bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural Aspects of Fracture Toughness
Authors: Weiss V , Kasai Y , Sieradzki K
Published: March 2009

For most technical materials the dominant mechanism resisting crack extension is plastic deformation. Continuum mechanics analysis shows that fracture toughness, in addition to depending on Young's modulus, flow stress, strain hardening exponent, and yield strain, should be nearly proportional to the effective fracture ductility obtained for the stress state characteristic for the region ahead of the crack; plane stress or plane strain. The original equation for plane-strain fracture toughness-equibiaxial ductility is refined to include the effects of strain hardening. Such a correlation has been experimentally confirmed for steels; KIc was found to be proportional to the effective equibiaxial ductility. A model for the thickness effect on Kc has been developed on the basis of these observations and is in fair agreement with experimental results.

The dominant microstructural events that control ductility, and therefore fracture toughness, are void nucleation, void growth, and void coalescence. Void nucleation at an inclusion—matrix interface is governed by the value of the interface strength—flow stress difference and is, consequently, temperature sensitive. Models for void growth mechanisms show the void coalesence strain to be a strong function of the nuclei density but rather insensitive to temperature. Qualitative relationships are presented which give some insight into the microstructural causes for ductility and fracture toughness transitions (or their absence in face-centered-cubic materials) with temperature, and can serve for the development of new high-toughness materials.
Relationship Between Tensile Properties and Microscopically Ductile Plane-Strain Fracture Toughness
Authors: Sailors RH
Published: March 2009

An equation has been derived which will permit plane-strain fracture toughness, KIc, to be calculated from a knowledge of uniaxial tensile properties. After corrections for constraint and strain hardening the plane-stress rigid plastic crack opening displacement expression was found to describe accurately experimental crack opening displacement for the plane-strain condition. The crack tip strain distribution was measured and found to be compatible with an r−1 strain distribution within a small region ahead of the crack tip. A length parameter was identified and shown to be proportional to mean-free ferrite path in steels. From the proposed behavior of crack tip instability, it was possible to better understand the observed trend of decreasing fracture toughness with increasing yield strength and how this trend can be altered by control of the microstructure.
Mechanical Behavior Model for Graphites
Authors: Buch JD
Published: March 2009

A physically based statistical theory of fracture for polycrystalline bulk graphite is presented. It is based on the inherent weakness of graphitic grains normal to the a–b plane and a coincidence alignment of these planes which has been found to have a dominant influence on strength. These concepts lead to a self-consistent treatment of the tensile fracture of graphite on the basis of the physical parameters of grain size, grain orientation, grain cleavage stress, porosity, fracture toughness, and specimen volume. This interpretive analytical model for the fracture of graphite provides a method for predicting the mechanical and fracture behavior of graphite as a function of its microstructure. The concepts and logic are applicable to other material systems.
An Electronic System to Monitor the Effects of Changes in Water Quality on Fish Opercular Rhythms
Authors: Morgan WSG
Published: March 2009

A rapid automatic biological monitoring system, intended to complement physical-chemical monitoring techniques, has been developed which utilizes the fact that fish opercular rhythms increase under toxic conditions. Any increase which is above the rate to be expected under normal conditions is monitored electronically. An in-built visual alarm system serves as an advance warning of the development of a critical toxic condition. The system also has the ability of controlling toxic industrial discharges, thus aiding the preservation of the quality of receiving waters.
A Biological Monitoring System Employing Rheotaxis of Fish
Authors: Besch WK , Kemball A , Meyer-Waarden K , Scharf B
Published: March 2009

An automatic toxicity monitoring and alarm device using rheotaxis is described. This device can also be used for static laboratory tests. When loss of rheotaxis along with surfacing are used as criteria for acute poisoning instead of death, the time for toxicity tests required would be considerably shortened. Visual observation of some other parameters of behavior, such as schooling, would yield additional valuable information about the specific effects of a certain poison or a particular concentration of it. Methods are proposed which allow even unskilled personnel to make these observations. Loss of rheotaxis and surfacing can be recorded automatically. Testing of the automatic monitoring device in the laboratory led to the development of a multichannel, automatically recording test apparatus.
Rapid Assessment of Water Quality Using the Fingernail Clam, Musculium transversum
Authors: Paparo AA , Sparks RE
Published: March 2009

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 substage 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 10−3 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.
A Laser-Based Optical Filtering System to Analyze Samples of Diatom Communities
Authors: Dickson KL , Slocomb JP , Cairns J , Almeida SP , Eu JKT
Published: March 2009

Biomonitoring systems designed to protect the integrity of aquatic ecosystems must satisfy two complementary requirements if they are to be used in a successful management program. First, they must generate reliable information with respect to the current biological status of the ecosystem; second, they must be capable of reducing the lag time in the feedback of this information. This paper describes a biomonitoring system, currently being developed, that employs coherent optical spatial filtering techniques to rapidly identify diatoms and process species-abundance information. Preliminary results indicate that the optical problems associated with such a system can be overcome satisfactorily, although investigations are continuing into the problem of interfacing a microscope directly to the optical system. We envision that this system can eventually be employed in a management program along with chemical and physical data to obtain full beneficial use of the ecosystem without damage.
The Importance of Monitoring Change
Authors: Patrick R
Published: March 2009

This paper demonstrates how 25 years of more-or-less continuous monitoring of the Savannah River and of the Sabine River is able to show the effects of man's use of the river over time. The kinds of perturbation which are evident by such monitoring are the building of dams, the increase in organic pollution, and the effects of small amounts of toxic pollution. It demonstrates how this type of monitoring with stations located in various parts of the river can indicate the origin of pollution loads. Monitoring that is carried out continuously by the use of diatometers and intermittently by the study of major groups of organisms living in a river or estuary produces the best combination of facts concerning river conditions and water quality.
Time as a Factor in Biomonitoring Estuarine Systems with Reference to Benthic Macrophytes and Epibenthic Fishes and Invertebrates
Authors: Livingston RJ
Published: March 2009

Estuarine and coastal populations undergo regular short- and long-term fluctuations in various functions which approximate diurnal, tidal, seasonal, and annual periodicities. This, together with a highly unstable physical environment, leads to considerable variation in temporal relationships of estuarine communities thus complicating biological monitoring programs. The implications of temporal variation of the natural environment are discussed relative to the biological sampling necessary to account for such variability; examples are taken from studies in three bay systems along the Gulf coast of north Florida.

The natural physicochemical functions in coastal systems are associated with rapid (diurnal) as well as long-term (seasonal) variations which should be determined from carefully designed sampling programs if causative elements of the impact of pollutants are to be determined. Against this background, the timing of pollutant entry into the system could control the actual nature of the impact. This should be related to natural cycles of various organisms in a given system after adequate determination of the timed sequence of biological variation. Regular changes of assemblages of epibenthic organisms, though often temporally stable on an annual basis, are only roughly synchronized with seasonal patterns of key physical functions such as temperature and salinity. Community structure can be masked or distorted by inadequate sampling either on a short-term or seasonal basis. This, together with seasonally directed changes in the actual impact of a given pollutant, should be taken into consideration in the design of a given biomonitoring program. The goals of each project should be reconciled with the short- and long-term variations of the biological system in question.
Results of a Round Robin Test Program on Hardness Conversion of Ferritic Stainless Steels
Authors: Heberling TG
Published: March 2009

A round robin program was conducted to determine the hardness conversions for ferritic stainless steels. Each of six participating laboratories conducted hardness tests on specimens representing nine grades, each having varying amounts of cold reduction. Conversions were established to the Rockwell B scale from Rockwell 15T, 30T, 45T, and A scales.

In all cases, the Wilson Chart (Chart No. 52—Wilson Instruments Division, American Chain and Cable Company) conversion fits the least squares round robin data line better than does the ASTM Method E140 austenitic conversion. The Wilson Chart conversion line falls within the 95 percent confidence band of the round robin data for the conversions to Rockwell B from Rockwell 30T, 45T, and A. For the 15T to Rockwell B conversion, the Wilson line falls outside the 95 percent confidence limits for values below HRB 80.

As a result of this round robin program, a joint task group was organized under ASTM Subcommittees A-01.13 and E-28-06 to determine what changes should be made in the hardness conversion tables in ASTM Methods A 370 and E 140. The recommendations of this task group are currently being balloted.
Use and Reproducibility of a Gage to Measure the Lateral Expansion of Charpy V-Notch Impact Specimens
Authors: Holt JM
Published: March 2009

Because the lateral expansion that occurs on the compression side of the Charpy V-notch specimen, directly opposite the notch, appears to be a direct measure of notch ductility and appears to be independent of strength variation and of chemical composition, its use as a notch-ductility criterion is increasing. During the years that U. S. Steel Corporation has been measuring lateral expansion, a gage was developed for measuring this value rapidly. This paper describes the gage and the method for using it and presents the results of a test program conducted on standard specimens of A36 and ASTM 514 Type F steels to determine the accuracy and reproducibility of lateral-expansion measurements made with this gage. Measurements were made at several U. S. Steel Corporation plants that produce or use plates to ensure that plant personnel are able to obtain the same values as those obtained at a research laboratory, within an allowable tolerance.

The results of the test program may be summarized as follows: (1) The accuracy of the measurements was the same as the accuracy of the dial indicator that was integral with the gage; for the standard 1-mil gage, this accuracy is ±2 mils (1 mil = 0.001 in.). (2) The reproducibility of measurements made with the standard gage was about the same as the accuracy, that is, ±2 mils. (3) Prior experience in using the gage is not necessary to obtain this degree of reproducibility. (4) Plant personnel can obtain values that are in agreement with those obtained at a research laboratory. (5) Measurements made with micrometers were accurate and were generally reproducible to the same degree as the gage; however, considerably greater care is required in making micrometer measurements, and, for this reason, the use of the dial gage is recommended over the use of micrometers.

Improved precision can be obtained by replacing the standard 1-mil dial indicator with a 1/10-mil (0.0001 in.) dial indicator at modest additional cost.
Protocol for the Evaluation of Poison Prevention Packaging
Authors: Perritt AM
Published: March 2009

The protocol for the evaluation of poison prevention packaging is the procedure to meet government standards for conducting child-proof unit tests involving child and adult panel testing. It was established by a joint government-industry committee on safety closures and then modified by the Food and Drug Administration which also developed poison prevention packaging standards. Currently the Consumer Product Safety Commission and the Environmental Protection Agency are responsible for poison prevention packaging on products.

Protocol parameters are test units, panelists (considered both by age and number), testing time, testing place, and interviewers.

The major problems in protocol studies are the strict requirements for specific age and sex groupings of panelists, communications with nursery schools, what is a safe-on position, and adult acceptance of poison prevention packaging.

A thorough quality assurance program including auditing of marketed products should follow protocol testing.
The Technical Advisory Committee on Poison Prevention Packaging and Its Function
Authors: Cooper MR
Published: March 2009

The Consumer Product Safety Commission (CPSC), pursuant to the Poison Prevention Packaging Act (PPPA), has legislative responsibility for the Poison Prevention Packaging Technical Advisory Committee (TAC). The TAC has representatives of federal agencies (as well as consumers), manufacturers of household substances, representatives of the packaging and closure industries, and members of the scientific and medical fields. Consistent wih the CPSC's mandate under the PPPA, the TAC examines the need for special packaging to protect children from serious personal injury or illness resulting from handling, using, or ingesting various substances. In order to require protective packaging, the product must be one likely to cause serious personal injury to a child five years of age or under. The TAC must also look to whether such special packaging is technically feasible, practical, and appropriate.
Quality Control of Special Packaging (Child-Resistant) Caps
Authors: Moroze JP
Published: March 2009

Various quality control programs instituted in compliance with the requirements of the Poison Prevention Packaging Act of 1970 concerning the use of child-resistant closures on aspirin-containing products are described.
Container Changes—Quality and Quantity
Authors: Nichols TE
Published: March 2009

The advent of child-resistant closures, while desirable for safety, has brought about the demand for closer tolerance in bottle (container) design and quality. These results have increased total package costs to the consumer while oftentimes resulting in subtotal package function.
Canadian Standards Association Services in Standards and Certification for Child-Resistant Packaging
Authors: Shaw CW
Published: March 2009

This paper explains the services rendered by the Canadian Standards Association (CSA) as a national standards writing body and as a testing laboratory. The paper shows how CSA certified that a given product line or system meets a specified standard once a prototype has been satisfactorily tested to the requirements of that standard.

The historical development in Canada of child-resistant packaging is related with the development in the United States of the “child-adult test protocol.”

The need for scientific test measurements of the anthropometric forces used in opening and closing child-resistant packages is explained. The use of these scientific test measurements has enabled the CSA to certify that packages in the marketplace are effectively identical to those originally submitted to the child-adult protocol test.

Several provincial governments in Canada have mandated the CSA certification of child-resistant packages. In so doing, these governments have established a “preclearance” of a package's child resistant and adult use capabilities. Otherwise, the need to prove compliance or non-compliance of the package's intended integrity in the marketplace remains a burden-some and difficult problem of resolve.
What is Thermal Fatigue?
Authors: Spera DA
Published: March 2009

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.
Thermal Fatigue and Its Failure Prediction for Brittle Ceramics
Authors: Hasselman DPH , Badaliance R , Chen EP
Published: March 2009

The thermal fatigue behavior of a soda-lime-silica glass subjected to water quench and silicon-nitride subjected to thermal environment of a turbine engine was predicted from data of slow (subcritical) crack growth. A numerical integration technique was developed to calculate the extent of slow crack growth for each thermal cycle over the total duration of the transient thermal stress and temperature, as well as the total number of cycles required for catastrophic failure to occur. Good agreement between the predicted and experimental data was found. The results indicate that, for reliable prediction of thermal fatigue resistance, an estimate of critical flaw-depth based on a statistical (such as the Weibull) theory of brittle fracture is necessary.
Some Thermal Fatigue Characteristics of Mild Steel for Heat Exchangers
Authors: Laub JS
Published: March 2009

Thermal fatigue of mild steel has received little attention until recently even though this material is used extensively in heat exchangers for gas-fired appliances. A survey of the thermal fatigue problem of thin shell mild steel structures subjected to arbitrary temperature fields is given. Data from end-constrained thermally cycled test specimens is also presented. These data have been validated through use in developing production heat exchangers.
A New Software Concept for Computerized Materials Testing
Authors: Richards FD
Published: March 2009

A general purpose software system for computerized materials testing is described, and although the software was specifically developed for materials testing applications, it has been used in other real time data acquisition and reduction applications with success (for example, the system was used to reduce data stored in a transient recorder). The software is core resident and allows one to control materials tests in real time and record and reduce data from these tests in the high level, conversational BASIC language. Previous software for such applications usually required the user to have extensive computer programming skills. The system described greatly reduces the time necessary to write and debug programs for computerized materials test systems. The simplicity of the overall system makes the computerized materials test system available to a broader range of users.
Experience in Data Acquisition and Reduction for a Biaxial Mechanical Testing Program
Authors: Penn RW , Fong JT , Kearsley EA
Published: March 2009

The inadequacy of uniaxial mechanical testing data as a basis for predicting multiaxial deformation and fracture is well known. For optimal biaxial tests, computer control of simultaneous variation of loadings using hydraulic power under closed loop servocontrol is essential. Computer assistance in real time data reduction from a biaxial mechanical test is economical. Physical features of computer hardware, software, and a hydraulic biaxial system are described along with sample results illustrating cross effects in fatigue and yield surface calculations. Significance of the graphical output based on thin tube specimens of 1-in. (2.54-cm) nominal diameter, schedule 80, commercial grade polyvinyl chloride pipes, and the limitations of the present system are discussed.
Application of an On-Line Digital Data System in the Composite Materials Fatigue Laboratory
Authors: Stinchcomb WW , Reifsnider KL , Williams RS
Published: March 2009

An experiment-dedicated data acquisition and processing system used in concert with a closed-loop servocontrolled testing machine is described, and its application to research on the fatigue response of composite materials is presented. The testing facility has been used to obtain reliable fatigue damage data for composite materials by monitoring (semi) time-resolved changes in material properties during the course of fatigue tests for the purpose of achieving a better understanding of fatigue damage processes. Included in the paper are discussions of the laboratory equipment, experimental procedures, and use of the data handling system in fatigue research.
A Unique Concept in Gasket Technology for Reducing Vehicle Weight and Lowering Flange Design Costs
Authors: Passarella MT , Farnam RG
Published: March 2009

A gasket “system” consisting of a high-density core unitized with “tailored” stress-risers, permits the user of choosing rigid and/or lighter component flange castings; with a potential reduction of the number of capscrews needed for a durable flange joint. Subsequent loading necessary for a conventional compression seal could therefore be reduced, allowing a further reduction in tensile strength requirements for the mechanical fasteners. The elimination, or relief, of tight flange surface-machining tolerances are then possible, reflecting a cost savings.
Testing Gasket Materials for Design Purposes
Authors: Swick RH
Published: March 2009

Energy, pollution abatement, and economic factors are increasing the sealing requirements for gaskets. Sealability, Creep Relaxation, and Gasket Compression Tests are described which permit the logical design of a gasket to make and assure a long time satisfactory seal for each application. Test equipment is described and an example of sealing wavy flanges is given.
ASTM Classification System for Gasket Materials and Its Use
Authors: Stevenson RW
Published: March 2009

The origin and purpose of ASTM Standard F104 — Classification System for Nonmetallic Gaskets — is described as a method of characterizing a gasket material. The nature of its flexibility and versatility are outlined. Examples are made illustrating how the system is meant to be used by consumers who have definite requirements and wish to secure a gasket material which manufacturers could provide to meet these needs.
Influence of Chloride in Reinforced Concrete
Authors: Cook HK , McCoy WJ
Published: March 2009

The present state of knowledge regarding the action of chloride, principally calcium chloride, in reinforced concrete is reviewed, with special emphasis on its effect on the reinforcing steel. The reactions through which calcium chloride accelerates the set and strength of portland cement are explained, as well as the significance these reactions with cement have with regard to the potential corrosion of steel reinforcement in concrete. Calcium chloride's beneficial effects in ordinary reinforced concrete are enumerated, along with the precautions regarding its use in prestressed concrete and special situations. The deterioration of bridge decks and the significance of the “chloride content corrosion threshold” that has been suggested for bridge decks are discussed. It is pointed out that the limit for chloride that has been suggested as a guide to determine the extent of repair to existing bridge decks that have been subject to repeated application of deicer salts is not a requirement that should be applied to limit the chloride content of ordinary reinforced concrete. When the amount of commercial calcium chloride is limited to two percent by weight of cement, the degree of corrosion in ordinary reinforced concrete is insignificant if the concrete is reasonably dense and there is adequate cover over the steel.
Marine Corrosion Behavior of Bare and Metallic-Coated Steel Reinforcing Rods in Concrete
Authors: Baker EA , Money KL , Sanborn CB
Published: March 2009

Concrete failure can develop from many causes, for example, thermal gradients, fatigue, insufficient cover, admixtures, rebar material, and exposure location. Cracking of concrete in itself was not found to be detrimental but could lead to spalling and structural deterioration. Metallic-coated rebars are shown to prevent concrete spalling.
Epoxy Coatings for Corrosion Protection of Reinforcement Steel
Authors: Kilareski WP
Published: March 2009

The bridge deck deterioration problem has been attributed to the corrosion of the reinforcement steel. Epoxy coating of reinforcement steel provides a positive means of preventing salt-induced rebar corrosion. The epoxy coating process is a well-established manufacturing procedure capable of full-scale bridge deck production.
A Corrosion Inhibitor Formulated with Calcium Nitrite for Use in Reinforced Concrete
Authors: Rosenberg AM , Gaidis JM , Kossivas TG , Previte RW
Published: March 2009

The scarcity of good aggregate in Japan led to an investigation of the use of a corrosion inhibitor for reinforced concrete. Corrosion current measured on small test specimens soaked in limewater for one day with an impressed voltage of + 400 mV with respect to the saturated calomel electrode shows that the introduction of calcium nitrite diminishes the corrosion of reinforcing steel in the presence of admixed sodium chloride. Long-term tests on larger specimens partially immersed in saturated sodium chloride solution indicate that admixed calcium nitrite can prevent the open circuit potential of reinforcing steel from entering the active region. Calcium nitrite was found to enhance the strength of concrete. Calcium nitrite complies with the requirements of ASTM Specification for Chemical Admixtures for Concrete (C 494-71). The use of a calcium-based admixture is expected to sidestep the issue of alkali-aggregate reactions and subsequent deterioration of concrete.
Polymer-Modified Concretes in Bridge Deck Overlay Systems
Authors: Steele GW , Judy JM
Published: March 2009

Premature failure of portland cement concrete bridge decks is of national concern, particularly in those areas where chloride residues accumulate in the concrete from winter deicing operations. West Virginia's research and field usage indicates that the application of a relatively thin (1 to 2-in.) overlay of portland cement concrete or mortar containing a latex modifier may result in a significant increase in the useful life of bridge decks. Eighteen structures, including both new construction and renovation of existing decks, have received the latex-modified concrete overlay. Results to date have been most encouraging.
Cathodic Protection for Reinforcing Steel in Concrete
Authors: Vrable JB
Published: March 2009

Chloride-induced corrosion of the reinforcing steel in concrete is a major cause of premature concrete deterioration. This presentation describes the results of an investigation sponsored by the National Cooperative Highway Research Program (Project 12–13) into the use of cathodic protection as a method of suppressing the corrosion of reinforcing steel in highway bridge concrete decks. The principal cause of bridge-deck corrosion is salt used for snow and ice removal. In this study, factors affecting the cathodic protection of steel reinforcement in concrete were investigated, and a variety of impress-current and sacrificial-anode approaches to cathodic protection of bridge decks were examined in laboratory and model testing.

The results of electrochemical studies showed that corrosion can be controlled by the application of cathodic current to corroding steel in concrete. The minimum protective potential for cathodic protection was established. Studies showed that cathodic-protection current can result in a decrease in bond strength between the steel and the concrete. However, the decrease would be slight at the anticipated conditions of protection.

A method previously developed by the California Department of Transportation was examined in depth, and it was concluded that this method offered promise as an impressed-current system. A sacrificial-anode design with zinc anodes also was determined to hold promise.
Notched and Unnotched Fatigue Behavior of Angle-Ply Graphite/Epoxy Composites
Authors: Ramani SV , Williams DP
Published: March 2009

The axial fatigue behavior of both notched and unnotched graphite/ epoxy composites has been studied as part of a continuing research investigation. In unnotched studies, conducted on a [0/±30]3s AS/3501 laminate, S-N (Δσ-log Nf) curves were determined for various stress ratios R using simply supported test specimens. Specimens were fatigue tested up to 5 × 106 cycles. Apparent fatigue limits (defined as stress amplitude at 5 × 106 cycles) in tension-tension (T-T) and compression-compression (C-C) cycling occurred at about 60 percent of the respective static strengths. The overall results were expressed in the form of a constant life diagram (that is, a Goodman diagram) showing the relationship between mean stress and stress amplitude. The diagram shows a linear relationship and illustrates a skew-symmetry in fatigue life caused by the relatively low compressive strength of the unrestrained test specimens used. In effect, a maximum in stress amplitude occurs at a positive value of the mean stress. Results of this study are of significance in situations where structural members are buckling or crippling critical in design.
Fatigue Damage of Notched Boron/Epoxy Laminates Under Constant-Amplitude Loading
Authors: Roderick GL , Whitcomb JD
Published: March 2009

Fatigue damage in (0, ± 45) and (0, ± 45,90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy (SEM). In addition, limited tests for residual strength and stiffness were performed. Initially, fatigue damage in both (0, ± 45) and (0, ± 45,90) laminates occurred as intralaminar cracks around the edge of the hole. Then, whenever further damage developed, intralaminar cracks in the ± 45-deg plies began to propagate from the edge of the hole. Finally, in both types of laminates, primarily ± 45-deg fibers broke (prior to two-piece failure) where intralaminar cracks in the ± 45-deg plies had occurred. In the (0, ± 45) laminates, the 45-deg plies developed intralaminar and transthickness cracks along lines parallel to the loading axis and tangent to the hole in the test specimen. This damage, which was most pronounced under compressive loads, had little effect on either strength or stiffness. In contrast, in the (0, ± 45,90) laminates, the ± 45-deg plies developed intralaminar cracks transverse to the loading axis. This transverse damage, which occurred primarily under tensile loads, affected the residual strength but not the stiffness and frequently resulted in catastrophic failure across the notch. The results of this study suggest that in boron/epoxy laminates the 45-deg plies play a key role in the fatigue process.
Effects of Moisture and Fatigue on the Residual Mechanical Properties of S-Glass/Graphite/Epoxy Hybrid Composites
Authors: Hofer KE , Bennett LC , Stander M
Published: March 2009

The static mechanical properties of S-glass/high-strength graphite/ epoxy hybrid composites were investigated before and after exposure to high humidity for 1000 h. Graphite-to-glass ratios of 0, ∞, 1, and 2 were studied. Both unidirectional (0 deg) and quasi-isotropic fiber orientations were studied.

In general, the stress cycling caused a decline in the static tensile strength, an increase in the Poisson's ratio, and no change whatever in the elastic modulus of the base and hybrid composites. The addition of moisture did not result in a basic alteration in the behavior of the hybrid or base composites after stress cycling.
Fatigue of Composites at Cryogenic Temperatures
Authors: Kasen MB , Schramm RE , Read DT
Published: March 2009

A comparison has been made between the wearout rates of [0/± 45/0] boron/epoxy and boron/aluminum composites in low-cycle fatigue at 295 and 76 K. Using degradation of modulus as the wearout criterion, these preliminary data indicate that cryogenic temperatures have a negligible effect on either tensile or compressive fatigue performance of boron/epoxy. A similar indication was obtained for boron/ aluminum in tensile fatigue. These conclusions are substantiated by high-cycle fatigue results on boron/epoxy.
Frequency Effects on a Stiffness-Based Fatigue Failure Criterion in Flawed Composite Specimens
Authors: Reifsnider KL , Stinchcomb WW , O'Brien TK
Published: March 2009

An important result of our investigations of the fatigue response of composite materials has been the identification and characterization of the effect of frequency of cycled loads (or strain). Frequency has been found to significantly influence the fatigue response of boron/epoxy and boron/aluminum plate specimens with a center hole. A large data base for strain-controlled testing of boron/epoxy and boron/aluminum at different frequencies has been reported earlier. More recently, we have extended the data base to include load-controlled test results for boron/epoxy and boron/aluminum using stiffness change as the primary damage parameter, and allowable stiffness change as a failure criterion. In general, the data show that low-frequency fatigue loading produces more concentrated, local, hole-related damage with corresponding greater specimen stiffness reduction. In contrast, high-frequency loading produces more dispersed damage with more axial micro-structure-related damage and less stiffness reduction. Since these results are true for two widely different materials and different testing conditions, the authors believe that these effects are representative of the mechanics of the phenomenon, and do not represent isolated effects. It appears that frequency effects can be expected in many fiberous composites and that they are large enough to be of significant consequence in many engineering applications.
Designing for Integrity in Long-Life Composite Aircraft Structures
Authors: Walter RW , Johnson RW , June RR , McCarty JE
Published: March 2009

Results of test programs conducted to obtain structural performance information essential to the design of long-life composite aircraft structure are presented. Static, fatigue, and fracture tests were conducted on T300/5208 and T300/5209 graphite/epoxy laminate specimens which were representative of full-scale strength-designed laminates. Results showed that static tensile and compressive strength are significantly degraded by discontinuities and impact damage. Laminates with representative fiber damage are relatively insensitive to cyclic tensile loadings; however, cyclic compressive loading results in finite fatigue lives. Impact damage which caused barely visible fiber failure was found to reduce fatigue performance below that defined for an open hole. The graphite/epoxy laminates tested were found to be fracture sensitive. Laminate stacking sequence was found to have a significant influence on fracture strength and failure mode.
Analysis and Investigation of Small Flaws
Authors: Talug A , Reifsnider K
Published: March 2009

Stress analysis of a single-edge-cracked specimen under uniaxial tension is performed by employing a Williams stress function and the boundary point collocation method. Full-field and singular stress fields are analyzed for small and large cracks, and it is shown that the inclusion of the nonsingular stresses in the description of the state of stress in the vicinity of the crack tip becomes significantly more important as the crack length decreases.
Analysis of Crack Growth Following Compressive High Loads Based on Crack Surface Displacements and Contact Analysis
Authors: Dill HD , Saff CR
Published: March 2009

A method for prediction of crack growth behavior based on analysis of crack surface contact stresses has been extended to include compressive effects. The method is based on evaluations of the effective minimum stress intensity occurring during a load cycle. An analysis of crack surface displacements during loading and unloading is used to determine the permanent plastic deformation left in the wake of the growing crack. Contact stresses are determined by treating the interference as a wedge between the crack surfaces and performing an elastic-plastic analysis of stresses caused by the wedge. Comparisons of predictions with test data show the method can accurately account for the effects of compression loads. stresses, strains, crack propagation
Load Interaction Effects on Fatigue Crack Growth in A514F Steel Alloy
Authors: Mills WJ , Hertzberg RW , Roberts R
Published: March 2009

Variable-amplitude fatigue tests of A514F steel alloy were performed within a linear-elastic fracture mechanics framework in order to characterize the retardation response of a cyclic strain softening material. Results of single and multiple overload tests on A514F steel alloy suggested that a material's cyclic properties have little effect on the phenomenology of retardation behavior. For instance, single high load excursions (of different magnitudes and at different baseline ΔK levels) in this cyclic strain softening alloy caused fatigue crack growth rate retardation trends comparable to those exhibited by 2024-T3 aluminum, a cyclic strain hardening alloy. In addition, under complex loading conditions, the A514F steel alloy, like the 2024-T3 aluminum alloy, exhibited maximum interaction between single peak load excursions when two peak cycles were separated by a small distance.

Additional retardation caused by a greater number of overload cycles more than compensated for increased crack extension during the high load excursions. Electron fractographic results are presented and discussed in terms of the macroscopic crack growth rate findings.
Round-Robin Crack Growth Predictions on Center-Cracked Tension Specimens under Random Spectrum Loading
Authors: Chang JB
Published: March 2009

A round-robin analysis was conducted by ASTM Task Group E24.06.01 on Application of Fracture Data to Life Prediction to predict the fatigue crack growth in 2219-T851 aluminum center-cracked-tension (CCT) specimens subjected to flight loadings in random cycle-by-cycle format. Baseline data furnished to each participant of the round-robin analysis are described. These data consisted of constant amplitude crack growth data, specimen dimensions, initial crack sizes, and test spectrum tables. Analytical predictions and their correlation to test data are summarized.
A Root-Mean-Square Approach for Predicting Fatigue Crack Growth under Random Loading
Authors: Hudson CM
Published: March 2009

A round-robin analysis was conducted which evaluated and compared different methods currently in practice for predicting crack growth under random loading. This report describes the prediction method used by the Fracture Mechanics Engineering Section (FMES) at NASA-Langley Research Center. It also presents the ratios of the predicted lives to the test lives for eleven of the thirteen specimens tested.

For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82. Considering that the normal scatter in fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions, these ratios are quite good.

The analysis procedure used by FMES was relatively simple. The loading history for each specimen was analyzed to determine the root-mean-square maximum and minimum stresses. The predictions were then made by assuming the tests had been conducted under constant amplitude loading at the root-mean-square maximum and minimum stress levels. Only a relatively simple computer program and a desk-top computer were required to make these predictions.
A Crack-Closure Model for Predicting Fatigue Crack Growth under Aircraft Spectrum Loading
Authors: Newman JC
Published: March 2009

Experiments on metallic materials have shown that fatigue cracks remain closed during part of the load cycle under constant- and variable-amplitude loading. These experiments have shown that crack closure is a significant factor in causing load-interaction effects (retardation and acceleration) on crack growth rates under variable-amplitude loading.

The present paper is concerned with the development and application of an analytical model of cyclic crack growth that includes the effects of crack closure. The model was based on a concept like the Dugdale model, but was modified to leave plastically deformed material in the wake of the advancing crack tip.

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 plate 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 Task Group E24.06.01 round-robin analysis.
Method for Laboratory Determination of Jc
Authors: Sumpter JDG , Turner CE
Published: March 2009

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 Jc.
Relevance of Nonlinear Fracture Mechanics to Creep Cracking
Authors: Nikbin KM , Webster GA , Turner CE
Published: March 2009

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.
Mixed Mode Fracture in Anisotropic Media
Authors: Williams JG , Birch MW
Published: March 2009

Tests were performed on straight-grained timber to give Mode I fractures in three geometries, and satisfactory K1 data were produced. Mode II tests were more difficult to perform, and the data correlated on a constant net 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 KIc fracture criterion independent of KII.
Mean Stress and Environmental Effects on Near Threshold Fatigue Crack Growth
Authors: Mautz J , Weiss V
Published: March 2009

The effect of mean stress and environment on the threshold and near threshold fatigue crack propagation behavior has been studied for D6ac steel and for 7050-T73651 aluminum. Fatigue crack propagation experiments were conducted in the range of 10−7 to 10−9 in./cycle (2.5 × 10−9 to 2.5 × 10−11 m/cycle) at 375 Hz.

A mean stress effect on the threshold stress intensity factor range, ΔKth, is only observed for low mean stresses, in the regime of the minimum stress intensity factor, Kmin, 0≤Kmin≤ 2 ksi √in. (2.2 MN/m3|2), typically 0≤R ≤0.5. For higher values of Kmin, the fatigue crack propagation threshold is controlled by ΔKth. For the high test frequency used, no effects of humid argon and room air as compared to a dry argon environment were observed on the fatigue crack propagation threshold ΔKth. Environmental effects were noted in the near threshold region. For D6ac steel room air produced the highest crack propagation rate while dry and wet argon produced identical but lower crack propagation rates for the same ΔK values. For 7050-T73651 alumium both wet argon and room air environments produced the highest crack propagation rates, while dry argon produced lower crack propagation rates. Changing the test frequency for 375 to 100 Hz had no noticeable effect on the threshold and near threshold region results for D6ac steel in room air but in dry argon 100 Hz gave slightly higher crack propagation rates with respect to 375 Hz.