J. Eng. Mater. Technol. 1983;105(4):235-241. doi:10.1115/1.3225652.

Plastic strains at the roots of notched specimens of Inconel 718 subjected to tension-compression cycling at 650°C are reported. These strains were measured with a laser-based technique over a gage length of 0.1 mm and are intended to serve as “benchmark” data for further development of experimental, analytical, and computational approaches. The specimens were 250 mm by 2.5 mm in the test section with double notches of 4.9 mm radius subjected to axial loading sufficient to cause yielding at the notch root on the tensile portion of the first cycle. The tests were run for 1000 cycles at 10 cpm or until cracks initiated at the notch root. The experimental techniques are described, and then representative data for the various load spectra are presented. All the data for each cycle of every test are available on floppy disks from NASA.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):242-249. doi:10.1115/1.3225653.

2024 aluminum tubes, heat treated to a T6 and T8 temper, were tested in combinations of tension-internal pressure and tension-torsion loading. Yield loci and flow behavior were determined for both modes of loading and compared to theoretical predictions. Both tempers of 2024 aluminum exhibited crystallographic textures and anisotropic yield and flow. Hill’s quadratic yield criterion and the associated flow rule under-estimate balanced biaxial yield and flow, which is consistent with hydraulic bulge data on other face-centered cubic metals. Hill’s nonquadratic criterion, which adds one additional parameter, and Bassani’s criterion, which adds two parameters, predict the anisotropic yield behavior much more accurately. Predictions of the complete flow behavior, including strain paths, with these anisotropic criteria could be improved markedly by including provisions for planar anisotropy.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):250-256. doi:10.1115/1.3225654.

This paper describes two biaxial experiments which investigated time and rate effects in the yield and deformation behavior of type 316 stainless steel at room temperature. The first experiment was aimed at determining the effect of probing rate on small-offset yield behavior. The primary aim of the second experiment was to investigate time-dependent flow after loading beyond initial yield. An additional aim was to investigate the effect of radial (3 σ12 = σ11 ) and nonradial preloads on the yield and hardening behavior. The first experiment showed that for the limited range investigated, 100 to 500 με/min, the probing rate had little effect on yield behavior. The small differences observed in the size and position of certain yield surfaces were shown to be related to the sequence in which the yield loci were determined. The second experiment showed that yield surfaces suffered considerable distortion from their initial near-circular form after both radial and nonradial preloads beyond initial yield. It also showed that the hardening behavior was predominantly kinematic for both types of preload. The strain-time data obtained after the preloads in this experiment showed characteristics typical of creep curves. A transient flow period was observed with high initial strain rates diminishing one or two orders of magnitude during the 0.5-h hold periods. This means that in detailed mechanical modeling of this material, careful attention should be given to time-dependent effects, even at room temperature.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):257-263. doi:10.1115/1.3225655.

History effects of prior creep on subsequent plasticity were studied for type 316 stainless steel at 600°C under combined torsion and tension. Following each of three different amounts of prior torsional creep, plastic deformation tests were performed under torsions in the same and opposite directions of the prior creep and axial tension, respectively. The experimental results showed the marked influence of prior creep on subsequent plasticity. That is, the flow stress in the subsequent plastic deformation after creep became larger than the one in the corresponding pure plastic test where the prior creep strain in the combined creep-plasticity test was replaced by a plastic strain of the same amount. Finally, predictions by means of existing separated and unified constitutive equations were discussed on the basis of the experimental results.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):264-267. doi:10.1115/1.3225656.

Tensile necking in anisotropic bars is analyzed in the spirit of P. W. Bridgman’s treatment of the isotropic case. Anisotropic plastic flow causes an initially axisymmetric bar to develop an elliptical neck. Using physical approximations analogous to Bridgman’s, an approximate analytical solution for the stress distribution is obtained. The solution is shown to be asymptotically correct in two important limiting cases: (a) the fully developed anisotropic neck, and (b) the isotropic limit. In the latter case it is shown that the solution is a member of a one-parameter family of solutions, which includes the Bridgman and the Davidenkov and Spiridonova solutions.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):268-272. doi:10.1115/1.3225657.

A compact shear specimen configuration, consisting of three legs with the outer two loaded axially in a direction opposite to the inner one, has been used for several mixed-mode fracture studies. From a detailed computer analysis of this specimen, it is shown that the loading boundary conditions play an extremely important role in determining the state of stress at the crack tip. By simply changing the flexibility of the loading fixture, the specimen can be subjected to a range of mixed mode conditions from almost all Mode I to virtually pure Mode II. Data of other researchers are reviewed in light of this finding. It is shown that by applying loads obliquely to the outer legs pure Mode I loading may also be obtained with this specimen.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):273-279. doi:10.1115/1.3225658.

Interaction of fatigue with corrosion and creep has been analyzed through a parameter [Fi ] introduced at the crack propagation stage. Assuming the effect of corrosion and creep to become dominant below a certain frequency, a model is proposed which is able to explain the stress-hold and the strain-hold effects on the fatigue life in time dependent fatigue. Beyond a certain period stress-hold leads to time-dependent and strain-hold leads to cycle-dependent interaction life. By suitably evaluating the parameter [Fi ], life under any type of loading condition can be estimated. Based on the parameter, an interaction diagram is proposed for predicting the fatigue life in time dependent high temperature low cycle fatigue.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):280-285. doi:10.1115/1.3225659.

The effects of various loading wave forms on the fatigue crack growth rate of 2 1/4 Cr-1Mo steel at 482 and 538°C tested in air have been determined. Scanning electron fractography was used to measure the fatigue striation spacing on the fracture surface of strain controlled push-pull fatigue tests. The fatigue striation spacing was then used as a monitor of the fatigue crack growth rate in these specimens once a fatigue crack had been initiated. Constant strain hold periods were introduced during each cycle at various points of the hysteresis loop. Both increasing temperature and strain range increased the fatigue crack growth rate for continuously cycled tests as expected. However, when a hold period was introduced, the crack growth rate was dominated by the time that preceded each strain reversal; temperature and strain range effects became secondary to hold time. The effect of hold periods for the conditions examined is primarily crack tip oxidation rather than creep crack growth during the hold period.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):286-294. doi:10.1115/1.3225660.

Cr-Mo-V steels are used extensively as the rotor material in the High Pressure and Intermediate Pressure Sections of modern steam turbines. The toughness of these rotors has a major influence on the reliability and efficiency of the turbine and the overall economy of operation and maintenance of the plant. The metallurgical factors affecting the toughness of the rotors and the methods to improve the toughness are now understood better than ever before. This paper will present a broad overview of the materials and design aspects of the toughness of Cr-Mo-V rotors with emphasis on the salient results of recent research programs aimed at improving their toughness.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):295-300. doi:10.1115/1.3225661.

As an integral part of the punch press monitoring research program, the Acoustic Emission (AE) signal emitted from a Minster1 #3 punch press is completely characterized in terms of signal component identification, relative timing and signal amplitude of each component. The AE signal generated during punching is found to consist of three components: initial impact, shear fracture and rupture. Effects of stock hardness are then examined in terms of relative timing and amplitude of those three components. Good correlations are found between stock hardness and the corresponding AE signals (and thus AE counts).

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):301-306. doi:10.1115/1.3225662.

In a previous paper, the acoustic emission (AE) signal emitted from a Minster1 #3 punch press was completely characterized and effects of stock hardness were examined. The AE signal emitted during punching was found to consist of three components: initial impact, shear fracture and rupture. Effects of stock hardness on the AE signal were then examined in terms of relative timing and amplitude of these three components and an excellent correlation was found between AE count and stock hardness. As a continuation, effects of stock thickness, tool size and tool wear are examined in this report. Similar to the previous study, their effects are investigated qualitatively in terms of relative timing and amplitude of the AE component and quantitatively in terms of AE count. Again good correlations are found between these process variables and the AE signals.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):307-312. doi:10.1115/1.3225663.

Directionally solidified materials are being increasingly used in aircraft engines. These alloys are anisotropic due to the well aligned crystalline structure with additional considerations including large grain sizes and perturbations in the local orientation. In this paper, the Bishop-Hill method is combined with nonlinear optimization techniques to predict the anisotropic plastic behavior of an ideal directionally solidified FCC material subjected to off-axis uniaxial loadings. A comparison of these results is made with a continuum theory.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1983;105(4):313-318. doi:10.1115/1.3225664.

Incremental failure was observed when two different loading conditions, pressure and expansion, were applied alternatively to an expansion joint. Neither of the conditions was capable independently of failing the expansion joint. When the conditions occurred together, only a small amount of plasticity was observed. But when the expansion was cycled while holding pressure constant, incremental plastic deformation occurred during each cycle which was cumulative to that of past cycles. The joint was dimensionally unstable over a large number of expansion cycles. Analytical and experimental results are presented in an attempt to explain the observed phenomenon.

Commentary by Dr. Valentin Fuster


Commentary by Dr. Valentin Fuster


J. Eng. Mater. Technol. 1983;105(4):319. doi:10.1115/1.3225666.
Topics: Fatigue design
Commentary by Dr. Valentin Fuster

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