![]() ![]() Post flooding damage assessment of earth dams and historical reservoirs using non-invasive geophysical techniques This suggests the possibility of assessing damage severity using ultrasonic techniques. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. Measurements on the shear stiffnesses show behavior similar to the transverse moduli. On the other hand, the transverse moduli obtained from ultrasonic measurements decrease continually until 1200 C. This agrees well with the results of destructive tests by other authors. The Youngs' modulus in the fiber direction as obtained from ultrasonic measurements decreases significantly at 600 C but retains its original value at temperatures above 1200 C. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400 C, for 100 hr. Oxidation damage is assessed in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. Ultrasonic measurements using the surface wave method are found to correlate well with measurements of degradation of mechanical properties obtained independently by other authors using destructive methods. Results indicate that most microcracks produced by thermal shock are located near sample surfaces. Thermal shock treatment from different temperatures up to 1000 C is applied to produce the microcracks. Thermal shock damage is assessed in ceramic samples of reaction bonded silicon nitride (RBSN). This damaged-induced anisotropy is determined by measuring the velocities of ultrasonic waves in different propagation directions. It focuses on damage caused by thermal shock or oxidation at elevated temperatures, which often results in elastic anisotropy. This paper addresses the application of ultrasonic sensing to damage assessment in ceramics and ceramic matrix composites. We compare the results of the linear and nonlinear techniques, and value them against the visual damage evaluation.Īssessment of damage in ceramics and ceramic matrix composites using ultrasonic techniquesĬhu, Y. At the same time, measurement of resonant frequencies and damping ratios as function of vibration amplitude are performed using a frequency domain technique as well as a time domain technique. At different levels of damage, a modal analysis is carried out, assuming the structure to behave linearly. In this paper, nonlinear vibration techniques are applied to investigate stages of progressive damage in RC beams induced by static loading tests. Reinforced concrete (RC) structures are subject to microcrack initiation and propagation at load levels far below the actual failure load. Giri, C.ĭamage assessment in reinforced concrete using nonlinear vibration techniques This study demonstrates that satellite-based geospatial techniques can effectively add spatial perspectives to natural disaster damages, and in particular for this case study, tornado damages. Consequently, linear regression models, even incorporating just a single band, appear effective in identifying F-scale damage categories using satellite imagery. Our results indicate strong relationships between spatial indices computed within a local window and tornado F-scale damage categories identified through the ground survey. We employed several geospatial approaches, specifically the Getis index, Geary's C, and two lacunarity approaches to categorize damage characteristics according to the original Fujita tornado damage scale (F-scale). Using one of the strongest tornado events in US history, the Oklahoma City Tornado, as a case example, we digitized the tornado damage path and co-registered the damage path using pre- and post-Landsat Thematic Mapper image data to perform a damage assessment. Satellite image analysis, because of its global ubiquity, its ability for repeated independent analysis, and, as we demonstrate here, its ability to verify on-site damage assessment provides an interesting new perspective and investigative aide to researchers. Although necessary for complete assessment of damage areas, ground-based damage surveys conducted in the aftermath of natural hazard passage can sometimes be potentially complicated due to on-site difficulties (e.g., interaction with various authorities and emergency services) and hazards (e.g., downed power lines, gas lines, etc.), the need for rapid mobilization (particularly for remote locations), and the increasing cost of rapid physical transportation of manpower and equipment. Remote sensing of a natural disaster's damage offers an exciting backup and/or alternative to traditional means of on-site damage assessment. Categorizing natural disaster damage assessment using satellite-based geospatial techniques
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