Showing papers in "ASTM special technical publications in 1976"
TL;DR: In this paper, an attempt is made to apply the J-integral concept as an elastic-plastic criterion for fatigue crack growth, and the results show correlation with Jintegral values estimated from load versus deflection hysteresis loops.
Abstract: An attempt is made to apply the J-integral concept as an elastic-plastic criterion for fatigue crack growth. Compact tension fracture specimens of A533B steel are subjected to gross cyclic plastic deformations, and fatigue crack growth rates up to 0.01 in./cycle are obtained. The results show correlation with J-integral values estimated from load versus deflection hysteresis loops. Also, agreement is obtained with the extrapolation of linear elastic fatigue crack growth rate data.
395 citations
TL;DR: In this article, a fracture mechanics approach was used to study high-temperature creep crack propagation, and crack growth rates were correlated with the C*-parameter which is an energy rate line integral.
Abstract: A fracture mechanics approach was used to study high-temperature creep crack propagation. Crack growth rates were correlated with the C*-parameter which is an energy rate line integral. For materials conforming to a nonlinear stress and strain rate relationship in the steady-state creep range, specifically, those which can be properly idealized as purely viscous (negligible elastic and transient creep effects), C* characterizes the crack tip stress and strain rate fields. Crack growth rate tests were conducted in the creep range on a discaloy superalloy at 1200°F (920 K). Two specimen geometries were tested, a center cracked panel and a compact geometry, to establish the geometry independence of this approach. The results showed that crack growth rate correlated with the C*-integral, while other parameters (K and nominal stress) failed to adequately characterize crack growth rate.
355 citations
TL;DR: In this article, a procedure compatible with linear elastic fracture mechanics (LEFM) and crack opening displacement (COD) testing was suggested for finding a three-point bend specimen with COD.
Abstract: Possible methods for evaluating J for a three-point bend specimen are reviewed and the effects of slow crack growth, experimental limit load, and lateral constraint noted. A procedure, compatible with linear elastic fracture mechanics (LEFM) and crack opening displacement (COD) testing, is suggested for finding J c .
123 citations
TL;DR: In this article, the fracture mechanics approach to fatigue crack growth may be extended by the use of the J-integral concept, so that large scale plasticity effects are included.
Abstract: Fatigue crack growth rate data are obtained for center cracked specimens of A533B steel subjected to elastic-plastic cyclic loading. Cyclic J-integral values estimated from load versus deflection hysteresis loops are correlated with these growth rate data. The relationship obtained is in agreement with previous elastic-plastic data on compact specimens and also with linear elastic data on large size compact specimens. These experimental data suggest that the fracture mechanics approach to fatigue crack growth may be extended by the use of the J-integral concept, so that large scale plasticity effects are included.
118 citations
TL;DR: In this article, the authors analyzed the growth rate of creep crack on double cantilever beam (DCB) specimens for aluminium alloy RR58 and a chromium-molybdenum-vanadium steel.
Abstract: Creep crack growth tests, conducted on contoured double cantilever beam (DCB) specimens are described for aluminium alloy RR58 and a chromium-molybdenum-vanadium steel. The results are analyzed in terms of J, the rate equivalent of the J contour integral, which is a nonlinear fracture mechanics parameter. Direct proportionality is found between crack growth rate, ˙a and j. The treatment is shown to reveal a unification of the linear elastic fracture mechanics and net section or reference stress descriptions of creep cracking.
100 citations
TL;DR: In this article, a J I c test procedure using a single deeply cracked specimen is proposed, where the crack extension is measured by partially unloading the specimen to determine the elastic compliance.
Abstract: A J I c test procedure using a single deeply cracked specimen is proposed. The crack extension is measured by partially unloading the specimen to determine the elastic compliance. J I c tests were made using ASTM A469 steel. Compact specimens from ½T to 5T were tested. No size effect was found. Results from two independent laboratories are presented and are in agreement. The errors due to simple formulation of J I calculation, periodic partial unloading, and simplified analysis for the extension of deep cracks in compact specimens are explored. The measurement point of crack extension for establishing J I c is discussed. The results indicate that a practical and effective single specimen test procedure has been developed.
98 citations
Journal Article•
TL;DR: In this article, an incremental theory of plasticity was used to predict crack-closure and crack-opening stresses during the crack-growth process under cyclic loading, and the calculated crackopening stresses were found to be quantitatively consistent with experimental measurements.
Abstract: Experiments have shown that fatigue cracks close at positive loads during constant-amplitude load cycling. The crack-closure phenomenon is caused by residual plastic deformations remaining in the wake of an advancing crack tip. The present paper is concerned with the application of a two-dimensional, nonlinear, finite-element analysis using an incremental theory of plasticity to predict crack-closure and crack-opening stresses during the crack-growth process under cyclic loading. A two-dimensional finite-element computer program, which accounts for both elastic-plastic material behavior and changing boundary conditions associated with crack extension and intermittent contact of the crack surfaces under cyclic loading, has been developed. An efficient technique to account for changing boundary conditions under cyclic loading was also incorporated into the nonlinear analysis program. This program was used subsequently to study crack extension and crack closure behavior in a center-cracked panel under constant-amplitude and two-level block loading. The calculated crack-opening stresses were found to be quantitatively consistent with experimental measurements.
94 citations
TL;DR: In this article, a survey of variable-amplausitude loading as applied in test programs is given, with an analysis of the consequences for prediction techniques. But the authors focus on the effects of variableamplitude loading on fatigue cracks.
Abstract: The paper starts with a discussion on loads in service, after which a survey is given of various types of variable-amplitude loading as applied in test programs. The various phenomenological aspects of fatigue damage associated with fatigue cracks are indicated. Interaction effects between cycles of different magnitudes are defined. Methods for measuring interaction effects, examples of interaction effects, and possible explanations are reviewed. This includes both tests with simple types of variable-amplitude loading (overloads and step loading) and more complex load-time histories (program loading, random load, and flight-simulation loading). New evidence on crack closure is presented. Various types of prediction methods are discussed. The paper is primarily a survey of the present knowledge, with an analysis of the consequences for prediction techniques.
88 citations
TL;DR: In this paper, an alternate method to those of Bueckner and Rice is presented for the derivation of the two-dimensional weight function for determining crack tip stress intensity factors.
Abstract: An alternate method to those of Bueckner and Rice is presented for the derivation of the two-dimensional weight function for determining crack tip stress intensity factors. The weight function has r - 1 | 2 type displacement singularity at the crack tip. It is shown that this singular field can be formulated using Westergaard stress functions in a manner similar to the method used for r 1 | 2 type fields in crack tip displacements. A straight-forward approach for obtaining weight functions for cracked finite bodies is presented. This technique can be combined in a simple fashion with the finite element method. As an example, a weight function for the SEN strip is obtained in this manner. Moreover, closed form infinite body weight functions are also developed and used to derive some well-known stress intensity factor formulas.
86 citations
Journal Article•
TL;DR: In this paper, the potential interference of crack surfaces is determined from analyses of elastic displacements during loading and unloading and of the permanent deformation left in the wake of a growing crack.
Abstract: A method for prediction of crack growth behavior has been developed, based on evaluations of stress intensity caused by crack surface contact. The potential interference of the crack surfaces is determined from analyses of elastic displacements during loading and unloading and of the permanent deformation left in the wake of a growing crack. The potential interference is treated as a wedge acting behind the crack tip and the contact stresses created by this wedge are computed through an elastic-plastic analysis. The effective stress intensity range used for crack growth prediction is found by subtracting the stress intensity caused by these contact stresses from the applied stress intensity range. Comparisons of crack growth behavior predicted by this method and that measured in constant amplitude tests, with and without high loads, and in block spectrum tests have shown that the method accounts for load interaction effects in these cases. These effects include delayed retardation following high loads, crack growth acceleration during high loads, and dependence of growth rates on number of high loads.
78 citations
TL;DR: In this paper, a procedure is formulated to derive approximate stress intensity factors for both part-through and through-the-thickness cracks originating at open holes and holes containing either loaded or unloaded close tolerance fasteners.
Abstract: A procedure is formulated to derive approximate stress intensity factors for both part-through and through-the-thickness cracks originating at open holes and holes containing either loaded or unloaded close tolerance fasteners. The procedure is checked with known solutions for stress intensity factors of one or two through-the-thickness cracks emanating from an open hole in a plate subjected to uniaxial or biaxial loading. Stress intensity factors computed from this procedure for the above mentioned cases agree within seven percent of known results for the crack length to hole radius ratios, L/r, of 0.05 < L/r < ∞. The procedure is then used to derive stress intensity factors for through cracks at loaded close tolerance fasteners in a plate, and for semi-elliptical cracks at open holes and at loaded and unloaded close tolerance fastener filled holes in a thick plate. Stress intensity factors for these part-through cracks are presented in graphical forms as a function of position around the crack periphery, for various crack aspect ratios and crack length to hole radius ratios. Finally, these stress intensity solutions for semi-elliptical cracks at a fastener hole in a thick plate are used to estimate stress intensity factors for quarter-elliptical cracks originating at a fastener hole in a finite thickness plate.
TL;DR: In this article, a two-parameter fracture criterion has been derived which relates the linear-elastic stress-intensity factor at failure, the elastic nominal failure stress, and two material parameters.
Abstract: A two-parameter fracture criterion has been derived which relates the linear-elastic stress-intensity factor at failure, the elastic nominal failure stress, and two material parameters. The fracture criterion was applied to center-crack tension, compact, and notch-bend fracture specimens made of steel, titanium, or aluminum alloy materials tested at room temperature. The fracture data included a wide range of crack lengths, specimen widths, and thicknesses. The materials analyzed had a wide range of tensile properties. Failure stresses calculated using the criterion agreed well (plus or minus 10 percent) with experimental failure stresses. The criterion was also found to correlate fracture data from different specimen types (such as center-crack tension and compact specimens), within plus or minus 10 percent for the same material, thickness, and test temperature.
TL;DR: In this paper, a two-dimensional finite element method is used to develop stress intensity factor solutions for continuous surface flaws in structures subjected to an arbitrary loading, where the arbitrary loading produces a stress profile σ acting perpendicularly to a given section S of the structure.
Abstract: A two-dimensional finite element method is used to develop stress intensity factor solutions for continuous surface flaws in structures subjected to an arbitrary loading. The arbitrary loading produces a stress profile σ acting perpendicularly to a given section S of the structure. The stress profile is represented by a third degree polynomial σ = A 0 + A 1 x + A 2 x 2 + A 3 x 3 Stress intensity factor solutions are developed for continuous surface flaws introduced in particular sections S in the structure considered. Solutions are developed for a surface flaw in a flat plate, for both circumferential and longitudinal flaws inside a cylindrical vessel, and for circumferential flaws at several locations inside a reactor vessel nozzle. The superposition principle is used, and the crack surface is subjected successively to uniform (σ = A 0 ), linear (σ = A 1 x), quadratic (σ = A 2 x 2 ), and cubic (σ = A 3 x 3 ) stress profiles. The corresponding stress intensity factors (K I ( 0 ) , K I ( 1 ) , K I ( 2 ) , K I ( 3 ) ) are then derived for various crack depths using the calculated stress profile in the region of the crack tip. The total stress intensity factor corresponding to the cracked structure subjected to the arbitrary stress profile is expressed as the sum of the partial stress intensity factors for each type of loading. K I = K I ( 0 ) + K I ( 1 ) + K I ( 2 ) + K I ( 3 ) = √πa[A 0 F 1 + 2a/π A 1 F 2 + a 2 /2 A 2 F 3 + 4a 3 /3π A 3 F 4 ] where, a is the crack depth and F 1 , F 2 , F 3 , and F 4 are the magnification factors relative to the geometry considered. The results are presented in terms of magnification factors versus fractional distance through the wall (a/t) and reveal the strong influence of the geometry of the structure and of the crack orientation. The stress intensity factor solutions obtained using this method are compared to solutions obtained using other methods, when available. In the case of the plate geometry, the solution obtained for the linear loading (σ = A 0 + A 1 x) is shown to agree well with the boundary collocation solution reported by Brown and Srawley. The stress intensity factor solutions for the circumferential and longitudinal cracks in the cylindrical vessel compare well with solutions obtained by Labbens et al using the weight functions method proposed by Bueckner, and are also in good agreement with the solution for uniform loading (σ = A 0 ) obtained using the line spring method proposed by Rice.
TL;DR: In this article, three criteria for growth under tensile loads are reviewed and, although they proceed on distinct bases, give similar results, a corollary to a minimum energy hypothesis is inferred.
Abstract: Mixed mode fracture in two dimensions has been of recent interest via study of a crack at an arbitrary angle to the axis of applied load. Three criteria for growth under tensile loads are reviewed and, although they proceed on distinct bases, give similar results. A corollary to a minimum energy hypothesis is inferred. A compression model is suggested and examined in terms of two criteria. Comparisons to data, to the extent they are available, are considered; observations on the nature of the data are followed by suggestions for further research.
TL;DR: In this paper, the authors present the results of the first phase of an investigation sponsored by the National Cooperative Highway Research Program, Project 12-14, to study subcritical crack growth in steel bridge members.
Abstract: Well-conceived procedures used to study the safety and reliability of structures recognize that the performance of a structure or a structural component is governed not only by material properties but also by the design; fabrication, inspection, erection, and use of the structure. These parameters govern the initiation of subcritical cracks and their propagation to critical dimensions, and therefore, determine the useful fatigue life of structural components subjected to load fluctuations. This paper presents the results of the first phase of an investigation sponsored by the National Cooperative Highway Research Program, Project 12-14, to study "Subcritical Crack Growth in Steel Bridge Members." The paper describes the fatigue-crack-growth behavior of various bridge steels (A36, A588-A, A588-B, A514-B, A514-E, and A514-F) under variable-amplitude random-sequence stress spectra such as occur in actual bridges. The fatigue crack growth-rate data were obtained by using wedge-opening-loading specimens tested under variable-amplitude random-sequence load spectra that are represented by a Rayleigh distribution function. The data obtained for these steels showed that the average fatigue crack growth rates, da/dN, under variable-amplitude random-sequence load fluctuation and under constant-amplitude load fluctuation agreed closely when da/dN was plotted as a function of the root-mean-square stress intensity factor range, ΔK r m s . Thus, within the limits of the present investigation, the average fatigue crack-growth rates, da/dN, of various bridge steels subjected to variable-amplitude random-sequence load fluctuations, such as occur in actual bridges and to constant-amplitude load fluctuations, can be represented by the equation da dN = A (ΔK r m s ) n where ΔK r m s is the root-mean-square stress intensity factor fluctuation, and A and n are material constants.
TL;DR: The toughness of wrought, high-strength aluminum alloys is related to the amount, type, and morphology of coarse constituent particles, intermediate size dispersoids, and fine (down to about 0.001 μm) precipitates.
Abstract: The toughness of wrought, high-strength aluminum alloys is related to the amount, type, and morphology of coarse (larger than about 1 μm) constituent particles, intermediate size (about 0.02 to 0.5 μm) dispersoids, and fine (down to about 0.001 μm) precipitates. High toughness can be attained by minimizing the size and volume fraction of constituent particles, increasing the interdispersoid distance, refining the intragranular precipitate in 2XXX alloys, and controlling the intergranular precipitate in 7XXX alloys. For highest toughness in 7XXX alloy products where low residual stress is desired, rapid quenching followed by the minimum amount of cold work required for mechanical stress relief is recommended.
TL;DR: In this paper, the influence of forging schedule and subsequent heat treatment on the microstructure and mechanical properties of three a + β titanium alloys has been investigated by using light and thin foil electron microscopy.
Abstract: The influence of forging schedule and subsequent heat treatment on the microstructure and mechanical properties of three a + β titanium alloys has been investigated. The alloys studied were Ti-6Al-4V, Ti-6Al-6V-2Sn, and Ti-6Al-2Sn-4Zr-6Mo. The microstructural comparisons included (a +β) finished and β-processed material, variations in primary a volume fraction, primary a particle aspect ratio, and the nature of the transformation products. Careful selection of forging history and heat treatment permitted comparisons of fracture properties at essentially constant strength levels. This paper describes the influence of forging and heat treatment on the microstructure of these alloys as shown by light and thin foil electron microscopy. The microstructural information was then used to analyze the variations in topography of both fatigue and fast fracture regions as observed by scanning electron microscopy. In some cases, good correlation between fracture topography and microstructure has been established but such correlations depend on microstructure and on loading conditions. For example, fast fracture in the β-processed materials occurs largely along prior β-phase grain boundaries, whereas fatigue cracks propagate by a predominantly transgranular mode. Further, the occurrence of fatigue striations strongly depends on microstructure and on the cyclic stress intensity, with cyclic cleavage predominating at low growth rates in those alloy conditions containing primary a particles which have at least one dimension greater than ∼25 μm. Other correlations between fracture topography, microstructure, and properties were obtained and comments for microstructure selection to control properties are included.
TL;DR: In this article, the existence of a plane or axisymmetric cracked body of an influence or Green's function, depending on the geometry of the body, allows calculation by means of a simple integral of the stress intensity factor.
Abstract: The existence for a plane or axisymmetric cracked body of an influence or Green's function, depending on the geometry of the body, allows calculation by means of a simple integral of the stress intensity factor. In this way the respective influence of geometry and load in K calculation are separated. The relationship between this function and the compliance for a concentrated force applied on the crack is shown. Starting from complex mathematical considerations, Bueckner defined weight functions equivalent to the influence functions and of particular advantage for analytic as well as numerical purposes. Moreover he showed that weight functions behave like d - 1 at the distance d from the crack tip. In the sequel we shall refer to weight functions, since they are studied more deeply from a mathematical point of view and are known more widely than influence functions. A practical calculation method of weight functions by finite elements is shown. This method can be used for any bidimensional cracked body, plane or axisymmetric. Curves of nondimensional weight functions are given for cylindrical geometries currently used in engineering. It is pointed up that this method is more flexible than the use of handbooks which, in spite of their great interest, cannot foresee all the geometries and loads which are met in engineering problems.
Journal Article•
TL;DR: In this article, the occurrence of pitting corrosion in copper tubes carrying cold supply waters has been investigated in relation to carbon residues in the bore of the tube from the bright annealing operation, the hardness and composition of the metal, and water composition.
Abstract: The occurrence of pitting corrosion in copper tubes carrying cold supply waters has been investigated in relation to (a) carbon residues in the bore of the tube from the bright annealing operation, (b) the hardness and composition of the metal, and (c) water composition. The electrode potential of tubes in several supply waters has been used to assess their susceptibility to pitting corrosion. It is concluded that pitting occurs only in certain types of water with a low level of organic matter in tubes containing more than a critical amount of carbon residue in the bore. Hardness of the metal appears to have little effect on susceptibility to pitting corrosion, but the addition of about 1 percent tin to the copper substantially reduces the rate of pitting for a given level of carbon contamination in the bore. The significance of these findings is reviewed in the light of service experience with copper water tubes in the United Kingdom.
TL;DR: In this article, an equivalent constant-amplitude concept is developed based on the crack-closure phenomenon and on results of pilot tests that showed that the crack opening load remained essentially constant while cracks grew under repeating random-load sequences containing several thousand load peaks.
Abstract: To simplify crack-growth calculations, an equivalent constant-amplitude concept is developed based on the crack-closure phenomenon and on results of pilot tests that showed that the crack-opening load remained essentially constant while cracks grew under repeating random-load sequences containing several thousand load peaks. An equation of crack growth equivalence resulting from derivations based on the crack closure crack growth law is obtained and used to determine a relationship between an equivalent number of cycles of constant-amplitude loading and the distribution of the random loads, the exponent in the crack growth law, and the ratio of the crack-opening load to the maximum load. The validity of the concept is tested experimentally on six different random-load sequences. Good agreement is found between experimental results and theoretical predictions.
TL;DR: In this article, a modification to the Wheeler fatigue crack retardation model is proposed, which allows the model to be used without reliance on data fitting and, therefore, without the subsequent limiting to a specific material or a specific set of loading parameters.
Abstract: A modification to the Wheeler fatigue crack retardation model is proposed. The modification allows the model to be used without reliance on data fitting and, therefore, without the subsequent limiting to a specific material or to a specific set of loading parameters. The new model is used to predict existing data for the number of delay cycles following a single overload in 2024-T3 aluminum, 4340 steel, and Ti-6Al-4V titanium alloy. All predictions were within essentially a factor of two of the experimental data.
TL;DR: In this article, the elastic and the fully plastic solutions were used to interpolate behavior from the small-scale yielding range to the fully-plastic range and the relations between the J-integral, load point displacement, crack opening displacement, and the applied load were developed.
Abstract: General procedures are proposed which utilize the elastic and the fully plastic solutions to interpolate behavior from the small-scale yielding range to the fully plastic range. The relations between the J-integral, load point displacement, crack opening displacement, and the applied load thus developed, are applicable to test configurations and cracked bodies in general. To assess the accuracy of the estimated relationships, a detailed numerical investigation, which employs an accurate finite element approach, is carried out for a particular configuration under antiplane shear. The results obtained from the full numerical calculations, for values of the applied load well into the fully plastic range, are in excellent agreement with the estimated results.
TL;DR: In this article, four overload patterns, tension, compression-tension, tension-compression, tension compression, and compression compression, were used to evaluate the performance of pre-cracked compact specimens of 2024-T3 and 7075-T6 aluminum alloys.
Abstract: Modified pre-cracked compact specimens of 2024-T3 and 7075-T6 aluminum alloys were subjected to four different overload patterns followed by subsequent constant-amplitude steady-state loading with R =P l i n /Pl m a x equal to 0, -½, -1, and -2. The overload patterns were tension, compression-tension, tension-compression, and compression. Cyclic loading with negative stress ratio, R, drastically reduced crack-growth retardation. The higher the negative R ratio the greater the reduction in retardation. Overload ratios, OLR =P h m a x /Pl m a x , ranging from 2.0 to 3.0 were used. For compression overloads, the OLR ranged from -2.0 to -4.0. High compression overloading was detrimental and dependent upon subsequent R ratio loading. Substantial fracture surface abrasion near the mid-thickness occurred for higher negative R ratios. Striations were not readily found in this region, however, they were quite evident near the edges, which indicated crack closure was greater near the mid-thickness. The 2024-T3 gave better crack growth life than 7075-T6 in some loading conditions, while the opposite was true for other loadings. The results indicate negative R ratio must be considered in retardation models and that retardation life cannot be modeled based solely on overload plastic zone sizes.
Journal Article•
TL;DR: In this paper, the effect of single overloads on room-temperature fatigue crack growth has been studied in two steels of markedly different yield stresses and the evidence suggests that overload retardation is primarily due to residual compressive stresses generated in the crack tip region, and associated with crack closure effects.
Abstract: The effect of single overloads on room-temperature fatigue crack growth has been studied in two steels of markedly different yield stresses. The observed retardation effects have been presented and the evidence suggests that overload retardation is primarily due to residual compressive stresses generated in the crack tip region, and associated with crack closure effects. The results have been rationalized in terms of a fatigue crack growing through overload plastic zones of different shapes and sizes associated with plane stress and plane strain deformation.
TL;DR: In this article, the authors performed tests on straight-grained timber to give Mode I fractures in three geometries, and satisfactory K I data were produced Mode II tests were more difficult to perform and correlated on a constant not section shear stress basis indicated some form of shear yielding failure.
Abstract: Tests were performed on straight-grained timber to give Mode I fractures in three geometries, and satisfactory K I data were produced Mode II tests were more difficult to perform, and the data correlated on a constant not section shear stress basis indicated some form of shear yielding failure The mixed mode tests used tension specimens with the grain at various angles, and very good data were obtained which gave a constant K I c fracture criterion independent of K I I
TL;DR: In this article, the effects of the dissimilar metal, the solution composition, and area ratio have been evaluated using galvanic current and weight loss measurements and the results obtained have been explained based on mixed potential theory.
Abstract: In a systematic study of galvanic corrosion of aluminum alloys the effects of the dissimilar metal, the solution composition, and area ratio have been evaluated using galvanic current and weight loss measurements. In 3.5 percent sodium chloride, galvanic corrosion rates of the aluminum alloys 1100, 2024, 2219, 6061, and 7075 decrease with the nature of the dissimilar metal in the order: silver > copper > 4130 steel >> stainless steel nickel > Inconel 718 >> Ti-6A1-4V Haynes 188 > tin > cadmium. Coupling to zinc did not lead to cathodic protection of the aluminum alloys as shown by weight loss data, although the aluminum alloys were the cathode in the aluminum-zinc couple. The potential difference of uncoupled dissimilar metals has been found to be a poor indicator of galvanic corrosion rates. Dissolution rates of aluminum alloys coupled to a given dissimilar material are higher in 3.5 percent sodium chloride than in tap water and distilled water where they are found to be comparable. The effect of area ratio A C /A A has been studied in 3.5 percent sodium chloride for area ratios of 0.1, 1.0, or 10. The galvanic curent was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density i g A with respect to the anode has been found to be directly proportional to the area ratio (i g A = k 1 A C /A A ), while the dissolution rate r A of the anode was related to area area ratio by r A = k 2 (1 + A C /A A ). The results obtained have been explained based on mixed potential theory. Electrochemical methods for measurements of galvanic currents are described in the Appendix.
TL;DR: In this article, historical developments in the field of thermal fatigue from 1838 to the present are reviewed, and it is hypothesized that we have advanced from qualitative to quantitative understanding of the thermal fatigue process and can now make life predictions with factor-of-two reliability for conventional metals.
Abstract: Definitions are suggested for terms such as thermal fatigue, thermal-mechanical fatigue, and thermal-stress fatigue. Historical developments in the field of thermal fatigue from 1838 to the present are reviewed. It is hypothesized that we have advanced from qualitative to quantitative understanding of the thermal fatigue process and can now make life predictions with factor-of-two reliability for conventional metals.
TL;DR: In this paper, the most feasible method of utilizing potentially non-durable coarse aggregates is to reduce maximum particle sizes and the needed reduction can be determined from laboratory freeze-thaw tests and is found to vary with source.
Abstract: Primary considerations in the selection of materials for coarse aggregate are those pertaining to freeze-thaw durability and the development of D-cracking in highway and airfield pavements. Two aspects of the problem are of particular importance: moisture movements and critical saturation of the aggregate, and the response of the aggregate to cyclic freezing and thawing in concrete. Laboratory studies of coarse aggregates have indicated that nondurable materials are generally of sedimentary origin and may reach critical saturation when the concrete is in direct contact with either free water or capillary-held water. Absorption-adsorption and mercury intrusion studies have revealed differences in the pore structure of durable and nondurable materials, while laboratory tests of aggregates in concrete differentiate performance during freezing and thawing in line with field service records. The most feasible method of utilizing potentially nondurable coarse aggregates is to reduce maximum particle sizes. The needed reduction can be determined from laboratory freeze-thaw tests and is found to vary with source. Gravel sources have the option of crushing oversize material for using naturally finer material to improve durability, while crushed stone sources may use alternatively selective quarrying to produce higher quality aggregates. Proper evaluation of aggregate materials is contingent on establishing laboratory procedures directed expressly to the problem of D-cracking.
TL;DR: In this paper, various electrochemical techniques for predicting galvanic corrosion behavior of metals are described and evaluated on the basis of practicality using specific galvanic couples as examples, and some serious shortcomings of the existing techniques and warns of the dangers of their improper use.
Abstract: The various electrochemical techniques for predicting galvanic corrosion behavior of metals are described. Each method is evaluated on the basis of practicality using specific galvanic couples as examples. The paper describes some serious shortcomings of the existing techniques and warns of the dangers of their improper use.
TL;DR: The results suggest that an intracellular trans-membrane potential change (surface effect) is necessary to activate ciliated cells of small clams, and that inhibition of ciliary activity in intact clams would impair feeding and respiration.
Abstract: An apparatus for testing the effects of drugs on the ciliary beating rate of clam gills has been modified to rapidly (15 min to 1 h) assess the effects of water quality factors on a sensitive organism, the fingernail clam, Musculium transversum. The gill and adductor muscles of the clam are excised and placed in a petri dish through which a continuous flow of molluscan Ringers solution or a test solution can be maintained. Normal ciliary activity of the gill preparation can be maintained for at least eight days. The ciliary beating rate is determined by synchronizing the rate of flashing of the sub-stage lamp of a microscope, with the rate of beating of the cilia. Synchronization is achieved when the metachronal ciliary wave appears to stand still. The first water quality factor selected for testing by the rapid method was potassium, because potassium concentrations are higher in the Illinois River where fingernail clams have largely died out, than in the Mississippi River where the clams are still abundant. The apparatus provided statistically reliable results in a short period of time. There are significant differences in the responses of large (7 to 11 mm) and small (1 to 5 mm) clams to: (a) removal and subsequent addition of potassium, (b) variation of maintenance dosage of potassium in the washing solution, and (c) lag period of response to a specific dose. The results suggest that an intracellular trans-membrane potential change (surface effect) is necessary to activate ciliated cells of small clams. This latter change in small clams would account for the relatively short lag period for potassium activation. Potassium levels required for maintenance of a basal ciliary beating rate are 10 - 3 M (39.1 mg/litre) for small clams and 10 - 6 M (0.039 mg/litre) for large clams. Greater concentrations are cilioinhibitory. Lesser concentrations are generally cilioexcitatory, but concentrations less than 10 - 8 M (0.00039 mg/litre) and 10 - 9 M (0.000039 mg/litre) are insufficient to sustain basal rates in large and small clams, respectively. Potassium concentrations in certain rivers, such as the Illinois and Mississippi, are high enough to cause cilioinhibition in gill preparations from large fingernail clams. Inhibition of ciliary activity in intact clams would impair feeding and respiration. The effects of potassium on the survival, growth, and reproduction of intact fingernail clams are currently being determined and will be related to the effects observed by means of the rapid method.