bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro Selection for Fusarium Wilt Resistance in Gladiolus
Authors: Nasir Idrees Ahmad , Riazuddin Sheikh
Published: April 2008

Cormels pieces of four Fusarium susceptible Gladiolus cultivars (Friendship, Peter Pears, Victor Borge and Novalux) formed friable calli when cultured in vitro on Murashige and Skoog basal medium containing various concentrations of auxin and cytokinin. The friable calli established cell suspensions. Plantlet regeneration was obtained from the control callus, control cell suspension derived callus and in vitro selected Fusarium oxysporum Schlecht. resistant cell‐lines of Friendship. The in vitro cormlets showed 85–95% germination after breaking dormancy of 8 weeks at 4 °C. Cell suspensions of all four Gladiolus cultivars were found to be highly sensitive to fusaric acid. Gradual increase in fusaric acid concentrations to the cell‐suspension cultures decreased cell growth considerably. One albino plant was found from the second generation of the in vitro selected cell line of Friendship. The albino plant was found to be highly susceptible to F. oxysporum. The cormlets of all in vitro selected cell lines of Friendship were inoculated with a conidial suspension of the F. oxysporum before planting and were also sprayed with the same spore suspension for further characterization when the height of plants was about 6 cm. The four selected cell lines showed the same response whether or not they were inoculated with conidia of the F. oxysporum. Plantlets of all of the selected cell lines exhibited significant growth as compared with the control after application of conidia of the F. oxysporum.
Species‐specific Response of Photosynthesis to Burning and Nitrogen Fertilization
Authors: Zhang Yanfang , Niu Shuli , Xu Wenhua , Han Yi
Published: April 2008

The present study was conducted to examine photosynthetic characteristics of three dominant grass species (Agropyron cristatum, Leymus chinensis, and Cleistogenes squarrosa) and their responses to burning and nitrogen fertilization in a semiarid grassland in northern China. Photosynthetic rate (Pn), stomatal conductance (gs), and water use efficiency (WUE) showed strong temporal variability over the growing season. C. squarrosa showed a significantly higher Pn and WUE than A. cristatum and L. chinensis. Burning stimulated Pn of A. cristatum and L. chinensis by 24–59% (P < 0.05) in the early growing season, but not during other time periods. Light‐saturated photosynthetic rate (Pmax) in A. cristatum and the maximum apparent quantum yield (Φmax) in A. cristatum and L. chinensis were significantly enhanced by burning (16–67%) in both the fertilized and unfertilized plots. The main effect of burning on Pn, Pmax and Φmax was not significant in C. squarrosa. The burning‐induced changes in soil moisture could explain 51% (P = 0.01) of the burning‐induced changes in Pn of the three species. All three species showed positive responses to N fertilization in terms of Pn, Pmax, and Φmax. The stimulation of Pn under N fertilization was mainly observed in the early growing season when the soil extractable N content was significantly higher in the fertilized plots. The N fertilization‐induced changes in soil extractable N content could explain 66% (P = 0.001) of the changes in Pn under N fertilization. The photosynthetic responses of the three species indicate that burning and N fertilization will potentially change the community structure and ecosystem productivity in the semiarid grasslands of northern China.
Spatiotemporal Patterns and Dynamics of Species Richness and Abundance of Woody Plant Functional Groups in a Tropical Forest Landscape of Hainan Island, South China
Authors: Zhang Zhi‐Dong , Zang Run‐Guo , Qi Yao‐Dong
Published: April 2008

Tropical forests are among the most species‐diverse ecosystems on Earth. Their structures and ecological functions are complex to understand. Functional group is defined as a group of species that play similar roles in an ecosystem. The functional group approach has been regarded as an effective way of linking the compositions of complex ecosystems with their ecological functions. To understand the variation of functional groups in species‐rich ecosystems after disturbance, the present study investigated the spatial pattern and temporal dynamics of woody plants in a typically fragmented natural forest landscape of Hainan Island in South China. The study area was classified into eight landscape types based on vegetation type, disturbance manner and the time of recovery. The woody plant species were aggregated into seven functional groups based on the growth form, successional status and plant size. The results gained from the present study showed that all functional groups, except for the emergent and canopy tree species, were present in all eight landscape types. Each landscape type had different numbers of dominant functional groups. There are similar species richness and stem abundance structure among functional groups between mid‐successional clear cut lowland rainforest and old growth tropical coniferous forest. This similarity exists in selective logged lowland rainforest and old‐growth lowland rainforest, as well as among landscape types of montane rainforest. The functional groups with the same successional status had similar patterns of species richness and stem abundance ratios among different landscape types. The variation patterns of functional groups along the successional stages in terms of species richness and stem abundance among the tropical lowland rainforest landscape types were more similar to each other than those in the tropical montane rainforest landscape types. This study provides further support for the competition‐colonization tradeoff and successional niche theory as opposed to models of neutrality and ecological equivalence.
Environmental Economic Geography
Authors: Hayter Roger
Published: April 2008

This article advocates evolutionary institutionalism as a conceptual platform to launch a systematic approach to environmental economic geography. Evolutionary institutionalism interprets industrial transitions through the lens of innovative behaviour that is shaped by reciprocal economic and non‐economic processes and periodically restructures economies in the form of new techno‐economic paradigms (TEP). In this approach, environment–economy relations need not be zero‐sum games, as is often assumed. Rather, as a result of innovation and choice, these relations have been recalibrated historically and can be redefined again towards developing a green TEP in which development and sustainability are co‐imperatives. It is argued that the mandate of environmental economic geography is to assess and prescribe how place makes and should make a difference to a green TEP and the article sketches a research agenda to promote this goal. This research agenda focuses on the themes of regions as institutions, remapping resource use and sustainable value chains.
Effectiveness of real‐time virtual sonography‐guided radiofrequency ablation treatment for patients with hepatocellular carcinomas
Authors: Kitada Takatoshi , Murakami Takamichi , Kuzushita Noriyoshi , Minamitani Kaori , Nakajo Kazuya , Osuga Keigo , Miyoshi Eiji , Nakamura Hironobu , Kishino Bunichiro , Tamura Shinji , Hayashi Norio
Published: April 2008

Aim:  Real‐time virtual sonography (RVS) can synchronize B‐mode ultrasound (US) images with multiplanar reconstruction (MPR)–computed tomography (CT) images on the same screen in real time. The purpose of this study was to evaluate the effectiveness of RVS for radiofrequency ablation therapy (RFA) of hepatocellular carcinomas (HCC) in which it was difficult to identify contours or margins by B‐mode US.

Methods:  Sixty‐three consecutive patients with a solitary HCC of less than 3.5 cm in diameter were enrolled in this study. Thirty‐nine patients with HCC clearly detectable by B‐mode US underwent conventional RFA, while the remaining 24 with obscure tumor lesions underwent RVS‐guided RFA. A follow‐up study of RFA treatment was performed every 3 months using enhanced CT imaging of the arterial and portal phase (at least 24 months). The accuracy of needle insertion was confirmed by measuring the gap between the needle insertion line and the center of the tumor from MPR–CT images.

Results:  The local recurrence rate of the RVS‐guided RFA group was similar to that of the conventional RFA group (8.3% vs 7.7%), despite the difficulty of detecting tumor lesions in the former group. The mean gap between the needle insertion line and the center of the tumor was 1.6 mm (0–3.2 mm) in eight patients treated with RVS‐guided RFA.

Conclusion:  RVS‐guided RFA can be useful for treating HCC that are difficult to detect by B‐mode US.
Effect of genipin on the biliary excretion of cholephilic compounds in rats
Authors: Mikami Masaki , Takikawa Hajime
Published: April 2008

Aim:  Genipin, a metabolite of geniposide, is reported to stimulate the insertion of multidrug resistance protein 2 (Mrp2) in the bile canalicular membrane, and to cause choleresis by increasing the biliary excretion of glutathione, which has been considered to be a substrate of Mrp2. In the present study, the effect of colchicine on the choleretic effect of genipin was investigated. The effect of genipin on the biliary excretion of the substrates of bile salt export pump and Mrp2 was also studied.

Methods:  After bile duct cannulation into rats, genipin was administered at the rate of 0.2 μmol/min/100 g, and the effect of colchicine pretreatment (0.2 mg/100 g) was examined. Metabolites of genipin in the bile were examined by a thin layer chromatography. Taurocholate (TC), sulfobromophthalein (BSP), and pravastatin were infused at the rate of 1.0, 0.2 and 0.3 μmol/min/100 g, respectively, and the effect of genipin co‐administration was examined.

Results:  Genipin increased bile flow and the biliary glutathione excretion, and those increases were not inhibited by colchicine. The biliary excretion of genipin glucuronide was less than 10% of the genipin excreted into bile. The biliary excretion of TC, BSP, and pravastatin was unchanged by genipin co‐administration.

Conclusion:  It was indicated that colchicine‐sensitive vesicular transport has no role on the genipin‐induced insertion of Mrp2 to the canalicular membrane. Choleresis of genipin is considered to be mainly due to the increased biliary glutathione excretion by genipin, not by the biliary excretion of glucuronide. TC had no effect on the biliary glutathione excretion.
Intrahepatic multicystic biliary hamartoma: report of a case
Authors: Kai Keita , Takahashi Tomohide , Miyoshi Atsusi , Yasui Takaharu , Tokunaga Osamu , Miyazaki Kohji
Published: April 2008

Multicystic biliary hamartoma is a very rare hamartomatous nodule in the liver, which has recently been described as a new category of hepatic nodular lesion. We herein report the case of a 55‐year‐old man histopathologically diagnosed with this entity following surgery. A solitary multilocular lesion in the liver was pointed out by ultrasonography during a systemic examination for a positive HBs antigen. This nodule could not be definitively diagnosed by radiologic modalities, including computed tomography, magnetic resonance imaging and arteriography. The patient underwent a partial resection of the posterior segment of the liver. The nodule was a localized lesion which measured 5 × 3 cm at the widest point and displayed a honeycomb appearance. Histologically, it consisted of ductal structures, periductal glands, fibrous connective tissues containing blood vessels, and bile‐like materials and xanthogranulomatous inflammation within some ducts. Liver parenchyma was not present in the nodule and the bile ducts were not dilated in the background liver. The ductal epithelium expressed biliary type cytokeratins (CK7 and 19) in immunohistochemical studies. These histopathological features were consistent with multicystic biliary hamartoma, and we discuss this rare case in detail in this report.
A valine to phenylalanine mutation in the precore region of hepatitis B virus causes intracellular retention and impaired secretion of HBe‐antigen
Authors: Chen Chien Yu , Crowther Carol , Kew Michael C. , Kramvis Anna
Published: April 2008

Aim:  Hepatitis B virus (HBV) e antigen (HBeAg) is translated from precore mRNA as a precore/core protein, which is post‐translationally modified to give rise to the protein that is secreted into the serum. The G1862T mutation in HBV occurs in the bulge of the encapsidation signal within the pregenomic RNA. When the precore mRNA is translated, this mutation results in a valine to phenylalanine substitution at the −3 position to the signal peptide cleavage site at the amino end of the precursor protein. The aim of this study was to determine whether this mutation could affect HBV replication and/or HBeAg expression.

Methods:  Following transfection of Huh 7 cells, HBV replication was followed using real time polymerase reaction (PCR) and expression of HBeAg expression was monitored using confocal microscopy.

Results:  HBV replication was reduced when this mutation was introduced into genotype D but not into genotype A replication‐competent constructs. Using mutant HBeAg‐expressing plasmids, we demonstrated a 54% reduction in HBeAg secretion relative to the wild type. Confocal microscopy demonstrated that the mutant HBeAg accumulated in the endoplasmic reticulum, endoplasmic reticulum intermediate compartment and Golgi. These aggregates of mutant protein increased in size following treatment of the cells with a proteasome inhibitor, MG132, and had the hallmark features of aggresomes. They attracted ubiquitin, heat shock proteins and proteasomes and were isolated from the cytosol by the intermediate filaments, vimentin and cytokeratin.

Conclusion:  The formation of aggresomes, as a result of the G1862T mutation, may play a contributory role in HBV‐induced liver disease.
Unsteady Heat Transfer Measurements from Transonic Turbine Blades at
Engine Representative Conditions in a Transient Facility
Authors: Allan W. D. , Ainsworth R. , Thorpe S.
Published: April 2008

The unsteady heat transfer measurements about a transonic turbine blade at engine representative Mach and Reynolds numbers are presented. High density, fast-response thin film gauges are employed at the midheight streamline. A description of the novel development of gold gauges together with a brief overview of their calibration and signal processing is presented. Detailed time and phase-averaged measurements have been obtained, providing insight into the role of upstream nozzle guide vane (NGV) wakes and shock features. These heat transfer results compliment recent fast-response aerodynamic results on this and similar transonic profiles, which highlight the dominance of the upstream vane-rotor interaction over convected wake segments, particularly in light of unsteady turbine blade loading. From a heat transfer standpoint, however, while the periodic shock events contributed to abrupt, localized heat transfer enhancements, the influence of NGV wake segments on the boundary layer could not be discounted when duration of unsteadiness was considered.
Development of a Highly Reduced Mechanism for Iso-Octane HCCI Combustion With Targeted Search Algorithm
Authors: Tham Y. F. , Bisetti F. , Chen J.-Y.
Published: April 2008

This paper describes recent development of iso-octane skeletal and reduced mechanisms for speeding up numerical simulations of homogeneous charge compression ignition (HCCI) engines. A novel targeted search algorithm is developed to systematically screen species for quasisteady state (QSS) assumption in order to reduce the mechanism size while maintaining accuracy. This new approach is especially found useful when the chemical kinetics involve complex ignition pathways. Using the iso-octane mechanism developed by LLNL, a skeletal mechanism with 215 species (Skeletal-215) and a reduced mechanism with 63 non-QSS species (Reduced-63) were constructed. Evaluations of the performances of the Skeletal-215 and the Reduced-63 were extensively conducted for the operation regimes in HCCI engine applications. Both mechanisms are found satisfactory in predicting start of combustion and minor emission species.
A New Acoustic Model for Valveless Pulsejets and Its Application to Optimization Thrust
Authors: Zheng F. , Ordon R. L. , Scharton T. D. , Kuznetsov A. V. , Roberts W. L.
Published: April 2008

Due to its simplicity, the valveless pulsejet may be an ideal low cost propulsion system. In this paper, a new acoustic model is described, which can accurately predict the operating frequency of a valveless pulsejet. Experimental and computational methods were used to investigate how the inlet and exhaust area and the freestream velocity affect the overall performance of a 50cm pulsejet. Pressure and temperature were measured at several axial locations for different fuel flow rates and different geometries. Computer simulations were performed for exactly the same geometries and fuel flow rates using a commercial CFD package (CFX) to develop further understanding of the factors that affect the performance of a valveless pulsejet. An acoustic model was developed to predict the frequency of these valveless pulsejets. The new model treats the valveless pulsejet engine as a combination of a Helmholtz resonator and a wave tube. This new model was shown to accurately predict geometries for maximum thrust. The model was further extended to account for the effect of freestream velocity. Evidence is provided that valveless pulsejet generates the highest thrust when the inherent inlet frequency matches the inherent exhaust frequency.
Finite Element Analysis of Whisker-Reinforced SiC/Al Composites Subjected to Cryogenic Temperature Thermal Cycling
Authors: Levy A. , Papazian J. M.
Published: April 2008

Thermo-elastoplastic finite element methods are used to investigate the thermal cycling of SiC whisker-reinforced aluminum-matrix composites. In a previous investigation, the development of residual stresses and plastic deformation during cooling from a typical solution-treatment or annealing temperature to room temperature was studied. In the present paper we investigate changes in these residual quantities during thermal cycling, including cycling to cryogenic temperatures, and the effect of these changes on subsequent mechanical behavior. The effective coefficients of thermal expansion and convergence to a stable cyclic loop are also examined.
Stress Intensity Factors for Multiple Cracks in an Adhesively Bonded Sandwich Sheet
Authors: Nishimura T.
Published: April 2008

A new method is proposed for analyzing stress intensity factors of multiple cracks in an adhesively bonded metallic sandwich sheet. Using a basic solution of a single crack and taking unknown density of surface tractions and adhesive shear stresses, Fredholm integral equations and compatibility equations are formulated based upon stress free condition along each crack and displacement continuity between the sheets and adhesive layers, respectively. These equations are solved simultaneously, and the stress intensity factors of multiple cracks are determined from the derived density of tractions. It is shown that the mutual interaction of multiple cracks in a sandwich sheet is smaller than that in a monolithic sheet. Also, mutual interaction of cracks in the same sheet is smaller than that of cracks in the different sheets.
Modeling of Viscoplastic Adhering Process by a Finite Element Technique
Authors: Takahashi Y. , Koguchi T. , Nishiguchi K.
Published: April 2008

The intimate contacting of rough surfaces in the solid state bonding of metals is modeled by a finite element method. The finite element method can be applied to the large deformation process of rate sensitive materials. The material used is an oxygen free copper. We treat only the case that the intimate contact is the rate controlling step in the solid state adhering process which can be realized under high vacuum and high temperature conditions for copper at least. The intimate contacting process is assumed to be produced by viscoplastic deformation after the initial local contact is made by instantaneous plastic deformation. The calculated results are in good agreement with the experimental ones. The model can predict the interfacial deformation during the solid state bonding carried out under high pressure conditions.
Issues in Thermal Contact and Phase Change in Porosity Prediction
Authors: Huang H. , Suri V. K. , Hill J. L. , Berry J. T.
Published: April 2008

One of the major objectives of solidification modeling is to determine, prior to pouring, whether porosity, such as massive cavities and dispersed pores, are likely to appear in the casting. The numerical solutions of solidification heat transfer alone, however, cannot provide such information. In order to predetermine the presence of porosity, various criteria functions have been proposed by a number of investigators. These criteria functions are associated with cooling rate, thermal gradient, solidus velocity and local solidification time, etc. Since these parameters can be derived from numerical solutions, the reliability of porosity prediction largely depends on the accuracy of the numerical solutions employed. Thermal contact and phase change affect the numerical solutions significantly, and hence the local values of the predicted parameters. Consequently, these phenomena must be given special attention. This paper addresses some important aspects of thermal contact and phase change in determining the values of criteria functions. The free thermal contraction method is used to describe the variation and distribution of the heat transfer coefficient at the casting/mold interface. The phase change problem is treated by the heat source/sink algorithm. The sensitivity of criteria functions and the role of computational error are also discussed.
Heat Transfer Effects During Solidification of Semicrystalline Polymers
Authors: Erhun M. , Advani S. G.
Published: April 2008

The build-up of the residual stresses in the plastic parts are directly affected by the transient temperature distribution during the solidification stage of the semicrystalline polymers. Hence for crystallizable polymers, it is important to couple the crystallization kinetics with the transport of heat flow to determine the thermal history during solidification. In this paper, an experimental study of solidification of two semi-crystalline polymers under quiescent conditions is carried out to examine the influence of crystallization kinetics on the thermal history. The selected model materials are Nylon-66 and Poly Ethylene Terephalate (PET). The temperature profiles and the location of the solidification front are recorded during the cooling process. The experimental results are compared with the classical heat diffusion model and also with a numerical approach which couples the crystallization kinetics to the heat diffusion equation by modifying the phase change temperature based on the overall cooling rate in the crystalline domain. The front movement and the solidification temperature predictions of the coupled model are in good agreement with the experimental observations.
Numerical Simulation of the Coinjection Molding Process
Authors: Turng L. S. , Wang V. W. , Wang K. K.
Published: April 2008

Coinjection molding comprises sequential or concurrent injection of two different but compatible polymer melts into a cavity in which the materials laminate and solidify. This innovative process offers the inherent flexibility of using the optimal properties of each material or modifying the properties of the molded part. The lack of previous experience and engineering know-how has made numerical analysis a useful tool for enhancing the engineers’ capability to handle this special process. This paper presents the methodology for analyzing the flow of two different polymer melts injected sequentially into a three-dimensional thin cavity. This study is distinct from numerous previous works dealing with single polymer melts typically used in the conventional injection molding process. As an illustration, a comparison between the predictions and experimental data for a co-injected part is presented, together with other relevant output showing the effect of different material properties on the outcome of the coinjection molding process.
Production of a Finely Dispersed AlPb-Coating
Authors: Berrenberg Th. , Steinbach I. , Rommerskirchen M. , Mergen R.
Published: April 2008

The paper presents initial results of a modified planar flow casting process with the aim of producing a multilayer composite material with an AlPb-alloy-based coating. The monotectic AlPb system is characterized by rapid separation behavior of the components in the liquid phase. The coarsening of Pb precipitates due to diffusion-and coagulation-effects is estimated and with regard to the required microstructure, Al with finely dispersed Pb, the necessary cooling rate and the temperature gradient perpendicular to the substrate are deduced. Based upon these assumptions the numerical simulation aided design of the thermal process is described. Experimental results, achieved on a pilot plant, are shown and the microstructure of the produced multilayer composite is discussed.
Viscoplastic Behavior and Modelization of an Austenitic Stainless Steel (17-12 SPH) at High Temperature (T = 600°C), Under In and Out of Phase Cyclic Tension-Torsion Loading
Authors: Delobelle P. , Lachat R.
Published: April 2008

The results of experiments performed on an austenitic stainless steel of the type 316L at a temperature of 600°C are presented. The tests were made under both unidirectional (1D) and bidimensional (2D) cyclic tension-torsion loading, both in and out of phase with one (case of 2D ratchet) or two cyclic components. For the 2D loadings, it is shown that a weak supplementary hardening ΔH+ appears which is mostly a function of the degree of phase difference φ between the strain components and the ratio R between the maximum amplitudes of these components. These observations conform qualitatively to those already reported for ambient temperature but quantitatively it is shown that the maximum amplitude of this supplementary hardening is a strongly decreasing function of the temperature. A simple phenomenological formulation is proposed which, when integrated into a unified viscoplastic model developed elsewhere, leads to a correct representation of the experimental results.
Yield and Flow Behavior of Initially Anisotropic Aluminum Tube Under Multiaxial Stresses
Authors: Takeda Takenobu
Published: April 2008

By means of combining Drucker’s yield function with Hill’s quadratic yield function, an anisotropic yield function of the sixth degree is proposed. It is able to include the effects of the third deviatoric stress invariant and initial anisotropy. Experiments are carried out on fully annealed 1050 aluminum tubes under multiaxial stress states. By applying proportional loadings of axial load, internal pressure and torsion to the specimens, the change in yield stress with a rotation of the principal stress axes and the difference between the directions of the principal stress and principal strain increment are examined. The yield surface in the tension-internal pressure stress field reveals orthotropic anisotropy. The yield surface in the tension-torsion stress field lies outside von Mises’ yield surface. Such behavioral characteristics can be expressed precisely by the proposed yield function. In addition, it is experimentally verified that the normality rule is obeyed in strain behavior.
Elastic-Plastic Response of Sintered Porous Iron Under Uniaxial Strain Cycling
Authors: Kim K. T. , Kwon Y. S.
Published: April 2008

Elastic-plastic responses of porous iron under uniaxial strain cycling between two fixed values of strain are investigated. A special set of constitutive equations is formulated by including isotropic, kinematic and saturation hardening responses. The theoretical results from the constitutive equations are compared with experimental cyclic data for porous iron, with various porosities.
Effect of Turbulent Heat Transfer on Continuous Ingot Solidification
Authors: Shyy W. , Pang Y. , Hunter G. B. , Wei D. Y. , Chen M.-H.
Published: April 2008

For many continuous ingot casting processes, turbulent heat transfer in the molten pool plays a critical role which, along with buoyancy and surface tension, is responsible for the quality of the end products. Based on a modified low Reynolds number k-ε two-equation closure, accounting for the phase change and mushy zone formation, the effect of turbulent heat transfer on the solidification characteristics during titanium alloy ingot casting in an electron beam melting process is investigated. The overall heat transfer rate is enhanced by turbulent transport via two sources, one through the correlated velocity and temperature fluctuations present for both single- and multi-phase flows, and the other through the correlated velocity and release of latent heat fluctuations which are unique to the flows with phase change. The roles played by both mechanisms are identified and assessed. The present turbulence model predicts that although the mushy zone defined by the mean temperature field is generally of substantial thickness as a result of the convection effect, the actual instantaneous zone thickness varies substantially due to turbulence effect. This finding is in contrast to the traditionally held viewpoint, based on the conduction analysis, of a generally thin mushy zone. The impact of turbulent heat transfer on local dendrite formation and remelting is illustrated and the issues involved in model development highlighted.
Variations in Fracture Toughness for Alloy 718 Given a Modified Heat Treatment
Authors: Mills W. J. , Blackburn L. D.
Published: April 2008

Heat-to-heat and product-form variations in the JIC fracture toughness for Alloy 718 were characterized at 24, 427, and 538°C using the multiple-specimen JR-curve method. Six different material heats along with three product forms from one of the heats were tested in the modified heat treated condition. This heat treatment was developed at Idaho National Engineering Laboratory to improve the impact toughness for Alloy 718 weldments, but it has also been found to enhance the fracture resistance for the base metal. Statistical analysis of test results revealed four distinguishable JIC levels with mean toughness levels ranging from 87 to 190 kJ/m2 at 24°C. At 538°C, JIC values were 15 to 20 percent lower than room temperature toughness levels. Minimum expected values of JIC (ranging from 72 kJ/m2 at 24°C to 48 kJ/m2 at 538°C) and dJR/da (27 MPa at 24 to 538°C) were established based on tolerance intervals bracketing 90 percent of the lowest JIC and dJR/da populations at a 95 percent confidence level. Metallographic and fractographic examinations were performed to relate key microstructural features and operative fracture mechanisms to macroscopic properties.
Inelastic Deformation Under Nonisothermal Loading
Authors: Chan K. S. , Lindholm U. S.
Published: April 2008

The objective of this paper is to evaluate, both experimentally and analytically, the appropriate forms of the hardening evolution equations in unified constitutive models for conditions involving nonisothermal loading. Critical experiments were performed for a cast nickel-base superalloy by using variable temperature tensile, creep, and cyclic tests in the 538°C–982°C temperature range. These experimental results were compared with both isothermal data and predictions of the Bodner-Partom elastic-viscoplastic theory to assess the effects of thermal history on constitutive behavior. The results indicate that the hardening evolution equations based on isothermal data are applicable for nonisothermal loading of these precipitation strengthened alloys. Additional thermal history effect terms in the hardening evolution equations were not required beyond those accounting for the variation of material constants with temperature. Using material constants determined solely from isothermal data, the inelastic deformation behavior of B1900 + Hf subject to thermomechanical loading were adequately predicted by the Bodner-Partom model.
Comparison of Fatigue Tests of Two Plastics, Three Composites and an Aluminum Alloy Obtained on Four Different Types of Fatigue Machines
Authors: Findley W. N. , Sutherland R. L.
Published: April 2008

The results of fatigue tests of two thermoplastics (cellulose acetate and polystyrene), three composites (laminated plastics of paper, canvas, and fiberglass) and one aluminum alloy (25-ST) are reported. Four different types of fatigue machines were used to test most of the above materials. The fatigue machines were: rotating-cantilever-beam, constant-amplitude-of-deflection, and constant-amplitude-of-force, types, all of which tested specimens in bending, and a constant-amplitude-of-deflection machine which tested specimens in direct tension and compression. Results from the four machines are compared and the cause of differences is explored.
Statistical Inferences on Cleavage Fracture Toughness Data
Authors: Stienstra D. , Anderson T. L. , Ringer L. J.
Published: April 2008

A method to predict lower bound cleavage fracture toughness values from small data sets is presented. The method is derived from a Weibull statistic based micromechanical analysis and can be applied in the ductile-brittle transition region. Lower bound predictions can compare well with the ASME KIR and KIC design curves. Difficulties in comparing Weibull shape parameters calculated by different methods are also discussed and several calculation methods are compared with a Monte Carlo simulation. The preferred methods are the maximum likelihood estimators (MLEs), least squares with the (i−.5)/n centralizing approach, or a simple estimation scheme which gives a “Good Linear Unbiased Estimator.”
Application of Bodner Viscoplastic Theory to Pressure-Shear Plate Impact Experiment
Authors: Gilat A. , Tsai J.
Published: April 2008

An application of the unified elastic-viscoplastic constitutive theory of Bodner [5] is presented. The material parameters in the theory, which includes directional hardening, are determined from results of uniaxial stress tests at constant strain rates. The constitutive equations are then used in numerical modeling of pressure-shear plate impact experiment. The results show that the measured normal component of the wave agrees well with the calculated profile. A small discrepancy, which can be accounted for by the presence of a Bauschinger effect, exists between the theoretical and the experimental shear component of the wave profiles.
Mechanical Characterization of IM7/8551-7 Carbon/Epoxy Under Biaxial Stress
Authors: Colvin G. E. , Swanson S. R.
Published: April 2008

This paper presents the results of a detailed characterization of the relatively new IM7/8551-7 carbon/epoxy material system under conditions of multiaxial stresses applied to both laminae and laminates. IM7 is a high elongation, high strength carbon fiber, and the 8551-7 matrix is a high toughness epoxy resin. The lamina tests provided a failure envelope for combinations of transverse tension or compression and in-plane shear, and illustrated that the matrix dominated strength properties exhibit a strong dependence on the state of stress. The transverse strains at failure were found to be higher than for previous epoxy systems examined, and the shear stress-strain curves showed significant nonlinear behavior. These features apparently contribute to the “toughness” of the resin. Laminated specimens in a quasi-isotropic configuration were tested in tension-tension and tension-compression stress states. In previous work on other fiber/resin systems it has been shown that laminate ultimate failure could be correlated by means of fiber direction strain in a critical ply, independent of matrix cracking and the details of the laminate configuration and state of stress. However, different fiber strain values must be used for tension and compression. The behavior of quasi-isotropic IM7/8551-7 laminates appears to follow the observations noted above, with the important exception that laminate tension failure strain is lower than unidirectional coupon strain. The compression values are significantly higher than seen previously with AS4/3501-4 laminates, but as usual lower than the tension values. The results raise presently unresolved issues about the effect of the resin and possibly the processing variables on the delivered laminate strength.
Microstructure as a Criterion for the Selection of Hot Working Process Parameters for Plain Medium Carbon Steel
Authors: Cohen R. E. , Durham D. R.
Published: April 2008

Cylindrical compression specimens of 0.42 carbon steel were deformed at temperatures from 816 to 982°C (1500–1800°F) and at average strain rates of 0.5 to 3.0 s−1, to a true strain of 0.47. This testing was performed at the lower bound of the dynamic recrystallization region, where dynamic recovery can predominate. After deformation, the insulated specimens were allowed to slowly cool to room temperature under near equilibrium conditions. The resulting microstructures were examined by optical microscopy to determine whether there were significant variations, and if any observed variations could be related to the processing parameters. In the overall range of these temperatures and strain rates, there were changes in grain size and distribution. A large number of the tests produced similar structures in the middle range of temperatures. However, substantial differences were observed at the higher temperatures, with strain rate effects being particularly noticeable. At the lowest temperatures, interesting features of the microstructure were attributed to the proximity of the testing temperature to the transformation temperature.
Estimation of Flow Stress of Porous Sintered Metals From Hardness Test With Pyramidal and Spherical Indenters
Authors: Tabata T. , Masaki S.
Published: April 2008

Relationship between hardness and flow stress in uniaxial compression is investigated for porous sintered metals. Hardness is defined here as the applied load divided by the surface area of the indentation. When the semi-angle α of the pyramidal indenter is 68 deg, i.e., the Vickers hardness indenter, the ratio of the hardness to the flow stress decreases with decreasing relative density ρ However, when α is 45 deg, the ratio is 2.7 regardless of the value of ρ. The ratio of the Brinell hardness to the flow stress decreases with decreasing ρ when the diameter ratio d/D of the impression to the spherical indenter is 0.4. When d/D is 0.8, the ratio is nearly constant regardless of ρ. The flow stress of sintered metals can, therefore, be estimated from the hardness measured by the pyramidal indenter with the semiangle of 45 deg or from the Brinell hardness at a diameter ratio of 0.8.
Progress in the Design of an Improved High-Temperature 1 Percent CrMoV Rotor Steel
Authors: Bodnar R. L. , Michael J. R. , Hansen S. S. , Jaffee R. I.
Published: April 2008

Silicon-deoxidized, tempered bainitic 1 percent CrMoV steel is currently used extensively for high-temperature steam turbine rotor forgings operating at temperatures up to 565°C due to its excellent creep rupture properties and relative economy. There is impetus to improve the creep rupture strength of this steel while maintaining its current toughness level and vice versa. The excellent creep rupture ductility of the low Si version of this steel allows the use of a higher austenitizing temperature or tensile strength level for improving creep rupture strength without loss in creep ductility or toughness. When the tensile strength of this steel is increased from 785 to 854 MPa, the creep rupture strength exceeds that of the more expensive martensitic 12CrMoVCbN steel currently used for high-temperature rotor applications where additional creep rupture strength is required. The toughness of 1 percent CrMoV steel is improved by lowering the bainite start (Bs) temperature in a “superclean” base composition which is essentially free of Mn, Si, P, S, Sb, As and Sn. The Bs temperature can be lowered through the addition of alloying elements (i.e., C, Ni, Cr, and Mo) and/or increasing the cooling rate from the austenitizing temperature. Using these techniques, the 50 percent FATT can be lowered from approximately 100°C to below room temperature, which provides the opportunity to eliminate the special precautionary procedures currently used in the startup and shutdown of steam turbines. The most promising steels in terms of creep rupture and toughness properties contain 2.5 percent Ni and 0.04 percent Cb (for austenite grain refinement and enhanced tempering resistance). In general, the creep rupture strength of the superclean steels equals or exceeds that of the standard 1 percent CrMoV steel. In addition, the superclean steels have not been found to be susceptible to temper embrittlement, nor do they alter the room temperature fatigue crack propagation characteristics of the standard 1 percent CrMoV steel. These new steels may also find application in combination high-temperature-low-temperature rotors and gas turbine rotors.
Tensile Strength of Stitching Joint in Woven Glass Fabrics
Authors: Lee Chienhom , Liu Dahsin
Published: April 2008

Stitching has been found to be able to improve the interlaminar strength of composite laminates. Its application as composite joining has been also explored. This study examined the tensile strength of some stitched composite beams made of woven glass fabric and epoxy matrix. The effects of stitching parameters on joining strength were evaluated by both experimental technique and finite element method. It was found that there were two basic ways to improve the strength of stitching joint. One was to use high-density stitching in nonoverlap joint and the other was to use chain stitching in overlap joint. However, the former could give smoother surface and more uniform thickness than the latter. In addition, it was concluded from this study that stitching joint was more suitable for woven fabrics than for unidirectional prepreg tapes.
Methods for Determining the Mode I and Mode II Fracture Toughness of Glass Using Thermal Stresses
Authors: Gillanders J. T. , Riddle R. A. , Streit R. D. , Finnie I.
Published: April 2008

The fracture toughness of soda-lime glass was measured by applying thermal stresses to center-cracked plates. Mode I cracking was achieved by chilling the crack faces. The stress intensity factor was obtained by combining temperature measurements with a finite element solution. The average value of KIC = 0.77 MN/m3/2 based on three tests agrees well with values in the literature for a water-free environment. Mode II cracking was achieved by applying a temperature gradient normal to the crack. A value KIIC = 1.6 MN/m3/2 was obtained in two tests using a finite element computation based on the temperature distribution computed from the specimen’s thermal boundary conditions.
Enhancement Techniques for Ultrasonic Nondestructive Evaluation of Composite Materials
Authors: Wooh S. C. , Daniel I. M.
Published: April 2008

Conventional ultrasonic C-scanning sometimes produces distorted and degraded images due to a variety of reasons, including surface roughness, beam dispersion, extraneous noise and imperfect fidelity of the total acquisition system. Enhancement techniques, using computer data acquisition and processing, can be used to enhance and restore the image. Enhancement techniques described include contrast stretching and median filtering, histogram equalization, thresholding, dynamic thresholding, thresholding depending on boundary characteristics, one-dimensional segmentation and intensity scans with hidden line removal. These enhancement techniques were applied and illustrated for five different types of damage in graphite/epoxy composite materials: (1) Embedded film patch in quasi-isotropic laminate; (2) impact damage in quasi-isotropic laminate; (3) matrix cracking due to static loading of crossply laminate; (4) fatigue damage in crossply laminate; and (5) thermally induced cracks in a thick crossply laminate. There is no single technique that is optimum in all cases. A suitable combination of techniques must be selected for optimum image quality.
Micro-Radiography and Tomography for High Resolution NDT of Advanced Materials and Microstructural Components
Authors: Maisl M. , Reiter H. , Ho¨ller P.
Published: April 2008

Quality assessment of advanced materials like high strength ceramics and fibre reinforced composites requires detection and characterization of early damage and defects like cracks and pores even with linear dimensions of only 10 μm. Structures of the same size must be distinguishable in components of precision mechanics and electronics. This paper discusses some applications of microfocal X-ray radiography and high resolution computed tomography in nondestructive evaluation of such components. The latter can be looked at as a nondestructive microscopic technique imaging cross sections of an object. Results of investigations using a tomographic unit with a resolution capability of the order of magnitude of 20 μm are presented.
Beam-to-Mode Conversion in an Aluminum Plate for Ultrasonic NDE Applications
Authors: Lu I. T. , Felsen L. B. , Klosner J. M.
Published: April 2008

In a multilayer elastic plate, weak debonding in the horizontal direction parallel to the plate boundaries is insensitive to ultrasonic compressional (P) waves impinging perpendicularly, and can therefore not be detected by conventional vertically oriented reflection schemes. One of the methods for generating along the flaw line shearing stresses, to which the flaw responds, is to orient the input beam obliquely. Unlike vertically impinging beams, multiply reflected oblique beams eventually are converted into guided modes. The horizontal ranges over which the field in the unflawed plate is beam-like or mode-like must be well understood for selection of a diagnostic NDE scheme with “good” features for detection and identification. The present analytical model study explores the conversion and P-SV coupling processes for an oblique Gaussian P beam input in an aluminum plate. Special attention is given to physical features in the computed data that are relevant for “good” NDE algorithm construction.
The Effect of Temperature on the Material Damping of Graphite/Epoxy Composites in a Simulated Space Environment
Authors: Spirnak G. T. , Vinson J. R.
Published: April 2008

An experimental method for measuring material damping is described, which employs a free-free beam lightly supported at the nodes. A thermal space environment is simulated by measuring the material damping in air at temperatures ranging from −65°F to 225°F, and then subtracting out the effects of atmospheric damping. This method saves considerable time, cost and experimental difficulties associated with performing the experiments in a vacuum. Graphite/epoxy AS4/3501-6 composite beam specimens were tested. At room temperature, the [0°]12 composites were found to have an average damping ratio of 0.0556 percent. The [90°]12 composites were found to have an average material damping ratio of 0.55 percent. These data agree well with the theoretical models and experimental measurements performed in a vacuum. The material damping ratio is temperature dependent over the range −65°F to 225°F, increasing with increasing temperature. For the [0°]12 composite, the material damping ratio varies from 0.0397 percent at −65°F to 0.083 percent at 225°F. For the [90°]12 composite, the material damping ratio varies from 0.408 percent at −65°F to 0.860 percent at 225°F.