Matching Items (2)
Description
Cavitation erosion is a significant cause of wear in marine components, such as impellers, propellers or rudders. While the erosion process has been widely studied on metals, the effect of cavitation on polymers is not well-understood. The stress response in metals differs greatly from that of polymers, e.g. rate and temperature effects are far more important, thus damage and wear mechanisms of polymers under cavitating flows are significantly different. In this work, heat-driven failure caused by viscous dissipation and void nucleation resulting from tensile stresses arising from stress wave reflections are investigated as two possible material failure mechanisms.
As a first step in developing a fundamental understanding of the cavitation erosion process on polymer surfaces, simulations are performed of the collapse of individual bubbles against a compliant surface e.g. metallic substrates with polyurea coatings. The surface response of collapse-driven impact loads is represented by a idealized, time-dependent, Gaussian pressure distribution on the surface. A two-dimensional distribution of load radii and durations is considered corresponding to characteristic of cavitating flows accelerated erosion experiments. Finite element simulations are performed to fit a response curve that relates the loading parameters to the energy dissipated in the coating and integrated with collapse statistics to generate an expected heat input into the coating.
The impulsive pressure, which is generated due to bubble collapse, impacts the material and generates intense shock waves. The stress waves within the material reflects by interaction with the substrate. A transient region of high tensile stress is produced by the interaction of these waves. Simulations suggests that maximum hydrostatic tension which cause failure of polyurea layer is observed in thick coating. Also, the dissipated viscous energy and corresponding temperature rise in a polyurea is calculated, and it is concluded that temperature has influence on deformation.
As a first step in developing a fundamental understanding of the cavitation erosion process on polymer surfaces, simulations are performed of the collapse of individual bubbles against a compliant surface e.g. metallic substrates with polyurea coatings. The surface response of collapse-driven impact loads is represented by a idealized, time-dependent, Gaussian pressure distribution on the surface. A two-dimensional distribution of load radii and durations is considered corresponding to characteristic of cavitating flows accelerated erosion experiments. Finite element simulations are performed to fit a response curve that relates the loading parameters to the energy dissipated in the coating and integrated with collapse statistics to generate an expected heat input into the coating.
The impulsive pressure, which is generated due to bubble collapse, impacts the material and generates intense shock waves. The stress waves within the material reflects by interaction with the substrate. A transient region of high tensile stress is produced by the interaction of these waves. Simulations suggests that maximum hydrostatic tension which cause failure of polyurea layer is observed in thick coating. Also, the dissipated viscous energy and corresponding temperature rise in a polyurea is calculated, and it is concluded that temperature has influence on deformation.
ContributorsPanwar, Ajay (Author) / Oswald, Jay (Thesis advisor) / Dooley, Kevin (Committee member) / Chen, Kangping (Committee member) / Arizona State University (Publisher)
Created2015
Description
Cavitation bubbles in the human body, when subjected to rapid mechanical load, are being increasingly considered as a possible brain injury mechanism during contact sports and military operations. Due to this great importance, it is essential to fundamentally understand the cavitation bubble dynamics in varying biological systems. In this dissertation, experimental and theoretical characterization of cavitation dynamics in soft matters from tissue simulant soft gels (e.g., agar, agarose, and gelatin) to actual live cells are performed.First, cavitation nucleation and bubble growth in different types of tissue simulants are studied under translation impact. The critical acceleration that corresponds to onset of cavitation bubble burst is measured in the soft gels and individual gel types indicate significantly different trends in the critical acceleration and bubble shape (e.g., A gel-specific sphere-to-saucer transition) with increasing gel stiffness. Possible underlying mechanisms of the experimental observations are provided in the concepts of a damaged zone and crack propagation. This study sheds light on potential links between traumatic brain injuries and cavitation bubbles induced by translational acceleration, the overlooked mechanism in the literature.
Second, a drop-tower-based repetitive impact tester is newly designed to mimic biological systems under a wide range of impact conditions including high strain rate as well as repeated loadings. Theoretical approach based on a two-degree-of-freedom mass-spring-damper model simulates the transient dynamic response of the system with experimental validations. As one of main implications, a novel noncontact detecting method is developed to capture initial cavitation nucleation during successive drop events. This study also observes impact characteristics dependent cavitation bubble responses, which have not been characterized by other methods (e.g., laser or ultrasound induced cavitation rheology).
Finally, although significant efforts have been made in the dynamic response of tissue simulants, there is a huge knowledge gap between the soft gels and actual live cells due to the lack of the experimental capability and of knowledge for complicated cell responses. Newly designed in vitro experimental setup and systematic characterization of specific cell types, i.e., Hs27 fibroblasts, enable a testing of spatio-temporal responses of cells under mechanical impact by controlling their static and dynamic behaviors.
ContributorsKim, Chunghwan (Author) / Kang, Wonmo WK (Thesis advisor) / Acharya, Abhinav AA (Committee member) / Rajagopalan, Jagannathan JR (Committee member) / Oswald, Jay JO (Committee member) / Kim, Jeonglae JK (Committee member) / Arizona State University (Publisher)
Created2023