Showing papers by "Anish Kumar published in 2007"

Low Velocity Impact Damage Characterization of Woven Jute—Glass Fabric Reinforced Isothalic Polyester Hybrid Composites

Abstract: This study explores the effects of hybridization of glass fiber on low velocity impact behavior and damage tolerance capability of woven jute fabric composite. Laminates were fabricated by the hand lay—up technique using a mold and cured under light pressure at room temperature. Low velocity impact tests were conducted on jute and hybrid samples (150 × 150 mm) using an instrumented drop weight impact tower. All the samples were impacted at four different energy levels by changing the drop height, and load—energy—time plots were recorded using data acquisition software. Some of the samples were subjected to the non-destructive test (C-scan) to study the nature and extent of damage and to measure the delamination area. Post-impact tension tests were conducted to assess the damage tolerance capability of the composites. The results of the study indicated that jute laminates have better impact energy absorption capacity than jute—glass hybrid laminates; however their damage tolerance capability is less than j...

Characterization of aging behaviour in M250 grade maraging steel using eddy current non-destructive methodology

Abstract: The aim of the study is to investigate the effect of aging of solution annealed M250 grade maraging steel on the microstructure, room temperature hardness and eddy current (EC) parameters. Specimens of M250 maraging steel were subjected to solution annealing at 1093 K for 1 h followed by aging at 755 K for various durations in the range of 0.25–100 h. The hardness was found to increase continuously with aging due to precipitation of intermetallics reaching a maximum and decreased there after due to reversion of martensite to austenite. The aging treatment led to three major microstructural changes, i.e. decrease in dislocation density and quenched-in point defects during initial aging (up to 0.25 h), increase in volume fraction of intermetallic precipitates at intermediate duration and a systematic increase in reverted austenite at longer duration (beyond 40 h). These microstructural changes alter the electrical resistivity/magnetic permeability which, in turn, influence the induced voltage in eddy current coil. Two EC parameters, viz. magnitude and phase angle of the induced voltage were studied for heat treated specimens. The study revealed that a good correlation exists between EC parameters and microstructural changes in M250 maraging steel specimens.

Characterization of Aging Behavior in M250 Grade Maraging Steel Using Ultrasonic Measurements

Abstract: Ultrasonic measurements have been carried out in M250 grade maraging steel specimens subjected to solution annealing at 1093 K for 1 hour followed by aging at 755 K for various durations in the range of 0.25 to 100 hours. The influence of aging on microstructure, room temperature hardness, and ultrasonic parameters (longitudinal and shear wave velocities and Poisson’s ratio) has been studied in order to derive correlations among these parameters in aged M250 maraging steel. Both hardness and ultrasonic velocities exhibit almost similar behaviors with aging time. They increase with the precipitation of intermetallic phases, Ni3Ti and Fe2Mo, and decrease with the reversion of martensite to austenite. Ultrasonic shear wave velocity is found to be more influenced by the precipitation of intermetallic phases, whereas longitudinal wave velocity is influenced more by the reversion of martensite to austenite. Unlike hardness and ultrasonic velocities, the Poisson’s ratio exhibits a monotonous decrease with aging time and, hence, can be used for unambiguous monitoring of the aging process in M250 maraging steel. Further, none of the parameters, i.e., hardness, ultrasonic velocity, or Poisson’s ratio, alone could identify the initiation of the reversion of austenite at early stage; however, the same could be identified from the correlation between ultrasonic velocity and Poisson’s ratio, indicating the advantage of using the multiparametric approach for comprehensive characterization of complex aging behavior in M250 grade maraging steel.

Ultrasonic Spectral Analysis Methodology for Thickness Mapping of Electrochemical Hydrogen Meter Thimbles

Abstract: An ultrasonic spectral analysis based methodology has been developed and successfully implemented to measure wall thickness in the range of 0.3 to 0.7 mm in iron thimbles using low frequency ultrasonic waves (around 10 MHz). Conventional ultrasonic techniques cannot be used in such cases because of the low thickness of the thimble and the presence of curvature. Using a low frequency (15 MHz) immersion transducer and low digitization (under 200 MHz), an accuracy of ±10 μm has been achieved. The importance of the window for selection of time domain data for spectral analysis has been clearly brought out. A software program has been developed for automated thickness measurement across a line scan and for displaying the surface plot of thickness variations using the developed methodology.