Investigation of microstructure changes in Al2O3-YSZ coatings and YSZ coatings and their effect on thermal cycle life

Yttria-stabilized zirconia (YSZ) coatings and Al2O3-YSZ coatings were prepared by atmospheric plasma spraying (APS). Their microstructural changes during thermal cycling were investigated via scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). It was found that the microstructure and microstructure changes of the two coatings were different, including crystallinity, grain orientation, phase, and phase transition. These differences are closely related to the thermal cycle life of the coatings. There is a relationship between crystallinity and crack size. Changes in grain orientation are related to microscopic strain and cracks. Phase transition is the direct cause of coating failure. In this study, the relationship between the changes in the coating microstructure and the thermal cycle life is discussed in detail. The failure mechanism of the coating was comprehensively analyzed from a microscopic perspective.

Damage Analysis of Composite Sheet Under Thermal Load

The goal of this research is to carry out a 3-dimensional finite detail approach evaluation of a composite plate cracked under thermal loading. The results of the mechanical properties of the composite, the orientation angle of the fibers, the geometric form of the plate, the thermal loading and the crack length had been studied to show their influence on the variation of the integral J. It is concluded that the integral J increases with the increase of crack size, temperature variation and reduce in fiber orientation perspective (e). To complete the work a probabilistic analysis was carried out.

Crack paths in multiaxial fatigue of C45 steel specimens and correlation of lifetime with the thermal energy dissipation

The work deals with the analysis of the multiaxial fatigue damage of a C45 steel and its relationship with the thermal energy dissipation used in the last decades to estimate the uniaxial fatigue behavior of metals. For this purpose, thin-walled samples made of quenched and tempered C45 steel were tested under completely reversed combined axial and torsional cyclic loadings with different biaxiality ratios and phase-shift angles. The analyses of the crack paths at the initiation of the failure were performed after a 50% of stiffness loss that corresponded to a crack size ranging from 10 to 20 mm; afterwards, the characteristic crack paths of each loading condition were analysed by using a digital microscope to identify the direction of the crack at the initiation. The fatigue crack initiation points were inspected using a Scanning Electron Microscope after having broken under static tensile loading all specimens previously tested under fatigue. The specific heat loss per cycle was measured during the fatigue tests by applying the cooling gradient technique. Nevertheless, the fatigue damages observed are dependent on the load condition, the Q parameter was able to collapse all the axial, torsional and multiaxial fatigue test results in a sole scatter band

A novel approach for detection and classification of re-entrant crack using modified CNNetwork

Purpose In the purpose of the section, the cracks that are in the construction domain may be common and usually fixed with the human inspection which is at the visible range, but for the cracks which may exist at the distant place for the human eye in the same building but can be captured with the camera. If the crack size is quite big can be visible but few cracks will be present due to the flaws in the construction of walls which needs authentic information and confirmation about it for the successful completion of the wall cracks, as these cracks in the wall will result in the structure collapse. Design/methodology/approach In the modern era of digital image processing, it has captured the importance in all the domain of engineering and all the fields irrespective of the division of the engineering, hence, in this research study an attempt is made to deal with the wall cracks which are found or searched during the building inspection process, in the present context in association with the unique U-net architecture is used with convolutional neural network method. Findings In the construction domain, the cracks may be common and usually fixed with the human inspection which is at the visible range, but for the cracks which may exist at the distant place for the human eye in the same building but can be captured with the camera. If the crack size is quite big can be visible but few cracks will be present due to the flaws in the construction of walls which needs authentic information and confirmation about it for the successful completion of the wall cracks, as these cracks in the wall will result in the structure collapse. Hence, for the modeling of the proposed system, it is considered with the image database from the Mendeley portal for the analysis. With the experimental analysis, it is noted and observed that the proposed system was able to detect the wall cracks, search the flat surface by the result of no cracks found and it is successful in dealing with the two phases of operation, namely, classification and segmentation with the deep learning technique. In contrast to other conventional methodologies, the proposed methodology produces excellent performance results. Originality/value The originality of the paper is to find the portion of the cracks on the walls using deep learning architecture.

Characterization of Internal Fatigue Cracks in Aluminum Alloys by Simulation of Phase Contrast Tomography

Synchrotron Radiation Computed Tomography (SRCT) allows a better detection of fatigue cracks in metals than laboratory CT due to the existence of phase contrast. However the presence in reconstructed images of fringes at the edges of objects generated by Fresnel diffraction makes it difficult to identify and analyze the cracks quantitatively. Simulations of phase contrast synchrotron tomography images containing cracks with different sizes and shapes are obtained by using GATE software. Analyzing the simulation results, firstly, we confirmed that the bright parts with strong contrast in SRCT image are streak artifacts; secondly, we found that the gray scale values within the cracks in SRCT images are related to the crack size; these simulation results are used to analyse SRCT images of internal fatigue cracks in a cast Al alloy, providing a clearer visualisation of damage.

The Huge Missing Factor in LBB Analysis - How A Circumferential Through-Wall-Crack in A Pipe System Changes the Flexibility and Reduces the Applied Moments

In typical leak-before-break (LBB) analyses in the nuclear industry, the uncracked piping normal operating forces and moments are applied in a cracked-pipe analytical procedure to determine normal leakage, and the combined forces and moments under normal operating condition and safe shutdown earthquake seismic loading are used in a fracture analysis to predict margins on "failure". The International Piping Integrity Research Program (IPIRG) performed in 1990 to 1998 provided some insights to typical LBB behaviors where pipe system tests were conducted with simulated seismic loadings. The test results showed a large margin on LBB which was also recognized in 2011 when the Argentinian Atucha II plant was analyzed using a robust full FE model. It was found that when circumferential through-wall cracks were put in the highest stressed locations, the applied moment dropped for both normal operating and N+SSE loading as the crack length increased. The through-wall crack size for causing a double ended guillotine break (DEGB) was greater than 90%-percent of the circumference. Similar results were also found for a petrochemical pipe system where thermal expansion stresses are much higher than the primary stresses. Even with very low toughness materials, the critical crack size leading to DEGB was greater than 80% of the circumference. The implication of this work is that pragmatically there is much higher margin for DEGB failure in nuclear plant operation, and efforts would be better focused on the potential for a small-break loss-of-coolant accident (SB-LOCA).

Fatigue life analysis of pressure vessel based on residual strength and crack size

In the field of pressure vessel fatigue life, the study of fracture failure is very important. Based on the Paris law, the relation model between fatigue crack size and residual fatigue life is established by considering the circumferential stress. The relationship between the crack length and the crack depth is introduced. According to the specific structure of the pressure vessel, the relationship model between the fatigue crack size and the residual strength is established based on the residual strength allowable value. The S-N curve of pressure vessel is obtained based on two models. The fatigue life of the pressure vessel is predicted combined with the actual test data. By comparing with the actual service life, the feasibility of the model is verified, which provides a new method for predicting the residual life of pressure vessels.

Influence of Fatigue Crack Formation and Propagation on Reliability of Steel Members

During the years of bridge exploitation, many degradation processes and external influences attack its structure. Therefore, bridge reliability and durability is decreasing in time. On the other hand, the traffic load remains almost the same or even higher than in the past. However, bridges should not to become the limiting component of communication capacity and traffic reliability. Regarding to reliability, bridges should be assessed from the viewpoint of the Ultimate Limit States (ULS) and Serviceability Limit States (SLS). Within the ULS, cross-sections and members are verified for various types of stressing and their combinations, and also for fatigue at the same time. The cross-sectional verification, e.g., for bending stresses and fatigue, is done independently according to corresponding criteria of the ULS determined for strength verification a fatigue assessment separately. The presented article deals with the steel railway plate girder bridge with bottom member deck, in which there is an effort to prove the effect of the crack in tension bottom flange due to fatigue stressing on the change of bending resistance over time. The analytical calculation was derived and at the same time, the probabilistic approach of the influence of the fatigue crack size on the change of the cross-sectional resistance and reliability over time was used.

Fatigue Damage Evaluation of Compressor Blade Based on Nonlinear Ultrasonic Nondestructive Testing

Nonlinear ultrasonic testing is highly sensitive to micro-defects and can be used to detect hidden damage and defects inside materials. At present, most tests are carried out on specimens, and there are few nonlinear ultrasonic tests for fatigue damage of compressor blades. A vibration fatigue test was carried out on compressor blade steel KMN, and blade specimens with different damage degrees were obtained. Then, the nonlinear coefficients of blade specimens were obtained by nonlinear ultrasonic testing. The results showed that the nonlinear coefficient increased with the increase in the number of fatigue cycles in the early stage of fatigue, and then the nonlinear coefficient decreased. The microstructures were observed by scanning electron microscopy (SEM). It was proven that the nonlinear ultrasonic testing can be used for the detection of micro-cracks in the early stage of fatigue. Through the statistical analysis of the size of the micro-cracks inside the material, the empirical formula of the nonlinear coefficient β and the equivalent crack size were obtained. Combined with the β–S–N three-dimensional model, an evaluation method based on the nonlinear ultrasonic testing for the early fatigue damage of the blade was proposed.

The Crack Angle of 60° Is the Most Vulnerable Crack Front in Graphene According to MD Simulations

Graphene is a type of 2D material with unique properties and promising applications. Fracture toughness and the tensile strength of a material with cracks are the most important parameters, as micro-cracks are inevitable in the real world. In this paper, we investigated the mechanical properties of triangular-cracked single-layer graphene via molecular dynamics (MD) simulations. The effect of the crack angle, size, temperature, and strain rate on the Young’s modulus, tensile strength, fracture toughness, and fracture strain were examined. We demonstrated that the most vulnerable triangle crack front angle is about 60°. A monitored increase in the crack angle under constant simulation conditions resulted in an enhancement of the mechanical properties. Minor effects on the mechanical properties were obtained under a constant crack shape, constant crack size, and various system sizes. Moreover, the linear elastic characteristics, including fracture toughness, were found to be remarkably influenced by the strain rate variations.