Showing papers by "Ajit Mal published in 1989"

Ultrasonic Evaluation of Adhesive Bonding

Abstract: The capabilities of existing ultrasonic nondestructive evaluation (NDE) methods for the strength-related properties of bonds in structural components is reviewed. The severe limitations of conventional NDE methods in yielding quantitative results are indicated. Some recent results of a joint theoretical and experimental program of research using leaky Lamb waves (LLW) in laboratory specimens are presented. The LLW technique is shown to have several advantages over conventional techniques. Potential applications of the technique to determine non-destructively the quality of bonds in a variety of models are discussed.

Elastic Waves in Layered Media with Interface Features

Abstract: A simple and efficient matrix method is applied to analyze the reflected waves from a layered plate with certain interface features. It is shown that a thin, adhesive layer can be modeled as an equivalent elastic interface with zero thickness characterized by two adjustable parameters. The accuracy of the model is examined through comparison with calculations from the exact case in which the adhesive layer is explicitly modeled. The influence of the imperfect interface on the velocity of layer guided waves is investigated.

Recent Advances in the Application of Leaky Lamb Waves to the Nondestructive Evaluation of Adhesive Bonds

Abstract: In earlier work, the feasibility of applying the Leaky Lamb Wave (LLW) method to the nondestructive evaluation (NDE) of bonded rubber/metal structures was demonstrated. The capability of LLWs to detect and delineate flaws at the bond line was proven, even when the adherends remain in intimate contact. However, variations in adherend properties, surface orientation and thickness can adversely affect detection of bond flaws and assessment of bond quality. In this paper, parameters which degrade both LLW sensitivity and resolution to bond flaws are discussed. Examples of the effects of cold work, thickness change and specimen tilt are presented along with bond flaw detection and characterization results. Also, advances in the theory of bond flaw NDE by LLWs are presented.

Leaky Lamb Wave Phenomena in Composites Using Pulses

Abstract: The leaky Lamb wave (LLW) phenomenon in composite laminates has been studied using pulses rather than tone burst or continuous waveforms. For unidirectional laminates, the leaky wave pulses propagating obliquely to the fibers are shown to be strongly influenced by the presence of flaws within the laminate. The differences in the pulse characteristics have been employed to detect and image ply-gaps, delaminations, and variations in the resin/fiber ratio in laboratory specimens. Moreover, the depth distribution of porosity, simulated by microballoons, has been clearly shown with a C-scan system. Theoretical simulations of pulse propagation have been conducted for multilayered, multiorientation laminates, and the calculated reflected pulses are in close agreement with those obtained from the LLW experiments for a variety of specimens.

Ultrasonic NDE of Thick Composite Laminates

Abstract: The feasibility of using relatively low frequency leaky Lamb waves (LLW) for the quantitative characterization of thick composites is discussed. A coordinated theoretical and experimental program of research has been carried out in an effort to understand the behavior of the leaky wavefield produced by thick composite laminates. Good correlation between theoretical predictions of the LLW spectra and laboratory measurements has been achieved for the specimens. The need for further research to develop a full or understanding is indicated.