MS, University of Cincinnati, 2024, Engineering and Applied Science: Mechanical Engineering

Vibration based methods for Structural Health Monitoring (SHM) have become increasingly popular over the last few decades. In this field, non-contact measurement techniques have garnered a lot of attention due to its capacity to provide spatially dense full-field measurements. One such method is photogrammetry, which works on the technique of tracking an object or feature on the surface of a structure. This study proposes a fully non-contact method for estimating the Operational Deflection Shape (ODS) of a plate-like structure based on detecting and tracking a laser projected feature which can provide a dense measurement grid and has no permanent effect on the surface of the structure being measured. It has been long established that any local damage to a structure defined by a loss of stiffness causes local anomalies in the structure's ODS, which can be localized by taking the second derivative of the ODS, commonly known as its curvature. In this study, a damage index is formulated for plate-like structures using higher order derivatives, namely the second, fourth and sixth derivatives, with different orders of accuracy and is shown to successfully identify damage with no knowledge of the structure's undamaged state. The derivatives are computed using the central finite difference scheme. Both experimental and numerical studies are conducted to test the robustness and efficacy of the proposed index. In the numerical investigations, a Finite Element Model (FEM) is used to simulate and extract the natural frequencies and mode shapes of a plate-like structure under free-free boundary conditions. The robustness of the proposed damage index is studied for varying levels of measurement errors, simulated by adding white Gaussian noise. The effects of different parameters like the location and size of the damage are also studied. In the experimental investigation, a damaged steel plate is acoustically excited using an electric speaker at a frequency very close to o (open full item for complete abstract)

Committee: Yongfeng Xu Ph.D. (Committee Chair); Allyn Phillips Ph.D. (Committee Member); Jay Kim Ph.D. (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2004, Engineering : Mechanical Engineering

The dissertation is to address the need, in contact mechanics, of efficient and effective solutions to certain 3-D contact problems. The solutions developed here are based on underlying analytical solutions to pyramidal loading elements. This feature, along with other characteristics, distinguishes this method from other numerical solutions. The research work is logically divided into three subsequent parts, each of which addresses a particular aspect of the project: (1) Developed analytical solution sets in closed form to pyramidal loading profiles. First, a set of Boussinesq-Curruti equations to linear/bilinear distribution of normal and tangential loading over a triangular area are derived and evaluated. Second, solution sets to normal and tangential surface loading pyramids are constructed. The work provides a solution set to a basic loading element, which is the foundation of the development of effective and efficient semi-analytical solutions to 3-D contact problems with general geometry and loading profile. (2) Developed a semi-analytical approach (non-incremental algorithm) to 3-D normal contact problems with friction. This approach treats normal contact (indentation) phenomenon as a static problem. Based on fully coupled governing equations, the algorithm of contact detecting and stick/slip partitioning is designed as nested iterations, to fulfill contact boundary conditions. The computation shows that it is an efficient algorithm. Numerical examples are presented to show the accuracy and efficiency of the method.(3) Developed a semi-analytical approach (incremental algorithm) to 3-D contact problems with friction. This approach treats contact as a dynamic problem. The general dynamic models are simplified into quasi-static models in many practical cases that inertial force can be ignored. The incremental algorithm is designed to solve the quasi-static problems. The computation shows that the algorithm works very well for cases featuring both similar and di (open full item for complete abstract)

Committee: Dr. EDWARD BERGER (Advisor) Subjects: Engineering, Mechanical