Publications

In this study, an elastic model for static and nonlinear impact responses of a composite sandwich plate on an elastic half-space including the anti-plane core effect is developed. The effects of the elastic half-space and the anti-plane core are studied, and the contact force history and maximal deflection are predicted. Compared to the available analytical static analysis of rigid plates on a solid half-space and the numerical finite element modeling using LS-DYNA, the proposed theoretical method shows its validity and advantages in predicting the static and impact behaviors of sandwich plates sitting on a solid half-space. The predicted non-uniform distribution of transferred force under static load sheds new light on the understanding of force action mechanism between the sandwich system and the solid half-space. The two important impact factors (i.e., the maximal deflection and the peak contact force) provided by this study can be used to determine the damage size and position. Further, the semi-analytical model developed can be served as a basis for optimal design of fully backed sandwich collision protection systems, of which both minimizing the rebounded residual velocity of the projectile and keeping the underneath protected structures intact are important.

This paper presents an innovative approach that utilizes infused images from vibration signals and visual inspections to enhance the efficiency and accuracy of structure health monitoring through GoogLeNet. Scrutiny of the structure of GoogLeNet identified four key parameters, and thus, the optimization of GoogLeNet was completed through manipulation of the four key parameters. First, the impact of the number of inception modules on the performance of GoogLeNet revealed that employing eight inception layers achieves remarkable 100% accuracy while requiring less computational time compared to nine layers. Second, the choice of activation function was studied, with the Rectified Linear Unit (ReLU) emerging as the most effective option. Types of optimizers were then researched, which identified Stochastic Gradient Descent with Momentum (SGDM) as the most efficient optimizer. Finally, the influence of learning rate was compared, which found that a rate of 0.001 produces the best outcomes. By amalgamating these findings, a comprehensive optimized GoogLeNet model was found to identify damage cases effectively and accurately through infused images from vibrations and visual inspections.

Mode shape curvature-based method was originally developed to identify the damage in one-dimensional beam structures. In this paper, the method is generalized to fit for identification of damages in plate structures, using two-dimensional mode shape curvatures. The modified method only requires the first few curvature mode shapes of the plate before and after damage. To evaluate the effectiveness of the proposed method, numerical simulations considering different types of and multiple damages as well as experimental modal analysis on a steel plate with clamped and free edges have been conducted. The final results show that the proposed method works well to detect the damages.

A new fatigue model suitable for polymer matrix composites is proposed, based on dimensional analysis of testing and material variables involved in a fatigue test. The new model has a good physical and theoretical foundation ... | Find, read and cite all the research you need on Tech Science Press

The major objective of this study is to correlate rocking foundation performance parameters with their capacity parameters and earthquake demand parameters using results obtained from 142 centrifuge and shaking table experiments, which include a variety of soil conditions, foundation geometries, structural models, and types of ground motions. The analysis presented in this paper considers all experimental results together, collectively as big data, through nondimensional parameters to identify hidden relationships among different parameters in a capacity-demand-performance framework. Rocking system performance parameters such as seismic energy dissipation in soil, permanent settlement, peak and permanent rotation, tipping-over stability ratio, self-centering ratio, rocking moment capacity, and acceleration amplification ratio are correlated with rocking system capacity parameters such as critical contact area ratio, rocking coefficient, and slenderness ratio of rocking systems and the earthquake demand parameters such as Arias intensity and peak ground acceleration of earthquake. It is found that energy dissipation and settlement correlate reasonably well with rocking coefficient and Arias intensity of earthquake, while peak rotation and acceleration amplification ratio correlate reasonably well with slenderness ratio, rocking coefficient, and peak ground acceleration of earthquake. Rocking foundations in clayey soils show superior performance in terms of seismic energy dissipation and permanent settlement compared to those in sandy soils, especially for relatively small to medium intensity shakings, and the ability of rocking foundations to de-amplify the earthquake motion increases as the magnitude of shaking increases.

Aerospace structures experience a severe amount of stress over their life cycle. For example, structures located on the exterior surface of a space shuttle often undergo severe stress due to the presence of variable pressure and high gravity. Additionally, with a huge influx of small and micro-sized satellites, the probability of an impact in the outer-space orbits is now a concerning factor. There is also a presence of similar disturbing events for commercial flights. Only within the USA, the incidents of planes striking birds are more than 40 times on average per day, as per a report published by the Federal Aviation Administration (FAA) in 2019. Now, the skin of the planes and the rockets are usually made of various composite light-weight materials and multiple layers of specially engineered tempered glasses to withstand excessive stress due to the variation of pressure and temperature and unwanted impacts of a small scale. However, repetitive occurrences of impacts on the skin of the aerospace structures, even on the small-scale, may lead to the generation of severe mechanical stress which can lead to a catastrophic incident. Hence, it is imperative to identify, locate, analyse and monitor any accidental impact on aerospace structures in realtime. Various kinds of strain sensors are generally used for aerospace structures. However, the application of such sensors is restricted in places where visibility is enforced, such as the cockpits and windows. Such restriction can be overcome by incorporating a special kind of layout of optical fibre sensors that use fibre Bragg grating (FBG) principle. Specifically, FBG principle can be enforced in specially designed fibre optics. When light travels through such fibre optics, a specific wavelength of light (Bragg wavelength) reflects in the opposite direction. In the presence of any miniscule mechanical stress on such fibre optics, its physical deformation creates an axial strain. This then results the Bragg wavelength to be shifted. This proportional shift caused by the strain due to an event of impact can be physically measured using optical interrogators. Moreover, use of optical fibres on glasses does not significantly impede the visibility. The non-destructive damage assessment (NDDA) of impacts on aerospace structures by using the FBG optical sensors involves multiple steps, such as location estimation, time identification and magnitude quantification in correctly evaluating an event of impact. Furthermore, a remote and real-time scheme is usually preferred in such NDDA operations. This book chapter presents a real-time and wireless structural health monitoring method for analysing impact responses of aerospace structures using FBG optical sensors. A theoretical background is discussed, and a laboratory-scale experimental measurement is presented.

An original model for impact analysis of elastic-plastic sandwich beams is presented, and the effect of sandwich damping is uniquely introduced in the analysis by considering the gradient of beam compliance. By incorporating the compliance (or stiffness) and compliance gradient of the sandwich beams to the equation of motion of the projectile, the standard mass-spring model for the sandwich system is uniquely recovered. Both the elastic and elastic-plastic impact processes are analyzed and compared with elastic model of no sandwich damping effect. The proposed impact model is validated with the elastic finite element analysis using LS-DYNA. A parametric study on the influences of velocity and mass of the projectile on the impact response of elastic and elastic-plastic sandwich beams is conducted, and it reveals the significant contribution of the sandwich damping and plasticity to the impact response.

Pervious concrete has been widely used in parking lots and airport fields. However, excessive cracking and spalling issues of pervious concrete remain a challenge for its adoption in wider applications, since its binding material proportion is low and the use of fine aggregates is nearly zero. When loaded in compression, failure appears first in the weak concrete zone, induced by the random distribution of voids. The process continues until failure of the whole specimen. Fibre-reinforcement delays crack generation and enhances the strength of the host matrix. However, the bonding mechanism between the fibre and concrete matrix is a controversy in the literature. In this study, the influence of polypropylene fibre inclusion on the strength and stiffness of pervious concrete microstructure was studied through delicate interface modelling. Two-dimensional microstructures of pervious concrete were generated using Matlab and Ansys parametric design languages. A cohesive-zone technique was then used to model the interface between fibres and the concrete matrix. Load–displacement plots were thus obtained in Ansys for specimens under compression for various void–fibre percentages and different treated interface properties.

Due to increased traffic volumes and damaged bridge structures, there is a pressing need to develop a collision protection system for highway bridges against over-height truck impact. In this study, a linear elastic model for impact response of bottom face sheet-rigidly supported sandwich structures including shear-off effect is developed. The solutions of discrete model, concentrated and distributed loading cases for collision protection I-Lam system are obtained, of which the contact force history and maximum deflection are predicted. Compared to the LS-DYNA finite element analysis (FEA), the proposed analytical methods show their accuracy and simplicity in predicting the impact response. The discrete model shows a better correlation with FEA predictions; while the model with distributed forces overestimates the deflection of the top face sheet but under-evaluates the peak contact force. The relatively simple and accurate models developed can be used to approximate the impact response of rigidly supported sandwich structures.

The growing demand for real-time damage assessment necessitates development of an efficient inverse analysis algorithm with consideration of practical issues such as uncertainty in measurement. A mathematical model-based inverse analysis scheme is proposed to identify impact locations and reconstruct impact load time history of a simply supported plate through multiple levels of analysis. The proximity of the impact location is first determined by the triangulation method and the impact location is then refined by minimization of an objective function through the particle swarm optimization method (PSO). Loss of data due to filtration is addressed in a further level by performing an interval analysis based on extreme measurement errors. The outcome of the analyses is a mean impact location, a load time history, and a range of likely deviations. The extreme deviation in impact location is shown by bounding lines, which form a rectangle. The deviation in load time history is also shown by upper and lower bounding sinusoidal curves. The results of the analyses indicate that the proposed method can effectively locate the impact point and reconstruct the load time history even with the existence of noise in the measured response.

This paper presents a coupled, dynamic vehicle and honeycomb composite sandwich bridge deck interaction model.The composite sandwich deck consists of E-glass fibers and polyester resin.Its core consists of corrugated cells in a sinusoidal configuration along the travel direction.First, analytical predictions of the effective flexural and transverse shear stiffness properties of the sandwich deck were obtained in the longitudinal and transverse directions.These were based on the modeling of equivalent properties for the face laminates and core elements.Using the first order shear sandwich theory, the dynamic response of the sandwich deck was analyzed under moving dynamic loads.A dynamic vehicle simulation model was used for the latter, assuming that the deck response is the only source of excitation (i.e., its roughness was assumed to be negligible).Subsequently, the dynamic load factors of the sandwich bridge deck were calculated for different traveling velocities.The results suggest that the dynamic load factors vary with the traveling speed and increase significantly with decreasing deck stiffness.Considering multiple degrees of freedom for the vehicle further amplifies the dynamic loading factor and increases the vibration generated by vehicles.

Displacement is critical when it comes to the evaluation of civil structures. Large displacement can be dangerous. There are many methods that can be used to monitor structural displacements, but every method has its benefits and limitations. Lucas-Kanade (LK) optical flow is recognized as a superior computer vision displacement tracking method, but it only applies to small displacement monitoring. An upgraded LK optical flow method is developed in this study and used to detect large displacement motions. One motion controlled by a multiple purpose testing system (MTS) and a free-falling experiment were designed to verify the developed method. The results provided by the upgraded LK optical flow method showed 97 percent accuracy when compared with the movement of the MTS piston. In order to capture the free-falling large displacement, the pyramid and warp optical flow methods are included in the upgraded LK optical flow method and compared with the results of template matching. The warping algorithm with the second derivative Sobel operator provides accurate displacements with 96% average accuracy.

An effective procedure is proposed for scanning and separating the vertical (flexural) and torsional–flexural frequencies of thin-walled girder bridges by a moving single-axle test vehicle, modeled as a two degree-of-freedom (DOF) system to account for the vertical and rocking motions. The response of the vehicle is not directly used, since it may mask the bridge frequencies by self frequencies. Instead, the wheel-bridge contact responses are used for being free of vehicle’s frequencies. To start, closed-form solutions are derived for the vertical, lateral, and torsional vibrations of the mono-symmetric beam. Then, the contact responses are calculated from the vehicle responses, considering the discrete nature of field data. The vertical and torsional–flexural frequencies of the bridge are separated by using the vertical and rocking motions derived from the contact responses without prior knowledge of the mode shapes. The proposed technique is numerically validated with the following conclusions: (1) the wheels’ contact responses outperform the vehicle response in that more high frequencies of the bridge can be detected; (2) the torsional–flexural​ frequencies can better be detected from the wheel closer to the bridge edge; and (3) the vertical and torsional–flexural frequencies of bridges can be successfully separated by the proposed procedure even in the presence of pavement roughness, which is helpful for field applications.