Showing papers in "ASTM special technical publications in 1981"

A crack-closure model for predicting fatigue crack growth under aircraft spectrum loading

Abstract: The development and application of an analytical model of cycle crack growth is presented that includes the effects of crack closure. The model was used to correlate crack growth rates under constant amplitude loading and to predict crack growth under aircraft spectrum loading on 2219-T851 aluminum alloy sheet material. The predicted crack growth lives agreed well with experimental data. The ratio of predicted to experimental lives ranged from 0.66 to 1.48. These predictions were made using data from an ASTM E24.06.01 Round Robin.

Theory of electron-avalanche breakdown in solids

Abstract: Electron-avalanche breakdown in solids is explained by a theory that is predictive and agrees with experimental results for the magnitude of the breakdown field and its temperature dependence, pulse-duration dependence, material-to-material variation, and wavelength dependence for λ > 1 μm. The good agreement between experiment and theory with no parameters adjusted is obtained by using improved magnitudes and energy dependences of the electron-phonon relaxation frequencies. The contributions of both optical and acoustical phonons to electron loss and diffusion must be included. The breakdown field E B is calculated by solving an eigenvalue equation obtained from the diffusion transport equation. Simple models and interpretations of the diffusion equation afford physical insight into breakdown and render the breakdown conditions predictable. Preliminary results indicate that the diffusion approximation fails for wavelengths considerably shorter than 1 μm, but that E B decreases with decreasing X as a result of multiphoton absorption before the diffusion approximation fails.

Estimations on J-integral and tearing modulus T from a single specimen test record

Abstract: This paper presents methods for evaluating the J-integral and the tearing moduli from a single test record. Several different aspects of the problem have been combined in this work. An overview of the conditions for separability of the load into multiplicative functions of displacement and crack length as well as for the existence of it-factors is presented. The consequences of expressing J by a Merkle-Corten type formula are explored in terms of the crack increment, da, the tearing modulus, T, and J itself, including the case of growing cracks. A simple method is suggested to obtain the correct J for crack growth and T from nothing more than the test record itself; the procedure is applied to available experimental data and the results are compared with those obtained by other formulae. Additional physical interpretation is given on the T m a t -versus-T a p p stability criterion and the remaining compliance capacity C C R is defined.

State of the Art: Laboratory Strength Testing of Soils

Abstract: A review and evaluation of the advantages and limitations of laboratory equipment for measuring the shear strength of soils are presented. Equipment evaluated include direct shear, torsional shear, simple shear, triaxial,multiaxial (true triaxial), plane strain, hollow cylinder triaxial, and directional shear devices. The evaluation indicates that the impetus to obtain parameters for constitutive equations and modeling has resulted in the development of improved equipment and testing techniques; specifically, the development of multiaxial (true triaxial) and hollow cylinder triaxial test equipment. Although these devices are more versatile, the conventional solid cylinder triaxial test is still the most popular. The evaluation suggests that direct shear and simple shear devices are best utilized by designers who have gained experience applying the results from such tests to structures that have behaved satisfactorily. Proper consideration must be given to the effects of membrane penetration, end restraint saturation and consolidation procedures, and rates of loading in any testing program.

A Simple Crack Closure Model for Prediction of Fatigue Crack Growth Rates Under Variable-Amplitude Loading

Abstract: A model for the prediction of growth rates of fatigue cracks in aluminium alloys is presented. The model is based on an approximate description of the crack closure behavior and can be used to predict effects of crack growth acceleration and retardation observed experimentally under variable-amplitude loading. A computer program was developed for analysis of fatigue crack growth. It was used to analyze the effect of certain parameter variations in a flight simulation load spectrum on the crack growth rate. For 7075-T6 thin sheet material the results are compared with experimental data.

Measurement of the Hydraulic Conductivity of Fine-Grained Soils

Abstract: The purpose of this paper is to review the state of the art in the measurement of hydraulic conductivity of fine-grained soils. Both field and laboratory tests for saturated and partially saturated soils are considered. For saturated soils, field tests are to be preferred because they permeate a larger volume of soil, thus taking into account the effects of macrostructure better than laboratory tests. Field tests are generally best performed by using a cylindrical piezometer tip, installed by methods that minimize disturbance, and measuring flow under a constant head. Laboratory tests offer the advantage of economy. Laboratory specimens should be as large as practical and should be oriented to produce flow in the direction of maximum hydraulic conductivity. The permeant should be a fluid similar to that encountered in the field. Without proper experimental technique, the conductivity measured in the laboratory may differ from the field value by several orders of magnitude. Field tests for unsaturated soils are not well developed and can only be recommended for cases where water will be ponded on the surface of a site. The most versatile laboratory techniques are the instantaneous profile method using tensiometric or psychrometric probes, and the pressure plate outflow method. The best method to use depends on the soil suction expected in the field.

Reliability of the Bacterial Luminescence Assay for Determination of the Toxicity of Pure Compounds and Complex Effluents

Abstract: The bacterial luminescence toxicity assay has been under development for 2 years. The assay procedure has been significantly improved in that five dilutions of a toxicant or effluent can be assayed simultaneously along with a control. A median effective concentration (EC 5 0 ) can be generated 30 min after sample collection. The reproducibility of the assay using sodium lauryl sulfate as a standard displayed a coefficient of variation of 15 to 20 percent. The data presented compare Microtox EC 5 0 data for pure compounds and literature data on median lethal concentrations (LC 5 0 ) for fish. In addition, over 50 complex effluent samples were assayed with Microtox. These same samples were assayed simultaneously using standard fish testing procedures. The data show that a good correlation exists between the bacterial luminescence assay and conventional testing procedures.

Fitting Models to Composite Materials Fatigue Data

Abstract: A new procedure for fitting fatigue models (consisting of a deterministic equation defining the shape of the S-N curve and a probabilistic description of the data scatter) is presented. The procedure consists of (1) transforming the fatigue data into equivalent static strength data by using the deterministic equation in the fatigue model with unknown parameters, (2) obtaining the maximum-likelihood estimates for the parameters of the (two-parameter Weibull) distribution describing the equivalent static strength data, and (3) repeating Steps 1 and 2 until the largest maximum-likelihood estimate of the shape parameter is obtained. The procedure can handle runouts and tab failures through progressive censoring. Finally, the procedure is well defined when small fatigue data samples are available.

Bioaccumulation and Chronic Toxicity of Bis(tributyltin) Oxide (TBTO): Tests with a Saltwater Fish

Abstract: The accumulation and depuration of bis(tributyltin) oxide (TBTO), a widely used active ingredient in antifouling paints, and its acute and chronic toxicity to sheepshead minnows (Cyprinodon variegatus) were determined. Equilibrium between the concentration of carbon-14-labeled-TBTO in seawater and in fish tissues was not reached after 58 days of exposure. The maximum observed bioconcentration factor in whole fish was ×2600. The maximum observed bioconcentration factors for the muscle, viscera, and remains were ×1810, X4580, and X2120, respectively. Sheepshead minnows depurated 52 percent of the 1 4 C-TBTO within 7 days and 74 percent after 28 days. The 21-day median lethal concentration (LC 5 0 ) for sheepshead minnows exposed to TBTO was 0.96 ppb. The only statistically significant effect observed in the life-cycle test was mortality of the F 0 fish in the mean measured TBTO concentration of 4.8 ppb. There was an obvious concentration-response relationship in mortality of the F 1 fish, although, no statistically significant differences in mortality were detected between the control and the TBTO-exposed treatments. The surviving F 1 fish exhibited no signs of abnormal development, nor was growth decreased as a result of F 0 exposure to TBTO concentrations ≤1.0 ppb. Tissue samples from the life-cycle test, analyzed for total tin, confirmed the bioconcentration of TBTO, showed the accumulation to be concentration dependent, and indicated that the fish were actively metabolizing TBTO into its lower and less toxic alkyl moieties.

Off-Axis Fatigue of Graphite/Epoxy Composite

Abstract: Off-axis static and fatigue behavior of AS/3501-5A graphite/epoxy was studied in an effort to characterize the matrix/interface-controlled failure. Seven different off-axis angles were tested: 0, 10, 20, 30, 45, 60, and 90 deg. Initial (static) and post-fatigue residual strength were obtained together with S-N relationships. Fracture surfaces were examined through photomicrographs and stereo (three-dimensional) scanning electron microscope (SEM) photographs, in order to delineate failure modes, and the results of these inspections are discussed. The off-axis static strength, including scatter, was fully characterized by a polynomial and a nondimensional strength parameter. Essentially, no strength or modulus degradation was observed in the specimens surviving fatigue loading of 10 6 cycles regardless of the off-axis angle or fatigue stress level. When fatigue stress level is normalized with respect to static strength, all data seem to fall on the same S-N curve. Fatigue failure occurred without any warning or visible damage. Matrix failure characteristics vary with off-axis angle and appear in the form of serrations and axial and transverse cracks. Large scatter in life was observed at all off-axis angles; however, since the number of specimens employed in the present study is not sufficient to provide meaningful statistical S-N data, a more detailed investigation of the off-axis (and angle ply) behavior of graphite/epoxy composites is warranted.

Further Developments in the Design and Analysis of Adhesive-Bonded Structural Joints

Abstract: Previously developed computer programs for analyzing stepped-lap adhesive-bonded joints and doublers have been modified to permit the inclusion of variable adhesives as well as nonuniform adherends. The new version of the analysis program is described with reference to examples illustrating the effects of load redistribution around flaws and porosity. The loss of strength associated with pinched-off edges is illustrated, and the benefits of deliberately thickening the adhesive layer in the immediate vicinity of the ends of the overlap are demonstrated. The changes in shear load transfer due to softening of some of the adhesive by moisture absorption while the remainder either has never been soaked or has dried out locally are discussed.

Electrochemical impedance techniques in corrosion science

Abstract: A review is presented of the use of impedance techniques in corrosion science. Emphasis is placed on defining the type of data that is required in corrosion studies, and then comparing different methods for generating therequired information by electrochemical impedance methods. The performance characteristics of the various techniques, including cost, are critically compared to assist readers in selecting the most appropriate system for their needs.

Bolt-Bearing Fatigue of a Graphite/Epoxy Laminate

Abstract: Graphite/epoxy laminates (T300/5208) were tested under bolt-bearing loads for a range of bolt clampup torques and for several test conditions involving water. High clampup torque improved both the static strength and fatigue limit by about 100 percent compared to a simple pin-bearing case, which had no through-the-thickness constraint. The static strength improvement was explained in terms of failure modes. Bolt clampup also influenced the hole elongation that developed before failure. For both the static and fatigue tests, the hole elongations were much larger for the low-torque-clampup case than for the pin-bearing case or for tests with moderate clampup torques. Tests in water degraded static bearing strength only slightly, but reduced the fatigue limit about 40 percent below that for tests conducted in air.

Borehole Shear Test in Geotechnical Investigations

Abstract: The concept of Borehole Shear presents a unique alternative in shear strength testing of soil and rock in that tests may be conducted rapidly on the sides of the hole on relatively undisturbed material; therefore the inherent problems associated with obtaining equivalent information from laboratory tests are eliminated. In contrast to other methods of measuring in situ shear strength (that is, vane shear, cone penetrometer and pressuremeter) the Borehole Shear Test (BST) and Rock Borehole Shear Test (RBST) give discrete values of friction angle and cohesion; therefore more complete analyses may be made for such fundamental problems as bearing capacity and slope stability. In the past the BST has been considered a drained test and the effective parameters Φ' and c' have been reported. This may not always be the case. The general use, operation, assumptions, and problems of the test are examined and examples of the interpretation of results are given. Because of the time, economics, and accuracy of this method, the technique of Borehole Shear should see increased use in future in situ geotechnical testing.

Alternating-Current Impedance Measurements Applied to Corrosion Studies and Corrosion-Rate Determination

Abstract: The general features of the a-c impedance at a metal-electrolyte interface as a function of frequency are depicted, and recently developed measurement techniques are described. It is established that at low and very low frequencies, down to the millihertz domain, relaxation phenomena are found in those cases where the assumptions used in Stern's derivation are not met. Under such conditions polarization resistance techniques can hardly be used owing to experimental and theoretical reasons. Charge transfer resistance, when used instead of polarization resistance in a Stern's type equation, is proved to overcome these difficulties on the basis of a theoretical derivation. Correlation between charge transfer resistance and corrosion rate is illustrated by practical examples of pure iron and anodized aluminum alloys.

Acoustic Emission Behavior and Monitoring of Soils

Abstract: As far as nondestructive testing methods are concerned, acoustic emission techniques are relatively recent additions to the rock monitoring area (dating from the late 1930's) and to the metal testing area (dating from the 1950's). Its application to soils is an even more recent event with little activity prior to the 1970's. However, over the past five to ten years, interest has been generated in the soils area to the point where at least five equipment manufacturers are currently marketing acoustic emission systems specifically for geotechnical engineering applications. This activity is seemingly well founded, for acoustic emissions are indeed generated by deforming soil masses and technical feasibility is now firmly established. This state-of-the-art paper on acoustic emission activity in soils presents these findings on the basis of fundamentals, small-scale laboratory tests, and large-scale laboratory tests. Furthermore, the technique has been applied to field situations in a number of cases. These include slope stability monitoring of dams and embankments, soil movements arising from horizontal and vertical deformations, seepage monitoring, and grout/hydrofracture monitoring. Specific case histories in each group are presented. Collectively taken, the information available seems encouraging enough for many investigators to use the technique for a wide variety of applications. With a multifaceted attack, the current qualitative status of the technique (that is, no acoustic emission indicates stability; low acoustic emission indicates small movement; moderate acoustic emission indicates larger movement; high acoustic emission indicates instability) should move into a better defined quantitative status. In this latter case, acoustic emission signatures of different soils could lead to instant assessment of actual stress levels in any given situation. (Authors)

Plane-Strain Testing of Sand

Abstract: Sand was tested under triaxial conditions, plane strain conditions, and conditions where the intermediate principal strain (∈ 2 ) varied between the limits for triaxial and plane strain. Tests were performed using a variety of specimen sizes and shapes, a range of densities from loose to dense, and a range of confining pressures from 70 to 3450 kN/m 2 (10 to 500 psi). The results of these tests provide useful guidelines for plane strain testing of cohesionless soils: (1) Plane strain and triaxial test results differ most for dense specimens tested at low pressures, (2) Plane strain equipment need not be elaborate. Specimens with square cross sections and simple lubricated end plates can be used for plane strain tests, and (3) The end plates need not enforce a condition of perfect plane strain. Tests with values of ∈ 2 as large as 40 percent of the axial strain at failure result in essentially the same value of the angle of internal friction (Φ) as do perfect plane strain tests.

Some Considerations in the Statistical Determination of the Shape of S-N Curves

Abstract: This paper discusses the need for defining the shape of S-N curves, the various kinds of test data available for this purpose, and the problems in their statistical evaluation, including the assumptions that must be made.A method is proposed for finding the "cutoff" point, that is the endurance at which conventionally shaped S-N curves change slope to the horizontal. It is based on maximum likelihood principles and deals with runouts in a statistically acceptable way. A sharp or a continuous transition from the horizontal to the sloped straight line log S/log N curve may be considered. The method can be used for analysis and comparison of fatigue test results with a computer program, described and listed elsewhere by the authors, but it is subject to certain amendments, which are described in the paper.

An analysis of several fatigue crack growth rate (FCGR) descriptions

Abstract: This report presents the results of a round-robin life-prediction effort conducted by ASTM Task Group E24.04.04 on FCGR Descriptions. The fatigue crack growth rate (FCGR) data supplied to the task group participants for description purposes are provided along with the definition of the life-prediction effort and results. It is shown that the majority of the participants could describe the FCGR data well enough that the resulting constant amplitude life predictions were within ′20 percent of the test lives for more than 80 percent of the tests.

Multi-Parameter Yield Zone Model for Predicting Spectrum Crack Growth

Abstract: A systematic technique is presented for modeling crack growth load interaction effects due to spectrum loading. The Multi-Parameter Yield Zone (MPYZ) model accounts for crack growth retardation, acceleration, and underload effects. The load interactions are attributed to the residual stress intensity due to the plastic deformation at the crack tip. Fatigue crack growth was predicted and compared with test data for a variety of spectrum loadings.

Failure Analysis of Composite Laminates with a Fastener Hole.

Abstract: : Stress and strength analysis of composite laminates with a through the thickness circular hole, under uniaxial tensile load has been conducted. The hole is filled with a rigid core simulating a bolt. As a representation of the force at the bolted joint, displacement boundary conditions are applied to the rigid core. The stress analysis is based on treating the laminate as a homogeneous plate using finite element technique. The strength analysis is based on the tensor polynomial failure criterion applied to each constituent ply orientations. The ultimate laminate failure strength is based on the last ply failure stress. The resulting predictions of strength are found to be conservative as compared to experimental values. (Author)

Load sequence effects on the fatigue of unnotched composite materials

Abstract: A more comprehensive version of an earlier fatigue and residual strength degradation model is proposed to predict the effect of load sequence on the statistical fatigue behavior of composite laminates. The model, which reduces to various fatigue models proposed in the literature by means of approximations, is verified by a survey of experiments on glass/epoxy laminates. It is shown that the correlation between the model and the test results under dual stress levels is reasonable, and that a simplified version of the model is verified by experiments on graphite/epoxy laminates in which the correlation between theoretical predictions and results under dual stress levels is satisfactory. The model is also shown capable of predicting the effect of proof loads on the fatigue behavior of composite materials.

Compression Fatigue Behavior of Graphite/Epoxy in the Presence of Stress Raisers

Abstract: Graphite/epoxy composites are being applied to aircraft structures because of their demonstrated capability to reduce weight and increase life. Although composites have better fatigue properties than metals, their behavior differs significantly. Unlike metals, composites exhibit excellent tensile fatigue behavior-the constant amplitude fatigue strength at 10 7 cycles being close to static ultimate. Compression and reversed loading fatigue behavior in the presence of stress raisers, however, has not been well characterized. This program was therefore undertaken to determine the characteristics of composites under these conditions. Two stress raisers were considered; the first was an open hole and the second was damage resulting from low velocity, hard object impact. For the open hole specimen, constant and variable amplitude tests were performed to determine the significance of compression fatigue and to investigate the failure mechanism. These tests indicated that the fatigue life under compression and reversed loading is less than for tension-tension loading and will be an important design consideration in future composite applications. The failure mechanism appeared to be local progressive failure of the matrix near the stress raiser resulting in delamination, and final failure by fiber buckling. The variable-amplitude loading results also demonstrated the unconservativeness of Miner's rule for making analytical predictions. In order to determine the nature and significance of impact damage to generic composite structural elements, low velocity impact and residual properties tests were conducted on solid laminate specimens of 42 and 48 plies thick and on honeycomb sandwich specimens with 12-ply composite face sheets. Results of post impact properties tests indicate subvisual damage can degrade compression static and fatigue strength, although subvisual damage will not propagate under moderate (0.003) cyclic strain.

Theoretical Characterization and Comparison of Resonant-Probe Microwave Eddy-Current Testing with Conventional Low-Frequency Eddy-Current Methods

Abstract: During the past two years small ferromagnetic resonators (FMR) operating at frequencies above 1000 MHz have been shown to offer promise as a new type of eddy-current probe for surface-breaking cracks in metals. Strong signals have been obtained from both electrical discharge machining (EDM) notches and actual fatigue cracks, and the FMR probes have been shown to have lift-off discrimination capability. Since the skin depth at these microwave frequencies is of the order of microns, the surface currents must penetrate the crack and, in order to detect its presence, the flaw detection mechanism must be necessarily somewhat different in detail than for conventional low-frequency eddy-current methods, where the flaw has dimensions typically of the order of the skin depth. A general theory, based on the Lorentz reciprocity relation and applicable to all types of detection systems, is reviewed and used as a vehicle for comparing microwave with low-frequency eddy-current techniques. In the microwave case, the FMR resonator is emphasized but other probe geometries are also considered.

Applications of Acoustic Emission Techniques to Rock and Rock Structures: A State-of-the-Art Review

Abstract: This paper presents a state-of-the-art review of the subject of acoustic emission as it pertains to the area of rock mechanics, and includes references to some 150 recent papers. Although a limited discussion of laboratory oriented studies are included, the major thrust of the paper is to field applications in geotechnical engineering. The paper first discusses the general concepts involved in the acoustic emission technique and briefly reviews the early history of the subject. This is followed by a general discussion of techniques currently in use for monitoring and analysis of acoustic emission data, and a description of a number of recent and on-going field studies where acoustic emission techniques are being employed in the general area of geotechnical engineering. Finally, the paper considers the various limitations of the technique as well as areas where further research and development are considered necessary.

Fatigue behavior of graphite-epoxy laminates at elevated temperatures

Abstract: An examination and analysis is presented of the elevated temperature fatigue behavior of multidirectional graphite-epoxy laminates in terms of single lamina behavior. The laminate strength is predicted by considering the cyclic stress field in each lamina, the interlaminar stresses, and the experimentally determined temperature-effect 'shifting factors'. The initial failure of a lamina in a laminate is examined first in terms of stress redistribution, and then in terms of total failure and final laminate fracture; these analytical results are then compared with the actual fatigue behavior of T300/5208 graphite-epoxy composite laminates. In view of the agreement obtained, it is concluded that the temperature 'shifting factors' introduced here enable one to predict long-term behavior at a given temperature from short-time testing at elevated temperatures.

Scanning Reference Electrode Techniques in Localized Corrosion

Abstract: The principles, advantages, and implementations of scanning reference electrode techniques are reviewed. The technique locates the position of localized corrosion, and can be used to monitor the development of corrosion and changes in the corrosion rate under a wide range of conditions. Data related to pitting, intergranular corrosion, welds, and stress-corrosion cracking are presented.

A Root-Mean-Square Approach for Predicting Fatigue Crack Growth under Random Loading

Abstract: A method for predicting fatigue crack growth under random loading which employs the concept of Barsom (1976) is presented. In accordance with this method, the loading history for each specimen is analyzed to determine the root-mean-square maximum and minimum stresses, and the predictions are made by assuming the tests have been conducted under constant-amplitude loading at the root-mean-square maximum and minimum levels. The procedure requires a simple computer program and a desk-top computer. For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82, which is a good result, considering that the normal scatter in the fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions.

The Use of A-C Field Measurements to Determine the Shape and Size of a Crack in a Metal

Abstract: An instrument designed to measure the a-c field accurately has been built and fully tested on steel, aluminium, and titanium. These field measurements can be interpreted in terms of crack size, which provides a new technique for nondestructive testing (NDT) that requires no prior calibration. This paper describes the basic electronic measuring system, theoretical derivations of the electrical-field distribution, and application to industrial problems such as crack measurement in threads, shafting, welded connections, etc.

Random Spectrum Fatigue Crack Life Predictions With or Without Considering Load Interactions

Abstract: The validity of using constant amplitude crack growth rate data for the prediction of fatigue crack growth behavior and lives of center-cracked tension (CCT) specimens under random spectrum loadings was assessed. Analytical predictions obtained from the EFFGRO computer program were the results from two different approaches. One approach did not account for the load interaction effects to the fatigue crack growth, while the other approach considered both the tensile overload retardation and the compressive load acceleration effects as well as the reduction of overload retardation effect caused by the compressive load immediately following the tensile overload. This paper describes the fatigue crack growth rate equation, the load interaction model, the numerical procedure, and the cycle counting technique used in the EFFGRO program. Results from other studies, including the sensitivity of the overload shut-off ratio, the crack growth rate constants determination procedure, and the range-pair counting effects to the prediction accuracies, are also presented.