Master of Science, University of Akron, 2010, Civil Engineering

A vibration-based testing methodology is presented that assesses fatigue behavior of material for metallic structure. To minimize the testing duration, the test setup is designed for a base-excited multiple-specimen arrangement driven in a high-frequency resonant mode, which allows completion of fatigue testing in an accelerated period. A high performance electro-dynamic exciter (shaker) is used to generate harmonic oscillation of cantilever beam specimens, which are clasped on the shaker armature with specially-designed clamp fixtures. The shaker operates in closed-loop control with dynamic specimen response feedback provided by a scanning laser vibrometer. A test coordinator function is developed to synchronize the shaker controller and the laser vibrometer, and to complete the closed-loop scheme: the test coordinator monitors structural health of the test specimens throughout the test period, recognizes change in specimen dynamic behavior due to fatigue crack initiation, terminates test progression, and acquires test data in an orderly manner. Topological design is completed by constructing an analytical model and performing finite element analysis for the specimen and fixture geometry such that peak stress does not occur at the clamping fixture attachment points. Experimental stress evaluation is conducted to verify the specimen stress predictions. A successful application of the experimental methodology is demonstrated by validation tests with aluminum specimens subjected to fully-reversed bending stress.

Committee: Gun Jin Yun Dr. (Advisor); Craig C. Menzemer Dr. (Committee Member); Wieslaw K. Binienda Dr. (Committee Member) Subjects: Engineering

Master of Science, University of Akron, 2006, Civil Engineering

The main objective of this study is to show the specific capabilities of the Scanning Laser Vibrometer (SLV) for global damage detection using a recent defect energy parameter technique proposed by Saleeb and coworkers. The experimental technique used for extraction of signature is the first and most important part in any damage detection technique. Signatures considered here are full-field SLV measurements for modal shapes and associated frequencies of plated structures. The damage feature extraction capability was studied extensively by analyzing various simulation and experimental results. The practical significance in structural health monitoring is that the detection at early stages of small-size defects is always desirable. The amount of changes in the structure's response due to these small defects was determined to show the needed level of accuracy in the experimental methods. The signal – noise ratio of experiment shows the capability of the same experiment to be used for damage detection purpose. Various experiments were performed to verify a significant signal – noise ratio for a successful detection. Very high number of scanning points, for optical experimental measurement, for any civil structure can be impractical and uneconomical. So, a pragmatic direction for the development of new experimental measurement tools was studied where different number of scanning points and different types of statically loaded simulations were performed to verify the specific capabilities of the defect energy parameter technique. It was further observed that powerful graphic user interface should also be an integral part in any present in the damage detection scheme for successful and more accurate detection. Furthermore, some potential use of SLV techniques in detection are provided, both for dynamic and static applications.

Committee: Atef Saleeb (Advisor) Subjects:

Master of Science, University of Akron, 2005, Civil Engineering

There is a pressing need to develop effective techniques for structural health monitoring (SHM), so that the safety and integrity of the structures can be improved. The main objective of this study is to evaluate the dynamics-based damage detection techniques for the plate-type structures using smart piezoelectric materials and modern instrumentation like Scanning Laser Vibrometer (SLV). The study comprises of testing an E-glass/epoxy composite plate with an embedded delamination and an aluminum plate with a saw-cut crack using two different actuator-sensor systems: (1) SLV with PZT (lead-zirconate-titanate) actuators (PZT-SLV), and (2) Polyvinylidenefluoride (PVDF) sensors with PZT actuators (PZT-PVDF). The numerical finite element (FE) analysis is also performed to complement the damage detection. Three relatively new damage detection algorithms (i.e., Simplified Gapped Smoothing Method (GSM), Generalized Fractal Dimension (GFD), and Strain Energy Method (SEM)) are employed to analyze the experimental and numerical mode shape data and Uniform Load Surface (ULS). From the damage detection outcomes, it is observed that the PZT-SLV system proves to be more convenient and effective, and it is capable of scanning a large number of points over the entire plate specimens; while the PZT-PVDF system, in which the curvature mode shapes are directly acquired, exhibits good sensitivity to damage. The damage detection algorithms like the GSM, GFD and SEM based on the utilization of three consecutive mode curvatures (modes 3 to 5) and resulting ULS curvature successfully identify the presence and location of delamination in the composite plate; however, they do not show much success in locating the saw-cut crack in the aluminum plate with the same mode curvatures. Using the transverse bending dominated modes (e.g., modes 6 and 12), the above damage detection algorithms are capable of locating the saw-cut crack in the aluminum plate. Due to refined analysis of FE approach, all t (open full item for complete abstract)

Committee: Pizhong Qiao (Advisor) Subjects: