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:

MS, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

Metamaterials are artificially engineered materials that exhibit properties not found in any naturally occurring materials. Recently, there has been a significant interest in locally resonant elastic metamaterials because of their remarkable ability to attenuate shock and vibration significantly due to the presence of bandgaps, defined as the frequency range in which elastic waves cannot propagate. The existing literature on metamaterials assumes that the structure remains intact and undamaged. However, all the structures in the real world are inevitably susceptible to damage caused by the factors such as manufacturing defects, material impurities, corrosion, etc. It is crucial to understand how metamaterials perform when subjected to damage for their effective utilization. The main objective of this research is to address the insufficient knowledge on monitoring and evaluating the structural health of locally resonant elastic metamaterials, specifically with regard to detecting any damage. This research aims to develop a physics-based mathematical framework to explain the fundamental structural dynamics of damaged metamaterials. A new damage detection method has been formulated to detect the extent of damage and locality in locally resonant elastic metamaterials. This method involves utilizing the driving point FRFs to determine the damage index for undamaged and damaged metastructures under consideration. The existence of damage introduces anomalies in the Frequency Response Functions (FRFs), and multiple high-magnitude peaks have been observed inside the bandgap region for the damaged metamaterials. These peaks result from the occurrence of highly localized modes near the damage location. The presented method has been extensively validated through FE simulations using ANSYS and experimental modal analysis using a laser Doppler vibrometer. The results showed excellent agreement, thus providing a reliable way to evaluate the structural health of locally resonant el (open full item for complete abstract)

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

Doctor of Philosophy, Case Western Reserve University, 2006, Mechanical Engineering

Researchers have already demonstrated that vibration in a simple planetary gear train can be reduced by properly indexing the planet pinions so that their spacing errors tend to cancel. Their kinematic analysis applied only to the special case of planet spacing errors in the form of runout. The present research expands on that concept by considering a general kinematic solution, that is, for all spacing errors. It is hypothesized that by this technique one can reduce the kinematic transmission error attributable to vibration and noise. The first part of this research is a feasibility study evaluating whether this technique, based upon a kinematic analysis for reducing the spacing error, will tend to reduce gear noise. The equations are first developed for the simple planetary where the planets may be simply indexed to produce the minimum net transmission error. Then the technique is expanded to the compound planetary. In the latter case the gears must be timed so the planets cannot be simply indexed, but must be exchanged with other gears. This is called planet matching. The analyses are conducted at “snapshots” by advancing the gear train by one tooth increments. The goal is to find the planet assembly combination which produces the minimum peak to peak net transmission error. Transmission error is well accepted as the greatest source of gear noise in simple gear pair systems. In the planetary gear train, however, transmission error is a much more complex concept and has no universally accepted definition. I postulate that it is the overall train error, entitled net transmission error, which should be minimized. The gear noise reduction strategy was tested by experiment. In support of the experimental work, net transmission error was measured across the planetary in a fully functioning industrial transmission by means of laser vibrometry. The second part of this research evaluates the application of rotational laser vibrometers as applied to transmission error meas (open full item for complete abstract)

Committee: Maurice Adams (Advisor) Subjects: Engineering, Mechanical

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, 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: