bluuebunny/crossref_metadata_2025 huggingface dataset:
Strength and Stress-Strain Characteristics of Clays Subjected to Seismic Loading Conditions
Authors: Thiers GR , Seed HB
Published: March 2009

An attempt is made to relate the results of unconfined compression tests on saturated clays to the strength and bilinear stress-strain parameters which will govern the behavior of the clay during and after earthquakes.

Simple-shear pulsating-load tests on three soils indicate that while the decrease in dynamic strength with number of cycles increases with the failure strain observed in static strength tests, a plot of the product of failure strain x dynamic strength (in percent of static strength) against number of cycles is about the same regardless of the failure strain.

Cyclic-loading triaxial compression tests in which the peak strain was controlled were also performed on the three soils. After 200 cycles of loading the compressive strength was measured under static conditions. It was found that when the peak cyclic strain is less than one half the static failure strain, the strength after cyclic loading is at least 80 percent of the original strength. For larger strains higher strength losses were observed.

The nonlinear stress-strain curves obtained from various cycles in the cyclic loading tests were approximated by a bilinear model defined by three parameters (two moduli and a yield strain). The decrease in the ratio of dynamic modulus/ original static modulus with the ratio of cyclic strain-failure strain is about the same for all three soils for a given number of cycles. A similar relationship for yield strain was found, although this parameter increases with cyclic strain and is virtually unaffected by number of cycles.

The static modulus of each soil tested was greatly reduced by the cyclic loading, decreasing to about one half its original value in tests where the cyclic strain was one half the failure strain.
Factors Affecting the Cyclic Loading Strength of Soil
Authors: Lee KL , Fitton JA
Published: March 2009

Pulsating loading triaxial tests were performed on saturated samples of soil to determine the effect of grain size, grain-size distribution, and grain shape on the strength of soil under simulated earthquake loading conditions. Comparing soils tested at the same relative density and confining pressure it was found that fine silty sands were the weakest, with 3/4-in. gravel being two times stronger and compacted clay being up to three times stronger. The effect of grainsize distribution and grain shape was considerably less significant than the grain size.
Torsional Shear Testing Technique for Dynamic Properties of Clay
Authors: Krizek RJ , Franklin AG
Published: March 2009

The testing technique and apparatus described herein implement the determination of dynamic stress-strain-time properties of clay soils over several decades of the frequency spectrum, including the normal frequency range of most earthquakes. The basic device used for these tests is the Weissenberg rheogoniometer, with some modifications to enhance its adaptability to testing soils. The soft clay test specimens are held in a cone-and-plate sample holder, while a hollow cylinder geometry is more suitable for stiff clay specimens. These geometries satisfy reasonably well the desirable condition that stresses and strains be homogeneous within the test specimen, and they allow tests to be conducted over a wide range of moisture contents. The specimens are subjected to oscillatory torsional shear deformations, and the moment response is measured; with the use of the specimen geometry and the homogeneity of stress and strain, these deformations and forces are readily converted to shear stresses and shear strains. In addition to the magnitudes of stress and strain, the time difference between corresponding points on the stress and strain curves is measured, allowing computation of a phase angle between stress and strain. Two types of oscillatory tests are particularly convenient to perform in this apparatus; in one case, the frequency is maintained constant while the deformation amplitude is varied, while in the other case, deformation amplitude is held constant and frequency is varied. Data obtained by this technique allow the evaluation of several aspects of the dynamic clay behavior, such as the effect of stress history, the degree of nonlinearity in the stress-strain response, and the extent to which presently available theories, such as linear viscoelasticity, can be used to interpret the mechanical behavior. For example, the energy dissipated in a unit volume of the sample over a single cycle of deformation can be calculated by using the phase angle and the stress and strain amplitudes; alternatively, this dissipated energy can be measured directly by means of a hysteresis loop, and the two values can be compared.
Case Histories in Foundation Vibrations
Authors: Margason BE , McNeill RL , Babcock FM
Published: March 2009

Reliable analysis of foundation vibrations is available for practicing engineers. Present techniques follow those based on an elastic half-space model. The frequency of maximum response and geometric damping is obtained from machine and foundation geometry and the soil shear modulus. Knowing the unbalanced machine forces and moments, amplitudes can also be obtained. Five case histories illustrate the accuracy of these techniques. Case one is for two V-12, 4000-hp engines; it compares a predicted rocking frequency of 342 rpm with measured frequencies of 339 and 341 rpm. Case two illustrates the validity of predicting rocking amplitudes for a four-cylinder horizontal compressor; the predicted rocking motion of 0.0042 in. compares well to the 0.003 in. actually measured. Case three describes the AMRAD radar tower; the predicted average rocking frequency of 7.5 Hz compares well with 6.3 Hz measured after construction. Agreement in the torsional mode is not as good. Case four illustrates the analysis of a large car shredder subjected to transient moments; using a phase-plane analysis the predicted rocking frequency is 7 Hz compared to a measured frequency of 7.6 Hz. Case five demonstrates the accuracy of a simple transient excitation test for obtaining the frequency and damping of a passive foundation slab.
Effect of Temperature and Strain Rate on Low-Cycle Fatigue Resistance of AISI 304, 316, and 348 Stainless Steels
Authors: Berling JT , Slot T
Published: March 2009

Results are reported of strain-controlled, low-cycle fatigue experiments conducted on annealed AISI 304, 316, and 348 stainless steels at temperatures of 430, 650, and 816 C with strain rates of approximately 4 × 10-3, 4 × 10-4, and 4 × 10-5 s-1. The investigation generally shows that fatigue life measured in terms of sustained loading cycles is affected adversely by the increase in temperature and by the decrease in strain rate. The test results were generated with servo-controlled, hydraulic testing machines using inductively heated hourglass-type specimens. Cyclic stress-strain data are compared with monotonic stress-strain data obtained from tension tests performed at the same temperatures and strain rates.
Low-Cycle Fatigue Study of Columbium Alloy D-43
Authors: Swindeman RW
Published: March 2009

A machine was developed to study the low-cycle fatigue characteristics of refractory metals in vacuum at high temperatures. Operating capability included temperatures up to 1400 C, loads to 4.45 × 104 N (10 ksi), and frequencies from static to 10 Hz. The machine operated in a push-pull mode and was stroke controlled.

To minimize material required for testing, grips were designed to operate at nearly the same temperature as the specimen. A typical specimen geometry was a rod, 76 mm long with a test section 12.7 mm long and 5.18 mm in diameter.

A series of tests was performed on a columbium alloy, D-43, at temperatures ranging from 20 to 1204 C and cyclic plastic strains from 0.3 to 4 percent. Data at 20, 871, and 1093 C revealed that D-43 conformed to the Coffin-Manson equation, wherein cycles to failure was related to plastic strain range by a power function.

The plastic strain resistance was found to increase with increasing temperature and to exhibit a maximum around 871 C. Up to 1024 C cyclic strain resistance remained better than or equivalent to that at room temperature.

Posttest examination of specimen revealed ductile, transgranular failures at all temperatures.
Effect of Temperature on the Fatigue of Nickel at Varying Oxygen Pressures
Authors: Stegman RL , Shahinian P
Published: March 2009

The fatigue of high-purity nickel in reversed bending has been studied as a function of oxygen pressure at temperatures of 20, 300, 425, and 550 C. The environmental effect was examined further as a function of strain at 300 and 550 C. S-shaped curves of fatigue life versus pressure obtained at each temperature were generally similar to one another in shape but did show some differentiating features. At all four temperatures there is a transition region in which fatigue lives drop fairly sharply with increases in oxygen pressure until a high pressure plateau is reached at what is termed the maximum transition pressure. This transition pressure is about the same at 300 C as at 20 C but progressively increases with further temperature increases. When these transition pressures are evaluated in terms of a theoretical model of the environmental effect, the agreement is found to be good at low temperatures. However, at high temperatures, the increase in transition pressure is much greater than would be predicted. This shift is attributed to oxidation along crack surfaces reducing the number of oxygen molecules which can reach the advancing crack tip. Supporting evidence is presented in the form of an activation energy calculation. While there was no apparent effect of strain on the maximum transition pressure at either 300 or 550 C, a higher strain decreased the magnitude of the environmental effect at the lower temperature. This behavior probably is related to strain hardening at the lower temperature which is not present at the higher temperature.
Influence of Temperature on Reversed Creep
Authors: Kitagawa M , Jaske CE , Morrow J
Published: March 2009

Torsional reversed creep data are presented for tubular specimens of commercially pure aluminum to illustrate the influence of test temperature on creep deformation resistance under repeated stress reversals. Test temperatures range between 300 and 510 K. These data plus results on other metals show that multiple stress reversals cause a deceleration of creep deformation at test temperatures below about 0.4 of the absolute melting temperature. A significant acceleration of creep may occur at higher temperatures. An optimum temperature for maximum acceleration of creep occurs at a temperature of approximately half of the melting temperature.

The engineering significance of the decrease in creep deformation resistance at high temperatures due to multiple stress reversals is discussed. Creep rupture time and the failure life in high-temperature fatigue or thermal fatigue with large hold times may be reduced significantly by an acceleration of creep at high temperatures.
High-Temperature Low-Cycle Fatigue Experiments on Hastelloy X
Authors: Carden AE , Slade TB
Published: March 2009

Low-cycle fatigue behavior of Hastelloy X at elevated temperature is presented. We studied the effects of test temperature, cycle frequency, and stress temperature arrangement with special attention given to the minimum ductility (short-time tension test) at or near 1300 F. Isothermal fatigue data at 800, 1300, 1500, and 1800 F are presented along with strain controlled thermal fatigue data for temperature ranges of 600 to 1800, 800 to 1300, and 1800 to 1300 F. The method of universal slopes can be used to describe the fatigue behavior under elevated isothermal and cyclic thermal fatigue conditions. The thermal fatigue behavior determined from controlled strain tests can be applied to the thermal cycle behavior of bundles of thin tubes joined to a rigid plate.
Some Microstructural and Alloying Effects Upon Low-Cycle Fatigue Life of Pressure Vessel Steels
Authors: DePaul RA , Pense AW
Published: March 2009

Loading by constant deflection reversed bending was applied to Lehigh cantilever fatigue specimens of a plain carbon steel, A-516, and three low-alloy steels, A-302, A-387B, and HY-80. Fatigue life over the 5000 to 100,000 cycle range was investigated at a loading frequency of 200 cpm. The effect of microstructure was observed by comparing the fatigue resistance of specimens of equal tensile strength but different heat treatment histories. Normalized structures proved to be superior to the corresponding spray quenched and tempered conditions when using total strain range as the test parameter. Where similar structures were compared, the 100,000 cycle fatigue life was found to be related to tensile strength. The fatigue resistance of the low-alloy steels was influenced markedly by heat treatment while the plain carbon steel essentially was unaffected. Increased alloy content altered the slope of the fatigue curve such that the plain carbon steel tends to be superior in the 5000 cycle range, while the low-alloy steels excel above the 20,000 cycle region. This results in a grouping of the curves as to steel composition.
Effect of Microstructure on the Fatigue Properties of Ti-6Al-4V Bar
Authors: Bartlo LJ
Published: March 2009

Microstructure can have a significant effect on the mechanical properties of titanium alloys. The extent of this effect on the fatigue properties of the Ti-6Al-4V alloy in small diameter bar (0.625 in., 15.875 mm) was studied. Microstructural variations were produced by heat treating from 1550 to 1950 F at 100 F intervals. Three different cooling rates (furnace cooling, air cooling, and water quenching) were employed for each temperature. The room-temperature tensile, smooth, and notch-fatigue properties were evaluated for each thermal condition.

Thermal treatments that resulted in grain coarsening were found to lower the fatigue strength of the alloy. Beta quenching resulted in good tensile and fatigue strengths but low tensile ductility. Optimum tensile and fatigue properties occur in material consisting of fine grained alpha-beta structures or in material containing mixtures of fine primary alpha and martinisitic alpha.
Atmospheric Stress Corrosion Testing of Aluminum Alloys
Authors: Romans HB , Craig HL
Published: March 2009

Results are given for stress corrosion studies carried out on a number of aluminum alloys. Testing was done at Aruba, Netherlands Antilles, Kure Beach, N. C., and Richmond, Va. These sites provided environments that ranged from tropical marine to mild industrial. Failure times are compared with laboratory and service results. One aim was to study the effect of prolonged aging at ambient temperatures. In aluminum-magnesium alloys this aging may produce a metallurgical structure which makes these alloys subject to stress corrosion cracking. Specimens aged at higher temperatures do show this response in laboratory and atmospheric tests. From these accelerated data, Arrhenius plots predict these alloys should become susceptible within two to five years if aged at ambient temperatures. However, test results do not bear this out. It is possible to draw erroneous conclusions from only one type of test. For at least one alloy, the rate of failure is much more rapid in the atmosphere than in an accelerated laboratory test. This has been attributed to an interaction between specimens tested in a communal solution. In conclusion, either a laboratory or an atmospheric test is, in itself, insufficient to characterize the stress corrosion behavior of an engineering material. These two tests give data that are complimentary instead of supplementary. Both types are necessary to evaluate the potential hazards of a material having some degree of stress corrosion susceptibility.
Atmospheric Exposure of Light Metals
Authors: Brandt SM , Adam LH
Published: March 2009

This paper summarizes a ten-year atmospheric corrosion test program for aluminum and magnesium base alloys sponsored by the American Society for Testing and Materials under the direction of committee B-7 on Light Metals and Alloys Subcommittee VIII on Atmospheric Exposure Tests.

The program included fourteen cast, nine wrought, and three clad aluminum alloys and five cast and four wrought magnesium alloys. The specimens, exposed at five outdoor exposure sites in the United States, were tested after exposure periods of six months, one, three, five, and ten years.

The tensile strength of the exposed specimen was compared to that of the control specimen which was stored in a sealed container. The per cent changes in tensile strength for the exposed specimens compared to the control specimens are included in the data presented.
Corrosion Test Results on Fifteen Ferrous Metals After Seven-Years Atmospheric Exposure
Authors: Mannweiler GB
Published: March 2009

This is a progress report covering findings on the removal of ferrous corrosion specimens that had been exposed for seven years to the atmospheres of five different test sites, which included rural, marine, and industrial environments. The materials employed were ten malleable and pearlitic malleable irons, two ductile irons, and three rolled steels. Previous removals of companion sets of specimens had been made after one- and three-years' exposure. A final set is scheduled for removal in 1970 after twelve-years' exposure. The appearance of the corroded plates and weight losses were evaluated.
Hard-Rolled Aluminum Alloys
Authors: Mattsson E , Lindgren S
Published: March 2009

In 1955 exposure tests were started with the following architectural aluminum alloys in hard-rolled condition: high-purity aluminum, commercial purity aluminum (with and without 0.14 per cent copper), AlMn1.2 (with and without 0.14 per cent copper), AlMg0.65, AlMg2.5, Alclad (with core of AlMn1.2 and cladding of AlZn1). Panels of the alloys were exposed on five sites in Sweden with rural, marine, urbanmarine, and industrial atmospheres.

After one-, three-, six-, and ten-years' exposure, specimens were taken in and examined with respect to pitting, layer corrosion, and change in mechanical properties.

From the results it may be concluded that the hard-rolled AlMg alloys are well suited for architectural purposes. There is no risk of blistering, and the pitting corrosion resistance is as good as for unalloyed aluminum. With hard-rolled, unalloyed aluminum of commercial purity and AlMn1.2, both without copper, the risk of blistering cannot be disregarded, at least not in a marine atmosphere. Here layer corrosion blisters were formed on the alloys mentioned in most cases already during the first year of exposure. After the initial period, however, they generally developed very slowly. One way to overcome the susceptibility to blistering apparently is to add about 0.1 to 0.2 per cent copper. Another remedy might be to use alloys in half-hard condition, which is common practice. The alclad surface developed a rather rough appearance.

It may be concluded that all the alloys tested will last for several decades in outdoor use, as far as the mechanical properties are concerned. Corrosion, however, may affect the appearance by pitting, blistering, roughening, and discoloration. Often, however, such “aging phenomena” may be regarded as an attractive patina.
Atmospheric Corrosion of Aluminum and Its Alloys: Results of Six-Year Exposure Tests
Authors: Carter VE
Published: March 2009

Results of atmospheric corrosion tests on four aluminum alloys at five sites in Great Britain showed that corrosion, in the form of pitting, increased with atmospheric pollution. Corrosion/time curves became parallel to the time axis within two years at mild sites but at polluted industrial sites had not done so in six years. Aluminum alloys were more heavily attacked than high-purity aluminum, and a pure aluminum cladding gave considerable protection to an aluminum-copper-magnesium alloy.
Atmospheric Corrosion of Carbon and Low Alloy Cast Steels
Authors: Briggs CW
Published: March 2009

Nine carbon and low alloy cast steels cast in panel form, some machined and others unmachined, were exposed in marine and industrial atmospheres for periods of one-, three-, seven-, and 12-years and recorded as to weight loss information. The weight loss was converted to corrosion rate in terms of inches penetration per year (ipy) and milligrams lost per square decimeter per day (mdd). Comparisons were made and cast steels containing nickel, copper, or chromium as alloying elements have corrosion resistance superior to carbon cast steels or those containing manganese when exposed to atmospheric environments. Increasing the nickel and the copper contents of cast steel increases the corrosion resistance in all three atmospheric environments. Unmachined cast steel surfaces, with the casting “skin” intact, had no significant effect on the corrosion resistance of cast steels when compared to machined surfaces regardless of the atmospheric environment.
Performance of Aluminum Alloys at Other Test Sites
Authors: Ailor WH
Published: March 2009

The well documented pattern of corrosion behavior for aluminum alloys is confirmed for the seven-year exposures at Corpus Christi, Tex.; Richmond, Va.; McCook, Ill.; and the Kure Beach, N. C., 800-ft site. A decrease in the corrosion rate, as determined by weight loss, was evident for all sheet alloys after about the second exposure year. Likewise, the depth of pitting decreased with time: very slight increases in depth were noted between the second and seventh years in most cases.

Results indicate that the McCook site is the most severe, with the Richmond location, the Corpus Christi exposure, and Kure Beach 800-ft site in order of decreasing severity.

The value of cladding basic alloys such as 3003 and 6061 was demonstrated again. The claddings effectively protected the core alloys from pitting and general corrosion and the clad alloys showed negligible changes in mechanical properties at all sites after seven years.

Other than the 2024 aluminum-copper alloy which showed intergranular corrosion for some hard tempers at the most severe sites, all alloys showed pitting corrosion to some extent. Maximum pit depths included 14.7 mils for the 2024-T36 alloy, 10.0 mils for the 5154-H34 aluminum-magnesium alloy, 5.2 mils for the aluminum-magnesium silicide alloy 6061-T6, and 6.3 mils for the high-purity aluminum sheet. With the exception of the 2024 metal, these deepest pits occurred at the McCook site. The deepest pit found on the Kure Beach 800-ft site panels measured 6.1 mils, and the deepest pit for most Corpus Christi panels was 5.4 mils (2024 alloy panels having some intergranular attack had measured pits as deep as 14.7 mils).

A corrosion rate of 0.175 milligrams per square decimeter per day (mdd) for 2024-T36 alloy at McCook was the highest found. If we exclude the 2024 alloys, no corrosion rate greater than the 6061-T6 rate of 0.125 mdd was found. High purity aluminum showed rates from a low of 0.004 mdd at Kure Beach to 0.044 mdd at McCook.
Effect of One Per Cent Copper Addition on the Atmospheric Corrosion of Rolled Zinc
Authors: Dunbar SR
Published: March 2009

Atmospheric corrosion characteristics of a commercial rolled zinc alloy containing 1 per cent copper and one unalloyed grade were evaluated after two- and seven-year exposures under the Committee B-3 1957 test program on atmospheric corrosion of nonferrous metals. Comparisons were made with the behavior of three unalloyed grades included in a 20-year Committee B-3 program initiated in 1931. The usefulness of tension tests for determining corrosion rates was explored in both programs.

Weight loss determination appears to be the most reliable means of assessing corrosion rates for zinc. Good agreement among zinc corrosion rates in the two programs was obtained. Zinc composition was found not to significantly influence corrosion rates.

Pitting occurred in the copper bearing alloy most probably as a result of local galvanic action. The pit depth-total penetration ratio decreases as total penetration increases. Tensile properties of zinc were not significantly affected after seven-year exposure. Therefore, pitting is not believed to be of practical importance.

Tension tests are not useful for evaluating corrosion damage in zinc unless a means of compensating for aging effects can be found.
Measurement of Atmospheric Factors Affecting the Corrosion of Metals
Authors: Guttman H , Sereda PJ
Published: March 2009

Atmospheric factors, namely, time of wetness of corroding metal panels, panel temperature, and atmospheric sulfur dioxide and atmospheric chloride content, were measured at four inland and three coastal North American test sites while corrosion data for steel, copper, and zinc were being developed. Corrosion losses experienced by panels of these metals which were exposed at different times of the year for similar periods of time showed considerable variation at all sites.

Statistical analyses show conclusively that the atmospheric factors measured completely control the rates of corrosion at all sites for at least the initial month. For longer periods of time control of the corrosion process remains with the atmospheric factors in some cases, and in others it is gradually transferred to factors related to the changing surface conditions resulting from accumulation of corrosion products and foreign agents.

At the sites where the atmospheric factors control corrosion, the empirical equations developed enable one to predict the corrosion losses of steel, copper, and zinc from a knowledge of the atmospheric factors. They also now make it possible to account for variations in observed corrosion losses experienced by panels exposed at different times of the year.
Stress Intensity Factor for an Elliptical Crack Approaching the Surface of a Plate in Bending
Authors: Shah RC , Kobayashi AS
Published: March 2009

Stress intensity factor for an embedded elliptical crack approaching the free surface of a semi-infinite solid and subjected to a linearly varying pressure is presented in a nondimensional form as a function of position around the crack periphery, crack aspect ratio, and crack distance from the free surface. These stress intensity factors are determined numerically using an alternating technique with two solutions. The first solution deals with an elliptical crack subjected to normal loading expressible in a polynominal of x and y. The second solution involves stresses in a half space due to prescribed normal and shear stresses on the surface. Stress intensity factors for an elliptical crack approaching the free surface of a plate subjected to pure bending are then determined. Stress intensity factors for a semi-elliptical surface crack in a plate subjected to pure bending are also estimated for various crack aspect ratios and crack depth to plate thickness ratios.
A Study of Local Stresses Near Surface Flaws in Bending Fields
Authors: Marrs GR , Smith CW
Published: March 2009

A set of photoelastic experiments utilizing stress freezing and slicing techniques was conducted in order to estimate stress fields near naturally grown deep surface flaws in plates under approximately cylindrical bending fields. Geometries investigated ranged over crack depth to crack length ratios of approximately 0.25 to 0.45 and over crack depth to plate thickness ratios of approximately 0.35 to 0.45. Results were compared to an approximate theory devised by F. W. Smith [6]. In order to achieve a comparison consistent with linear elastic fracture mechanics, the effect of the experimental non-linear zone due to finite rotations very near the crack tip was minimized by extrapolating across it. The plastic zone correction in the Smith theory was neglected.

Results indicated that the Smith theory will predict the proper order of magnitude of the stresses near the crack border both in the region of maximum crack penetration and where the crack border intersects the tensile surface of the plate. However, in all tests the predicted stresses were lower than the experimental stresses in the former region and higher than the experimental stresses in the latter region.
Stress Intensity Factors for Surface Cracks in Bending
Authors: Grandt AF , Sinclair GM
Published: March 2009

Fracture mechanics solutions applicable to surface cracked plates in bending are studied. The flawed plate is modeled as a two-dimensional beam containing a spring to find the stress intensity factor at the point of intersection of a semielliptical surface crack with the free boundary. Results are given for cracks of various shapes and sizes. These findings, along with previous analytical solutions obtained from the literature, are then compared with experimental data. Since it is difficult to measure surface cracks in metals, polymethylmethacrylate, a transparent polymer, was selected for the test material. First, the relation between fatigue crack growth rate and range in stress intensity is calibrated for polymethylmethacrylate. Measured fatigue crack growth rates for surface flaws in bending are then used to calculate experimental values for the stress intensity factor which are compared with theory.
Some Crack Tip Finite Elements for Plane Elasticity
Authors: Wilson WK
Published: March 2009

Two types of finite elements which can adequately represent the singular stress state at the tips of cracks in plane elastic structures are presented. By combining these special crack tip elements with more conventional finite elements, a more efficient analysis of crack structures is possible. One element is circular in shape and its imposed displacement pattern is that of the four leading symmetric terms of the Williams stress function. The other element is triangular in shape and its imposed displacement pattern is that associated with the crack tip singularity. The convergence and efficiency of these elements is studied.
Fatigue Threshold Crack Propagation in Air and Dry Argon for a Ti-6Al-4V Alloy
Authors: Bucci RJ , Paris PC , Hertzberg RW , Schmidt RA , Anderson AF
Published: March 2009

Fatigue crack propagation experiments on a Ti-6A1-4V alloy were carried out within the framework of linear elastic fracture mechanics. Crack propagation results encompassing a wide range of fatigue crack growth rates, Δa/ΔN, and stress intensity range, ΔK, were plotted in the conventional manner (that is, log-log plots of Δa/ΔN as a function of ΔK) for studies conducted in room temperature air and dry argon environments. Corresponding fatigue striations formed in both environments were measured and compared with macroscopic crack extension rates.

Examination of very low fatigue crack propagation rates at low ΔK levels disclosed a stress intensity threshold level below which Mode I fatigue crack propagation became insignificant.

In a limited investigation at very low fatigue crack growth rates, the fatigue threshold levels were observed to decrease with increasing stress ratio, R (ratio of σmin/σmax= Kmin/Kmax). The influence of stress ratio also was observed at ΔK levels above the threshold; cyclic crack growth rates increased for the increased values of R. However, for the ranges of ΔK, R, and growth rate considered in this work, the R ratio influence appeared most pronounced at the lowest growth rates and lessened with increasing ΔK.

Comparable fatigue crack growth tests (R = 0.33) conducted on the Ti-6A1-4V alloy in air and inert dry argon at room temperature yielded almost identical results for cyclic crack growth rates encompassing those associated with the fatigue threshold (Δa/ΔN ≃5 × 10-9 in./cycle) upward past 10-5 in./cycle. Within this range, the fracture surface morphology changed from a cleavage-like appearance at threshold levels to a typically striated and dimpled appearance at higher growth rates.

No significant difference in fatigue crack growth rate behavior was reported for Ti-6A1-4V specimens tested in either the STA (solution treated and aged) or STA + annealed heat treated condition.
The Effect of Frequency upon the Fatigue-Crack Growth of Type 304 Stainless Steel at 1000 F
Authors: James LA
Published: March 2009

The fatigue-crack growth rate of Type 304 stainless steel was studied at 1000 F with cyclic frequencies ranging over approximately 4 1/2 orders of magnitude. It was found that as frequency decreased, the fatigue-crack growth rate showed a significant increase, and the behavior could be characterized by an equation of the form da/dN = A(f) [ΔK]n, where the exponent n represents a constant for all of the frequencies studies.
The Nature of Stimuli
Authors: Foster D , Danker WH
Published: March 2009

Since our primary objective is to aid ASTM, a review was made of the materials evaluated by ASTM. It was found that these materials could be roughly classified into ten major groups (Table 1). Then the characteristics of these materials were grouped as stimuli opposite the receptor they affect (Table 2).
Vision
Authors: McNamara BP
Published: March 2009

Vision is a complex phenomenon consisting of several basic components. Sight from external sources is brought to a focus on the retina of the eye. Changes are produced which initiate electrical impulses. These are conducted over the optic nerve and optic tract to the brain where the visual sensation is perceived and interpreted.
Intercorrelation of the Senses
Authors: Stone H , Pangborn RM
Published: March 2009

Receptors, such as the eye, the ear, the organs of smell and taste, and the more diffuse sensory equipment of the skin, are found in all higher animals. Not all of the senses are equally helpful to the organism; the hawk's keen visual acuity is well documented, as is the bat's auditory sensitivity to meaningful echoes and the bloodhound's perception of olfactory clues. Although man derives comfort from touch and the pleasures of odors and tastes, his world is largely regulated by sound and light, calling into play the senses he finds most valuable in communication, navigation, and detection of objects at a distance. The conception of size, shape and color, or proximity and remoteness of light and shade, assist us in relating to our environment to a much greater degree than do the other senses. For example, texture, essentially a function of touch, can be conveyed visually from distant objects, after the individual has had sufficient preliminary experience. Through experience and association, we can conceptualize sensations of sound, touch, pain, temperature, taste, and odor by merely viewing the stimulus object. Misjudgments, of course, are known to occur.
Psychological Principles of Subjective Evaluation
Authors: Klemmer ET
Published: March 2009

The papers in this series on Physiology of the Senses describe the nature of man's receptors in terms of the ranges of stimulation to which they are sensitive and other key properties of these sensors. In addition to the characteristics of peripheral sense organs (such as sensory adaptation) which are important in assessing the results of subjective tests, there are many psychological factors of less obvious physiological basis which must be considered. The most significant and general of these psychological factors is the relevance of the judge's or observer's responses in the test situation for predicting the behavior of the ultimate consumer. Indeed, this is the very heart of the problem of subjective evaluation and is the first topic of the present section. There are also a large number of psychological factors which appear as extraneous or confounding effects. While not central to the test procedures, these may invalidate predictions made on the basis of subjective tests. A list of such confounding factors is given in the second part of this section, along with a definition of each.
Concentrations of Odorous Vapors in Test Chambers
Authors: Turk A
Published: March 2009

Odor test chambers are used either for evaluation of odor-reducing devices, or to provide odor-free environments in which a jury can measure the odors of materials, products, or foods. It is important to consider the factors that determine the changing and equilibrium concentrations of odorous vapors in such chambers.
Measurement of Irritation
Authors: McNamara BP
Published: March 2009

Irritation is a local action on the skin or mucosal tissue. It can be induced by thermal, mechanical, chemical, or electrical stimulation. The stimulation evokes impulses from the receptor organ. The impulses may be conveyed over neural pathways to the brain where they are translated into perceptual sensations, that is, warmth, cold, itching, pain. Impulses also may be carried to muscles or glands which react to the stimulus.
Principles of Psychological Test Methods (Judgmental Methods—Appearance)
Authors: Hoffman JA
Published: March 2009

The visual appearance of a surface or volume is related to the illumination by which it is viewed, the conditions under which it is viewed, and the visual response characteristics of the observer. The appearance characteristics of greatest interest are those relating to: 1. Luminance (brightness, lightness). 2. Specular reflectance (gloss, luster, sheen). 3. Chromaticity (hue and saturation). 4. Transparency (translucence). 5. Nonuniformity (texture, pattern, contrasting areas such as those caused by flaws or foreign substances, etc.).
An Assessment of Accelerated Testing
Authors: Yurkowsky W , Fulton DW
Published: March 2009

The state of the art in accelerated life testing at the part level is assessed and found to be far less advanced than generally believed. Requirements and procedures to be followed in developing valid testing methods are presented. The use of a multidisciplined approach is found to be essential.
Determination of Degradation of Nylon 66 Using Differential Scanning Calorimetry
Authors: Long TS
Published: March 2009

An analytical technique which will detect degradation in nylon 66 has been developed. This is accomplished by means of differential scanning calorimetry (DSC). The technique makes use of the double melting point phenomena to determine various degrees of degradation. This method requires a very small sample size (4 mg) and can be completed within 2 h. A discussion of other techniques and the disadvantages of each is also given. Finally, a relationship between the analytical technique and the physical properties of nylon 66 is presented.
The Early Detection of Fatigue Damage by Exoelectron Emission and Acoustic Emission
Authors: Moore JF , Tsang S
Published: March 2009

The paper describes the development of nondestructive test methods capable of determining the extent of fatigue damage and providing a means of predicting the future safe life of aerospace materials and structures. The fatigue process of 1100-0 aluminum was studied by means of exoelectron emission and acoustic emission measurements. The exoelectron observations were made in both vacuum and air. The exoelectron emission measurement in vacuum was accomplished by counting the emission events for selected time intervals. The measurements in air were performed using a specially developed current-measuring system with a resolution of 10-15 A. The acoustic emission measurement in air was based on the number of acoustic events occurring in selected time intervals during fatigue. The exoelectron emission curves exhibited an early rapid rise and fall of emission intensity, and again a rapid rise near the end of the test. The initial emission decrease coincided with metallurgically observed changes of surface slipbands. There was also a trend indicative of a stress-independent relationship between the change of exoelectron emission current and the percentage of life after a selected number of fatigue cycles. Analysis of the acoustic emission data showed a marked increase in emission rate in less than 50 percent of the fatigue life of the material.
Empirical Strength Theories
Authors: Sendeckyj GP
Published: March 2009

The formulation of empirical strength criteria is considered and some general principles that should be satisfied by all strength criteria are discussed. The available strength criteria for isotropic materials, with unequal strengths in tension and compression, are discussed in the light of the general principles. Some recent criteria for anisotropic materials are also presented. Contributions from the Russian literature are extensively referenced.
Predicting the Service Life of Neoprene Launch Tube Liner Pads for the Poseidon Missile
Authors: Rudd GE , Meier JF , Rosenblatt GB
Published: March 2009

Molded neoprene liner pads used to support the Poseidon missile in the launch tube were found to stiffen with time. Increasing the postcure reduced the stiffening rate. By aging pads at several moderately elevated temperatures it is possible to predict the service life of pads with several different postcures. The results of such aging tests, including the predicted service lives, are presented in this paper.
Fundamentals of Radiation Effects Testing
Authors: Sinclair EE , Simmons JM , Zwilsky KM
Published: March 2009

The basic effects of irradiation, such as transmutation re-actions, hardening, void formation and high temperature embrittlement are reviewed. Testing for these effects takes the form of pre-post testing as well as in-reactor observations. Pre-post testing consists of measuring a property out-of-reactor, and measuring the same property after the material has been exposed to the neutron environment. Although changes in properties of a material can be determined before and after irradiation, the influence of a neutron flux on rate processes such as creep must be determined in-pile.

Characterization of the reactor environment including neutron dosimetry and temperature measurements are discussed, and examples of predictive testing of materials for reactor fuels, cladding, components and pressure vessels are reviewed.
Techniques for Smooth Specimen Simulation of the Fatigue Behavior of Notched Members
Authors: Stadnick SJ , Morrow J
Published: March 2009

The initiation of fatigue cracks in a notched member is determined by the local cyclic stress and strain at the notch root. A relationship, proposed by Neuber, is used to relate the notch root stress-strain response to the nominal stress in the notched member. Further, several methods based on Neuber's rule allow a smooth cylindrical specimen to be used to simulate the stress-strain behavior of the notch root metal. The fatigue life of the smooth specimen is shown to furnish a satisfactory estimate of the fatigue life of the notched member, and the stress-strain plot of the smooth specimen is useful in understanding the local effects on the notch root metal of various nominal load histories. Results are reported for notched specimens subjected to variable load histories and for the corresponding smooth specimen simulations for 2024-T4 and 7075-T6 aluminum, aircraft quality 4340 steel, and Ti-8Al-1Mo-1V.
Apollo Quality Through Predictive Testing
Authors: White GC
Published: March 2009

Successful operation of a machine by a man is contingent upon meeting the following condition: the capability of the machine must be compatible with the capability of the man in the environment which they will see together. How do we achieve this compatibility? Through testing of hardware and training of people in the best simulation of operational environment that is economically feasible. This paper discusses the testing performed during the Apollo program and its relationship to the Engineering, Qualification, Manufacturing, Maintenance and Training aspects of the program. Illustrative examples of Apollo experience are used to highlight the discussion.
Fatigue Life Predicton for Weldments with Internal Cavities
Authors: van der Zanden AM , Robins DB , Topper TH
Published: March 2009

A method evolved for determining the local stress-strain response of notched members is extended to predict fatigue resistance of weldments with internal cavities. It is applied to both stress-relieved samples and as-received weldments. Test results from stress-relieved samples show good agreement with life predictions based on prestrained fully reversed strain controlled smooth specimen tests.

A calculation of inelastic deformations induced in the weld metal of as-received samples indicates that localized stresses will be of yield stress magnitude on the first load application. A fatigue parameter then incorporates ensuing mean stress effects. Good life predictions obtained in this application, where the local stress history is complex, demonstrate the adequacy of this method of analysis.
Stress Corrosion Cracking of Copper Metals
Authors: Thompson DH
Published: March 2009

Four factors that cause stress corrosion cracking are sufficient stress, a suitable corrodent, a susceptible alloy, and time. The nature and sources of both applied and residual stress are discussed. The sources of residual stress that are peculiar to the brass industry are described. The copper (Cu) metals are listed in order of their relative susceptibility to stress corrosion cracking. Zinc (Zn) in Cu contributes to the probability of its cracking; nickel (Ni) in Cu metals tends to inhibit it. Stress corrosion cracking is not instantaneous, so time is a factor in its occurrence. Various methods for the prevention of stress corrosion cracking are discussed. Some examples of stress corrosion cracking in service are described. Probability is discussed in relation to its role of predicting the stress corrosion cracking of Cu metals. Testing of Cu metals for their resistance to stress corrosion cracking may employ loops or U-bends. Applied stress may be effected by dead weight loading or by the use of springs. Corrodents may be chemical solutions, natural environments (atmosphere, sea water) or exposure to service environments. The metallographic appearance of stress corrosion cracks in Cu alloys is described as are the crack paths in brass and in other metals.

Liquid metal embrittlement is similar to stress corrosion cracking but is thought not to be identical. The similarities and differences are discussed. Mercury (Hg) is used to test for the presence of residual stress in brass, however Hg is an extremely dangerous metal in contact with any Cu alloy. The possible sources of Hg are mentioned. A chiller which failed by Hg cracking is described. Other liquid metals may cause cracking of Cu alloys including low melting alloys which are used in tube bending.
Overview of Corrosion Cracking of Titanium Alloys
Authors: Feige NG , Covington LC
Published: March 2009

Titanium depends upon the protective nature of a surface film, essentially an oxide, for its corrosion protection. Stress corrosion cracking results when the local breakdown of that film occurs causing a significant shift in the composition of the electrolyte and establishing electrochemical currents in the restrictive area which combine to prevent repassivation of the site.

Extensive testing has been conducted to define the threshold stress (KIscc) to sustain the electrochemical reaction. A large variation is seen between alloy, heat treatment, and mill conversion practice which can be related back to the notch and its strain conditions and the sensitivity of the alloy to the electrolyte present in the notch area. It has been demonstrated by rapid freezing of the reaction site that the electrolyte is a highly acidic reducing environment, and is in such a region of the Pourbaix diagram that the passive film will not reform. The electrochemist can further define the alloys susceptibility by evaluating the anodic current density in the pit area to sustain pitting and the cathodic current density to charge hydrogen. The pH of the electrolyte controls the hydrogen uptake efficiency at the cathodic site. Hydrides, formed at the local cell cathodic site under subsequent anodic control will react and pit at low anodic current density.

Stress corrosion cracking in the titanium alloys is the ability of the structure or test configuration to sustain by a moving crack front an actively corroding local site of a nonpassivating electrolyte. The classical argument as to whether the halogen or hydrogen are the cracking species is obscure, as both are interacting to sustain the reaction.