Abstract
RESEARCH ARTICLE
Nayef Alhajraf*
ABSTRACT
Wave propagation in solids depends not only on the frequency and wavelength, but also the characteristics of the medium, such as its elastic properties (moduli E, G) and its density ?. In this project, a composite aluminum pipeline was studied to enhance the understanding of the elastic oscillations performed by the particles of the material when the latter is subjected to external load and the structure is intact or includes a defect. A finite element model was created in Abaqus software representing a pipeline with a flange in the middle. The model was duplicated to analyze separately the case of a pipe with a transversal crack. As such, two models were studied: (a) pipe, and (b) pipe with defect. The exciter was modeled on one of the two sides of either model and the excitation was introduced via a concentrated load applied on the axial direction with a frequency of 80 kHz and a given periodic amplitude. Care was taken so that the magnitude of the load would not tense the structure beyond its elastic limit and enter the plasticity zone. A sensor node was placed at the other end of the pipe to monitor the signal response. The models were meshed using 8-node brick elements (C3D8R) and standard material properties of aluminum were assigned. The determination of element size (0.008-0.02 m) and time increment (1.0e-6) was done considering 5-10 elements per calculated wavelength and following the typical criteria of stability. The Abaqus/Explicit solver was used to perform a dynamic analysis for a time period of 1 sec. The simulations achieved to capture the wave propagation pattern in both pipe models with highest amplitude around 5.5e-10 m during the first 0.1 sec. The signal detected for the pipe without defect was clearly wider than in the case of the pipe with crack as higher amplitudes and lower attenuation was monitored at the sensor node. Small differences were calculated for the arrival time. Yet, the simulations were computationally affordable and showed the capacity of the method to represent the oscillations led by the restoring forces between particles and the inertia to establish equilibrium.
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