book Description
A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed. Milligan, Walter W. and Antolovich, Stephen D. Unspecified Center NASA-CR-4215, E-4543, NAS 1.26:4215 NAG3-503; RTOP 505-63-1B...
Author: R. W. Neu Publisher: ISBN: Category : Continuum mechanics Languages : en Pages : 17
Book Description
Crystal viscoplasticity enables one to correctly capture the anisotropic inelastic behavior of single crystal and directionally solidified alloys as well as the microstructural sensitivity in polycrystalline alloys. This paper reviews several physics-based crystal viscoplasticity models that have been established to predict the deformation response of Ni-base superalloys. The attributes of crystal viscoplasticity models necessary for predicting the creep-fatigue deformation are identified. Several new developments in constitutive modeling of Ni-base superalloys are discussed.
Author: Konstantin Naumenko Publisher: Springer ISBN: 331931629X Category : Science Languages : en Pages : 381
Book Description
This monograph presents approaches to characterize inelastic behavior of materials and structures at high temperature. Starting from experimental observations, it discusses basic features of inelastic phenomena including creep, plasticity, relaxation, low cycle and thermal fatigue. The authors formulate constitutive equations to describe the inelastic response for the given states of stress and microstructure. They introduce evolution equations to capture hardening, recovery, softening, ageing and damage processes. Principles of continuum mechanics and thermodynamics are presented to provide a framework for the modeling materials behavior with the aim of structural analysis of high-temperature engineering components.
Author: Donald C. Stouffer Publisher: John Wiley & Sons ISBN: 9780471021438 Category : Technology & Engineering Languages : en Pages : 522
Book Description
Using a totally new approach, this groundbreaking book establishesthe logical connections between metallurgy, materials modeling, andnumerical applications. In recognition of the fact that classicalmethods are inadequate when time effects are present, or whencertain types of multiaxial loads are applied, the new, physicallybased state variable method has evolved to meet these needs.Inelastic Deformation of Metals is the first comprehensivepresentation of this new technology in book form. It developsphysically based, numerically efficient, and accurate methods forpredicting the inelastic response of metals under a variety ofloading and environmental conditions. More specifically, Inelastic Deformation of Metals: * Demonstrates how to use the metallurgical information to developmaterial models for structural simulations and low cyclic fatiguepredictions. It presents the key features of classical and statevariable modeling, describes the different types of models andtheir attributes, and provides methods for developing models forspecial situations. This book's innovative approach covers such newtopics as multiaxial loading, thermomechanical loading, and singlecrystal superalloys. * Provides comparisons between data and theory to help the readermake meaningful judgments about the value and accuracy of aparticular model and to instill an understanding of how metalsrespond in real service environments. * Analyzes the numerical methods associated with nonlinearconstitutive modeling, including time independent, time dependentnumerical procedures, time integration schemes, inversiontechniques, and sub-incrementing. Inelastic Deformation of Metals is designed to give theprofessional engineer and advanced student new and expandedknowledge of metals and modeling that will lead to more accuratejudgments and more efficient designs. In contrast to existing plasticity books, which discuss few if anycorrelations between data and models, this breakthrough volumeshows engineers and advanced students how materials and modelsactually do behave in real service environments. As greater demandsare placed on technology, the need for more meaningful judgmentsand more efficient designs increases dramatically. Incorporatingthe state variable approach, Inelastic Deformation of Metals: * Provides an overview of a wide variety of metal responsecharacteristics for rate dependent and rate independent loadingconditions * Shows the correlations between the mechanical response propertiesand the deformation mechanisms, and describes how to use thisinformation in constitutive modeling * Presents different modeling options and discusses the usefulnessand limitations of each modeling approach, with material parametersfor each model * Offers numerous examples of material response and correlationwith model predictions for many alloys * Shows how to implement nonlinear material models in stand-aloneconstitutive model codes and finite element codes An innovative, comprehensive, and essential book, InelasticDeformation of Metals will help practicing engineers and advancedstudents in mechanical, aerospace, civil, and metallurgicalengineering increase their professional skills in the moderntechnological environment.
Author: Sharat Chand Prasad Publisher: ISBN: Category : Languages : en Pages :
Book Description
In this work, a constitutive theory is developed, within the context of continuum mechanics, to describe the creep deformation of single crystal superalloys. The con-stitutive model that is developed here is based on the fact that as bodies deform the stress free state that corresponds to the current configuration (referred to as the "natural configuration", i.e., the configuration that the body would attain on the removal of the external stimuli) evolves. It is assumed that the material possesses an infinity of natural (or stress-free) configurations, the underlying natural configuration of the body changing during the deformation process, with the response of the body being elastic from these evolving natural configurations. It is also assumed that the evolution of the natural configurations is determined by the tendency of the body to undergo a process that maximizes the rate of dissipation. Central to the theory is the prescription of the forms for the stored energy and rate of dissipation functions. The stored energy reflects the fact that the elastic response exhibits cubic symmetry. Consistent with experiments, the elastic response from the natural configuration is assumed to be linearly elastic and the model also takes into account the fact that the symmetry of single crystals does not change with inelastic deformation. An ap-propriate form for the inelastic stored energy (the energy that is `trapped' within dislocation networks) is also utilized based on simple ideas of dislocation motion. In lieu of the absence of any experimental data to corroborate with, the form for the inelastic stored energy is assumed to be isotropic. The rate of dissipation function is chosen to be anisotropic, in that it reflects invariance to transformations that belong to the cubic symmetry group. The rate of dissipation is assumed to be proportional to the density of mobile dislocations and another term that takes into account the damage accumulation due to creep. The model developed herein is used to simulate uniaxial creep of 001, 111 and 011 oriented single crystal nickel based su-peralloys for a range of temperatures. The predictions of the theory match well with the available experimental data for CMSX-4. The constitutive model is also implemented as a User Material (UMAT) in commercial finite element software ABAQUS to enable the analysis of more general problems. The UMAT is validated for simple problems and the numerical scheme based on an implicit backward difference formula works well in that the results match closely with those obtained using a semi-inverse approach.
Author: National Aeronautics and Space Administration (NASA)
Author: National Aeronautics and Space Administration (NASA)
Author: Walter W. Milligan
Author: Walter W. Milligan
Author: American Society of Mechanical Engineers. Winter Annual Meeting
Author: R. W. Neu
Author: Konstantin Naumenko
Author: 
Author: Donald C. Stouffer
Author: Sharat Chand Prasad
Author: