0


AWARDS

J. Eng. Mater. Technol. 1977;99(1):1. doi:10.1115/1.3443396.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):1. doi:10.1115/1.3443397.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Eng. Mater. Technol. 1977;99(1):2-15. doi:10.1115/1.3443401.

Widely used constitutive laws for engineering materials assume plastic incompressibility, and no effect on yield of the hydrostatic component of stress. However, void nucleation and growth (and thus bulk dilatancy) are commonly observed is some processes which are characterized by large local plastic flow, such as ductile fracture. The purpose of this work is to develop approximate yield criteria and flow rules for porous (dilatant) ductile materials, showing the role of hydrostatic stress in plastic yield and void growth. Other elements of a constitutive theory for porous ductile materials, such as void nucleation, plastic flow and hardening behavior, and a criterion for ductile fracture will be discussed in Part II of this series. The yield criteria are approximated through an upper bound approach. Simplified physical models for ductile porous materials (aggregates of voids and ductile matrix) are employed, with the matrix material idealized as rigid-perfectly plastic and obeying the von Mises yield criterion. Velocity fields are developed for the matrix which conform to the macroscopic flow behavior of the bulk material. Using a distribution of macroscopic flow fields and working through a dissipation integral, upper bounds to the macroscopic stress fields required for yield are calculated. Their locus in stress space forms the yield locus. It is shown that normality holds for this yield locus, so a flow rule results. Approximate functional forms for the yield loci are developed.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):16-22. doi:10.1115/1.3443395.

Ductile fracture of porous metals during forging was studied. The effect of the shape of sintered copper preforms on the forming limit is examined in upsetting with flat dies at room temperature. Cylindrical preforms with concave ends were found to show less barrelling during deformation and had a larger upsetting limit compared to those with flat ends. A fracture criterion for porous materials was proposed as a function of the history of the hydrostatic component of the stress. The criterion was applied to upsetting of sintered copper preforms. For calculation of the forming limit, the histories of the stress components at the equatorial free surface were obtained applying the plasticity equations for porous materials. The change in the density distribution during upsetting was measured.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):23-25. doi:10.1115/1.3443398.

Numerous studies on fatigue damage and fatigue crack propagation in the past dealt with these problems, either by a cumulative damage approach, or using crack propagation equations based on linear elastic fracture mechanics. Although these two approaches are not compatible, each is useful for predicting fatigue behavior correctly, but only within defined limits. This study introduces the “fatigue phase diagram”, which classifies different combinations of stresses and crack lengths in a given specimen, as zones in which different fatigue evaluation criteria, and possibly different fatigue mechanisms govern. Furthermore, a definition of the “threshold crack length” is proposed for consideration as the end of the crack initiation stage. It is suggested that most stress-intensity-range-threshold studies in the literature, were performed with stress range under the fatigue limit of the material, and therefore no crack initiation or propagation could have been measured. Any additional study should specify the zone of the tests on the fatigue phase diagram, so that correlations between different tests could be done with the proper data only.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):26-28. doi:10.1115/1.3443399.

A stochastic model for the fatigue of metals under repeated stress or strain is proposed. Fatigue lives up to crack initiation are investigated with the aid of a recent theory on a cumulative process and the mean values are plotted versus stress amplitudes. Of interest is the fact that this curve behaves as if the endurance limit existed when the parameters are adequately taken. Except the neighborhood of the endurance limit, the coefficients of variation are also calculated approximately.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):29-35. doi:10.1115/1.3443400.

A series of low-cycle fatigue tests was performed at 593 deg C on Fe-20 Cr-10 Ni and Fe-20 Cr-20 Ni (in weight percent) austenitic alloys in both the cast and wrought conditions. The as-cast alloys exhibited substantially longer cyclic lives than the wrought alloys or wrought Type 304 stainless steel. An effect of Ni content on fatigue life was noted for the cast alloys, but not for the wrought. Striation, measurements indicated that the majority of the cyclic life was spent in crack initiation and early growth in all cases, and the superiority of the cast alloys was almost entirely due to a greater resistance to crack initiation. Macroscopic crack-growth rates were found to be essentially independent of composition and microstructure. A 1-min tension hold time per cycle produced a significant reduction in cyclic life in all cases except for the as-cast high Ni alloy. The decrease in life appeared to be associated with the initiation of cracks from localized deformation at grain boundaries.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):36-41. doi:10.1115/1.3443402.

Experimental results are presented on the erosion of PMA (Powder Metallurgy Aluminum) alloys by a pulse of high pressure and high temperature combustible gases. The PMA alloys have been found to exhibit superior erosion resistance characteristics than wrought aluminum alloys. Of the PMA alloys tested, SAP materials (Sintered Aluminum Powder) were shown to be the best. The primary mechanism of the erosion of PMA alloys was found to be the melt and wipe off process. Combustion of aluminum that is responsible for the catastrophic erosion of wrought aluminum alloys was inhibited in PMA tests. Several hypotheses that explain erosion resistance of the PMA alloys have been postulated.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):42-46. doi:10.1115/1.3443403.

The interstage annealing of sheet-metal laminates is studied. A method of predicting the stretch-formability, as measured by the maximum possible uniform strain in simple tension, is proposed. Practical composite systems of potential commercial interest are examined. It is suggested that for certain sheet-metal laminates improved stretch-formability can be achieved as a consequence of a low-temperature, low-cost heat-treatment.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):47-51. doi:10.1115/1.3443405.

The maximum loads sustainable in both four-point bending and prebent hinge collapse tests of several materials have been determined at crosshead rates from 4.2 × 10−3 mm/s to 4.2 m/s (10−2 –104 in./min). All the materials exhibit a logarithmic dependence of flow stress on crosshead rate; this dependence is consistent with that previously reported for tensile deformation. Although there are some minor differences in the dynamic stress factors obtained by the bending and tensile methods, all the methods rank the materials in the same order. Thus, for materials evaluation the most convenient test method, which is usually the tensile test, can be chosen. For more complex loading geometries than considered here, scale model testing would yield the most reliable results.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):52-58. doi:10.1115/1.3443406.

A multistage continuous extrusion process based on a new concept is described and studied. The billet is driven through a series of dies by the viscous drag of a fluid flowing along its perimeter, allowing for an unlimited length of the extruded product. Design parameters are obtained from an analysis of the flow and of the stresses in the billet. The geometry of the dies, the extrusion chambers, and the optimal flow characteristics are determined. Technical problems such as buckling of the billet and temperature rise of the fluid are discussed. Experimental results with a one-stage unit are given and compared to the theoretical prediction.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):59-64. doi:10.1115/1.3443407.

The applicability of two familiar analytic descriptions of micromechanical deformation as equations of state for polycrystalline iron is discussed. These equations are the power law and the relationship based on reaction rate theory. It is shown that the reaction rate description fails to describe adequately individual stress relaxation events without invoking undue complexity from use of adjustable parameters. Moreover, even in that case, this formulation lacks the predictive capability required in an equation of state. Conversely, the power law is found not only to describe stress relaxation data properly but also to provide the capability of predicting stress relaxation following initial deformation by different loading paths. It thus appears to represent an equation of state for the material.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):65-69. doi:10.1115/1.3443408.

Thermal-elastic analyses of dissimilar metal transition weld joints of a 24″ sodium piping system were performed. This piping system is for Liquid Metal Fast Breeder Reactor application, operating at elevated temperature (965°F). These analyses form a basis for the selection of the material combination and weld preparation of the transition joints. Two material combinations were selected for weld joint thermal-elastic analysis: 2 1/4 Cr - 1 Mo ferritic steel to 316 stainless steel, and 2 1/4 Cr - 1 Mo steel to Incoloy 800, with Inconel 82 as the welding metal in both cases. Weld preparations with various geometries were assumed for each material combination. The transition joints were evaluated for thermal loadings due to the changes in sodium temperatures during anticipated operating conditions of the breeder reactor. Thermal analyses were performed to define the temperature time history in the metals; the temperature gradient across the wall thickness; and especially, the temperature distribution near the material interfaces. The magnitude of the temperature gradients and the temperature distribution as affected by the heat transfer characteristics of each material were of particular interest. Stresses created due to the differences of thermal expansion of the materials, radial and axial temperature gradients, and applied internal pressure were evaluated using finite element analysis methods. In this investigation, the materials were treated as elastic and isotropic. The contributions from the applied pressure and thermal loading were separated from the total stresses and the most important contributor was identified. The elastic analyses served for a preliminary evaluation of the transition joint selection. Based on the information obtained in stress versus material combination and the stress variation as a function of the geometry of the weld preparation, a weld design (material combination and geometry) was selected.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):70-75. doi:10.1115/1.3443409.

The mechanical properties of four cast high-strength steels, 4340, 15-5 PII stainless steel, and two maraging steels were examined. To provide a direct comparison with wrought steels split heats were prepared in which part of each heat was sand cast and the balance was forged and hot-rolled to plate. The KIc properties of the castings were comparable to the plate properties. Limited tests indicated that the cast steels also had reasonably good fatigue and stress corrosion cracking resistance. The castings showed surprisingly low Charpy values, which was attributed to notch acuity due to the more heterogeneous nature of the fractures in the cast structures. The overall results suggest that cast high-strength steels had satisfactory toughness and could be used in many applications.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):76-79. doi:10.1115/1.3443410.

Mises type of creep equations have been used widely to study creep and relaxation phenomena. In a study by Murakami and Yamada [1] inclusion of J3 , the third invariant of the deviatoric stress tensor, in the Mises type creep theories helped explain the deviations between experimental and theoretical results of a thick-walled cylinder creeping under an internal pressure. Similarly, the present study investigates the effects of including J3 in the creep constitutive equations on creep and relaxation in a circular plate with a central hole. The results show that inclusion of J3 in the creep equations tends to predict higher values of Σθ (tangential stress) in the creep problem and lower values of Σθ and Σr in the relaxation problem. Lower value of Σr in the relaxation problem implies a lower contact force at the interface of a press-fitted joint.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):80-82. doi:10.1115/1.3443411.

An accident involving a 3-wheeled vehicle resulted in personal injury and property damage. Analysis of the failure by direct observation, optical microscopy, transmission electron microscopy, and techniques involving mutual indentation hardness shows that the accident resulted from fatigue fracture in a ball-joint socket at one end of a strut connecting the frame to the rear axle. Absence of a suspension system in the vehicle was the most likely single cause of the fatigue fracture.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):83-85. doi:10.1115/1.3443412.

This is an account of a welded blower fan assembly which failed in operation with a large detached portion killing the owner. The circumstances, method of fabrication, and mode of operation are discussed. Failure was due to a combination of a design defect and a worn shaft.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1977;99(1):86-92. doi:10.1115/1.3443413.

Failure of a 440C stainless steel burst rod adaptor from the White Sands Missile Range Fast Burst Reactor is analyzed. The operational history of the adaptor, including nature of loading, radiation accumulation, and thermal environment, was examined. Problems associated with handling radioactive materials were overcome through careful monitoring and disposal. The chemical composition of the adaptor material was checked by x-ray and electron probe spectroscopy. The failure surface was examined and photographed at various magnifications, using optical and scanning electron microscopes. Areas of crack origin, rapid fracture, final breakoff, and abrasion from rebound are identified. Metallographic specimens were prepared, the grain structure examined, and hardness profiles obtained. The grain structure indicated the presence of microvoids and carbide segregation, and slight hardening was noted. Failure occurred at the base of a male thread in a region showing significant tool markings. Examination of the failure surface indicated crack initiation due to Stage I fatigue followed by rupture from shock overload. Recommendations to avoid similar occurrences are given.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Eng. Mater. Technol. 1977;99(1):93-94. doi:10.1115/1.3443414.
Abstract
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Eng. Mater. Technol. 1977;99(1):96. doi:10.1115/1.3443416.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In