Advanced Materials Research Vols. 463-464

Abstract: A nonlinear Rayleigh wave approach is presented for nondestructive evaluation of material damage in this paper. Rayleigh waves are experimentally generated and detected with wedge transducers, and the nonlinear parameters are measured at different stress levels for AZ31 magnesium alloy plate specimen. By experimental way, it is observed that there is a direct correlation between the acoustic nonlinearity measured with nonlinear Rayleigh waves and the level of plasticity. The result shows that there is a significant increase in the nonlinear parameters at monotonic tensile loads above the material’s yield stress, and it demonstrates the effectiveness of the proposed experimental procedure to track the surface damage in alloys.

Abstract: Aeroelastic problems of light weight structures of modern aerospace vehicles are the result of interactions between aerodynamics, structural and inertial forces. The mathematical model of the aeroelastic problem is based on the Lagrange equations of motion for the structural dynamics and on a quasi-steady approach of the generalized unsteady incompressible aerodynamic forces. The oscillations of such aeroelastic system can be suppressed using linear active control techniques. In the case when the control is saturated the stability domain shrinks. The describing function method is used in this paper to determine the periodic solutions of an experimental aeroelastic system for two control laws.

Abstract: This article based on the analysis of the characteristics and the content of the Mobile Scaffolding System (MSS) safety assessment, and according to the on-site inspection of the two MSSs, constructed the MSS metal structure safety assessment index system, and applied the expert scoring method to give the importance degree of every index, finally put forward the fuzzy comprehensive evaluation method for the evaluation criteria.

Abstract: The joining of dissimilar materials is of great importance in industry. Especially, if it is used as the lightest part of the machine parts, materials such as aluminum and magnesium can be joined with steels. Friction welding is one of the methods getting higher share among the other welding methods. In the process, heat is generated by conversion of mechanical energy into thermal energy at the interface of the work pieces during rotation under pressure. Some of the advantages of friction welding are high material save, low production time and being possible of welding of parts which are made by different metals or alloys. Friction welding can also be used in order to join the components that have circular or non circular cross – sections. In this study, stainless-steel and aluminum materials which is the example material was used in the friction welding experiments. The temperature distributions are experimentally obtained in the interface of joints that is formed during friction welding of joints having same geometry. This study was made using thermocouples at different locations of joint-interface.

Abstract: The aim of this paper is robot with vision system to interact with its environment. The task considered is recognizing and finding objects extracted from the image space. The work presents a Matlab program for different objects colour and shape recognition. The image taken by a low cost Web camera is processed and information is transferred to a robot controller for moving above the identified object.

Abstract: The Popov criterion for the stability of nonlinear control systems is considered. The Popov criterion gives sufficient conditions for stability of nonlinear systems in the frequency domain. It has a direct graphical interpretation and is convenient for both design and analysis. In the article presented, a table of transfer functions of linear parts of nonlinear systems is constructed. The tables includes frequency response functions and offers solutions to the stability of the given systems. The table makes a direct stability analysis of selected nonlinear systems possible. The stability analysis is solved analytically and graphically. Then it is easy to find out if the nonlinear system is or is not stable; the task that usually ranks among the difficult task in engineering practice.

Abstract: The work relates to practical conceivement and achievement of mecanical and action structure of an antropomorphe industrial robot with 4 freedom degrees + gripper, conceived at “C. Brâncuşi” University – Târgu Jiu for didactical usage. The work presents cinematical chain and building solutions used for mechanical structures, actionand comand systems and speed regulate system of an industrial robot.

Abstract: The study of hydro-thermal-mechanical process coupling in unsaturated porous material is very important due to its close relationship with environmental geomechanics engineering. The model established upon the deforming porous material mechanics is analyzed in this study. This model takes into consideration the phase change and heat effects. Four balance equations associated with four state variables including gas pressure, capillary pressure, temperature and displacement are imposed. Besides, the governing equations are discretized with the selected Galerkin method and the program has been developed. Using this program simulates two experiments, which representing the saturated non-isothermal consolidation phenomenon and rainfall experiment respectively. The results revealed that this multi-field coupled model is a useful tool to analyze the porous material that coupled with hydro-thermal-mechanical process.

Abstract: Unmanned Aerial Vehicles have seen a rapid development due to increased miniaturisation of technology, and their multiple usages in both military and civilian fields, thus making this business very profitable. Although the small UAVs are high enabling capabilities, they are still single-role (one flight, one mission). The present paper will present a comparative analysis of the solutions on flexible wing concept and will analyze the possibilities to use the morphing concept at small UAVs.

Abstract: The bending-torsional flutter characteristics of a cantilever composite wing subjected to engine thrust are presented. The engine thrust modeled as a follower force and the wing modeled as a two degree of freedom beam. In order to consider the spanwise and chordwise location and the properties of the engine location, the generalized function theory is used. Unsteady Theodorsen aerodynamic theory in time domain, is used. The general laminate composite theory is used for modeling the effects of the ply angles on the flutter boundary. The Ritz method is subsequently applied to convert the partial differential equations into a set of ordinary differential equations. In order to precisely consider the location of the engine Dirac delta function is used. Moreover, the numerical results are compared with the published results and excellent agreement is observed. Numerical results highlighting the effect of engine thrust on the wing instability, is presented.