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Considering the ever-increasing importance of composite patches applied to repair or reinforce composite structures, radical health monitoring of these patches seems inescapable. Thermography method is one of the most influential non-destructive methods applied to inspect the repaired structures. Since there are many parameters influencing defects detection in repaired composite structures, extracting the most influential method to determine these parameters is significantly important. In the present study, a repaired carbon fiber reinforced plastic (CFRP) composite structure having defects of different dimensions, types and features located in different depths, is investigated by experiment and finite element simulations to assess the influence of the experimental parameters, like the thermal excitation pulse duration and the best image frame. In thermal simulation, two criteria, maximum thermal variations versus time and path length, are developed to derive the most optimum heating duration and the best thermal frames. The obtained results are validated through defining direct and diagonal paths passing through defects demonstrated on thermography images and thermal map images. The average error of thermal variations on different paths displayed on thermography and simulation images is less than 4.5 percent which confirms the correspondence of obtained results of both mentioned methods. [ABSTRACT FROM AUTHOR]

The size and depth of defects significantly affect fatigue performance; the main purpose of this article is to clarify the effect of stress correction factors caused by defects on the fatigue life of α + β Type titanium alloy welded joints. In order to investigate the fatigue characteristics of α + β Type titanium alloy welded joints, axial constant amplitude loading fatigue tests were performed with a stress ratio of −1. The test results show that the fatigue life continues to increase as the stress amplitude decreases, and the failure modes can be classified into two types: interior failure and surface failure. A fatigue parameter (λ) determined by both defect depth and size was proposed which allowed for a good generalization of the data point distribution in short and long-life regions. The stress correction factor (W) related to the S–N characteristics was constructed by combining the λ and average defect size, and it effectively improved the dispersion of the test data. Continuing, the fatigue life prediction model was established under the condition that the defect type and size can be estimated or detected on the basis of the dislocation energy method. The results indicated that the evaluated values of the new life model associated with W are in good agreement with the test results. [ABSTRACT FROM AUTHOR]

The size and depth of defects significantly affect fatigue performance; the main purpose of this article is to clarify the effect of stress correction factors caused by defects on the fatigue life of α + β Type titanium alloy welded joints. In order to investigate the fatigue characteristics of α + β Type titanium alloy welded joints, axial constant amplitude loading fatigue tests were performed with a stress ratio of −1. The test results show that the fatigue life continues to increase as the stress amplitude decreases, and the failure modes can be classified into two types: interior failure and surface failure. A fatigue parameter (λ) determined by both defect depth and size was proposed which allowed for a good generalization of the data point distribution in short and long-life regions. The stress correction factor (W) related to the S–N characteristics was constructed by combining the λ and average defect size, and it effectively improved the dispersion of the test data. Continuing, the fatigue life prediction model was established under the condition that the defect type and size can be estimated or detected on the basis of the dislocation energy method. The results indicated that the evaluated values of the new life model associated with W are in good agreement with the test results.

The detection of hydraulic tunnel by robot is an effective means to solve the safety inspection of inclined shaft section of diversion tunnel. The crawling robot equipped with three-dimensional laser scanner and high-definition camera equipment was used to inspect the structure of the water diversion tunnel, and the defect information of the diversion tunnel section was obtained through threedimensional point cloud processing and defect data splicing. Combined with the defect data processing results, the structural defect characteristics and distribution law of the diversion tunnel were analyzed to realize the inspection and analysis of the irregular shape, uneven distribution and coexistence of multiple defects of the diversion tunnel. The results show that the defects in the diversion tunnel include cracks, leakage and reinforcement leakage, and the number of defects in the upper flat section is significantly more than that in the inclined shaft section, and cracks are the main defect type of the diversion tunnel. The cracks in the upper flat section are mainly distributed at the top of the tunnel, and most of the cracks are horizontal cracks perpendicular to the tunnel axis. Fractures in inclined shaft section are evenly distributed in all positions around the tunnel, and most of them are inclined fractures. It can be seen that there are great differences in the number of defects and fracture characteristics between the upper flat section and the inclined section. In the later safety inspection process, we should mainly pay attention to the expansion of fractures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microstructure and defect characteristics of SLM Al-Mg-Sc-Zr alloy were studied. • The fatigue behavior of TD and PD specimens were investigated. • Discussed effects of defect features on fatigue qualitatively and quantitatively. • A comprehensive fatigue damage parameter considering stress and defect was proposed. Additive manufacturing (AM) has broad application prospects in the field of aviation, whereas it remains a challenge to fully eliminate the manufacturing defects. As a result, the fatigue performance is poor and has a large scatter. The fatigue performance and life prediction method have become a major hindrance for the application of AM in aviation field. In this paper, the microstructure and defect characteristics of SLM Al-Mg-Sc-Zr alloy that built in transverse direction (TD) and parallel direction (PD) were studied. Then the fatigue performance was investigated, and the relationship between critical defect characteristics and fatigue life was analyzed qualitatively and quantitatively based on fracture analysis. The microstructure exhibits a bimodal grain structure with fine grain size. The defect study shown that there are more large-size defects and higher porosity in the PD specimens. The fatigue life is significantly influenced by the location, size and circularity of critical defects and stress amplitude. Correlation analysis suggested that the defect location is the most influential factor on fatigue performance, followed by stress amplitude, defect circularity and defect size. Finally, a fatigue life prediction model based on stress amplitude and defect characteristics of the critical defects was proposed. [ABSTRACT FROM AUTHOR]

Refill friction stir spot welding (refill FSSW) was used to weld 3.2-mm-thick 2060 aluminum alloy. Joint formation, defect characteristics and tensile-shear property were analyzed. Results show that keyhole can be completely eliminated under different plunge depths. However, defects such as void, unconnected welding, hook can be observed under the plunge depths of 3.4-4 mm. The size of the overall void initially increased and then decreased with the increase of the plunge depth, while the void was the smallest under the plunge depth of 3.4 mm. The unconnected defect at the lap interface gradually shrank a welding line from obvious crack. Different hook morphologies were observed under different plunge depths. The tensile-shear load of joint increased with the increase of the plunge depth and was up to the largest under the plunge depth of 4 mm. All the tensile-shear specimens fractured along the lap interface. Compared with the void, the unconnected defect had a greater influence on the tensile-shear property.

The defect characteristic and magnetic properties of CuFe1-xCrxO2 (x = 0.0–0.4) compounds have been investigated in detail. The results demonstrate that Cr3+ ions enter into the CuFeO2 lattice sites and induce local lattice contraction but do not change the valance state of Cu+ and Fe3+ ions. We calculate the positron annihilation lifetime in the bulk and vacancy defect trapping states by the atomic superposition method in 3 × 3 × 1 CuFeO2 super-cell. Combined with theoretical calculation results, the positron annihilation results indicate that the positrons are mainly annihilated in vacancy clusters in CuFe1-xCrxO2. The substitution of Cr3+ for Fe3+ ions decreases the open volume and increases the concentration of vacancy defects but does not change the integral defect surroundings at annihilation sites. Magnetization measurements manifest that doping with Cr3+ reduces the antiferromagnetic transition temperature and promotes the formation of short-range magnetic correlation. Meanwhile, the enhanced short-range magnetic correlation in Cr3+-doped CuFeO2 is more readily driven by thermal activation energy and a faster dynamic behavior can be seen in time windows.

Refill friction stir spot welding (RFSSW) was used to weld the 2060 aluminum alloy with 2 mm thickness. Joint formation, defect characteristics and mechanical properties were investigated. Results show that stir zone (SZ) is clarified into dynamic recrystallization zone (DRZ) and heat extruded zone (HEZ) due to different microstructural features. The size of void near the hook tip decreases with the increase of the plunge depth. Different hook morphologies are obtained under different plunge depths. The tensile-shear load of joint with the void defect initially decreases and then increases with increasing plunge depth. The mean loads of joints under different plunge depths are in the range of 5.1-5.8 kN. The void separates the hook from lap interface, so the cracks initiating from the hook propagate along the sleeve retreating path. The hook has a larger influence on the tensile-shear load of joint than void. All the tensile specimens present a shear-plug fracture mode.

The defect characteristic and magnetic properties of CuFe1-xCrxO2 (x = 0.0–0.4) compounds have been investigated in detail. The results demonstrate that Cr3+ ions enter into the CuFeO2 lattice sites and induce local lattice contraction but do not change the valance state of Cu+ and Fe3+ ions. We calculate the positron annihilation lifetime in the bulk and vacancy defect trapping states by the atomic superposition method in 3 × 3 × 1 CuFeO2 super-cell. Combined with theoretical calculation results, the positron annihilation results indicate that the positrons are mainly annihilated in vacancy clusters in CuFe1-xCrxO2. The substitution of Cr3+ for Fe3+ ions decreases the open volume and increases the concentration of vacancy defects but does not change the integral defect surroundings at annihilation sites. Magnetization measurements manifest that doping with Cr3+ reduces the antiferromagnetic transition temperature and promotes the formation of short-range magnetic correlation. Meanwhile, the enhanced short-range magnetic correlation in Cr3+-doped CuFeO2 is more readily driven by thermal activation energy and a faster dynamic behavior can be seen in time windows. [ABSTRACT FROM AUTHOR]

Refill friction stir spot welding (RFSSW) was used to weld the 2060 aluminum alloy with 2 mm thickness. Joint formation, defect characteristics and mechanical properties were investigated. Results show that stir zone (SZ) is clarified into dynamic recrystallization zone (DRZ) and heat extruded zone (HEZ) due to different microstructural features. The size of void near the hook tip decreases with the increase of the plunge depth. Different hook morphologies are obtained under different plunge depths. The tensile-shear load of joint with the void defect initially decreases and then increases with increasing plunge depth. The mean loads of joints under different plunge depths are in the range of 5.1-5.8 kN. The void separates the hook from lap interface, so the cracks initiating from the hook propagate along the sleeve retreating path. The hook has a larger influence on the tensile-shear load of joint than void. All the tensile specimens present a shear-plug fracture mode. [ABSTRACT FROM AUTHOR]

The development of coiled tubing operation technology has continuously improved with the higher requirements of coiled tubing on-line detection technology. The current coiled tubing field weak magnetic on-line detection system calculates the gradient of the signal for improving the locating precision. Quantitative identification of defect shape, based on the weak magnetic detection and magnetic leakage flux systems, is a key issue to evaluate whether coiled tubing can continue to be used. The 2-D finite-element models with different typical defect shapes were established, and the gradient changes of the magnetic-field intensity are calculated. The influence of defect size on signal characteristics is analyzed, and a functional model can be obtained. The signal characteristics of a 2-D self-leakage magnetic field were further analyzed, and a 2-D cloud image was established used to identify the shape of defects. The level of damage as a result of coiled tubing use is evaluated according to the identified defect shape, which is significant for a quantitative description of defects and the accurate evaluation of conditions in the coiled tubing on-line inspection system. This research of identification of defect shape and size makes up the disadvantage that weak magnetic detection can only judge whether the defect of log exists or not. [ABSTRACT FROM AUTHOR]

Magnetic flux leakage (MFL) principle is widely used in detecting defects in cross-country pipelines. The tools based on the MFL techniques termed as instrumented pipeline inspection gauge (IPIG) are frequently used as per statutory requirement. The tool identifies the location of metal loss and also characterizes the size of metal loss defects in terms of length, width along circumference and depth in terms of percentage loss. Tool velocity in terms of frequency of data acquisition is important parameter whose effect on the MFL signal and on the defect quantification has been studied. Operation of linear pull through rig under various combinations of MFL tool parameters such as velocity, frequency and spatial sampling has been developed. A set of experiments by varying velocity from 0.25 to 2 m/s keeping frequency constant at 450 Hz have been carried out. MFL signals obtained from all known defects have been analyzed for its nature and quantifying the dimension of defect. The effect of velocity on individual dimensions of the defect has been studied in this work. Within the limitation of the experiments carried out, the present work indicates that smaller defects cannot be reported with better accuracy. Also, the velocity is seen to have a significant effect in characterizing the length of the defect using IPIG especially for defects of larger area. [ABSTRACT FROM AUTHOR]

A detailed cause-and-effect stochastic model is developed to relate the type, size, location, and frequency of observed defects to the final yield in IC manufacturing. The model is estimated on real data sets with a large portion of unclassified defects and uninspected layers, and in presence of clustering of defects. Results of this analysis are used for evaluating kill ratios and effects of different factors, identifying the most dangerous cases and the most probable causes of failures, forecasting the yield, and designing optimal yield-enhancement strategies. [ABSTRACT FROM AUTHOR]

• The very high cycle fatigue strength of titanium alloy fabricated by additive manufacturing is much lower than that of the traditional process. • Combining with the weak zone, Δ K FGA is analyzed, and it is found that the size of the FGA plastic zone was similar to the width of the martensitic laths. • Failure critical dimension is obtained and a new fatigue life relationship is established based on defect characteristics. • Based on probability statistics, the influence of maximum defect size on fatigue behavior is discussed. Tensile and fatigue behaviors of selective laser melted titanium alloy were investigated in the as-built condition. The alloy has a high defect density, and its tensile properties are comparable to those of wrought alloys, but the fatigue strength is significantly reduced. The FGA plastic zone is similar to the martensite laths width. The critical size of fatigue failure is analyzed by the K-T diagram. A new value is obtained based on the defect characteristics. Using the probability statistical, the maximum effective size of the defect considering the shape was calculated, and the competitive relationship of the defects was analyzed by volume density. [ABSTRACT FROM AUTHOR]