284 research outputs found
Custom vs. prefabricated post systems: in-vitro testing and numerical study of failure modes
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Finite Element analysis of a new customized composite post system for endodontically treated teeth
No full textThis paper investigated the mechanical behavior of a new customized post system built up with a composite framework presently
utilized for crowns, bridges, veneers and inlay/onlay dental restorations. The material has been shaped so to follow perfectly the
profile of the root canal in order to take advantage of the better mechanical properties of composites with respect to metallic alloys
commonly used for cast posts.
The analysis has been carried out with 3D finite element models previously validated on the basis of experimental work. The new
post system has been compared to a variety of restorations using either prefabricated or cast posts. The structural efficiency of the
new restoration has been evaluated for an upper incisor under different loading conditions (mastication, bruxism, impact).
Results prove that maximum stress values in restored teeth are rather insensitive to post types and materials. However, the new
customized composite restoration allows to reduce significantly the stresses inside the dentinal regions where conservative clinical
interventions are not possible
Axial Stereo-Photogrammetry for 360-deg measurement on tubular samples
No full textThis work presents a stereo-photogrammetry (SP) based procedure to perform whole-body measurements on tubular samples. Such a system is designed for future applications to the study of vascular wall mechanics. The use of a concave conical mirror surrounding the specimen makes it possible to capture the reflected 360 degrees surface with a single snapshot moving neither cameras nor object. Then, according to 3-D computer vision principles, a stereo camera system retrieves control points depth information from image-pairs of the investigated Surface. An axial-SP arrangement is selected since is more suitable for this specific application than the more popular lateral-stereo model.
In this paper, particular emphasis is given to a formulation taking into account even small camera misalignments. A calibration process based on optimization concepts is used together with a feature-based matching algorithm to efficiently find correspondence between highly distorted images reflected by the conical mirror.
Both theoretical and experimental analyses on calibrated samples demonstrated feasibility and accuracy of the proposed procedure. (c) 2006 Elsevier Ltd. All rights reserved
Local Strain for Fatigue Strength of Welded Structures
No full textField criteria, which are usually applied in fracture mechanics to ensure the structural integrity of cracked components, are extended to the fatigue design of welded joints, whose weld toe can be assimilated to a notch with a small tip radius. In particular, fatigue strength in terms of strain rather than of stress has been determined by applying stress cycles with different stress ratios R = sigma (min)/sigma (max). Finally, for the evaluation of the fatigue strength of welded joints in structural steel, a strain curve versus different R ratios is given to be compared with the service measured local strain at the weld toe
Measurement of the deflections experienced by electronic chips during weldment
No full textElectronic components can experience, during welding process to a circuit board, out-of-plane displacements whose magnitude may be not compatible with the welding technique tolerances to insure good bonding. Hence, this paper presents an experimental procedure based on Projection Computed-Aided Moiré (PCAM) to study the shape profile of electronic chips subjected to a thermal cycle that simulates a welding process. PCAM is an integrated system where a system of fringes is transformed via software in a continuous phase distribution from which the distorted shape of the chip can be retrieved.
In the test case, a voltage stabilizer has been heated at several different temperatures so to reproduce the various conditions which may occur in the welding process. Since the measurement is carried out after that the thermal field became uniform, the deformed shape of the chip will be a quadric surface (i.e., hyperboloid).
From the analysis of the chip deformed shape, it appears that the largest displacement gradients experienced by the chips tested in this study are such that good bonding of the welded assembly is however insured
Custom vs. prefabricated composite post systems: in-vitro testing and numerical study of failure modes
No full textThis work aims to analyze the performance of endodontically treated incisors restored with a composite framework currently utilized for crowns, bridges, veneers and inlay/onlay buildups. The novelty in this research is that the composite material is now shaped as a cast post so to follow the root cavity profile.
Experimental tests have been carried out on two sets of endodontically treated central maxillary incisors in order to evaluate the mechanical behavior of Customized Composite Post System (CCPS) with respect to Standard Post Restorations (SPR). Preliminary three-point-bending tests served to characterize restorative materials under investigation. FEM analysis helped to understand better the failure mechanisms seen in the experiments.
It was found that CCPS flexural stiffness is almost the same as healthy dentine (less than 10% difference). Furthermore, CCPS restored teeth showed higher resistance to fracture than the SPR ones and their failure patterns were protective to the remaining tooth structure
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