Cosmin Mihai Miriţoiu

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.

Study about the Influence of Two-Steps Sintering (TTS) Route for an Alloy Based on Titanium

This paper describes the influence of two-steps sintering regime temperatures concerning the final properties of titanium hydride based alloy obtaining by Two-Steps Sintering (TTS) route, which is a method that is part of the Powder Metallurgy (PM) technology. The initial titanium hydride powder has been mixed with some metallic powders as: Alumix, Mn, Zr, Sn and graphite was added in different proportions for improving the final mechanical properties. The Two-Steps Sintering (TTS) route have been applied for obtaining a low-cost Ti- alloy. The effect of the sintering regime temperatures on the height and diameter shrinkages and density for these alloys based on titanium hydride powder was studied

The NASGRO Method - Comparison Model for the Crack Growth Rate Calculus

The products materials failure process subjected to a time variable loading can be watched and controlled through the study of an important parameter from the “Fracture Mechanics” given by the crack growth rate or the cracking rate. This is marked with da/dN, sometimes da/dt, representing the length variation a at a fatigue loading cycle. From the most used models for its study, one can remember: methods that use the American standards ASTM, Paris formula model or the Walker one. The model called NASGRO or FNK is used to study the crack growth evolution in NASA studies, being a more complex method, for the cracking process. The results obtained were compared to the ones determined with the above methods. For the tests, steel samples R520 were used, CT type, with side notch. The loading cycle was made with the asymmetry coefficient R= 0.5, at the temperatures: 293K, 252K and 213K.

An Experimental Study Regarding the Vibratory Behaviour for Some Textile Composites

The paper presents the results of our research in the elaboration and characterization of composites type epoxy - textile fiber and vibration behaviour. These were made by pressing, and the textile fibers we tested were cotton, flax, hemp and wool. Starting from the dynamic response of composite beam with damping (which is in free vibration), there is established a way to determine the damping factor. There has been experimentally determined the damping factors for some samples: sample 1 – built from cotton; sample 2 – built from hemp; sample 3 – built from flax; sample 4 – built from whool.

The Crack Length Growth – A Fracture Parameter in a Stainless Steel Influenced by the Loading Test

The defects or micro-cracks that exist in a product mass from the elaboration phase, can extend controlled or not, because of a variable solicitation applied to a product or a sample. The Fracture Mechanics parameter that highlight the crack propagation in time is its rate growth marked as da/dN and represents the crack advancement length during a solicitation cycle. This can be studied based on some mathematical models obtained from some propose models, experimentally determined. In this paper, a propagation process analysis is made of a fracture crack by an axial-eccentric fatigue loading for a 10TiNiCr175 stainless steel. CT type flat samples were loaded with an asymmetry coefficient R= 0.3, for the solicitation temperatures: T= 293K (20°C), T= 253K (-20°C), respectively T= 213 K (-60°C). The crack growth increase was studied by three most used mathematical models: the polynomial method standardized according to ASTM E647, method proposed by Paris and method proposed by Walker.

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.

The Influence of Two Extra Carbon Fiber Layers over the Damping Properties for Sandwich Bars with Polypropylene Honeycomb Core

In this paper we will build some new and original composite sandwich bars reinforced with two and four layers of carbon fiber (in the upper and lower sides), 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. The bars will have the polypropylene honeycomb core with 10 and 15 mm and the width of 45 mm. The bars will be clamped at one end and free at the other. We will consider several free lengths of: 200, 230, 260, 290, 320 and 350 mm. We will highlight how the damping factor will increase if two extra carbon fiber layers are added in the upper and lower sides of the sandwich bars.

The Reinforcement Effect of Two Extra Carbon Fiber Layers on the Flexural Rigidity and Young Modulus for Sandwich Bars with Honeycomb Core

In this paper we will build some new and original composite sandwich bars reinforced with two and four layers of carbon fiber (in the upper and lower sides), with the core made of polypropylene honeycomb. For these sandwich bars, we will use the next experimental setup: we will clamp them at one end and we will leave the other free. Using an accelerometer, we will record the eigenfrequencies. Bu using the eigenfrequencies values and the Euler-Bernoulli theory, there is established a procedure to determine the bars flexural rigidity and dynamic Young modulus. We will consider the bars as having 320 and 350 mm free lengths. We will highlight how the two extra carbon fiber layers will influence the flexural rigidity values and the dynamic Young modulus.

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.