Ultrasonics and acoustic emission in nondestructive evaluation of viscoelastic solids-elastomer, human cornea and asphalt

Ultrasonics and acoustic emission (AE) are useful tools for the evaluation of materials in a non-destructive manner. For viscoelastic solids, the measurements of wave velocity and attenuation coefficient at a certain frequency range can lead investigators to the characterization of the viscoelastic properties of the materials.; This dissertation first introduces some fundamental wave propagation theories which our ultrasonic and acoustic emission techniques are based on.; Chapter two covers the measurements of longitudinal and shear wave properties on six selected rubbers. Waveforms of both longitudinal and shear waves are recorded and digitized through a data acquisition device. Cross-correlation method and Fast Fourier Transformation (FFT) are used to process the digitized data and then the wave speed and attenuation coefficient can be calculated.; Chapter three includes the ultrasonic characterization of biomechanical properties of the human cornea after the removal of the corneal epithelium, the outmost layer of cornea. The Young's moduli are calculated as 9.9 {dollar}pm{dollar} 2.1 {dollar}times{dollar} 10{dollar}sp6{dollar} Pascals and 3.7 {dollar}pm{dollar} 1.8 {dollar}times{dollar} 10{dollar}sp7{dollar} Pascals for the cornea samples prepared in saline and in dextran at 2.25MHz and 22{dollar}spcirc{dollar}C.; In the fourth chapter, the effect of the Bowman's layer on the ultrasonic measurements is studied. An excimer laser is used to remove the Bowman's layer and the shear properties of the cornea with and without the Bowman's layer are characterized by ultrasonics. The results show that at 2.25MHz cornea is stiffer with rather than without the Bowman's layer.; The fifth chapter, asphalt concretes prepared by three compaction methods are characterized by ultrasonics and AE. We observed that wave speeds of both longitudinal and surface waves from the three types of specimens show significant differences. It signifies that our ultrasonic and AE techniques have the ability to characterize the asphalt concretes in a non-destructive manner.; In the last chapter, AE is used to the analysis of cavitation in confined asphalt thin film. We find that most of the failures in the confined asphalt are due to cavitation. The failure surface of the asphalt specimen has been compared with the mechanical history, AE source identification and intensity, and it proves that the AE can trace the occurrence of microcavitation.