Effect of Oval Defect on Propagation of Fundamental Lamb Wave

Complicated Lamb wave propagation in structures can cause a misinterpretation in defect location and sizing during nondestructive inspections. A visualization of Lamb wave interactions with oval defects was carried out in our study to investigate the phenomenon of fundamental Lamb wave interaction around defect by using a reduced model of plate in ABAQUS. The visualized wave propagations with oval shape of through defects in plates demonstrated different patterns of wave interactions for the symmetric and anti-symmetric modes. The results also visualized the mode conversions around defects which converted from the incident waves. The visualized changes on the wave structures due to wave interaction with defects is important to increase our understanding on the guided wave propagation and reduce misinterpretation in nondestructive inspection when using the wave modes during inspection on large structures.

Epitaxy of Arsenic-Pressure-Controlled MBE-Grown GaAs Layers

Surface morphologies of the molecular beam epitaxy (MBE)-grown GaAs layers using the background-arsenic-pressure-control method were investigated. The growth parameters, such as substrate temperature, growth rate, epilayer thickness, As/Ga ratio, doping concentration, substrate type, etc., are related to the observed oval defect density. Protrusions and Ga-droplets caused oval defects during growth. The origin of the oval defects in our system is found to be the gallium oxide, not Ga "spitting" from the effusion cell.