Present Series Of Tests Research Articles

The measurement of near-threshold fatigue crack growth

Near-threshold fatigue crack propagation rates have been measured in an aluminium bronze alloy using four different test methods: conventional load shedding; load shedding at constant K max ; stress-relief annealing and the testing of inherant surface defects. All four methods gave the same results, both for the threshold stress intensity factor, ΔK th , and for crack propagation rates in the near-threshold regime. It has been suggested by a number of authors that experimental results in this regime are strongly influenced by stress history and defect type. The present series of tests shows that this is not the case for this alloy; this provides evidence for the validity of the stress intensity threshold as an engineering parameter.

Effect of repeated loading on the strength of clay

The behaviour of soils under dynamic loading conditions has been studied. There exists a large amount of data indicating that a reduction of strength in a soil takes place but that the amount of this reduction is limited. On the other hand some authors claim that such a reduction is not possible because the ultimate undrained shear strength of a given saturated soil depends only on its void ratio and structure. In this paper it is attempted to bring some clarification to this conflict and in doing so the Critical State Model is employed. Fifty-eight dynamic and nine static triaxial tests have been conducted on samples consolidated from a water content twice the liquid limit to different consolidation pressures. The soil used in experiments is ‘Arnavutköy Kaolini’ with a liquid limit of w L = 65% and plastic limit w P = 30%. The results of the present series of tests indicate that the main effect of dynamic loading is on the increase of the pore water pressure which in turn causes the soil to behave like an overconsolidated soil. Previous research has shown that the void ratio of an overconsolidated soil sample decreases at the shear zone during shearing. All the results expressed above, as well as the results of tests conducted during this research, indicate that a reduction in the shear strength occurs in a normally consolidated clayey soil due to the repeated loading application.

An experimental investigation of the post-buckled efficiency of Z-section stringer-skin panels

A stiffened panel, designed so that failure in compression will occur afterinitial buckling, suffers a loss of axial stiffness due mainly to buckling of the skin between stringers and a consequent loss of flexural rigidity of the panel as a whole. The stringers will then carry an increasing proportion of the total compressive load, provided that the stringers themselves are of sufficient buckling resistance. Failure — due either to flexural buckling of the complete panel or to some other mode of stringer failure — can occur at a load substantially in excess of skin buckling. Behaviour of this kind is commonly found in very light structures for which it may be desirable to concentrate the load carrying capacity in certain discrete members, with a minimum gauge skin in between. However, a post-buckled design may also be preferred in rather more heavily loaded structures, in an attempt to reduce the loss of efficiency in a practical design when some restriction on, say, minimum stringer pitch is imposed. The purpose of the present series of tests is to investigate the post-buckled efficiency of a particular family of Z-section stringer-skin panels, of a design representative of current practice, with a stringer pitch chosen to be close to one-third of the effective panel length.

Effect of Orally Administered 15(R)-15-Methyl Prostaglandin E2and/or an Anticholinergic Drug on Meal-induced Gastric Acid Secretion and Serum Gastrin Level in Patients with Duodenal Ulcers

The purpose of the present series of tests was to measure and compare the effects of ingestion of gelatin capsules containing 15(R)-15-methyl PGE2 (PG) and/or an anticholinergic drug (methscopolamine bromide, Pamine) on meal-induced gastric acid secretion and serum gastrin level. Eleven duodenal ulcer patients were stimulated by a 5% peptone meal. Acid secretion was determined by the intragastric titration technique, and serum gastrin was measured by radioimmunoassay. The tests were randomized and double-blind. PG alone given 30 min before a test meal at a dose of 50 micrograms or 100 micrograms produced no side effects and inhibited meal-stimulated acid secretion by about 43% and 55%, respectively. Gastric acid inhibition after a single dose of PG was most pronounced in the first hour of a test meal and was accompanied by almost complete suppression of the meal-induced serum gastrin level. Pamine alone in a dose of 2.5 mg reduced gastric acid response to a meal by about 29% but caused a further rise of postprandial serum gastrin level over control values. The combination of PG, 50 micrograms, and Pamine, 2.5 mg, did not result in significantly greater acid inhibition (about 48%) than when either compound was given alone. When the higher dose of PG (100 micrograms) was given together with Pamine (2.5 mg), the degree of inhibition produced by PG alone was not changed. It is concluded that PG given orally in capsules is a potent inhibitor of gastric acid and serum gastrin response to a meal and that this effect may be of potential value in the treatment of peptic ulcer disease.

Hemagglutination by lectins in Friedreich's ataxia.

SummaryCoded erythrocyte samples from ten individuals with Friedreich*š ataxia, from parents of five of these individuals, and from five unrelated control individuals were subjected to lecţin agglutination tests at three temperatures; before and after trypsinization; and before and after treatment with echinocyte-producing sodium salicylate and stornato^ cyte-pröducing tetracaine followed by shape-fixation with glutaraldehyde. The aġglutinins tested were the polycationic poly-L-lysirie (PLL) and four lectins with different saccharide specificities: soybean agglutinin, wheat germ agglutinin, Ufex europeus agglutinin (VEA) and concana-valin A. Altogether, over 45,000 individual test wells were scored, the status of each blood donor with respect to diagnosis being disclosed to the experimenters only after all results were tabulated.The majority of these tests revealed no significant difference among the three groups of blood samples. A few tests did reveal statistically valid (p<0.0l) differences between groups, the most significant of which were the following: Trypsin ized control RBC were more sensitive, on average, to agglutination by VEA (fucose-inhibited) than were RBC of ataxies or their parents. Non-trypsinized control “stomatocytes” were less sensitive, on average, to agglutination by PLL than were those of ataxies or their parents. Trypsinization appeared, on average, to sensitive control but not ataxia or parent RBC to PLL-agglutination. Other differences of borderline (p-0.01-0.025) or near borderline (p = 0.025-0.05) significance were also noted. None of the statistically significant, Friedreich's ataxia-telated differences in median agglutination titers were large, the greatest being about threefold, and in every case the ranges of individual titers within the differing groups overlapped. Thus, none of these tests at present offers a method of pre clinic al diagnosis or carrier detection, and only further tests can establish whether even the differences observed in the present series of tests are reproducible.

Bulge forming of vessels from flat blanks

A forming process is suggested for producing vessels or containers of required shape from sheet metal by drawing, ironing and bulging under internal pressure and axial compressive force in one continuous operation. The process has been successively applied in the present series of tests for forming spherical and conical aluminium vessels.

Approximate shock-free transonic solution for a symmetric profile atzero incidence.

by that around a large angled unpitched cone and that the undersurface can be roughly predicted from such an assumption. Further evidence of such flow behavior comes from the oil dot flow visualization which shows that up to 45° the surface streamlines lie along straight lines generated from the nose tip. Furthermore, a measurement of the undersurface pressure distribution on the body and wings at one chord position taken in one test on a sting supported model also illustrated that, as in Ref. 3, fairly constant spanwise pressure was attained. In Fig. 4 is plotted the standoff angle of the shock A0S, on the windward side of the model, for different angles of attack (defined by the angle of the cone body axis to the stream) obtained from both free flight and fixed model shadowgraph photographs. Flow resemblance mentioned in the last paragraph was used to produce the following successfully applied prediction procedure. The pressure over the whole of the undersurface of the wing-cone configuration was assumed to be constant and equal to that on an unpitched cone which would generate a shock wave with half-angle equal to the angle of the windward side standoff shock 6S, obtained from the experiments, (i.e., equal to a + 0c + A0s, from Fig. 4). The integrated pressure thus obtained gives the predicted CL vs L/D curve given in Fig. 2 (called here conical flow theory) which is seen to coincide reasonably well with the measured data. This prediction provided the CL ~ a curve which was supplied to the computer program described earlier. A final comparison is made in Fig. 2 with experimentally determined force coefficients of other appropriate configurations. The lift coefficient on the wing-cone configuration at high incidences as measured in the present series of tests and as predicted by the conical flow theory ties in well with the low incidence data of Reggiori on a similar configuration.3 The maximum lift coefficient (CL)max, achieved by the wing-cone body with lower surface concavity (present results give (CL)max~0.8) exceeds those of the NASA Space Shuttle 040A configuration [Ref. 5, (C L)max = 0.57] by 40% and a flat delta [Ref. 2, (QJmax = 0.65] by 23%. To conform to the comparisons of Fig. 2, the value of (CL)max used was based on the reference area equal to the planform area of the complete Space Shuttle configuration. This required that the (CL)max based on an effective wing area quoted in Ref. 5 as 0.675 be reduced by 18%. This

Experimental study of the failure mechanism and strength characteristics of fiber bundles and composites

The primary aim of this investigation was to establish the strength characteristics of S-glass fiber bundles and composites subjected to quasi-static loading. Ten glass-bundle specimens and glass-fiber unilayer specimens, each containing thirty-one approximately equally spaced fibers (S-glass, 0.00485-in. diameter) were prepared and tested in an Instron machine at three strain rates (0.0265 in./in./min, 0.66 in./in./min and 26.5 in./in./ min). Grid lines were placed on composite specimen producing interference moire fringes with a reference master grid placed in front of the specimen. The specimens were observed photographically during deformation. The experimental bundle strength compares well with that obtained on the basis of Daniels' theory. The experimental standard deviation is, however, much larger than that predicted theoretically. The experimental mean composite strength is compatible with that obtained on the basis of rule of mixtures and Gucer-Gurland models. The Zweben crack-propagation criterion [E2(fC)=1] gives too low a value for the composite strength. A new criterion [E3(fC)=1] is suggested for the present test series. Due to the rather large standard deviation and the small number of test samples it was not possible to quantitatively evaluate the effect of rate of straining. However, it is observed that, within the range of strain rates employed, the effect of strain rate on bundle and composite strengths does not exceed 20 percent and 10 percent, respectively.

Central cholinergic blockade and two-way avoidance acquisition: The role of response disinhibition

The effects of scopolamine hydrobromide on two-way avoidance learning by rats were studied in various experimental conditions, selected so as to vary the extent to which response-suppressing tendencies interfere with active avoidance acquisition. Previous experiments had repeatedly shown an avoidance facilitation by central antimuscarinics in the following conditions: discrete-trial two-way test with non-directional light as CS, 5-sec CS-US intervals, 1.5 mA shocks, 30-sec intertrial intervals (ITI's), intertrial responses (ITR's) punished, absence of partition or barrier in the shuttle-box, and six separate 50-trial sessions at about 24-hr intervals. In the present series of tests, the control performance was markedly enhanced, and the scopolamine facilitation correspondingly attenuated, when ITR's were not punished and a central partition still absent, but not when ITR's were not punished and partition present. The drug effect was reversed, i.e. in the direction of a retardation of learning, when ITI's of 70 sec or more were used, and when all training (with 30-sec ITI's) was given in a single 300-trial session. Two experiments with different shock intensities, however, did not give reliable evidence of a drug × intensity interaction. These results give additional support to the hypothesis that response disinhibition after central cholinergic blockade can account for most, if not all the data on antimuscarinics and active avoidance acquisition, i.e. for the data obtained in experiments without change of state at some stage of training or testing.

Thermal Alteration of Sandstones

Abstract With the advent o underground heating operations, interest has developed in the alteration of rock properties by high-temperature treatment. In the present work a number of sandstones were heated to temperatures in the range of 400 to 800C under both atmospheric and simulated reservoir pressures. Permeabilities increased by at least 50 per cent and sonic velocities and breaking strengths decreased by an equivalent amount. Differential thermal expansion and other reactions of constituent mineral grains are the causes of these alterations. Introduction In the underground combustion of petroleum reservoirs. Temperatures of the order of 600C are reported to have been reached in the combustion zone. At this temperature rocks are subject to extensive thermal alteration. Temperatures of this magnitude and higher may also occur in subsurface formations when subjected to bottom-hole heating, thermal drilling operations, and underground nuclear explosions. Temperatures of this magnitude might also be generated by conventional rock drilling methods at points of bit-tooth contact. In earlier work, the permanent deformation of rocks resulting from heating was reported. Major structural damage of rocks occurs due to differential thermal expansion of mineral constituents. A number of mineral alterations including crystal versions, loss of water of crystallization and dissociation, may also contribute to changes in physical structure and properties of rock. In the present work, samples of three typical sandstones were had to several temperatures up to a maximum of 800C and then allowed to cool to room temperature. Heating was done under both atmospheric pressure and simulated reservoir pressure conditions. Physical properties of the samples were measured before and after healing and comparisons made. Measured properties included permeability, sonic velocity, breaking strength and fracture index. Changes in physical properties were compared to changes in mineralogical characteristics as determined by thin-section. X-ray diffraction and chemical tests. EQUIPMENT AND PROCEDURE Two outcrop sandstones (Bandera and Berea) and one sub-surface sandstone (St. Peter) were selected for the tests. These samples have a wide range in composition and physical properties as shown in Table 1.The first series of tests was made on 2-in. diameter by 5-in. long test specimens. Test specimens used in all later work were 3/4-in. diameter by 1 1/8-in. long. this being the specimen size required for heating at simulated reservoir pressures. After careful washing, the cores were oven dried at 100 +/- 5C for a minimum of 24 hours before the tests were run. Test specimens were heated in an electric furnace at a constant rate of temperature increase of 3C per minute. When maximum temperature of the run was reached, the sample was allowed to soak for one hour. The furnace was then cooled to room temperature at the same rate of 3C per minute. The entire heating operation was designed for reproducibility without subjecting the test specimens to excessive thermal shock. For samples heated under simulated reservoir pressures. a pressure cell designed by Dean was used (Fig. 1). The core sample was inserted into a thin-walled (0.006 to 0.01-in.) copper cup which was then mounted in a high- pressure cell. Provisions were made for the application of internal pore pressure as well as confining pressure. Tests showed that the thin-walled copper cup closed tightly around the core and satisfactorily transmitted confining pressure to the core. The core was heated by placing the entire cell into the electric furnace. The heating program was the same as that used in the atmospheric pressure runs: temperature rise of 3C per minute to maximum temperature of the test, soaking at maximum temperature for one hour. and cooling at a rate of approximately 3C per minute. The cell was designed to withstand 5,000 psi at 1,000C. However, since it was considered likely that repeated heating and cooling would in time weaken the steel, 2,000 psi at 850C was set as a working limit. In the present series of tests, the pore pressure was held constant at 750 psi and the confining pressure at 1,500 psi. The pressure source was a high-pressure nitrogen tank. The two pressures were controlled manually but are accurate well within +/- 50 psi. JPT P. 589ˆ

Mechanical properties of pyrolytic graphite

Abstract : A series of mechanical strength and thermal expansion tests was carried out from room temperature to 5000 F on the two microstructural types of current production pyrolytic graphite. Results indicate that with appropriate precautions in selecting test material, machining and testing specimens, current production pyrolytic graphites yield higher, more reliable mechanical property values. The contribution of process improvements to this increase cannot be specifically separated although it may show up principally in allowing more of a given batch of material to be selected. The present series of tests shows pyrolytic graphite to have an ultimate 'a' direction tensile strength of 18,000 = 2,000 psi at room temperature rather than previously found values of 11,000 = 5,000 psi. The largest difference between surface nucleated and continuously nucleated material was obtained in torsional tests parallel to the planes; values of 1555 = 60 and 2880 = 265 psi were obtained respectively throughout the temperature range to 5000 F.

Embrittlement of Tungsten and of Molybdenum

A RECENT paper from this laboratory1 described the embrittlement of tungsten wire if it be heated in atmospheres containing even traces of ammonia. This work has been extended and has revealed a fact, unobserved in the original study, which furnishes further information which may be helpful in understanding the mechanism. In earlier experiments, the procedure was to heat a length of wire, leaving untreated ends which, since they had not been embrittled, could be clamped in the tensile testing machine without fear of fracture there. The disadvantage of this procedure is that the specimen under test had regions which reached lower temperatures than the central portion, so that any minimum in the embrittlement/treating-temperature curve would not be shown. This aspect was studied in the present series of tests. In these, wire was first annealed so that primary recrystallization was complete2, and then reheated in nitrogen/hydrogen mixture containing 0.2 per cent ammonia. The whole specimens were then used for the test, neglecting those which broke in the clamps.

The hypoxia tolerance test of the heart in children

Summary Present knowledge of latent cardiac decompensation in children is inadequate.Accordingly, an attempt has been made to come closer to the problem of the reserve forces of the child heart by means of a comparative investigation of the tolerance tests performed on healthy as well as on sick children. For the tolerance test, respiration of air deficient in oxygen has been chosen,as applied earlier to adults by, among others, Dietrich and Schwiegk, Levy and Larsen. A special apparatus suitable for children of all ages, as well as for adults,has been constructed. It consists of an adjustable metal ring with a hood of Plexiglas mounted on one of the ends of the bedstead. Oiled silk is attached to the metal ring which is applied to the shoulders, back, and chest of the patient. In the respiration chamber thus obtained, nitrogen and air are introduced, the oxygen content of which acquires the desired constant value after four and one-half minutes. In the present test series, 9 per cent oxygen was used during ten minutesof tolerance testing. The result, which is of a preliminary nature, is briefly as follows: Thirtynormal cases reacted negatively. Sixteen of twenty-five cases of different heart diseases reacted positively. Seven of these cases represented active rheumatic carditis, four cases being patent ductus Botalli, one case another congenital vitium without cyanosis, one case of morbus ceruleus, and three cases of postmyocarditic conditions. In addition, a group of twenty-nine cases of third sound gallop has been subjected to the tolerance test; these patients have been examined by Carlgren and will be included in his work regarding the gallop rhythm. Nine cases (31 per cent) reacted positively, the twenty remaining, negatively. This result supports Carlgren's theory that the third sound gallop is, to some extent, to be considered a myocardial injury. An examination of the T-waves during the hypoxia test has shown that a considerably more marked depression of the T-wave in all three leads occurred in the cases reacting positively than in those which were not affected by the respiration of air deficient in oxygen. The pulse increased in rate during the tolerance test, both in normal andin pathologic cases. However, the data are still too limited to permit the drawing of any far-reaching conclusions. The test, which is easy to perform, takes only 15 minutes, is free from risks, and will, no doubt, be found suitable for routine clinical work. In contrast to the working tests with registration of the cardiac effect after the completion of the exertion, the respiration of air deficient in oxygen, as in the present case, has the advantage that the heart's reaction can be recorded during the actual tolerance test. This is, in all likelihood, particularly valuable with regard to children, where the heart is characterized by a rapid mode of reaction. Thus, all the changes appearing during the hypoxia test, in normal as well as pathologic cases, had resumed their original value five minutes after the termination of the tolerance test. For the purpose of studying more closely the effect of the hypoxia on thecirculation, larger normal and pathologic series are being planned where, apart from electrocardiographic and phonocardiographic registrations and pulse recording, measurements of the oxygen-saturation of the blood will also be carried out.

The Initial Stage of Plastic Deformation in Lead Under Compression

In the steady-creep stage in metals, stress (or resistance to deformation) is related to the velocity of deformation, in accordance with the hyperbolic-sine law, or the exponential law. These laws, however, fail completely to describe the initial stage of plastic deformation in lead. The present series of tests is an investigation of this initial stage in compression. An optical lever system and high speed kymograph have been employed. The photographic records obtained show the progress of deformation with time. The duration of the initial stage increases with the compressing load. For a load of 120.0 kg the duration is about 0.16 sec. It is found that a unique, initial deformation, independent of time, is associated with each load. From measurements on the deformation curves, resistances as functions of time have been calculated. These data indicate a linear relationship between the resistance R and time t: R=l+mt,where l=a parameter of small value, evidently a correction term, and m=rate of increase of resistance. Using this equation and the dynamic constants of the apparatus, deformation curves in good agreement with experiment have been derived. Resistance in the initial stage appears to be only approximately a function of deformation alone

A study of the possible catalytic effect of some metals and alloys on the changes occuring in refined cotton seed oil during storage

L AST year the authors were privileged to report on A Study of the Possible Catalytic Effect of Some Metals and Alloys on the Changes Occurring in Crude Cotton Seed Oil During Storage. This vear a similar study is being reported, using refined cotton seed oil to complete the study of possible catalysis of the more common metals and alloys on this type of vegetable oii. The same containers used in the first series were used in the refined oil test. In reviewing the previous paper, it was found that copper and copper bearing metals influenced both the color and flavor of the crude oil and produced toward the end of the storage period (5 months) a gelatinous substance, the iodine value of which indicated a polymerized body. The Hastelloy Metal (a moly'bdenun-iron-nickel alloy) also produced an undesirable effect, causing an early rancidity which became very pronounced with age. Of the remaining metals included in the experiment, no single specimen could be selected as being outstanding in quality based on the color and loss tests obtained. The metals used in the present series of tests are shown in Table I with their approximate compositions.

The Theory of Two Factors versus the Sampling Theory of Mental Ability

DR. WILLIAM BROWN has published in NATURE of May 12 a communication on “The Theory of Two Factors versus the Sampling Theory of Mental Ability”. The matter is too involved to be discussed adequately in a letter, but I wish to record that I do not agree that this otherwise very valuable experiment is an experimentum crucis between my views and those of Prof. Spearman, partly because I do not think Dr. Mackie's formulæ are applicable in this way, but mainly because the tetrad-differences had been trimmed down to the narrow scatter shown, by the choice of tests, by the rejection of one of those originally chosen, by the rejection of one of the remaining correlation coefficients, and by the elimination by partial correlation of a large group factor. It is not in dispute that by these means a set of tests can be arrived at which give zero tetrads within the limits of sampling error and can then be described by a parameter g and as many parameters s as there are tests. I would like to add that I admire and value the work done by Dr. Brown and Dr. Stephen-son in arriving at the present series of tests.