1,031 research outputs found
Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition
Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies
(V) were identified in ZnO nanorods (NRs) grown by low cost chemical bath
deposition. A transient behaviour in the photoluminescence (PL) intensity of
the two V states was found to be sensitive to the ambient environment and
to NR post-growth treatment. The largest transient was found in samples dried
on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for
the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV
exposure exhibited a transient behaviour in full agreement with the PL
transient indicating a clear role of atmospheric O on the surface defect
states. A model for surface defect transient behaviour due to band bending with
respect to the Fermi level is proposed. The results have implications for a
variety of sensing and photovoltaic applications of ZnO NRs
Computed Tomography analysis of damage in composites subjected to impact loading
The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity. The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography
fatigue assessment by energy approach during tensile and fatigue tests on ppgf35
Abstract: Today, lightweight and low cost components can be obtained with short fibre reinforced plastics. The recyclable nature of these materials by comparison to thermoset matrixes composites is also clearly appealing. This paper investigates static and fatigue behaviour for a glass-fibre-reinforced polypropylene composite. Tensile tests were carried out using DIC and IR Camera. Stress vs strain curves and temperature evolution associated to the applied tensile stress were determined. The trend of the surface temperature of the specimen during fatigue tests was analyzed
Fatigue life prediction of high strength steel welded joints by Energy Approach
AbstractTwo full-field techniques were applied for the study of the base material and welded specimens, made of S690QL steel: digital image correlation and thermographic techniques. Static and fatigue tests were carried out. The thermographic measurements can be used to predict the fatigue, with a great saving in time and effort. Fatigue tests at increasing loads were carried out by a stepwise succession, applied to the same specimen, for applying an energy-based approach. The predictions of the fatigue life, obtained by means of the Energy Approach, were compared with the values obtained by the traditional procedure
aluminum honeycomb sandwich for protective structures of earth moving machines
Abstract The design and the assembly of the vehicles subjected to the risk of crushing from falling objects have to consider such danger and provide the operators with suitable safety systems. Generally, falling object protective structures for earth moving machines consist of vertical elements, connected by transversal elements, covered by a roof. The latter has the aim to protect the operators from falling objects and it is usually made of a steel skeleton with a metal plate. In this study, sandwich panels were proposed as technical solution for the impact protection from falling objects in earth moving machines. A very light and cheap aluminum honeycomb core (AA3003 alloy and cell size = 19 mm) was considered as design solution and was subjected to static and dynamic full-scale tests. The results were analysed according to the performance requirements of ISO 3449 standard. The experimental results confirmed that the honeycomb structures are well suitable for designing absorber devices in vehicles protective structures in order to ensure occupant safety
Microwave small-signal modelling of FinFETs using multi-parameter rational fitting method
An effective approach based on a multi-parameter rational fitting technique is proposed to model the microwave small-signal response of active solid-state devices. The model is identified by fitting multibias scattering-parameter measurements and its analytical expression is implemented in a commercial microwave circuit simulator. The approach has been applied to the modelling of a silicon-based FinFET, and an excellent agreement is obtained between the measured data and model predictions
Theoretical Approach for Developing the Thermographic Method in Ultrasonic Fatigue
AbstractIn the last years, several approaches were developed in literature for predicting the fatigue strength of different kinds of materials. One approach is the Thermographic Method, based on the thermographic technique. This study is devoted to the development of a theoretical approach for modeling of surface and undersurface fatigue crack initiation and temperature evolution during ultrasonic fatigue test. The proposed model is based on the statistical description of mesodefect ensemble and describes an energy balance in materials (including power of energy dissipation) under cyclic loading. The model allows us to simulate the damage to fracture transition and corresponding temperature evolution in critical cross section of a sample tested in very high cyclic fatigue regime
- …