Applied Mechanics and Materials Vol. 307

Abstract: The effect of the Fermi level position Ef on the electron transport of different molecular assembly system (MAS) conformations is investigated. The model contains up to six 1,4-dithiolbenzene (DTB) molecular under fixed intermolecular distance d=3.9 Å. The simulation results show that with Ef near the HOMO-LUMO mid gap, the curves show only 3 modes of operation: 1) the conductance gap region (CG); 2) the linear region; and 3) the saturation region. More than 3 different regions of operation were observed when Ef becomes close to LUMO. The threshold voltage Vth, the conductance gap and VIP decrease, while the conductance peak increases. More importantly, in addition to the effect of physical parameter N, which involves the -orbital interactions, enhancing the -orbital interactions strength by reducing HLG, the Fermi level position is another important factor in determining the current flow.

Abstract: Numerical simulations have been performed to study the effect of the temperature T on the electronic transport through a small group of molecular assembly system (MAS) by presenting I-V and G-V characteristics analysis for different geometry structures. The model involves 1,4-dithiolbenzene (DTB) (HSC6H4SH) molecules stacked in one dimension (1D). The MAS contains two DTB molecules packed in parallel geometrical arrangement. The relationship between the threshold voltage Vth and d the intermolecular spacing (which involves the -orbital interactions) is investigated when T ranges from 50 to 325 K. At fixed temperature, the system in the regime of stronger -interactions obtained with close DTB molecular unit (d=3.3Å), reduces Vth. Vth decreases approximately by 2.2 V when d changes from 3.3 to 6.9 Å. The temperature rise effect is another important factor that could reduce Vth . When T increases from 50 to 325 K, Vth decreases linearly, approximately by 1.2 V. More importantly, our simulation results correspond to L. Cai et al’s experimental results[24], the threshold voltage for switching molecular wire decreases as the temperature increases.

Abstract: Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance are required. Due to its high fatigue strength, SAE 52100 is recently being used not only for the production of bearings but also shafts. In this work, quenched SAE 52100 steel fatigue strength under rotating bending was investigated. Especially, we focus on “fisheye around inclusion” where the fatigue crack starts. Quantitative evaluation of its optical micrograph has not been enough carried out. In order to develop easy evaluation method for the fisheye area, we apply homology technique to the optical observation.

Abstract: A new online pre-hardening (OPH) equipment for quenching die steel has been developed by University of Science and Technology Beijing (USTB) and Dongbei Special Steel Group in Dalian Special Steel Co., LTD. OPH equipment consists of strong cooling water jet, medium cooling water jet, weak cooling water jet, air-water spray, and side water jet and has flexible cooling and control ability. Based on the equipment, online quenching process of AISI P20 (3Cr2Mo) die steel was performed by numerical simulation and production experiment. The result of temperature field by numerical simulation agrees well with experiment result, which can prove that numerical simulation can be a very good guidance for production experiment. Experimental tempering metallographic structure of the whole P20 plate is tempered troostite and the tempering hardness difference of P20 die steel can be controlled within 3 HRC in the whole plate under quenching process by numerical simulation. The prediction technology of numerical simulation can meet the different cooling rate control and make quenching process comply with preset quenching route to guarantee material microstructure and performance.

Abstract: Bamboo plays an important role as a kind of vegetation with contribution to soil and water conservation, Mechanics property of roots play a crucial role in mechanics of soil-reinforcement. In order to find the tension properties of the bamboo roots underground, the tensile experiment for the roots of four kinds of sympodial bamboo, Bambusa distegia, Dendrocalamopsis oldhami, Dendrocalamus giganteus and Chimonocalamus dumosus, was implemented in the field. The experiment employed our own portable experimental equipment for testing tensile characteristics of root. Tensile force and strain rate of roots with different diameters was tested for these four kinds of bamboo. Then, their tensile strength and elastic modulus were obtained through calculation. The experimental results show that the tensile force of sympodial bamboo root increases regularly by the power function regular the increase of the root diameter, and the tensile strength of root reduces along with the increase of root diameter by the power function. The average anti-tension of these four bamboo roots is Bambusa distegia (59.47N), Chimonocalamus dumosus(58.65N), Dendrocalamus giganteus(43.51N) and Dendrocalamopsis oldhami(40.8N), and their average tensile strength is Dendrocalamus giganteus(30.24Mpa), Bambusa distegia(23.14MPa), Dendrocalamopsis oldhami(22.83MPa) and Chimonocalamus dumosus(18.14MPa). The ultimate strain has limitation from 14% to 18%. The average elastic modulus is Dendrocalamus giganteus(169.86MPa), Bambusa distegia(166.37MPa), Dendrocalamopsis oldhami(158.36Mpa) and Chimonocalamus dumosus(135.56MPa). Compared to the four kinds of bamboo, Dendrocalamus giganteus root has the best comprehensive tensile properties. Next are Bambusa Distegia root, Dendrocalamopsis oldhami root, and Chimonocalamus dumosus root respectively. Compared with the common of Pinus tabulaeformis, Betula platyphylla, Larix gmelinii,clumping bamboo roots have better tensile mechanical properties.

Abstract: To improve the evaluation level for aviation maintenance support system and provide a good decision-making for aircraft maintenance support, a quantitative evaluation method for aviation maintenance support ability is proposed. first the evaluation index system for aviation maintenance support ability is given on the basis of factor analysis for aviation maintenance support system, and then using Analytic Hierarchy Process to determine the weight of each influence factor, finally, based on fuzzy mathematics method, the three-level fuzzy synthetic evaluation model is established. The actual example validates is feasibility and effectiveness.

Abstract: To improve product quality in manufacturing process, a dynamic quality control method based on relation analysis is proposed. With the method, the dynamic regulated principal component analysis is constructed by introducing discount factor to eliminate the autocorrelation via the data, and the limit of multiple control charts is calculated by squared prediction error (SPE) statistics. Then, a dynamic adjusting policy by support vector machine (SVM) is proposed based on control chart pattern recognition. Finally, a case study for applicability is presented to verify the proposed method.

Abstract: This paper presents selected results of postal survey focused on advanced manufacturing technology adoption and utilization that was carried out in the Czech Republic two years ago. We have narrowed our focus on motivation of managers of manufacturing companies to invest in modern technology here. We believe that the most important motives are strongly linked to potential benefits that are associated with particular technology and that is why we have studied various benefits of advanced manufacturing technology and we put it into context of the problems the managers have to face nowadays. Our results show that from this perspective there are many good reasons to invest in modern technology.

Abstract: In the paper a production model with failures is presented where successive failure-free times are supposed to have normal distributions and are followed by normally distributed times of repairs. Unknown parameters of the distribution are estimated using e.g. empirical moments approach. Predictions of unknown parameters are done using classical regression method. Having Mean Time To First Failure, and Mean Time of Repair a disturbance robust predictive schedule is generated using an immune algorithm and rule Minimal Impact of Disturbed Operation on the Schedule.

Abstract: This paper presents a service-oriented After-sales services system in Mechanical Engineering Industry. Typical After-sales services include status tracking services by customers, customer services, assignors and assignees. Therefore, the proposed After-sales service tracking management system work in the progress from the case study is conducted. Our system can connect with other service-related systems, such as enterprise content management repository system and business process management system. The After-sales services system is developed by consulting and visiting the machine tools manufacturers.