Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Finite element analysis of the behavior of bonded composite patches repair in aircraft structures
Get PDFThis paper aims to analyze the multi-effects of the glass fiber reinforced polymer (GFRP) composite patch to repair the inclined cracked 2420-T3 aluminum plate. Three-dimensional finite element method (FEM) was used to study the effect of GFRP composite patch with different stacking composite laminate sequence, [0°]4, [90o]4, [45o]4, [0o/45o]2s and [0°/90°]4s on the crack driving force, J-integral, of inclined cracked 2420-T3 aluminum plate. Furthermore, the effects of patch geometry, number of layers, single or double side patch and crack incline angle are described.
The present results show that the patch has a high effect in case of a crack in pure mode I. Furthermore, the effectiveness of the composite patch is increasing with the crack length increases. Moreover, the efficiency of the composite patch has a high effect by changing the fiber orientation, the number of layers, and the single or double side patch
Analytical solution for statif bending analyses of functionally grades plates with porosities
Get PDFThe paper examines a static bending of porous functional plates (FGP) and rectangular plate solutions, based on an underlying high-order shear deformation theory. The proposed high-order shear deformation theory, as opposed to other theories, includes four unknowns. For this reason, a new shear strain function is considered. The technique of Navier is used in closed-form FGP solutions. Results of deflections and stresses are presented for simply supported border conditions. Current figures are contrasted with the non-poreous plate deflecting solutions and the literature's stresses. Effects of different parameters, including thickness, gradient index and porosity of FGM plates, are discussed
Numerical Analysis and Verification of Residual Stress in T Joint of S355 Steel
Get PDFT joint is a widely used welding form. The welding deformation and residual stress produced during the welding process will affect the integrity and reliability of the structure. In this study, S355 low alloy steel was used as test material, and the thermal-mechanical coupling characteristics of multi-layer welding were combined with SYSWELD finite element software to calculate the residual stress of T joint after welding. The residual stress of multi-layer welding T joint with tangent tube and sheet after welding was measured by X-ray diffraction method. The results showed that the numerical simulation agreed well with the experimental results. For the transverse residual stress, the maximum residual stress appeared near the weld toe, and the transverse stress perpendicular to the weld direction presented tensile stress at the weld center and presented stress at the tube surface far from the weld. For the longitudinal residual stress, the maximum residual stress also appeared near the weld toe, and the value was the largest at the center of the weld and decreased along the direction perpendicular to the weld. The research results can provide a reference for actual welding design
Building crack monitoring based on digital image processing
Get PDFBuilding crack monitoring is of great value to the judgment of building safety. In this study, the digital image processing technology was studied and applied to the monitoring of building cracks. Crack images were collected by CCD camera, and then operations such as graying, correction, denoising and segmentation were carried out to obtain clear crack images. The obtained images are processed morphologically to further improve the quality. Finally, the width and length of cracks are calculated. In the case analysis, the results of 15 cracks measured by microscope were taken as the standards and compared with the calculated results. The results showed that the results calculated in this study and the manual measurement results differed little, and the average error of the width and length is 0.021 mm and 0.024 mm respectively, which suggested that the method proposed had high reliability. The findings of this study provides a new idea for the further development of building crack monitoring field, which is conducive to the accurate assessment of building safety
Study on the thermal cycle of Wire Arc Additive Manufactured (WAAM) carbon steel wall using numerical simulation
Get PDFThe thermal behavior in WAAM process is a significant cause for thermal stress. In this paper, a 3D model of a four-layer wall is built in ABAQUS software in order to investigate the thermal behavior in a carbon steel (ASTM A36) WAAM wall. Moreover, the effects of substrate preheating temperature and travel speed on the temperature distribution are studied. The modelling results show that with increase in number of deposited layers, the peak temperature increases but average cooling speed decreases. Furthermore, substrate preheating increases peak temperature of fist layer and decreases its average cooling speed. Regarding simulation results, the travel speed has major effects on the thermal behavior of deposited layers.  
Unified methodology for characterisation of global fatigue damage evolution in adhesively bonded joints
Get PDFThe present work concentrates on the development of a methodology for evaluating the fatigue performance of single and double lap adhesively bonded joints subjected to constant or variable fatigue loading. Firstly, a methodology was developed to monitor the evolution of permanent deformation, stiffness degradation and hysteresis losses of single lap joints subjected to constant amplitude fatigue load. Hereto, the global deformation of the adhesive joint was monitored using the digital image correlation technique (DIC). A MATLAB code was developed to evaluate and visualize the stiffness degradation and energy dissipation (hysteresis loops) occurring during a complete fatigue test. Secondly, this methodology was optimized to evaluate the properties of double lap joints with two different bond line thicknesses. The results of both constant and variable amplitude fatigue tests show the relation between stiffness degradation and increase in hysteresis losses with increase in number of fatigue cycles or thus fatigue damag
Uniformity of thickness of metal sheets by patchwork blanks: potential of adhesive bonding
Get PDFThe sheet metal forming operations generally involve the production of parts characterized by a non-uniform thickness distribution. However, in some cases, a product characterized by a distribution of thicknesses that is as uniform as possible may be desirable. This result can be obtained by using multiphase processes or by subtraction or addition of material from the blank. In this work, which deals with the method for adding material, an innovative methodology has been proposed as an alternative to the welding process. Specifically, the methodology is based on the bonding of a patch (before the deformation process), on the base plate with a constant thickness, in the area that most suffers from the thinning caused by the forming process. In this way, it was possible to influence the deformation of the patchwork blank and its thicknesses distribution. Through finite element analysis, it was possible to study the formability of a patchwork blank by varying the thickness and size of the patch, in order to produce an axially symmetric component by stretching through a hemispherical punch. Preliminary experimental tests demonstrated the reliability of the bonding and the potential of this method to uniform the final thickness of the sheet
Plastic stress intensity factor behavior at small and large scale yielding
Get PDFIn this paper the plastic stress intensity factor (SIF) is used to study the coupling effects of loading biaxiality, material properties and cracked body configuration in both the small- and large-scale yielding ranges. A finite element (FE) analysis is performed for a cracked Mode I plane strain plate subjected to biaxial tension/compression loading. The governing parameter of the elastic–plastic crack-tip stress field In factor at the crack tip, J-integral, and the plastic SIF, are calculated as a functions of loading biaxiality and applied stress levels. Special emphasis is put on the behavior of J-integral and the plastic SIF for specified test specimen geometries under mixed mode loading. Finally, the applicability of the plastic SIF approach to large-scale yielding analysis is also discussed
Inelastic deformation and destruction of fiber-laminated polymer composites in stress concentration zones
Get PDFThe article is devoted to the experimental study of the laws of inelastic deformation of structural polymer composites in the presence of macroinhomogeneous fields. The work uses a three-dimensional optical system and a method of digital image correlation, thermoscanning equipment. The relationship between the selected parameters of the correlation analysis and the scale level of the deformation processes is shown. Experimental data were obtained confirming the presence of a large-scale effect of strength in a certain range of structural parameter values, data on the features of the deformation of composites with various reinforcement schemes, as well as in the presence of technological defects. Recommendations on the use of a video system for calibration and sensitivity assessment of integrated fiber-optic sensors are presente
Fatigue Life Simulation and Analysis of Aluminum Alloy Sheet Self-piercing Riveting
Get PDFThe fatigue life prediction model of self-piecing riveting components of aluminum alloy is established and the effects of roughness and residual stress on fatigue life of self-piercing riveting components is analyzed by the model. Finite element software ABAQUS and fatigue analysis software FE-SAFE are used to study the effects of roughness and residual stress on the fatigue life of self-piecing riveting components through finite element simulation and mathematical statistics multivariate orthogonal regression experiment. The quantitative relations between fatigue life and three variables (roughness, residual stress and maximum stress) are fitted, and the variation trend of fatigue life with roughness and residual stress is obtained. The order of influence of roughness, residual stress, maximum stress and two interactions on fatigue life is as follows: residual stress, interaction between roughness and residual stress, roughness. When the maximum stress is fixed, the fatigue life decreases with the increase of roughness with a certain residual stress, and the fatigue life decreases with the increase of roughness with a certain residual stress. The average error between the fatigue experiment results and the simulation results is 9.74%, which proves that the simulation results are reliable