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Abstract
This paper presents the characterization of fatigue crack in the A283 Grade C steel using the MMM method by identifying the effects of magnetic flux leakage towards the crack growth rate, da/dN, and crack length.The previous and current research on the relation between MMM parameters and fatigue crack effect is still unclear and requires specific analysis to validate that. This method is considered to be a passive magnetic method among other Non-Destructive Testing (NDT) methods. The tension-tension fatigue test was conducted with a testing frequency of 10 Hz with 4 kN loaded, meanwhile the MMM response signals were captured using a MMM instrument. A correlation between the crack growth rate and magnetic flux leakage produces a sigmoid shape curve with a constant values which present the gradient, m value is in the ranges of 1.4357 to 4.0506, and the y-intercept, log C in the ranges of 4×10-7 to 0.0303. Moreover, a linear relation was obtained between the crack length and magnetic flux leakage which present the R-Squared values is at 0.830 to 0.978. Therefore, MMM method has their own capability to investigate and characterize the fatigue crack effects as a main source of fracture mechanism for ferrous-based materials.

Key Words
fatigue crack effect; MMM signal response; magnetic flux leakage; crack growth rate; crack length

Address
Department of Mechanical & Materials Engineering, Faculty of Engineering and Build Environments, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia.

Abstract
The determination of the stress intensity factor at the crack tip is one of the most widely used methods to predict the fatigue life of aircraft structures. This prediction is more complicated for repaired cracks with bonded composite patch. This study is used to compute the stress intensity factor (SIF) and crack opening displacement (COD) for cracks repaired with single and double-sided composite patches. The effect of the presence of disbond region in adhesive at the crack was taken into consideration. The results show that there is a considerable reduction in the asymptotic value of the stress-intensity factors and the crack opening displacement at the crack tip. The use of a double-sided patch suppresses the bending effect due to the eccentricity of the patch on one side only.

Key Words
stress intensity factor (SIF); crack opening displacement (COD); crack; bonded composite repair; disbond

Address
(1) Aicha Benchiha, Kouider Madani: LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, Cité Ben M'hidi, Sidi Bel Abbes, Algeria;
(2) Sebastien Touzain, Xavier Feaugas: La Rochelle University, Laboratoire des sciences pour l'ingénieur pour l'environnement (LASIE), La Rochelle, France;
(3) Mohan Ratwani: R-Tec, Rolling Hills Estates, CA 90274, USA.

Abstract
The objective of this work was to evaluate the ductile cracked structures with bonded composite patch used in probabilistic elastic plastic fracture mechanics subjected to tensile load. The finite element method is used to analyze the stress intensity factors for elastic case, the effect of cracks and the thickness of the patch (er) are presented for calculating the stress intensity factors. For elastic-plastic the Monte Carlo method is used to predict the distribution function of the mechanical response. According to the obtained results, we note that the stress variations are important factors influencing on the distribution function of (J/Je).

Key Words
composite; finite element method; fracture mechanics; elastic-plastic; probabilistic analysis

Address
(1) BelaÏd Mechab, Mourad Chama, Khacem Kaddouri: LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89 Cité Ben M'hidi 22000, Sidi Bel Abbes, Algeria;
(2) Djelloul Slimani: Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89 Cité Ben M'hidi 22000, Sidi Bel Abbes, Algeria.

Abstract
The Poisson ratio reduction of symmetric hygrothermal aged [θm/90n]s composite laminates containing a transverse cracking in mid-layer is predicted by using a modified shear-lag model. Good agreement is obtained by comparing the prediction models and experimental data published by Joffe et al. (2001). The material properties of the composite are affected by the variation of temperature and transient moisture concentration distribution in desorption case, and are based on a micro-mechanical model of laminates. The transient and non-uniform moisture concentration distribution give rise to the transient Poisson ratio reduction. The obtained results represent well the dependence of the Poisson ratio degradation on the cracks density, fibre orientation angle of the outer layers and transient environmental conditions. Through the presented study, we hope to contribute to the understanding of the hygrothermal behaviour of cracked composite laminate.

Key Words
transverse cracking; poisson ratio; hygrothermal effect; Tsai model; desorption

Address
(1) M. Khodjet-Kesba, A. Benkhedda, B. Boukert: Laboratoire des sciences aéronautiques, Institut d'aeéronautique et des études spatiales, Université de Blida1, Blida, Algérie;
(2) E.A. Adda bedia: Laboratoire des Matériaux et Hydrologie, Université de Sidi Bel Abbes, Sidi Bel Abbes, Algérie.

Abstract
To avoid the cracks of cast-in-place concrete in shear pockets and seams in the traditional composite beam with precast decks, this paper proposed a new type of prefabricated steel truss-concrete composite beam (ab. PSTC beam) with pre-embedded shear studs (ab. PSS connector). To study the initial cracking load of concrete deck, the development and distribution laws of the cracks, 3 PSTC beams were tested under hogging moment. And the crack behavior of the deck was compared with traditional precast composite beam, which was assembled by shear pockets and cast-in-place joints. Results show that: (i) the initial crack appears on the deck, thus avoid the appearance of the cracks in the traditional shear pockets; (ii) the crack of the seam appears later than that of the deck, which verifies the reliability of epoxy cement mortar seam, thus solves the complex structure and easily crack behavior of the traditional cast-in-place joints; (iii) the development and the distribution laws of the cracks in PSTC beam are different from the conventional composite beam. Therefore, in the deduction of crack calculation theory, all the above factors should be considered.

Key Words
Prefabricated Steel Truss-Concrete Composite Beam (PSTC beam); precast deck; Preembedded Shear Studs (PSS Connector); epoxy cement mortar seam; deck crack test

Address
(1) Yanmei Gao, Zhixiang Zhou: State Key Laboratory Cultivation Base of Mountain Bridge and Tunnel Engineering, Chongqing Jiaotong University, 400074, China;
(2) Yanmei Gao, Zhixiang Zhou, Dong Liu: College of Civil Engineering, Chongqing Jiaotong University, 400074, China;
(3) Yinhui Wang: Ningbo Institute of Technology, Zhejiang University, School of Civil Engineering and Architecture, 315100, China.

Abstract
Fatigue crack initiated in welded tubular joints due to cyclic loading may produce harmful effect on the integrity of the tubular structures. To study such effect, both fatigue and static tests on nine circular tubular T-joint specimens made of carbon steel materials were carried out. The specimens were subjected to tensile loading in both fatigue and static tests. The load-displacement relation, the crack propagation and the failure mode of the specimens are all analyzed. The deterioration of the static strength of the cracked T-joints is also investigated and evaluated through an area reduction factor. Experimental results indicate that the static strength of a tubular T-joint with a surface crack seems to decrease slightly while a through crack has relatively remarkable effect on the reduction of the static strength. Additionally, experimental results also show that the toughness of the materials and the geometry of the specimens play an important role on the failure process of cracked tubular T-joints.

Key Words
tubular T-joints; fatigue crack; residual static strength; failure mode; experimental test

Address
(1) Yamin Wang, Yongbo Shao: School of Mechatronic Engineering, Southwest Petroleum University, Chengdu 610500, P.R. China;
(2) Shengzhi Song: R&D centre of Jungian Construction safety and disaster mitigation, Jiangsu Jianzhu Institute, Xuzhou 221116, P.R. China;
(3) Dongping Yang: Technology Inspection Center, China Petroleum & Chemical Corporation, Dong 257062, P.R. China.

Abstract
In this paper, the analysis of the behavior of surface cracks in finite-thickness plates repaired with a Boron/Epoxy composite patch is investigated using three-dimensional finite element methods. The stress intensity factor at the crack-front was used as the fracture criteria. Using the Ansys Parametric Design Language (APDL), the stress intensities at the internal and external positions of repaired surface crack were compared. The effects of the mechanical and geometrical properties of the adhesive layer and the composite patch on the variation of the stress intensity factor at the crack-front were examined.

Key Words
patch; stress intensity factor; surface cracks; bonded composite repairs

Address
Mohamed Merzoug, Abdelkader Boulenouar and Mohamed Benguediab: Laboratory of Materials and Reactive Systems - LMSR. University of Sidi Bel Abbes. BP. 89, City Larbi Ben Mhidi. Sidi Bel Abbes, Algeria

Abstract
In this paper, a new method has been proposed to detect crack in beam structures under moving mass using regularized extreme learning machine. For this purpose, frequencies of beam under moving mass used as input to train machine. This data is acquired by the analysis of cracked structure applying the finite element method (FEM). Also, a validation study used for verification of the FEM. To evaluate performance of the presented method, a fixed simply supported beam and two span continuous beam are considered containing single or multi cracks. The obtained results indicated that this method can provide a reliable tool to accurately identify cracks in beam structures under moving mass.

Key Words
crack detection; moving mass; frequencies; regularized extreme learning machine

Address
Department of Civil Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran.

Abstract
In this paper, the effect of matrix cracks on the buckling of a hybrid laminated plate is investigated. The plate is composed of carbon nanotube reinforced functionally graded (CNTR-FG) layers and conventional fiber reinforced composite (FRC) layers. Different distributions of single walled carbon nanotubes (SWCNTs) through the thickness of layers are considered. The cracks are modeled as aligned slit cracks across the ply thickness and transverse to the laminate plane, and the distribution of cracks is assumed statistically homogeneous corresponding to an average crack density. The first-order shear deformation theory (FSDT) is employed to incorporate the effects of rotary inertia and transverse shear deformation, and the meshless kp-Ritz method is used to obtain the buckling solutions. Detailed parametric studies are conducted to investigate the effects of matrix crack density, CNTs distributions, CNT volume fraction, plate aspect ratio and plate length-to-thickness ratio, boundary conditions and number of layers on buckling behaviors of hybrid laminated plates containing CNTR-FG layers.

Key Words
buckling; carbon nanotube-reinforced functionally graded composites; matrix crack; meshless kp-Ritz method

Address
School of Sciences, Nanjing University of Science and Technology, Nanjing 210094, China.

Abstract
Beam-column joints play a significant role in static and dynamic performances of reinforced concrete frame structures. This study contributes a numerical approach of topologically optimal design of carbon fiber reinforced plastics (CFRP) to retrofit existing beam-column connections with crack patterns. In recent, CFRP is used commonly in the rehabilitation and strengthening of concrete members due to the remarkable properties, such as lightweight, anti-corrosion and simplicity to execute construction. With the target to provide an optimal CFRP configuration to effectively retrofit the beam-column connection under semi-failure situation such as given cracks, extended finite element method (X-FEM) is used by combining with multi-material topology optimization (MTO) as a mechanical description approach for strong discontinuity state to mechanically model cracked structures. The well founded mathematical formulation of topology optimization problem for cracked structures by using multiple materials is described in detail in this study. In addition, moved and regularized Heaviside functions (MRHF), that have the role of a filter in multiple materials case, is also considered. The numerical example results illustrated in two cases of beam-column joints with stationary cracks verify the validity, benefit and supremacy of the proposed method.

Key Words
CFRP; composite; multiple materials; topology optimization; X-FEM; MRHF; crack; beam-column joint

Address
(1) Anh P. Nguyen, Thanh T. Banh, Dongkyu Lee, Jaehong Lee: Department of Architectural Engineering, Sejong University, Seoul 05006, Korea; (2) Joowon Kang: Department of Architecture, Yeungnam University, Gyeongsan 38541, Korea; (3) Soomi Shin: Research Institute of Industrial Technology, Pusan National University, Busan 46241, Korea.

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