Dr. Djarot Widagdo
Assistant Professor
Research Interest:
Dr. Widagdo’s research interests include experimental and computational fracture mechanics, and composite materials and structures
Education
- Bachelor Degree, (1995). Department of Mechanical Engineering, Institut Teknologi Bandung, Indonesia.
- Master Degree, (1998). Department of Engineering, Queen Mary University of London, UK.
- Doctoral Degree, (2004). Department of Engineering, Queen Mary University of London, UK. Dissertation: “Boundary element method for fracture mechanics analysis of cracked panels with composite repair patches”.
Latest Publications
Structural blastworthiness is an ability of a structure to deform with a controlled force and maintain a survival space around the occupants to minimize injury risks during a blast impact incident. A proposed blastworthy aluminum foam sandwich (AFS) construction is designed and optimized for armored vehicle (AV) protection. The proposed AFS structure consists of four main components, namely an occupant side plate (OSP), a struck side plate (SSP), an Al-foam core, and adhesive bonding layers. The blastworthy characteristics of the AFS were analyzed by using a non-linear finite element simulation methodology subjected to blast impact loading. The baseline numerical simulation was correlated to a single plate experimental data. In order to minimize acceleration and structural intrusion during the blast impact incident, the AFS design parameters were optimized by using the design for six sigma (DFSS) methodology to achieve a robust AFS structure and to screen the significant design parameters. The optimum design parameters are influenced mainly by the bonding pattern/strength, OSP and SSP material strength/thickness, and foam strength/thickness. The usage of optimized AFS on an AV shows very promising results for the structural blastworthiness application of a small armored vehicle. These findings will pave the way for a robust design of lightweight and efficient AFS construction for AV protection in the future.
A blastworthy structure is defined as a structure that has the ability to deform with a controlled force and preserve sufficient residual space around the occupants to limit bodily injury during a blast impact incident. In this research, a blastworthy aluminum foam sandwich (AFS) structure that consisted of an occupant side plate (OSP), a struck side plate (SSP), and an aluminum foam (Al-foam) core were numerically and experimentally subjected to blast-fragmented loading. The explosion with high-pressure shock waves was produced by steel-covered TNT, creating a synergistic blast and fragment loading. The interaction between the blast-fragment loading and the AFS created a unique perforation pattern due to Monroe’s effect. The measured blastworthiness characteristics included structural integrity, acceleration, and reaction force. A numerical modeling strategy to analyze the blastworthiness performance of the AFS structure was developed to capture the dynamic responses and the damage mechanism. Two types of blast loading, namely load blast enhanced (LBE) and smooth particle hydrodynamic (SPH) blast loading, were utilized along with the Cockcroft-Latham damage modeling on the AFS. A blast experimental setup with a fix-clamped method was used to evaluate the blastworthy characteristics of the panel to acquire the central acceleration and reaction force histories. A two-step process of experimental validation was carried out. First, a pre-test system validation with a very low explosive blast using 60 gram of TNT was conducted on the sandwich specimen to ensure the data acquisition system’s functionality and to obtain comparable data for system validation. Second, a blast impact test using 8 kg of steel-covered TNT was carried out to validate the numerical modeling results. The results of the numerical analysis showed that the LBE model had good agreement with the test data for the small deformation blast impact loading with 60 gram TNT. For the large deformation blast impact loading with 8 kg TNT, the SPH models provided excellent agreement with the damage mode and dynamic responses, where the acceleration and the reaction force performances were both within 6.1% and 6.4% of the experimental validation, respectively. As for the structural performance of the AFS construction, it was observed that the sandwich panel met the structural integrity requirements. There were no cracks or fractures in the OSP. The SSP and Al-foam absorbed more than 98.3% of the blast impact energy, providing extra protection for the OSP. This research contributes to the dynamic structural-response and damage investigation of AFS subjected to fragmented 8 kg TNT blast loading.
This paper presents results on the crushing behavior of aluminum foam–filled columns with square cross section. Here, the effect of inserting an aluminum foam to single–walled and double–walled columns were studied. Parametric study for both types of columns compared with single–walled and double–walled columns were also carried out. In this work, the effect of strain rate of the aluminum foam was considered in the material model. The numerical results were compared with the available experimental data and shown to be in a very good agreement. The models that considered the strain rate effect of foam core gave better predictions compared to the ones without considering the strain rate effect. It will result in higher energy absorption and bigger local deformation on corners resulting a slightly increase of the overall crushing force. It can be said that the strain rate of the foam core plays a quite significant role in crushing behavior of the foam-filled columns, and should be taken into account. The results also showed that the interaction between the foam core and the column wall will change the deformation mode from one localized fold to multiple propagating folds and lead to the increase of total mean crushing force of the column. Similar effect of foam filling was also found in double–walled foam–filled columns. Further investigation has been conducted on the effect of core thickness to the mean crushing force response of the columns. It is also found that increasing the core thickness in double–walled foam–filled column will improve the crushing behavior up to a point where there is still interaction between the walls. After that, the further increase of the core thickness will make the column response approaching the crushing force of single–walled foam–filled.
This paper presents a numerical and experimental study of several configurations of multi-cell columns compared to single-walled and double-walled columns subjected to dynamic axial impact forces. The impact of the columns was numerically analysed using FEM and also verified by experimental testing. The effect of the column mass and thickness of the multi-cell columns compared to single- and double-walled columns was also studied. The results showed that, by analysing a group of columns with the same thickness and weight, the energy absorption efficiency can be significantly improved by introducing internal ribs to the double-walled columns. The results showed that the crushing force of the middle ribs (MR) multi-cell columns was the highest, followed by the corner ribs (CR) multi-cell columns, the double-walled (DW) columns and the single-walled (SW) columns, respectively. © 2014 Elsevier Ltd. All rights reserved.
In this paper, an analytical prediction and numerical simulation of the behavior of square crash box structures having hole at corners on dynamic axial crushing are studied. The focus of the present theoretical prediction is to calculate the mean crushing force and maximum crushing force during the folding process subjected to axial impact loading. Then, the effect of hole size to the crushing response of square crash box structures was also evaluated. For validation, an explicit nonlinear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical method and theoretical prediction were in good agreement. The results showed that, by inserting holes at corners, the folding can be controlled to be always started from the hole, and peak crush load on the first fold can be reduced significantly. Meanwhile, the decreasing of mean crushing force is insignificant compared to the one without holes. Hence, the characteristic of impact energy absorption in a progressive buckling can be improved, the damage in passenger compartment can be minimized, and the deceleration level can be kept in safe level to prevent injury of the passenger.