Papers by Keyword: Vibration

Abstract: An analytical method is presented for free vibration of a symmetrically laminated rectangular plate with point masses, and experimental modal analysis is conducted to compare both sets of the frequency data. The problem is solved by an extending Ritz method to include kinetic energy caused by added point masses under any sets of edge conditions, and a frequency equation is derived by minimizing the energy functional. In numerical computation, the accuracy of the solution is studied by convergence test and comparison with the existing result in the specific case. Then, the experimental modal analysis is applied to measure the natural frequencies and mode shapes. The two sets of results are compared, and the validity of both theoretical and experimental approaches is established.

Abstract: The product quality of hard steel material formed by a shaping machine using HSS tools was studied under the influence of machining variables. The research focused on the effects of tool vibration on the surface roughness of the product. The experimental process was carried out by selecting the machining independent variables, namely: cutting speed (V) = 1 m/min; 2 m/min; 3 m/min; cutting thickness (a) = 1 mm, 1.5 mm, 2 mm; feeding motion (f) = 5 mm/step; 8mm/step; 10 mm/step. Shaping machine was operated with 3 fixed speed levels (n) of 21.8 rpm, 39 rpm and 59.8 rpm, respectively. The dependent variable, namely stroke per minute (n_p); and feed rate (V_f). The material used was ASTM A483-A high carbon steel. Vibration measurements were taken during machining using an ADXL 345 accelerometer and an Arduino Pro Mini with support for Arduino IDE 1.8.13 and USB TTL CP 2120 software. Vibration acceleration (a_f) on the tool was recorded and an evaluation was performed to determine the effects of machining variables on the final products. The results show that speed lavel of machine, feed rate , and cutting thickness majorly affect vibration. The lowest vibration was obtained at a speed (n) of 21.8 rpm, a feed rate (Vf) of 1 mm/s, and cutting thickness (a) of 0.2 mm. The highest vibration was obtained at n of 59.6 rpm, Vf = 1 mm/s and a of 0.4 mm. The quality of the product related to the surface roughness was mainly influenced by the machine speed levels. The roughness values ranged from 3.97 to 6.46 µm, with the lowest surface roughness or smoother surface achieved at a moderate speed of 39 rpm and higher surface roughness at high (59.8 rpm) and low (21.8 rpm) speeds.

Abstract: The occurrence of chatter during machining processes is a serious problem because of an excessive vibration that consequently dropped the quality of the machined surface. Especially on the turning process of tube shaped workpieces e.g. steel pipe that has relatively low stability limit represented by low critical depth of cut due to the naturally low dynamic stiffness of steel pipe. A cheap and simple method to increase the stability limits during the turning process of steel pipe has been developed in this research by using “Sand” as granular damper material to dissipate the elevated vibration energy. An experimental research is performed to investigate the performance of the sand damper by doing the cutting process of two different diameter the steel pipe that is filled up by sand. The result of the experiment shows that the 3 inch nominal diameter with fully filled of Sand can increase the stability limits from the critical depth of cut 0.68 mm (empty or without sand) up to 3.27 mm (full) or elevate by 4.8 times (almost fivefold). On the other hand, the 2.5 inch nominal diameter by filling with full of sand can improve stability limits from the critical depth of cut 0.95 mm (without sand) up to 3.05 mm or increase by 3.2 times. In simple words, the result of this research can be concluded that the increasing of the stability limits means also the elevated of the quantitative performance or the production rate of the turning process of Steel pipe almost up to fivefold. Keywords: Stability limits, chatter, sand damper, turning, steel pipe, vibration.

Abstract: In 21st century, battlefields are being occupied by Artificial Intelligence (AI) controlled machines and one of its kind is mini-unmanned aerial vehicles. Upon arming the mini-UAVs, the load distribution and characterizing the vibrational behavior are important for its safe operation. Usually, the gun recoil force gets transferred to the platform of the mini-UAV, leading to instability or failure of the platform along with the gun. Mini-UAVs being too small don’t have the space to set the conventional recoil reduction mechanism. So, it is important to design a mechanism or alternative propellant for achieving the equivalent explosive force instead of TNT. Also, the influence of explosion on the vibration characteristics of the mini-UAV is studied. The high-pressure gas is found as the best alternative to TNT material, for reducing the deflection produced. This work primarily concentrates on determining the deflection and frequency induced in mini-UAVs. By using a pressure canister arrangement, the vibration characteristics under recoil can be improved.

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: It is proposed to apply a composite sheet of viscoelastic material encapsulated in ABS plastic to be used in the design of a prototype of vibration isolator in the use of motor bases. The cyclical impact tests presented are carried out with an insulator unit named as a viscoelastic sheet that takes advantage of Hooke's law 3D. Using a vibrating equipment, reproductions of impacts are made to study the ability of the vibration isolator to resist impacts and evaluate its useful life. Through the analysis of force and variation in the response to its natural frequency of vibration, the evaluations and its behavior to the tests are established, and its change to a passive type of isolator. The evolution of the damage in the viscoelastic and the appearance of cracks is also shown.

Abstract: In this research, vibrations were added to the mold structure. In the molding process, each vibration was turned on during the filling process. Moreover, the mold structure was re-designed to insert the vibration equipment. The design of this equipment is an early version used to insert vibrations. This option was chosen to facilitate the process of manufacturing and installing the vibration part. However, the applied method still has some limitations, such as not exerting an impact on the exact position where the weld line occurs. To overcome this disadvantage and to help increase the vibrations of the insert, we used a flexure hinge placed inside the insert. This design helped to improve the flow disturbance and to accurately impact the position where the weld line occurred. Therefore, the results of our method are better than those of the method currently being applied.

Abstract: Polymer coatings are increasingly used in mechanical engineering. In particular, sheet composite elements are created on their basis. But the question of the influence of vibration loads on the bearing capacity of composite structures remains relevant. This work presents the results of an experimental study of the operation of composite structures when exposed to vibration loads. The choice of the parameters of the test bench is due to the frequencies of natural vibrations of the specimens under study. The frequencies were determined using generally accepted approximations. A test bench was developed for carrying out measurements. A vibration-absorbing foundation was used, a support frame with the element was attached on elastic suspensions to the outer frame. A scheme for cutting sheet elements for tensile testing was developed. Nine sheet elements made of reinforced polymer material were tested. The influence of the number of loading cycles on the material ultimate strength is investigated. It was established that the presence of a reinforced polymer coating leads to a decrease in the vibration amplitude when approaching the resonance frequencies. This is due to the internal deformation of the polymer coating. After removing the vibration load, no cracks were found on the specimens.

Abstract: This paper demonstrates a simple technique to detect vibration-induced fatigue cracks using a hybrid method by vibration and acoustic emission techniques. A thin aluminum plate of 6082-T6 was excited using a vibration shaker to achieve a bending mode where the maximum stress exhibited at the plate mid-span. To simulate crack formation, a sharp notch was created. This systematic setup allows mode I crack propagation through plate thickness. The development of cracks over time changed the natural frequency of the plate which leads to the reduction of vibration amplitudes. This experimental technique facilitates the identification of acoustic emission waves during the onset of damage in the presence of noise due to dynamic motion. The effect of crack development on Lamb waves was investigated. The acoustic emission signals were cross-correlated with a Gaussian window of a central frequency of 250kHz. The results show a reduction in the fundamental wave A₀, whilst an increase in S₀ wave amplitudes at some stages during crack extension. The current experimental work can be an alternative technique for vibration-induced fatigue test evaluation.

Abstract: The article discusses the issues of chatter damping during milling. The relationship between the amplitude of forced vibrations and the cutting speed has been established. The choice of the optimal values ​​of the cutting condition during end milling is proposed to ensure the minimum vibration amplitude.