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showing 10 items of 3756 documents
Laser Ultrasonic Testing for Estimation of Adhesion of Al2O3Plasma Sprayed Coatings
2001
Abstract The aim of the present study was to investigate the possibility of using a laser ultrasonic technique for the estimation of the adhesion of ceramic coatings, deposited onto metallic substrates by thermal spraying techniques. For this purpose, a pulsed Nd : YAG laser (λ = 1064 nm, 14 ns) was used to irradiate Al2O3 coatings, of different thickness (30–350 µm), deposited onto stainless steel substrates by atmospheric plasma spraying. The laser generated ultrasonic waves were in situ recorded at the epicentre using a laser heterodyne interferometer. The acoustic waveforms were correlated with the interaction between the pulsed laser radiation and the coated metal, taking into account …
Performance of asphalt mixes with high recycling rates for wearing layers
2016
The corresponding paper presents selected results of a research on the feasibility of going toward 100% recycling of asphalt pavements into surface courses through an increasing percentage of RA within the mixes. The research is carried out within a two-year CEDR Transnational Road Research project, AllBack2Pave, led by the Technische Universitaet Dresden (Germany), together with the University of Nottingham (UK) and the University of Palermo (Italy), and finalised in January 2016. The main objectives of the project are - to establish, through laboratory tests on binders and asphalt mixes, whether the use of high rates of RA is feasible in developing mixes with high level of durability, and…
Amorphous and crystalline polyetheretherketone: Mechanical properties and tissue reactions during a 3-year follow-up.
2007
The study was aimed to test the mechanical strength, structural stability, and tissue reactions of optically amorphous and crystalline polyetheretherketone (PEEK) plates during a 3-year follow-up in vivo and in vitro. The injection-moulded PEEK plates were implanted to the dorsal subcutis of 12 sheep, which were sacrificed at 6-156 weeks. Thereafter, the plates were subjected to tensile tests, and levels of crystallinity were assessed by differential scanning calorimetry (DSC). Histological evaluation was carried out using the paraffin technique. In vitro properties were examined with the tensile test and DSC at 0-156 weeks. Tissue reactions were mild and fairly similar for the amorphous an…
Investigation and modeling of the anomalous yield point phenomenon in pure tantalum
2014
International audience; The monotonic and cyclic behavior of commercially pure tantalum has been investigated at room temperature, in order to capture and understand the occurrence of the anomalous yield point phenomenon. Interrupted tests have been performed, with strain reversals (tensile or compressive loading) after an aging period. The stress drop is attributed to the interactions between dislocations and solute atoms (oxygen) and its macroscopic occurrence is not systematically observed. InfraRed Thermography (IRT) measurements supported by Scanning Electron Microscopy (SEM) pictures of the polished gauge length of a specimen during an interrupted tensile test reveal the nucleation an…
Impact of Gamma Radiation on Dynamic RDSON Characteristics in AlGaN/GaN Power HEMTs
2019
GaN high-electron-mobility transistors (HEMTs) are promising next-generation devices in the power electronics field which can coexist with silicon semiconductors, mainly in some radiation-intensive environments, such as power space converters, where high frequencies and voltages are also needed. Its wide band gap (WBG), large breakdown electric field, and thermal stability improve actual silicon performances. However, at the moment, GaN HEMT technology suffers from some reliability issues, one of the more relevant of which is the dynamic on-state resistance (R) regarding power switching converter applications. In this study, we focused on the drain-to-source on-resistance (R) characteristic…
The effect of alkaline treatment on mechanical properties of kenaf fibers and their epoxy composites
2015
Abstract In this work, kenaf fibers were pre-treated in a NaOH solution (6% in weight) at room temperature for two different periods (48 and 144 h). The chemical treatment of kenaf fibers for 48 h allowed to clean their surface removing each impurity whereas 144 h of immersion time had detrimental effect on the fibers surface and, consequently, on their mechanical properties. Untreated and NaOH treated kenaf fibers (i.e. for 48 h) were also used as reinforcing agent of epoxy resin composites. The effect of the stacking sequence (i.e. using unidirectional long fibers or randomly oriented short fibers) and the chemical treatment on the static mechanical properties was evaluated showing that t…
Real-Time Monitoring of Intergranular Corrosion Damage on AA2024
2017
The total porosity induced by the intergranular corrosion was selected as a monitoring parameter to follow in real-time the defect propagation of AA2024. The pertinence of eddy current (EC) probing has been tested on very thin foils of AA2024 (30 μm in thickness) in immersion conditions under potentiostatic control and in atmospheric conditions simulated by controlled salt spray experiments. Combining this nondestructive evaluation technique with a direct optical interrogation of the backside of the test specimen (derived from the foil penetration technique) allows one to discuss the contribution of both the dissolution in the depth and along the grain boundaries to the total porosity. In i…
Non-contact ultrasonic inspection of skin/core bond in honeycomb with lamb waves
2003
The assessment of skin/core bond in honeycomb samples was carried out by a bistatic ultrasonic non-contact system. Lamb waves were generated by a Nd:YAG pulsed laser and detected by an air-coupled capacitance transducer located in pitch-catch configuration. Periodically spaced line sources, generated on the sample surface using a four element lenticular array, allowed generation of narrow-band directional Lamb waves. Changes in amplitude of the transmitted signal permitted detection of skin/core disbonds.
Detection of defects buried in metallic samples by scanning microwave microscopy
2011
This paper reports the local detection of buried calibrated metal defects in metal samples by a new experimental technique, scanning microwave microscopy. This technique combines the electromagnetic measurement capabilities of a microwave vector network analyzer with the subnanometer-resolution capabilities of an atomic force microscope. The network analyzer authorizes the use of several frequencies in the range 1--6 GHz, allowing three-dimensional tomographical investigation, which is useful for the detection of bulk defects in metal materials.
Experimental validation of a fractional model for creep/recovery testing of asphalt mixtures
2012
Abstract Prediction of asphalt mixtures’ behavior during their service life is a challenge due to its complexity and sensitivity to environmental and loading conditions. It has been proved that, when subjected to loading conditions comparable with most pavement operating conditions, asphalt mixtures behave as linear visco-elastic (LVE) materials. Traditionally the LVE behavior of bituminous material is modeled via creep/recovery functions. In the past, several rheological models constituted by elastic and viscous elements arranged in series or in parallel (analogical models) have been proposed and specified for both bitumen and asphalt mixtures. The corresponding constitutive laws always in…