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Abstract
Cracks are common defects in concrete structures. Thus far, crack inspection has been manually performed using the contact inspection method. This manpower-dependent method inevitably increases the cost and work hours. Various noncontact studies have been conducted to overcome such difficulties. However, previous studies have focused on developing a methodology for non-contact inspection or local quantitative detection of crack width or length on concrete surfaces. However, crack depth can affect the safety of concrete structures. In particular, although macrocrack depth is structurally fatal, it is difficult to find it with the existing method. Therefore, an experimental investigation based on non-contact infrared thermography and multivariate machine learning was performed in this study to estimate the hidden macrocrack depth. To consider practical applications for inspection, an experiment was conducted that considered the simulated piloting of an unmanned aerial vehicle equipped with infrared thermography equipment. The crack depths (10–60 mm) were comparatively evaluated using linear regression, gradient boosting, and random forest (AI regression methods).

Key Words
AI; Concrete macrocrack; machine learning; infrared thermography; UAV

Address
Jaehoon Bae:Department of Architectural Design, College of Engineering Science, Chonnam National University, Jeonnam 59626, Republic of Korea Arum Jang:School of Civil, Environmental, and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea Min Jae Park:School of Civil, Environmental, and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea Jonghoon Lee:School of Civil, Environmental, and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea Young K. Ju:School of Civil, Environmental, and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea

Abstract
In this study, considering dissipated energy in fracture process zone (FPZ), a novel criterion based on maximum strain energy release rate (SER) for orthotropic materials is presented. General case of in-plane loading for cracks along the fibers is assumed. According to the experimental observations, crack propagation is supposed along the fibers and the reinforcement isotropic solid (RIS) concept is employed as a superior model for orthotropic materials. SER in crack initiation and propagation phases is investigated. Elastic properties of FPZ are extracted as a function of undamaged matrix media and micro-crack density. This criterion meaningfully links between dissipated energy due to toughening mechanisms of FPZ and the macroscopic fracture by defining stress intensity factors of the damaged zone. These coefficients are used in equations of maximum SER criterion. The effect of crack initiation angle and the damaged zone is considered simultaneously in this criterion and mode II stress intensity factor is extracted in terms of stress intensity factors of damage zone and crack initiation angle. This criterion can evaluate the effects of FPZ on the fracture behavior of orthotropic material. Good agreement between extracted fracture limit curves (FLC's) and available experimental data proves the ability of the new proposed criterion.

Key Words
crack initiation angle; fracture process zone; orthotropic materials; reinforcement isotropic solid model; strain energy release rate

Address
Zahra Khaji and Mahdi Fakoor:Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran

Abstract
In this study, the three-dimensional finite element method is used to analyze the behavior of corner cracks in finitethickness plates repaired with a composite patch. The normalized stress intensity factor at the crack front is used as fracture criterion. Comparison of stress intensity factor values at the internal and external positions of repaired quarter-elliptical corner crack was done, for three repair techniques. The influence of mechanical and geometrical properties of the adhesive layer and the composite patch on the variation of the stress intensity factor (SIF) at the crack-front was highlighted. The obtained results show that the application of double patch leads to a remarkable reduction of SIF at the crack front, compared to facial and lateral repairs.

Key Words
adhesive; bonded composite repair; corner crack; finite element method; stress intensity factor

Address
Abdelkader Boulenouar, Mohammed A. Bouchelarm:Laboratoire de Materiaux et Systemes Reactifs - LMSR. Djillali Liabes University of Sidi Bel Abbes. 22000 Sidi Bel Abbes, Algeria Noureddine Benseddiq:2Unite de Mecanique de Lille, EA 7512 UML, University of Lille, 59000 Lille, France

Abstract
In this study, a two-dimensional model of the contact problem has been examined using the finite element method (FEM) based software ANSYS and based on the multilayer perceptron (MLP), an artificial neural network (ANN). For this purpose, a functionally graded (FG) half-infinite layer (HIL) with a crack pressed by means of two rigid blocks has been solved using FEM. Mass forces and friction are neglected in the solution. Since the problem is analyzed for the plane state, the thickness along the z-axis direction is taken as a unit. To check the accuracy of the contact problem model the results are compared with a study in the literature. In addition, ANSYS and MLP results are compared using Root Mean Square Error (RMSE) and coefficient of determination (R2), and good agreement is found. Numerical solutions are made by considering different values of external load, the width of blocks, crack depth, and material properties. The stresses on the contact surfaces between the blocks and the FG HIL are examined for these values, and the results are presented. Consequently, it is concluded that the considered non-dimensional quantities have a noteworthy influence on the contact stress distributions, and also, FEM and ANN can be efficient alternative methods to time-consuming analytical solutions if used correctly.

Key Words
artificial neural network; contact mechanics; finite element method; functionally graded

Address
Murat YayIaci and Sevval Ozturk:Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey Ecren Uzun YayIaci:Surmene Faculty of Marine Science, Karadeniz Technical University, 61530, Trabzon, Turkey Mehmet Emin Ozdemir:Department of Civil Engineering, Cankiri Karatekin University, 18100, Cankiri, Turkey Sevil Ay:Department of Civil Engineering, Artvin Coruh University, 08100, Artvin, Turkey

Abstract
Localizing damages is an essential task to monitor the health of the structures since they may not be able to operate anymore. Among the damage detection techniques, non-destructive methods are considerably more preferred than destructive methods since damage can be located without affecting the structural integrity. However, these methods have several drawbacks in terms of detecting abilities, time consumption, cost, and hardware or software requirements. Employing artificial intelligence techniques could overcome such issues and could provide a powerful damage detection model if the technique is utilized correctly. In this study, the crack localization in flat and folded plate structures has been conducted by employing a Backpropagated Artificial Neural Network (BPANN). For this purpose, cracks with 18 different dimensions in thin, flat, and folded structures having 15°, 30° 45° and 60° folding angle have been modeled and subjected to free vibration analysis by employing the Classical Plate Theory with Finite Element Method. A Four-nodded quadrilateral element having six degrees of freedom has been considered to represent those structures mathematically. The first ten natural frequencies have been obtained regarding healthy and cracked structures. To localize the crack, the ratios of the frequencies of the cracked flat and folded structures to those of healthy ones have been taken into account. Those ratios have been given to BPANN as the input variables, while the crack locations have been considered as the output variables. A total of 500 crack locations have been regarded within the dataset obtained from the results of the free vibration analysis. To build the best intelligent model, a feature search has been conducted for BAPNN regarding activation function, the number of hidden layers, and the number of hidden neurons. Regarding the analysis results, it is concluded that the BPANN is able to localize the cracks with an average accuracy of 95.12%.

Key Words
crack detection; Finite Element Method; folded plates; machine learning; neural network; vibration

Address
Oguzhan Das:National Defence University, Air NCO Higher Vocational School, Department of Aeronautics Sciences, 35410, Izmir, Türkiye Can Gonenli:Ege University, Department of Machine Drawing and Construction, 35100, Izmir, Türkiye Duygu Bagci Das:Ege University, Department of Computer Programming, 35100, Izmir, Türkiye

Abstract
This study represents a numerical research in vibration and buckling of functionally graded material (FGM) beam comprising edge crack by using finite element method (FEM) and multilayer perceptron (MLP). It is assumed that the material properties change only according to the exponential distributions along the beam thickness. FEM and MLP solutions of the natural frequencies and critical buckling load are obtained of the cracked FGM beam for clamped–free (C-F), hinged–hinged (H-H), and clamped–clamped (C-C) boundary conditions. Numerical results are obtained to show the effects of crack location (c/L), material properties (E2/E1), slenderness ratio (L/h) and end supports on the bending vibration and buckling properties of cracked FGM beam. The FEM analysis used in this paper was verified with the literature, and the fundamental frequency ratio (w) and critical buckling load ratio (Pcr) results obtained were compared with FEM and MLP. The results obtained are quite compatible with each other.

Key Words
buckling; edge crack; finite element method; functionally graded material; multilayer perceptron; vibration

Address
Murat Yaylaci:Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey Ecren Uzun Yaylaci:Technology Transfer Office, Recep Tayyip Erdogan University, 53100, Rize, Turkey Mehmet Emin Ozdemir:Department of Civil Engineering, Cankiri Karatekin University, 18100, Çankiri, Turkey Şevval Ozturk:Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey Hasan Sesli:Department of Civil Engineering, Yalova University, 77200, Yalova, Turkey

Abstract
The stiffness evaluation of cracked base metal is of great guidance to fatigue crack reinforcement. By carrying out fatigue tests and numerical simulation of typical cracking details in steel box girder, the strain-degradation law of cracked base metal was analyzed and the relationship between base metal stress and its displacement (stiffness) was explored. The feasibility of evaluating the stress of cracked base metal based on the stress field at the crack tip was verified. The results demonstrate that the stiffness of cracked base metal shows the fast-to-slow degradation trend with fatigue cracking and the base metal at 50mm or more behind the crack tip basically lose its bearing capacity. Drilling will further accelerate stiffness degradation with the increase of hole diameters. The base metal stress has a negative linear relation with its displacement (stiffness), The stress of cracked base metal is also related to stress intensity factor and its relative position (distance, included angle) to the crack tip, through which the local stiffness can be effectively evaluated. Since the stiffness is not uniformly distributed along the cracked base metal, the reinforcement patch is suggested to be designed according to the stiffness to avoid excessive reinforcement for the areas incompletely unloaded.

Key Words
drilling stop-hole; fatigue cracking; roof-vertical stiffener; steel bridge deck; stiffness degradation

Address
Liang Fang, Zhongqiu Fu, Bohai Ji and Xincheng Li:College of Civil and Transportation Engineering, Hohai University, No. 1 Xikang Road, Nanjing, China

Abstract
In this study, the two-dimensional crack problem was investigated by using the finite element method (FEM)- based ANSYS package program and the artificial neural network (ANN)-based multilayer perceptron (MLP) method. For this purpose, a half-infinite functionally graded (FG) layer with a crack pressed through two rigid blocks was analyzed using FEM and ANN. Mass forces and friction were neglected in the solution. To control the validity of the crack problem model exercised, the acquired results were compared with a study in the literature. In addition, FEM and ANN results were checked using Root Mean Square Error (RMSE) and coefficient of determination (R2 ), and a well agreement was found. Numerical solutions were made considering different geometric parameters and material properties. The stress intensity factor (SIF) was examined for these values, and the results were presented. Consequently, it is concluded that the considered non-dimensional quantities have a noteworthy influence on the SIF. Also FEM and ANN can be logical alternative methods to time-consuming analytical solutions if used correctly.

Key Words
artificial neural network; finite element method; fracture mechanics; functionally graded layer; stress intensity factor

Address
Murat Yaylacl and Şevval Ozturk:Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey Ecren Uzun Yaylacl:Faculty of Engineering and Architecture, Recep Tayyip Erdogan University, 53100, Rize, Turkey Muhittin Turan:Department of Civil Engineering, Bayburt University, 69010, Bayburt, Turkey Mehmet Emin Ozdemir:Department of Civil Engineering, Cankiri Karatekin University, 18100, Çanklrl, Turkey Sevil Ay:Department of Civil Engineering, Artvin Coruh University, 08100, Artvin, Turkey

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