Advanced Materials Research Vols. 217-218

Abstract: Previous researchers investigated the failures of ball surfaces of silicon nitride bearings from the viewpoint of the ring crack model. They explained the process of flaking failures in terms of surface semi-circular cracks which grew by the stresses around the circumference of the contact circle. However, contrary to their explanation, we found that the ring crack model did not explain the process of the flaking failure of plates. In the present work we compare the growth directions of surface and subsurface cracks in order to find out which crack is more dominant in the process of the flaking failure. We carried out reciprocating-rolling contact fatigue (RCF) tests and concluded that the directions of arcs formed by the semi-circular surface cracks were dominated by subsurface crack growth direction.

Abstract: In the previous work, we found that the tensile stress occurring around the equator of the ball caused fatigue of the ball itself. Four groups of pre-cracks, whose surface lengths were 140μm, 220μm, 550μm and 700μm, were initiated on ball surfaces and the strength of these pre-cracked balls was measured. The static strengths and fatigue limits of all pre-cracked balls decreased with crack sizes. We concluded that the fatigue caused by a pre-crack located on the equator of the ball surface was important for understanding fatigue of silicon nitride balls. In the present work, carrying out fatigue tests of pre-cracked balls with 220μm cracks at three frequencies (5Hz, 20Hz and 35Hz) we found that the frequency had effect on speeds of the crack growths.

Abstract: In order to research the mechanic performance of 7A05 aluminum alloy, a series of tests, including tensile test about aluminum alloy substrate, tensile test about aluminum alloy butt welded joint, tensile test about transverse partition of aluminum alloy welded joint and hardness test were conducted. The results of these tests indicate that the strength and hardness of HAZ of this material exhibit a W-shaped reduction. There are an symmetrical softened area at 10~20mm from the center of weld. Due to ageing effect, the strength and hardness of HAZ can resume to 80%of the substrate one month after welding. Based on the analytical deduction and experimental data fitting, the theoretical strength model for HAZ of aluminum alloy is proposed. For the purpose of engineering design, the HAZ is transformed into a uniform strength reduction zone, the width and strength value is determined according to the principle of equal strength.

Abstract: This paper discusses two intelligent learning methods—Genetic Algorithms (GA) and Case- based Reasoning (CBR), and analyses the shortcomings of the current techniques of CBR. The new idea is put forward by using the GA and good-point-set to solve the problems of CBR. An improved GA and Good-point-set GA are quoted here. We have applied the two GAs to assign the weights automatically of attributes in CBR systems.

Abstract: AZ91D alloy matrix composites(MMCs) with volume fraction of 15%, 20%, 25% and 30% were prepared with the preform made of crystallized aluminum silicate short fibers as reinforcement and aluminum phosphate as binder by squeezing casting at high temperature. Dry sliding wear properties of the composites were tested by means of MM200 wear tester (block-on-ring configuration) against a hardened alloy steel counterface with hardness of 53HRC under loads of 10N, 20N, 30N, 40N and 50N and sliding speed of 0.47m/s and 0.92 m/ s, and wear morphology of the specimens was observed by SEM (scanning electron microscope). The results reveal that effects of sliding speed on wear rate of the composites are greater and more complex than on those of the AZ91D matrix alloy, which is closely related to not only volume fraction in the composites but also applied loads.

Abstract: In order to improve deposition speed of electroless nickel plating coating, composition of complex accelerating agent was optimized by orthogonal test, and SEM and its EDS was used to analyze the plating morphology. The results show that the deposition speed is increased to 27.5μm/h after 0.002g/L of cadmium sulfate, 0.05g/L of sodium dodecyl sulfate, 10g/L of malic acid and 15g/L of butanedioic acid was mixed into an electroless plating solution. The coating holds good surface quality and its phosphorus content is 14.03%, any pore was not found on the surface and decay resistance of the coating was improved.

Abstract: This note deals with a class of switched systems with nonlinear perturbations in mixed delayed state. Based on the multiple functional appoach, we establish a delay dependent stability condition via designing appropriate switching rule. This result indicates that if the norm of system matrices is small enough, the uniform asymptotic stability is always achieved.

Abstract: Different denoising methods are used in parameter identification for the dynamic load modeling and the specific approach is proposed. The effects of different denoising methods including mean filtering, medial filtering and wavelet denoising are discussed. Mean filtering method is not helpful to contain the step changes of the measurement voltage, thus is unsuitable for the parameter identification process. Medial filtering method and wavelet denoising methods are suitable for the parameter identification in dynamic load modeling. Furthermore, experiment results based on the measurement data show that the wavelet denoising method is more efficient in some aspects such as the accuracy of identification and SSE.

Abstract: We mainly give research and application status of iridium and iridium alloy materials in this paper, then prospect development tendency and application of the iridium alloy in the future. This paper based on density functional theory of first-principles plane wave method, choose local density approximation (LDA) potential to calculate the different doped amount of Ni in Ir Solid Solution System, found the impact on plastic property, the calculation results reveal that Ir44Ni4 began to show the plastic performance, With the increaseing of the adding Ni atom later, plastic performance becomes more and more strong.

Abstract: According to the repeatability characteristics of servo system, a fuzzy iterative learning controller is proposed which combining advantages of fuzzy control and iterative learning control. Fuzzy control has better robustness, and does not require accurate model of the system, only need the previous experience, the design method is simple. Fuzzy controller is used in the position-loop, but the static error is difficult to eliminate, iterative learning controller use the control error to adjust the previous control input to reduce the error of next time. The combination of these two intelligent control algorithms can improve the control performance of servo system effectively. Simulation results show that the fuzzy control combined with iterative learning control can achieve better control performance in servo system.