Showing papers by "Ajit Mal published in 2015"
TL;DR: Some of the useful properties of guided Lamb type waves are investigated, using analytical, numerical and experimental methods, in an effort to provide the knowledge base required for the development of viable structural health monitoring systems for composite structures.
65 citations
TL;DR: In this paper, a detailed study of the interaction of Rayleigh surface waves with defects in a thick aluminum plate is carried out using numerical simulations and laboratory experiments, which are shown to partially result in Lamb wave conversion.
51 citations
TL;DR: In this article, a pitch-catch method was used to induce and detect guided Lamb waves for damage detection in composite structures, including an aluminum plate and an aluminum honeycomb sandwich panel with woven composite face sheets.
Abstract: In composite structures, damages are often invisible from the surface and can grow to reach a critical size, potentially causing catastrophic failure of the entire structure. Thus safe operation of these structures requires careful monitoring of the initiation and growth of such defects. Ultrasonic methods using guided waves offer a reliable and cost-effective method for structural health monitoring in advanced structures. Guided waves allow for long monitoring ranges and are very sensitive to defects within their propagation path. In this work, the relevant properties of guided Lamb waves for damage detection in composite structures are investigated. An efficient numerical approach is used to determine their dispersion characteristics, and these results are compared to those from laboratory experiments. The experiments are based on a pitch-catch method, in which a pair of movable transducers is placed on one surface of the structure to induce and detect guided Lamb waves. The specific cases considered include an aluminum plate and an aluminum honeycomb sandwich panel with woven composite face sheets. In addition, a disbond of the interface between one of the face sheets and the honeycomb core of the sandwich panel is also considered, and the dispersion characteristics of the two resultant waveguides are determined. Good agreement between numerical and experimental dispersion results is found, and suggestions on the applicability of the pitch-catch system for structural health monitoring are made.
7 citations
TL;DR: In this paper, an experimental and numeri-cal studies are conducted, in an effort to understand the interaction of guided ultrasonic waves with simple models of the stiffener, in order to improve the reliability of ultrasonic damage detection in stiffened plate structures.
Abstract: Stiffeners are important structural components in modern composite and honey-comb structures. The safe operation of such composite structures, which are com-monly used in aeronautical applications, requires careful monitoring as hidden de-fects may compromise the structural safety. In order to improve the reliability of ultrasonic damage detection in stiffened plate structures, experimental and numeri-cal studies are conducted, in this paper, in an effort to understand the interaction of guided ultrasonic waves with simple models of the stiffener. Through a series of measurements in different positions, the amplitudes of scattered waves for various configurations of the stiffener are determined. Moreover, the group velocity of the waves in the stiffened structure is analyzed. The experimental findings are compared with results from numerical simulations. doi: 10.12783/SHM2015/248
4 citations
TL;DR: The major objectives of this research is to extend the current capabilities of ultrasonic methods to wider areas of coverage, faster inspection procedures, lower percentage of false positives and less dependence of manual operations.
Abstract: Composite materials are susceptible to hidden defects that may occur during manufacturing and service (e.g., foreign object impact) and may grow to a critical size, jeopardizing the integrity of the structure. Among the various existing techniques, guided wave methods provide a good compromise in terms of sensitivity to a variety of damage types or defects and extent of the area that can be monitored, given the ability of these waves to travel relatively long distances within the structure under investigation. Wave propagation in composite structures presents several complexities for effective damage identification. The material inhomogeneity, the anisotropy and the multi-layered construction lead to the significant dependence of wave modes on laminate layup configurations, direction of propagation, frequency, and interface conditions. This paper is concerned with the detection and characterization of small emerging or existing defects in composite structural components using a recently developed technique employing an array of surface mounted broadband ultrasonic transducers as actuators and sensors as well as theoretical analysis to interpret the recorded signals. The technique is applied to panels with different thicknesses, including stiffened specimens with stringer-panel disbonding. The major objectives of this research is to extend the current capabilities of ultrasonic methods to wider areas of coverage, faster inspection procedures, lower percentage of false positives and less dependence of manual operations. The method is based on the well known fact that guided waves are strongly influenced by inter-ply delaminations and other hidden defects in their propagation path.
2 citations