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In the process of aircraft structure X-ray images evaluation，there are some problems such as inaccurate crack segmentation and difficult crack detection under complex background. An intelligent evaluation model （ELAN-Seg） for X-ray crack images of aircraft structures is proposed based on efficient layer aggregation network. The ELAN-Seg model is compared with the DeepLabv3+ model in the crack segmentation ability of the Xray images. Combined with image processing technology，the crack length of model segmentation is evaluated，and the model is verified by X-ray images acquired during aircraft strength test and field maintenance. The results show that the segmented minimum crack length is about 3 mm，the ELAN-Seg model is more accurate in crack segmentation of complex background X-ray images，and the crack detection rate is less than 3.8%. The proposed model has engineering applicability.

With respect to the fatigue failure of typical bolted joints of aircraft subjected to the random block spectrum, the micro-observation technology was used to analyze the macro and micro fracture morphology characteristics, and to reveal the fatigue failure mode and micro failure mechanism of bolted joint. Combined with the fatigue load spectrum and micro fatigue strip characteristics of the bolted joint, the fatigue crack propagation and initiation life were quantitatively derived based on the Paris formula, and the relation between fatigue crack length to the load cycle number and flight hour are respectively developed. The results show that the fatigue crack of the bolted joint originates from the bottom surface of the bolted joints with stress concentration, showing the multi-source mode. The fracture surface possesses typical fatigue characteristics, including crack source zone, crack growth zone and instantaneous fracture zone. It is also found that the two-stage function formula can properly characterize the evolution law between the fatigue crack growth length to the cycle number and flight time during the whole fatigue life. The fatigue crack growth and initiation life were calculated as 3 147.7 and 615.4 hours, and the configuration and manufacturing process of the bolted joint need to be improved to meet the requirements of safety life design.

Objective To understand the current situation of the experimental miniature pig industry and promote its good development.Methods Using Questionnaire Star to design the survey content, the survey was conducted by targeted push and voluntary filling. The valid questionnaires collected were classified and summarized by EXCEL2010 software.Results A total of 35 entities participated in the survey, including 12 production entities and 23 user entities. There were 1 623 employees in the 35 entities, 927 (57.11%) with college degree or below, and 696 (42.89%) with bachelor degree or above. The largest number of employees have majors in animal science and animal medicine. The salary level of employees in the production entity is higher than that of the user entity, but the research output (published papers and patents) rate of the user entity in the past 5 years is higher than that of the production entity. The current inventory of miniature pigs in 12 production entities was 5 353, of which 3 471 (64.84%) were Bama pigs and 5 243 (97.95%) were ordinary grade pigs. The vaccination rate of swine fever and foot-and-mouth disease was 100%, and the animal mortality rate of seven entities was ≤3.0%. The profit of ordinary grade miniature pigs was 954 yuan/head, and that of SPF grade miniature pigs was 10 037 yuan/head.Conclusion It is suggested to strengthen market supervision, expand the channels for introducing professional and technical talents, accelerate the research of new quality testing technologies, promote the rapid transformation of miniature pig scientific research achievements, and establish a public service platform to strengthen information communication between supply and demand sides. We hope to work together with our colleagues to jointly promote the normalized, standardized, healthy and stable development of the experimental miniature pig industry.

High cycle fatigue P-S-N curve of material are important for the design of aero-engine strength. Based on the data processing requirement of the high cycle fatigue of aero-engine materials, a novel data processing method has been developed by proposing the criterion of selecting fitting model and the method for determining the critical stress between the medium and high fatigue cycle regions. Furthermore, the testing data of two common Ti-alloy materials in aero-engine are used to validate the present batch processing method, and the P-S-N curves in various conditions have been obtained. And the comparison of the process time between the present method and the conventional method has been conducted finally. The results show that the present data processing method is suitable not only for the data processing of the traditional high cycle fatigue issues, but also for the data processing of very high cycle fatigue issues. And the efficiency of data processing is significantly improved.

This paper proposes an ultra high frequency fatigue experimental approach based on electrodynamic shaker. The ultra high frequency fatigue specimen of TA11 titanium alloy sheet was designed after FEM calculation. The actual testing frequency of the designed specimen could be reached as high as 1756 Hz. The fatigue tests of both the ultra high frequency specimen and standard vibration fatigue specimen were carried out under the same stress level, and the consistency of test results was statistically verified. The results show that under the same stress condition,the testing results of the high frequency fatigue specimen proposed in this study are in good agreement with the experimental results of standard vibration fatigue specimen. Furthermore, the comparison of the present experimental results with the axial-loading fatigue and rotating bending fatigue results for the same material is conducted,and also a good consistency is obtained.

Fatigue crack propagation behaviors at high temperature are important preconditions for damage tolerance design in aircraft and engine structures.Therefore, fatigue tests were carried out on titanium alloy Ti-6Al-4V/ELI subjected to constant amplitude loading at two temperatures of 25 ℃ and 250 ℃ and three stress radios of 0.06, 0.5, -1 to determine fatigue crack propagation behaviors. Fatigue crack propagation da/dN-ΔK curves and da/dN-ΔK-R surfaces were obtained from experimental data by secant method. Those behaviors at different temperatures were compared and analyzed, and the interaction mechanism between high-temperature and fatigue load was deduced from fractographical study by SEM analysis.The results show that the larger the stress ratio R, the faster the rate of crack propagation of Ti-6Al-4V/ELI under the same temperature and stress intensity factors rangeΔK. Oxidation products and large numbers of secondary cracks are found on the fatigue fracture surfaces at high temperature and the destruction mode of crack propagation is gradually changed form cleavage to quasi-cleavage. Acceleration effect of oxidation and deceleration effect of secondary cracks combine affecting the crack propagation rate; when R is 0.5 or 0.06, those two seem equal and the effect of temperature is not obvious, while R is -1, more and deeper secondary cracks caused by fully interaction of high temperature and fatigue load make crack propagation rate at high temperature lower than that at room temperature.

A trace of Zn doped 0.997K0.37Na0.63NbO3-0.003BaBiO3 based lead-free piezoelectric single crystals were prepared by a seed-free, solid-state method. The effects of Zn doping on the growth, microstructure and electrical properties of the single crystals were systematically studied. The results show that the Zn doping does not change the perovskite crystalline structure of the crystals. Compared with many other dopants, Zn doping can effectively reduce or even avoid crystal cracking, and bending/warping deformation during the growth process. With the increase of Zn content, the volume of the grown crystal first increases and then decreases, while the roughness of the crystal exposed surface first decreases and then increases. When the Zn-doping content is 0.8at.%, the size of the crystal reaches the maximum value of 12 × 10 × 2 mm3. The influence of Zn-doping content on the main electrical properties of the crystals also shows a similar changing relationship. For the crystal doped with 0.8at.% Zn, excellent electrical properties can be obtained as below: d33 = 354 pC/N, Pr = 47.2 µC/cm2, Tanδ = 0.6%, kt = 0.68, εr = 515, Tc = 402 °C. The results imply that the crystal has promising development and application prospects. [ABSTRACT FROM AUTHOR]

K0.5Na0.5NbO3(KNN)-based piezoelectric single crystals have relatively high Curie temperature and piezoelectric properties. Seed-free solid state crystal growth (SFSSCG) method has many advantages, such as simple process, low cost, easy composition control and no seed crystal required, etc. In this work, (1 − x)[0.997(0.996K0.5Na0.5NbO3–0.004MnBiO3)–0.003B2O3]–xLi2CO3 (x = 0, 0.001, 0.003, 0.005, 0.007) single crystals were prepared by the SFSSCG method with B2O3 used as a sintering aid. And the effects of Li doping on the growth, morphology, structure and electrical properties of the crystals were investigated. The investigation results indicate that Li-doping is beneficial to the growth of the crystal. The formation of tetragonal phase, a secondary phase, is promoted by the addition of appropriate amount of Li, especially at 0.3at.%. The electrical properties of the crystals are enhanced obviously after Li-doped. When doped with 0.3at.% Li, the crystal has excellent piezoelectric properties as follows: d33 = 422 pC/N, tanδ = 0.034, TC = 429°C, and Qm=166, etc. These results suggest that the obtained crystals have potential and promising application prospects in the field of environmental-friendly piezoelectric devices. [ABSTRACT FROM AUTHOR]

Growth performance and meat quality are important traits for pig production. The aim of the present study was to investigate the molecular mechanisms underlying growth performance and meat quality, and to identify novel target molecules for predicting the growth performance and meat quality. The differentially expressed genes (DEGs) in Diannan small ears pigs (DSP) and Landrace pigs (LP) were assessed by RNA-sequencing analyzing technology. A total of 339 DEGs were obtained between DSP and LP. 146 DEGs were upregulated in LP compared with DSP and 193 DEGs were upregulated in DSP compared with LP. The DEGs were significantly enriched in 26 GO and 3 KEGG pathways. The protein–protein interaction (PPI) network with 201 nodes and 382 edges was constructed and 5 modules were extracted from the entire network. The identified upregulated expression of genes involved in glycolysis and myogenesis as well as extracellular matrix may be associated with fast body and muscle deposition rates in LP. Increased expression of genes involved in PPAR signaling pathway and fatty acid metabolism as well as oxidative phosphate processes could be related to the intramuscular fat deposition and meat quality in DSP. The present study may provide an improved understanding of the growth performance and meat quality. [ABSTRACT FROM AUTHOR]

Sandwich composites are susceptible to interfacial delamination, owing to the mismatches in the material properties between the face sheets and core. Previous studies have shown that stitching can improve the performance of sandwich composites. In this study, an analysis approach was developed to investigate the fracture behaviour of stitched foam sandwich composites. The stitched foam sandwich composites were manufactured by a vacuum-assisted resin transfer moulding process. Interlaminar tension tests revealed the effects of the linear thread density on the failure mechanisms of the stitched foam sandwich composites. Asymmetric double cantilever beam tests were performed to investigate the influences of the stitch thread reinforcement on the fracture behaviour. An analytical approach combining extended finite element method and nonlinear spring elements was proposed to predict the failure behaviour of the stitched sandwich composites. Experiment and simulation approaches were employed to investigate the influences of the stitch parameters (stitch pitch and linear thread density) on the ultimate load and energy absorption. The results show that stitched method can significantly enhance the mechanical properties of sandwich composites. The energy absorption and ultimate load values of the specimens tend to increase with an increase in the linear thread density or a decrease in the stitch pitch. [ABSTRACT FROM AUTHOR]