77 research outputs found
Detection of disbonds in multilayer structures by laser-based ultrasonic technique
Adhesively bonded multi-layer structures are frequently used, mostly in the aerospace industry, for their structural efficiency. Nondestructive evaluation of bond integrity in these types of structures, both after manufacturing and for periodic inspection during service, is extremely important. A laser-based ultrasonic technique has been evaluated for non-contact detection of disbonds in aluminum multi-layer structures. Two configurations have been used to detect disbonded areas: pitch-catch with unidirectional guided wave scan and through-transmission with bidirectional scan. Guided wave scanning was done with a laser line source and air-coupled transducer sensing at 500 kHz, 1 ;MHz, and 2 MHz. Signals showed attenuation of the main frequency component and frequency shift on disbonded areas, whereas, a regular and standard waveform is seen outside disbonds. In through-transmission the longitudinal wave at normal incidence was monitored with a 1 MHz probe. One sample showed, besides the introduced inserts, other disbonded areas. After the ultrasonic measurements the sample was cut to visually check adhesive and interfaces. The guided wave pitch-catch scan allowed fast inspection and quick indication of disbonded zones, while the through-transmission C-Scan provided better definition of defects but was slower and required access from both sides of the test part
Redesign of an auto-levelling base for submarine seismic sensor
The OBS (acronym of Ocean Bottom Seismometer) is a system to monitor the submarine
seismic activity. To properly work, an OBS system needs a suitable auto-levelling base to
maintain a fixed (horizontal) position during the measurement phases.
In this work a new auto-levelling base for submarine seismic sensors has been designed.
During the redesign process a preliminary phase of analysis of the state of art has been
made. Afterwards, the technological solutions chosen by different manufactures have been
critically analysed, and a full description of their functionalities, working principles and system
performances has been carried out. Later, some innovative concepts have been proposed.
Among these ones, the most interesting are the auto-levelling bases with spherical joint,
based on: air bearings, ball bearings and magnetic levitation systems.
The concept scoring method has been used to identify. as best concept, the auto-levelling
base with spherical joint and air bearings system.
Successively, the chosen concept has been implemented: the technical working principles
have been studied to choose the best solutions in terms of dimensions, shapes, materials of
all base components. A full parametric CAD model of the auto-levelling base has been also
created.
The new designed base, by using a very innovative auto-levelling system, allows to obtain
very good results as regards the accuracy of positioning, so ensuring a remarkable
improvement of the performances of the ocean bottom seismometers
Head Injury Criterion: mini review
Head Injury Criterion (HIC) is the most important parameter
in terms of human survival; it is indicative of brain injuries due to
the impact of the head in numerous cases, with a vehicle. This index
can be estimated by integrating the resulting acceleration of the
head (measured in its gravity center) in a time windo
Improving the Downwind Sail Design Process by Means of a Novel FSI Approach
The process of designing a sail can be a challenging task because of the difficulties in
predicting the real aerodynamic performance. This is especially true in the case of downwind sails,
where the evaluation of the real shapes and aerodynamic forces can be very complex because of
turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical
methods are very useful and reliable tools to investigate sail performances, and their use, also as a
result of the exponential growth of computational resources at a very low cost, is spreading more
and more, even in not highly competitive fields. This paper presents a new methodology to support
sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new
weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind
sails. The proposed method is parametric and automated and allows for investigating multiple
kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is
presented as a case study. Based on the numerical results obtained, an analytical formulation for
calculating the sail corner loads has been also proposed. The novel proposed methodology could
represent a promising approach to allow for the widespread and effective use of numerical methods
in the design and manufacturing of yacht sails
Influence of the Screw Positioning on the Stability of Locking Plate for Proximal Tibial Fractures: A Numerical Approach
Tibial fractures are common injuries in people. The proper treatment of these fractures is important in order to recover complete mobility. The aim of this work was to investigate if screw positioning in plates for proximal tibial fractures can affect the stability of the system, and if it can consequently influence the patient healing time. In fact, a more stable construct could allow the reduction of the non-weight-bearing period and consequently speed up the healing process. For that purpose, virtual models of fractured bone/plate assemblies were created, and numerical simulations were performed to evaluate the reaction forces and the maximum value of the contact pressure at the screw/bone interface. A Schatzker type I tibial fracture was considered, and four different screw configurations were investigated. The obtained results demonstrated that, for this specific case study, screw orientation affected the pressure distribution at the screw/bone interface. The proposed approach could be used effectively to investigate different fracture types in order to give orthopaedists useful guidelines for the treatment of proximal tibial fracture
Parametric Hull Design with Rational BĂ©zier Curves and Estimation of Performances
In this paper, a tool able to support the sailing yacht designer during the early stage of the
design process has been developed. Cubic Rational BĂ©zier curves have been selected to describe the
main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of
a set of parameters, say the length of waterline, the beam of the waterline, canoe body draft and some
dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical
constraints imposed on the curves (e.g., continuity, endpoint angles, curvature) have been conceived
aimed to avoid unreasonable shapes. These curves can be imported into any commercial Computer
Aided Design (CAD) software and used as a frame to fit with a surface. The resistance of the hull can
be calculated and plotted in order to have a real time estimation of the performances. The algorithm
and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the
usability and the precision of the tool, two existing sailboats with different characteristics have been
successfully replicated and a new design, taking advantages of both the hulls, has been developed.
The new design shows good performances in terms of resistance values in a wide range of Froude
numbers with respect to the original hulls
Real-time non-contact ultrasonic detection of surface defects on objects moving at high speed
Il rilievo di difetti superficiali durante le ispezioni periodiche è importante poiché in genere le
sollecitazioni sono maggiori in superficie e possono accelerare la crescita delle discontinuitĂ . I difetti superficiali
possono essere rilevati utilizzando alcuni metodi tradizionali di controllo non distruttivo, quali correnti indotte,
liquidi penetranti, polveri magnetiche ed ultrasuoni. Alcuni tra questi metodi possono essere usati solo in
condizioni statiche; gli altri presentano delle limitazioni per l’ispezione dinamica. I progressi recenti nel campo
dei sensori ultrasonori senza contatto ci hanno permesso di sviluppare un sistema semplice per l’ispezione in
tempo reale di corpi in movimento a velocitĂ elevata. Nel lavoro viene presentata la possibilitĂ di usare, col
sistema sviluppato, due metodologie, basate sugli ultrasuoni generati e ricevuti senza contatto con la struttura,
per rilevare difetti superficiali su corpi in movimento a 100 km/h, così da poter effettuare l’ispezione anche in
servizio. Una metodologia, basata sull’uso di laser e trasduttori senza contatto, utilizza i vantaggi delle onde
superficiali generate con il laser; l’analisi viene fatta sull’onda riflessa, creata dall’interazione dell’onda
superficiale con il difetto. Lo spessore superficiale ispezionato è selezionabile dalla lunghezza d’onda dell’onda superficiale generata. L’altra metodologia, basata sull’uso di trasduttori senza contatto, sfrutta gli svantaggi della
trasmissione degli ultrasuoni all’interfaccia aria/metallo; l’analisi viene fatta sulla diffrazione dell’onda riflessa
dalla superficie. L’esecuzione delle ispezioni risulta semplice con entrambe le tecniche. I risultati sperimentali
indicano una buona efficienza delle due metodologie proposte per il rilievo, in tempo reale, di difetti superficiali
su corpi in movimento ad alta velocitĂ The detection of surface defects during periodic inspection is important because, usually, the
stresses are higher at the surface, thus affecting the growth of the discontinuity. Surface defects can be detected
using some traditional non-destructive testing methods, such as eddy current, dye penetrant, magnetic particle
and ultrasonic. Some of these methods can be used only in static conditions; the others have limitations for the
dynamic inspection.
The recent progress in the field of non-contact ultrasonic sensors has led us to develop a simple system for the
real-time inspection of moving bodies at a high speed. The paper presents the possibility of using, with the
developed system, two methodologies, based on non-contact ultrasound, to detect surface defects on objects
moving at 100 km/h, so that in service inspection is possible. A methodology, based on laser and air-coupled
sensors, uses the advantages of laser-generated surface waves; the analysis is done on the reflected wave, created
by the interaction of the surface wave with the defect. The inspected surface layer can be selected from the
wavelength of the surface wave. The other methodology, based on air-coupled sensors, uses the disadvantages
of the ultrasound transmission at the air/metal interface; the analysis is done on the diffraction of the wave
reflected from the surface. The execution of the inspection is simple with both techniques. The experimental
results indicate a good efficiency of the two methodologies proposed for the real-time detection of surface
defects on objects moving at high speed
A New Automatic Process Based on Generative Design for CAD Modeling and Manufacturing of Customized Orthosis
As is widely recognized, advancements in new design and rapid prototyping techniques
such as CAD modeling and 3D printing are pioneering individualized medicine, facilitating the
implementation of new methodologies for creating customized orthoses. The aim of this paper is
to develop a new automatic technique for producing personalized orthoses in a straightforward
manner, eliminating the necessity for doctors to collaborate directly with technicians. A novel design
method for creating customized wrist orthoses has been implemented, notably featuring a generative
algorithm for the parametric modeling of the orthosis. To assess the efficacy of the developed
algorithm, a case study was conducted involving the design and rapid prototyping of a wrist orthosis
using Fused Deposition Modeling (FDM) technology. Subsequently, the developed algorithm was
tested by clinicians and patients. The results obtained indicate that the implemented algorithm is
user-friendly and could potentially enable non-expert users to design customized orthoses. These
results introduce innovative elements of originality within the CAD modeling, offering promising
solutions to the challenges associated with the design and production of customized orthoses. Future
developments could consist of a better investigation regarding the parameters that influence the
accuracy of the scanning and of the printing processes
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