Papers by Author: Krishnan Balasubramaniam

Abstract: A technique is proposed to predict crack growth for the estimation of Strain Energy Release Rate (SERR) of Double Cantilever Beam (DCB) bi-metallic specimen, employing ultrasonic Lamb waves. Techniques based on the Time-of-Flight (ToF) of the Turning Lamb Mode (TLM) and Direct Lamb Mode (DLM) explored to determine the crack growth. Sensitivity analysis revealed that the Lamb mode with low velocity is more sensitive to crack growth than that of the high velocity Lamb mode.

Abstract: Structural Health Monitoring (SHM) of aircrafts is of great relevance in the present age aircraft industry. The present study demonstrates three techniques that have the potential for the SHM of multi-layered composite structures. The first technique is based on multi-transmitter-multireceiver (MTMR) technique with tomographic methods used for data reconstruction. In the MTMR, the possibility of SHM using algebraic reconstruction techniques (ART) for tomographic imaging with Lamb wave data measured in realistic materials is examined. Defects (through holes and low velocity impact delaminations) were synthetic and have been chosen to simulate impact damage in composite plates. The second technique is a single-transmitter-multi-receiver (STMR) technique that is more compact and uses reconstruction techniques that are analogous to synthetic aperture techniques. The reconstruction algorithm uses summation of the phase shifted signals to image the location of defects, portions of the plate edges, and any reflectors from inherent structural features of the component. The third technique involves a linear array of sensors across a stiffener for the detection of disbanded regions.

Abstract: Any NDE process may be considered to involve three systems, each having a unique set of parameters that define its characteristics viz. (a) The Input to the material, (b) The material itself, and (c) The output response measured by the NDE system. Traditionally, the input and the material parameters are assumed known and numerous Forward Models have been developed that predict or estimate the output response function. Over the years, forward models are very well established and serve the key purpose, for improved interpretation of the, as well as to optimize the input parameters to obtain the desired, output response. The other two scenarios i.e. if the output response function in the form of measured data is available, to obtain one of system parameters, i.e. either the input function or the material properties, while the other one is assumed to be known are classified as Inverse Problems. Due to the availability of computational resources, the inverse problem solutions are becoming increasingly feasible. Typical applications include measurement of material properties such as modulus, viscosity, temperature, hardness and stress profiles, etc. This paper will discuss the different techniques and the kinds of problems that have been successfully addressed in the area of NDE and their implications on the expanding horizons in NDE.