1,720,962 research outputs found
Development and application of experimental methodologies for the mechanical characterization of non-linear materials exploited in the production of loudspeakers
No full textLa caratterizzazione di materiali utilizzati nella produzione di altoparlanti necessita dello sviluppo di tecniche investigative che si adattano alle specificità di ciascuna tipologia di materiale in esame. In questa tesi vengono quindi proposti approcci diversi in base al materiale e al tipo di caratterizzazione impiegata, ovvero statica/transitoria e dinamica.
Viene presentata una nuova caratterizzazione dinamica della carta basata su un metodo ibrido. Infatti, grazie all’utilizzo combinato del metodo agli elementi finiti e dell’analisi modale sperimentale, è stato possibile valutare le proprietà dinamiche meccaniche del materiale in termini di modulo conservativo e dissipativo all’interno di un ampio range di frequenze, In particolare, nel range di frequenze acustiche è stata individuata una relazione lineari tra le caratteristiche meccaniche della carta e la frequenza d’eccitazione.
Per quanto riguarda la gomma, è stato possibile analizzare la deformazione tridimensionale dei campioni sottoposti a carico uniassiale tramite lo sviluppo di un opportuno setup sperimentale. Ciò ha permesso di descrivere il comportamento viscoelastico del materiale medianti le leggi costitutive dei modelli generalizzati di Maxwell e di Kelvin-Voigt. Inoltre, la misura della deformazione tridimensionale ha permesso di identificare i limiti in termini di deformazione entro i quali le ipotesi di incomprimibilità e isotropia del materiale sono verificate.
La caratterizzazione dinamica ha sfruttato i dati ottenuti mediante prove di analisi dinamica termica al fine di sviluppare un nuovo approccio per la costruzione delle mastercurve del modulo conservativo e di quello dissipativo. I risultati sperimentali sono stati descritti mediante il modello di Havriliak-Negami, il quale è risultato essere un potente strumento per la determinazione dei fattori di shift necessari all’ottenimento della mastercurve in un ampio range di frequenze.
Le varie metodologie sviluppate hanno permesso di descrivere le proprietà meccaniche dei materiali in esame tramite modelli parametrici. I parametri così individuati possono essere facilmente impiegabili nelle simulazioni numeriche degli altoparlanti
Hybrid dynamic characterization of ultra-light materials by means of experimental and numerical modal analysis
No full textUser-Centred Product Design with Photorealistic Virtual Prototypes: A Case Study on Process Optimisation for Aesthetic Quality Enhancement
Full text linkIn Industry 4.0, companies must focus on human-centred design for a competitive edge. The 4USER project aims to establish a user-centred design method using an interactive Photorealistic Virtual Prototype (PVP) based on Extended Reality (XR) technology, objectifying customer requirements into technical specifications. The PVP overcomes limitations associated with traditional physical prototypes, serving as a quality benchmark for final products. The research focuses on a case study involving the development of sports rifles, emphasising the importance of aesthetic quality. The proposed semi-automatic process in Blender enables the generation of low-poly PVPs, incorporating hyper-realistic textures and high-frequency details. In particular, the overall process is composed of the following steps: i) wooden texture generation via the Wasserstein Generative Adversarial Network (WGAN); ii) model creation based on a low poly “Shrinkwrap Cage”; iii) integration of generated textures into the UV-mapped model. This approach accelerates the product development cycle, reduces costs, and facilitates efficient quality control
Measurement of firing impulse force in rifles
No full textDuring the recoil phenomenon, elevated forces are exerted within a period of time of few milliseconds. In this paper we developed a new experimental setup to determine the impulsive force exerted on the shoulder of the shooter during the firing action. The combined use of a load cell and a pressure matrix is found to be essential to achieve a complete characterization of the firing shock force due to the recoil. The experimental results have shown that the correlation between the two measuring systems allows to obtain a quantitative measure of the event of recoil. Indeed, the pressure matrix has proved to be able to detect the peak pressure and the corresponding peak force, whereas the load cell has allowed to investigate the temporal evolution of the force that is transmitted to the shoulder of the individual. Therefore, the analysis of the forces has shown how the combined use of two sensors is capable of achieving the maximum confidence with the experimental data as the two systems are complementary
A Jury Test Methodology for the Assessment of User Rifle Trigger Tactile Preference
Full text linkThis paper presents a methodology to evaluate the preference of the user in relation to the trigger of a rifle. The selected approach is based on a Jury Test methodology which is a well know assessment method used in several fields, such as the subjective perception of acoustic noise or sound evaluation. In this case, the subjective test is applied to the tactile perception of the user to the stimuli of the rifle trigger, thus exploiting the possible means of interaction the human has with the object of interest. This approach is really important to define a complete user experience, helping to reach an innovative vision in the design and development of the product.As the Jury Test collects subjective preferences given by the users, a methodology is presented to correlate objective indices to these subjective preferences. The correlation is performed considering different parameters of the rifle trigger, previously measured with a specific experimental campaign conducted on real rifles, using an elasticometer.A correlation analysis is presented to find the optimal values of the objective metrics in order to maximise the subjective preference. In particular the highest values of the preferences towards the rifle trigger are correlated to the parameter of the trigger force and displacement. Best values have been found to be low force applied to the trigger and low trigger displacement. This method proves therefore to be efficient in correlating the parameters of this application case providing quantifiable feedback on the product in the context of a User-Centred Design
A Shrinkwrap Method for Quickly Generating Virtual Prototypes for Extended Reality
Full text linkExtended Reality (XR) applications require Photorealistic Virtual Pro- totypes (PVPs), usually obtained by generating a polygon-based textured model of the original CAD (Computer Aided Design). Getting PVPs requires specific ren- dering and texturing software tools that experienced technicians use. Automatic simplification and conversion approaches from CAD to XR exist but are almost all focused on models without textures. The paper aims to establish a semi-automatic method for creating low-poly PVPs for XR starting from 3D CAD models. The process, implemented in Blender, consists of several steps. First, starting from a high-poly model imported from a 3D mechanicalCAD system, the modelling cage (a low-poly simplified version) is designed. Second, a low-poly variety ofthe CAD geometries are generated using Blender modifiers (i.e., shrinkwrap, subdivision surface and Boolean).Texture mapping is carried out on the cage. Then,bycombin- ing Shrinkwrap, Boolean and Subdivision Surface modifiers, the cage is projected on the CAD-imported high-poly model. Thus, it becomes a low-poly version ofthe same geometry. Finally, the Normal Baking process adds high-frequency details (e.g., engravings). Thanks to the generation ofaUV-Mapped cagewrapping up the component, in case of local modifications to the latter, Blender semi-automatically updates the PVP. The method was used on three stock versions of a sporting rifle. With an average duration of 23 min, the proposed approach more than halved the tim
Purified collagen I oriented membrane for tendon repair: an ex vivo morphological study.
Full text linkPurpose: Injured tendons have limited repair ability after full-thickness lesions. Tendon regeneration properties and adverse reactions were assessed ex vivo in an experimental animal model using a new collagen I membrane.
Methods: This multilamellar membrane obtained from purified equine Achilles tendon is characterized by oriented collagen I fibers and has been shown to sustain cell growth and orientation in vitro. The central third of the patellar tendon (PT) of 10 New Zealand White rabbits was sectioned and grafted with the collagen membrane; the contralateral PT was cut longitudinally (sham-operated controls). Animals were euthanized 1 or 6 months from surgery and tendons subjected to histological and Synchrotron Radiation-based Computed Microtomography (SRμCT) examination and 3D structure analysis.
Results: Histological and SRuCT findings showed satisfactory graft integration with native tendon; histological examination also showed ongoing angiogenesis. Adverse side-effects (inflammation, rejection, calcification) were never observed.
Conclusion: The multilamellar collagen I membrane can be considered as an effective tool for tendon defect repair and tendon augmentation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Sensor calibration of polymeric Hopkinson bars for dynamic testing of soft materials
No full textSplit Hopkinson pressure bar (SHPB) testing is one of the most common techniques for the estimation of the constitutive behaviour of metallic materials. In this paper, the characterisation of soft rubber-like materials has been addressed by means of polymeric bars thanks to their reduced mechanical impedance. Due to their visco-elastic nature, polymeric bars are more sensitive to temperature changes than metallic bars, and due to their low conductance, the strain gauges used to measure the propagating wave in an SHPB may be exposed to significant heating. Consequently, a calibration procedure has been proposed to estimate quantitatively the temperature influence on strain gauge output. Furthermore, the calibration is used to determine the elastic modulus of the polymeric bars, which is an important parameter for the synchronisation of the propagation waves measured in the input and output bar strain gate stations, and for the correct determination of stress and strain evolution within the specimen. An example of the application has been reported in order to demonstrate the effectiveness of the technique. Different tests at different strain rates have been carried out on samples made of nytrile butadyene rubber (NBR) from the same injection moulding batch. Thanks to the correct synchronisation of the measured propagation waves measured by the strain gauges and applying the calibrated coefficients, the mechanical behaviour of the NBR material is obtained in terms of strain-rate-strain and stress-strain engineering curve
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