bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationship Between the Fracture Toughness and the Crack Tip Radius
Authors: Taggart R , Wahi KK , Beeuwkes R 
Published: March 2009

The conditions that surround the tip of a sharp crack in a ductile metallic material dictate the onset of plastic flow and crack extension. The problem of predicting the onset of unstable fracture is related directly to the difficulty of measuring or calculating the actual stresses and strains within the plastic enclave that encompasses the crack tip. Beeuwkes has obtained an approximate solution for the elastic-plastic state in the vicinity of the crack tip and concludes that the crack tip radius after deformation together with the fracture strength at nil ductility of the material form the basis for a fracture criterion.
In this study measurements have been made of the crack opening of fatigue cracked double cantilever beam specimens of 6061-T6 and annealed 4340VM steel. The crack opening measurements have been used to compute the crack tip radius at different loads by fitting the experimental data with an nth order polynomial (n = 2, 4, 6, and 8). The polynomial for which the average deviation in the computed values is a minimum with respect to the measured values was chosen to represent the crack geometry. The values of the crack tip radius as given by this polynomial were plotted against the stress intensity factor.
It has been found for both the selected materials that the stress intensity factor and the crack tip radius follow a linear relation when plotted on a log-log basis. The stress intensity factor and the ratio of the crack tip radius to a critical crack tip radius also plot as a straight line on a log-log basis.
It is concluded that the concept of a critical crack tip radius is consistent with a crack extension model that depends on void coalescence and growth. The data also support the fracture criterion based on the elastic-plastic analysis proposed by Beeuwkes.
Some Monitoring and Analytical Techniques for the Study of Locomotor Responses of Fish to Environmental Variables
Authors: Kleerekoper H 
Published: March 2009

The adaptive significance of locomotor, specifically orientation responses in fishes to environmental stimuli, is emphasized. General locomotor behavior is usually extremely variable over time whereas the responses mentioned are, most frequently, very subtle.
Techniques are described to detect and quantify these responses by comparing locomotion before stimulation with that during exposure to the environmental variable(s) under study. Models for such comparison are based on time series analysis of relevant locomotor variables, such as frequency and size of turns, length and orientation of steps, velocity, and others. Two techniques for data acquisition of these variables, by means of electronic monitoring of locomotion under controlled physical and chemical conditions, are described in some detail.
Attention is called to the possible interaction of environmental conditions and the behavioral responses of fish, an aspect which, hitherto, has received too little consideration in studies on biological effects of environmental variables.
Some Methods for Hypothesis Testing and Analysis with Biological Monitoring Data
Authors: Green RH 
Published: March 2009

The problem considered here is whether a specified environmental change does, or does not, affect a biological community. Commonly used procedures are often inappropriate for the data or for the questions asked. Such procedures, as well as an appropriate one, are discussed and illustrated using a set of artificial data with properties similar to those of a real benthic community. Ninety-two stations on a kilometre grid are sampled for abundances of six benthic species and four environmental variables, before and after an increased inflow of dissolved salts.
A multiple regression model which assumes that species abundances are related to environmental variables in a linear additive manner yields inefficient and misleading results. Cluster analysis methods efficiently describe natural spatial patterns, but temporal changes are swamped by the spatial patterns and are not detected. A linear additive model which relates changes in species abundances to changes in environmental variables removes the variation due to spatial pattern from the analysis and clearly shows that biological changes related to increased salt concentration have occurred. Methods for describing the changes and testing related hypotheses are presented.
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.
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.
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.”
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.
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.
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.
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.
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.
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.
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.
Note on the Dependence of Crack Velocity on Driving Force for an Epoxy Adhesive
Authors: Mostovoy S , Crosley PB , Ripling EJ 
Published: March 2009

The dependence of crack velocity, ˙a, on driving force for an adhesive system was shown to be described by a curve having the shape of an inverted L. That is, at high values of ˙a, large increases in G caused small increases in ˙a while at low velocities, small increases in G cause large increases in ˙a. Since the data in the literature on polymethylmethacrylate (PMMA) and mild steel can also be represented by such a curve shape, the inverted L may represent the general dependence of ˙a on driving force.
The high velocity branch appears to be associated with rough fracture surfaces and the low velocity branch, with smooth fracture surfaces.
Brittle Fracture (KIc) Behavior of Cracks Emanating from Notches
Authors: Novak SR , Barsom JM 
Published: March 2009

Experimental and analytical studies were conducted under AISI sponsorship to determine the influence of short cracks emanating from notches on fracture behavior. All studies were conducted by using concepts of linear-elastic fracture mechanics (LEFM). The experimental studies were conducted on AISI 4340 steel at a high strength level (σys = 215 ksi = 1480 MN/m2) under plane-strain (KIc) conditions by using various types of fatigue-cracked as well as notched and fatigue-cracked specimens. The analytical studies were conducted by using recently developed theoretical KI analyses for notched and fatigue-cracked specimens.
The experimental results obtained by using various types of standard fatigue-cracked specimens demonstrated that the basic fracture-toughness behavior of 4340 steel is repeatable and reproducible within a relatively narrow range (KIc = 70±5 ksi √in. = 77±5.5 MNm−3|2). Limited experimental results on notched and fatigue-cracked double-edge-notched tension (DENT) specimens verified the accuracy of a recent theoretical KI analysis by Tada. Results for these notched and cracked DENT specimens exhibited good agreement with the baseline KIc behavior, but two to three times the amount of scatter usually observed in standard KIc tests (±5 to 10 percent). Tests demonstrated no significant differences in the basic fracture behavior (apparent KIc) of either pure-tension (DENT) specimens or essentially pure-bending (three-point-bend) specimens when tested with cracks emanating from notches. Apparent KIc results calculated by using traditional equations, in which the presence of the notch is ignored (treated as a crack of equivalent length), were elevated above the intrisic KIc level by less than 30 percent for all investigated combinations of specimen type, notch type, and the length of the fatigue crack beyond the notch tip (ΔaF).
The theoretical studies were conducted to develop an analytical criterion [(ΔaFaNρ)=¼] that predicts the depth beyond which a notch with an emanating crack can be treated as a crack of equivalent length. The engineering significance of this criterion is discussed. For values of the parameter that are greater than the criterion, traditional KI equations are accurate within ±5 to ±10 percent. For values less than the criterion, the stress-intensity (KI) at the tip of a short fatigue crack (of length ΔaF) emanating from a dull notch (of length, aN, and radius ρ) is always less severe than a crack of equivalent length, and the use of traditional KI equations can grossly overestimate the actual KI at the crack tip. For this short crack-length range, KI values must be calculated by using appropriate theoretical analyses that account for notch effects in order to minimize the conservative results of traditional analyses.
Included in the present work is a state-of-the-art summary of currently available theoretical KI analyses for cracks in the near vicinity of notches.