Contact Strength of Material

Contact is one of the common positions for relationship existing between surfaces of mechanical components with line or point shape, which lead to different stress condition between them. Classic Hertz theory solved the stress distribution of two components with different contact form. The different stress form of contact components will result in different failure modes, and different strength requirement is needed in design. For those works under conditions like classic Hertz contact, obvious plastic deformation should be avoided and the maximum stress should be smaller than the allowed limit stress which is usually equal to yield stress of material. While for the ones enduring load by extrusion of two contact surface, the crushing of two contact surface should be avoided and the maximum contact stress should be smaller than the ultimate strength of the material. But for those works under varying stresses, fatigue and wear are common failure modes. The typical failure form resulted from contact fatigue is pitting and spalling; the previous one usually results in small peeling of materials from surface and lots of small shallow pits will formed, while the spalling usually leads to lager part of material drop off from the surface and scrap of mechanical components. Wear is another failure form of components works under contact conditions, which is actually can be seen as the accumulation of pitting of asperities. Comparing the classic static strength theory and fatigue strength theory of material, the static contact strength is actually the limit condition of contact fatigue strength with the one circle stress loaded in the whole life. With the development of fatigue theory, lots of models were proposed to study the contact strength of material from the fracture mechanics view. The most popular ones are critical plane method and Dang Van multi-axial fatigue criterion, which are used to assess the crack initiation of materials works under contact load

Sparse Fast Fourier Transform and its application in intelligent diagnosis system of train rolling bearing

Healthy status monitoring of train bearing online is very meaningful work. But as traditional diagnosis system does, performing Fourier spectrum with the datum from more than 200 bearings in a marshalling train is an enormous challenge. Here a healthy status monitoring system of train rolling bearing based on Sparse Fast Fourier Transform (SFFT) is proposed. The monitoring system consists two sequential parts. First, extract fault features based on SFFT spectrum and other time-domain parameters. According to train bearing working environment, altogether 7 fault features are extracted in this paper. Another part is constructing a classifier based on BP neural network. Experimental results show that the system proposed here achieves gratifying results comparing with traditional fault diagnosis syste

Protective effects of Zhuifeng tougu on collagen-induced arthritis in DBA/1 mice

Purpose: To investigate the protective effects of Zhuifengtougu (ZFTG) on rheumatoid arthritis (RA) using collagen-induced arthritis (CIA) mouse modelMethods: DBA/1 mice were randomly divided into 7 treatment groups (n = 8): normal, positive control (CIA mice), CIA mice + total glucosides of peony (TGP), CIA mice + cyclophosphamide (CPA), CIA mice + 100 mg/kg ZFTG, CIA mice + 200 mg/kg ZFTG, and CIA mice + 400 mg/kg ZFTG. The serum levels of interleukin (IL)-1β, IL-6, IL-10, IL-17 and tumor necrosis factor (TNF)-αwere measured by enzyme-linked immunosorbent assay (ELISA). Western blot was used to determine the protein expression of B-cell lymphoma 2 (BCL-2), p53 and first apoptosis signal receptor (Fas).Results: Following drug administration, the arthritic index in CIA mice administered low-dose, mediumdose, or high-dose ZFTG (1.53 – 1.87), TGP (1.75 ± 0.42), or CPA (1.52 ± 0.36) was reduced significantly (p < 0.05), compared with positive control group (5.66 ± 0.73; p < 0.01). Levels of IL-1β, IL-6, IL-17 and TNF-α in serum and expression of Bcl-2, p53, and Fas were also significantly decreased (p < 0.05) in CIA mice administered ZFTG, TGP, or CPA, whereas IL-10 levels increased.Conclusion: These results suggest that ZFTG exhibit anti-rheumatic activity in CIA mice via modulation of inflammatory cytokines (IL-1β, IL-6, IL-10, IL-17 and TNF-α) and downregulation of the expressions of Bcl-2, p53, and Fas. Thus, ZFTG is a potential candidate drug for the treatment of RA.Keywords: Zhuifengtougu pill, Rheumatoid arthritis, Cytokines, Bcl-2, Fas, p5

Semilocal convergence analysis of an eighth order iterative method for solving nonlinear systems

In this paper, the semilocal convergence of the eighth order iterative method is proved in Banach space by using the recursive relation, and the proof process does not need high order derivative. By selecting the appropriate initial point and applying the Lipschitz condition to the first order Fréchet derivative in the whole region, the existence and uniqueness domain are obtained. In addition, the theoretical results of semilocal convergence are applied to two nonlinear systems, and satisfactory results are obtained

The allogeneic umbilical cord mesenchymal stem cells regulate the function of T helper 17 cells from patients with rheumatoid arthritis in an in vitro co-culture system

BACKGROUND: Previous in vivo studies have shown that mesenchymal stem cell (MSC) transplantation significantly improves the condition of a number of autoimmune diseases including autoimmune cerebrospinal meningitis, multiple sclerosis, glomerulonephritis and systemic lupus erythematosus. METHODS: To investigate the immunoregulatory effect of stem cell transplantation, human umbilical cord MSCs were co-cultured with peripheral blood mononuclear cells (PBMCs) from patients with rheumatoid arthritis (RA). Orphan nuclear receptor gamma (ROR-γ) mRNA and protein expression was detected with real-time PCR and Western blotting. Interleukin (IL)-17, IL-6 and tumor necrosis factor (TNF-α) in the cell culture supernatant were measured using a flow cytometric bead capture method. RESULTS: After 72 hours of co-culture, the mRNA and protein expression levels of ROR-γ in co-cultured PBMCs were decreased compared with that in PBMC of RA patients cultured alone (p < 0.05). Moreover, the decrement was positively related to the disease activity of RA (p < 0.05). Decreased secretion of IL-17, TNF-α and IL-6 were also found in co-culture supernatants of PBMCs from patients with severe and moderate disease activity, but not in supernatant from PBMCs cultured alone. The decreased cytokine expression levels were positively correlated to the concentrations of MSCs. In contrast, PBMCs from healthy controls or patients with mild RA did not show significant differences in ROR-γ expression or cytokine secretion following co-culture with MSCs as compared with those cultured alone. CONCLUSIONS: In vitro co-culture with MSCs down-regulated the inflammatory response of PBMCs from RA patients with severe disease activity, but had no significant effect on PBMCs from healthy controls or patients with mild disease activity, suggesting that the immunoregulatory role of MSCs may associate with the occurrence of inflammatory mediators

Calibration of the Radical Installation Limit Error of the Accelerometer in the Gravity Gradient Instrument

Gravity gradient instrument (GGI) is the core of the gravity gradiometer, so the structural error of the sensor has a great impact on the measurement results. In order not to affect the aimed measurement accuracy, limit error is required in the installation of the accelerometer. In this paper, based on the established measuring principle model, the radial installation limit error is calibrated, which is taken as an example to provide a method to calculate the other limit error of the installation under the premise of ensuring the accuracy of the measurement result. This method provides the idea for deriving the limit error of the geometry structure of the sensor, laying the foundation for the mechanical precision design and physical design