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.

Nonlinear vibrations due to the presence of FATIGUE CRACKs are suitable indicators for detecting CRACKs in the structure. Late detection of such CRACKs may lead to catastrophic failures. Therefore, identifying the behavior of the CRACKed structure is very important for the prevention of structural failures. In this study, the nonlinear vibration of a cantilever BEAM with a transverse breathing CRACK and bilinear behavior has been studied. For this purpose, the restoring force of the CRACKed BEAM is considered a nonlinear polynomial function. Then, using the method of multiple scales, the approximated equation of the CRACKed BEAM is solved, and the frequency-response curves for both harmonic and superharmonic resonances are extracted. Then, the sensitivity of the responses to the CRACK depth, CRACK location, excitation force amplitude, and damping coefficient are investigated. The CRACKed BEAM frequency-response curves in the primary resonance have become highly nonlinear due to the increase of the CRACK parameters and cause softening of the curves. Also, it was observed that the behavior of the BEAM in superharmonic resonance is highly sensitive to the presence of a FATIGUE CRACK in the structure.

There are several approaches for modeling the FATIGUE life and damage of asphalt pavements, such as stress-strain and damage mechanics. In this research, a simple mechanistic approach is used to explain the destruction of asphalt pavements. For asphalt reinforcement, two types of geosynthetic were used in the airfield at Imam Khomeini airport, Tehran. Non-reinforced, reinforced with a geogrid and geotextile specimens with dimensions of 50´63´381 mm were obtained from the asphalt slab field section. FATIGUE TESTs of this study have been conducted with a four point BEAM TEST and a FATIGUE load with a half-sin wave at a frequency of 10 cycle/sec (no rest period), has been used. The results indicated that specimens reinforced with geosynthetics exhibit a higher initial stiffness module and lower CRACK PROPAGATION rate than non-reinforced specimens.

In this paper the free vibration of a cantilever BEAM containing a breathing CRACK is investigated. Generally, the researchers have applied numerical methods to study the vibrational behavior of a CRACKed BEAM. In this research the governing equation of the motion for free vibration of the CRACKed BEAM is derived, and by applying suitable modifications and variable changes is expressed as the multiplication of a decaying exponential function by the Mathieu equation. By analyzing the parameters of the governing equation, this equation is solved by employing perturbation method. Presented method makes it possible to estimate damping characteristic of the system. The result shows that the system damping depends on the CRACK parameters, geometric dimensions, mechanical properties of the BEAM, and an increase in the CRACK depth results in an increase in the system damping. In order to validate the results, a comparison is made between the response of the CRACKed BEAM with a given CRACK depth and location obtained by the proposed analytical solution and that of the numerical method. Also, changes in fundamental frequency ratios versus CRACK severities are compared with those of the experimental results available in the literature. The obtained results from the proposed method agree well with the experimental results presented in the literature.

FATIGUE TESTing is commonly conducted using the single-edge notched BEAM (SENB) TEST, which is not simple to prepare. With the widely use of Superpvae gyratory compactor with its consistent circular compacted samples, the industry is keen to find ways to utilize these samples in TESTing. Therefore, the semi-circle notched BEAM (SCNB) FATIGUE TEST setup was introduced. However, there are no justified design criteria and/or standard TEST procedure to evaluate FATIGUE life of asphalt mixes using SCNB. Thus, there is a critical need for understanding the effect of the significance of each controlling TESTing parameters to evaluate Superpave mixes resistance to FATIGUE CRACKing using SCNB. In this study, common TESTing parameters were investigated and the failure point due to FATIGUE was clearly defined. In addition, when comparing TEST results to the Asphalt Institute (AI) model, it was found that the cyclic load range of 30% to 60% of the ultimate strength could be utilized as an appropriate range with a loading frequency of 1 Hz, at which TEST results illustrated that strain rate and loading range lay within reasonable range of AI design guidelines.

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.

In this paper, the continuous model for vibration analysis of a CRACKed BEAM developed by Shen and Pierre is modified. For this end, by some realistic assumptions, new functions for displacement and stress fields are proposed. Then, the equation of motion of the CRACKed BEAM with breathing CRACK is obtained via the Hu-Washizu variational principle. The new obtained equation of motion is self-adjoint. Moreovers, by employing the Galerkin method, the modes shape of BEAM with a breathing CRACK are obtained. Then, in order to obtain the time response of the CRACKed BEAM, a new bilinear model is introdused for the stiffness corresponding to each mode. Using this model, the governing equation of motion is converted into the standard form which can be analyzed by Lindstedt-Poincar’ method. The results show that response obtained throught the perturbation metod (Lindstedt-Poincar method) is composed of two parts. The main part is the response of a system with the equivalent stiffness, whith is equal to the main value of the stiffness corresponding to the fully open and fully close CRACK cases. The remaining part of the response consistence of the correction terms, which reflects the effect of opening and closing the CRACK during vibration. The results show that for a given CRACK parameters, redaction in natural frequencies for a FATIGUE-breathing CRACK are smaller than the ones caused by open CRACKs. Also, the results have been validated by the experimental and theoretical data reported in the literature. There is a good agreement between the results obtained through the proposed method and those obtained from the reported experimental data.