Advanced Materials and Structures IV

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Authors: Iulian Antoniac, Marian Miculescu, Mihaela Dinu
Abstract: The magnesium alloys has been intensively studied for their suitable mechanical properties, excellent biocompatibility and their ability to biodegrade in biological environments. Although magnesium biodegradable implants possess many desirable properties, it is important that the alloy is able to be tolerated by the body- the constitutional elements of magnesium-based alloys should be toxic free. In this study two binary magnesium alloys Mg-Ca0,8 and Mg-Ca1,8 were experimentally obtained by casting and was characterized in order to investigate the microstructure, mechanical properties and how alloying elements influenced the characteristics of this new alloys potentially used for orthopedic implants.
Authors: Marin Bane, Florin Miculescu, Ana Iulia Blajan, Mihaela Dinu, Iulian Antoniac
Abstract: The aim of this paper is to determine causes of failure of orthopedic implants like intramedullary nail based on explants analysis and materials characterization. The clinical performance, corrosion characteristics and metallurgical properties of some retrieved titanium femoral nails have been examined. The macroscopic and the microscopic investigation of explants help us to describe the breaking mechanism and to identify the potential causes that led to implant failure.
Authors: Si Min Li, Emrah Demirci, Vadim V. Silberschmidt
Abstract: Numerical modeling of bones is necessary for design of efficient surgical cutting tools that can provide low cutting forces, reduce damage and prevent thermal necrosis of bone tissue. Development of realistic numerical models of cortical bone tissue requires deep knowledge of its deformation behaviour. Deformation mechanisms of bones differ from those of metals, polymers and composites since bones consist of a living tissue with hierarchical microstructure. The aim of this study is to analyse deformation characteristics of the cortical bone tissue from both experimental and numerical perspectives. Initially, Vickers hardness tests were conducted at various anatomical positions on a cross-section of a bovine femur bone to observe location-based variation of its mechanical response. Various load magnitudes ranging between 1 kgf and 100 kgf were applied in the Vickers hardness tests to analyse the effect of anisotropy on damage evolution. These tests were simulated using a finite element scheme to reproduce the mechanical behaviour of bones in indentation. Finally, results of the hardness tests were compared with those obtained from finite element simulations.
Authors: Mircea Nicoară, Aurel Răduţă, Cosmin Locovei
Abstract: Fabrication of aluminum matrix composites reinforced with ceramic particles via powder metallurgy techniques present considerable advantages, especially large flexibility of reinforcement volume content. However since metal particles are considerably larger than ceramic reinforcement, ceramic clustering become more and more frequent as the reinforcement proportion increases, and high ratio plastic deformations are mandatory. An experimental program has been developed to determine particle redistribution of ceramic reinforcement by mean of large-ratio extrusion of aluminum composites, containing up to 20% vol. of reinforcement. Evaluation of particle redistribution by extrusion has been determined using a computer-based technique of image analysis for resulting optical micrographies.The image processing has included particle detection, particle measurement and classification.
Authors: Gigel Neagu, Florin Ştefănescu, Alexandrina Mihai, Iuliana Stan, Iuliana Odagiu
Abstract: The paper presents the principal aspects regarding the obtaining of the mixture aluminium - silicon carbide particles. It is discussed about the wetting conditions and the critical acceleration necessary for the incorporation of particles into the melt. The high values obtained for this parameter involve applying some methods to improve the wettability: the covering of the complementary material with a thin layer of Ni, the alloying of the aluminium melt, the overheating of the metallic bath and the heat treatment of the silicon carbide particles. Also, the mechanical stirring conditions necessary to realize the mixture are presented. The settling process of the silicon carbide particles in the melt as a function of particles size, shape and volumetric concentration is also analysed. The presence of complementary material leads to the growth of the mixture viscosity. Therefore, the liquid alloy was investigated like a continuous medium in connection with the apparent viscosity. The main aspects regarding the solidification of metallic composites processed by casting method based upon theoretical concepts, general knowledge about casting of composites and experimental data are discussed. Finally, the specific defects caused by an insufficiently controlled solidification process and prevention measures are shown.
Authors: Alexandrina Mihai, Florin Ştefănescu, Gigel Neagu, C.P. Mihai
Abstract: The paper presents some aspects concerning the use of infrared thermography (IRT) in the evaluation of composite pipes integrity. Composite pipelines made up of glass fibres reinforced epoxy resins are increasingly used, especially in oil and gas industry, for their good mechanical properties, combined with reduced weight and excellent behaviour under hostile environment conditions. Taking into account that high reliability is required for such pipe networks, it is mandatory to choose reliable non-destructive inspection (NDI) methods to achieve efficient structural health monitoring. The main advantages of the IRT inspection are: non-contact and non-dangerous examination. In order to characterize the integrity of composites pipes, first of all the researches were interested in obtaining a set of reference images and then to examine the samples before and after the impact stress test. The conclusions point out the schemes and the optimal parameters of evaluation as well as the application limits of thermographic inspection
Authors: Marius Pop-Calimanu, Traian Fleșer
Abstract: Jointing with rotary active element gains field through technological facilities offered nowadays. Own research have developed a model for studying the thermal fields and the plastic deformations of jointing composite materials Al/20%SiC combined by friction stir welding (FSW). In this article we will present the three-dimensional distribution of investigated fields, correlated with input parameters in the process. The process is performed with solid state components. The numerical results indicate that the maximum temperature in the FSW process increases with increasing speed of rotational tools. For high speed welding joint, should be increased, at the same time, the rotational speed to avoid welding defects.
Authors: Vaibhav A. Phadnis, Farrukh Makhdum, Anish Roy, Vadim V. Silberschmidt
Abstract: The use of composite materials such as carbon fiber-reinforced plastic (CFRP) has grown considerably in recent years, especially in aerospace, automotive, sports and construction industries. The properties such as high strength and stiffness, low weight, excellent fatigue and corrosion resistance have made them a useful material for light-weight applications. Though parts made from CFRP are often manufactured to a near-net shape, various machining processes such as drilling, can be used to facilitate assembly of structures. Drilling CFRPs involve penetrating through several plies of laminate, which causes high stresses and strains in the vicinity of the drilled hole. Thus, the machining process not only affects the overall hole quality but also initiates discrete damage phenomena such as micro-cracking, matrix burning; delamination and fiber pull out in the specimen. Moreover, the cutting edges of a drill wear dramatically out due to presence of highly abrasive fibers in the matrix, resulting in increased thrust forces that can cause interply delamination.
Authors: Grzegorz L. Golewski, Tomasz Sadowski
Abstract: Mode II fracture analysis is especially important. This mode is vital in relation to concrete, due to its relatively low shearing strength and high sensitivity to such type of stress. Nowadays, the structural concretes containing an additives of fly-ash are quite commonly used in the construction industry. Initial cracks origin and development research was carried out using samples for three concrete mixtures: concrete without silica fly-ash (FA), concrete with 20% and concrete with 30% FA additive. 150x150x150 concrete cube with two initial cracks was used as a test sample. Experimental investigation under Mode II fracture was carried out in concrete composites at early age (after 3, 7, 14 and 21 days). X-FEM method enables observation of defect initiation and development, there is no need to input the original conditions. Calculations used peak principal stress criterion. Most calculations coincide with results of experimental research. There was a convergence of: cracks shapes, FQ critical force values, force - displacement graphs.
Authors: Emrah Demirci, Xiao Nan Hou, Memiş Acar, Behnam Pourdeyhimi, Vadim V. Silberschmidt
Abstract: Nonwoven fabrics are web structures of randomly-oriented fibres, bonded by means of mechanical, thermal or chemical techniques. This paper focuses on nonwovens manufactured with polymer-based fibres and bonded thermally. During thermal bonding of such fibres, as a hot calender with an engraved pattern contacts the fibre web, bond spots are formed by melting of the polymer material. As a result of this bonding process, a pattern of bond points connected with randomly oriented polymer-based fibres form the nonwoven web. Due to their manufacturing-induced composite microstructure and random orientation of fibres, nonwovens demonstrate a complex mechanical behaviour. Two distinct modelling approaches were introduced to simulate the non-trivial mechanical response of thermally bonded nonwovens based on their planar density. The first modelling approach was developed to simulate the mechanical behaviour of high-density nonwovens, and the respective fabric was modelled with shell elements with thicknesses identical to those of the bond points and the fibre matrix having distinct anisotropic mechanical properties. Random orientation of individual fibres was introduced into the model in terms of the orientation distribution function in order to determine the material’s anisotropy. The second modelling approach was introduced to simulate low-density nonwovens, and it treated the nonwoven media as a structure composed of fibres acting as truss links between bond points.

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