Papers by Keyword: Dynamic Behavior

Abstract: Laminated composite beams are being used for many applications due to their high strength to weight ratio. To enhance the performance of laminated composites under dynamic loading, Magnetorheological (MR) and Electrorheological (ER) fluids have been considered to be added as embedded layers/segments to the conventional laminated structures. The present work focuses on the dynamic behavior of laminated composite beams incorporating MR fluid pockets (referred to as MR-laminated beams) under impulse loadings. A modified layerwise displacement theory is employed to account for the varying fluidity of MR pockets along the thickness direction. Four configurations of MR-laminated beams featuring multiple MR pockets distributed through the thickness and along the length have been examined. A parametric analysis explores the impact of magnetic field strength, number and placement of MR pockets, and boundary conditions on the dynamic response of the MR-laminated beams. The changes in natural frequencies concerning the size and location of activated MR pockets have been explored. Time-response analysis is conducted for MR-laminated beams subjected to impulse loading, considering various sizes and locations of activated MR pockets. The investigation highlights the significant influence of the MR pocket's location and size on the vibration response of MR-laminated beams. It is realized that the total stiffness, mass, and activation energy can be optimized according to the desired dynamic response of the beams. The proposed configuration for MR-laminated beam, results in a beam with 7% reduction in total mass while exhibiting fivefold increase in the corresponding natural frequencies, 40% increase in damping and 40% reduction in maximum amplitude.

Abstract: Nowadays, the availability of composite materials and their acceptable manufacturing cost, in addition to their high strength-to-weight ratio, has shifted the use of the materials from metal alloys to composite materials in the aircraft industry. In this paper, a comprehensive analysis of wing natural frequencies and deflection with regard to three different composite materials - carbon fiber, glass fiber, and Kevlar fiber - was conducted, and the results were compared with conventional metal alloys aluminum2024 and 7075-T6, while taking into account the anisotropic behavior of the composite materials. The results indicate that the metal alloys aluminum 2024 and 7075-T6 have the best properties, and consists of the most suitable materials for aircraft wings compared with other composite materials. In addition, the deflection of the wing using AL2024 was about 0.549 unit length and for 7075-T6 was about 0.547 unit length, which was almost less than half of the deflections of other proposed composite materials which are 1.252, 1.389, 1.293 unit length for glass fiber, Kevlar fiber and carbon fiber, respectively.

Abstract: High hardness armor (HHA) steels, when subjected to high deformation rates, are prone to adiabatic shear bands formation. These heterogeneities, formed in a narrow zone, are the result of an intense plastic deformation in which the rate of heat dissipation is low. The generated shear bands can lead to a decrease in ballistic performance and impose to an armor a catastrophic failures. The appearance of these bands may be related to the microstructure or the deformation rate to which the material is subjected. Therefore, this work aims to analyze the influence of the microstructure of an HHA steel, tempered at 310, 425 and 610° C for 2 h, after high deformation rates, in the appearance of adiabatic shear bands. Specimens were dynamic tested in a split Hopkinson pressure bar. It was shown that tempering temperature at 310 ° C for 2h, which produced bainite and martensite with high hardness, was the most susceptible to the adiabatic shear bands appearance.

Abstract: This paper presents a dynamic investigation of the body diode behavior of MOSFETs rated for 3.3kV applications. The body diodes of MOSFETs with different cell designs and pitch sizes have been used. The turn-off behavior of the body diode is compared to that of a 3.3kV JBS diode.

Abstract: To work out effective damping materials it is necessary to perfect analytical dependences linking dynamic properties of a composite with its structure-forming parameters. The analytical model of the particulate-filled polymers, based on the method of strain energy, convenient for engineering use and allowing to predict damping properties of a composite more reliable is given in this article. The detailed leading-out of formulas for scaling of a bulk modulus and loss factor of both two-phase and three-phase model of a composite is presented. Comparison of numerical values of damping characteristics under the derived formulas with experimental researches show that the offered model allows not only to show a qualitative pattern of dependence of dynamic behavior of a composite from degree of admission, but also to receive comprehensible quantitative results.

Abstract: The dynamic strain distribution behavior of a mortar block blasting was experimentally investigated. A small-scale blasting experiment using a mortar block with well-defined property was conducted and the dynamic strain distribution on the mortal block surface was analyzed using a Digital Image Correlation (DIC) method to establish the effective method for investigating the relationship between blast design and fracture mechanism. The block was blasted by simultaneous detonation of Composition C4 explosive charges with an electric detonator in two boreholes. The behavior of the block surface was observed by two high-speed cameras for three-dimensional DIC analysis and it was also measured by a strain-gauge for comparison. The three-dimensional displacements of the free surface of the block were obtained and dynamic strain distributions were computed. A point strain profile extracted from the analyzed strain distribution data was compared with a directly observed strain profile by the strain gauge.

Abstract: A great deal of attention is presently being drawn to the question of noise and vibration damping. One of the basic means of the effective damping of unfavorable noises and vibrations is the usage of special sheets with high vibration and noise damping properties in thin-slab structures. In this article the results of a study of the dynamic behavior (of the loss factor) of multilayer vibration damping sheets are being described. The aim of this article is to show the design optimization of multilayer vibration damping sheets, carrying a high loss factor. The theoretical prerequisites for the structure optimization of vibration damping sheets, having a high loss factor, have been determined. The experimental studies on the influence of the thickness of the vibration damping layer, thickness and Young’s modulus of experimental with theoretical data have also been carried out. More effective designs of multilayer vibration damping sheets have been scientifically substantiated.

Abstract: This paper presented a numerical model of a grinding wheel hub to analyze the dynamic behavior between CFRP hub and steel hub. Natural frequencies of the two different hubs were extracted with the help of finite element software ABAQUS. In addition, the vibration attenuation procedure in the process of free vibration of the hubs was also compared. The numerical results obtained from the model demonstrated that natural frequency of the CFRP hub is much higher than that made of steel owing to the great ratio of elastic modulus to density of carbon fiber. The CFRP hub has a better damping vibration characteristic which allows it to absorb vibration in grinding process to achieve a finer surface roughness.

Abstract: A 3D cell-based finite element model is employed to investigate the dynamic biaxial behavior of cellular materials under combined shear-compression. The biaxial behavior is characterized by the normal stress and shear stress, which could be determined directly from the finite element results. A crush plateau stress is introduced to illustrate the critical crush stress, and the result shows that the normal plateau stress declines with the increase of the shear plateau stress, which climbs with the increase of loading angle. An elliptical criterion of normal plateau stress vs. shear plateau stress is obtained by the nonlinear regression method.

Abstract: Fixtures are use to ensure the orientation and position of workpiece and cutting tools in machining systems. Drill bush guide / holder or are part of a specific category of elements and mechanisms, found in the fixtures structure: elements for size adjustment and guidance for cutting tools. These drill guide bush/ holder are used for guidance of drills, in order to ensure a certain position of the tool regarding the certain reference elements of the workpiece, or to increase the stiffness of drills, when the tool diameter is reduce, or when the surface of the machined workpiece is inclined. The drill bushes are placed in the fixture body, directly or through drill bush guide plates/ drill bush support plates. The characteristic feature of these bush plates is the console length. Sometimes, the bush guide plates can have large lengths that affect the dynamic stability. The bush guide plates are dynamically excited by the direct contact with the drill of the bush. If the natural frequency of vibration of the plate is equal or higher than the excitation frequency of the machining process, then the resonance phenomenon can appear.