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EDITORIAL

J. Eng. Mater. Technol. 1978;100(3):225-226. doi:10.1115/1.3443483.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Eng. Mater. Technol. 1978;100(3):227-232. doi:10.1115/1.3443484.

Since the wheelset (wheel-axle assembly) is one of the most important components of the equipment used in the Shinkansen (new high speed line), high reliability is required to prevent severe railway accidents. Since service on Shinkansen started in 1964, continuous efforts have been made to raise its reliability still more, by examination for cracks in the fretted part of the wheel seat, improvement of the induction hardening method, improvement of the press-fitting method of the axle on the wheels, measurement of the stress distribution of the axle in service and their effects on the endurance life of the axle assemblies. The results of research on the fatigue strength of axle assemblies and the development of maintenance techniques based on this research are presented.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):233-247. doi:10.1115/1.3443485.

The applicability of fracture mechanics to conventional isotropic materials has been well demonstrated. For fiber-reinforced materials, however, fracture mechanics investigations have met with mixed results. For collinear crack extension of a crack on a plane of symmetry in orthotropic materials, fracture behavior has been successfully predicted using linear elastic fracture mechanics concepts; however, extrapolation to other fiber orientation combinations has been less successful. This is because fracture in anisotropic materials is more complex than in isotropic materials and is governed by additional parameters such as fiber orientation, lamination order and the constitutive relations that describe the mechanical responses of the fiber, the matrix and the interface. This paper reviews the fundamentals of fracture mechanics for isotropic materials and discusses its extension to orthotropic materials. This is followed by a discussion of the variety of failure modes observed in composites and a review of the predominant fracture mechanics theories that attempt to predict fracture using semi-empirical parameters. The main aim of this paper is to present a survey of the field in its current state and to demonstrate the approach taken by each investigator. The paper concludes with two examples where linear elastic fracture mechanics concepts have been satisfactorily employed for composite materials.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):248-252. doi:10.1115/1.3443486.

The proposed standard C-shaped Specimen for KIc determinations according to ASTM E399 is readily adaptable to load line deflection measurement, and thus to J-integral assessment, using procedures currently being developed for other geometries. Tests have been conducted on quenched and tempered steels to provide comparisons of JIc and KIc using both C-shaped and compact tension specimens. The effect of specimen thickness on the crack growth resistance curve and JIc has also been examined and analyzed in relation to the allowed thickness range for the proposed test method. The Merkle and Corten corrections for the C-shaped Specimen have been calculated and compared to those for other specimen geometries. J estimates based on total displacement measurements have been found to be acceptable even at short relative crack depths.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):253-257. doi:10.1115/1.3443487.

The fracture criterion JIC is determined on SA-516-70 steel using precracked CVN specimens. The addition of an appropriate side-groove results in a better plane-strain condition at the crack tip and removes a major part of the absorbed energy due to lateral deformation. The value of JIC static is calculated from a single three-point-bend experiment. The displacement of the cracked front is followed by the measurement of the electrical resistance. We have shown that a single specimen is sufficient for determining JIC . Experiments on an instrumented Charpy machine were used for the calculation of the value of JICD . We assumed, for elasto-plastic behavior, that the maximum point of the load-displacement curve corresponds to the instability threshold of the crack. The values of JIC and JICD obtained by these two methods are compared and discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):258-266. doi:10.1115/1.3443488.

The principal purpose of this investigation was to study specimen size effects on elastic-plastic type R-curve using HY130 steel plate. Compact specimens ranging in size from 12T to 1T in planar dimensions and standardized on 1-inch thickness were used. Using an elastic-plastic concept developed in a companion program, it was shown that the R-curve is specimen size independent, even when nominal stress was well beyond general yield and the crack was propagating beyond maximum load. Using this observation, it is shown how instability can ge predicted under conditions ranging from elastic-plastic to fully plastic. This establishes the ground work for future studies on how R-curve is affected by specimen type or by stress triaxiality conditions.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):267-271. doi:10.1115/1.3443489.

The mechanical properties of weld heat-affected zones (HAZ’s) associated with the heavy section, nuclear quality weldments are evaluated and found to be superior to those of the parent base material. The nil ductility transition temperature (NDTT), Charpy impact and static and dynamic fracture toughness properties of a HAZ associated with a submerged arc weld and one associated with a manual metal arc weld are directly compared with those of the parent base material. It is concluded that the stigma normally associated with HAZ is not justified for this grade and quality of material and weld procedure.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):272-278. doi:10.1115/1.3443490.

A number of early light water reactor plants were constructed from materials having low initial Charpy upper shelf values and high copper and phosphorus content. As these elements have been shown to contribute the most to the radiation sensitivity of reactor pressure vessel material, there is a possibility that thermal annealing of the bellline regions of the these vessels may become necessary to meet Nuclear Regulatory Commission requirements for continued operation. Recognizing the possibility that thermal annealing treatment of the reactor vessel may become a reality, a program was started to determine the kinetics and mechanisms of thermal annealing to restore preservice fracture toughness and to develop engineering procedures for ready application to large-scale nuclear pressure vessels. This paper presents the program scope required for establishing the feasibility of and methodology for an in situ thermal anneal of an embrittled reactor vessel.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):279-286. doi:10.1115/1.3443491.

We describe a computer model for predicting ductile-fracture initiation and propagation. The model is based on plastic strain. Fracture starts or a crack extends when the integrated product of the equivalent plastic-strain increment and a function of the mean stress exceeds a critical value over a critical length. This critical length is characteristic of the microstructure of the material. The computer fracture model is calibrated by computer simulation of simple and notched round-bar tension tests and a precracked compact tension test. The model is then used to predict fracture initiation and propagation is the standard Charpy V-notch specimen. The computed results are compared with experiments. The model predicts fracture toughness from tests of standard surveillance specimens from nuclear-reactor pressure vessels and can be applied to fracture calculations for these vessels.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):287-293. doi:10.1115/1.3443492.

A “symmetric impact” experiment was used as the basis for comparing different models of the fracture mechanism in granite. Two different tensile fracture models were considered, but better results were obtained when both shear and tensile fracture were admitted. The combined model employs a fracture criterion based on static measurements of the tensile and triaxial compressive strength and emphasizes the role of bulking, which is related directly to the local rate of energy dissipation. It is shown that the behavior subsequent to incipient fracture has a major influence on the overall material response.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):294-302. doi:10.1115/1.3443493.

A simple extension of Hill’s formulation for anisotropic plasticity which accounts for the distortion of the yield surface, Mij , the strength differential between tension and compression, αi and the effective size of the loading surface, k, has been proposed. These material parameters, Mij , αi , and k, define the initial state of the material and vary with plastic deformation. The parameters describing the anisotropic state are determined from uniaxial tension and compression tests along the principal axes. It is shown that the yield stresses in tension and compression along the three principal axes are related by a constraint equation when the condition of incompressibility is imposed. Experimental data obtained from several anisotropic materials are reasonably consistent with the constraint equation. The anisotropic plasticity formulation is also shown to describe the yield surface of different HCP metals more closely than the Hill’s theory. Based on the proposed formulation, finite element calculations have been made for the notched and the three-point bend specimens. The calculated load-deflection relationships are in good agreement with the experimental results.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):303-309. doi:10.1115/1.3443494.

The history and the present state of the theory of sheet metal forming limits are reviewed. The theory of necking and plastic instability (Swift-Hill and Marciniak-Kuczyński models) is discussed and theoretical limit strains are calculated. The influence of the strain path on the theoretical limit strains is discussed with computational examples. At the present no theory can fully explain the localized necking in stretch forming.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):310-312. doi:10.1115/1.3443495.

A hole which is plastically expanded and then allowed to contract is referred to as coldworked. The residual strains around holes which were coldworked by an industrial process were measured in this work and compared with theoretical analyses. Agreement between theory and experiment is not very good.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):313-318. doi:10.1115/1.3443496.

Water heat pipes were fabricated from 316, 347, and 430 stainless steel, Monel 400, CDA 715, Inconel 600, and Incoloy 800. All of these materials generated varying amounts of hydrogen gas during the first few days of operation. However, as the heat pipes continued to operate, the amount of gas in each heat pipe, excluding 430 stainless steel, decreased by permeating through the heat pipe walls. Inconel 600 appeared to be the most acceptable material for water heat pipes by returning to isothermal operation over a short time period. An equation based on a diffusion dependent mechanism was developed that predicts heat pipe performance recovery rates.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1978;100(3):319-332. doi:10.1115/1.3443497.

The Manson-Haferd, Larson-Miller, and Orr-Sherby-Dorn time-temperature parameters were applied to creep-rupture data obtained from testing two batches of austenitic stainless steel weldments. It was found that none of these correlated the data satisfactorily. A new parameter, based on a modification of one proposed originally by Manson and by Goldhoff and Sherby, was found to adequately correlate the data. The Minimum-Commitment, Station-Function Approach of Manson and Ensign was also applied, the results of which supported those obtained from the analysis made using the parameters listed above. Finally, from the relationship between rupture-time and secondary creep-rate, it is suggested that the form of the rupture data may be useful in predicting the physical basis for creep.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Eng. Mater. Technol. 1978;100(3):333-335. doi:10.1115/1.3443498.
Abstract
Topics: Creep , Rupture
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Eng. Mater. Technol. 1978;100(3):336. doi:10.1115/1.3443499.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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