Showing papers on "Hardening (metallurgy) published in 1996"
TL;DR: In this article, an Armstrong-Frederick type hardening rule utilizing the concept of a limiting surface for the backstresses was proposed to predict long-term ratchetting rate decay as well as constant ratcheting rate for both proportional and nonproportional loadings.
Abstract: The existing plasticity models recognize that ratchetting direction strongly depends on the loading path, the stress amplitude, and the mean stresses, but their predictions deviate from experiments for a number of materials. We propose an Armstrong-Frederick type hardening rule utilizing the concept of a limiting surface for the backstresses. The model predicts long-term ratchetting rate decay as well as constant ratchetting rate for both proportional and nonproportional loadings. To represent the transient behavior, the model encompasses a memory surface in the deviatoric stress space which recalls the maximum stress level of the prior loading history. The coefficients in the hardening rule, varying as a function of the accumulated plastic strain, serve to represent the cyclic hardening or softening. The stress level effect on ratchetting and non-Masing behavior are realized with the size of the introduced memory surface. Simulations with the model checked favorably with nonproportional multiaxial experiments which are outlined in Part 2 of this paper.
398 citations
TL;DR: In this article, a degree of hydration-based description for the compressive strength, Young's modulus, uniaxial tensile strength, splitting tensile and flexural tensile strengths, Poisson's ratio and peak strain are all worked out based on an extensive experimental program on hardening concrete elements.
Abstract: For the evaluation of the risk of thermal cracking in hardening massive concrete elements, knowledge of the development of strength and deformability of early-age concrete is extremely important. Based on an extensive experimental research program on hardening concrete elements, a degree of hydration-based description for the compressive strength, Young's modulus, the uniaxial tensile strength, the splitting tensile strength, the flexural tensile strength, Poisson's ratio and the peak strain are all worked out. An extension of the formulation of Sargin for the stress-strain relation for short-term compressive loading leads to a degree of hydration-based stress-strain relation for hardening concrete. Good agreement with experimental results is reported.
284 citations
TL;DR: In this article, the effects of strain rate, temperature, and tungsten alloying on the yield stress and the strainhardening behavior of tantalum were investigated, and the results substantiate the applicability of these models for describing the high strain-rate deformation of Ta and Ta-W alloys.
Abstract: The effects of strain rate, temperature, and tungsten alloying on the yield stress and the strainhardening behavior of tantalum were investigated The yield and flow stresses of unalloyed Ta and tantalum-tungsten alloys were found to exhibit very high rate sensitivities, while the hardening rates in Ta and Ta-W alloys were found to be insensitive to strain rate and temperature at lower temperatures or at higher strain rates This behavior is consistent with the observation that overcoming the intrinsic Peierls stress is shown to be the rate-controlling mechanism in these materials at low temperatures The dependence of yield stress on temperature and strain rate was found to decrease, while the strain-hardening rate increased with tungsten alloying content The mechanical threshold stress (MTS) model was adopted to model the stress-strain behavior of unalloyed Ta and the Ta-W alloys Parameters for the constitutive relations for Ta and the Ta-W alloys were derived for the MTS model, the Johnson—Cook (JC), and the Zerilli-Armstrong (ZA) models The results of this study substantiate the applicability of these models for describing the high strain-rate deformation of Ta and Ta-W alloys The JC and ZA models, however, due to their use of a power strain-hardening law, were found to yield constitutive relations for Ta and Ta-W alloys that are strongly dependent on the range of strains for which the models were optimized
228 citations
TL;DR: The cracking of Si particles during plastic deformation has been studied for different microstructures produced by varying the solidification rate and length of solution treatment, and the number of cracked particles increases with the applied strain this article.
226 citations
TL;DR: In this paper, the effects of particle volume fraction and matrix temper on the flow and fracture characteristics of a series of particle-reinforced metal matrix composites under tensile and compressive loadings have been examined.
191 citations
TL;DR: In this article, two corrugated rail samples with different load have been investigated using a profilometer, nanoindentation technique and scanning electron microscopy, and the crystal refinement and the development of the microstructure are investigated by X-ray diffraction and transmission electron microscope.
188 citations
TL;DR: In this article, the characteristics of a category of Armstrong-Frederick hardening rules are examined, invoking both theoretical and experimental considerations, and the model is shown to be insensitive to the yield stress chosen.
173 citations
TL;DR: In this article, the authors investigated the channel cracking of elastic thin films in residual tension in the presence of yielding in the substrate material, where cracks or flaws oriented normal to the film-substrate interface propagate (or "channel") across the film.
Abstract: Thin bonded films have many applications In information storage and processing systems, for example, conducting, semiconducting and insulating films are used in integrated circuits, and thin magnetic films are used in disk storage systems In many cases, thin bonded films are in a state of residual tension, which can lead to film cracking Because cracking can alter desired film properties, methods for predicting it are needed The geometry considered in this work is one in which cracks or flaws oriented normal to the film-substrate interface propagate (or “channel”) across the film It is assumed that the film is brittle and the substrate is ductile Plane strain fracture analyses are used to investigate the channel cracking of elastic thin films in residual tension in the presence of yielding in the substrate material Although crack channeling induces yielding in the substrate, channel crack extension in the brittle film occurs under small scale yielding conditions The case of an elastic film bonded to an elastic substrate has been considered in earlier work, and is used as the basis for the current study A numerical model is used to extend the results from the fully elastic problem so that plastic yielding of the substrate is allowed Results are presented for an elastic-perfectly plastic substrate and for substrates exhibiting strain hardening A simple shear lag model of the problem without hardening in the substrate is discussed, which gives reasonable predictions for the dependence of dimensionless fracture quantities on the normalized loading over a wide range of material mismatches In addition, a method is presented by which shear lag modeling can be extended to cases in which the substrate exhibits strain hardening
167 citations
TL;DR: It was concluded that the reconstruction of the silicate network contributed to the increase in strength with time during the period after the gelation by cross-linking was completed.
Abstract: It has been reported that the silicate phase as well as the cross-linking of the polycarboxylic acid by aluminum and calcium ions played an important role in the hardening of glass-ionomer cement. The objective of this study was to investigate the structural change during hardening of the cements by means of infrared (IR) spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy and to confirm the role of the silica phase in the hardening of the cement. For that purpose, we measured the change in compressive strength of an experimental glass-ionomer cement, two commercial glass-ionomer cements, and a polycarboxylate cement and carried out 29Si and 27 Al NMR analyses of the cement samples after the strength measurement. In the IR spectra during hardening, a characteristic band of the silicate network around 1000 cm-1 shifted toward high frequency with time. The spectrum after hardening was similar to that for a hydrated amorphous silica structure. The 27Al NMR analysis showed that Al3+ ion...
138 citations
TL;DR: In this article, a model was developed to predict the austenite flow curves of low alloy and microalloyed steels, consisting of two expressions for stress, as a function of strain, temperature, strain rate and the chemical composition of the steel.
111 citations
TL;DR: In this article, the aging of AlZnMgCu alloys in a temperature range where the metastable phase η′ precipitates homogeneously, is examined with a three-fold point of view using the microstructural parameters measured previously by in situ small angle X-ray scattering experiments.
TL;DR: In this paper, the Bauschinger effect has been studied in an Al-7% Si-0.4% Mg casting alloy for a range of dendrite cell sizes and aspect ratios of the Si particles.
TL;DR: In this paper, it was shown that the Armstrong-Frederick hardening suitably calibrated and used in a class of models can yield reasonably good predictions of the rate of ratcheting for a range of cycle parameters.
TL;DR: In this paper, the authors investigated the limit flow stresses for transverse loading of metal matrix composites reinforced with continuous fibers and for uniaxial loading of spherical particle reinforced metal matrix composite composites.
TL;DR: In this article, Taylor-type polycrystal plasticity models with various single slip hardening laws are evaluated by studying the large strain behaviour of FCC polycrystals during reversed torsion.
TL;DR: In this paper, the fatigue and monotonic tensile properties of two electrodeposited and one wrought thin foil of copper were measured in a way similar to that used for bulk in order to determine if there is a difference.
TL;DR: In this article, the strength of the nanocrystalline solid solution depends on both solid solution hardening and grain boundary hardening while the latter makes the major contribution to the total strength.
TL;DR: A series of strain-controlled, low-cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths as discussed by the authors.
Abstract: —
A series of strain-controlled, low-cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths Present experiments have shown that there is additional hardening under non-proportional cyclic loading Non-proportional cyclic additional hardening also results in a shorter life for multiaxial low cycle fatigue A non-proportionality measure of strain path based on both a physical basis and macromechanical phenomena is proposed The loading path effect on additional hardening is also described well Low-cycle fatigue damage accumulation and the evolution process under non-proportional loading is analysed via the Continuum Damage Mechanics Model of Chaboche A non-proportinality measure is introduced in the damage evolution equation and a modified Coffin-Manson type formula is derived A novel fatigue life prediction approach based on the critical-plane concept of Brown and Miller is proposed
TL;DR: In this paper, Bui et al. proposed a geometrical description of distortional plastic hardening, including proportional expansion, translation, affine deformation, rotation, and distortion.
15 Apr 1996-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors examined the mechanical behavior of an alloy based on Fe40Al prepared from mechanically alloyed powders over a wide temperature range in the fine-grained, as-extruded state as well as after recrystallizing to a large grained state.
Abstract: The mechanical behaviour of an alloy based on Fe40Al prepared from mechanically alloyed powders was examined over a wide temperature range in the fine-grained, as-extruded state as well as after recrystallizing to a large-grained state. While the fine-grained material was strong and reasonably ductile at room temperature, in contrast with the weaker and more brittle large-grained material, at high temperature the strength fell to low values, similar for both materials. This behaviour is interpreted in terms of a contribution to strengthening due to the particles present, by Orowan hardening at low temperatures and by dislocation-particle interactions at high temperature, a contribution due to the grain size, which can harden at low temperatures and soften at high temperatures, and a contribution due to the matrix. The room temperature ductility seems to be dependent mostly on the grain size, since fine grain sizes can inhibit brittle crack formation.
TL;DR: In this paper, the cyclic response of the studied material may be described in terms of three different regimes within the plastic strain amplitude (ϵpl) range investigated, i.e. from 2 × 10−5 to 6 × 10 −3: at ϵpl below 10−4 the dominant cyclic deformation mechanisms are those correlated to planar glide of dislocations within the austenite which is the phase which carries a large part of the macroscopic strain in this first regime.
TL;DR: In this paper, a formulation of a model of thermo-elasto-plastic behavior of non-expansive saturated clays characterised by two plastic mechanisms is presented.
TL;DR: In this paper, the early stages of precipitation in an Al 1.1Cu1.7Mg alloy were studied using APFIM, transmission electron microscopy (TEM), and microbeam electron diffraction.
TL;DR: In this paper, a micromechanics study is carried out for the high strain rate deformation of ceramic particle reinforced metal matrix composites, where the ceramic particles are taken to be elastic, equal-sized, spherical and uniformly distributed in the matrix.
TL;DR: In this article, the role of hardening laws and surface roughness in the prediction of biaxial tensile limit strains of two A1 alloy sheet materials with different strain hardening characteristics was assessed.
TL;DR: In this article, six dilute (0.2, 0.5 and 1 at %) binary iron-base alloys with Co, Cr, Al, Si, Mn and Ni were prepared after scavenging inherent carbon with Ti.
Abstract: Six dilute (0.2, 0.5 and 1 at %) binary iron-base alloys with Co, Cr, Al, Si, Mn and Ni were prepared after scavenging inherent carbon with Ti. From tensile and stress relaxation tests in the temperature range of 77 to 450 K, stress-strain behaviours and thermal activation parameters were analysed as functions of solute content and temperature. In the four alloys containing Ni, Mn, Al and Si, solid-solution softening occurs below 250 K while solid-solution hardening occurs above 250 K. In the alloys containing Co or Cr, neither softening nor hardening due to solute additions occurs at any temperature. Detailed analysis of thermal activation parameters leads one to conclude that the solid-solution softening in the above mentioned four alloys is due to a decrease in kink energy with increasing solute content, while in the latter two alloys no change in kink energy occurs. On the other hand, there exists a strong solute concentration dependence of the athermal component, suggesting that the solid-solution hardening is due to the interaction of dislocations with groups of substitutional solute atoms that create lattice and modulus misfits.
TL;DR: In this article, the transformation from short-to long-range order in Haynes® Alloy 242, a nominal Ni 2 (Mo,Cr) domains/precipitates, during isothermal aging at temperatures between 550 and 750°C are reported using microhardness measurements, and optical and transmission electron microscopy.
01 Jan 1996
TL;DR: In this article, the authors focus on the viscoplasticity theory based on overstress (VBO) for small strain, isotropy, and isochoric inelastic deformation.
Abstract: This chapter focuses on the viscoplasticity theory based on overstress (VBO) for small strain, isotropy, and isochoric inelastic deformation. VBO is a unified theory without a yield surface representing a solid. The total strain rate is the sum of the elastic and inelastic strain rates. The inelastic strain rate is an increasing function of the overstress, the difference between the stress and the equilibrium stress, which is a state variable of the theory. The overstress is a measure of rate dependence. The purpose of the kinematic stress, a second state variable, is to model work hardening (softening) in monotonic loading. The isotropic stress or rate independent stress, the third state variable, is constant for cyclic neutral behavior. For cyclic hardening or softening, a growth law is needed. It also changes when high homologous temperature behavior is modeled. Asymptotic solutions for constant strain rate exist and are useful in the identification of rate-dependent and rate-independent contributions to the stress.
TL;DR: In this article, the ductility of copper alloys at a dose level as low as 0.2 dpa was found to be related to the intrinsic hardness of the grain interior and not to the grain boundary embrittlement.
TL;DR: In this paper, the authors studied the effect of aging on the cyclic deformation mechanism of stainless steel in terms of the deformation amplitude and deformation hardening-softening response, cyclic stress-strain curve and substructure evolution.