Papers by Author: Agus Sigit Pramono

Abstract: This research investigated the effect of the thickness of adhesive to the stiffness (Young’s modulus) of adhesive butt joint at high strain rate loading. A split Hopkinson pressure bar (SHPB) test is used to obtain the stress-strain response of join specimen at strain rate of 530±10 s^-1. The joint is composed of aluminum adherend bonded by epoxy adhesive with 0.5, 1, 2, and 3 millimeter of thickness variation. The results show that the joint deformed elastically and the stiffness increases with the increase of adhesive thickness. However, the rate at which the stiffness increases with thickness decreases at thick adhesive layer. The facts of this research are important for the improvement of the crashworthiness of structure such as automobile structures.

Abstract: This study described how the ironing process to manufacture 20 mm caliber bullet case. For this purpose, the first step is analyzing the process parameters, and then calculates the forces needed to make the formation of bullet case. Through the analysis of the process it is known, that the ironing process parameters most influential to the magnitude of forming force are the die angle α and the reduction of the wall thickness. In this study a simulation is conducted to determine a minimum required of forming force until the process successful. That means the required bullet case accordance with the determined specifications and geometry. The material used for bullet case caliber 20 mm is brass Cu30% Zn 70% early-shaped cup with 33.5 mm outer diameter, 3 mm thick and 37 mm high. Based on material strength calculation, the ironing force is determined with value of 50.01 kN. By using this value the maximum allowable wall reduction thickness in the ironing process is 26.7%. The simulation is carried out using finite element method on a variety of die angle such as α = 5°, 10°, 15°, 20° and 25° respectively. The simulation results show that the shell cannot through the die on each angle die. Similarly, in variation of reduction by 5%, 10%, 15%, 20% and 25%, the ironing process is also unsuccessful. However, by load of 138 kN, in the 26.7% reduction and at die angle α=5°, the ironing process to produce cylinder is successfully. Similarly by the same of wall thickness reduction, with force of 148 kN and the die angle of 10°, the ironing process is also successfully to fulfill the bullet case with a specified geometry.

Abstract: The variable stiffness and damping (VSVD) suspension system offers an interesting option to improve driver comfort in an energy efficient way. The aim of this study is to analyze the influence of the spring ratio on the VSVD. The realization of the VSVD is obtained by the application of variable damping with magnetorheological (MR) damper. In this study, the nonlinear damping force characteristic of the MR damper is modeled with the Bouc-Wen model and the road disturbance is modeled by a stationary random process with road displacement power spectral density. It is shown from simulation that VSVD has a potential benefit in improving performance of vehicle suspension.

Abstract: The quality of product of manufacturing industries depends on dimension accurately and surface roughness quality. There are many types of surface defects and levels of surface roughness quality. Ironing process is one type of metal forming process, which aims to reduce the wall thickness of the cup-shaped or pipes products, thus increasing the height of the wall. Manually surface inspection procedures are very inadequate to ensure the surface in guaranteed quality. To ensure strict requirements of customers, the surface defect inspection based on image processing techniques has been found to be very effective and popular over the last two decades. The paper has been reviewed some papers based on image processing for defect detection. It has been tried to find some alternatives of useful methods for product surface defect detection of ironing process.

Abstract: Chatter is a self-excited vibration that occurs during machining process. It becomes a limitation to productivity and reduces the surface quality of work piece. Increasing dynamic stiffness of the work piece will improve its stability limit against chatter occurrence.Initial linear-approach simulation performing finite element modal and harmonic response analysis of the work piece filled with granular stiffener (sand and gravel) is presented. Drucker-Prager granular frictional material model is chosen to represent sand and gravel used as stiffener. Drucker-Prager parameters are chosen based on the experiment setting condition.Effect of an addition of the granular stiffener on the dynamic stiffness of the work piece will be evaluated. The simulation results are verified by experiment results.

Abstract: This paper presents simulation of drawing force and thickness deformation in deep drawing which employs semi-active blank holder force system, to solve the problem of cracking and wrinkling. The method of slab with feed back control failure criteria, was employed to make the modeling system and the semi-active blank holder to prevent wrinkling and cracking in forming low carbon steel sheet, without lubrication (μ=0.4). In this study, the mechanical properties of the material were chosen since that they equivalent to those of low carbon steel with its thickness of 0.2 mm, k = 572 N/mm², UTS = 391 N/mm², yield stress = 309 N/mm² and n = 0.2. The diameter and the depth of the cylindrical cup-shaped product were 40 mm and 10 mm, respectively. Results from simulation have shown that the semi-active blank holder system can control very responsive against changing of deformation condition. The optimum of initial blank holder force is approximately 3000 N up to 4000 N. In the early stages (initial stroke), blank holder force system could be responsive to prevent cracking, and at the end of the punch stroke, it is very effective to prevent wrinkling. Simulation of semi-active blank holder force control system is excellent in model formation to prevent cracking and wrinkling.

Abstract: It is well fact known that automobiles are inefficient, wasting over 74% of energy stored in fuel as a heat. One important loss is the dissipation of vibration energy by shock absorbers in the vehicle suspension under the excitation of road irregularity and vehicle acceleration or deceleration. In this paper we design, characterize and test a regenerative electromagnetic shock absorber which can effectively recover the vibration from the road irregularity. Regeneration energy is main purpose of the design without omit vehicle comfort and handling. The dynamic model of the entire system of the electromagnetic shock absorber was proposed and described. The performance of the electric shock absorber obtained from simulations was compared toward the experiment results. Refers to the simulation, a quarter car will be able to harvest 45 Watt average power while passing C class roads with 50 km/h vehicle speed. A peak power of 45 Watt and average power of 11.43 Watt are attained from the prototype when oscillating speed of bench test at 0.1 m/s, the RMS value of suspension velocity when vehicle pass C class road with speed 50 km/h.

Abstract: Research on the dynamic strength of various materials such as metallic materials, polymers, concrete has been done by many researchers. The Split Hopkinson Bar method is still used to produce a high strain rate. In this method, a striker bar is usually launched using pressurized gas. However, high security system is required to prevent leakage as the operating pressure is very high. Avoiding the use of high-pressure gas, in this study, a mechanical system of springs used to propel the Striker Bar. By varying the spring deflection of 1 cm to 8 cm, a linear Striker Bar velocity from 2.17 m/s until 19.45 m/s is obtained. Aluminum alloy Al-2024 has been tested with this tool and it is found that at the maximum Striker Bar velocity, strain rate on the material can be reach 1132 s^-1, and dynamic compression yield strength increase 56% from quasi-static compression yield strength.

Abstract: This paper presents the importance of simulation of metal flow in deep drawing process which employs an antilock brake mechanic system. Controlling the force and friction of the blank holder is imperative to assure that the sheet metal is not locked on the blank holder, and hence it flows smoothly into the die. The simulation was developed based on the material displacement, deformation and deep drawing force on flange in the radial direction, that it is controlled by blank holder with antilock brake mechanic system. The force to blank holder was applied periodically and the magnitude of force was kept constant during simulation process. In this study, the mechanical properties of the material were choses such that they equivalent to those of low carbon steel with its thickness of 0.2 mm. The diameter and the depth of the cylindrical cup-shaped product were 40 mm and 10 mm, respectively. The simulation results showed that the application of antilock brake mechanic system improves the ability to control the material flow during the drawing process, although the maximum blank holder force of 13000 N was applied. The optimum condition was found when the drawing process was performed using blank holder force of 3500 N, deep drawing force of 7000 N, friction coefficient of 0.25 and speed of punch stroke of 0.84 mm/sec. This research demonstrated that an antilock brake mechanic system can be implemented effectively to prevent cracking in deep drawing process.