Research Projects

In-service degradation and fatigue damage assessment of the aerospace components made of aluminium alloys are critical factors to determine structural integrity. So, nondestructive evaluation (NDE) is desired to assess the state of fatigue damage to ensure safe operation and to determine remaining life of the components. Ultrasonic NDE is one of the most versatile methods among all NDE techniques. The strength of the components depends on the presence of microscopic imperfections generated during service due to fatigue. These imperfections serve as nucleation sites for fatigue crack generations. Therefore, evaluation of materials much before the generation of cracks is essential for assessing the integrity of the components. The dimensions of such imperfections are much lesser than the wave lengths used during conventional ultrasonic methods. So, conventional methods are insensitive to microstructural degradation in materials. Nonlinear ultrasonic (NLU) serves this purpose. NLU relies on generation of higher order harmonics during propagation of finite amplitude ultrasonic waves through degraded or nonlinear materials. The quantification of degradation or nonlinearities in the material is characterized by nonlinear ultrasonic parameter, β, which depends on the amplitude of harmonic components and fundamentals. Again conventional NLU technique is point to point measurement in which area under the measurement location can only be evaluated. On the other hand, guided wave ultrasonic is a long range inspection technique in which large distance can be inspected by accessing single position on the component. In this proposed nonlinear guided wave ultrasonic would be used to assess high cycle as well as low cycle fatigue damage in Al-Mg-Sc alloy. Despite continuous research works on ultrasonic NDE for damage evaluation of aluminium alloy have been done, no works have been found to assess fatigue damage in aluminium Al-Mg-Sc alloy. Although, conventional linear and nonlinear ultrasonic techniques are being used to evaluate damage in materials, but, no exhaustive works have been found on the use of nonlinear guided wave ultrasonic for the evaluation of rod/ cylindrical structures. Evaluation capabilities will be further improved by mixing various ultrasonic guided wave modes for the determination of nonlinearities generated during in-service degradation, which is also lacking in terms of research and applicability.