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Load Tests (load + test)
Selected AbstractsIn vitro fracture behavior of maxillary premolars with metal crowns and several post-and-core systemsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2006Wietske A. Fokkinga The in vitro fracture behavior of severely damaged premolars, restored with metal crowns with limited ferrule and several post-and-core systems, was investigated. Crowns of maxillary premolars were removed and canals were prepared with Gates Glidden drills and with Parapost drills. Groups of 11 samples were each treated with cast post-and-cores (Parapost XP, Wironium Plus) (group 1), prefabricated metal posts (Parapost XH) (group 2), prefabricated glass fiber posts (Parapost FiberWhite) (group 3), and custom-made glass fiber posts (EverStick Post) (group 4). Posts and composite cores and metal crowns in groups 2, 3, and 4 were adhesively cemented. Post-and-cores and crowns in group 1 were cemented with phosphate cement. Thermocycling was performed (6,000×, 5,55 °C). Two static load tests (30°) were applied. During the first load test (preloading) no failures occurred. Failure modes from the second load test were categorized into favorable and unfavorable failures. Mean failure loads among the four groups (group 1, 1845 N; group 2, 1718 N; group 3, 1812 N; and group 4, 1514 N) were not significantly different. Unfavorable failures were root fractures and favorable failures were postcrown displacements. No differences in frequencies of unfavorable/favorable failures were seen among the groups. The results suggest that different post-and-core systems have no influence on the fracture behavior of severely damaged premolars restored with metal crowns with limited ferrule. [source] Measurement of Viscosity of Densifying Glass-Based Systems by Isothermal Cyclic Loading DilatometryJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2004Aravind Mohanram This study describes the isothermal cyclic loading dilatometry (ICLD) technique to measure the viscosity of glass-based materials. We demonstrate its merit relative to constant-load techniques in minimizing the stress history effects (changes in shrinkage anisotropy and sample microstructure) that arise due to the application of an external load. A constant-load test overestimates the viscosity by an order of magnitude compared with a cyclic load test. To obtain accurate viscosity data, maximum loading rates and longer unloading periods are desirable as they reduce effects of shrinkage anisotropy on viscosity values. Representative data for a low-temperature cofired ceramic (LTCC) material are reported. Nonparametric statistical tests revealed insignificant differences between the viscosity data sets at 5% significance level and thus indicate good reproducibility of the testing methodology. [source] Reference-Free Damage Classification Based on Cluster AnalysisCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2008Hoon Sohn The ultimate goal of this study was to develop an in-site non-destructive testing (NDT) technique that can continuously and autonomously inspect the bonding condition between a carbon FRP (CFRP) layer and a host reinforced concrete (RC) structure, when the CRFP layer is used for strengthening the RC structure. The uniqueness of this reference-free NDT is two-fold: First, features, which are sensitive to CFRP debonding but insensitive to operational and environmental variations of the structure, have been extracted only from current data without direct comparison with previously obtained baseline data. Second, damage classification is performed instantaneously without relying on predetermined decision boundaries. The extraction of the reference-free features is accomplished based on the concept of time reversal acoustics, and the instantaneous decision-making is achieved using cluster analysis. Monotonic and fatigue load tests of large-scale CFRP-strengthened RC beams are conducted to demonstrate the potential of the proposed reference-free debonding monitoring technique. Based on the experimental studies, it has been shown that the proposed reference-free NDT technique may minimize false alarms of debonding and unnecessary data interpretation by end users. [source] In vitro fracture behavior of maxillary premolars with metal crowns and several post-and-core systemsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2006Wietske A. Fokkinga The in vitro fracture behavior of severely damaged premolars, restored with metal crowns with limited ferrule and several post-and-core systems, was investigated. Crowns of maxillary premolars were removed and canals were prepared with Gates Glidden drills and with Parapost drills. Groups of 11 samples were each treated with cast post-and-cores (Parapost XP, Wironium Plus) (group 1), prefabricated metal posts (Parapost XH) (group 2), prefabricated glass fiber posts (Parapost FiberWhite) (group 3), and custom-made glass fiber posts (EverStick Post) (group 4). Posts and composite cores and metal crowns in groups 2, 3, and 4 were adhesively cemented. Post-and-cores and crowns in group 1 were cemented with phosphate cement. Thermocycling was performed (6,000×, 5,55 °C). Two static load tests (30°) were applied. During the first load test (preloading) no failures occurred. Failure modes from the second load test were categorized into favorable and unfavorable failures. Mean failure loads among the four groups (group 1, 1845 N; group 2, 1718 N; group 3, 1812 N; and group 4, 1514 N) were not significantly different. Unfavorable failures were root fractures and favorable failures were postcrown displacements. No differences in frequencies of unfavorable/favorable failures were seen among the groups. The results suggest that different post-and-core systems have no influence on the fracture behavior of severely damaged premolars restored with metal crowns with limited ferrule. [source] Ductile fracture of commercial purity titanium at room temperatureFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2000G. Shatil An experimental and numerical program was carried out to examine and assess the deformation and fracture behaviour of alloys of commercial purity (CP) titanium. The material rate-dependent deformation under constant displacement rates and under sustained loads was directly simulated in finite element analyses using an implemented unified material model. The simulations predicted the fracture of compact tension specimens subjected to J,R tests and sustained load tests employing a dimensional analysis and strain-hardening approach. Differences between two batches with different oxygen contents were examined and the limitation of the material model was investigated. [source] The value of serum albumin in pretreatment assessment and monitoring of therapy in HIV/AIDS patientsHIV MEDICINE, Issue 6 2006HO Olawumi Objectives We sought to examine the utility of serum albumin measurement in staging AIDS and monitoring patients' response to therapy. Methods The possible importance of serum albumin measurement in assessing AIDS stage and in monitoring the response to highly active antiretroviral therapy using CD4 cell count and body weight as parameters was examined in 185 consecutive HIV-infected, therapy-naïve individuals who were recruited for antiretroviral therapy at the university of Ilorin Teaching Hospital. The regimen included lamivudine, stavudine and nevirapine. The diagnosis of AIDS was established through a combination of clinical features and HIV seropositivity using two different enzyme-linked immunosorbent assay techniques. Serum albumin level was determined by the Bromocresol green method, while the CD4 lymphocyte count was obtained using the Dynal T4 count method. Body weight was measured in kilograms with light clothes on. Results There were significant positive correlations between pretreatment albumin and both pretreatment CD4 cell count and pretreatment weight, and between post-treatment albumin and both post-treatment weight and post-treatment CD4 cell count up to a count of 700 cells/,L. There were also significant positive correlations between increase in serum albumin and both increase in body weight and duration of treatment. Conclusions We conclude that, in developing countries where many patients may not be able to afford to pay for CD4 cell counts and viral load tests, which are the traditional markers for HIV disease, serum albumin would be a very useful surrogate test for predicting severity of HIV infection and for clinical monitoring of response to antiretroviral therapy. [source] A modulus-multiplier approach for non-linear analysis of laterally loaded pile groupsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2007Chia-Cheng Fan Abstract A modulus-multiplier approach, which applies a reduction factor to the modulus of single pile p,y curves to account for the group effect, is presented for analysing the response of each individual pile in a laterally loaded pile group with any geometric arrangement based on non-linear pile,soil,pile interaction. The pile,soil,pile interaction is conducted using a 3D non-linear finite element approach. The interaction effect between piles under various loading directions is investigated in this paper. Group effects can be neglected at a pile spacing of 9 times the pile diameter for piles along the direction of the lateral load and at a pile spacing of 6 times the pile diameter for piles normal to the direction of loading. The modulus multipliers for a pair of piles are developed as a function of pile spacing for departure angle of 0, 90, and 180sup>/sup> with respect to the loading direction. The procedure proposed for computing the response of any individual pile within a pile group is verified using two well-documented full-scale pile load tests. Copyright © 2006 John Wiley & Sons, Ltd. [source] Microstructural deformation mechanisms of unsaturated granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2002J. A. Gili Abstract A discrete model for unsaturated granular soils has been developed. Three discrete entities have been defined: particles, water menisci and pores. Local interaction forces and water transfer mechanisms have been integrated into a model through the appropriate equilibrium and balance equations. The results of several numerical tests using this model have been described and discussed. Simulations include wetting and drying under load tests, the application of suction cycles and the effect of a deviatoric stress ratio on wetting-induced collapse. The model reacts just as true granular soil samples behave in laboratory tests. The model provides a new insight into the internal mechanisms leading to large-scale features of behaviour such as wetting-induced collapse or the increase in soil strength provided by suction. The paper also stresses that matric suction changes acting on a granular structure are capable of explaining most of the macroscopic features of stress,strain behaviour. Copyright © 2002 John Wiley & Sons, Ltd. [source] Anion effects on the stress corrosion cracking behaviour of aluminium alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2003R. Braun Spannungsrisskorrosion; Aluminiumlegierungen; Chloride; halogenfreie Anionen Abstract The stress corrosion cracking behaviour of plate material of the aluminium alloys 2024-T351, 8090-T8171, 7475-T651, and 7075-T7351 was investigated performing constant load tests. Short transverse tensile specimens were permanently immersed in aerated aqueous 0.6 M Na2Cl solutions with additions of Na2SO4, NaNO3, NaHCO3, NH4HCO3, Na2HPO4, Na2SO3 or Na2CO3. The concentration of the added salts was 0.06 M. The applied stress was 100 MPa, except with 7075-T7351 specimens, which were loaded at 300 MPa. Environment induced failure was not observed in neutral 0.6 M NaCl solution. The various salts added promoted intergranular stress corrosion cracking with the alloys 2024-T351, 8090-T8171, and 7475-T651. Threshold stresses were generally below 100 MPa. For 8090-T8171 exposed to chloride containing electrolytes with additions of sulfate, hydrogen phosphate, or sulfite, threshold stresses were approximately 100 MPa or higher. Similar results were obtained for 7475-T651 plate when immersed in chloride-hydrogen phosphate and chloride-carbonate solutions. Alloy 7075-T7351 was resistant against intergranular stress corrosion cracking. Specimens suffered pitting corrosion during immersion in the corrosive environments. Failure observed with 7075-T7351, in particular when exposed to the chloride-nitrate solution, was associated with reduction of cross-sectional area due to pitting and transgranular stress corrosion cracking. Anioneneinflüsse auf das Spannungsrisskorrosionsverhalten von Aluminiumlegierungen Das Spannungsrisskorrosionsverhalten von Plattenmaterial der Aluminiumlegierungen 2024-T351, 8090-T8171, 7475-T651 und 7075-T7351 wurde in kurzer Querrichtung untersucht. Dauertauchversuche wurden unter konstanter Belastung in wässrigen 0,6 M NaCl Lösungen mit 0,06 M Zusätzen von Na2SO4, NaNO3, NaHCO3, NH4HCO3, Na2HPO4, Na2SO3 oder Na2CO3 durchgeführt. Die aufgebrachte Spannung betrug 100 MPa, außer bei Zugproben der Legierung 7075-T7351, die mit 300 MPa belastet wurden. Während bei Auslagerung in neutraler Natriumchlorid-Lösung kein Versagen beobachtet wurde, lösten die zugegebenen Salze bei den Legierungen 2024-T351, 8090-T8171 und 7475-T651 interkristalline Spannungsrisskorrosion aus. Die kritischen Grenzspannungen lagen überwiegend unter 100 MPa. Bei Auslagerung in chloridhaltigen Elektrolyten mit beigegebenen Sulfat-, Hydrogenphosphat- oder Sulfitionen waren die kritischen Grenzspannungen für die Legierung 8090-T8171 etwas höher; sie hatten einen um 100 MPa oder darüber liegenden Wert. Gleiches galt für die Legierung 7475-T651 in chloridhaltigen Lösungen mit Hydrogenphosphat- oder Carbonatzusätzen. Plattenmaterial der Legierung 7075-T7351 war in den untersuchten Elektrolyten beständig gegen interkristalline Spannungsrisskorrosion. Die Proben wurden jedoch durch Lochkorrosion geschädigt. Querschnittsverminderung infolge Lochkorrosion und transkristalliner Spannungsrisskorrosion führten zum Versagen von Zugproben der Legierung 7075-T7351 innerhalb der maximalen Prüfdauer von 30 Tagen, insbesondere bei Auslagerung in eine chlorid-nitrathaltige Lösung. [source] Spatially resolved defect studies on fatigued carbon steelPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007P. Eich Abstract Several samples of the common ferritic tool steel AISI 1045 were fatigued in cyclic load tests. The local distribution of the Von-Mieses stress ,VM was simulated using the finite elements method (FEM). In the regions of interest, where ,VM reaches maximum values, the defect distribution was measured spatially resolved by Doppler-spectroscopy (DBAR) employing the Bonn Positron Microprobe (BPM). The lateral distribution of the S-parameter, which could be described by a simple model derived from linear fracture mechanics, corresponds well with the simulated Von-Mieses stress. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ein neues Verfahren zur Berechnung des räumlichen passiven Erddrucks vor TrägernBAUTECHNIK, Issue 7 2007Carsten Neuberg Dr.-Ing. In diesem Beitrag wird ein einfaches Berechnungsverfahren zur Bemessung horizontal belasteter, in den Untergrund eingebetteter Träger vorgestellt, das für baupraktische Aufgaben geeignet ist. Grundlage für die Herleitung sind die Ergebnisse von Messungen an Bauwerken, Modellversuchen und in besonderem Maße die Ergebnisse von numerischen Simulationen. Dazu wurde eine modifizierte Diskrete-Elemente-Methode (DEM) benutzt. Die Grundlagen für dieses Rechenverfahren sind in einem vorangegangenen Beitrag vorgestellt worden. A calculation method for the spatial passive earth pressure acting on girders. This paper presents a calculation method for vertical girders in cohesionsless soils. Measurements on buildings and model experiments are the basis. The Distinct Element Method (DEM) was extended and improved to enable the numerical simulation of load tests. Based on this knowledge, conditions not covered by experiments was simulated by means of the DEM. Accordingly, the test matrix could be extended. With the results of these simulations a new calculation method was derived. [source] | ||||||||||||||||