bluuebunny/crossref_metadata_2025 huggingface dataset:
A Large Diameter Triaxial Apparatus to Measure Pore Pressure and Displacements on a Pre-existing Shear Zone/Plane
Authors: Su Xueqing , Tannant Dwayne D. , Martin C. Derek , Morgenstern Norbert R. , Cyre Gerry
Published: March 2009

The development of an apparatus to measure pore pressure and displacements on a pre-existing shear zone/plane during triaxial testing is presented. The apparatus includes a newly developed 405-mm diameter triaxial cell, a miniature pore pressure transducer for monitoring shear-induced pore pressures, and a displacement transducer for measuring shear displacements. Tests were performed by mounting the pore pressure transducer onto the face of a pre-existing shear plane in the specimen and installing the displacement transducer inside the triaxial cell to monitor local deformations. The results reveal that pore pressures measured on the shear plane and the base of specimens of Athabasca clay, Highvale mudstone, and Fort McMurray highly weathered limestone are identical at a shear displacement rate equal or less than approximately 18 mm/day. This implies that when the shear displacement rate is less than about 18 mm/day for rocks/soils that have a permeability greater than 10−8∼10−9cm/s, the pore pressure obtained from in situinstrumentation, which may not be set exactly on the shear plane, can be used as the shear zone pore pressure.
Shear Wave Velocity of a Compacted Clayey Silt
Authors: Clariá Juan J. , Rinaldi Víctor A.
Published: March 2009

Loess deposit covers an extensive area in the central region of Argentina. Improvement of the stress-strain behavior of loess in the field usually includes compaction. In practice, in situ shear wave velocity is suggested as an alternative to control compaction density of loess. In this work, specimens of loess were compacted in the laboratory by means of the Standard Proctor Test at different moisture contents. After compaction, the moisture content of the specimens was varied by the wetting or drying processes. Matric suction was measured. The specimens were subjected to isotropic compression tests and shear wave velocity was measured by means of bender elements. The present study allows us to evaluate the influence of density, water content, confining pressure, and the different soil structures obtained during compaction, on the measured shear wave velocity of the compacted loess. It was observed that although shear wave velocity depends on compaction density, under certain circumstances, wave velocity may be mainly controlled by soil structure and suction forces. A simple relationship was proposed to approach the observed experimental trends.
A Short-circuit Electromagnetic Sensor for Measurement of Soil Complex Permittivity
Authors: Xu Yanqing , Shang Julie Q. , Yanful Ernest K.
Published: March 2009

An electromagnetic sensor is developed for characterization and detection of contamination in geomaterials. The sensor can be used to detect changes in physical and chemical properties of soil and groundwater based on changes in the complex permittivity. The major advantage of the sensor design is the adaptation of short-circuit coaxial line configuration, which makes it readily employed for in situ implementation. A close-form algorithm is developed to convert the measured electromagnetic reflection coefficients S11* by the short-circuit sensor to the complex permittivity of the testing materials. This paper presents a description of the sensor as well as its algorithm developments and the results of complex permittivity measurement. The study indicates that the short-circuit sensor produces reliable measurement of complex permittivity of soil-water systems and can be further developed for in situ contamination detection of soil and groundwater.
Study of a Displacement Measurement Method Inside a Small-Sized Model Ground in Laboratory Test
Authors: Baek Wonjin , Moriwaki Takeo , Sasaki Yasushi
Published: March 2009

In order to understand the complex mechanism of the three-dimensional consolidation behavior of clayey ground improved by the vertical drain system, it is desired to observe the three-dimensional displacements inside the model ground in a series of laboratory tests. However, there is no available example to measure the internal displacement in a small-sized model ground in the laboratory tests because it is impossible to disregard the influence of burying the measuring equipment into the small-sized ground. Baek et al. (2002,2004) proposed a method for measuring the radial displacement in a specimen with vertical drain by measuring the intensity of the magnetic field induced by a very small magnet buried in the specimen by magnetometers set outside the specimen. This measuring method using calibration curves, which show relationships between the position of the magnet and the measured intensity of the magnetic field in the calibration test, was modified by using the theoretical solution of the magnetic field induced by a magnet (Baek et al. 2006). In this paper, combining these previous studies, the whole system for measuring the displacement inside a small-sized model ground improved by vertical drain is described. Then, the reliability of the internal displacements obtained by these methods is discussed in comparison with the numerical solutions obtained by the finite difference method based on the three-dimensional elasto-viscous consolidation theory.
Effects of Swelling During Saturation in Triaxial Tests in Clays
Authors: Cho Wanjei , Holman Terence P. , Jung Young-Hoon , Finno Richard J.
Published: March 2009

Effects of swelling during saturation in triaxial tests on compressible Chicago glacial clays are assessed from results of triaxial compression tests on block samples cut from excavations, thin-wall Shelby tube samples, and reconstituted specimens. The results are presented in terms of the stress-strain response during saturation, k0 reconsolidation and shearing. Bender element tests were also performed to investigate the effects of swelling on the shear wave velocities during k0 reconsolidation. Results showed that the swelling during saturation lowered the shear wave velocity, thereby inferring a change in the original structure of natural clay. Responses at strains less than 0.01 % were most affected by the saturation-induced swelling. To minimize these changes, it is recommended that the measured residual stress is applied prior to saturating the soil. Based on these results, the saturation stage should be considered as much a part of a triaxial test as consolidation and shearing.
Rapid Pseudo-Static Measurement of Hysteretic Capillary Pressure-Saturation Relationships in Unconsolidated Porous Media
Authors: Chen Lixia , Miller Gerald A. , Kibbey Tohren C. G.
Published: March 2009

An automated system was developed for a rapid measurement of detailed hysteretic capillary pressure-saturation (Pc-S) relationships, including primary drainage, main imbibition, and scanning loops. The method makes use of a slow-dynamic (pseudo-static) measurement method which is able to duplicate static results while expanding the pressure range over which high permeability capillary barriers can be applied, and increasing the quantity of hysteretic data that can be collected. The method is demonstrated for two sands and three silts for capillary pressures as high as 1000 cm water (98 kPa). For the experiments shown, primary drainage and main imbibition loops were completed within approximately 6.5 h for all materials, with full runs, including multiple scanning curves, completed in less than 20 h. A model for selection of pressure rates needed to duplicate static results is presented and is found to produce results consistent with empirically-determined rates. The model also predicts the effects of system resistance on dynamic response and is found to be in good agreement with experimental results, particularly for slower rates approaching those needed for pseudo-static conditions.
A Multi-purpose Platform for Horizontal Subsurface Investigation
Authors: Ahn T , Allouche EN , Yanful EK
Published: March 2009

Site characterization using horizontal directional drilling (HDD) can provide an effective means of evaluating the geotechnical and geoenvironmental characteristics of sites with limited access such as beneath structures, roads, and runways.

The Smart Subsurface Horizontal Investigation Probe (SSHIP) is an innovative platform capable of investigating the geotechnical and geoenvironmental properties along a horizontal alignment by combining an array of miniature sampling tubes and a logging tool. The device is controlled from the surface and can transmit data in real-time over a distance of up to 300 m. The results of bench-scale tests aimed at evaluating the usefulness of two miniature sensors, a miniature resistivity probe (MRP) and a miniature cone penetrometer (MCPT), for various soil conditions, are presented.

Combining sampling, logging, and real-time communication capabilities, the SSHIP supports exciting new potential applications in the areas of geotechnical and geoenvironmental site investigations.
Stress-Strain Behavior of a Granular Fill Measured by a New Plane-Strain Apparatus
Authors: Wanatowski D , Chu J
Published: March 2009

In this paper a new plane-strain apparatus is described. The main feature of the plane-strain apparatus is that the intermediate principal stress can be measured by four submersible pressure transducers. Experimental data obtained from drained tests on very loose to medium dense sand are presented. The strength and deformation behavior of the sand under plane-strain conditions and shear band formation are studied. The results show that the failure envelope obtained from plane-strain tests is lower than that from triaxial tests. However, in terms of friction angle, the value obtained from plane-strain tests is higher than that from triaxial tests. The critical state line obtained under plane-strain conditions is also different from that under axisymmetric conditions. Under plane-strain conditions, shear bands occur for medium loose to dense specimens. However, no visible shear bands are observed for very loose specimens. This is consistent with the study reported by Han and Vardoulakis (1991) but different from that by Finno et al. (1996, 1997).
A New Setup for Measuring Go during Laboratory Compaction
Authors: Ismail MA , Rammah KI
Published: March 2009

Soil stabilization by compaction plays an important role in foundation engineering, both for construction and maintenance. Compaction specifications often require achievement of an in situ dry density (ρd) of 90–95% of the maximum value obtained from laboratory standard or modified Proctor test. However, ρd is not a design parameter per se; it is rather used to infer other parameters such as strength and stiffness through some empirical relationships. This paper describes a setup and procedure by which the small-strain (dynamic) shear stiffness can be measured accurately by propagating elastic shear wave through the stabilized material during laboratory compaction. The method enables measurement of the shear modulus [Go(ij)] in both horizontal and vertical planes. The ratio between Go in these two orthogonal planes (i.e., Ghh and Ghv) is a measure of the degree of stiffness anisotropy, and this could be used as input parameter in deformation calculations. The setup is designed so that it can be readily incorporated into the familiar Proctor test.
Interpreting Variable-head Tests Performed in Open Boreholes or Monitoring Wells with Several Screens
Authors: Chapuis RP
Published: March 2009

Variable-head permeability tests can be performed in open boreholes or monitoring wells having either a long screen or several screened zones. In all cases, a test involves several layers composed of fractured rocks or pervious soils. In the hole or the pipe, the static water level represents some mean value of the hydraulic heads within the aquifer layers, a complex pattern of water circulation having been established within the open hole or the screened aquifers. This paper provides first the equation relating the static water level to the hydraulic and geometric parameters of the aquifers, and then the extended theory for variable-head tests under such conditions. According to theory and numerical analyses, such tests should provide straight semi-log head responses and velocity graphs. In real conditions, however, as shown by a series of field tests performed in a monitoring well equipped with three screens, broken line velocity graphs may be obtained. Such piecewise linear lines indicate that the product “hydraulic conductivity × shape factor” varies during the test within one or several aquifer layers. These variations can be related to internal erosion, which happens close to a screen when the gradient and seepage forces change direction during testing. This is confirmed by numerical modeling.
Application of Soil Stiffness Gauge in Assessing Small-Strain Stiffness of Sand with Different Fabrics and Densities
Authors: Sawangsuriya A , Bosscher PJ , Edil TB
Published: March 2009

The soil stiffness gauge (SSG) exhibits particular promise for determining the in situ soil stiffness at small strains. Because the SSG is new, its application in laboratory stiffness measurements is limited. The use of the SSG in assessing small-strain stiffness of sand with different fabrics, densities, and specimen sizes is presented herein. Two types of test containers were utilized and the results indicate that the SSG stiffness obtained from both containers show a similar trend but are offset by a constant value, which might be due to the effect of specimen dimensions and boundary configurations. A comparison with other small-strain stiffness tests indicates that the Young's moduli obtained from the seismic tests are consistently higher than those from the SSG tests. The plots of shear modulus versus shear strain amplitude suggest that the SSG modulus appears to be corresponding to a strain amplitude level higher than the strain amplitude of the seismic test, even though the SSG induces a strain amplitude comparable to that of seismic tests. Nonetheless, the SSG is found to be a potential and useful device for assessing the stiffness of sand with different fabrics and densities.
Validation and Calibration of a Laboratory Experimental Setup for Cross-Well Radar in Sand
Authors: Farid M , Alshawabkeh AN , Rappaport CM
Published: March 2009

Cross-well radar (CWR) uses electromagnetic wave antennas lowered into sampling wells, to image the dielectric properties of soil and detect scattering objects such as contaminants (in this case, dense nonaqueous phase liquids (DNAPLs)). To better understand the physics of CWR in soils, it is necessary to experimentally evaluate the behavior of antennas and electromagnetic (EM) waves. A proto-type model of an infinite soil medium was experimentally simulated by constructing a pilot-scale facility, referred to as SoilBED. The most important issue in any experimental research is the repeatability, reproducibility, and reliability of the results. This paper evaluates different factors affecting experimental data collection in order to achieve the required specifications to collect reproducible and reliable data. Antenna depth and insertion problems, soil disturbance, and boundary condition effects were experimentally evaluated. Other (desired or undesired) transmission couplings were studied, and efforts were conducted to eliminate the undesired paths. The calibrated and validated setup can be and is used for different purposes other than DNAPL detection, such as soil and antenna characterization, theoretical simulation validation, and inverse scattering by various materials in dry or saturated soil backgrounds.
Determination of the Transitional Fines Content of Mixtures of Sand and Non-plastic Fines
Authors: Yang S , Lacasse S , Sandven R
Published: March 2009

Sand-silt mixtures show different behavior with different fines content. The transitional fines content (TFC) is a key parameter which can indicate if the soil behaves as a sand-dominated or as a fines-dominated material. The determination of the TFC for a sand-silt mixture and the possible ways of obtaining the TFC from index data and the triaxial test results are discussed in this study.
Nonlinear Curve-Fitting Procedures for Developing Soil-Water Characteristic Curves
Authors: Sreedeep S , Singh DN
Published: March 2009

Measurement of soil suction for developing soil-water characteristic curve, SWCC, is a laborious and time-consuming task. On the other hand, commercially available databases that employ empirical fitting functions or the estimation algorithms for establishing the SWCC are quite costly and hence, beyond the reach of many. In such a situation, application of two simple nonlinear curve-fitting procedures (viz., a spreadsheet based program, SBP, and Levenberg-Marquardt Algorithm, LMA) for developing the drying SWCC was investigated. The utility and efficiency of these fitting procedures have been demonstrated by comparing the results vis-à-vis those obtained from a dewpoint potentiameter, WP4, and a knowledge-based database, KBD. In addition to this, efforts were made to develop correlations between the parameters used in the SWCC fitting functions and the physical properties of the soil, which can be determined quite easily by conducting routine laboratory tests. It has been demonstrated that these correlations can be used very efficiently for indirect estimation of the SWCC of the fine-grained soil.
How Quantitative is Electron Spectroscopy for Chemical Analysis?—An Evaluation of the Significant Factors
Authors: Wagner CD
Published: March 2009

The technique of dividing photoelectron line areas by elemental sensitivity factors or standard intensities can be applied to single-phase systems but not to multiple-phase systems. Elements other than transition metals can be determined with a standard deviation of 10 percent if photoelectrons of similar energy are used. Larger errors result from using lines of widely different energies because of variations in mean free path ratios among materials, and, more importantly, surface contamination. Transition metals pose special problems because of the prevalence of multielectron processes.
The Use of Soft X-Ray Photoemission Spectroscopy to Study the Adsorption of Oxygen on the (110) Surface of Gallium Arsenide and Gallium Antimonide
Authors: Pianetta P , Lindau I , Spicer WE
Published: March 2009

We discuss the use of synchrotron radiation in the photon energy range between 32 and 300 eV for performing very surface sensitive X-ray photoemission spectroscopy. The usefulness of this technique is illustrated with results for the chemisorption of oxygen on the (110) surface of both gallium arsenide (GaAs) and gallium antimonide (GaSb). Binding energy shifts in the 3d levels of gallium, arsenic, and antimony due to chemisorbed oxygen can be seen for oxygen coverages below 5 percent of a monolayer combining the surface sensitivity of Auger electron spectroscopy with the precise chemical information of X-ray photoemission spectroscopy. When oxygen is adsorbed on GaAs, charge is transferred from the surface arsenic atoms to the chemisorbed oxygen with no breaking of back bonds and, consequently, no oxidation of the surface. In GaSb, on the other hand, there is simultaneous charge transfer from both the surface gallium and antimony atoms, indicating that back bonds are broken and oxide formation is taking place. The escape depth for GaAs (110) was also measured for electron kinetic energies between 20 and 200 eV.
Quantitative Analysis by Secondary Ion Mass Spectrometry
Authors: Newbury DE
Published: March 2009

Quantitative analysis by secondary ion mass spectrometry (SIMS) involves reduction of spectral intensities to compositional values by the use of either empirical sensitivity factors or a physical model of ion emission. Of the several physical models available, the local thermal equilibrium (LTE) model is the one most easily applied to the analysis of an arbitrary multielement specimen. The accuracy of SIMS analysis by both the LTE model and by sensitivity factors has been compared on a series of well-characterized glass samples.

Error factor histograms have been prepared for several hundred elemental determinations. For the LTE analysis, approximately 50 percent of the analyses fall within a factor of two of the accepted value, and 80 percent fall within a factor of five. For analysis with elemental sensitivity factors derived from the glasses, approximately 80 percent of the analyses lie within a factor of two and over 95 percent within a factor of five of known values. quantitative analysis materials thermodynamic equilibrium micro-analysis mass spectrometry.
X-Ray Photoelectron Spectroscopy and Secondary Ion Mass Spectrometry: A Multitechnique Approach to Surface Analysis
Authors: Shepard A , Hewitt RW , Baitinger WE , Slusser GJ , Winograd N , Ott GL , Delgass WN
Published: March 2009

The combination of X-ray photoelectron spectroscopy (XPS) with secondary ion mass spectroscopy (SIMS) promises to provide a powerful new approach both to quantitative analysis of surface composition and to the elucidation of surface molecular structure. In this work, we have tested our ultrahigh vacuum XPS/SIMS system to characterize a variety of metal, alloy, and metal oxygen surfaces. We report on the examination of clean silver surfaces where ions of clusters up to Agn+ where n = 1 to 5 have been observed. Studies have also been carried out on iron/ruthenium catalyst surfaces and on clean indium foils exposed to controlled doses of oxygen. In general, we have tried to illustrate the advantages of this combined technique.
Fracture Resistance of Ti-5A1-2.5Sn Extra-Low Interstitial Castings
Authors: Fiftal CF , Bolstad DA , Misra MS
Published: March 2009

Fracture toughness and cyclic crack propagation data for Ti-5A1-2.5Sn extra-low interstitial (ELI) castings, 0.51 and 2.54 cm (0.20 and 1.00 in.) thick, at 394, 294, 77, and 20 K (250, 70, −320, and −423° F), are presented. Both surface flaw and compact tension geometries were tested. Comparison is made with other titanium alloys in both wrought and cast forms. Crack propagation resistance is comparable to wrought Ti-5A1-2.5Sn ELI, even with the extremely coarse as-cast grain size encountered.
Fracture Toughness Behavior of Unaged Beta-III Titanium
Authors: Rack HJ
Published: March 2009

The dynamic fracture toughness behavior of unaged Beta-III (Ti-10.2 Mo-6Zr-4.5Mo) titanium has been investigated. Both solution treatment practice and subsequent test temperature have been found to affect the fracture toughness. Decreasing the solution treatment temperature from 1255 to 1005 K generally led to a decrease in the fracture toughness over the entire range of test temperatures investigated. In addition, decreasing the test temperature from 473 to 77 K also resulted in lower fracture toughness. These reductions in fracture toughness have been shown to be related to the introduction of increasing amounts of a localized shear fracture mode with both decreasing solution and test temperature. Based on these observations, a model has been proposed which describes the stress/strain conditions at the tip of a propagating crack that appear to enhance shear fracture. Finally, it has been suggested that the principal metallurgical variable controlling the choice of fracture mode transition from either dimple to cleavage or dimple to shear dimple in unaged metastable β titanium alloys is the primary deformation mechanism. Twinning tends to promote shear instability while slip may be associated with low temperature cleavage crack propagation.
Screening Test Method Development for Fracture Resistance Measurements in Thin-Gage Titanium
Authors: Judy RW , Goode RJ
Published: March 2009

Titanium sheet products in gages less than 12.5 mm are used for many lightweight, highly efficient structures. Since these materials are very expensive, in many cases their use requires that very careful attention be given to the prevention of crack growth and fracture. One result of this design approach is that minimum allowable fracture resistance values are specified for mill products; screening tests for quality assurance are required to certify that these minimum values of fracture resistance are met for each sheet of material. The dynamic tear (DT) test was developed for this purpose for heavier section materials (16 mm and thicker) for steels, aluminum alloys, and titanium alloys. Correlations of DT energy values with linear-elastic fracture mechanics parameters enables the determination of KIc values on a routine basis by methods that are quicker and less expensive than direct measurement of KIc. Additionally, the DT test can be used to measure fracture resistance properties of materials in the elastic-plastic and plastic ranges, which is not possible by linear-elastic methods. Past studies of the effect of specimen dimensions on measured DT energy values have shown that the fracture resistance of materials can be expressed in terms of a constant Rp. Using the relationships developed for heavier section materials, a study involving several titanium alloys in thicknesses ranging from 2.5 to 12.7 mm showed that the fracture behavior of thin-section titanium alloys could be rationalized by these methods.
Fracture Resistant Titanium-Aluminum Laminate
Authors: Throop JF , Fujczak RR
Published: March 2009

In an exploratory program for the development of damage tolerant materials for aircraft and helicopter structures, it has been found that laminated panels composed of mill-annealed Ti-6A1-4V sheet and alclad 2024-T3 sheet provided unusual fatigue and fracture resistance. Lamination of these two materials by explosive bonding results in a damage-tolerant fatigue resistant laminate.

Notched-beam specimens were fatigue cycled in pure bending at 30 Hz. The value of stress intensity factor range for crack propagation rates of 2.54 × 10-9 m/cycle (10-7 in./cycle) or less appears to be about 17.5 MN/m3/2 (16 ksiin.) For values of ΔK less than 35 MN/m3/2 (32 ksiin.) the fatigue crack propagation rate measured in the laminate is smaller than that of either the aluminum alloy or the titanium alloy. Room temperature fracture toughness tests of fatigue precracked beams made of equal thickness layers of the two materials give values higher than those of the component alloys. An interlaminar shear strength of 99 MN/m2 (14.3 ksi) was measured.

While complete evaluation of this laminate will require extensive testing, the early indications are that the damage tolerance is superior to that of either of the component metals because of the energy absorbing capacity provided by the laminated construction. Crack growth is retarded by the ductile cladding which forms the welded interfaces, and impact energy is absorbed in deformation and delamination. Moreover, because of favorable residual stresses the laminate appears to have a higher threshold for fatigue crack propagation than either of the component metals. This permits a larger defect size to be sustained without fatigue crack propagation at a given stress level, or a higher stress level to be endured with a given defect size.
Low Temperature Fracture Behavior of a Ti-6A1-4V Alloy and Its Electron Beam Welds
Authors: Tobler RL
Published: March 2009

The effects of electron beam welding on the fracture behavior of a recrystallization annealed, extra-low-interstitial Ti-6A1-4V alloy have been investigated at temperatures in the ambient-to-cryogenic range. Plane strain fracture toughness (KIc) and subcritical crack growth parameters were measured using compact specimens 10 to 25.4 mm thick. These parameters can be used to predict the safe operating lifetimes of cryogenic pressure vessels and other welded Ti-6A1-4V structures.

At intermediate stress intensity factors and within the data scatter for replicate tests, the growth rates of fatigue cracks sited in the fusion and heat-affected zones of electron beam weldments were temperature insensitive and nearly equivalent to rates for the base metal. However, electron beam welding introduced a zone of low fracture toughness at the heat-affected-zone/fusion-zone boundary. The KIc value for this boundary zone at liquid nitrogen temperature (76 K) was 51 MPa/m1/2, 16 percent lower than the base metal. The base metal fracture toughness increases between 4 and 295 K, with an abrupt transition to higher KIc values occurring at temperatures between 76 and 125 K. Static load cracking, temperature effects, and specimen orientation effects on the fracture behavior of this titanium alloy are central topics of discussion.
Effect of Time at Load on Fatigue Response of [(0/ ± 45/90)s]2 T300/5208 Graphite-Epoxy Laminate
Authors: Sendeckyj GP , Stalnaker HD
Published: March 2009

Results of an experimental program, designed to test a time at load fatigue failure hypothesis for composites, are discussed. In order to minimize the influence of various test and material variables, testing was performed using a trapezoidal loading waveform with constant loading rates and sufficiently long hold times at load to minimize the effect of hysteresis heating. The results indicate that the fatigue life of [(0/ ±45/90)s]2 T300/5208 graphite-epoxy specimens can be explained by using time at load as a fatigue criterion.
Preliminary Development of a Fundamental Analysis Model for Crack Growth in a Fiber Reinforced Composite Material
Authors: Kanninen MF , Rybicki EF , Griffith WI
Published: March 2009

This paper describes the preliminary development of a mathematical model for the strength of fiber reinforced composites containing specific flaws. The approach is to embed a local heterogeneous region (LHR) surrounding the crack tip into an anisotropic elastic continuum. By direct consideration of the individual failure events that are activated near the flaw tip, a strength prediction can be made from the basic properties of the composite's constituents. Computations for arbitrary flaw size and orientation have been performed for unidirectional composites with linear elastic-brittle constituent behavior. The mechanical properties were nominally those of graphite epoxy. With the rupture properties arbitrarily varied to test the capability of the model to reflect real fracture modes in fiber composites, it is shown in this paper that fiber breakage, matrix crazing, crack bridging, matrix-fiber debonding, and axial splitting all can occur during a period of (gradually) increasing load prior to catastrophic fracture. Qualitative comparisons with experimental results on edgenotched unidirectional graphite epoxy specimens have also been made.
Fatigue of Notched Fiber Composite Laminates: Analytical and Experimental Evaluation
Authors: Kulkarni SV , McLaughlin PV , Pipes RB , Rosen BW
Published: March 2009

This paper describes the analytical/experimental correlation study performed to develop an understanding of the behavior of notched boron/epoxy laminates subjected to tension/tension fatigue loading. The static failure analysis of notched laminates used herein treats the following modes of failure: axial cracking in the load direction, and transverse cracking across the specimen. The “mechanistic wearout” fatigue analysis uses this static failure model and embodies the concept that material properties in the notch region are continually changing with cyclic loading and that, if these properties are known at a given time, they could be used in the static failure analysis to compute residual strength and preferred mode of crack propagation. In order to verify the fatigue model, an experimental program of limited scope was undertaken to obtain boron/epoxy lamina static and fatigue data (longitudinal and transverse tension and in-plane shear), unnotched [02/±45]s laminate static data, and notched [02/±45]s laminate static and fatigue data. Laminate fatigue behavior was determined from lamina fatigue data, and analysis predictions were compared with the notched-laminate fatigue data. The specific phenomena of interest are the initiation of fatigue damage and its growth as a function of load cycles, fatigue life and mode of failure, and the residual strength after a predetermined number of cycles and the corresponding mode of failure. Certain predicted phenomena such as the increase in residual strength after fatigue loading and both axial and transverse damage growth were observed experimentally. However, correlation of theory and experiment was hampered by the following factors: delamination of the 0-deg surface layers in the region of the longitudinal projection of the notch diameter, lack of statistically significant data base for lamina fatigue properties in general, and absence of lamina axial compression fatigue data in particular. The principal deficiency appears to be the lack of a capability to predict growth of delaminations. Therefore, the interplay of stacking sequence and various failure modes needs to be investigated analytically and experimentally in detail.
Nondestructive Tests for Shear Strength Degradation of a Graphite-Epoxy Composite
Authors: Kaelble DH , Dynes PJ
Published: March 2009

The effects of hydrothermal aging (100°C in water) on the shear strength properties of a graphite-epoxy composite have been studied. Fiber surface treatments were employed to produce controlled rates and extents of hydrothermal degradation in the laminated composite. A study was conducted to develop methods of specifically detecting and identifying the extent and mechanism of hydrothermal aging. This study shows that hydrothermal aging concurrently degrades the bonded fiber-matrix interface, produces changes in the chemical network structure of the epoxy matrix, and modifies the differential stress balances imposed by fiber constraints upon the epoxy continium phase. The degradation state of the fiber-matrix interface was detected through correlation of surface energetics analysis, ultrasonic characterization, and moisture take-up. The state of the bulk epoxy was evaluated by differential scanning calorimetry, specific heat measurements, infrared and dynamic mechanical spectroscopy, and thermo-mechanical analysis. The fiber-matrix stress state was delineated by thermal expansivity, dynamic mechanical spectroscopy, and ultrasonic response. These nondestructive measurement techniques for hydrothermal aging form the basis for detailed analysis of the relations between materials response and composite performance and reliability.
Failure Analysis of the Split-D Test Method
Authors: Knight CE
Published: March 2009

The Split-D test is used to determine unidirectional tensile strength of filament wound composites, but it has a known stress concentration in the ring near the D edge. A finite element stress analysis and a statistical strength theory are used to assess the influence of the stress concentration on the ultimate strengths calculated for the composites from the Split-D test. Stress distributions are presented for the conventional Split-D ring as well as the elongated ring specimens. The influence of material variability via the Weibull parameter, m, on the predicted failure level is shown. In general, materials with an average variability (m < 40) will yield Split-D test results above 90 percent of the true strength.
A Perturbation Solution for Interlaminar Stresses In Bidirectional Laminates
Authors: Hsu PW , Herakovich CT
Published: March 2009

This paper considers a thin, elastic, bidirectional, symmetric composite laminate subjected to a uniform axial strain. All interlaminar stresses are determined by a 0th-order perturbation analysis of the governing equations. The method of solution considers the laminate to be composed of an interior region (removed from the free edge) and a boundary layer region. The interior region is analyzed by dropping terms related to powers of the thickness-to-width ratio h/b in the dimensionless elasticity equations. The boundary layer region is studied by introducing a stretching transformation to the governing equations. A uniform solution is then formed by satisfying Prandtl's matching principle of perturbation theory.

Results for a four-layer, bidirectional graphite-epoxy laminate are compared with existing finite difference results. It is shown that the perturbation analysis provides more insight into the stress distribution near the free edge.
Evaluation of Composite Curing Stresses
Authors: Pagano NJ , Hahn HT
Published: March 2009

A recently developed approach to predict the initial stress field within a composite laminate after fabrication processing is examined in some detail. In this approach, the material response is assumed to be elastic with temperature-dependent properties. With the introduction of the concept of a stress-free temperature, it is shown that this position is defensible by use of deformation measurements on unsymmetric angle-ply units. Implications concerning the influence of the curing stress field on initial damage level (first-ply failure) are studied analytically. The predictions indicate a marked effect of curing stress in certain laminates. The consequences of combined moisture and thermal effects on initial damage level also are discussed.
Lamination Residual Strains and Stresses in Hybrid Laminates
Authors: Daniel IM , Liber T
Published: March 2009

The influence of hybridization in angle-ply laminates on curing residual strains and stresses was investigated. The specimens were graphite/Kevlar 49/epoxy and graphite/S-glass/epoxy laminates of various stacking sequence variations of the basic [±45/02]s construction. The ±45-deg plies and, in some cases, half the 0-deg plies were graphite/epoxy. Residual stains were determined experimentally following previously developed techniques by taking the difference between the unrestrained thermal strain of an individual ply and the restrained strain of that ply within the laminate. It was found that stacking sequence did not have an influence on measured residual strains. In the graphite/Kevlar/epoxy group, the transverse (ɛ90) strain in the 0-deg Kevlar plies is the highest, exceeding 9 × 10−3, reflecting the high-transverse thermal expansion of unidirectional Kevlar. The transverse strain in the 0-deg graphite plies is much lower, reaching a peak value of 5.6 × 10−3. In the graphite/S-glass/epoxy group the transverse strains in the 0-deg S-glass plies are relatively low, compared to similar strains in the 0-deg graphite plies. Residual strains in the graphite plies do not seem to be influenced much by the type and number of hybridizing plies. Residual stress computations show that at room temperature the transverse to the fibers residual stresses exceed the static strength for the graphite plies and reach values up to 75 percent of the transverse strength for the glass plies. The residual stresses in the Kevlar plies are high enough to cause early transverse failure of these plies before the laminate is cooled down to room temperature.
Boron/Aluminum Skins for the DC-10 Aft Pylon
Authors: Elliott SY
Published: March 2009

Three boron/aluminum aft pylon “boat tail” skins were designed, fabricated, and installed on three DC-10 aircraft for a five-year flight service demonstration test. Inspection and tests of the skins will establish the ability of the composite to withstand long-time flight service exposures to high temperatures, sonic fatigue, and flutter. The results of a preliminary testing program yielded room and elevated temperature data on the tension, compression, in-plane shear, interlaminar shear, bolt bearing, and tension fatigue properties of the oriented eleven-ply boron/aluminum laminates, and this information, together with a stress analysis, was used to obtain Federal Aviation Administration approval. Present state-of-the-art technology was used in the fabrication of the skins, and these were installed on the existing titanium substructure with the same number and size mechanical fasteners as are used for the present titanium skins.
Time-Temperature-Stress Dependence of Boron Fiber Deformation
Authors: DiCarlo JA
Published: March 2009

Flexural stress relaxation (FSR) and flexural internal friction (FIF) techniques were employed to measure the time-dependent deformation of boron fibers from −190 to 800°C. The principal specimens were 203-μm (8 mil) diameter fibers commercially produced by chemical vapor deposition (CVD) on a 13-μm tungsten substrate. The observation of complete creep strain recovery with time and temperature indicated that CVD boron fibers deform flexurally as anelastic solids with no plastic component. The mechanical relaxation processes responsible for the anelasticity were found to be controlled by a continuous distribution of thermally activated relaxation times τ = τ0 exp(Q/kT). Excellent fit of the FSR data with FIF data was obtainable across more than seven time decades by assuming that all processes have the same lnτ0 (= −33.1) but are continuously and broadly distributed in energy Q. The incorporation of the derived distribution parameters into anelastic theory yielded simple analytical equations to describe the time-temperature-stress dependence of CVD boron fiber deformation at low strains. In order to extend the flexural results to high strain and conditions of axially applied stress, an analysis of fiber axial deformation was made using data from the literature and our own fracture measurements. For the latter study, etched fibers were employed to ensure coreinitiated fracture. A model of a “composite” fiber with an anelastic sheath and elastic core was assumed in order to convert fracture stress versus time-temperature data to anelastic relations descriptive of axial deformation. These results in combination with literature data confirm the flexural result that up to at least 800°C all non-elastic axial behavior of CVD boron fibers can be explained solely by anelastic mechanisms. Diameter, core, coating, etching, and manufacturing source appear to affect negligibly boron sheath anelasticity. With a simple empirical model to account for observed stress effects, final analytical equations and curves are presented to describe total axial deformation strain. These relations are further developed to demonstrate the significant effects of anelasticity on such fiber/composite properties as modulus, creep, creep recovery, stress relaxation, and damping capacity. Finally, under the elastic-core/anelastic-sheath model, modern boron fibers on tungsten substrates are shown to have predictable fracture stresses for time-temperature conditions ranging from impact to long time stress rupture. Possible techniques for altering these stresses are discussed.
Moisture Absorption and Desorption in Epoxy Composite Laminates
Authors: Shirrell CD , Halpin J
Published: March 2009

Epoxy composite laminates absorb moisture from the atmosphere via a diffusion controlled process and undergo changes in both mechanical properties and dimensional shapes. This paper reviews the nature of moisture absorption by epoxy composites and the resultant effects upon the laminate.
Inductively Coupled Plasma-Atomic Emission Spectroscopy: An Alternative Approach to “Flameless” Atomic Absorption Spectroscopy
Authors: Fassel VA
Published: March 2009

Atomic emission spectroscopy (AES) combined with an inductively coupled plasma (ICP) excitation source is discussed as an attractive alternative approach to “flameless” atomic absorption spectroscopy for the determination of trace elements in liquid samples of limited volume. The AES-ICP approach offers the potential advantage of: (a) being able to perform these determinations on a simultaneous multielement basis, and (b) possessing an unusual degree of freedom from interelement effects if solution nebulization techniques are utilized. For 1-ml sample volumes, the relative powers of detection (ng/ml) of the AES-ICP approach are comparable to the values reported for flameless atomic absorption procedures.
Dispersive Clay at Sobradinho Dam
Authors: Bourdeaux G , Imaizumi H
Published: March 2009

Sand filter tests using cylindrical specimens with a circular hole and large prismatic specimens with a vertical slot were performed extensively. Results reveal that compacted sand filters which obey a conventional filter criterion, act safely to control and seal leaks through cracks in compacted impervious soils comprised of dispersive clay. The dispersive clays in the area of the Sobradinho Dam project occur predominantly in the alluvium as far as the “sodium concentration in pore water of soils” criterion is concerned. X-ray diffraction on clay minerals shows the presence of montmorillonite, common in these dispersive clays. Field and laboratory observation on properties of the soils leads to utilization of nondispersive clays at three conjunctions with concrete structures to minimize any risk of occurrence of internal erosion adjacent to them.
Erodibility Tests on a Sensitive, Cemented Marine Clay (Champlain Clay)
Authors: Dascal O , Pouliot G , Hurtubise J
Published: March 2009

Laboratory tests conducted on the erodibility of a sensitive, cemented clay (Champlain clay) have indicated highly dispersive characteristics (sodium cations content of the pore water, 85 to 90 percent; Soil Conservation Service Laboratory Dispersion Tests, 60 to 100 percent). Pinhole tests performed on undisturbed and remolded specimens have also confirmed the high erodibility of the clay. However, field observations and investigations could not substantiate this behavior; on a practical basis, the clay formation cannot be considered as a dispersive, erodible material. The particular nature and mineralogy of the clay can probably explain the discrepancy. The mineralogical analysis of the clay shows that is composed mainly (90 percent plus) of inert, nonclay minerals; consenquently, the deflocculation mechanism of erosion cannot be considered. It seems that the chemical composition of the pore water is not related to the mineralogy of the clay, but rather to the environmental conditions prevailing during its formation. The high sensitivity of the clay, which liquefies around the hole when the specimen is punched with a pin, probably explains the positive pinhole test results recorded.
Development and Use of the Soil Conservation Service Dispersion Test
Authors: Decker RS , Dunnigan LP
Published: March 2009

This paper presents information from and experience with a test developed by the Soil Conservation Service (SCS) to identify dispersive clay soil. Background information on erosion and piping problems, which led to the development of the test, are reviewed. Comparisons of the SCS dispersion test with field performance and pinhole test data are made.
Amelioration of Tunnelling Susceptible Soils in the Hunter Valley, New South Wales, by Modification of Clay Double-Layer Interactions
Authors: Elliott GL
Published: March 2009

The resultant force between van der Waals attraction and net free energy of interacting clay double layers has been calculated for a typical tunnelling susceptible soil in the Hunter Valley, N. S. W., Australia. Double-layer theory accounts adequately for the instability of this soil and for its response to wetting.

Double-layer theory has been used to derive a sodium absorption ratio versus sum of cations stability diagram for this soil specimen. The slope of the line separating flocculation and dispersion approached seven.

The soil was prepared with sodium and calcium chloride salts at different concentrations at and around the threshold of flocculation as predicted by double-layer theory. Aggregate stability, dispersal index, and behavior in model dams confirmed the predicted behavior