A Combined Machine Learning and Model Updating Method for Autonomous Monitoring of Bolted Connections in Steel Frame Structures Using Vibration Data

This research paper presents a novel structural health monitoring strategy based on a hybrid machine learning and finite element model updating method for the health monitoring of bolted connections in steel planer frame structures using vibration data. Towards this, a support vector machine model is trained with the discriminative features obtained from time history data, and those features are used to distinguish between damaged and undamaged joints. An FE model of the planer frame is considered where the fixity factor (FF) of a joint is modeled with rational springs and the FF of the spring is assumed as the severity level of loosening bolts. The Cat Swarm Optimization technique is further applied to update the FE model to calculate the fixity factors of damaged joints. Initially, the method is applied to a laboratory-based experimental model of a single-story planer frame structure and later extended to a pseudo-numerical four-story planer frame structure. The results show that the method successfully localizes the damaged joints and estimates their fixity factors

Guided wave based nondestructive analysis of localized inhomogeneity effects in an advanced sandwich composite structure

In this paper, we present a nondestructive analysis of localized inhomogeneity effects on guided wave propagation in an advanced sandwich composite structure. In the process, guided wave dispersion curves were semi-analytically determined for the structure to accurately identify different wave modes in experimental and numerical analysis signals. Finite element simulation of wave propagation in the target structure was then carried out in ABAQUS and validated with the experiment. Significant influences on the wave mode amplitudes were observed due to the presence of a localized inhomogeneity in the structure. An inhomogeneity identification strategy was prepared based on the amplitude changes in the registered guided wave signals from a predefined piezoelectric transducer network. The influence of varying elastic modulus and mass-density of the inhomogeneous region on the wave mode amplitudes and the corresponding inhomogeneity-index magnitudes were also studied

Wave propagation in a honeycomb composite sandwich structure in the presence of high-density core using bonded PZT-sensors

Honeycomb Composite Sandwich Structure (HCSS), is one of the novel materials that has been adopted universally to form major structural components of aerospace, marine and automotive vehicles due to its high strength to weight ratio and high energy-absorption capabilities. In this research paper, the scope to study the general characteristics of guided wave (GW) propagation in an HCSS plate with the presence of a high-density (HD) core subjected to timedependent transient surface excitations is presented numerically and experimentally. Significant effects are detected due to the presence of HD core in terms of decay in amplitude and reduction in group velocity of the output GW signals. A two-dimensional (2D) numerical model is made in ABAQUS. An effective non-reflecting boundary condition (NRBC) is modeled in ABAQUS in order to mitigate the undesirable boundary reflections during numerical simulation. Good agreements between the numerical and experimental results are noticed for all the cases studied

Study of guided wave propagation in a honeycomb composite sandwich plate in presence of a high-density core region using surface-bonded piezoelectric transducers

"Honeycomb Composite Sandwich Structure" (HCSS), is a novel material that has been adopted globally as a major structural component in aerospace, marine and automotive vehicles due to its high strength to weight ratio and high energy-absorption capability. In this study, a combined numerical and experimental study is carried out in an effort to understand the attributes of the propagating Guided Wave (GW) modes in the presence of a High-Density (HD) core zone in a HCSS. Owing to the complex structural characteristics, the GW propagation study in HCSS with HD-core zone inherently possesses many challenges. Therefore, Two Dimensional (2D) numerical simulations of wave propagation in the HCSS without and with HD-core region are accomplished using surface bonded Piezoelectric Wafer Transducers (PWTs). Results of the numerical study show that the presence of the HD core leads to substantial decrease in the amplitude and the group velocity of the output GW signal. In order to validate the results of the simulation, experiments were conducted, which shows good agreement between the experimental and numerical results is in all the cases considered. In order to study the effect of size of the HD core zone on the group velocity and the amplitude of the propagating wave modes, a parametric study is also carried out for a selected range of the HD core widths. It is observed that the group velocity and the amplitude of the received GW modes are just about inversely proportional to the HD core width

Ultrasonic guided wave propagation and detection of high density core region in a honeycomb composite sandwich structure using embedded piezoelectric transducers

An organized numerical and experimental study is carried out in order to understand ultrasonic guided wave (GW) propagation and interaction with a high density (HD) core region in a honeycomb composite sandwich structure (HCSS). Also the location of HD core region in a HCSS using embedded piezoelectric wafer transducer (PWTs) is investigated in this study. Due to complex structural characteristics, the study of guided wave (GW) propagation in HCSS with HD-core region inherently carries many challenges. Therefore, a three-dimensional (3D) numerical simulation of GW propagation in the HCSS with and without HD core region is carried out using embedded PWT network. It is observed that the presence of HD core significantly reduces the amplitude of the propagating GW modes. In order to verify the numerical results, experiments are conducted in the laboratory. A good agreement between the numerical and experimental results is observed, in all the cases studied. Finally, based on the change in amplitude of the received GW modes, the location of an unknown HD core region, within the PWT array is determined by applying a probability based signal difference coefficient (SDC) algorithm