			Home About us Contact

Test Specimens (test + specimen)

Distribution by Scientific Domains

Polymers and Materials Science	35%
Engineering	25%
Medical Sciences	23%
Chemistry	5%
3 Other Domains	12%

Selected Abstracts

Retention of luting agents on implant abutments of different height and taper

CLINICAL ORAL IMPLANTS RESEARCH, Issue 5 2005
Mario Bresciano
Abstract Objective: The purpose of this study was to evaluate the retention of four cements used to lute metal restorations onto computer designed and manufactured titanium implant abutments of different heights and convergence angles. Material and methods: Test specimens consisted of metal coping cemented on Procera® titanium abutments of 5, 7, and 9 mm of height, and of 0°, 4°, and 8° of convergence angle. The cements used were zinc-phosphate, zinc oxide-eugenole, polyurethane resin with and without vaseline. The samples were tested in a universal testing machine. The mean uniaxial load at point of separation was determined. The results were statistically evaluated with ANOVA. Results: The luting agent, the height, and the taper influence the retention of metal casting on customized CAD,CAM implant abutments. Conclusion: The most retentive cement was zinc-phosphate, followed by polyurethane, polyurethane plus vaseline, and zinc oxide-eugenol. Résumé Le but de cette étude a été d'évaluer la rétention de quatre ciments utilisés pour cimenter des restaurations métalliques sur des piliers implantaires en titane usinés et conçus par ordinateur de différentes hauteurs et angles de convergence. Des spécimens tests consistaient en capsules métalliques cimentées sur des piliers titane Procera de cinq, sept et neuf mm de hauteur et des angles de convergence de zéro, quatre et huit degrés. Les ciments utilisés ont été le phosphate de zinc, l'eugénol oxyde de zinc, la résine polyuréthane avec ou sans vaseline. Les échantillons ont été testés par une machine à test universelle. La charge uniaxiale moyenne au point de séparation a été déterminée. Les résultats étaient statistiquement évalués par l'ANOVA. Tous les éléments influençaient la rétention de ces piliers implantaires. Le ciment le plus rétentif était le phosphate de zinc suivi par le polyuréthane, polyuréthane+vaseline et enfin l'eugénol oxyde de zinc. Zusammenfassung Ziele:,Das Ziel der Studie war, die Retention von vier Zementen, welche für die Befestigung von Metallrekonstruktionen auf im Computer entworfenen und durch Computer hergestellten Implantatsekundärteilen aus Titan mit verschiedenen Höhen und Konvergenzwinkeln verwendet werden, zu untersuchen. Material und Methoden:,Die Testkörper bestanden aus Metallkappen, welche auf Procera Titansekundärteile mit einer Länge von 5, 7 und 9 mm und mit einem Konvergenzwinkel von 0°, 4° und 8° zementiert wurden. Die verwendeten Zemente waren Zink-Phosphat, Zinkoxid-Eugenol und Poliurethan-Resin mit und ohne Vaseline. Die Proben wurden in einer Universal-Testmaschine untersucht. Es wurde der mittlere uniaxiale Belastungspunkt der Separation bestimmt. Die Resultate wurden mittles ANOVA statistisch ausgewertet. Resultate:,Der Zement, die Höhe und die Konizität beeinflussen die Retention von Metallkappen auf individuell hergestellten CAD,CAM Implantatsekundärteilen. Schlussfolgerung:,Der retentivste Zement war Zink-Phosphat, gefolgt von Poliurethan, Poliurethan plus Vaseline und Zinkoxid-Eugenol. Resumen Objetivo:,La intención de este estudio fue evaluar la retención de cuatro cementos usados para cementar restauraciones metálicas sobre pilares de titanio de implantes diseñados y manufacturados por ordenador de diferentes alturas y ángulos de convergencia. Material y métodos:,Los especimenes de prueba consistieron en copins de metal cementados sobre pilares de titanio Procera de 5, 7 years 9 mm de altura, y 0°, 4° years 8° de ángulo de convergencia. Los cementos utilizados fueron fosfato de zinc, óxido de zinc-eugenol, resina de poliuretano con o sin vaselina. Las muestras se probaron con una máquina universal de pruebas. Se determinó la carga media uniaxial en el punto de separación. Los resultados se evaluaron estadísticamente con ANOVA. Resultados:,El agente cementante, la altura, y la influencia de la conicidad la retención del vaciado metálico sobre los pilares de implantes CAD,CAM hechos a medida. Conclusión:,El cemento mas retentivo fue el de fosfato de zinc, seguido por poliuretano, poliuretano mas vaselina, y óxido de zinc-eugenol. [source]

Health Monitoring of Rehabilitated Concrete Bridges Using Distributed Optical Fiber Sensing

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2006
Wei Zhang
As newly developed techniques, distributed optical fiber sensing (DOFS) have gradually played a prominent role in structural health monitoring for the last decade. This article focuses on the employment of two types of DOFS, namely fiber Bragg grating (FBG) and Brillouin optical time domain reflectometry (BOTDR), into an integrated HMS for rehabilitated RC girder bridges by means of a series of static and dynamic loading tests to a simply supported RC T-beam strengthened by externally post-tensioned aramid fiber reinforced polymer (AFRP) tendons. Before the loading tests, a calibration test for FBG and another one for BOTDR were implemented to, respectively, obtain good linearity for both of them. Monitoring data were collected in real time during the process of external strengthening, static loading, and dynamic loading, respectively, all of which well identified the relevant structural state. The beam was finally vibrated for 2 million cycles and then loaded monotonously to failure. Based on the bending strength of externally prestressed members, ultimate values for the test specimen were numerically computed via a newly developed simplified model, which satisfactorily predicted the ultimate structural state of the beam. And then the alert values were adopted to compare with the monitoring results for safety alarm. The investigation results show a great deal of applicability for the integrated SHM by using both DOFS in rehabilitated concrete bridges strengthened by external prestressing. [source]

Compensation of actuator delay and dynamics for real-time hybrid structural simulation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2008
M. Ahmadizadeh
Abstract Compensation of delay and dynamic response of servo-hydraulic actuators is critical for stability and accuracy of hybrid experimental and numerical simulations of seismic response of structures. In this study, current procedures for compensation of actuator delay are examined and improved procedures are proposed to minimize experimental errors. The new procedures require little or no a priori information about the behavior of the test specimen or the input excitation. First, a simple approach is introduced for rapid online estimation of system delay and actuator command gain, thus capturing the variability of system response through a simulation. Second, an extrapolation procedure for delay compensation, based on the same kinematics equations used in numerical integration procedures is examined. Simulations using the proposed procedures indicate a reduction in high-frequency noise in force measurements that can minimize the excitation of high-frequency modes. To further verify the effectiveness of the compensation procedures, the artificial energy added to a hybrid simulation as a result of actuator tracking errors is measured and used for demonstrating the improved accuracy in the simulations. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Online test using displacement,force mixed control

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2005
Peng Pan
Abstract This paper proposes an online test technique that employs mixed control of displacement and force. Two types of mixed control, ,displacement,force combined control' and ,displacement,force switching control' are proposed. In displacement,force combined control, one jack is operated by displacement-control, and another is operated by force-control. Validity of the combined control technique is demonstrated by a series of online tests applied to a base-isolated structure subjected to horizontal and vertical ground motions simultaneously. The substructuring technique is employed in the tests, and the base-isolation layer is tested, with the rest of the structure modeled in the computer. Displacement-control and force-control were adopted for simulating the horizontal and vertical response, respectively. Both displacement- and force-control were implemented successfully despite interference between the two jacks. Earthquake responses of the base-isolated structure involving the effects of varying axial forces on the horizontal hysteretic behavior of the base-isolation layer were simulated. In the displacement,force switching control, the jack was operated by displacement-control when the test specimen was flexible but switched to force-control once the specimen became stiff. Validity of the switching control technique was also checked by a series of online tests applied to the base-isolated structure subjected to vertical ground motions. Switching between displacement-control and force-control was achieved when the axial force applied to the base-isolation layer changed from tension to compression or from compression to tension. Both the displacement- and force-control were successful even with many rounds of switching. The test revealed that large accelerations occurred on the floor immediately above the base-isolation layer at the instants when the axial force of the base-isolation layer changed from tension to compression. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Inclined standing contact fatigue

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2003
B. ALFREDSSON
ABSTRACT An experimental method is presented, in which a sphere is repeatedly pressed against a surface with an inclined contact load. The method is a development of the normally loaded standing contact fatigue test. Experiments are performed for three inclination angles below the angle of friction and the results are compared to those of the normally loaded standing contact fatigue test. The influence of tangential load on endurance limit load, number of cycles to crack initiation, contact mark appearance and crack behaviour in the surface as well as in cut views are evaluated. The surface crack behaviour outside the contact mark is analysed based on the cyclic contact stresses in the test specimen. The trajectories of the largest principal stresses are followed in both the surface view and in the cut view on the symmetry plane. These stress trajectories are compared to the experimental crack results. The connection between the inclined standing contact fatigue cracks and surface distress micro-cracks is also discussed. [source]

Linking the flame-retardant mechanisms of an ethylene-acrylate copolymer, chalk and silicone elastomer system with its intumescent behaviour

FIRE AND MATERIALS, Issue 6 2005
Anna Hermansson
Abstract In this paper the flame-retardant mechanisms of a flame-retardant system consisting of ethylene-acrylate copolymer, chalk and silicone elastomer are linked to its foaming process and to its formation of a final intumescent structure. Thermocouples were placed inside and at the surface of cone calorimeter test specimens in order to measure the temperature at different depths during the formation of the intumescent structure. The temperature and visual observations of the foaming process were then linked to chemical reactions seen with thermogravimetric analysis and also coupled with earlier knowledge of the flame-retardant mechanism. A correlation is seen between the chemical reactions, the temperature (inside and at the surface of a cone calorimeter test specimen) as measured by thermocouples and visual observations in the intumescent process. Further, the outcome of this study provides useful information for achieving a deeper understanding of the flame-retardant mechanisms of the ethylene-acrylate copolymer, chalk and silicone elastomer system. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Scanning electron microscopic observation of oil/wax/water/surfactant system

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2005
K. Ikuta
We observed the internal structure of an oil/wax/water/surfactant system using a scanning electron microscope to investigate the relationship between its hardness and state of wax crystal. The molten wax (hydrogenated jojoba oil, ceresin, polyethylene wax, carnauba wax, or microcrystalline wax) was cast in a home-made spiral mold of aluminum foil for preparing the test specimen for SEM observation. In hydrogenated jojoba oil a fine frame-like crystal structure, the so-called ,card-house structure,' was observed but not in other waxes. The mixture of hydrogenated jojoba oil and water showed a few small droplets deposited on the roundish wax frame-like structure. On the other hand, waxes other than hydrogenated jojoba oil did not change their internal structure when they were mixed with water. This result suggested that hydrogenated jojoba oil showed uniquely high affinity for water. In the system of oil, water, surfactant, and various kinds of waxes, their crystal structure, hardness, and the shape of dispersed water particles were remarkably changed with the combination of waxes. In the system with ceresin and carnauba wax, the hardness measured by a card-tension meter was high, and the internal crystal structure was fine and amorphous. The water particle in the ceresin and carnauba wax system had a smaller diameter than that in the system containing hydrogenated jojoba oil. The system containing hydrogenated jojoba oil showed a card house-like wax crystal structure without high hardness. It was considered that the wax crystal structure played an important role in providing hardness and in contributing to the water distribution in the oil/wax/water/surfactant system. [source]

Thermal properties and flame retardancy of polyglycidyloxypropyl silsesquioxane/layered titanate nanocomposites

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Miyuki Harada
Abstract Polyglycidyloxypropyl silsesquioxane, which has an excellent heat resistance, was combined with sheet-like and spherical titanate as nano-fillers. The burning property of the composites was related to the shape of the dispersed titanate. A burning test was carried out according to the UL-94 test method. As a result, though the test specimen burned from one end to the other in the spherical titanate filled composite system, a fire extinguishing property was observed in the sheet-like titanate filled composite system. The extinguishing time of the latter system classified V-0 in the specification test. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Why would cement porosity reduction be clinically irrelevant, while experimental data show the contrary

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2005
D. Janssen
Abstract Laboratory bench tests have shown that porosity reduction increases the fatigue life of bone cement specimens. Clinically, however, the effect porosity reduction is subject to debate. We hypothesized that the discrepancy between clinical and experimental findings is related to differences in the stress distribution, which is typically uniform in experimental test specimens, while stress concentrations exist in cement around hip implants. We simulated fatigue failure of cement in a finite element model of an experimental test specimen and of a transverse slice of a total hip arthroplasty with a sharp-cornered stem. Four levels of porosity were introduced. In the fatigue test specimen model, the fatigue life clearly was dependent on the level of porosity, while in the transverse slice model, the level of porosity had virtually no effect on failure of the cement mantle. The results of the simulations confirmed our hypothesis. In simulations of laboratory tests, pores clearly acted as crack initiators, while in the simulation of a real total hip reconstruction, crack formation was governed by local stress singularities. This explains why the beneficial effect of cement porosity reduction on the lifetime of total hip reconstructions may be hard to detect clinically. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source]

Layered silicate/epoxy nanocomposites: synthesis, characterization and properties

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2004
Nehal A. Salahuddin
Abstract Novel epoxy-clay nanocomposites have been prepared by epoxy and organoclays. Polyoxypropylene triamine (Jeffamine T-403), primary polyethertriamine (Jeffamine T-5000) and three types of polyoxypropylene diamine (Jeffamine D-230, D-400, D-2000) with different molecular weight were used to treat Na-montmorillonite (MMT) to form organoclays. The preparation involves the ion exchange of Na+ in MMT with the organic ammonium group in Jeffamine compounds. X-ray diffraction (XRD) confirms the intercalation of these organic moieties to form Jeffamine-MMT intercalates. Jeffamine D-230 was used as a swelling agent for the organoclay and curing agent. It was established that the d001 spacing of MMT in epoxy-clay nanocomposites depends on the silicate modification. Although XRD data did not show any apparent order of the clay layers in the T5000-MMT/epoxy nanocomposite, transmission electron microscopy (TEM) revealed the presence of multiplets with an average size of 5,nm and the average spacing between multiplets falls in the range of 100 Å. The multiplets clustered into mineral rich domains with an average size of 140,nm. Scanning electron microscopy (SEM) reveals the absence of mineral aggregate. Nanocomposites exhibit significant increase in thermal stability in comparison to the original epoxy. The effect of the organoclay on the hardness and toughness properties of crosslinked polymer matrix was studied. The hardness of all the resulting materials was enhanced with the inclusion of organoclay. A three-fold increase in the energy required for breaking the test specimen was found for T5000-MMT/epoxy containing 7,wt% of organoclay as compared to that of pure epoxy. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Oily calcium hydroxide suspension (Osteoinductal) used as an adjunct to guided bone regeneration: an experimental study in rats

CLINICAL ORAL IMPLANTS RESEARCH, Issue 6 2007
Andreas Stavropoulos
Abstract Objectives: To evaluate whether an oily calcium hydroxide suspension (OCHS) promotes bone healing when used as an adjunct to guided bone regeneration (GBR). Material and methods: Rigid, hemispherical, teflon capsules were placed with their open part facing the lateral surface of the ramus on both sides of the mandible in 10 adult Wistar rats. In each animal, one capsule was filled out with an OCHS (test) before placement, while the capsule on the other side was left empty (control). After 4 months of healing, the animals were sacrificed and histological sections containing the capsules and the neighboring soft and hard tissues were prepared. On three to four sections taken by uniformly random sampling from each specimen, the relative volumes of (1) the newly formed bone (mineralized bone and marrow), (2) the soft connective tissue, (3) the residual OCHS, and (4) the acellular (empty) space inside the capsule were estimated by a point-counting technique, and expressed as percentage of the space originally created by the capsule. Results: There was no new bone formation inside the capsules in all but one test specimen, where only a minimal amount of newly formed bone could be observed in continuation with the lateral surface of the ramus. OCHS had a homogenous appearance and occupied the major portion (79.4%) of the space created by the capsule. No signs of active resorption of the material could be observed. On the contrary, 31.5% of the space provided by the capsule was filled out with newly formed bone in the control group. The new bone had a trabecular appearance with large marrow spaces filled with hematopoietic and fatty marrow. The rest of the capsule space in the controls appeared empty. Conclusion: OCHS may hamper bone healing when used as an adjunct to GBR. [source]

Restoring satisfactory status in ThinPrep Pap test specimens with too few squamous cells and containing microscopic red blood cells

DIAGNOSTIC CYTOPATHOLOGY, Issue 10 2008
Ph.D., Yijun Pang M.D.
Abstract Treatment of specimens that contain excessive blood can effectively reduce the unsatisfactory rate; however, a considerable number of unsatisfactory specimens remain. We evaluated the effectiveness of reprocessing unsatisfactory specimens that had too few squamous cells and contained microscopic red blood cells (TFSQRBC). Out of the 688 unsatisfactory specimens at microscopic screening, 197 (28.63%) were TFSQRBC that were reprocessed by treatment of glacial acetic acid (GAA). Red blood cells were observed clogging the pores in the filter of the ThinPrep device. After reprocessing, 129 (68.48%) yielded a satisfactory diagnosis, which accounted for a reduction of the unsatisfactory rate by 18.25%. In the restored satisfactory specimens, abnormal diagnoses of 1 high-grade squamous intraepithelial lesion (HSIL) (0.78%), 3 atypical glandular cells (AGC) (2.33%), and 13 atypical squamous cells of undetermined significance (ASCUS) (10.08%) were made. The abnormal diagnoses in this group of patients were significantly higher than that in the general population screened. Reprocessing unsatisfactory ThinPrep® (TP) specimens of TFSQRBC can reduce the unsatisfactory rate of the TP Pap test significantly and is a cost-effective measure. The initially unsatisfactory specimens are more likely to represent cases with an abnormal diagnosis, which also justifies the effort of reprocessing this group of specimens. Adjustment of the pore size on the ThinPrep filter device may reduce the interference of red blood cells. Diagn. Cytopathol. 2008;36:696,700. © 2008 Wiley-Liss, Inc. [source]

Comparison of displacement coefficient method and capacity spectrum method with experimental results of RC columns

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2004
Yu-Yuan Lin
Abstract For the performance-based seismic design of buildings, both the displacement coefficient method used by FEMA-273 and the capacity spectrum method adopted by ATC-40 are non-linear static procedures. The pushover curves of structures need to be established during processing of these two methods. They are applied to evaluation and rehabilitation of existing structures. This paper is concerned with experimental studies on the accuracy of both methods. Through carrying out the pseudo-dynamic tests, cyclic loading tests and pushover tests on three reinforced concrete (RC) columns, the maximum inelastic deformation demands (target displacements) determined by the coefficient method of FEMA-273 and the capacity spectrum method of ATC-40 are compared. In addition, a modified capacity spectrum method which is based on the use of inelastic design response spectra is also included in this study. It is shown from the test specimens that the coefficient method overestimates the peak test displacements with an average error of +28% while the capacity spectrum method underestimates them with an average error of -20%. If the Kowalsky hysteretic damping model is used in the capacity spectrum method instead of the original damping model, the average errors become -11% by ignoring the effect of stiffness degrading and -1.2% by slightly including the effect of stiffness degrading. Furthermore, if the Newmark,Hall inelastic design spectrum is implemented in the capacity spectrum method instead of the elastic design spectrum, the average error decreases to -6.6% which undervalues, but is close to, the experimental results. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Increase in the fracture toughness and bond energy of clay by a root exudate

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008
B. Zhang
Summary Root exudates help drive the formation of the rhizosphere by binding soil particles, but the underlying physical mechanisms have not been quantified. This was addressed by measuring the impact of a major component of root exudates, polygalacturonic acid (PGA), on the interparticle bond energy and fracture toughness of clay. Pure kaolinite was mixed with 0, 1.2, 2.4, 4.9 or 12.2 g PGA kg,1 to form test specimens. Half of the specimens were washed repeatedly to remove unbound PGA and evaluate the persistence of the effects, similar to weathering in natural soils. Fracture toughness, KIC, increased exponentially with added PGA, with washing increasing this trend. In unwashed specimens KIC ranged from 54.3 ± 2.5 kPa m,1/2 for 0 g PGA kg,1 to 86.9 ± 4.7 kPa m,1/2 for 12.2 g PGA kg,1. Washing increased KIC to 61.3 ± 1.2 kPa m,1/2 for 0 g PGA kg,1 and 132.1 ± 4.9 kPa m,1/2 for 12.2 g PGA kg,1. The apparent bond energy, ,, of the fracture surface increased from 5.9 ± 0.6 J m,2 for 0 g kg,1 to 12.0 ± 1.1 J m,2 for 12.2 g kg,1 PGA in the unwashed specimens. The washed specimens had , of 13.0 ± 1.9 J m,2 for 0 g kg,1 and 21.3 ± 2.6 J m,2 for 12.2 g PGA kg,1. Thus PGA, a major component of root exudates, has a large impact on the fracture toughness and bond energy of clay, and is likely to be a major determinant in the formation of the rhizosphere. This quantification of the thermodynamics of fracture will be useful for modelling rhizosphere formation and stability. [source]

Numerical modelling of fatigue crack initiation and growth of martensitic steels

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2010
N. JEZERNIK
ABSTRACT This paper presents a numerical simulation of micro-crack initiation that is based on Tanaka-Mura micro-crack nucleation model. Three improvements were added to this model. First, multiple slip bands where micro-cracks may occur are used in each grain. Second improvement deals with micro-crack coalescence by extending existing micro-cracks along grain boundaries and connecting them into a macro-crack. The third improvement handles segmented micro-crack generation, where a micro-crack is not nucleated in one step like in Tanaka-Mura model, but is instead generated in multiple steps. High cycle fatigue testing was also performed and showed reasonably good correlation of proposed model to experimental results. Because numerical model was directed at simulating fatigue properties of thermally cut steel, edge properties of test specimens were additionally inspected in terms of surface roughness and micro-structural properties. [source]

Characterization of strength properties of thin polycrystalline silicon films for MEMS applications

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2007
R. Boroch
ABSTRACT The aim of this work is to characterize the strength properties of polycrystalline silicon (polysilicon) with the use of tensile and bending test specimens. The strength of thin polysilicon films with different geometry, size and stress concentrations has been measured and correlated with the effective size of the specimen and its stress distribution. The test results are evaluated using a probabilistic strength approach based on the weakest link theory with the use of STAU software. The use of statistic methods of strength prediction of polysilicon test structures with a complex geometry and loading based on test values for standard material tests specimen has been evaluated. [source]

Sphere contact fatigue of a coarse-grained Al2O3 ceramic

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2006
T. FETT
ABSTRACT The opposite sphere test is an appropriate tool to determine crack-growth exponents for fatigue under repeated contact loading. Lifetime measurements for a coarse-grained Al2O3 are reported. To explain the fatigue exponents that strongly deviated from those obtained in cyclic bending tests, a fracture mechanics analysis was carried out. It was aimed at determining the correct stress intensity factor solution for the tests, including limited dimensions of test specimens deviating from the case of a cone crack in a half space. Cone crack development was observed microscopically and the related stress intensity factors were computed for the observed crack shape. For modelling the fatigue behaviour, it is assumed that the fatigue effect is influenced by a reduction of the shielding term of crack growth resistance due to periodical friction between the grain-interlock bridges in coarse-grained alumina. This results in a loss of traction at the junctions, crack tip shielding is reduced, and the effective load at the crack tip is increased. [source]

Cleavage fracture of RPV steel following warm pre-stressing: micromechanical analysis and interpretation through a new model

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9-10 2006
S. R. BORDET
ABSTRACT In this paper, the warm pre-stress (WPS) effect on the cleavage fracture of an 18MND5 (A533B) RPV steel is investigated. This effect, which describes the effective enhancement of the cleavage fracture toughness at low temperature following a prior loading at high temperature, has received great interest in light of its significance in the integrity assessment of structures, such as nuclear pressure vessels, subjected to thermal transients. Several loading cycles between room temperature (RT) and ,150 °C are considered: Load-Unload-Cool-Fracture (LUCF), Load-Cool-Fracture (LCF) and Load-Cool with Increasing K-Fracture (LCIKF). All experiments complied with the conservative principle, which states that no fracture will occur if the applied stress intensity factor (SIF) decreases (or is held constant) while the temperature at the crack-tip decreases, even if the fracture toughness of the virgin material is exceeded. The experimental results indicate that an effective WPS effect is present even at small pre-load (Kwps= 40 MPa,m), and that a minimum critical slope (,,K/,T) in the LCIKF cycle has to be exceeded to induce cleavage fracture between RT and ,150 °C. Numerical modelling was performed using mixed isotropic and kinematic hardening laws identified on notched tensile (NT) specimens, tested in tension to large strains (up to 40%), followed by large compressive strains. Detailed microstructural investigations on compact tensile (CT) and NT fracture test specimens were performed so as to determine the nature of the cleavage initiation sites, as well as the local mechanical conditions at fracture. Based on this local information, a new cleavage model was calibrated and applied to predict the probability of cleavage fracture after WPS: it is shown that the predictions are in good agreement with the experimental results. [source]

Interaction equations for multiaxial fatigue assessment of welded structures

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2004
M. BÄCKSTRÖM
ABSTRACT Multiaxial fatigue data from 233 welded test specimens taken from eight different studies have been evaluated based on three published interaction equations for normal and shear stress. The interaction equations were obtained from SFS 2378, Eurocode 3 and International Institute of Welding (IIW) recommendations. Fatigue classes for normal and shear stress were obtained directly from the design guidance documents. Additionally, mean fatigue strengths were determined by regression analysis of bending only and torsion only data for different specimen types. In some cases, the S,N slopes assumed by the different standards were not appropriate for the test data. Specimens that showed significantly different cracking locations or cracking mode between bending and torsion were not easily correlated by the interaction equations. Interaction equations work best in cases where both the normal stress and the shear stress tend to produce crack initiation and growth in the same location and in the same direction. The use of a damage summation of 0.5 for non-proportional loading as recommended by IIW was consistent with experimental observations for tube-to-plate specimens. Other codes used a damage sum of unity. [source]

Effects of solidification structure on tear resistance of Al,7% Si,0.4% Mg cast alloys

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2004
S.-W. HAN
ABSTRACT The tear resistance behaviour of Al,7% Si,0.4% Mg cast alloys was examined using Kahn-type tear test specimens. Tests were performed for two permanent mould casts with an ordinary dendrite structure and a semi-liquid die cast with a globular cell and fine grain structure. The microstructure of the two permanent mould casts was controlled by the cooling rates and the addition of Ti elements. Tear resistance was evaluated by the ,pop-in' stress, the energies required for crack initiation, UEi and the crack propagation, UEp. Special attention was paid to an effective microstructural parameter for tear resistance improvement. Pop-in, indicating sudden crack extension and arrest, was observed in all specimens. Homogeneous deformation occurs near the notch tip of the semi-liquid die cast, characterized by a refined grain structure. Refinement of the grain size is more effective than that of the dendrite cell size or eutectic Si particle size to increase the energy for crack initiation. Unit propagation energy, UEp, can be converted into a critical stress intensity factor, Kc, which in the semi-liquid die cast was improved due to an increased amount of slant or shear fracture surface. [source]

Linking the flame-retardant mechanisms of an ethylene-acrylate copolymer, chalk and silicone elastomer system with its intumescent behaviour

Study on heat transfer characteristics of porous metallic heat sink with conductive pipe under bypass effect

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009
Sheng-Chung Tzeng
Abstract The work investigated the forced convection heat transfer of the heat sink situated in a rectangular channel by considering the bypass effect. The fluid medium was air. The relevant parameters were the Reynolds number (Re), the relative top by-pass gap (C/H), and the relative side by-pass gap (S/L). The size of the heat sink was 60 mm (L)×60 mm(W)×24 mm(H). Two heat sinks were employed as test specimens: (A) the 0.9-porosity aluminum foam heat sink and (B) the 0.9-porosity aluminum foam heat sink with a 20 mm diameter copper cylinder. The copper cylinder was used as a conductive pipe of heat sink. The average Nusselt number was examined under various forced convection conditions. Experimental results demonstrate that increasing by-pass space decreased the Nusselt number. Besides, the average Nusselt number of mode B heat sink was higher than that of mode A heat sink by 30% for the case without by-pass flow. The heat transfer enhancement by the copper cylinder would decline as the by-pass space grew. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20247 [source]

Influence of Interface Characteristics on the Mechanical Properties of Hi-Nicalon type-S or Tyranno-SA3 Fiber-Reinforced SiC/SiC Minicomposites

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010
C. Sauder
The tensile behavior of CVI SiC/SiC composites with Hi-Nicalon type-S (Hi-NicalonS) or Tyranno-SA3 (SA3) fibers was investigated using minicomposite test specimens. Minicomposites contain a single tow. The mechanical behavior was correlated with microstructural features including tow failure strength and interface characteristics. The Hi-NicalonS fiber-reinforced minicomposites exhibited a conventional damage-tolerant response, comparable to that observed on composites reinforced by untreated Nicalon or Hi-Nicalon fibers and possessing weak fiber/matrix interfaces. The SA3 fiber-reinforced minicomposites exhibited larger interfacial shear stresses and erratic behavior depending on the fiber PyC coating thickness. Differences in the mechanical behavior were related to differences in the fiber surface roughness. [source]

Impact of in-line atmospheric plasma fluorination of carbon fibers on the performance of unidirectional, carbon fiber-reinforced polyvinylidene fluoride

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010
Siti-Ros Shamsuddin
Abstract Unidirectional, carbon fiber-reinforced polyvinylidene fluoride (PVDF) composites were manufactured using a powder impregnation process with integrated in-line continuous atmospheric plasma fluorination of carbon fibers to produce unidirectional carbon fiber/PVDF tapes with a fiber volume fraction of 60 ± 2%. Carbon fiber/PVDF tapes were processed into composite laminate test specimens by compression moulding and interface-dominated composite properties were studied. Short-beam shear test results showed an improvement of up to 70% for the composite laminates containing atmospheric plasma-fluorinated T700 carbon fibers with a fluorine content of 3.7 at. %, as determined by X-ray photoelectron spectroscopy. The flexural strength and modulus of the laminated carbon fiber/PVDF composites containing APF-treated T700 carbon fibers also increased by 45% and 38%, respectively. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:86,97, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20175 [source]

Mechanical and thermal properties of polypropylene/sugarcane Bagasse composites

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007
B. Ramaraj
Abstract To determine the possibility of using sugarcane bagasse (SCB) waste as reinforcing filler in the thermoplastic polymer matrix, SCB-reinforced polypropylene (PP) composites were prepared. The PP and SCB composites were prepared by the extrusion of PP resin with 5, 10, 15, and 20 wt % of SCB filler in a corotating twin screw extruder. The extruded strands were cut into pellets and injection molded to make test specimens. These specimens were tested for physicomechanical properties such as tensile, flexural, Izod, and Charpy impact strengths, density, water absorption, and thermal characteristics, namely, heat deflection temperature (HDT), melt flow index, and thermogravimetric analysis. It was found that the flexural strength increased from 23.66 to 26.84 MPa, Izod impact strength increased from 10.499 to 13.23 Kg cm/cm, Charpy impact strength increased from 10.096 to 13.98 Kg cm/cm, and HDT increased from 45.5 to 66.5°C, with increase in filler loading from 5 to 20% in the PP matrix. However, the tensile strength and elongation decreased from 32.22 to 27.21 MPa and 164.4 to 11.20% respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3827,3832, 2007 [source]

Adherence of Streptococcus mutans to various restorative materials in a continuous flow system

JOURNAL OF ORAL REHABILITATION, Issue 3 2004
S. Eick
summary, A continuous flow system was developed to evaluate the adhesion of Streptococcus mutans ATCC 25175 to filling materials (Ariston, Tetric, Dyract, Compoglass, Vitremer, Aqua Ionofil, Ketac Fil, amalgam, Galloy and ceramics as controls). Streptococcus mutans was added to saliva-coated test specimens, and a nutrient broth permanently supplied over a time period of 48 h and then the weight of plaque, the number and viability of the bacteria adhering to the materials were determined. The weights of artificial plaque on all filling materials tested were higher than those on ceramics, the highest values were measured on the glass,ionomers. The amount of plaque correlates with the surface roughness, whereas there was no correlation of the surface roughness with the number of colony-forming units (CFU) of S. mutans. The CFU of adhering S. mutans also depends on the viability of the bacteria. The plaque on Ketac Fil contained a high number of viable bacteria. The fluorides of glass,ionomers do not efficiently prevent the attachment and the viability of S. mutans. [source]

Fluoride release and uptake by four new fluoride releasing restorative materials

JOURNAL OF ORAL REHABILITATION, Issue 9 2003
P. Dionysopoulos
Summary, The present study compared the initial fluoride release and release following refluoridation of a conventional glass,ionomer Ketac-Molar (ESPE), a resin-modified glass,ionomer, Vitremer (3M), and two compomers F-2000 (3M) and Hytac (ESPE). Fifteen test specimens were prepared for each brand and immersed in deionized water. The fluoride released was measured every 2 days for 22 days. Refluoridation of the test specimens was done with solutions of 0·02, 0·04 and 0·2% NaF for 5 min on days 22, 30, 38 and 46. The fluoride released from recharged specimens was measured every 2 days until day 54. The fluoride release was highest during the first days after preparation, after which it decreased sharply and then more slowly. The four materials became ,recharged' with fluoride following repeated fluoride exposure in solution, the 0·2% solution being the most effective. From a clinical point of view, the results from this study imply that all the restorative materials tested may act as intra-oral devices for the controlled slow release of fluoride at sites at risk of recurrent caries. Fluoride release and uptake by four new fluoride releasing restorative materials. [source]

Why would cement porosity reduction be clinically irrelevant, while experimental data show the contrary

Effect of Aluminum Oxide Addition on the Flexural Strength and Thermal Diffusivity of Heat-Polymerized Acrylic Resin

JOURNAL OF PROSTHODONTICS, Issue 6 2008
Ayman E. Ellakwa BDS
Abstract Purpose: This work was undertaken to investigate the effect of adding from 5% to 20% by weight aluminum oxide powder on the flexural strength and thermal diffusivity of heat-polymerized acrylic resin. Materials and Methods: Seventy-five specimens of heat-polymerized acrylic resin were fabricated. The specimens were divided into five groups (n = 15) coded A to E. Group A was the control group (i.e., unmodified acrylic resin specimens). The specimens of the remaining four groups were reinforced with aluminum oxide (Al2O3) powder to achieve loadings of 5%, 10%, 15%, and 20% by weight. Specimens were stored in distilled water at 37°C for 1 week before flexural strength testing to failure (5 mm/min crosshead speed) in a universal testing machine. Results were analyzed by one-way analysis of variance and post hoc Tukey paired group comparison tests (p < 0.05). Weibull analysis was used to calculate the Weibull modulus, characteristic strength, and the required stress for 1% and 5% probabilities of failure. Cylindrical test specimens (5 specimens/group) containing an embedded thermocouple were used to determine thermal diffusivity over a physiologic temperature range (0 to 70°C). Results: The mean flexural strength values of the heat-polymerized acrylic resin were (in MPa) 99.45, 119.92, 121.19, 130.08, and 127.60 for groups A, B, C, D, and E, respectively. The flexural strength increased significantly after incorporation of 10% Al2O3. The mean thermal diffusivity values of the heat-polymerized acrylic resin (in m2/sec) were 6.8, 7.2, 8.0, 8.5, and 9.3 for groups A, B, C, D, and E, respectively. Thermal diffusivities of the composites were found to be significantly higher than the unmodified acrylic resin. Thermal diffusivity was found to increase in proportion to the weight percentage of alumina filler, which suggested that the proper distribution of alumina powders through the insulating polymer matrix might form a pathway for heat conduction. Conclusion: Al2O3 fillers have potential as added components in denture bases to provide increased flexural strength and thermal diffusivity. Increasing the flexural strength and heat transfer characteristics of the acrylic resin base material could lead to more patient satisfaction. [source]

An investigation into the surface fatigue of materials and thin layers using a sliding diamond spherical segment

LUBRICATION SCIENCE, Issue 2 2000
Ivan Iliuc
Abstract Methods for testing the surface fatigue of materials or thin layers normally involve configurations with two or more rolling balls or discs. Such equipment and test specimens are quite complicated, and for a large number of experiments, costly. Testing could be considerably simplified if the stressing of the material surface were performed with a sliding natural diamond spherical segment. A diamond on steel (or any different material) friction pair has the particular attribute that sliding wear is absent. Under these circumstances, after a certain number of strain cycles, fatigue failure of the investigated surface or layers appears. A particularly relevant application is investigation of the adhesion of a DLC layer. [source]