The design, construction and installation of marine structures, according to the specific conditions of the implemented region and the loads on them, is in the field of the most advanced engineering issues, and today many researches have been carried out in its various fields under the loads caused by waves and sea currents. . One of the main issues in the design of marine platforms is the phenomenon of Fatigue in connections., and Fatigue analysis by different methods, including spectral and deterministic method and determining the Fatigue life of the platform, is necessary. Due to the repetitive nature of the loads caused by the waves, the tubular members of the structure that are connected to each other with welded joints are exposed to repeated stresses and if the loading continues, rupture due to Fatigue is likely. . Due to the special geometrical shape of these connections, there are points with high stress concentration, which are very prone to the phenomenon of Fatigue, and for this reason, the Fatigue analysis of structural connections as the weakest points against Fatigue is one of the important factors in the design of platforms. In this research, the analysis of Crack Propagation due to Fatigue in the connections of fixed offshore metal platforms has been discussed and the existing platforms in the Persian Gulf region have been used, which is the same as the SPD 15 platform located in the South Pars region. To prepare the model, the maps of the National Iranian Oil Company were used, and the wave force was applied to the structure in the main directions, and Crack expansion analysis was performed. Abaqus software, which is a finite element program, has also been used for modeling.

Automatic Crack Propagation and stable Fatigue Crack growth as complicate problems in fracture mechanics are studied. In this study The Extended Finite Element Method (XFEM) is utilized because of several drawbacks in standard finite element method in Crack Propagation modeling. Estimated Crack paths are obtained by using Level Set Method (LSM) in coupling with XFEM for 2D mixed mode Crack Propagation problems. Stress intensity factors for mixed mode Crack problems are numerically calculated by using interaction integral method completely based on familiar path independent J-integral method. Different Crack path growths are shown for different types of boundary conditions. Also, stable Fatigue Crack growth due to numerous cycles of loading using Paris law is presented. Finally, some experimental results and analytical solutions for stress intensity factors are concerned to guarantee the numerical estimated Crack path growths and stress intensity factors respectively.

In this paper, a suitable method is presented to predicate Fatigue Crack Propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as function depending on SIFs resulted by external load, weld residual stress and overload. Weight function is applied to calculate SIF resulted by weld residual stress. Also, a method is introduced to determine overload SIF and overload stress ratio. Then Fatigue Crack Propagation equation is modified for our purpose. In other words, a simple and efficient method is presented in this paper for predicting Fatigue Crack Propagation rate in welded joints when the overload is happening. Finally, for evaluating this modified equation, experimental methods are applied. Test samples were M(T) geometry made of aluminum alloy with a longitudinal weld by the Gas Tungsten arc welding process. Modified equation has a good agreement with the experimental model presented in this field.

Concrete is the most important material in geotechnical projects and constructions which that due to the cyclical loading and Fatigues were always under failures. The Fatigue is natural events were occurred in under cyclical loaded materials which causes very complex failures in under low stress and in elastic behavior. Although the concrete behavior and changes under axial loading are studied, but failure mechanism of Fatigue and Crack Propagation on concrete (as the main factor to failure) is on obscurity. The investigation of Crack Propagation process from the beginning to failure under cyclic axial loading can be identified the Fatigue mechanism. This study tired to monitoring and modeling the Crack Propagation mechanism under the cyclic uniaxial compressive strength (UCS ) in axial loading of concrete specimens which help to understands of Crack Propagation and developed path in the body. For this purpose, the concrete specimens are tested by UCS, take photos repetitively (in 5 loading-unloading cycles) and used the image-processing techniques (IPT) for Crack detection, Propagation and simulation of the failure in concrete. The simulation results shown the IPT is good performance to Crack Propagation detections and Propagation process is perfectly simulated by IPT.

Due to industrial advances and the application of more dynamic loads, it is necessary to pay more attention to the Fatigue issue. Among non-destructive methods, the acoustic emission method has become a standard and reliable method in recent years. With the aim of online structural monitoring of the aircraft propeller that undergoes Cracks in the hub part, this article investigates and determines the characteristics of acoustic emission in the growth of aluminum 2025 Fatigue Crack. Referable research on the loading frequency considered in this research has not been conducted for this alloy. In this project, the characteristics of acoustic emission in the Fatigue Crack growth of aluminum alloy 2025 for online structural monitoring have been investigated and determined. Acoustic emission tests have been performed in two parts: bending Fatigue test with the aim of initiation of Fatigue Cracks in aluminum alloy 2025 specimens and following tensile tests with the aim of growth of Fatigue Cracks. According to the received acoustic emission information, various diagrams are plotted. Analyzing the results from online acoustic emission monitoring showed, the acoustic emission method can be considered as a suitable and reliable technique for detecting Crack initiation and Crack growth in aluminum alloy 2025.

Modeling of Crack Propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode Crack growth in linear elastic fracture mechanics. Crack growth process is simulated by an incremental Crack-extension analysis based on the maximum principal stress criterion, which is expressed in terms of the stress intensity factor.In this paper, a procedure to correct the direction of Crack Propagation in the analysis of finite element is presented to ensure that a unique final Crack path is achieved for different analysis of a problem by using different increments of Crack. For each increment of Crack extension, finite element method is applied to perform a single region stress analysis of the Cracked structure. Results of this incremental Crack extension analysis are presented for several geometries.

Modeling of Crack Propagation by a finite element method under mixed mode conditions is of prime importance in the fracture mechanics. This article describes an application of finite element method to the analysis of mixed mode Crack growth in linear elastic fracture mechanics. Crack - growth process is simulated by an incremental Crack-extension analysis based on the maximum principal stress criterion which is expressed in terms of the stress intensity factor. In this paper a procedure is employed to correct direction of Crack Propagation to ensure that a unique final Crack path is achieved for different analysis of a problem by using different increments of Crack. For each increment of Crack extension, finite element method is applied to perform a single - region stress analysis of the Cracked structure. Results of this incremental Crack – extension analysis are presented for several geometries.

In this research, the influence of thermal cycling on the fracture toughness and maximum load in mode I delamination of polymer matrix composites (PMCs) was investigated experimentally and analytically. To eliminate the effect of the remote ply orientation on the fracture toughness during delamination initiation and Propagation, double cantilever beam (DCB) specimens with a stacking sequence of [0]16 using unidirectional glass fibers and epoxy resin were considered. The specimens were thermal-cycled between 15°, C and 65°, C for 50-150 cycles. One group of uncycled specimens were tested at the commencement of the investigation as a control group. During the DCB test and receiving universal tensile machine results, the specimens were inspected by 2 real-time cameras to record the delamination length and initial Crack tip opening displacement (ICTOD). The strain energy release rate (SERR) approach was used for obtaining the critical fracture toughness (GIC) from the experimental data. By employing the digital image correlation (DIC) method, the initial Crack tip separation profile was obtained. The measured bridging laws were used with cohesive elements in ABAQUS commercial software to accurately model the delamination Propagation in DCB specimens. Investigation of load variations revealed that critical fracture toughness in mode I of delamination is firmly affected by the thermal Fatigue process.

The construction of Latiyan Buttress Dam was finished in 1968. The result of dam instrumentation indicated that till July of 1970 the dam was in a suitable situation. However at that time vertical Cracks were observed on the walls of buttress 10/11, for the first time. These Cracks were located on both sides of the gate control room, which extend from the crest level down to the floor of control room. The rehabilitation operations were done by injection of epoxy into the Crack openings in winter 1970, but it did not work properly and the Cracks opened again in summer 1971. Measurement of opening and closing of Cracks shows a cyclic loop behavior affected by seasonal variations in temperature. The latter seems to be the major cause of Cracking. In this study finite element analysis of Crack Propagation has been done by use of Nonlinear Fracture Mechanics concepts and Smeared Crack Method. In this method its suggested that the Crack will be replaced by a continuum with changeable physical properties. If the failure criterion is met, Cracking takes place in the direction normal to the maximum principal stress. After Cracking, the stiffness of concrete normal to the Crack plane is reduced and concrete model becomes orthotropic. Therefore by Propagation of Crack in the structure the finite element mesh will not change while the material behavior relation changes. At first we find the distribution of temperature in the dam body by Heat Transfer Analysis for both summer and winter. Then by applying different static load combinations, the load combination that produce the Crack is found. The result of static analysis demonstrates that applying the following load combination would cause high tensile stresses in the Cracked region: Dam Weight + Hydrostatic Pressure + Summer Temperature Load + Lateral Pressure of Adjacent Blocks By analyzing of the model under cyclic temperature loads it is concluded that after a while the results should become steady and increasing the loading cycles does not make major differences in the results. We can conclude that by applying static loads the Crack pattern wont propagate and the dam wont get in danger. It means that to keep services of this dam it is not necessary to do rehabilitation operations to resist static loads and the dam is safe in the normal loading conditions.