Ichsan Setya Putra

Development of a Railway Track Displacement Monitoring by Using Digital Image Correlation Technique

To avoid an unnecessary catastrophic accident due to a failure of a railway track, it is important to have a reliable condition monitoring system for the railway track. The integrity of the railway track can be assessed by monitoring the displacement field of the track, which can then be used to determine the strain and stress field. By knowing the stress history of the track and the S–N curves of the track material, the remaining life of the railway track can be predicted. In the present work, a simple system to monitor and record the displacement field of the railway track has been developed by using Digital Image Correlation (DIC) technique. The set–up to monitor the displacement field of the railway track was developed using a high speed video camera of Nikon J1 to capture the image of the railway track when the train passing through. The DIC technique was then employed off line to measure the displacement field of the 2D image captured. The results showed that the full field displacement measured by using DIC technique gives a good agreement compared to the finite element results. The full field displacement can be used to calculate the strain-stress field, and later on the remaining life assessment can be conducted based on the results.

Steel Plate Behavior under Blast Loading-Numerical Approach Using LS-DYNA

Plate is one of the most common structural elements, which appears in a wide range of applications: steel bridges, blast-resistance door, and armored vehicles. In this paper, the behavior of steel plates under blast loading was studied through numerical approaches using LS DYNA and then the results were compared with the experiment results obtained from existing literatures. The study of a clamped square plate exposed to blast loading in three distinct stand-off distances. Three different methods of modeling blast loading were used, namely: empirical blast method, arbitrary Lagrangian Eulerian (ALE) method, and coupling of Lagrangian and Eulerian method. The empirical blast method was deployed by using key card *LOAD_BLAST in LS-DYNA. In ALE method, Langrangian and Eulerian solution were combined in the same model and the fluid-structure interaction (FSI) handled by coupling algorithm. In coupling method, the engineering load blast in LS-DYNA (*LOAD_BLAST_ENHANCED) was coupled with the ALE solver. In terms of central deflection and computational time, the coupling method appeared to be the best method which is very time-effective and showed a good correlation with the experiment data.

Measurement of Mechanical Properties of St 37 Material at High Strain Rates Using a Split Hopkinson Pressure Bar

The dynamic mechanical properties of a material are important keys to investigate the impact characteristic of a structure such as a crash box. For some materials, the stress-strain relationships at high strain rate loadings are different than that at the static condition. These mechanical properties depend on the strain rate of the loadings, and hence an appropriate testing technique is required to measure them. To measure the mechanical properties of a material at high strain rates, ranging from 500 s-1 to 10000 s-1, a Split Hopkinson Pressure Bar is commonly used. In the measurements, strain pulses are generated in the bars system, and pulses being reflected and transmitted by a test specimen in the bar system are measured. The stress-strain curves as the material properties of the test specimen are obtained by processing the measured reflected and transmitted pulses. This paper presents the measurements of the mechanical properties of St 37 mild steel at several strain rates using a Split Hopkinson Pressure Bar. The stress-strain curves obtained in the measurement were curve fitted using the Power Law. The results show that the strength of St 37 material increases as the strain rate increases.

Numerical and Experimental Impact Analysis of Square Crash Box Structure with Holes

Numerical and experimental study of the effects of center holes located at opposite sides on dynamic axial crushing of thin-walled square aluminum extrusions column are presented in this paper. The results showed that, by inserting the holes, the impact energy absorption characteristic in a progressive buckling can be improved as the starting location of the plastic deformation is always from holes and peak crush force can be decrease, so that the deceleration does not exceed the limit that can injure the passenger when frontal impact occurs. Here, the results of numerical simulations, conducted using an explicit finite element code, are compared with experimental results for various hole diameter. The results shows that the peak crushing force is decrease, while the mean crushing force is relatively constant.

Low Velocity Impact Analyses of Prismatic Columns Using Finite Element Method

This paper presents the study of prismatic columns of different cross sections subjected to low velocity impact, which are commonly used as energy absorber components in vehicles. The impacts of the columns were numerically analyzed using FEM. Four cross sections were considered, i.e. square, hexagonal, octagonal and circular. For each cross section, columns with several combinations of perimeters and thicknesses were analyzed. The results showed that, for columns with equal perimeter and thickness, those with circular cross sections have the highest mean crushing force and those with square cross sections have the lowest crushing forces. Furthermore, keeping all other parameters constant, columns with thicker wall have significantly higher crushing force while columns with longer perimeter have only slightly higher crushing force. This parametric information will be very useful for modern automotive industry in designing front longitudinal members within an acceptable safety level.

Probabilistic Fracture Mechanics Analysis of Multiple Cracks in Cylindrical Pressure Vessel

In this work, a probabilistic fracture mechanics analysis of multiple cracks in a cylindrical pressure vessel was conducted. The analysis was performed to predict service life of a pressure vessel with a certain level of reliability if the vessel has a multiple internal surface cracks that interact each other. The stress intensity factor of multiple cracks configuration was determined from the stress intensity factor of a single surface crack in a plate subjected to uni-axial load and the interaction factor between the cracks. In this work, the Swift’s crack link-up criterion was employed. These parameters together with several other stochastic parameters, i.e. initial crack size, Paris’s crack propagation constants and fracture toughness, were then used to calculate the probability of failure with a certain level of reliability. The failure probability was simulated using guided direct simulation, for cycle-by-cycle crack propagation, to find the expected service life and the mode of failure (leak or break). A case study of a high-pressure vessel having different initial crack sizes have been simulated and the service life with 99,99% reliability were determined.

PERFORMANCE EVALUATION OF THE CORRELATION AND SMOOTHING METHODS OF THE DIGITAL IMAGE CORRELATION AND ITS APPLICATION TO THE OPENING SPECIMENS

Digital Image Correlation (DIC) has been known as one of the non-intrusive experimental methods in solid mechanics. This method has several advantages such as full-field examination, robustness of the algorithms, and the instantaneous visualization of the results. The key of this method is to find the displacement vectors by using a certain correlation method. In this paper, two correlation methods are performed and evaluated, i.e. cross-correlation and FFT (Fast Fourier Transformation) correlation. Performance of these methods in term of error analysis and processing time wre evaluated. Error analysis was performed by using self-generated artificial images with several desired parameters. The results showed that the cross-correlation has less fluctuation results and more constant accuracy. The average processing time of FFT technique is 64% of the cross correlaton. Smoothing algorithms are applied to the displacement results. The results of the smoothing process are compared to the original one to verify the effect of the algorithms. This smoothing process is the important step if the derivative parameters of the displacements such as stress and strain distribution need to be obtained. The complete DIC algorithms are then applied to measure the displacements of the plate with circular and rectangular opening specimens by using experimental images. The result showed that this technique can produce displacement field with good accuracy.

Buckling Analysis of Shells with a Circumferential Crack

In this paper, buckling analysis of cylindrical shells with a circumferential crack is presented. The analyses were performed both numerically using FEM and experimentally. The numerical analyses and experiments were conducted for several crack lengths and radius of curvature, and two different boundary conditions were applied, i.e. simply support and clamp in all sides. The results show the effect of the presence of crack to the critical buckling load of the shells. There are good agreements between experimental and numerical results.

Numerical simulation of SHPB to measure the mechanical properties of aluminium foam material at high strain rate by using MAT 163 modified crushable foam

Aluminium foam is a kind of metal foam material which has large energy absorption capability. The mechanical properties of aluminium foam material in high strain rates could be measured by using SHPB. Numerical simulation is used as the initial step to measure mechanical properties of this material. MAT 163 modified crushable foam used as material model in the SHPB numerical simulation of aluminium foam. Numerical simulation showed a quite close results to experimental data.

Stress Analysis of the Impactor Assembly of the Dropped Weight Impact Testing Machine

This paper presents the stress analysis of an impactor assembly of a dropped weight impact testing machine. A finite element analysis was performed to calculate the stress occurred on the impactor during the impact which should be less than its yield strength. By varying the level of the reaction load from the specimen to the impactor, the maximum load that can be withstand by the impactor assembly without plastic deformation was predicted. Then, several simulations were carried out to find the best way to increase the load limit of the impactor. It was found out that increasing the thickness of box to 7 mm and both the diameter of arm and frame-column to 40 mm will increase the load limit by 236%.