scispace - formally typeset
Search or ask a question

Showing papers in "Journal of Engineering Materials and Technology-transactions of The Asme in 1980"


Journal ArticleDOI
TL;DR: In this article, the effects of void nucleation occurring during the deformation history on forming limit curves are considered for both in-plane and punch stretching employing a constitutive model of a porous plastic solid.
Abstract: The effects of void nucleation occurring during the deformation history on forming limit curves are considered for both in-plane and punch stretching employing a constitutive model of a porous plastic solid. Both plastic strain controlled and stress controlled nucleation processes are simulated by a two parameter void nucleation criterion. For in-plane stretching, plastic strain controlled nucleation can have, in certain circumstances, a significantly destabilizing effect on the forming limit curve. However, within the framework of plane stress theory which neglects the enhance­ ment of the hydrostatic stress due to necking, a stress controlled nucleation process is not found to be significantly destabilizing. In punch stretching a ductile rupture criterion, which limits the maximum volume fraction of voids, as well as the ap­ pearance of a well defined thickness trough, is adopted as a localized necking criterion. Only plastic strain controlled void nucleation is considered here in out-ofplane stretching. The resulting forming limit curves have the same shape as those obtained previously with void nucleation neglected.

1,239 citations


Journal ArticleDOI
TL;DR: In this article, an initial study was made of characteristics of ultralow growth rate fatigue crack propagation in thick-section, normalized 2 1/4 Cr-1Mo pressure vessel steel (ASTM A387, Class 2 Grade 22), and a new approach was presented in terms of the role of oxide debris from moist environments in promoting crack closure.
Abstract: As part of an ongoing program to examine subcritical flaw growth in candidate steels for proposed coal gasifier pressure vessels, an initial study is made of characteristics of ultralow growth rate fatigue crack propagation in thick-section, normalized 2 1/4 Cr-1Mo pressure vessel steel (ASTM A387, Class 2 Grade 22). Crack propagation data are generated over a wide range of growth rates, from 10−8 to 10−2 mm/cycle, for load ratios between 0.05 and 0.80 at ambient temperatures in low pressure environments of moist air, dry hydrogen gas and dry argon gas. Particular emphasis is placed on behavior at near-threshold growth rates, below 10−6 mm/cycle, approaching the so-called threshold stress intensity for fatigue crack growth, ΔK0 . Near-threshold growth rates, in addition to showing a marked sensitivity to load ratio, are found to be significantly enhanced in gaseous hydrogen compared to air. Similar environmentally-enhanced growth is observed in argon gas. To account for such results, previous models of threshold behavior based on environmental factors (e.g., hydrogen embrittlement) are questioned, and a new approach is presented in terms of the role of oxide debris from moist environments in promoting crack closure. This oxide-induced closure model is found to be consistent with most experimental observations of near-threshold fatigue crack propagation behavior and is proposed as a mechanism for environmental effects at ultra-low growth rates.

203 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the development of a high-speed torsional testing machine and results obtained on the strain-rate dependent strength of copper at large shear strains.
Abstract: This paper describes the development of a high-speed torsional testing machine and results obtained on the strain-rate dependent strength of copper at large shear strains. Test techniques and data obtained are intended to be useful in applications such as ballistics and machining. For copper, the results indicate positive strain hardening behavior to very large strains under low rate, isothermal conditions and the transition to adiabatic thermal softening, shear instability and localization (shear banding) at high rates.

111 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used microstructural features of fracture surfaces of structural materials (e.g., austenitic stainless steels, low-alloy steels) as a guide in the formulation of generalized damage-rate equations that include interaction between a crack and cavities in a given environment.
Abstract: Elevated-temperature failure of structural materials (e.g., austenitic stainless steels, low-alloy steels) used in energy-conversion systems can occur by fatigue, creep, or by interactive processes involving creep, fatigue, and environment. The fracture surfaces of these materials exhibit a variety of microstructural features depending upon the type of material, strain rate, temperature, environment, hold times, and sequence of waveshapes. These microstructural observations have been used as a guide in the formulation of generalized damage-rate equations that include interaction between a crack and cavities in a given environment. Crack-propagation rate as well as total life of a fatigue specimen have been calculated by integrating the damage-rate equations over the inelastic strain history of the specimen, and compared with experimental results.

85 citations


Journal ArticleDOI
TL;DR: In this paper, several strategies for numerical time-integration of some stiff constitutive models of inelastic deformation are presented for the integration of one such model for the case of uniaxial deformation under various prescribed histories of stress or strain.
Abstract: Several strategies for numerical time-integration of some stiff constitutive models of inelastic deformation are presented in this paper. Numerical results and comparisons are presented for the integration of one such model for the case of uniaxial deformation under various prescribed histories of stress or strain. A simple one step Euler type integration scheme with automatic time-step control, which can be easily adapted to the solution of multiaxial boundary value problems, appears promising.

76 citations





Journal ArticleDOI
TL;DR: In this article, an annular plate made of an orthotropic elastic-plastic material that is isotropic in the plane of the plate was modeled as a blankholder and the effect of blankholder stiffness on wrinkling was investigated.
Abstract: The onset of flange wrinkling in the Swift cup test is analyzed as a plastic bifurcation problem. The flange is modelled as an annular plate made of an orthotropic elastic-plastic material that is isotropic in the plane of the plate. The critical drawing stress and displacement obtained employing a deformation theory of plasticity and a flow theory of plasticity are compared. The effects of flange geometry and material properties on wrinkling are investigated. Employing a simple linear elastic spring model of the blankholder, the effect of blankholder stiffness on wrinkling is studied. The present results for the critical stress at the onset of wrinkling and for the number of wrinkles are compared with those obtained previously employing a beam model of the flange.

45 citations




Journal ArticleDOI
TL;DR: In this paper, the problem of obtaining a meaningful value of toughness from small Charpy-size surveillance specimens, tested at temperature corresponding to the upper shelf where ductile fracture predominates, is investigated.
Abstract: The problem of obtaining a meaningful value of toughness from small Charpy-size surveillance specimens, tested at temperature corresponding to the upper shelf where ductile fracture predominates, is investigated. Following the procedures of Green and Knott for measurement of crack opening displacements at initiation of ductile fracture, a test procedure is adopted in which small precracked Charpy-size bend specimens are side-grooved to increasing depths and tested to failure under both quasi-static and dynamic loading rates. Values of the J-contour integral at maximum load (J max) for specimens side-grooved in excess of 30% are found to agree, within acceptable limits, with valid initiation J(Ic) fracture toughness values determined independently using multispecimen resistance-curve techniques. Three nuclear pressure vessel materials were evaluated at temperatures between 71 and 177 C, which correspond to upper shelf temperatures. The test procedure described offers a simple, inexpensive, small specimen compromise for estimating the fracture toughness at the onset of ductile fracture from a single Charpy-size bend test piece for both quasi-static and dynamic loading rates. This approach could be readily adopted in nuclear surveillance programs for toughness evaluation of unirradiated and neutron-irradiated pressure vessel steels.



Journal ArticleDOI
TL;DR: In this article, the effects of carbon content in the workpiece and of added carbon in the gas atmosphere on hardness, compound layer thickness, and diffusion layer thickness were investigated in ion-nitride processing and it was shown that when the treatment time is sufficiently long, the maximum hardness is obtained at a temperature near 450°C.
Abstract: This paper deals with ion-nitride processing and is primarily concerned with the effects of carbon content in the workpiece and of added carbon in the gas atmosphere on hardness, compound layer thickness, and diffusion layer thickness. Increased carbon content in the workpiece increases the compound layer thickness, but decreases the diffusion layer thickness. On the other hand, an optimal amount of added carbon in the gas atmosphere will increase the compound layer thickness as well as the diffusion layer thickness and hardness. It is found that the ion-nitriding temperature at which maximum hardness is attained is governed by the ion-nitriding time. When the treatment time is made sufficiently long, the maximum hardness is obtained at a temperature near 450°C.


Journal ArticleDOI
TL;DR: In this article, five gas turbine disk alloys representing a range of strengths and processing methods were tested for resistance to both cyclic crack initiation and propagation at 650 C using a 0.33 Hz fatigue cycle and a cycle incorporating a 900 s tensile dwell.
Abstract: Five gas turbine disk alloys representing a range of strengths and processing methods were tested for resistance to both cyclic crack initiation and propagation at 650 C using a 0.33 Hz fatigue cycle and a cycle incorporating a 900 s tensile dwell. At the low strain ranges pertinent to disks, resistance to crack initiation increased with increasing tensile yield strength among the alloys, though the advantage was somewhat smaller for the creep fatigue cycle. Cyclic crack growth resistance, however, decreased with increasing strength and very markedly so for the dwell cycle.



Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment on the JIC fracture toughness behavior of Alloy 718 was characterized at room temperature, 427°C and 538°C, and two different heat treatments were used: the conventional (ASTM A637) treatment, and a modified heat treatment designed to improve the toughness of alloy 718 base metal and weldments.
Abstract: The effect of heat treatment on the JIC fracture toughness behavior of Alloy 718 was characterized at room temperature, 427°C and 538°C. Two different heat treatments were used: the conventional (ASTM A637) treatment, and a modified heat treatment designed to improve the toughness of Alloy 718 base metal and weldments. The elastic-plastic JIC fracture toughness response of the modified Alloy 718 was found to be superior to the JIC behavior exhibited by the conventional material over the entire test temperature range. Metallographic and fractographic examinations of Alloy 718 fracture surfaces revealed that the inferior fracture resistance of the conventional superalloy was attributed to the presence of coarse δ precipitates throughout the conventional matrix. The increased fracture toughness response of the modified Alloy 718 was related to the dissolution of coarse δ precipitates during the high temperature solution anneal employed in the modified treatment.

Journal ArticleDOI
TL;DR: In this paper, a reference curve was developed for nuclear pressure vessel steel on the basis of a set of precracked instrumented Charpy V-notch tests, and the reference curve can be readily used to define a lower bound relationship between fracturemore-toughness and temperature.
Abstract: A large base of K/sub IC/, K/sub Id/ and J/sub IC/ (R-curve) fracture toughness data has been used to develop reference toughness curves. The most successful results were obtained when a sigmoidal function was fitted to data from which the heat-heat variation in both the temperature and fracture toughness had been reduced by referencing. Several referencing procedures have been studied, but the only one found to be successful in this work was based upon the precracked instrumented Charpy V-notch test. The tanh function K = A + B tanh (T - To/C) (K = toughness, T = temperature, and A, B, T/sub 0/ and C are coefficients which give the best fit between curve and data) fitted to precracked instrumented Charpy V-notch test data provided suitable referencing quantities. Using the coefficients A and B to reference fracture toughness, and T/sub 0/ and C to reference temperature, lower bound reference curves were developed. Weighted, nonlinear regression procedures were used to define lower bound reference toughness curves for each of three stress intensification rates. The lower bound was the statistical global tolerance bound to the referenced data. The reference curves can be readily used to define a lower bound relationship between fracturemore » toughness and temperature for nuclear pressure vessel steel on the basis of a set of precracked instrumented Charpy V-notch tests.« less

Journal ArticleDOI
TL;DR: In this paper, the existence of initial defects and residual stresses eliminated the initiation stage of fatigue crack growth, and stress range was found to be the controlling factor for crack propagation, and limits on live load stresses have been adopted for steel bridges.
Abstract: Steel bridges are subjected to live loads which produce variable stress ranges in bridge components. At welded bridge details, the existence of initial defects and residual stresses eliminate the initiation stage of fatigue crack growth, and stress range is found to be the controlling factor for crack propagation. Laboratory tests have resulted in stress range-fatigue life relationships for various bridge details. These data correlate well with fracture mechanics theory and with field data. Limits on live load stresses have been adopted for steel bridges. Coupled with material fracture toughness requirements, the stress range limits minimize the probability of fatigue and fracture in steel bridges.







Journal ArticleDOI
TL;DR: In this article, a new macroscopic criterion for brittle fracture in the state where in biaxial or triaxial stresses, compressive stress predominates is proposed.
Abstract: On the basis of traditional fracture criteria and numerous data on the fracture under multiaxial stresses, we propose a new macroscopic criterion for brittle fracture in the state where in biaxial or triaxial stresses, compressive stress predominates. We base our theory on the concept of fracture mechanics, especially of mode II fracture. Our criterion is expressed as follows, τc = τ0 + ζ1 (σ1 + σ3) + ζ2σ2 where τ0 = (KIIc/KIc). at is the imaginary pure shearing strength of the material, ζ1 = (KIIc/KIc) (at/ac) – 1/2 and ζ2 are the coefficients corresponding to the restraint for crack propagation. The criterion may be applicable to mode II fracture which occurs in the state where compressive stress is predominant.