Papers by Author: Anghel Cernescu

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Authors: Camelia Szuhanek, Nicolae Faur, Anghel Cernescu
Abstract: The objective of this numerical study was to evaluate the stress induced by orthodontic loading in anchorage implants and surrounding tissues. Orthodontic implants were included in this study. 3D geometrical models were constructed and material characteristics were taken from the literature. Finite element models were created based on the geometry and material characteristics of the screws. Orthodontic horizontal loads of 2 N were applied, and the biomechanical parameters were evaluated by colored scales. The highest von Mises values were recorded around the implant neck area and at the bone-implant interface.
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Authors: Nicolae Faur, Cristina Bortun, Liviu Marsavina, Anghel Cernescu, Otilia Gombosi
Abstract: The complete dentures are realized by different acrylic resins and different technologies. These materials are fragile and frequently appear crack and fractures of these dentures. Also, theses materials as well as the technologies of performing these dentures are expensive. In order to avoid the ultimate failure of the complete dentures, for each case there is necessary a numerical simulation as a preliminary stage before the effective performance of the denture. In order to realize the numerical simulation of the complete denture there is necessary to know the mechanical and elastic properties of the acrylic resins. This paper presents the results of experimental investigations performed in order to determine the mechanical and elastic properties of complete denture materials. A 3D laser scanner was used for the elaboration of the geometrical model of the complete dentures. In this way, using the reverse engineering technology there was realized a very accurate geometrical model. Finite element analysis was used to estimate the durability of the same complete dentures. The calculation model was finally validated by a fatigue experimental test.
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Authors: Cristina Bortun, Nicolae Faur, Anghel Cernescu, Liliana Sandu
Abstract: The welded joints are used in the technology of the removable partial dentures for the rehabilitation of their metal component. The welding procedure and the adequate equipment are established according to the components dimension, the quality of the alloys used and the dentures section. The modifications within the welded structures can be investigated by means of non-destructive tests such as the radiography or the analysis with finite elements. The work was based on the experimental checking of the optimal procedures of welded joint of the alloys of CoCrMo in order to increase their durability. The welded joints were performed in a butt joint configuration with addition of material on the alloys of CoCrMo used in the technology of the framed dentures. The finite elements method was used (software Solid works 2007) in order to simulate the welding process (thermal analysis) and to assess the residual stress areas appeared after the various welding procedures.
185
Authors: Mihaela Amarandei, Lucian Bogdan, Anghel Cernescu, Liviu Marşavina, Jenel Marian Pătraşcu, Dinu Vermeşan
Abstract: Nitinol (NiTi) is a biocompatible nickel titanium alloy widely used in medical applications and devices. In anterior cruciate ligament (ACL) reconstruction surgery of the knee, fine wires of NiTi are used because of its high elasticity and good memory shape behavior. In surgical procedures these wires are exposed to mechanical stress and high deformations. This paper presents the results of the tests performed on fine NiTi wires of 1.1 mm and 0.73 mm in diameter, exposed to tensile load, which frequently appears in orthopedic surgery. The tests were done at a temperature of 37o C, in order to observe the influence of tensile stress on the mechanical properties of NiTi. The obtained material properties are in good correlation with data from manufacturers. These results are useful in durability evaluation of fine NiTi wires utilized in surgical procedures.
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Authors: Anghel Cernescu, Heikki Remes, Pauli Lehto, Jani Romanoff
Abstract: The all-metal web-core sandwich structure consists of two face plates stiffened by one-directional system of web plates. These web core sandwich structures are used in many structural applications such as ship hulls, offshore platforms, bridge decks, and industrial platforms. However, the stress variation caused by the service loadings can be a determinant factor for crack initiation and growth until early failure of the entire structure. This paper presents an experimental study on fatigue crack growth rate in base material from a face plate after rolling and welding. The study is focused on the analysis of the stress ratio and crack closure effect on the fatigue crack growth rate in two directions. There is a significant stress ratio effect on fatigue crack growth rate, much more pronounced in the case of crack propagation in the longitudinal direction than in the transverse propagation. For all tests, the crack closure effect is more pronounced at low stress intensity factor range (in the threshold domain).
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Authors: Ion Dumitru, Anghel Cernescu
Abstract: The purpose of this study was making evident the overload effect in a spectre with constant amplitude cycles. The crack growth simulation was made on cracked specimen and was studied for four loading cases. Fatigue crack growth rate was calculated applying NASGRO equation and the crack growth retardation analyzed.
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Authors: Anghel Cernescu, Nicolae Faur, Cristina Bortun
Abstract: Total dentures are made of acrylic resins and artificial teeth. Among the prevalent fracture types of the dentures, 29% was a mid-line fracture, in which 68% were observed in maxillary complete dentures and 28% in mandibular complete dentures. Due to the large number of failures recorded on the maxillary dentures, several studies were conducted to establish the causes that produce these failures but also to find solutions for their prevention. One source of information about the strength of a maxillary denture under the applied load, is represented by the establishment of the stress and strain state during the loading. Different methods have been used for investigating the strain or stress distribution during deformation of dentures. The purpose of this paper is to evaluate the stress and strain state of a maxillary denture loaded in compression until the final fracture. For this study, electrical resistance strain gage were used for evaluation the strain and stress distribution in the maxillary denture made of different acrylic resins. Based on observations from practice, the strain gages were applied on the middle line of the denture at the base of the incisors and respectively on the sides of the denture, under molars. The dentures were loaded until failure and were registered the strains in the located strain gages. Also, for each type of acrylic resin were determined separately the mechanical properties of elasticity and strength. Based on the tests conducted were determined the critical stress and strain in the areas of interest. In all the tests carried out the fracture occurred in the median area of the denture and the crack was initiated between the incisor teeth. The stress and strain field associated with the crack initiation mode showed a strong influence of geometry on the fracture strength of denture. Also the type of acrylic resin has a significant effect on the fracture strength of complete denture either by strength capacity but especially by their ability to elasticity. Based on this analysis have been established new criteria for selection of acrylic resins, not only for aesthetic reasons but also for elasticity and strength reasons.
171
Authors: Anghel Cernescu, Jani Romanoff, Heikki Remes
Abstract: During the last period the interest on the sandwich structures has became more favorable due to the strength to weight ratio. In the same manner, in ship building field the lightweight structures became more and more attractive. With increasing the usage fields has increased the need to study the behavior of these structures. In general all the sandwich structures loaded in bending shows an effect of the secondary bending moment. In the case of web core sandwich panels used in ship structures has been observed a pronounced effect of the secondary bending moment on laser welded joints. Considering this, the paper presents an analysis of the fracture strength of laser welded joints of a web core sandwich structure, due to the effect of secondary bending moment. In the first part, the paper analytical formulation of the secondary bending moments and their effect on welded joints. This effect is explained on the basis of angle α defined in the paper and which depends on the thickness of the face plate, the thickness of the web plate and respectively the height. The paper continues with a numerical analysis of the stress and strain state from a web core sandwich beam and where also it is analyzed the effect of the secondary bending moment on the fracture strength of laser welded joints. Based on the carried out study it was observed that for high thickness of the web plate the effect of secondary bending moments is the overloading of the welded joints, instead for small thickness of the web plate the effect of the secondary bending moments can be of the unloading the welded joints. However, a small thickness of the web plate can affect the rigidity of the structure. Therefore, based on this study was proposed a solution to reduce the secondary bending moment without reducing the stiffness of the sandwich panel. The analysis conducted in this paper can be a design criterion for the web core sandwich structures.
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Authors: Nicolae Faur, Liviu Marsavina, Anghel Cernescu, Christian Neş, Emanoil Linul
Abstract: At the stress-strain tests for the overhead electrical conductors stranded in alternate directions (aluminum conductor steel reinforced - ACSR), the locking mode of the specimen ends on the tensile machine represents a difficult problem which if is not correctly solved may seriously influence the results obtained. The stress-strain tests are performed according to standards as the European Standard EN 50182:2001. The specimen must have a length imposed by the conductor diameter, but not less than 10m. During the stress-strain tests the specimen is loaded in steps at successive cycles of loading- unloading (30%, 50%, 70%, 85% of Rated Tensile Stress –RTS). Finally, in order to determine the breaking forces, the conductor is loaded up to total breaking. In these conditions, the test success is decisively influenced by the correct locking of the conductor in the grips. The locking of the conductor ends is usually performed by casting the conductor ends in the gripping devices, after the wires ends reflection. In this paper there is presented a new locking method of the conductor ends by separation of the steel wires from the aluminum ones and their separate winding on two drums with helical groove. The tests performed have confirmed that this method is cheaper, and not influencing the real behavior of the conductor.
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