Applied Mechanics and Materials Vols. 395-396

Abstract: Ultrafine WC-Co cemented carbide cutting inserts were prepared by direct low pressure sintering and low pressure sintering after the powder pretreatment, tool life tests of continuous cutting superalloy GH2132 were carried out, respectively. ZEISS continuous zoom stereo microscope and microphotograph system were used to observe flank surface wear morphology of the cutting inserts, and analysis the topography and elements of central wear region of flank surface by X-ray energy dispersive spectrometry and scanning electron microscope. The results show that the main wear mechanism of ultrafine cemented carbide cutting inserts is adhesive wear, and the wear resistance of ultrafine cemented carbide cutting inserts that low pressure sintering after powder pretreatment is superior to direct sintering, powder pretreatment helps increase the resistance of abrasive wear, adhesive wear and oxidative wear as well as diffusive wear of cutting inserts.

Abstract: A fractured shaft was made of 45 steel. The properties and reasons of the shaft were found by micro and macro observation on fracture surfaces, metallographic examination and hardness testing. The results showed that the fracture mode of the shaft were one-off overload fracture of the central zone and fatigue fracture of the brim. The fatigue source zone was in the subsurface. The fracture was caused by the original defects existed in the shaft central zone. It propagated an about 140 mm crack in operation. The crack source propagated laterally along the big crack edge, which resulted in fracture morphology and fracture forms became complicated. The shaft heart material was made of ferrite-pearlite, inclining widmanstatten structure. According to the YB31-64 standard, it rated column C level 1.Due to uneven grains, mixed crystal phenomenon existed. In addition, because the shaft surface heat treatment process control improperly, the surface hardness was not high to reach the structure standard by quenching and tempering treatment.

Abstract: The stresses near the free edge of the interface of a joint of dissimilar materials after a change of the temperature can be described as the sum of one or two singular terms and a regular term which is independent of the distance and the geometry angles and . The regular stress terms are important for the stress distribution near the singular point. The emphasis in this paper is placed on giving an explicit form of the regular term by using a concept of equivalent edge load.

Abstract: Taylor impact tests are used as experimental and numerical tests for determining the mechanical behavior of materials subjected to high strain rates. Taylor impact tests are numerically simulated in the velocity range from 150m/s to 250m/s. Deformations of different impact velocity; impact damages of the axis centre; and the reasons of impact damage are discussed in the numerical simulation of Taylor impact test.

Abstract: The fundamental theory about the constitutive relationship of hyperelastic model has been introduced and the model of super-elastic coating has been simulated in this paper. The static stiffness of different coating thickness has been calculated considering the hyperelasticy and viscoelasticity. Through the studying, because of the increasing of deformation, the compression static stiffness of the hyperelastic coating will be increased; while the tension static stiffness of the hyperelastic coating will be decreased. Moreover, the static stiffness is only related to the relative deformation not the absolute deformation.

Abstract: The self-lubricant wear-resistant NiCr/Cr₃C₂-10%WS₂ coating and wear-resistant NiCr/Cr₃C₂ coating were obtained on Ti6Al4V by laser cladding. Microstructure of the coatings was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS). The wear properties were evaluated using a ball-on-disc wear tester under dry sliding condition. The results show that the laser cladding NiCr/Cr₃C₂-10%WS₂ composite coating has good friction-reducing and anti-wear capabilities at ambient.

Abstract: Ductile fracture is one of the defects in metal plastic forming. For predicting and preventing fracture occurs, a criterion describing the fracture accurately is necessary, especially in the case of numerical simulation. Three criterions, i.e. Cockcroft-Latham, McClintock, Rice & Tracey, were compared experimentally to decide the suitable one for GCr15 bearing steel. The damage values of the criterions were obtained through the standard tension and compression test. The blanking of the GCr15 sheet with 5mm thickness was numerical simulated with three criterions separately and conducted in laboratory. By comparing the blanking section of simulation and experiment, it was found that the McClintock criterion is the best one for describing the GCr15 bearing steel ductile fracture in these three criterions.

Abstract: Based on the probability theory, combined with the deterministic method for estimating the fatigue fracture mechanics, the formula was deduced to calculate the fatigue crack propagation life of examples components. The uncertainty and randomness of main assessment parameters were considered:initial crack size, practical working load,fracture toughness, mechanical intensity and coefficients. Since there are not many data, Weibull distribution was adopted to denote the life distribution of equipment approximately. A computer program was developed by using numerical integration method, and the fatigue life under given reliability and credit degree was solved. Analysis result shows that MonteCarlo simulation method can reflect objectively the uncertainty of assessment parameters and overcome the shortcomings of certainty assessment methods.

Abstract: In this paper, the analyzing and modeling of the friction coefficient in sliding bearing is reported. Based on the grey system theory, the effects of rotational speed and load on the friction coefficient of the sliding bearings are investigated. The grey relational grade is an important parameter to measure the effects of rotational speed and load on friction coefficient of the sliding bearings. The grey relational grade analysis shows that load has an even more significant effect upon the friction coefficient compared with rotational speed. On the basis of analyzing and processing the experimental data, a nonlinear model for friction coefficient of a sliding bearing have been set up by NARMAX Non-Linear Auto-Regressive Moving Average with Exogenous Input. It was found that the NARMAX Non-Linear model has good accuracy and is applicable for the calculation of friction coefficient in sliding bearing.

Abstract: That the key components of Water-based hydraulic components are easy to wear down in the course causes sealing performance degradation and then arises leakage, which affects water-based component life and hydraulic system operational reliability. Considering the characteristics of ceramic materials, the ceramic method is applied to improve the key parts of water-based component, and then wear and failure mechanism analysis was done on ceramic water-based component.