bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of End Restraint on Volume Change and Particle Breakage of Sands in Triaxial Tests
Authors: Ueng T-S , Tzou Y-M , Lee C-J
Published: February 2009

The distributions of volume change and particle breakage within specimens were compared for uniform sands in drained triaxial tests with and without lubricated end platens. The results showed that the volume change at failure, either dilation or compression, of the sands was slightly higher for lubricated specimens at a higher failure strain than for unlubricated specimens, and the difference was proportional to the total volume change at failure. The sands exhibited insignificant differences in uniformity of volume change for specimens with and without lubricated ends under loading before the peak strength. However, a distinctly larger volume change at the middle portion of unlubricated specimens was observed after the loading reached the peak strength. Similar results were obtained for the particle breakage within the specimens in triaxial tests. End lubrication induced more uniform particle breakage of sands after the peak strength was reached. Finally, Rowe's stress-dilatancy theory was evaluated with considerations of dilatancy factor and particle breakage. Particle breakage was found very important in considering strength and volume change of sands.
Effects of End Conditions on Triaxial Compressive Strength for Cohesionless Soil
Authors: Goto S , Tatsuoka F
Published: February 2009

Drained triaxial compression tests of Toyoura sand were carried out with conventional triaxial apparatus to evaluate the effects of sample slenderness and end conditions on triaxial compression strength. It was found that the maximum difference in the angle of internal friction φd for different test conditions employed was about ±1°. At the same time, the effects of the sample slenderness and each end condition on the strength value could be clearly identified.
Effects of Height-to-Diameter Ratio in Triaxial Specimens on the Behavior of Cross-Anisotropic Sand
Authors: Lade PV , Wasif U
Published: February 2009

The drained stress-strain, volume change, and strength behaviors of sand with cross-anisotropic fabric were studied in triaxial compression tests. Dense specimens with square cross-sections, height-to-diameter (H/D) ratios of 1.0 and 2.5, and lubricated ends were employed. Specimens consisting of relatively long, flat sand grains were prepared with cross-anisotropic grain structure, whose axis of rotation was inclined at various orientations from vertical to horizontal. The specimen boundary conditions (flexible membrane and lubricated, rigid end plates) had different effects on the results for specimens with H/D = 1.0 and 2.5. The specimens with H/D = 2.5 exhibited distinct, but temporary drops in their prefailure stress-strain curves, and the friction angles changed in a consistent pattern over a range of 5.5°. In comparison, the specimens with H/D = 1.0 showed more smooth stress-strain behavior, and their friction angles were essentially constant with very little effect of orientation.
State-of-the-Art Paper: Cubical Devices: Versatility and Constraints
Authors: Arthur JRF
Published: February 2009

The main types of cubical shear devices are described and classified according to the applied boundary conditions. There is no attempt to include all or even a large selection of individual designs; examples are used to develop a critical review of the types used presently and the way in which these are evaluated. The need to consider the material and specimen to be tested when deciding on the appropriate shear device is emphasized. The chosen examples amply illustrate the wide range of uses of the devices; special attention is given to the application of controlled rotation of principal stress directions. The capability of cubical devices to accept undisturbed samples after straightforward trimming is seen as enough to ensure future developments. A major theme is constraint unintentionally imposed through the boundaries; recognition, assessment, and reduction or elimination of boundary constraint are extensively considered. Classification of stress-strain data as true, comparative, or corrected is advocated as a means of ensuring proper data quality. An example is given from current work at the author's laboratory.
The Cambridge True Triaxial Apparatus
Authors: Airey DW , Wood DM
Published: February 2009

In true triaxial apparatus, samples of soil are subjected to three independent principal stresses and strains. Such apparatus can readily be used for controlled exploration of principal stress or principal strain space to provide information concerning the anisotropic response of the soil to aid the development of constitutive relations.

The Cambridge true triaxial apparatus has recently been reconstructed and is described in its new form. Some experimental data from a stress controlled test on kaolin are presented as an illustration of the capabilities of the apparatus and as an illustration of alternative ways in which such data may be presented while maintaining maximum objectivity.
A True Triaxial Cell for Soil and Rock
Authors: Michelis P
Published: February 2009

The design and performance of a membrane-piston, high-pressure (σ2 − σ3 ≦ 300 MN/m2) cell are presented. This device is similar to the one used for standard triaxial tests differing only in the stresses, σ2 and σ3, which are independently applied through flexible polyvinyl chloride (PVC) fluid cushions on prismatic specimens. The cell has been used extensively for monotonic-cyclic, compression-tension, plane strain-plane stress tests on a variety of materials.

The design and construction of a similar cell, which fulfills different requirements, are also presented. It uses flexible fluid cushions to transmit pressures up to 250 MN/m2 for σ1, and fluid cushions and fluid chamber pressure for stresses σ2 and σ3, respectively. It transmits uniform boundary loading to large specimen surfaces (19 by 19 by 19 cm), allowing both the development of unrestrained large deformation and its reliable measurement at several locations. The cell possesses a substantial degree of experimental flexibility for testing isotropic and anisotropic materials under drained and undrained conditions as well as ease of assembly and dismantling.
A New Independent Principal Stress Control Apparatus
Authors: Mochizuki A , Mikasa M , Takahashi S
Published: February 2009

A newly designed independent principal stress control apparatus is presented together with some typical test results obtained by the apparatus. The minor principal stress on a cuboidal specimen, σx, is loaded by air pressure in the triaxial cell, and two couples of rigid platens are used to load the major and intermediate principal stresses, σz and σy.

This apparatus has the following features: 1. The axial stress, σz, is applied from the underside of the specimen, the reaction being supported by a frame in the cell. It makes both the anisotropic consolidation and extension test possible; it also makes the preparation of sand or soft clay specimens very easy. 2. A new device to load intermediate stress, σy, was developed to minimize the friction between lateral loading platens and the specimen. 3. A new system to measure the specimen deformation is also developed with a no-contact gap sensor which moves up and down during the test. It can measure the total volume change and also the change of the shape of the specimen.

Some typical results of triaxial test, plane strain test, and independent stress control test on two sands are presented. Deformation or distribution of strain of the specimen observed by no-contact gap sensor is also discussed.
Effects of Residual Elements in Heavy Forgings: Past, Present, and Future
Authors: Bodnar RL , Cappellini RF
Published: February 2009

In the past, steelmakers of heavy forgings had considerable flexibility with regard to materials specifications. Today there is increasing emphasis on clean steels with extremely low residual element content, particularly with respect to heavy forgings for high-temperature applications. The clean steels are of interest primarily due to their improved ductility, toughness and uniform mechanical properties. Future materials specifications can be expected to reflect the current interest in “superclean” steels. However, the shift to clean steel specifications has greatly reduced the steelmaker's processing options for producing such steels. In addition, in some cases the clean steels have created new problems for the forgemaster (e.g., machining and meeting mechanical property and NDE specifications).

This paper provides a steelmaker's perspective on the role of residual elements in heavy forgings. The paper also contains a summary of some of the historical events which led to the need for reduction in residual element levels. Innovations which have allowed the steelmakers to meet the challenge for lower residual levels are also discussed. The forging grades which are given focus include: Ni-Mo-V, Ni-Cr-Mo-V, Cr-Mo-V, and 12Cr-Mo-V-Cb-N turbine rotor steels and 2¼Cr-1Mo, A508 Class 2, and A508 Class 4 pressure vessel steels. The role of traditional residual elements, such as P, S, Cu, Sb, As, Sn, Ca, Al, H, O, N, B, and rare earths, as well as the current interest in maintaining very low Mn and Si, are discussed as they relate to steelmaking, forging, heat treatment, machining, and service life. Residual elements as they relate to segregation, inclusion type, overheating, hardenability, temperability, temper embrittlement, creep embrittlement, hydrogen flaking, and stress corrosion cracking are also discussed.
New Low Chromium Ferritic Pressure Vessel Steels
Authors: Todd JA , Swindeman RW , Klueh RL
Published: February 2009

Much progress has been made in developing chromium-molybdenum steels with improved hardenability, elevated temperature strength, toughness, and resistance to environment. The new low alloy steels, intended for heavy-wall pressure vessels operating at temperatures in excess of 450°C and pressures up to 30 MPa, are fully bainitic for maximum strength and toughness, and are resistant to temper embrittlement, hydrogen embrittlement, and hydrogen attack. Microstructural studies have shown that alloys containing 3%Cr and 1.5%Mo exhibit improved heat treating characteristics as they rapidly temper to produce stable alloy carbides, which are resistant to hydrogen attack. Such steels could replace 2.25Cr-1Mo steel for service to 480°C. Higher creep strengths can be achieved in modifications of 2.25Cr-1Mo or 3Cr-Mo steels containing up to 0.25% vanadium.
Development of Nickel and Nickel-Iron Aluminides for Elevated-Temperature Structural Use
Authors: Liu CT
Published: February 2009

This paper summarizes recent work on alloy design of Ni3Al alloys for structural use at elevated temperatures. Efforts on alloy development have been focused on four areas: (1) improvement of ductility at ambient temperatures, (2) enhancement of high-temperature strength by solid-solution effects, (3) alleviation of dynamic embrittlement in oxidizing environments, and (4) fabrication improvement. Nickel aluminides with promising properties have been developed by microalloying with boron and macroalloying with chromium, zirconium (or hafnium), and iron additions.
Alloy Chemistry and Microstructural Control to Meet the Demands of the Automotive Stirling Engine
Authors: Stephens JR
Published: February 2009

The automotive Stirling engine now under development by DOE/NASA as an alternative to the internal combustion engine imposes severe materials requirements for the hot portion of the engine. Materials selected must have low cost and contain a minimum of strategic elements so that availability is not a problem. Heater head tubes contain high pressure hydrogen on the inside and are exposed to hot combustion gases on the outside surface. The cylinders and regenerator housings must be readily castable into complex shapes having varying wall thicknesses and be amenable to brazing and welding operations. Also, high strength, oxidation resistance, resistance to hydrogen permeation, cyclic operation, and long-life are required. A research program conducted by NASA Lewis focused on alloy chemistry and microstructural control to achieve the desired properties over the life of the engine. Results of alloy selection, characterization, evaluation, and actual engine testing of selected materials will be presented. The purpose of this paper is to describe the effects of alloy chemistry and microstructure on the oxidation/corrosion behavior, strength (endurance), and resistance to hydrogen permeability of candidate alloys.
Control of Fiber Architecture for Tough Net-Shaped Structural Composites
Authors: Ko FK , Whyte DW , Pastore CM
Published: February 2009

A design concept is introduced to address the need for a significant improvement in strength and toughness of composites through control of the fiber architecture. A three-dimensional (3-D) braided structure is used to illustrate the approach. The mechanical properties of the 3-D braid metal matrix and ceramic matrix composites are compared with composites reinforced by various fiber architecture. In order to provide a rational means for the design and control of the microstructure of the fiber architecture, a processing science base has been established by means of a fabric geometry model (FGM) relating material properties, microstructure, fiber architecture, processing parameters, and composite properties.
The Road to a Truly Authoritative Chemical Dictionary
Authors: Loening KL
Published: February 2009

While a number of chemical dictionaries are on the market, there is an indisputable need for a truly authoritative one in which the definition of each term is carefully formulated and checked by a panel of experts in the field. The International Union of Pure and Applied Chemistry (IUPAC) through its Interdivisional Committee on Nomenclature and Symbols (IDCNS) has begun a project aimed at eventually producing such a dictionary.

A brief history of the project is given. The organization of IUPAC is summarized, and the publications procedure by which nomenclature and terminology documents gain official IUPAC status is described. These documents represent the data base from which the initial Compendium of Chemical Terminology: IUPAC Recommendations has been produced. In the Compendium, terms along with their definitions are reproduced from IUPAC-approved documents published through 1985 in the fields of physical, inorganic, organic, macromolecular, and analytical chemistry. Terms from the fields of applied and clinical chemistry are to be added later. Some examples of editing decisions are presented.

Since each of the terms with its definition has been approved by an expert IUPAC commission, this compendium represents a real first step toward a truly authoritative chemical dictionary. It is hoped that in due time relevant terms with their definitions taken from official documents outside of IUPAC will also be included.
A Terminologist's and a Chemist's Look at Chemical Neologisms
Authors: Sonneveld WB , Loening KL
Published: February 2009

After a brief historical introduction, the creation and development of scientific terms from the linguistics point of view are outlined. The terms “neologism” and “neonym” are defined and their characteristics are listed. After pointing out the basic principles of neonymy, the principal methods of neonymic formation of chemical terms are cited and illustrated by examples taken from recent nomenclature recommendations issued by the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Biochemistry (IUB), the World Health Organization (WHO), the International Standards Organization (ISO), and other international organizations. Other examples are taken directly from the chemical literature. Topics represented by these examples include systematic versus trivial names for chemical compounds, names for elements of atomic numbers greater than 100 recommended by IUPAC, names for enzymes recommended by IUB, international nonproprietary names for pharmaceuticals issued by WHO and those of pesticides issued by ISO. Problems arising from words used in ordinary language also having chemical meanings are discussed. In addition, the danger and confusion resulting from assigning new meanings to old terms are illustrated.

Finally, the factors leading to acceptance or rejection of chemical neologisms are examined, again illustrated by a number of case histories. Some conclusions to be kept in mind by future coiners of chemical neologisms are presented.
Reverse Expansion—The Unification of Eight ASTM E-7 Glossaries
Authors: McKee CW
Published: February 2009

ASTM Committee E-7 on Nondestructive Testing is composed of ten technical subcommittees. Volume 03.03 of the Annual Book of ASTM Standards presently contains eight glossaries which have been issued by these subcommittees, and other definitions can be found in an additional ten methods and practices. A review of these 17 documents has revealed several terms with two dissimilar definitions, and in some cases these definitions had been issued by one subcommittee. In an attempt to bring some order out of this chaos, we are proceeding as follows: 1. All terms (eight to date) which are common to the various disciplines have been placed under the jurisdiction of the editorial subcommittee. 2. A master glossary, which will contain all the terms currently found in the 17 documents, is being developed. 3. This glossary will be divided into sections, one for each subcommittee, and each of the technical subcommittees will retain jurisdiction over all the terms in its section. The eight common terms and any subsequent similar terms will appear in a separate section. 4. Where two or more definitions for one term currently exist, both will be shown until the subcommittee decides to eliminate one, combine them, or redefine the term. 5. A list of all terms in all the sections, showing in which section they may be found, will be appended to the master glossary. 6. If new subcommittees are added or new glossaries required, the terms will be added to the master glossary as a new separate section.
The Weight of Mass or the Mess of Weight
Authors: Gat U
Published: February 2009

The ambiguity of the term weight, meaning either the force of gravity or mass, is analyzed. It is shown that through the historical development of technical understanding the distinction between mass and force of gravity has been obscure. The confusion is further aggravated by the use of units with the same name for either mass or force. Contemporary technology is vulnerable to errors and misunderstandings due to the ambiguity of the term weight. SI uses clearly distinguishing unit names for mass and force, that is, kilogram and newton. It is recommended that the term weight be avoided and if used be restricted to mean force of gravity.
A Uniform Pure Shear Testing Specimen for Adhesive Characterization
Authors: Weissberg V , Arcan M
Published: February 2009

A new versatile stiff adherend test specimen is proposed. This specimen induces a uniform pure shear stress state practically free of tension and compression in the adhesive layer. The versatility of the specimen consists in the fact that, by loading the specimen in a rotated position, a mixed mode (MI + MII) or (MI + MIII) may be induced, but the present paper deals only with the pure shear case.

Comparative finite element calculations of stress distributions, especially at the free adhesive edge, and strain-energy-release rates of cracked specimens, were performed. Experimental determinations provided accurate stress-strain curves of the adhesive systems tested as well as direct verifications of the strain-energy-release rate concept in adhesive joints.
Deformations and Strains in a Thick Adherend Lap Joint
Authors: Post D , Czarnek R , Wood JD , Joh D
Published: February 2009

Displacement fields in a thick adherend lap joint were measured by high-sensitivity moiré interferometry. Contour maps of in-plane U and V displacements were obtained across adhesive and adherend surfaces. Loads ranged from a modest load to a near-failure load. Quantitative results are given for displacements and strains in the adhesive and along the adhesive/adherend boundary lines. The results show nearly constant shear strain in the adhesive, nonlinear strains as a function of load or average shear stress, and viscoelastic or time-dependent response. Longitudinal normal strains in the adhesive are nearly two orders of magnitude less than the shear strains.

With its subwavelength displacement resolution and high spatial resolution, moiré interferometry is especially well suited for deformation studies of adhesive joints.
Special Mixed Finite Elements for Interfacial Stress Analysis of Adhesively Bonded Joints
Authors: Aivazzadeh S , Bichara M , Ghazal A , Verchery G
Published: February 2009

Various special triangular and rectangular mixed finite elements for the static analysis of adhesive joints are presented. These finite elements take into account the continuity conditions at the interface, including the displacements and transverse stresses as variables, and they are developed for two-dimensional elastic behavior. Two processes have been developed to construct the finite elements through the use of Reissner's variational principle: the elimination process and the relocalization process.

Several numerical examples are presented which illustrate the accuracy of the interface finite elements by comparison with the classical finite elements displacement method.
Debonding Characteristics of Adhesively Bonded Woven Kevlar Composites
Authors: Mall S , Johnson WS
Published: February 2009

The fatigue damage mechanism of an adhesively bonded joint between fabric reinforced composite adherends was investigated with cracked-lap-shear specimens. Two bonded systems were studied: fabric Kevlar 49/5208 epoxy adherends bonded together with either EC 3445 or FM-300 adhesive. For each bonded system, two specimen geometries were tested. In all specimens tested, fatigue damage occurred in the form of cyclic debonding; however, the woven Kevlar specimens gave significantly slower debond growth rates and higher fracture toughness than previously found in the non-woven adherend specimens. The surfaces for the woven adherends were not smooth; rather, they had regular crests (high spots) and troughs (low spots) due to the weave pattern. Radiographs of the specimens and examination of their failure surfaces revealed that fiber bridging occurred between the crests of the two adherends in the debonded region. The observed improvements in debond growth resistance and static fracture toughness are attributed to this bridging.
Effect of Adhesive Debond on Stress-Intensity Factors in Bonded Composite Panels
Authors: Bigelow CA
Published: February 2009

Stress-intensity factors are calculated for a cracked infinite sheet adhesively bonded to a stringer, and debonding of the adhesive layer is predicted. The stringer is modeled as a semi-infinite sheet. Adhesive nonlinearity is also included. Both the sheet and stringer are treated as homogeneous, orthotropic materials. A set of integral equations is formulated and solved to obtain the adhesive shear stresses and crack-tip stress-intensity factors. Adhesive debonding is predicted using a rupture criterion based on the combined adhesive stresses. A through-the-thickness crack is located in the infinite sheet perpendicular to the edge of the stringer. When the crack is not under the stringer, the debond extends along the edge of the stringer. When the crack tip is beneath the stringer, the debond extends to the crack tip, then along the edge of the stringer. Stress levels required for debond initiation decrease as the crack tip is moved beneath the stringer. With a nonlinear adhesive, the debond initiates at higher applied stress levels than in linear adhesive cases. Compared with the linear adhesive solution, modeling a nonlinear adhesive causes the stress-intensity factor to decrease when debonding is included.
Static Strength of Bolted and Adhesively Bonded Joints for Steel Structures
Authors: Albrecht P , Sahli AH
Published: February 2009

This study examined the slip resistance and ultimate strength of splices of tensile and flexural members for steel structures that were adhesively bonded and clamped with high-strength bolts. It was found that the adhesive fails and the splice slips into bearing when its shear strength is exceeded or when an adherent yields. Up to the slip load, a bonded and bolted splice transfers the load by shear in the bondline, with the bolts acting as a clamping device. Beyond the slip load, the splice can transfer the load only by shear in the bolts. The strengths of the adhesive and the bolts are not additive. Guidelines are recommended for the design of adhesively bonded and bolted joints.
Stress-Intensity Factors for Corner Cracks in Rectangular Bars
Authors: Raju IS , Newman JC
Published: February 2009

This paper presents stress-intensity factors for a wide range of quarter-elliptical corner cracks in rectangular bars. Cracked configurations were subjected to remote tension, in-plane bending, or out-of-plane bending. The ratio of crack depth to crack length ranged from 0.2 to 2; the ratio of crack depth to specimen thickness ranged from 0.2 to 0.8; and the ratio of crack length to specimen width ranged from 0.04 to 0.8. The configurations analyzed varied from a square bar to a very wide plate. These particular crack configurations were chosen to cover the range of shapes and sizes that have been observed to grow in experiments conducted on rectangular bars. The stress-intensity factors were calculated by a three-dimensional finite-element method. Finite-element models employed singularity elements along the crack front and linear-strain elements elsewhere. The models had about 7000 degrees of freedom. Stress-intensity factors were calculated using a nodal-force method.

The present results were compared with other numerical results for a quarter-circular corner crack configuration. The present results along the interior of the crack generally agreed within 3% with those from the literature. Some larger differences (3 to 13%) were observed near the intersection of the crack front and the free surfaces (in the boundary-layer region). Thus, analyses were also performed to study the effect of mesh refinement in the boundary-layer region and the influence of Poisson's ratio on the distribution of stress-intensity factors.
Some Remarks on Three-Dimensional Fracture
Authors: Folias ES
Published: February 2009

In this paper, the author presents the effect of specimen thickness on the stress concentration factor of a plate that has been weakened by a circular hole. The results compare very well with existing results on thin and very thick plates and bridge the data gap between them. Furthermore, the solution is shown to be derived from the same general solution from which the three-dimensional crack problem solution can be derived. The author also, by analogy, draws some conclusions regarding the behavior of the stress intensity factor.
Line Spring Model and Its Applications to Part-Through Crack Problems in Plates and Shells
Authors: Erdogan F , Aksel B
Published: February 2009

This paper, after giving a general description of the line spring model, covers the problem of the interaction of multiple internal and surface cracks in plates and shells. The shape functions for various related crack geometries obtained from the plane strain solution and the results of some multiple crack problems are presented. The problems considered include coplanar surface cracks on the same or opposite sides of a plate; nonsymmetrically located coplanar internal elliptic cracks; and, in a very limited way, the surface and corner cracks in a plate of finite width and a surface crack in a cylindrical shell with fixed end.
Methodology for Mixed-Mode Stress-Intensity Factor Calculations
Authors: Moyer ET
Published: February 2009

A method is presented for the calculation of mixed-mode stress-intensity factors for three dimensional crack fronts. The method uses the nodal forces for the calculation. The strength of this approach is the accuracy of nodal force calculations and the avoidance of the assumption of plane strain. The methodology is described for general crack fronts. The special case of a straight crack front is presented in detail. An example problem is solved with a reference solution. The results of the present method agree to within 3% of the reference value.
Structural Integrity of Rail in Railroad Track in the United States
Authors: Orringer O , Steele RK
Published: February 2009

The resistance of rail to fatigue crack propagation and fracture are discussed. Preliminary results of crack growth calculations are presented to illustrate the correlation of an elementary crack growth model with a full-scale experiment. The possible effects of current trends in railroad operations on safe crack growth life and damage tolerance of rail are noted.
On the Application of R-Curves and Maximum Load Toughness to Structures
Authors: Anderson TL , Gordon JR , Garwood SJ
Published: February 2009

An approximate procedure is presented which allows a ductile fracture analysis to be performed with a single fracture toughness value measured at maximum load in a small-scale test. This maximum load toughness value is used to predict an R-curve which is then used to predict maximum stress and crack extension. Predictions from this approach are compared with experimental data from 20 wide-plate specimens made from various ductile materials. A limited number of these specimens are also analyzed using experimental R-curves in order to investigate the effect of the assumed shape of the R-curve on predictions. In addition, an analysis is presented which allows one to determine the critical tearing modulus required for a structure to exhibit collapse controlled failure. Potential applications of these analyses are discussed.
Dynamic Measurement of Crack-Tip Opening Displacement
Authors: Sharpe WN , Waclawiw Z , Douglas AS
Published: February 2009

Crack opening displacements were measured at two positions very close to the tip of a crack in three-point bend specimens that were loaded explosively. Indentations were placed across the fatigue precrack at locations 100 μm and 200 μm behind the tip. These indentations, when illuminated with a laser, generate fringe patterns in space, and the motion of these fringes is proportional to the displacement between them. The fringe motion was monitored with photomultiplier tubes and an oscilloscope and converted to crack-tip opening displacement (CTOD). Explosive loading of the specimens generated stress-intensity factors increasing at a rate of 3 × 106 MPa m1/2/s.

A soft tool steel was used as a prototype material for this technique development because its material response is similar to the tough materials that are to be studied in the future. Both CTOD and crack-tip opening angle were measured in a search for an appropriate measure of resistance to dynamic fracture. Quasi-static tests were also conducted using the same measurement techniques plus a clip gage. A dynamic critical stress-intensity factor (not plane strain) was determined using a slope reduction procedure based on the static tests. The results show little change in dynamic fracture toughness for this material with increasing loading rate. The experimental techniques show promise for further dynamic studies.
Line Spring Method of Stress-Intensity Factor Determination for Surface Cracks in Plates Under Arbitrary In-Plane Stresses
Authors: Yang CY
Published: February 2009

The elastic line spring model is updated to accept arbitrarily distributed loads acting on plates to allow determination of stress-intensity factors of surface cracks under various types of loading, such as thermal stress and residual stress. The governing integral equations are modified, owing to the inclusion of the nonlinear loads. Careful numerical treatment and computer programming can make the analysis very efficient. It has been shown that a 16-point KI-distribution along a crack front can be obtained within 0.025 s (central processing unit) using Cray computer systems, which is at least four orders of magnitude faster than the finite-element analysis of the same problem. The outstanding computational efficiency makes the line spring model practical for many time-dependent fracture analyses in engineering applications.

Cracks with different shapes, namely, semielliptical, part-circular, and triangular cracks are investigated, and the results agree very well with the existing finite-element analysis solutions.
Wide-Plate Crack-Arrest Testing: Evolution of Experimental Procedures
Authors: deWit R , Low SR , Fields RJ
Published: February 2009

Between September 1984 and December 1985, five wide-plate crack-arrest tests on A533B quenched and tempered steel were carried out on the 26-MN tensile capacity universal testing machine at the National Bureau of Standards. Each test was different with respect to the conditions of testing, specimen configuration, and instrumentation used to monitor the dynamic response of the specimen during crack propagation and subsequent arrest. The progressive changes in test procedure discussed here represent attempts to obtain desired crack-run and crack-arrest behavior and to improve the quality of the data collected. Also, the optimization of strain gage locations and the final choice of recording instrumentation are reported in detail. Two techniques for measuring crack velocity are compared. Efforts to cause crack initiation and propagation at lower values of stress-intensity factor than were found in the first test are also discussed.
Fracture Analyses of Heavy-Section Steel Technology Wide-Plate Crack-Arrest Experiments
Authors: Bass BR , Pugh CE , Merkle JG , Naus DJ , Keeney-Walker J
Published: February 2009

A series of six wide-plate crack-arrest tests was recently completed by the Heavy-Section Steel Technology program at the National Bureau of Standards, Gaithersburg, MD, using tensile-loaded specimens of A533 Grade B Class 1 steel. Crack-arrest data were obtained at temperatures in the transition range and above the onset of the Charpy upper shelf, thereby providing a basis for the development and evaluation of improved fracture-analysis methods. The 1 by 1 by 0.102-m single-edge-notched (SEN) specimens were welded to long straight pull tabs and subjected to a transverse linear temperature gradient before loading. The crack tips were sharpened by hydrogen-charging an electron-beam weld. The tests were designed to obtain crack arrest near the middle of the specimen where the temperature would produce a high-toughness level in the upper transition region of the material. The specimens were instrumented with strain gages and thermocouples. Initial static design calculations were made using textbook formulas. Additional calculations, using an assumed set of KID versus ˙a and T relations and an effective stress wave concept, confirmed the reasonableness of tentative design parameters. Pretest and posttest dynamic finite-element calculations were performed for each test. Computed results are compared with transient data for crack-line strains, crack speed, crack-opening displacement, arrest location, and postarrest tearing. Results from both application-mode and generation-mode dynamic analyses are presented. The arrest toughness values calculated from the test data are summarized for temperatures ranging from the transition into the Charpy upper-shelf range.
Comparison of Analysis and Experimental Data for a Unique Crack Arrest Specimen
Authors: Ayres DJ , Fabi RJ , Schonenberg RY , Norris DM
Published: February 2009

A new fracture test specimen has been developed to study crack extension and arrest in nuclear reactor vessel steels subjected to stress-intensity factor and toughness gradients similar to those in postulated pressurized thermal shock situations. A summary of the results of all the tests performed is presented to illustrate the range of crack arrest and crack reinitiation conditions observed. One test of this specimen with the corresponding stress analysis is described in detail. During this test the crack initiated, extended, arrested, reinitiated, extended again, and reached a final arrest. Comparison of detailed dynamic elastic-plastic finite-element analyses and dynamic strain and displacement measurements of the crack extension, arrest, and reinitiation events, combined with topographic analysis of the fracture surfaces, has led to a new understanding of the crack extension and arrest process. The results of the tests demonstrate crack arrest in a rising stress-intensity field at near-upper-shelf temperature conditions and show that the toughness required for arrest is lower than would be predicted by the analysis procedures usually employed for pressurized thermal shock evaluations.
Fatigue Crack Propagation Behavior and Damage Accumulation Relationships in an Aluminum Alloy
Authors: O'Connor BPD , Plumtree A
Published: February 2009

Damage accumulation was studied in strain-cycled aluminum Alloy 6066-T6 cylindrical fatigue specimens. The damage was assessed by measuring the ratio of cracked to cross-sectioned areas and monitoring the apparent modulus changes after different life fractions. Both these methods were found to correlate well. Stage II fatigue crack propagation was established when the surface crack length had attained a critical value of approximately 700 μm. A linear relationship with crack depth ensued. Below this value, the crack depth was small by comparison and damage levels were below 1%. Over 60% of the fatigue life was spent in Stage I (or surface-dominated) crack growth where the cracked area was insignificant. From a practical point of view, damage was considered to begin after this life fraction and a damage mechanics model was successfully applied to the experimental results.

Damage accumulation rates were related directly to crack growth rates as a result of the relationship between damage and the cracked area. Hence, damage accumulation may be described by a Paris type of equation.

Tests at low strains involving a large amount of elasticity (elastic-to-plastic strain ratios of the order of 600) were found to maintain low damage levels over longer life fractions compared with higher strain cycled tests (with ratios of 25 and less). Damage at a given life fraction in tests with elastic-to-plastic strain ratios below approximately 25 were found to be similar. Under these conditions Miner's rule may be applied.
Fatigue Crack Growth at High Load Ratios in the Time-Dependent Regime
Authors: Nicholas T , Ashbaugh NE
Published: February 2009

Experimental crack growth rates were determined in Inconel 718 middle cracked tension [M(T)] specimens at 649°C under conditons of high frequency (10 to 100 Hz) and high load ratio, R. Under these conditions, the material experiences cycle-dependent crack growth as well as time-dependent crack growth. At very high R values approaching unity, the observed growth rates are lower than those obtained under sustained load at the same mean load in the absence of the superimposed cyclic loading. Tests on compact tension [C(T)] specimens at lower frequencies were used to demonstrate the existence of three regions of behavior—cycle-dependent, mixed mode, and time-dependent.

A linear cumulative damage model was used to predict the growth rates due to combined cycle-dependent and time-dependent mechanisms. The model was developed from 427°C data for the cyclic term and sustained load crack growth data for the time-dependent term. Although the model cannot predict the synergistic effect at high R, it provides a reasonable representation of much of the data. The authors conclude that the use of low-temperature data for the cyclic term is inadequate for representing the threshold values and growth rates at low ΔK values at the higher temperature.
Fatigue Crack Growth in Aircraft Main Landing Gear Wheels
Authors: Nagar A
Published: February 2009

Fracture analysis of aircraft landing gear wheels under service-simulated operating loads using various fatigue crack growth characterization techniques is presented. Baseline constants for the wheel forging alloy 2014-T6 aluminum are established. The stress-intensity factors for a two-dimensional surface crack are developed using a proposed load model for the wheel's flange/bead seat radius. Crack growth predictions are performed using a modified crack growth (CRKGRO) program under spectrum load blocks. New stress-intensity factor subroutines for combined loads are added to the program library. The analytic results are compared with measured crack growth data during full-scale structural tests. Good agreement between analytic and structural test results was obtained, and a damage characteristic curve for the wheel flange is proposed. Qualitatively, fracture surface observations supported proposed crack-tip load models, state of stress, and crack growth data.
Gene Probes as a Tool for the Detection of Specific Genomes in the Environment
Authors: Barkay T , Sayler GS
Published: February 2009

Gene probes hold great promise as a tool in environmental sciences. They may be used to detect specific genotypes, to follow gene flow process, to delineate complex taxonomic aggregates, and to monitor genetically engineered organisms in the environment. The sensitivity of the method is currently limited by experimental procedures, and its specificity depends on the nature of the DNA sequences used as probes and the efficacy of lysing methods. Variable genetic determinants which code for the same trait determine the universality of gene probes. Finally, the method is highly feasible in terms of cost, speed, and expertise. Current and future developments in molecular microbial ecology are likely to contribute toward the improvement of the probing methodology for the full realization of its potential in environmental sciences.
Plasmid Mobility in the Ocean Environment
Authors: Grimes DJ , Somerville CC , Straube W , Roszak DB , Ortiz-Conde BA , MacDonell MT , Colwell RR
Published: February 2009

Evidence of plasmid selection and genetic exchange in natural aquatic environments, including the ocean, includes: (a) high incidence of plasmid-containing strains in polluted areas; (b) presence of free DNA in natural environments; (c) co-existence of identical plasmids in different cohabiting strains; and (d) data from in situ plasmid transfer experiments. Current research in our laboratory regarding plasmid mobility in the ocean centers around viable but nonculturable bacteria, cloning of ecologically significant genes, genetic exchange between deep sea bacteria under pressure at low temperature, and development of 16S ribosomal DNA probes for tracking genetically engineered microorganisms that are released to natural environments.
Long-Term History of Eutrophication in Washington Lakes
Authors: Brugam RB
Published: February 2009

Paleolimnological techniques were used to reconstruct past changes in lake water quality at Meridian Lake, Washington. A core was taken from the lake and dated using 210Pb and pollen analysis. Diatom microfossils showed two periods of increasing trophic status. The first came in the 1880s when the watershed was deforested, and the second occurred in the late 1940s when the watershed was developed for suburban housing. In the Meridian core, eutrophication was indicated by increasing percentages of Asterionella formosa in the fossil diatom assemblage. In 15 other western Washington lakes where core tops and bottoms were examined, Asterionella also increased with human disturbance. On the basis of previous laboratory measurements of nutrient-limited growth, Asterionella seems to be adapted to lakes with high phosphorus levels but low silica levels—characteristics of lakes which have eutrophied.
An Evaluation of the Screening Level Concentration Approach for Validation of Sediment Quality Criteria for Freshwater and Saltwater Ecosystems
Authors: Neff JM , Cornaby BW , Vaga RM , Gulbransen TC , Scanlon JA , Bean DJ
Published: February 2009

The U.S. Environmental Protection Agency (EPA) has initiated an effort to develop sediment quality criteria for both freshwater and marine ecosystems. The Screening Level Concentration (SLC) approach is one of several methods EPA is evaluating for calculating sediment quality criteria. The SLC approach uses field data on the cooccurrence in sediments of benthic infaunal invertebrates and different concentrations of the nonpolar organic contaminant of interest. The SLC method is designed to estimate the highest concentration (normalized to sediment organic carbon concentration) of a particular nonpolar organic contaminant in sediments that can be tolerated by approximately 95% of benthic infauna. As such, the SLC value could be used in a regulatory context as the concentration of a contaminant in sediment that, if exceeded, could lead to environmental degradation.

This paper describes the method for calculating the SLC and evaluates the SLC approach empirically for nonpolar organic contaminants in freshwater and marine sediments in terms of its statistical properties and its dependence on the characteristics of the data base. SLCs are calculated for five contaminants in freshwater sediments (total polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane (DDT), dieldrin, chlordane, and heptachlor epoxide) and nine contaminants in saltwater sediments (total PCBs, DDT, naphthalene, phenanthrene, fluoranthene, benz(a)anthracene, chrysene, pyrene, and benzo(a)pyrene). The method used to calculate SLCs is illustrated for total PCBs in freshwater and saltwater sediments. Differences in SLC values for PCBs and DDT between freshwater and saltwater sediments are discussed. The SLC approach demonstrates sufficient merit to warrant further evaluation and elaboration. Given a large enough data base and minor modifications of the methods for calculating an SLC for a specific contaminant, the approach can provide a conservative estimate of the highest concentration, normalized to sediment organic carbon, that 95% of the benthic infauna can tolerate in sediment.
A Technique for Better Sediment Characterization
Authors: Knapp KA , Dysart BC
Published: February 2009

A two-phase technique for determining the particle size distribution (PSD) of a sediment sample was developed. The hydrometer method of PSD analysis was selected for this research. For each sample, standard preparation for PSD analysis, that is, chemical dispersion of soil aggregates, was preceded by nondispersed PSD analysis. Resulting data were plotted as percentage finer by weight (arithmetic scale) versus grain size in millimeters (log scale). Each sediment sample's curve comprised a dispersed portion and a nondispersed portion. These curves can be used to describe the transport behavior of the soil, information that is necessary for the rational choice and design of effective erosion control measures. Sensitivity analysis, including investigation of the effects of sampling approach, temperature, dispersing time, meniscus, and concentration, showed this technique to be a simple, quick, reproducible, and inexpensive means of characterizing an eroded material.