bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluating Engineering Alloys in Compression
Authors: Chait R , Curll CH
Published: March 2009

Testing in compression has several attractive features when compared to the more frequently employed tension test. To take full advantage of these features, it is necessary to obtain deformation that is as close to homogeneous as possible. This paper describes how homogeneous compression can be obtained, paying particular attention to specimen dimensions and lubrication techniques. Comparison is made to deformation under nonhomogeneous conditions. Stress-strain curves obtained in compression for various engineering materials are presented. These curves represent uniform or homogeneous compression. For some metals, there is excellent agreement between the compressive flow curves and those obtained in tension, provided the latter is corrected for necking. However, it is shown that, for high-strength steels, there is not the expected agreement between the compressive and tensile flow curves. The resistance to compressive deformation is greater than to tensile deformation. This effect, termed a strength differential effect, is shown to be independent of the amount of plastic strain. However, it is affected by temperature, since it increases as the temperature is lowered.
Rational Basis and New Methods for Proportional Limit, Machine Stiffness, Critical Stress Intensity, and Crack Velocity Measurements
Authors: Clough RB
Published: March 2009

This paper is a summary of some new measurement techniques that have been developed recently at the National Bureau of Standards for measurement of proportional limit of elasticity, machine stiffness, critical stress intensity, and crack velocity. These seemingly unrelated measurements all result from the rational basis of a single type of equation relating specimen and machine kinetics. In a regime of linear elasticity, the concept of a limit beyond which the specimen elastic gage length displacement is no longer proportional to load is referred to as proportional limit if the gage length begins to exhibit plastic deformation, and is referred to in a precracked specimen as critical stress intensity if the crack begins to extend in length. Multiaxial plastic yielding is also discussed. Machine stiffness and crack velocity are other measurements which can be obtained through the specimen-machine equation. The relationship of the new stiffness measurement to the International Standards Organization (ISO) proposed method and advantages of the new method are discussed. Methods of measuring stiffness in constant load rate and constant strain rate tests are outlined. A method of measuring the proportional limit or critical stress intensity which does not use a displacement gage of any type is also given; this should prove useful in hostile environments. Other related topics discussed include loading transients and rate sensitivity.
Static Mean Stress and Cyclic Yield Strength
Authors: Weissmann GF , Davis JA
Published: March 2009

The cyclic yield strength of metals depends on the cyclic plastic deformation, the static mean stress, the number of cycles, and the frequency. For a number of different alloys, the cyclic yield strength in bending was determined as a function of the plastic deformaion and the mean stress. The application of a static stress always caused a reduction of the cyclic yield strength. The magnitude of the reduction depends on the type of material investigated. The results are discussed with respect to possible spring applications.
Determination of Plastic or Creep Strains by Grids
Authors: Manjoine MJ
Published: March 2009

A method of determining permanent strains by pre- and post-measurements of a grid of reference points or lines on a test specimen, a component, or a model under test is described. The characteristics of the grid at elevated temperature and some of the limitations are presented.

The grid of points or lines is generated by a photographic and electrodeposition process. The determinations of the deformations can be accomplished by direct measurements of the model or photographs of the deformed grid. Measurements of grid lines after extended periods at elevated temperature gave reliable strain distributions.
Stress Relaxation in Bending
Authors: Parikh P , Shapiro E
Published: March 2009

This paper describes a technique for stress relaxation measurement in bending at ambient and elevated temperatures. This technique utilizes a double-triangle-shaped specimen which is loaded at three points. The load remaining in the specimen at any time during the test is determined using a lift-off technique. This technique satisfies ASTM Recommended Practice for Stress-Relaxation Tests for Materials and Structures (E 328-75). The use of an analytical expression for extrapolation of short-time data to predict behavior at long times is also presented. Data of two copper alloys, phosphor bronze and nickel silver, are extrapolated to estimate the stress relaxation at 100 000 h.
Comparison of Manual to Automatic Unloading During Relaxation Tests
Authors: Schmieder AK , Robinson RS
Published: March 2009

Relaxation tests are commonly made using the two following procedures: first by using a special machine, load is removed automatically in many small steps as the strain tends to increase. In the second procedure, a creep machine is used, and the load is reduced manually whenever the strain reaches a certain limit. In this case, the number of stress steps down is relatively small. One of a pair of specimens was tested by each method for several materials and the relaxation curves compared. They were found to be in good agreement when the magnitude of the stress step down is chosen in a particular manner. The factors involved in this choice are discussed in detail. The incremental creep curves obtained at each stress level of the manual test are compared with the normal creep curves at constant load. The previously reported disagreement between the results of these two methods of relaxation testing are discussed, and an explanation is offered.
Poison Prevention Packaging—A Retrospective View
Authors: Maisel GS
Published: March 2009

The Poison Prevention Packaging Act of 1970 introduced a new concept to the prevention of accidental poisonings among young children. Heretofore, programs were geared to educating adults to the necessity of taking certain precautionary measures to make the child's environment safe. This was now supplemented by programs aimed at inhibiting the ability of the child from gaining access to the available substance by penetrating the package. Declines, particularly reflected in mortality figures, have been dramatic since the inception of the program. Standards promulgated for child resistance and adult effectiveness have required changes in technology and consumer acceptance. Producers, consumers, and the regulatory agency itself have had to make accommodations to the concept of promoting and accepting some inconvenience for a projected gain.
Variety of Child-Resistant Closures Available
Authors: Vere M
Published: March 2009

A child-resistant package must be convenient and easy for an adult to open while it foils the attempts of four and five-year-old children to open it. It must be technically feasible and appropriate for the product while continuing to function for the expected use life of that product.

Successful designs are based on the physical and mental limitations of children in the specified age group. These designs fall into five basic classes: snap caps, continuous-threaded closures, lug-style closures, unit packaging, and aerosol overcaps.

A description of packages for each of these classes is included in this paper noting that the categorization is loose, and there is considerable design variation within each class.
Quality Control for the Manufacture of Child-Resistant Closures
Authors: Julian RK
Published: March 2009

Since manufacturers of child-resistant closures have no absolute method of determining whether a package is effective, they are dependent on their engineering, quality control, and management groups to develop an acceptable quality control procedure. This paper discusses the functions of these groups and how they coordinate their efforts to devise effective systems to handle the unique problems inherent in the production of child-resistant packaging.
Case Study—Conversion to Child-Resistant Packaging
Authors: Ray TO
Published: March 2009

This paper is meant to convey the pertinent experience of converting a traditional proprietary pharmaceutical package through three different child-resistant packages. Attention is given to product stability, incoming component testing, torque or sealing specifications, production history, and customer satisfaction.
The Development of ASTM Standards on Child-Resistant Packaging
Authors: Saylor ER
Published: March 2009

The provisions of the Poison Prevention Packaging Act of 1970 and the related protocol testing procedures provided the packaging industry with a need for industry-wide physical standards to provide a means for assuring that production of individual special packaging components continues to comply with the requirements of these regulations. Members of the packaging industry came together under ASTM and developed standards for child-resistant snap caps and closures requiring two simultaneous dissimilar motions. Standards for aerosol child-resistant closures are also being developed.
Enforcement Under the Poison Prevention Packaging Act
Authors: Poth RG
Published: March 2009

The Consumer Product Safety Commission (CPSC) administers the packaging requirements of the Poison Prevention Packaging Act. Effective enforcement is critical to the successful administration of the Act. The enforcement policy adopted is based upon concentrated coverage to the problem areas. These are identified by injury data, a poor level of compliance by a particular industry, or a new regulation becoming effective. Coverage is concentrated by simultaneously inspecting as large a percentage of the entire industry as possible throughout the country. The impact of the concentrated coverage is reinforced by the prompt initiation of appropriate regulatory action against all those firms found in violation of the law. Obtaining industry compliance with the packaging standards through enforcement is one of the ways in which the CPSC seeks to reduce the risk of injuries to young children.
Child-Resistant Packaging and Consumer Reaction
Authors: Dana M
Published: March 2009

In spite of heavy pressure from some consumer activist groups urging the Consumer Product Safety Commission (CPSC) to faster, broader, and more stringent action, an increasing number of consumers are confused, unaware, or antagonistic to the spread of more child-resistant packaging. Some feel child safety is a parent-adult responsibility, not a government or industry sole responsibility. Increasingly, the feeling arises that all safety requirements should be a joint responsibility of the producer, retailer, government regulation, and consumer buyer.

Resentment over what they feel is a current government attitude that it knows what is best for all of us comes out in many consumer letters and verbal statements. Consumers feel that they should be given a chance to speak up effectively before the CPSC requires new safety standards for any product. They want to know what the “trade off” will be in higher cost, lower convenience, or the loss of the right to free choice. What the consumers are saying is: “make the packaging child resistant, if we must, but do not make it Grandma proof.”
Nonlinear Analysis of a Tapered Disk Thermal Fatigue Specimen
Authors: Mowbray DF , McConnelee JE
Published: March 2009

Calculations of the stress-strain response of a common tapered disk thermal fatigue specimen are presented. The calculations were made by complete nonlinear finite element solution and by a simpler method employing the elastic strain-invariance principle. The results are used to show the effect of several common test variables on the resulting stress-strain response, to assess the effect of various material behavior and structural analysis assumptions on the stress-strain response, and to explore the application of several high-temperature fatigue damage prediction methods to transient thermal fatigue loading.
Thermal Stress Concentration Factors in Large Shafts
Authors: Gonyea DC
Published: March 2009

The concentration of thermal stress in a shaft subjected to a ramp surface temperature change has been investigated. The concentration occurs at a step change in shaft diameter, and the temperature and stress responses are calculated by the finite element method. A thermal stress concentration factor (TSCF) is defined, and an analytical expression is given which defines the concentration factor in terms of the geometric parameters. Over the range of transient conditions studied, it is observed that the TSCF is insensitive to the surface temperature ramp rate. A comparison illustrates that the TSCF can be significantly different in numerical value than mechanical stress concentration factors.
Low-Cycle Fatigue Analysis of the Turbine Disk for the National Aeronautics and Space Administration High-Temperature Turbine Rig
Authors: Tepper S
Published: March 2009

The high-pressure, high-temperature turbine test rig was designed for the National Aeronautics and Space Administration to test turbine components in an environment that simulates current and future gas turbines operating at 41 atm (600 psi) and 2204°C (4000°F). This paper illustrates the design approach that led to selection of a typical test rig component: the turbine disk. The final configuration of the rotor assembly and the turbine disk was determined by analysis of low-cycle fatigue and creep.
Thermal-Stress Fatigue Behavior of Twenty-Six Superalloys
Authors: Bizon PT , Spera DA
Published: March 2009

The comparative thermal-stress fatigue resistances of 26 nickel- and cobalt-base alloys were determined by fluidized bed tests. Cycles to cracking differed by almost three orders of magnitude for these materials, with directional solidification and surface protection showing definite benefit. The alloy-coating combination with the highest thermal-stress fatigue resistance was directionally solidified NASA TAZ-8A with an RT-XP coating. Its oxidation resistance was also excellent, showing approximately a ½ percent weight loss after 14 000 fluidized bed cycles.
Thermomechanical Fatigue Crack Propagation in an Anisotropic (Directionally Solidified) Nickel-Base Superalloy
Authors: Gemma AE , Langer BS , Leverant GR
Published: March 2009

Strain-controlled thermomechanical fatigue tests were performed on two nickel-base superalloys, directionally solidified (DS) Mar-M200 plus hafnium and conventionally cast B-1900 plus hafnium. The DS alloy was tested at various angles (θ) to the direction of grain growth. It was found that crack growth rates were a minimum for the DS alloy tested parallel to the direction of grain growth (crack propagating normal to the direction of grain growth). The crack growth rate increased for other orientations in the sequence θ = 15, 30 or 90, and 45 deg until equivalence was reached with rates for the conventionally cast alloy, B-1900 plus hafnium. A linear elastic fracture mechanics approach was extended to strain-controlled crack growth as a function of θ for the DS alloy. Prediction of crack growth rates as a function of ϑ was achieved by normalizing with the elastic modulus. The sequencing of crack growth rates with θ and a smooth-to-rough fracture surface transition are explained on the basis of the orientation dependence of crack opening displacement for a given strain intensity range.
Vacuum Thermal-Mechanical Fatigue Behavior of Two Iron-Base Alloys
Authors: Sheffler KD
Published: March 2009

Isothermal and thermomechanical fatigue tests conducted in ultrahigh vacuum on Type 304 stainless steel and A286 alloy have shown significant effects of frequency and combined temperature-strain cycling on fatigue life. Results of isothermal tests at elevated temperatures in the creep range indicate reduced life with decreasing frequency. Combined temperature-strain cycling further reduces fatigue life with respect to isothermal lives measured at the maximum temperature of the applied thermal cycle. Life reductions observed with in-phase thermal cycling (tensile deformation at high temperature, compressive deformation at low temperature) are attributed to grain boundary ratcheting effects resulting from unreversed tensile grain boundary sliding. Results of out-of-phase tests (compressive deformation at high temperature, tensile deformation at low temperature) were confused in Type 304 stainless steel by the occurrence of geometric instabilities in the hourglass specimens. In the low ductility A286 alloy, where geometric instabilities were not observed, out-of-phase life reductions are attributed to grain boundary cavitation resulting from unreversed compressive grain boundary displacements (ratcheting) which could not be accomodated by intragranular deformation of the high-strength low-ductility matrix.
Instability Effects in Thermal Fatigue
Authors: Coffin LF
Published: March 2009

This paper considers shape changes which develop progressively in hourglass specimens subjected to fully reversed cyclic plastic strain applied in a variety of mechanical and thermal waveforms. While the strain at the minimum diameter is controlled, off-center locations subjected to cyclic plastic strain undergo ratcheting. Two major off-center shape changes have been observed: barreling and necking. The paper discusses the reasons for these changes.
Digital and Analog Computer Equipment and Its Application to In-House Testing
Authors: Boggs BC , Mondol NK , McQuown RE , Anderson JG
Published: March 2009

Analog, digital, and hybrid computers in structural static and fatigue testing under simulated real-life environmental conditions are described. The primary emphasis is on the use of minicomputers for cyclic load control which is still in the experimental stage.

The primary mission of the authors' laboratory is full scale fatigue testing using flight-by-flight load sequences. The size of the structures and the large number of loading channels require the use of digital computer equipment. Work to combine both the function generation and load control functions is described, together with current progress, which is based on a full size variable sweep wing fatigue test and the testing of a large air vehicle's wing carry-through box structure.
Fatigue Testing Using a Digital Computer-Based System
Authors: Donaldson KH , Dittmer DF , Morrow J
Published: March 2009

The use of a digital computer-based materials test system for evaluating the fatigue resistance of metals is described. Some examples of the types of tests employed in fatigue research are given. These include tests involving the control of strain with time such as cyclic stress-strain and low cycle fatigue. In addition, experiments are described that require the control of variables that must be calculated from the real time response of the specimen. Included are cyclic plastic strain control and tests in which the ratio of plastic to elastic cyclic strains is held constant.

These common fatigue evaluation tests are shown to be quickly and easily programmed through the use of an operator oriented interactive computer language. On-line data reduction capabilities of the system are shown to produce test results in a readily useable format.
Use of Multistation Computer System for Laboratory Data Acquisition and Control
Authors: Utah D , Malik HJ
Published: March 2009

This paper describes the functions and the methods of operation of the computerized data acquisition and control system used in the authors' fatigue laboratory. The computer, a real-time multiprogramming system with digital/analog and analog/digital interfaces, controls and takes data for various complex fatigue experiments simultaneously through use of programs developed by the laboratory personnel. Such programs, the capabilities of the system, and typical applications are discussed.
Application of the Digital Computer to an Accelerated Fatigue Model
Authors: Lim CK , Kuklentz RJ
Published: March 2009

This paper presents the application of a sensor-based digital computer for data acquisition and control in the study of the generalized Prot accelerated fatigue model. The usefulness of this model is greatly enhanced by the existence of modern-day facilities such as the closed-loop electrohydraulic fatigue testing system and the sensor-based computer for data acquisition and control. A brief overview of the entire laboratory automation system and a particular emphasis on the fatigue testing system are presented.
Digital Computer Controlled Threshold Stress Intensity Factor Fatigue Testing
Authors: Kaisand LR , LeFort P
Published: March 2009

The integrity of many structures depends on their resistance to fatigue crack propagation which is a function of the stress intensity factor. Furthermore, there appears to be a threshold level of the stress intensity factor range, ΔKth, below which crack growth is greatly inhibited.

This paper describes a test method used to determine crack growth rate data in the region of this threshold value. The technique utilizes crack opening displacement as the controlled variable.

Control is provided by programming a digital minicomputer to supply the command signal to the closed-loop servocontrolled test system. Use of the computer allows continuous operation and automatic data acquisition and reduction with a minimum of operator surveillance.
Tightening Process Equipment Gasketed Joints Safely
Authors: Staples BG
Published: March 2009

Torque versus load measurements were conducted on SA-193, Grade B-7 bolts to establish friction characteristics under dry and lubricated conditions, using strain gages with appropriate read-out. Similar torque-load ratio figures were obtained for a series of different size clamps, employing a Tinius-Olsen tensile testing machine for which suitable fixtures were designed and constructed.

With the data produced from these investigation and projected failure loads, it was possible to establish maximum torque limits which would fall within predetermined safety requirements. The equipment used in this investigation is explained and the calculations discussed.
The Relationship Between Bolt Load and Leak Rate in a Gasketed Joint
Authors: Raut HD
Published: March 2009

A method of testing gaskets for leak rate under varying bolt loads is described. The date, curves and procedures are given for a test to determine the effect of preload on the subsequent leak rate behavior of a joint with an asbestos gasket.
Sealability Characteristics of Gasket Materials
Authors: Kessler FJ
Published: March 2009

A test assembly used to evaluate the sealability of materials at various flange pressures is described. The assembly, and the techniques which have been developed permit a wide range of compositions to be evaluated for sealing characteristics. The apparatus is designed to use an inert gas, hence interaction between the gasket material and the sealed medium is at a minimum. Data obtained with this test have been correlated with actual field applications.
Formed-In-Place Gaskets: Concept vs Reality
Authors: Tokarski J
Published: March 2009

The concept of formed-in-place gaskets is an attractive one. The ability to make any size and shape of gasket on the spot and the low inventory involved has prompted many to try the formed-in-place principle at one time or another. However, failures have occurred because of an incomplete understanding of the mechanics of formed-in-place joints. These mechanics are discussed along with application methods for formed-in-place materials.
Effect of Cement Composition on Corrosion of Reinforcing Steel in Concrete
Authors: Mehta PK
Published: March 2009

The tricalcium aluminate present in portland cement is known to be effective for chloride removal and can thus provide protection against steel corrosion. Contradictions are found in literature with regard to the minimum tricalcium aluminate content of a cement which is desirable to prevent corrosion of reinforcing steel in concretes exposed to chlorides. A review of both published experimental data and some theoretical considerations are presented to show that not only the amount of tricalcium aluminate present but also its crystallographic type and the source of chloride are necessary factors in predicting the corrosion behavior of steel in reinforced concrete.
Recent Research on Galvanized Steel for Reinforcement of Concrete
Authors: Cook AR , Radtke SF
Published: March 2009

This paper presents data which show that galvanized rebar is superior to untreated steel. Through extensive testing and laboratory experimentation, this paper provides data to resolve the question of whether or not there is an improvement in galvanized rebar's corrosion resistance over unprotected steel. Tests were performed on bridge structures ranging in age from 3 to 23 years.
Concrete Bridge Deck Deterioration in Pennsylvania
Authors: Peterson PC
Published: March 2009

Concrete bridge deterioration is a serious problem in Pennsylvania. The causes of cracking, scaling, and spalling are related to prevalent design and construction practices. Although improved criteria and specifications will help solve the problem, new materials and techniques are needed. The Pennsylvania Department of Transportation has used galvanized and epoxy-coated reinforcement bars and latex-modified concrete overlays extensively.
Vermont's Experience with Bridge Deck Protective Systems
Authors: Frascoia RI
Published: March 2009

Intrusion of moisture and deicing chemicals into reinforced concrete bridge decks results in premature deterioration of the concrete and corrosion of the reinforcing steel. Vermont's search for an effective waterproofing system which would seal bridge decks and thus prevent intrusion of the moisture and chlorides has resulted in the application and evaluation of 29 different membrane systems since 1971. A number of the protective membranes have been in service for sufficient time to draw conclusions on their effectiveness. The results of followup evaluations show that several systems have provided complete protection to the bridge decks while a number of other materials have prevented chloride intrusion except in areas where deicing chemicals are often trapped due to the ponding effect of curb lines and expansion dams. Such results suggest that the simple and inexpensive materials could be specified for sealing the major portion of a deck surface if a compatible and impervious membrane material is placed over poorly drained areas. Difficulties encountered with the application of sophisticated and expensive membrane systems have resulted in a theory that the search for the most effective waterproofing system should concentrate on uncomplicated and less costly materials which could be applied without difficulty.

The results of laboratory tests indicate that liquid-applied membranes offer substantial protection, even when pinholes and bubbles occur in the coatings, when contrasted with the chloride intrusion which occurs in untreated concrete. The tests also show the relationship between resistivity readings and chloride penetrations and suggest that readings well below the generally accepted standard of 500 000 Ω may be acceptable.
The Use of Concrete Polymer Materials for Bridge Deck Applications
Authors: Kukacka LE
Published: March 2009

The rapid deterioration of concrete bridge decks as a result of the increased use of deicing salts is one of the most severe problems facing the highway industry today. One possible solution to the problem is the use of concrete polymer materials. The materials of prime interest are polymer-impregnated concrete and polymer concrete, both of which have excellent durability and strength properties. Three potential applications (repair of deteriorated bridge decks, polymer impregnation of new bridge deck surfaces, and full impregnation of precast deck panels) have been studied in laboratory and field tests, and the results have been encouraging. These results and economic considerations are described in the paper. The work in each of the areas is currently being implemented by the Federal Highway Administration.
Cathodic Protection: A User's Perspective
Authors: Ward PM
Published: March 2009

This paper discusses the advantages and disadvantages of cathodic protection as a means of extending the life span of reinforced concrete bridge decks. The cost of cathodic protection is compared to the cost of other methods of rehabilitating such structures. Also included is a brief review and discussion of the data collected during the first year of operation of a cathodic protection installation on a reinforced concrete bridge deck with details on mix design of the coke breeze asphaltic concrete, results of resistivity, and voltage drop data taken through the coke breeze asphaltic concrete and the portland cement concrete, as well as actual corrosion criteria versus E/log i curves.
Development of a Cold-Poured Bridge Deck Membrane System
Authors: Meader AL , Schmitz CG , Henry JE
Published: March 2009

A two-component asphalt-extended urethane membrane was developed which satisfies the requirements demanded of a waterproofing membrane for protecting reinforcing steel in concrete bridge decks from corrosion. A technique for application of the membrane is described which essentially eliminates blister formation. Blisters caused by thermal expansion of gases in the concrete have been a constant problem with liquid-applied membranes. The technique consists of: applying a black prime coat to the deck, allowing the black-primed deck to heat up by absorbing radiation from the sun, and applying the membrane after the maximum average deck temperature has been reached. The black prime increases the absorptivity of the deck, causing it to heat up more than an unprimed deck. It thus avoids the sudden increase in temperature caused when a dark membrane is applied over a white deck on a sunny day. Then, by applying the membrane after the sun has passed its zenith and the deck temperature has started to fall, blister formation caused by the outgassing of the concrete deck is avoided. This technique works equally well on damp or dry decks. The system is completed by applying a tack coat of hot asphalt and a 2-in. overlay of asphalt concrete.
Effect of Compression on Fatigue Properties of a Quasi-Isotropic Graphite/Epoxy Composite
Authors: Ryder JT , Walker EK
Published: March 2009

The effect of compressive loading on the fatigue properties of a quasi-isotropic graphite/epoxy composite is discussed. Tests were conducted using parallel-sided, unnotched T300/934 graphite/epoxy coupons cured at 177°C (350°F). Results are based on a large sample size (number of coupons tested at a particular test condition) which allowed a statistically significant evaluation of data scatter. All tests were conducted at room temperature. Fatigue tests were conducted at 10 Hz under constant-amplitude loading. Static tensile and compressive properties were obtained for coupons without prior fatigue damage. Tension-tension and tension-compression fatigue stress-life curves were qualitatively evaluated using a small sample set at each stress level. Three specific stress levels were chosen and the extent of data scatter defined for each type of fatigue loading. Additional coupons were subjected to the same amount of fatigue damage and half were tested for tensile residual strength degradation and half for compressive. Such residual strength tests were conducted at the same two fatigue maximum stress levels for both tension-tension and tension-compression fatigue. Data scatter was larger for static compression tests than for static tension tests. Static and fatigue failure modes were dissimilar. Compressive load excursions reduced fatigue life especially at lower stress levels. At stress levels where fatigue failures occurred, degradation in residual strength due to fatigue also occurred. Data analysis was performed using three-parameter Weibull asymptotic fits, which proved to be superior in predicting failure rates than two-parameter fits. The effect of sample size on descriptions of data scatter and accuracy of extrapolation is discussed.
Mechanisms of Fatigue Crack Growth in Boron/Aluminum Laminates
Authors: Kendall DP
Published: March 2009

Laminated boron/aluminum sheets of 0, ± 60, 0, ± 60, and 0-deg layer orientation were notched and subjected to tension-tension (T-T) fatigue loading. Fatigue cracks were monitored visually and the fatigue cycling terminated at various amounts of fatigue crack growth.

Crack growth rates were evaluated in terms of a fatigue crack growth rate law based on fracture mechanics.

Some specimens were then loaded to fracture and the fracture surfaces examined by scanning electron fractography. Other similar specimens were examined by progressively removing the aluminum matrix by a selective etching technique. Each layer of fibers was thus exposed and could be examined in the scanning electron microscope (SEM).

The results obtained show that the extent of fracture of the 0-deg layers of fibers is the same as the extent of the visible fatigue crack on the surface of the specimen. For the 60-deg layers, the extent of fiber fracture may be significantly less than the extent of the visible crack.

The extent of fatigue crack growth in the matrix material in the interior of the specimen exceeds the length of the surface crack by several fiber diameters.
A Study of Fatigue Damage in Composites by Nondestructive Testing Techniques
Authors: Chang FH , Gordon DE , Gardner AH
Published: March 2009

The methodology and experimental results of damage mechanism studies in graphite/epoxy composites using a modified X-ray nondestructive testing technique and continuous acoustic emission monitoring (AEM) method are presented. Fracture specimens were fabricated from Narmco 5208/T300 and Narmco 5208/ Modmor II graphite/epoxy composites with different ply orientations chosen to exhibit fiber failure and linear and nonlinear matrix failures. The specimens with center slits were subjected to tensile ramp loading, constant-amplitude cyclic loading, and an air combat fighter randomized flight-by-flight spectrum loading. During tensile ramp loading, the specimens were monitored by an X-ray “movie” to observe the damage initiation and growth in the areas around the slit tips. An opaque additive was injected in the slit opening to enhance the damage indications. For specimens undergoing cyclic loading and fatigue spectrum loading, periodic X-ray records were made for damage growth monitoring. Continuous AEM was conducted on specimens undergoing tensile ramp loading.

The actual fatigue damage initiation and growth within the composite laminates can be observed by the periodic X-ray records of the specimens. These observations were correlated with the AEM results. Three parameters measurable by the AEM system— accumulated counts, amplitude distribution, and frequency spectrum—characterized fatigue damage initiation and growth in different fiber directions. Damage redistribution mechanisms in the fatigue specimens can be observed from the damage growth study.
Evaluation of Flawed Composite Structure Under Static and Cyclic Loading
Authors: Porter TR
Published: March 2009

This paper presents the results of a program investigating the effects of initial defects on the fatigue and fracture response of composite laminates. The structural laminates investigated were a typical angle-ply laminate, a polar/hoop-wound pressure vessel laminate, and a typical engine fan blade laminate. Defects investigated were full- and half-penetration circular holes, full- and half-penetration slits, and countersink holes. Results are presented showing the effects of the defect size and type on the static fracture strength, fatigue performance, and residual static strength. The results of inspection procedures are shown, describing the effect of cyclic and static loadings on damage propagation in composite laminates. The data in this study were used to define proof test levels as a qualification procedure in composite structure subjected to cyclic loading.
Mechanical Properties of Carbon Fiber-Reinforced Polymethylmethacrylate for Surgical Implant Applications
Authors: Pilliar RM , Bratina WJ , Blackwell RA
Published: March 2009

Reinforced bone cement containing a small amount of short, high-modulus carbon fibers dispersed randomly in surgical polymethylmethacrylate bone cement has been developed and successfully used in a few cases for neoplastic bone replacement. The mechanical properties of this material were evaluated with respect to the bone cement used presently in prosthetic and restorative orthopaedic surgery. Superior mechanical properties were observed in reinforced acrylic compared with unreinforced material; specifically, monotonic tensile strength increased from 28 to 38 MPa (4060 to 5510 psi) and monotonic tensile, cyclic tensile, and compressive modulii were significantly higher in reinforced acrylic. An increase of about 50 percent in fatigue strength was achieved at long lives (105 cycles), that is 15 MPa (2175 psi) as compared to 10 MPa (1450 psi) for unreinforced acrylic.

Both reinforced and unreinforced surgical acrylic are porous materials by virtue of their mode of preparation, that is, operating room conditions. Additional comparative studies were performed only on carbon-reinforced full-density acrylic. The relatively small improvement in mechanical properties for these full-density systems is accounted for by poor fiber distribution.

Strain-rate dependence of tensile properties studied over the 5 × 10-6 to 2 × 10-2s-1 range was found to be low for both reinforced and unreinforced porous acrylics.

The fracture surfaces of the static and cyclically loaded specimens studied by scanning electron microscopy (SEM) revealed the role of intrinsic voids and the carbon fibers in the process of crack initiation and propagation.
Fatigue and Proof-Testing of Unidirectional Graphite/Epoxy Composite
Authors: Awerbuch J , Hahn HT
Published: March 2009

Proof-testing has shown with a high level of confidence that a unique relationship exists between the static strength and the fatigue life or residual strength in unidirectional graphite/epoxy (T300/5208) composite. However, damage, especially visible damage, caused by proof-testing seems to shorten the life and reduce the residual strength. Failure initiation in fatigue is mainly in the form of longitudinal cracking, starting along the edges at lower stresses. Temperature increase follows the same trend as predicted by the solution of a heat conduction equation with a constant rate of heat generation except immediately before the final failure. Although the reason is not clear, the tensile modulus increases after fatigue. For mathematical simplicity and operational ease, a two-parameter Weibull distribution seems adequate for the analyses of scatter in strength and life.
The General Cyclic Stress-Strain Response of Aluminum Alloys
Authors: Laird C
Published: March 2009

The cyclic stress-strain response of a wide range of binary, ternary, and complex commercial and experimental-commercial aluminum alloys has been investigated. In addition to constant-amplitude tests, incremental, block, random loading tests, and other specialized tests have been used in assessing cyclic response. The conditions under which cyclic hardening or softening occur have been elucidated, and general conclusions have been drawn about cyclic response in aluminum alloys.
Fatigue Analysis of Cold-Worked and Interference Fit Fastener Holes
Authors: Rich DL , Impellizzeri LF
Published: March 2009

Crack initiation and crack growth behavior were determined experimentally for aluminum and titanium specimens with fastener holes that were either cold worked or were propped by interference fit fasteners. The specimens were subjected to a randomized flight-by-flight spectrum. Analytical procedures were evaluated, based on correlation with the test data. These procedures included elastic-plastic analysis which was utilized to determine the stress-strain distributions surrounding the fastener holes. Estimates of elastic proportional limits in tension and compression were based on material cyclic stress-strain characteristics. Purely elastic analysis was used to determine the KT and stress gradient for the propped fastener holes with various ratios of plate-to-fastener modulus of elasticity. Finite-element model elastic-plastic computer results provided the stress-strain distributions for the cases of superimposed cold working and external loading, and superimposed interference fit fasteners and external loading. Approximate analytic equations were developed to fit the finite-element model computations. These equations were used to calculate the stress-strain excursions that would occur during flight-by-flight spectrum fatigue loading. The stress-strain excursions were then used to enter strain-life curves to compute crack initiation. They were also used to determine stress intensities to enter da / dn versus ΔK curves to compute crack growth. The delay in crack initiation due to beneficial compressive residual stresses that would be induced during spectrum loading was accounted for by using a stress ratio correction factor based on strain-life data generated at different stress ratios. Crack growth retardation due to periodically applied high loads was accounted for, using the Wheeler plastic zone model. The comparison of the crack initiation life calculations to the test data was favorable if initiation was defined as the development of a 0.25-mm crack. Good agreement between the crack growth calculations and the test data was also obtained for growth from a 0.25-mm crack.
Sulfur Bacteria
Authors: Fjerdingstad E
Published: March 2009

During the last few years sulfur bacteria, to an increasing extent, have been put to use in the biological estimation of pollution. In their investigations algologist have described new genera and new species of sulfur bacteria, and biochemists have established new designations for inclusions in sulfur bacteria. In this paper biochemical, ecological, and physiological investigations have been considered only to the extent of their being of value to the knowledge of sulfur bacteria.

In modern taxonomy the genera of sulfur bacteria are divided into different groups: Phototrophic Bacteria including green and red sulfur bacteria, Gliding Bacteria containing the colorless sulfur bacteria of the genera Beggiotoa, Thioploca, Thiothrix, Achromatium, and Peloploca, Budding Bacteria containing the genus Thiodendron, and Chemolithrotrophic Bacteria containing the genera Sulfolobus, Thiobacterium, Macromonas, Thiovulum, and Thiospira. The author considers that in this paper it would be most appropriate to retain the designation Chlorobacteria for green sulfur bacteria, Rhodothiobacteria for red sulfur bacteria, and Leucothiobacteria for colorless sulfur bacteria; this is in accordance with Lauterborn, Bavendamm, and many other authors. This is preferable for the practical use of sulfur bacteria as a means of estimating the degree of pollution. Furthermore, these designations are in common use in Europe.
Crack Growth Behavior of Center-Cracked Panels under Random Spectrum Loading
Authors: Rudd JL , Engle RM
Published: March 2009

An assessment is made of the analytical capability to use constantamplitude fatigue crack growth rate data for center-cracked panels to predict the crack growth behavior of center-cracked panels subjected to random flight-by-flight spectrum loading. This paper is one of six such assessments made by members of ASTM Task Group E24.06.01 on Application of Fracture Data to Life Prediction. Crack growth predictions for 13 center-cracked tension specimens were made by the authors without prior knowledge of the test results. Analytical/experimental correlations and a study of the sensitivity of the correlations to two input parameters of the analysis are presented. Also presented is a comparison of the analytical/experimental correlations of the authors to those of the other members of Task Group. It is concluded that it is possible to accurately predict the crack growth behavior of center-cracked panels subjected to random flight-by-flight loading using center-cracked panel constant amplitude fatigue crack growth rate data.
Random Spectrum Fatigue Crack Life Predictions With or Without Considering Load Interactions
Authors: Chang JB , Szamossi M , Liu K-W
Published: March 2009

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.
Derivation of a Low-Cycle Fatigue Relationship Employing the J-Integral Approach to Crack Growth
Authors: Mowbray DF
Published: March 2009

Some recent results from investigations in nonlinear fracture mechanics centering about the J-integral are utilized to derive a low-cycle fatigue relationship. The derived relationship has the form of the well-known Coffin-Manson equation, but differs from it in that the controlling variable is predicted to be applied strain energy density rather than plastic strain range. This predicted controlling variable appears to closely parallel several energy-related functions proposed during the past 15 year period.
Application of Fracture Mechanics to the Thermostructural Failure of Graphite
Authors: Starrett HS , Cull AD , Irwin GR
Published: March 2009

Thermostructural failure of materials used in reentry vehicles is an important problem. This paper is an experimental and analytical study of a testing facility in which these materials are thermostructurally evaluated. Radio frequency energy is used to induce a steep, radial temperature gradient in a disk-shaped specimen. A KI solution for this specimen is developed by a semiempirical procedure; it is used to analyze the experimental data. Experiments were performed on ATJ-S (WS) graphite. Comparison of the results from the KI solution are compared to contemporary KI values for this graphite. Currently, the KI solution is inadequate for design purposes; however, it shows the potential of providing a better understanding of the thermostructural fracture process.
Fracture Toughness of ATJ-S Graphite and CVD Carbon-Carbon Composites at Elevated Temperatures
Authors: Hettche LR , Tucker TR
Published: March 2009

The fracture toughness and flexural strength of ATJ-S polycrystalline graphite and two chemical-vapor-deposited (CVD) carbon-carbon composites (CVD/felt and CVD/filament wound) are reported for temperatures between 20 and 2000°C. For both the ATJ-S and CVD/felt materials, the toughness and strength are found to rise linearly with increasing temperature. The properties of CVD/filament wound composite exhibit the greatest directional dependence of the materials examined. When the machined notch is oriented perpendicular to the reinforcing filaments, the CVD/filament wound specimens fail by delamination, precluding any fracture toughness determination.

Results of scanning and transmission electron microscopy of the fracture surfaces are also presented. In the case of the polycrystalline graphite, a preference for interfacial separation and, to a lesser extent, cleavage separation are observed.