Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Mechanical Engineering


The erosion of 18 Ni (250) maraging steel, 2024 and 2011 aluminum alloys was studied. The specimens were subjected to thermal and thermomechanical treatments to obtain various microstructures and mechanical properties. The erosion tests were conducted under ambient conditions with 125 (mu)m SiC particles impacted at a velocity of 50 m/s and an angle of 30(DEGREES) to the specimen surface;The variation of erosion has been related to the microstructures and the resulting mechanical properties. It was found that the presence of a soft phase increased the erosion resistance of a hard matrix. The overaging resulted in the growth of precipitate size which also increased the erosion resistance. An increase in the size or concentration of the dispersed alumina particles in phenol formaldehyde matrix also showed an increase in the erosion resistance, but the increased size was more effective. In general, it was found that the erosion resistance varies inversely with hardness and directly with ductility;Dynamic photoelasticity techniques were used to visualize the impact induced stresses and strain rates in polyurethane rubber and polycarbonate. The residual stress field and the damage caused by impact and plowing were also studied. It was found that the dynamic stress field caused plastic deformation near the impact location and propagated with a leading pressure pulse followed by a shear wave. A surface wave also travelled away from the impact location with a tensile stress front leading a compression. The reflected tensile waves did not nucleate any cracks in the substrate. The residual stress field extended up to a distance of three times the impact crater radius;Scanning electron microscopy of the eroded surfaces and debris revealed that erosion was accompanied by a large amount of plastic deformation. The eroded material was in the form of small flakes which were formed due to a combination of cutting, plowing, and crack propagation mechanisms.



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Mahmood Naim



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156 pages