Dumitru Bolcu

Orthopaedic Modular Implants Based on Shape Memory Alloys

Intelligent materials are those materials whose physical characteristics can be modified not only through the charging factors of a certain test, but also through diverse mechanisms involving a series of additional parameters like luminous radiation, temperature, magnetic or electric fields etc. The use of intelligent materials in medical sciences offers to the economic medium the safest way to launch effective, highly-feasible and especially biocompatible products on the internal and international markets. The most important alloy used in biomedical applications is Ni–Ti, Nitinol (Nickel Titanium Naval Ordinance Laboratory), an alloy of an almost equal mixture of nickel and titanium, which is able to fulfil functional requirements related not only to their mechanical reliability but also to its chemical reliability and its biological reliability. Superelastic Nitinol alloys are becoming integral to the design of a variety of new medical products. The very big elasticity of these alloys is the most important advantage afforded by this material, but by no means the only or most important one. To highlight the value of superelastic Nitinol to the medical industry, we can present other properties: biocompatibility, kink resistance, constancy of stress, physiological compatibility, shape-memory deployment, dynamic interference, fatigue resistance hysteresis, and MRI compatibility (Duerig et al., 1999; Friend & Morgan, 1999; Mantovani, 2000; Pelton et al., 2000; Ryhanen et al., 1999). These properties were used for manufacturing medical products including stents, filters, retrieval baskets, and surgical tools. There are many metals exhibit superelastic effects, but only Nitinol based alloys is biologically and chemically compatible with the human body (Kapanen et al., 2002; Raghubir et al., 2007; Shabalovskaya, 1995; Yeung et al., 2007). In vivo testing and experience indicates that Nitinol is highly biocompatible, more so than stainless steel. The extraordinary compliance of Nitinol clearly makes it the metal that is most similar mechanically to biological materials. This improved physiological similarity promotes bony ingrowths and proper healing by sharing loads with the surrounding tissue, and has led to applications such as hip implants, bone spacers, bone staples, and skull plates. NiTi applications in orthopaedics currently include internal fixation by the use of fixatives, compression bone stables used in osteotomy and fracture fixation, rods for the correction of scoliosis (Yang et al., 1987), shape memory expansion staples used in cervical surgery (Sanders et al., 1993), staples in small bone surgery (Mei et al., 1997), and fixation systems for suturing tissue in minimal invasive surgery (Musialek et al., 1998). Several types of

Experimental Determinations of the Eigenmodes for Sandwich Bars with Different Core Reinforced with Metal Fabric

In this paper, starting from the theoretical background of modal identification, it is established an experimental method used to determine the eigenmodes of some composite bars with the core made of polypropylene honeycomb and polystyrene reinforced with metal fabric. The single-point excitation method is used. This method has been widely used in modal tests and it consists in applying a force in a given point and recording the vibratory structure response in all interest points, including the excitation point. Although the single-point excitation requires a minimum of equipment, it needs a laborious analysis to perform extensive result processing in order to interpret the dynamic behaviour of the structure under test.

Calculation of the relative uniformity coefficient on the green composites reinforced with cotton and hemp fabric

In this paper it is studied the influence of discontinuities on elastic and mechanical properties of green composite materials (reinforced with fabric of cotton or hemp). In addition, it is studied the way variations of the volume f the reinforcement influences the elasticity modulus and the tensile strength for the studied composite materials.In order to appreciate the difference in properties between different areas of the composite material, and also the dimensions of the defective areas, we have introduced a relative uniformity coefficient with which the mechanical behavior of the studied composite is compared with a reference composite.To validate the theoretical results we have obtained we made some experiments, using green composites reinforced with fabric, with different imperfection introduced special by cutting the fabric.

THEORETICAL AND EXPERIMENTAL RESEARCH ON THE TORQUE VARIATION OF THE BODY PASSING THROUGH LANDMARKS

This paper presents analytical expressions of the vertical reactions of the car wheels. These mathematical expressions take into account the inertia forces which are expressed by two main components of acceleration of the reference system chosen. The vertical reactions of the wheels and the torque acting on the body are determined by analytical and experimental methods in case of movement among the landmarks when the vehicle speed is 25 km/h. Theoretical results are compared with data obtained from experimental tests. Approximation values of the two data sets validates the theoretical model adopted.

Study about the Vehicle Orientation on the Trajectory during Transient Movements

In this paper, it is deduced the ordinary differential equation that results in angle variation between the vehicle mass centre rate and the vehicle fore-aft axis. There are presented the wheels turning angles variations dependent on the angle that gives the vehicle orientation on trajectory. There are studied the following cases: the transfer from linear to circular motion, the transfer from circular to linear motion and the movement amidst poles. For each of these motions, there are presented the vehicle orientation angle variations on trajectory for three distinct rates. It is also presented the travelling rate influence on how the vehicle is situated on trajectory.

Theoretical and Experimental Researches Regarding the Influence of the Suspension Car Stiffness on the Dynamic Behavior of Vehicles

In this paper the authors present the results of theoretical and experimental research in order to optimize suspension rigidity in case of Daewoo Nubira vehicle. The paper presents the mathematical model obtained by assimilating car with a dynamic system with 5 rigid solids with elastic and viscous linking between them. Theoretical results obtained based on this model and the experimental results are presented, and it is presented a solution to optimize suspension in order to remove the negative effects observed driving on gravel runways or damaged runaways. Theoretical results, compared with the experimental ones, allow us to say that it is possible to optimize suspension by analyzing specific parameters equivalent mathematical model.

Experimental determinations of the eigenmodes for composite bars made with carbon and Kevlar-carbon fibers

For modal identification, the single-point excitation method has been widely used in modal tests and it consists in applying a force in a given point and recording the vibratory structure response in all interest points, including the excitation point. There will be presented the experimental recordings for the studied bars (with Kevlar-carbon or carbon fibers), the frequency response function in Cartesian and polar coordinates. By using the frequency response functions we determine the eigenparameters for each bar. We present the final panel of the eigenmodes (with the damping factors, eigenfrequencies and critical damping) for each considered bar. Using the eigenfrequency of the first determined eigenmode, the bars stiffness has been determined. The presented bars can be used in practical engineering for: car or bus body parts, planes body parts, bullet-proof vests, reinforcements for sandwich beams, and so on.

Experimental Determinations of the Damping Factor for Composite Sandwich Bars Reinforced with Two Carbon Fiber Layers

In this paper we will build some new and original composite sandwich bars reinforced with two layers of carbon fiber, with the core made of polypropylene honeycomb. Starting from the dynamic response of these bars that are in free vibration, we will establish a procedure to determine their damping factor per unit mass and per unit length. We will also determine the bars eigenfrequencies (for the first eigenmode). The bars will have the core with 10, 15 and 20 mm and the free lengths of: 200, 230, 260, 290, 320 and 350 mm. The eigenfrequencies can be used in a future research to determine the bars stiffness. The stiffness values are important if these type of composite bars are used as frames for concrete forming, because the displacements when the concrete is molded are smaller if the stiffness has high values.

The Damping Study for Dammar Composites Reinforced with Natural Fibers

In this paper we have studied the vibration damping for composite bars made by dammar based natural resin, the reinforcement being made by flax, cotton, silk and hemp fibers. There were made rectangular section samples (5x10 mm) with 220 mm length. The bars were clamped, the free length being 100 mm, 120 mm, 140 mm, 160 mm and 180 mm. For each bar, the free vibrations made by an initial deformation, obtained by inserting an external force in the free end, were recorded. In each case, the measured vibration was under-damped.

Modal Parameters Identification for some Sandwich Bars Reinforced with Fiber-Glass

In this paper, there are built new composite bars with different core: with the core made of polypropylene honeycomb and polystyrene reinforced with fiber-glass. Starting from the theoretical background the modal parameters identification, there will be established an experimental method used to determine the eigenparameters of the sandwich bars. In the end, some comparisons between the eigenparameters will be made.