Dynamic Compression Behavior of a Mg–Gd-Based Alloy at Elevated Temperature

Changping Tang,Kai Wu,Wenhui Liu,Di Feng,Guoliang Zuo,Wuying Liang,Yue Yang,Xu Chen,Quan Li,Xiao Liu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6

The dynamic compression behavior and microstructure evolution at 400 °C of an extruded Mg–8Gd–4Y–Nd–Zr alloy withdifferent tempers were investigated. The peak-aged samples exhibit the highest compressive strength, followed by as-extrudedsamples and over-aged samples. The highest dynamic compressive strength of 582 MPa was achieved by peak-aged samplecompressed at 1224 s−1. The high strength was attributed to the formation of abundant thermally stable βʹ precipitates andsome dynamic precipitates. The dynamic compressive strength of peak-aged sample and over-aged sample is not sensitiveto strain rates, while that of the as-extruded sample is sensitive to strain rates. The dynamic compressive strength of the asextrudedalloy can reach 535 MPa when compressed at 2024 s−1. The high strength was mainly ascribed to the formationof numerous dynamic precipitates and the work hardening effect caused by dislocations. The cracks are composed of crackthat is 45° to loading direction on the cylindrical surface and crack on the compressed surface. Microstructure observationindicates that the crack was easily propagated along the interface between the adiabatic shear band and matrix, grainboundaries. The equilibrium phase β in over-aged sample was unable to hinder the crack propagation.

A novel geometric error modeling optimization approach based on error sensitivity analysis for multi-axis precise motion system

Hao Tang,Changping Li,Zilin Zhang,고태조 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7

In this paper, a novel error modeling approach for multi-DOF precise motion platform (MPMP) based on the error sensitivity analysis (ESA) is introduced. Sensitivity analysis (SA) is widely adopted for finding the essential parameters in system in mathematical way. This paper leads an error sensitivity analysis based on Monte Carlo thought into geometric error model. Through comparing the variance between the set of evaluated error and corresponding orientation deviations, a sensitive order with several sensitive levels can be developed. Conventional error modeling method only concentrates the systematic accuracy, while calculation efficiency is also important. Thus, this error modeling optimization approach based on sensitivity analysis is beneficial for the high-accuracy and high-quantity manufacture environments, which is more precise and effective. It also can save the computational volume for the calculation in error model. A case study of the new error modeling optimization procedure for six-axis stage in the alignment in optoelectronic packaging system (OPS) is carried out. The time-consumed results indicate that the optimized error model can not only keep high-accuracy requirement, but also improve the computational efficiency, which is informative and effective for MPMP motion control. For large number working situation, the optimized error model is available as well.

A geometric error modeling method and trajectory optimization applied in laser welding system

Hao Tang,Zilin Zhang,Changping Li,고태조 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.8

In this paper, a geometric error modeling method is carried out on six-axis motion platform (SMP) in laser welding system (LWS), and an optimized algorithm is proposed for the alignment in LWS based on the error model. First, the topological structure of the given SMP is analyzed, and related homogeneous transformation matrices which are used for standing the orientation of SMP are established. By these matrices, the geometric error model is developed mathematically. Then, the error model is used for predicting the alignment deviations. A corresponding series of experiments for calculating the optical power loss in alignment are employed, and the comparison between simulation and experiments results indicate the validation of the error model. Furthermore, an optimized algorithm is applied to search the optimum aligning trajectory. Compared to conventional method, this algorithm has a broader range in searching extreme value, which can reduce the computational volume and improve the efficiency. It is also beneficial for improving the success rate of escaping from the local minimum spot and finding the optimum alignment spot. The error model is helpful to analyze the error propagation process and improve the alignment efficiency in LWS, which can be applied to other similar multi-axis precise system.

Adaptive Cooperation for Bidirectional Communication in Cognitive Radio Networks

( Yuan Gao ),( Changping Zhu ),( Zhixiang Deng ),( Yibin Tang ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.3

In the interweave cognitive networks, the interference from the primary user degrades the performance of the cognitive user transmissions. In this paper, we propose an adaptive cooperation scheme in the interweave cognitive networks to improve the performance of the cognitive user transmissions. In the proposed scheme for the bidirectional communication of two end-source cognitive users, the bidirectional communication is completed through the non-relay direct transmission, the one-way relaying cooperation transmission, and the two-way relaying cooperation transmission depending on the limited feedback from the end-sources. For the performance analysis of the proposed scheme, we derive the outage probability and the finite-SNR diversity multiplexing tradeoff (f-DMT) in a closed form, considering the imperfect spectrum sensing, the interference from the primary user, and the power allocation between the relay and the end-sources. The results show that compared with the direct transmissions (DT), the pure one-way relaying transmissions (POWRT), and the pure two-way relaying transmissions (PTWRT), the proposed scheme has better outage performance. In terms of the f-DMT, the proposed scheme outperforms the full cooperation transmissions of the POWRT and PTWRT.

Spectrum Hole Utilization in Cognitive Two-way Relaying Networks

( Yuan Gao ),( Changping Zhu ),( Yibin Tang ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.3

This paper investigates the spectrum hole utilization of cooperative schemes for the two-way relaying model in order to improve the utilization efficiency of limited spectrum holes in cognitive radio networks with imperfect spectrum sensing. We propose two specific bidirectional secondary data transmission (BSDT) schemes with two-step and three-step two-way relaying models, i.e., two-BSDT and three-BSDT schemes, where the spectrum sensing and the secondary data transmission are jointly designed. In the proposed cooperative schemes, the best two-way relay channel between two secondary users is selected from a group of secondary users serving as cognitive relays and assists the bi-directional communication between the two secondary users without a direct link. The closed-form asymptotic expressions for outage probabilities of the two schemes are derived with a primary user protection constraint over Rayleigh fading channels. Based on the derived outage probabilities, the spectrum hole utilization is calculated to evaluate the percentage of spectrum holes used by the two secondary users for their successful information exchange without channel outage. Numerical results show that the spectrum hole utilization depends on the spectrum sensing overhead and the channel gain from a primary user to secondary users. Additionally, we compare the spectrum hole utilization of the two schemes as the varying of secondary signal to noise ratio, the number of cognitive relays, and symmetric and asymmetric channels.

Tool life evaluation of CFRP drilling with three kinds of drill

Xinyi Qiu,Pengnan Li,Changping Li,Qiulin Niu,Shujian Li,Tae Jo Ko,Lingyan Tang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.7

Serious tool wear in CFRP drilling is one of the key problems to be solved urgently. Firstly, a suitable indirect evaluation index of tool life is selected according to the literature. The critical delamination force was obtained by blind hole pushing experiment. Then, tool wear experiments were carried out with double point angle drill, stepped drill and reverse edge compound drill to analyze the variation rules of the thrust force, exit burr, exit delamination and tear with tool wear. Threshold values of exit delamination, tearing and critical thrust force were compared with each evaluation index one by one to study the causes of drills failure. The results indicated that the maximum tool wear position was the outer corner. Among the three types drills, the thrust force, delamination factor and burr angle of the reverse edge compound drill are smaller. The double point angle drill fails due to the excessive thrust force, while the stepped drill and the reverse edge compound drill fail due to the hole exit delamination exceeding the threshold. The number of drilled holes of the reverse edge compound drill is 100 % and 25 % higher than that of the double point angle drill and the stepped drill, respectively. Therefore, the reverse edge compound drill is suitable for drilling CFRP.

Effect of Temperature and Strain Rate on Deformation Mode and Crack Behavior of 7B52 Laminated Aluminum Alloy Under Impact Loading

Wenhui Liu,Ping Cao,Chenbing Zhao,Yufeng Song,Changping Tang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.11

The dynamic mechanical behaviors of 7B52 laminated aluminum alloy under different impact deformation conditions wereinvestigated using split Hopkinson pressure bar, optical microscopy, electron backscatter diffraction and transmission electronmicroscopy. The results show that the 7B52 laminated aluminum alloy displays positive strain rate sensitivity and negativetemperature sensitivity. Cracks are formed firstly at the interface between the 7A62 hard layer and the 7A01 middle layerunder a low strain rate of 2200 s−1. When the strain rate increases to 3500 s−1, the deformation shear band is firstly formed inthe 7A52 soft layer. The deformation shear band transformed to the transition shear band with the increase of strain rate, andthen crack initiated. Adiabatic shear bands and cracks are formed in both of the hard and soft layers when samples impactedat a high strain rate (5500 s−1). Most of the cracks and adiabatic shear bands are unable to penetrate the middle layer dueto the good toughness of the 7A01 alloy. The deformation of each layer of 7B52 laminated aluminum alloy becomes moreuniform when the temperature increases, which was attributed to the reduction of difference in strength among the threelayers and the coordinating effect of grain boundary on deformation.