| Wave Attenuation in Thick Graphite/Epoxy Composites |
92 |
|
| Authors:
A. K. Mal; Y. Bar-Cohen
|
 | Attenuation of waves in graphite/epoxy composite laminates is studied through an ultrasonic experiment and theoretical analysis of the recorded waveforms. The specimens are immersed in water and insonified by a beam of acoustic waves in a pitch-catch transducer arrangement. The received signals are analyzed by means of a theoretical model in which the composite is assumed to be a transversely isotropic and dissipative medium. A simple model of dissipation is ... |
|
| Elastic Characterization of Diamond Films by Acoustic Microscopy |
AUG 91 |
|
| Authors:
R. D. Weglein; A. K. Mal
|
| As the development of diamond-like films (DLFs) progresses and emerges from the research environment, the need for rapid, large-scale non- destructive inspection becomes even more important. The metrology or reflectometer mode of the acoustic microscope is used to inspect the layered structure consisting of DLFs deposited on silicon substrates. A measured acoustic material signature (AMS) for DLF on silicon is used to determine the surface acoustic wave (SAW) velocity and ... |
|
| Determination of the Dynamic Elastic Moduli of Composite Materials by Leaky Lamb Wave Experiment |
91 |
|
| Authors:
A. K. Mal; M. R. Karim; Y. Bar-Cohen
|
| An ultrasonic technique for the determination of the dynamic elastic moduli of fiber-reinforced composites through the analysis of guided wave speeds in laboratory specimens in the form of laminates is described. The wave speeds are measured by means of a recently developed technique called the leaky Lamb wave (LLW) technique. A functional relationship between the wave speed in the laminate, frequency and the dynamic elastic moduli of the material is ... |
|
| Ultrasonic Nondestructive Evaluation of Cracked Composite Laminates |
91 |
|
| Authors:
A. K. Mal; C. C. Yin; Y. Bar-Cohen
|
| Two typical defects, delamination and transverse cracking, were investigated by means of the leaky Lamb wave experiment. Specially prepared samples of unidirectional and cross-ply graphite/epoxy laminates containing delaminations and fatigue cracks were subjected to the experiment. The characteristics of the delamination and matrix cracking were determined through the analysis of guided wave dispersion data as well as pulse shape and spectral characteristics of bulk wave reflected from the specimens. (Authors) ... |
|
| Determination of the Elastic Constants of Composites through the Inversion of Leaky Lamb Wave Data |
90 |
|
| Authors:
M. R. Karim; A. K. Mal; Y. Bar-Cohen
|
| A numerical approach is presented for the inversion of Leaky Lamb Wave (LLW) data to determine material properties of composite materials and of a given layer in a multilayered plate, using the simplex algorithm. Within the speed and memory limitations of the computers on which it runs, the technique is capable of computing the parameter values that best fit a particular set of data points, given an analytical model for ... |
|
| a ray analysis of acoustic pulses reflected from a thick composite plate immersed in a fluid |
90 |
|
| Authors:
A. K. Mal; C. C. Yin; Y. Bar-Cohen
|
| the physical nature of the waves produced within a unidirectional fiber-reinforced composite plate immersed in a fluid and insonified by an obliquely incident plane acoustic wave is discussed by means of the ray analysis. for incidence beyond the smallest critical angle, only a small number of mode converted rays are shown to have significant amplitude after reflection and refraction at the two interfaces. the successive mode-converted pulses are shown to ... |
|
| Ultrasonic Evaluation of Adhesive Bonding |
89 |
|
| Authors:
Y. Bar-Cohen; A. K. Mal; C. C. Yin
|
| 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 ... |
|
| Ultrasonic Evaluation of Adhesive Bonding |
89 |
|
| Authors:
Y. Bar-Cohen; A. K. Mal; C. C. Yin
|
| 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 ... |
|
| CHARACTERIZATION OF FILM ADHESION BY ACOUSTIC MICROSCOPY |
JUN 87 |
|
| Authors:
A. K. Mal; R. D. Weglein
|
| this paper briefly reviews the relevant features of the acoustic microscope instrumentation before describing the experiments on layered samples and their preliminary interpretation. the authors then present computed wave dispersion curves for the two lowest modes that may propagate in this particular regime and conclude with a comparison of the measured and computed results. (author/ntiac) |
|
| THE INFLUENCE OF MATERIAL DISSIPATION AND IMPERFECT BONDING ON ACOUSTIC WAVE REFLECTION FROM LAYERED SOLIDS |
JUN 87 |
|
| Authors:
A. K. Mal; C. C. Yin; Y. Bar-Cohen
|
| the authors present a technique for the rapid evaluation of the reflection coefficient and study the variations in its characteristics due to the presence of material attenuation and bonding layers. (author/ntiac) |
|
| RAYLEIGH WAVE DIFFRACTION FROM SURFACE-BREAKING DISCONTINUITIES |
NOV 86 |
|
| Authors:
A. K. Mal; B. R. Tittmann; L. A. Ahlberg
|
| this letter presents theoretical and experimental results treating the interaction between rayleigh waves and surface-breaking discontinuities, such as cracks and grooves, in the regime where crack depth is large compared to the rayleigh wavelength. particular emphasis is placed on the mode conversion to bulk waves at the crack tip. radiation patterns are presented for both the longitudinal and shear wave contributions. the experimental data agree well with theory and show ... |
|
| REFLECTION OF BONDED ACOUSTIC BEAMS FROM A LAYERED SOLID |
AUG 86 |
|
| Authors:
A. K. Mal; T. Kundu
|
| this paper discusses the interface related wave phenomena in a solid consisting of a top layer (insb) which is bonded to a homogeneous substrate (si) by means of a relatively thin and low velocity bonding material (epoxy). the same problem is also considered for a plate obtained by removing the substrate as a reasonable model of the layered solid containing a large debond at the epoxy-si interface. dispersion curves are ... |
|
| RESPONSE OF AN ELASTIC PLATE TO SURFACE LOADS AND BURIED DISLOCATION SOURCES |
JUL 84 |
|
| Authors:
N. Vasudevan; A. K. Mal
|
| the response of an elastic plate to sources of acoustic emission is a problem of current interest in the development of nondestructive inspection methods. so far the two main approaches that have been used to calculate the response are the ray theory and the normal mode technique. in this paper the authors present another method based on a classical integral transform technique. working in the frequency domain, the spectral response ... |
|
| CALCULATION OF THE ACOUSTIC MATERIAL SIGNATURE OF A LAYERED SOLID |
AUG 83 |
|
| Authors:
A. K. Mal; T. Kundu
|
| this paper describes the development of a model for better understanding of focused-beam, reflection mode acoustic microscopy (fram). this is a comprehensive theoretical model of the system in which all of the wave phenomena occurring within the solid are fully accounted for. the basic ingredients of the theory are described, and representative new results are presented. (author/ntiac) |
|
| PROJECT SCATTERING OF ELASTIC WAVES |
SEP 82 |
|
| Authors:
A. K. Mal; LAWRENCE LIVERMORE NATIONAL LAB CA
|
| the major objective of the research was to generate solutions of a number of crack diffraction problems which have potential applications in the ultrasonic nondestructive evaluation of structural elements. only simplified prototype problems were considered so that their solutions could be obtained without recourse to highly elaborate numerical schemes. the emphasis was on obtaining accurate results for idealized geometries which could serve as standards for evaluating numerical or other approximate ... |
|
| DIFFRACTION OF SH WAVES BY A NEAR SURFACE CRACK |
AUG 81 |
|
| Authors:
A. K. Mal
|
| the diffraction of time harmonic plane sh waves by a crack of finite length located within an otherwise homogeneous isotropic elastic half space is considered. the crack is arbitrarily oriented to the surface of the medium and may or may not intersect the surface. the crack opening displacement is calculated by two methods. in the first method an accurate numerical solution is obtained via a singular integral equation formulation. in ... |
|
Reports by Author
