The creep-fatigue interaction in directionally solidified nickel-base superalloy was analyzed with the modified Chaboche-based unified viscoplasticity constitutive model. The model features the ...anisotropic material behavior, hardening/softening, and stress relaxation. Simple low-cyclic fatigue and specified hold time experiments were conducted on a directionally solidified superalloy (DZ125) at temperatures over 760°C. The material parameters were optimized considering its tensile, cyclic and creep behavior with the Levenberg–Marquardt optimization procedure. The model was constructed in FORTRAN and integrated in FEA software UMAT/ABAQUS. The results show that experimental and simulated hysteresis loop size/shape, peak stresses, stress relaxation, and related areas are closely matched. The modified constitutive model was found to be instrumental for revealing the fatigue and creep-fatigue interaction behavior of such materials and can be used for practical applications.
With the purpose of minimizing the makespan of three-machine job shop scheduling problem with intermediate transfer, in this study, a new model was built to perform the makespan minimization, which ...was proved to be strongly NP-hard. From this model a heuristic algorithm was subsequently derived with a worst-case error bound. The proposed model and derived algorithm were verified through computational experiments carried out on a couple of small size random instances. The results show that the heuristic algorithm possesses a tight worst-case bound of 2. This research presents an approach for obtaining the optimal solutions of the NP-hard problem within a reasonable time.
Low‐cycle fatigue tests were conducted on the directionally solidified nickel‐base superalloy DZ125 at 850 °C in the unexposed and exposed specimens for 2, 15, 25 and 50 h in hot corrosion ...environment. The pre‐exposed specimen exhibited a lower life than unexposed specimens. Fatigue cracks in the unexposed specimens are initiated from defects near the surface, while the cracks of exposed specimens preferentially occur on the surface. Hot corrosion damage in fatigue life was found to be associated with the reduction of the bearing area. A novel life prediction methodology based on continuum damage mechanics was proposed to predict the experimentally observed decrease in low‐cycle fatigue life with increasing prior exposure time.
Abstract We studied the effect of vasoactive intestinal peptide (VIP) on angiogenesis in the ischemic boundary area after focal cerebral ischemia. Adult male Sprague–Dawley rats underwent middle ...cerebral artery occlusion for 2 h. A single dose of VIP was given via i.c.v. injection at the beginning of reperfusion. Immunohistochemistry and Western blotting were performed to assay angiogenesis and brain levels of vascular endothelial growth factor (VEGF) protein, respectively. In addition, the expression of VEGF and its receptors (flt-1 and flk-1), as well as endothelial proliferation, was measured using rat brain microvascular endothelial cells. Immunohistochemical analyses revealed significant ( P <0.05) increases in the numbers of bromodeoxyuridine (BrdU) positive endothelial cells and microvessels at the boundary of the ischemic lesion in rats treated with VIP compared with rats treated with saline. Western blotting analysis showed that treatment with VIP significantly ( P <0.05) raised VEGF levels in the ischemic hemisphere. In addition, treatment with VIP increased flt-1 and flk-1 immunoreactivity in endothelial cells. In vitro , incubation with VIP significantly ( P <0.01) increased the proliferation of endothelial cells and induced the expression of VEGF, flt-1 and flk-1 in endothelial cells. The stimulatory effect of VIP on the proliferation of endothelial cells was significantly ( P <0.01) inhibited by SU5416, a selective inhibitor of VEGF receptor tyrosine kinase. Our data suggest that treatment with VIP enhances angiogenesis in the ischemic brain, and this effect may be mediated by increases in levels of VEGF and its receptors.
With the increase in populations with suboptimal health and chronic diseases, consumer demands for health foods, especially food products with health functions. The flaxseed was a complex mixture ...mainly consisting of flaxseed oil, flaxseed protein, dietary fibre (including cellulose and flaxseed gum), carbohydrates and secoisolariciresinol diglucoside (SDG). To investigate the effects of expanded flaxseed meal (EFM) intervention on the hypoglycaemic and lipid-lowering functions of rats on a high-fat, high-sugar (HFHS) diet, EFM was fed to six groups (z = 8) of Sprague–Dawley (SD) rats: normal control, HFHS model, positive treatment control, and low-, medium-, and high-dose EFM (5%, 10% and 20% mass fraction EFM, respectively) groups. The results (8 weeks later) were as follows: (1) medium- and high-dose EFM achieved similar inhibitive effects on blood glucose levels compared with positive treatment (5.94±0.32 mmol/L); (2) all EFM doses significantly reduced total cholesterol, triglyceride and low-density lipoprotein cholesterol levels in the blood plasma of SD rats and (3) EFM significantly increased glutathione peroxidase, superoxide dismutase and catalase activities, increased glutathione levels, and reduced the malondialdehyde content in the plasma of SD rats (P < 0.05). Therefore, EFM mitigated the adverse effects produced by HFHS diet on physiological functions, effectively regulated blood glucose and lipid metabolism, enhanced plasma antioxidant capacity and alleviated oxidative stress in SD rats with a certain dose–effect relationship among the EFM dose groups. Hepatic histological morphologies indicated that EFM also improved the size and density of lipid droplets in the liver of the rats and inhibited the onset of fatty liver. These results suggest that EFM is a potentially useful raw material in the development of blood glucose and lipid-lowering food products.
A simple method for preparing LiTi
2O
4 is reported in this paper. Characterization by the X-ray diffraction method indicated that the LiTi
2O
4 had formed with the spinel crystal structure. The ...particle size and shape of the compound were observed by scanning electron microscopy techniques. The superconducting and electrochemical properties of LiTi
2O
4 spinel have also been investigated. The results showed that this material is not only a superconductor with critical temperature,
T
c
=
13
K, but also a promising anode material, which showed discharge specific capacity (240
mAh
g
−1) and excellent cycling ability in the range of 3.00–0.01
V at certain current density (20
mA/g).
In order to explore the ablation law and characteristics of carbon/carbon composite materials on the surface thermal protection of hypersonic vehicles under the condition of particle erosion, the ...ablation test of a 4D C/C composite was carried out based on a small plasma simulated ablation test system. Four sets of experiments were designed according to different temperature and particle concentration. After the test, two kinds of ablation rate were measured, and the microscopic ablation morphology was observed by scanning electron microscope (SEM) and the ablation behavior was analyzed. The results show that, under the equivalent test conditions, the rate of jet temperature increases, and the material ablation rate increases. With the increase of particle concentration, the two kinds of ablation rate of materials increased, the maximum mass ablation rate was 0.0363 g·s−1, and the line ablation rate was 0.053 mm·s−1. The temperature affects the thermal erosion rate of the material, while the particle mainly causes mechanical erosion. The particle has a coupling effect of heat transfer and mechanical destruction on the material, and the material ablation is intensified. Moreover, due to the strong corrosion resistance of carbon fiber, the overall corrosion resistance of materials has obvious anisotropy.
This study evaluated the outcomes of using porous tantalum rods for the treatment of osteonecrosis of the femoral head (ONFH). We performed core decompression and inserted porous tantalum implants in ...149 patients (168 consecutive hips) with ONFH. Hips had large (65), medium (64), or small (39) lesions; 63 lesions were lateral, 68 were central, and 35 were medial. Conversion to total hip arthroplasty (THA) was the end point of this survey. A total of 130 cases (138 hips) were followed. The mean follow-up time was 38.46 ± 5.76 months; 43 hips (31%) were converted to or needed THA. Of the 43 hips requiring THA, 33 had large lesions, including 1 medial, 3 central, and 29 lateral lesions; 9 had medium, lateral lesions, and 1 hip had a small, lateral lesion. Bone grafting was used in 59 hips, with 3 hips failing; 40 of 79 hips without bone grafts failed. The sum distances between the tops of the rods and the lateral lesion boundaries (SDTL, mm) were measured in anteroposterior and lateral radiographs. In the failure and spared groups, the average SDTLs were 7.65 ± 2.759 and 0.83 ± 2.286 mm, respectively. The survival of porous tantalum rods used for treating early-stage ONFH was affected by the size and location of the lesion, whether or not a bone graft was used, as well as the distance between top of the rod and the lateral boundary of the lesion.
•A unified SVR fatigue life model with 17 dimensionless inputs is developed to for Ni-based superalloy family.•The proposed model achieves a good prediction accuracy for both LCF and HCF regimes ...under wide loading conditions.•An evaluation method for model generalization based on the model uncertainty and data dependence is established.•Dimensionality reduced SVR models that trained with key features reorganized remains the acceptable life prediction accuracy.
Machine learning (ML) approaches, especially the supervised learning methods, show enormous advantages in fatigue investigation, whereas few works follow the interest in the generalization and uncertainty estimation of these data-drive approaches. Within this content, a supervised ML method based on the support vector regression (SVR) for key features identification of fatigue life is presented for the Ni-based superalloy family. The unified SVR model is effective at predicting lives for the Ni-based superalloy family under wide loading conditions and fatigue regimes compared with the classical fatigue life models. In addition, a model fusion method is employed to estimate the uncertainty and data dependency of the SVR model, with which the training strategy produces an important effect on the accuracy and stability of the predicted results. It is found that the coefficient of the uncertainty achieves the optimum where the training percentage is 70% of the modelling samples. After input variable selection by the pairwise Pearson correlation and key feature reorganization, the dimensionality reduced SVR model remains an acceptable accuracy. Predictably, the total strain range and the test frequency are recognized as the highly correlated variables with the fatigue life investigating from the perspective of datasets. The trained ML model and uncertainty estimation approach provide potential tools for fatigue investigation under complex loading conditions. Going forwards, it would be beneficial to generalization ability and uncertainty estimation of a ML model for unified fatigue life modelling.
Directionally solidified (DS) and single crystal (SC) Ni-based superalloys inevitably underwent microstructural degradation induced by the harsh operating environment. For the safety service and ...economic overhaul, constructing a quantitative mapping chain from service process to microstructural degradation and to property deterioration is critically essential. The present work started with stress-free and stress-assisted pre-service treatments of a DS Ni-based superalloy to obtain microstructures with different degraded states. An imaging process based on two-phase rotary chord length distributions was established to extract the high dimensional statistical information for identifying the morphology and size features of microstructures. To reduce the dimension of the statistical information and quantitatively characterize the microstructural states in fewer parameters, principal component analysis was employed to capture the core microstructural indicators, which was utilized to establish the response surface between the deterioration of fatigue resistance and the microstructural degradation. Finally, a multi-output support vector regression (SVR) model was constructed to map between service process and microstructural degradation. The results showed acceptable accuracy to estimate the microstructural degradation of pre-serviced alloys. Meanwhile, the framework provides a technical chain for the waste determination and microstructural degradation estimation of the hot section components made by DS and SC Ni-based superalloys.
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•A two phase chord length distribution approach to extract the morphology and size information from microstructural SEM images for Ni-based superalloys was established and the image-related robustness of the algorithm was provided.•A multi-output support vector regression model was developed to build the quantitative map between service and aging process and microstructural degradation states.•A quantitative map of service process-microstructural degradation-property deterioration was constructed based on the TP-CLD and SVR approach.
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