bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Backcalculation Procedure Based on Dispersion Analysis of FWD Time-History Deflections and Surface Wave Measurements Using Artificial Neural Networks
Authors: Kim YR , Xu B , Kim Y 
Published: April 2008

A new layer moduli backcalculation procedure using transient measurements from both a falling weight deflectometer (FWD) test and a surface wave test is presented in this paper. This algorithm employs numerical solutions of a multi-layered half-space based on Hankel transforms as a forward model and Artificial Neural Networks (ANNs) for the inversion process. Two ANNs are used in series; a depth to a stiff layer is predicted first and used as input for the second ANN to be used for the prediction of layer moduli.
Falling weight deflectometer (FWD) and surface wave tests were performed on experimental pavement sections in North Carolina with different asphalt mixture types and surface conditions. Dispersion analysis was performed on FWD transient deflections and surface wave test measurements using the Short Kernel Method. Conventional backcalculation was also performed on FWD deflections using the MODULUS 5.0 program. It was concluded that the dispersion-based backcalculation method is sensitive to changes in upper layer condition and results in less variable sub-surface layer moduli and more accurate prediction of depth to a stiff layer than the conventional backcalculation does using FWD peak deflections.
Variations of Constraint and Plastic Zone Size in Surface-Cracked Plates Under Tension or Bending Loads
Authors: Aveline CR , Daniewicz SR 
Published: April 2008

Elastic-plastic finite element analyses of surface-cracked plates are performed using the commercial finite element code ANSYS. Various crack geometries are analyzed under tension and bending loads. A constraint factor dependent on the location along the perimeter of the surface crack, similar to the global constraint factor defined by Newman, is presented. This newly defined constraint factor is the averaged normal stress to flow stress ratio acting on a line originating on and perpendicular to the crack front at a prescribed location and terminating at the perimeter of the plastic zone on the crack plane.
The plastic zone shape and size around the three-dimensional crack front determined from the finite element analyses are also presented. The analyses indicate that the maximum plastic zone size occurs beneath the free surface (2° &lt; ϕ &lt; 5°). Geometry and applied loading parameters are considered in equations relating them to constraint along the crack front.
Calculation of Stress Intensity Factors for Cracks of Complex Geometry and Subjected to Arbitrary Nonlinear Stress Fields
Authors: Glinka G , Reinhardt W 
Published: April 2008

Fatigue cracks in shot-peened and case-hardened notched machine components are subjected to stress fields induced by the external load and residual stresses resulting from the surface treatment. Both stress fields are characterized by nonuniform distributions, and handbook stress intensity factor solutions are in such cases unavailable, especially in the case of planar nonelliptical cracks. The method presented here is based on the generalized weight function technique enabling the stress intensity factors to be calculated for any Mode I loading applied to arbitrary planar convex and embedded crack. The stress intensity factor can be determined at any point on the crack contour by using one general weight function discussed in the paper. The weight function, mA, can be sufficiently well described by two quantities, i.e., the distance, ρ, from the load point, P(x, y), on the crack surface to the point, A, on the crack front where the stress intensity is to be calculated and the length, Γc, of the inverted crack contour. The stress intensity factors are calculated by integrating the product of the stress field and the weight function over the entire crack area.
The general weight function and calculated stress intensity factors are validated against arious numerical and analytical data. The numerical procedure for calculating stress intensity factors for arbitrary nonlinear stress distributions is briefly discussed as well. Several examples of typical input data and stress intensity factor results are presented including embedded and edge cracks subjected to two-dimensional stress fields. The method is particularly suitable for modeling fatigue crack growth in the presence of complex stress fields.
Fatigue Crack Growth Threshold Stress Intensity Determination via Surface Flaw (Kb Bar) Specimen Geometry
Authors: Bain KR , Miller DS 
Published: April 2008

Many aircraft component failures originate from small-surface flaw cracks in highly stressed locations. It is therefore desirable to measure the threshold stress intensity factor that simulates the key conditions of high-stress and small semicircular surface crack shape. Such a technique has been developed and demonstrated on multiple titanium and nickel-base alloys. This technique is effective at both room and elevated temperatures and at both low and high mean stress.
The test method is described in detail, but in brief a small EDM flaw is made on the surface of a rectangular specimen. The crack length is monitored via electrical potential drop technique. The crack length and aspect ratio versus the change in electrical potential across the crack tip has been measured and is used to control the load shed during the experiment. Load sheds up to C = - 1181 m-1 have been demonstrated to give comparable thresholds to those measured using single edge notch or compact tension geometries with lower shed rates. Typical experimental results on both Ti-6Al-4V and an advanced nickel-base superalloy (KM4) are shown at both room temperature and elevated temperatures. This technique allows a rapid determination of threshold stress intensity factor for a material in a manner simulating the types of constraint experienced in components.
Residual Strength Analyses of Riveted Lap-Splice Joints
Authors: Seshadri BR , Newman JC 
Published: April 2008

Aging aircraft may develop multiple-site damage (MSD) that can reduce the structural integrity of fuselage structures. The existence of small cracks emanating from adjacent rivet holes in a fuselage lap-splice joint is of major concern. The residual strength of a panel with a lead crack is greatly reduced by the presence of smaller collinear cracks compared to that of only a lead crack. Recent studies in predicting the residual strength of flat and curvilinear panels with riveted lap-splice joints gave quite encouraging results, but some difficulties arose in modeling small cracks at rivet-loaded holes. Thus, there was a need to conduct detailed fracture analyses of the crack-linkup phenomenon in lap-splice joints with rivet-loaded fasteners.
The objective of this paper was to analyze the crack-linkup behavior in riveted-stiffened lap-splice joint panels with small MSD cracks at several adjacent rivet holes. Analyses were based on the STAGS (STructural Analysis of General Shells) code with the critical crack-tip-opening angle (CTOA, Ψc) fracture criterion. To account for high constraint around a crack front, the “plane strain” core option in STAGS was used. The importance of modeling rivet flexibility with fastener elements that accurately model load transfer across the joint was discussed. Fastener holes were not modeled, but rivet connectivity was accounted for by attaching rivets to the sheet on one side of the cracks that simulated both the rivet diameter and MSD cracks. Residual strength analyses made on 2024-T3 alloy (1.6-mm thick) riveted-lap-splice joints with a lead crack and various-size MSD cracks were compared with test data from Boeing. Analyses were conducted for both restrained and unrestrained against buckling conditions. Comparison of these analyses with lap-splice-joint test panels, which were partially restrained against buckling, was generally bounded by the restrained and unrestrained failure loads.
SIDD Installation and Direct Design for Reinforced Concrete Low-Head Pressure Pipe
Authors: Heger FJ 
Published: April 2008

This paper describes the principal technical provisions in a proposed ASCE Standard Practice for the Direct Design of Buried Reinforced Concrete Low-Head Pressure Pipe using the same new standard installations (SIDD) as recommended in ASCE 15–93, Standard Practice for Direct Design of Buried Precast Concrete Pipe Using Standard Installations (for reinforced concrete gravity flow pipe). The proposed standard practice defines installation requirements and structural analyses for moment, thrust, and shear produced by external loads that are the same as given in ASCE-15. It incorporates design procedures for combined circumferential tension produced by internal pressure and flexure produced by external loads that are essentially in compliance with both ASTM C361 and AWWA C302 and as recommended in AWWA Manual M9. These provisions and the cited referenced standards use load factors that are larger than those used in various standards for direct design of gravity flow pipe and they further limit the maximum combined stress in the reinforcement by inclusion of a limiting maximum design yield strength of 40,000 psi, regardless of the actual yield strength of the reinforcement. There are further limits on the reinforcement stress produced by internal pressure alone as well as on the tensile stress in the uncracked concrete pipe wall that are essentially the same as given in the above standards for low-head pressure pipe.
In addition to providing the requirements and structural effects of SIDD installations, the proposed standard fills a gap in the existing standards for design of low-head concrete pipe by incorporating rational methods for calculating radial tension and shear strengths. Radial tension strength is required to resist the bending moments at the crown and invert produced by external loads. The presence of internal pressure does not increase the required radial tension strength, and the same methods used for gravity flow pipe may be used for determining the radial tension strength of low-head pressure pipe. Shear strength is another matter. The circumferential tension produced by internal pressure produces a significant effect on shear strength. Research by Dr. M. P. Collins and coworkers in Canada is the basis for new more rational procedures for shear strength of flexural members in the AASHTO LRFD Highway Bridge Specification. These are adopted and simplified for use over the range of wall thickness and strain variations applicable to low-head pressure pipe so that for the first time a rational procedure is available in the proposed standard to calculate the shear strength of low-head concrete pipe. Application of the new procedure to pipe designs for the higher fill heights combined with the highest pressure limits in the design tables of ASTM C361 indicates an adequate factor of safety for those designs, including adequate shear strength.
Field Tests of Concrete Pipe Performance During Backfilling
Authors: McGrath TJ , Selig ET , Webb MC 
Published: April 2008

Full-scale field tests were conducted on the campus of the University of Massachusetts, Amherst, to evaluate the pipe-soil interactions that take place as pipes are buried and backfilled. The program included concrete, polyethylene, and corrugated steel pipe. This paper focuses on the data from the concrete pipe tests, and assesses it in light of the assumptions of the SIDD design approach adopted by ASCE and AASHTO.
Tests included two types of soil backfill, three compaction levels, three trench widths, varying haunching effort and one test with controlled low strength material. Eleven tests were conducted with 900 mm (36 in.) inside diameter pipe and three installations with 1500 mm (60 in.) inside diameter pipe. Primary measurements on the concrete pipe during backfilling and compaction included pipe-soil interface pressures, soil density, and soil stresses.
Results show significant variations in pipe behavior as a result of installation practices and generally confirm the assumptions of the SIDD design method. Compaction of backfill in the region from the springline to 45 to 60 degrees below the springline has a significant positive effect in mitigating poor bedding and haunching conditions, and the use of soft bedding is effective in reducing invert pressures on the Pipe.
Comparison of Ice Hockey Helmet Impact Attenuation Tests on Steel and Elastomeric Impact Surfaces
Authors: Sabelli J , Morehouse CA 
Published: April 2008

United States ice hockey helmet standards were developed with an elastomeric surface for impact attenuation tests. These tests measure peak acceleration as a function of impact velocity. Recently, other standards have specified a flat steel impact surface, with a lower impact velocity (3.96 m/s as opposed to 4.50 m/s) to compensate for the greater hardness of the surface. It has been proposed that the U.S. standard be revised to use the steel impact surface, with the lower impact velocity.
A series of tests was conducted to determine whether tests performed with the proposed lower impact velocity on steel would yield peak acceleration results equivalent to test results with the higher impact velocity on an elastomeric surface. Tests were performed on three different models of ice hockey helmets. Impact tests were conducted at 4.50 m/s on the elastomeric surface, 3.96 m/s on steel, and 4.20 m/s on steel. Results are compared for the three impact schemes.
Thermo-mechanical Out-of-Phase Fatigue Life of Overlay Coated IN-738LC Gas Turbine Material
Authors: Zamrik SY , Renauld ML 
Published: April 2008

Thermomechanical fatigue (TMF) is a unique type of fatigue process in which a component is simultaneously subjected to fluctuating loads and temperature. Isothermal life prediction techniques are often not applicable to TMF conditions since mechanical properties are temperature dependent with different damage mechanisms. There are two major cycles in TMF: the in-phase (IP) cycle where the maximum strain peak coincides with the maximum temperature and the out-of-phase (OP) cycle where the maximum strain and the lowest temperature coincide.
Experimental and analytical methods are developed to address the effect of thermomechanical strain cycling on coated nickel base superalloy IN-738LC material which is a γ' (Ni3Al) strengthened material used primarily for land based gas turbine blades. The coating system was a NiCoCrAlY overlay type. Tubular specimens in the two conditions, coated and uncoated, were primarily tested in out-of-phase (OP) TMF loading with a temperature range of 482–871°C. Using a viscoplastic concept which accounts for strain/temperature cycling response of substrate and coatings in terms of hysteresis loops which characterize the evolution of stress/strain/cycle up to mid-life cycle, a life prediction model was developed incorporating the effect of creep (strain hold-period), environment, and temperature. Test results show the OP TMF type cycle is the most damaging cycle for the coated IN-738LC material when compared to both in-phase and isothermal cycles. All experiments were strain-controlled with a triangular waveform and a strain-ratio A = εamp/εmean = ∞.
Development and Industry Acceptance of Nuclear Gauges
Authors: Troxler WF 
Published: April 2008

Mr. William F. Troxler delivered the keynote speech at the ASTM SYMPOSIUM ON CONSTRUCTION AND CONTROLLING COMPACTION OF EARTH FILLS, presented on July 1, 1999 in Seattle, Washington. As an original contributor to in-situ moisture and density measurement, Mr. Troxler detailed the history of how these devices were developed and accepted in the construction industry.
Beginning with his early work for the US Department of Agriculture and NC State University School of Agriculture to develop a device to measure the water content, Mr. Troxler describes how this device was combined with a similar device that measures the density of soils to create the surface moisture/density gauges used in the highway construction industry. The first models of this device were unacceptable because of the errors created by the chemical composition and other factors. Mr. Troxler explains how the development of calibration blocks with permanent density and moisture content values improved the gauge precision to the extent that the devices were more precise than current methods employed in the industry. Additional points of interest are included to explain how the nuclear moisture/density gauge became a standard test method in the industry.
NRCS Experience with Field Density Test Methods Including the Sand-Cone, Nuclear Gage, Rubber Balloon, Drive-Cylinder, and Clod Test
Authors: McCook DK , Shanklin DW 
Published: April 2008

Engineers of the Natural Resources Conservation Service (formerly the Soil Conservation Service), USDA, instituted a testing program to determine the reliability and reproducibility of several types of field density test methods. Tests were performed at several embankment construction sites in the Southeastern United States. Several different soil types were encountered in the embankment projects. On test pads constructed under normal field conditions, researchers measured the compacted dry density and water contents by the nuclear gage, sand-cone, drive-cylinder, and clod tests. The research compares the results of the various tests and discusses the conclusions of the researchers on reliability and accuracy of the various tests.
Conclusions of the studies include important aspects of each test that were found to explain variations and errors in the tests that were performed. The paper emphasizes errors common to the tests evaluated. Recommendations based on the studies of the NRCS are included. Advantages and disadvantages of methods are discussed. Data from the study sites is included to illustrate repeatability and comparisons of the various methods to each other. Data from the study sites are included to illustrate repeatability and comparisons of the various methods with each other.
Impact of Heavy Metals (Pb, Zn, and Cr) on the Hydraulic Conductivity of Sand/Bentonite Liner
Authors: Thériault P , Galvez-Cloutier R , Winiarski T 
Published: April 2008

This research was conducted to study the changes in permeability of a sand/bentonite liner made under standard compaction conditions and permeated with solutions containing the heavy metals Pb+2, Zn+2 and/or Cr+3. The fine particle size distribution and the free swelling capacity of the bentonite were taken as indicators of the impact of contaminants on the liner's properties.
Generally, particles of bentonite were coarser when in contact with solution ontaining heavy metals. Its free swelling capacity decreased when heavy metal concentrations increased. It is shown that with heavy metal solutions the permeability of a sand/bentonite liner increased by three orders of magnitude. The ion Cr+3 which had a greater impact on the free swelling capacity may have led to a rapid change in permeability. When permeability increased rapidly, heavy metals were present earlier and in higher concentration at the outlet of the liner.
Resorption Profile and Biological Response of Calcium Phosphate filled PLLA and PHB7V
Authors: Jones NL , Cooper JJ , Waters RD , Williams DF 
Published: April 2008

A study was performed to assess the effects of tri-calcium phosphate filler on the tissue response, mechanical properties and degradation characteristics of injection moulded poly L-lactide (PLLA) and poly-hydroxybutyrate co valerate (7 mole % valerate) (PHB7V).
Test pieces for mechanical evaluation were prepared according to ASTM and British Standards. These were aged both in vitro, using a phosphate buffered saline solution (PBS) at pH 7.4 and 37°C and in vivo, subcutaneously using Dutch rabbits. Tensile strength of the materials was monitored, together with molecular weight (Mw) of the polymer as determined by gel permeation chromatography (GPC). The host response to intraosseous implants placed transcortically in the femurs of New Zealand rabbits, was assessed using an undecalcified, unstained, polarised light technique on resin embedded and polished sections.
The materials had good biocompatibility. The bone response to the polymers and composites was very similar. Histology showed that new bone was formed at the defect site, which grew up to the material surface and remodelled into new physiological bone tissue. The rate of degradation of the poly-L-lactide and it's composite with tri-calcium phosphate as assessed by tensile strength and Mw was found to be consistent with the rate for bone healing. Poly-hydroxybutyrate co valerate and its composite with tri-calcium phosphate degraded more slowly.
A Constitutive Model for Long-Term Behavior of Polymers
Authors: Skrypnyk ID , Spoormaker JL , Kandachar P 
Published: April 2008

This paper describes a constitutive model for long-term behavior of plastics. The Struik theory of physical aging is adapted for use with the earlier proposed generalization of the Schapery model. Experimental data on creep and recovery behavior for different elapsed times are necessary to build the model. The parameter identification procedure is based on a minimization of the total error between experimental data and model prediction.
The model has been verified using extensive experimental data on long-term creep and recovery of polypropylene, reported by the National Physical Laboratory (NPL, Teddington, U.K.). The model has shown the ability to work with the independent data; it sufficiently describes the variation of strains in time for loading history, which contains several loading steps. The maximum deviation of the model prediction from the experimental data in a control set is less than 11% to 12%. The average deviation is less than 4%.
Accelerated Strength Testing of Thermoplastic Composites
Authors: Reeder JR , Allen DH , Bradley WL 
Published: April 2008

Constant ramp strength tests on unidirectional thermoplastic composite specimens oriented in the 90° direction were conducted at constant temperatures ranging from 149°C to 232°C. Ramp rates spanning 5 orders of magnitude were tested so that failures occurred in the range from 0.5 s to 24 h (0.5 to 100 000 MPa/sec). Below 204°C, time-temperature superposition held allowing strength at longer times to be estimated from strength tests at shorter times but higher temperatures. The data indicated that a 50% drop in strength might be expected for this material when the test time is increased by 9 orders of magnitude. The shift factors derived from compliance data applied well to the strength results.
To explain the link between compliance and strength, a viscoelastic fracture model was investigated. The model, which used compliance as input, was found to fit the strength data only if the critical fracture energy was allowed to vary with stress rate. This variation in the critical parameter severely limits its use in developing a robust time-dependent strength model. The significance of this research is therefore seen as providing both the indication that a more versatile acceleration method for strength can be developed and the evidence that such a method is needed.