Ajit Mal

Abstract: Advanced composite materials are being increasingly used in state-of-the-art aircraft and aerospace structures due to their many desirable properties. However, such composite materials are highly susceptible to developing internal damage. Thus, safe operation of such structures requires a comprehensive program of effective nondestructive inspection and maintenance of their critical load bearing components before the defects grow and become unstable, resulting in failure of the entire structure. Ultrasonic guided wavebased methods have the potential to significantly improve current inspection techniques for large plate-like structural components due to the waves’ large propagation range and sensitivity to defects in their propagation path. The application of guided waves for nondestructive evaluation (NDE) of real structures, however, requires a thorough understanding of the characteristics of guided waves in composite structures in the presence and absence of any defects. In this paper, the interaction of guided waves with a core–skin disbond in a composite sandwich panel is studied using a semi-analytical method, numerical simulations, and laboratory experiments. It is shown that the disbond causes complex mode conversion at its leading and trailing edges. The theoretical findings are verified with laboratory experiments, and the applicability of the proposed pitch–catch setup for NDE of complex composite structures for damage detection is discussed. [DOI: 10.1115/1.4037544]

TL;DR: In this paper, a tensile fatigue test was conducted on a graphite/polymer composite and a cross-ply composite material to evaluate the stiffness of the composite material during fatigue.

TL;DR: In this paper, a mixed integral equation method is applied for the calculation of elastic wave fields in unbounded solids containing general anisotropic inclusions and voids, which does not require the infinite medium Green's functions for both the matrix material and the inclusion material.

TL;DR: In this article, the attenuation of graphite/epoxy composite laminates is studied through an ultrasonic experiment and theoretical analysis of the recorded waveforms, in which the measured and calculated waveforms of the reflected signal are compared.

TL;DR: An approximate analytical method with acceptable accuracy is developed as an alternative to the purely numerical approach used in PZFlex and the mechanical and thermal effects in two-layered fluid material systems induced by high-frequency focused ultrasound are calculated.