Advances in Strength of Materials

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Authors: Dan Mihai Constantinescu, Marin Sandu, Eniko Volceanov, Mircea Găvan, Ştefan Sorohan
Abstract: Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour of a tough, brittle, and high energy absorbing material. Strain gauges techniques and data acquisition were used throughout this research. A static-dynamic equivalence is done through a calibration procedure of the measuring system. The experimental strain history is completely acquired till the failure of the ceramic tile. Numerical simulation of impact tests gives additional insight on the complicated phenomena. Low velocity impact testing revealed different patters of failure, depending on the conditions of impact, and the capacity of this material to be used in particular purpose designed applications.
Authors: Ivelin V. Ivanov, Tomasz Sadowski
Abstract: The plywood material is widely used in civil engineering and furniture industry as cheap, strong, and lightweight material. The progressive failure of the plywood is difficult to be modeled and predicted because of the complexity of its structure and the interaction between different modes of orthogonal damages and interlayer failure. The microstructure of the wood determines the failure of the plies. A micromechanical material model of wooden veneers is developed, which is based on a representative volume cell (RVC) taken from the tubular microstructure of the wood and represented as a truss structure with longitudinal, transverse, and diagonal bar finite elements. The damage variables prescribed for each type of the bars determine the progressive degradation of the material stiffness. The 2-D damage material model of wooden veneers is utilized as user-defined material in continuum shell elements of ABAQUS™ finite element code. The parameters of the model are determined to simulate the behavior of single veneers in tension tests in different directions of loading. Together with cohesive elements representing the interface between the plies, the suggested model can be used to simulate and analyze the progressive failure and damage interaction in the plywood. The simulations could give us better understanding of the complex failure of the plywood, the succession of the damage development and reveal the weakest link in the material. The analysis can be used for optimization of the plywood layup.
Authors: Eduard Marius Craciun, Tomasz Sadowski
Abstract: In this paper we study the behaviour of a Mode I crack in a pre-stressed wood composite material. A mathematical model is associated to the mechanical problem. Starting from the boundary, constitutive and far field conditions we obtain the representation of the incremental displacement, stress and strain fields using two complex potentials. Using numerical analysis we determine the critical value, which causes crack propagation and the direction of crack propagation in a particular case of a Pine wood composite.
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.
Authors: Sergiu Antonie, Cosmin Sinescu, Meda Negrutiu, Carmen Sticlaru, Radu Negru, Philippe L. Laissue, Mihai Rominu, Adrian Gh. Podoleanu
Abstract: The quality of the evaluation of implant insertion could be investigated by implant bone interface analysis. In this study the numerical simulation, tensional stamps and optical coherence tomography as a noninvasive method were used in order to evaluate these interfaces. The system contains two interferometers and one scanner. For each incident analysis a stuck made of 61 slices was obtain. These slices were used in order to obtain a 3D model of the implant bone interface. The results obtained point out the existence of gaps between the implant and the bone. In conclusion the optical coherence tomography could be used for implant bone interface investigation.
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.
Authors: Dan Ioan Stoia, Nicolae Faur, Mirela Toth-Taşcău, Laurenţiu Culea
Abstract: The paper describes the biomechanical behavior of a cervical implanted unit (CIU) in two conditions: during the physiological and extreme loading. In order to reveal these behaviors, the anatomical structure composed by the C2 and C3 cervical vertebras was implanted using a plate-screws metal structure. The implant was design to perform dynamical, by allowing longitudinal, transversal and rotational movements. The physiological conditions were simulated by the pulsatory negative loading, while the extreme loading was simulated by the alternant symmetrical loading. The tests reveal two behaviors: the durability of the CIU in the physiological loading conditions and the failure of the structure under extreme load.
Authors: Laurenţiu Culea, Cristina Bratu
Abstract: The study aims at analyzing the stress state of the human skull with FEA, simulating the loads due to the insertion of rapid palatal expanders with two or four arms. A 3D CAD solid model of a human skull has been created starting from CT slices. Using FEA, forces that simulate the loads developed by the expander have been applied to the solid model of the skull to determine the stress state.

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