A Study on Fracture Behavior and Impact Stability of Sintered Rare-earth Permanent Magnets

Li Wei,Li Anhua,Wang Huijie,Dong Shengzhi,Guo Yongquan 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The fracture behavior and mechanical characteristics of sintered rare-earth magnets were investigated. It shows that the fracture behavior and bending strength of the magnets obviously exhibit anisotropy. Sm-Co magnets tend to cleavage fracture in the close-packed (0001) plane or in the (10 11 ) plane. The fracture mechanism of Nd2Fe14B magnet mainly appears to be intergranular fracture. The anisotropy of fracture behavior and mechanical strength of sintered rare-earth magnets is caused mainly by the strong crystal-structure anisotropy and the grain alignment texture. The effects of Nd content, and Pr, Dy substitution on the impact stability of Nd2Fe14B magnets were also reported.

Hole exit damage and tool wear during the drilling of CFRP with a double-point angle drill

Pengnan Li,Xinyi Qiu,Changping Li,Qiulin Niu,Anhua Chen,고태조 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5

The control of hole exit damage and hole wall quality poses a considerable challenge during the drilling of carbon fiber-reinforced plastic (CFRP). This study aims to study the effect of the cutting edge type on the aforementioned issues. First, a comparative study between hole exit damage caused by a twist drill and a double-point angle drill was conducted to investigate the influences of the chisel, principal, and secondary cutting edges on hole exit damage. The maximum damage ring caused by the double-point angle drill is smaller than that caused by the twist drill because the drop speed of the cutting force in the secondary cutting edge drill during the exit stage of the double-point angle drill is less than that of the twist drill. Then, the double-point angle drill was used to determine the effects of tool wear on thrust force and hole wall damage. Outer corner wear and flank wear were investigated, and hole wall damage mechanisms were discussed. The damage of missing fibers does not worsen with an increase in tool wear, but the damage of fiber pullout becomes more serious due to increased cutting force. Consequently, a double-point angle drill bit is preferable for drilling holes on CFRP.

Effect of Microstructure on the Corrosion Resistance of Nd-Fe-B Magnets

Jiajie Li,Wei Li,Anhua Li,Minggang Zhu,Bin Lai,Mingge Zhou 한국자기학회 2010 한국자기학회 학술연구발표회 논문개요집 Vol.2010 No.12

Effect of Microstructure on the Corrosion Resistance of Nd-Fe-B Permanent Magnets

Jiajie Li,Wei Li,Anhua Li,Rui Zhao,Bin Lai,Minggang Zhu 한국자기학회 2011 Journal of Magnetics Vol.16 No.3

High performance Nd-Fe-B magnets can be manufactured by both sintering and hot deformation. The corrosion behaviors of the magnets prepared by the two processes were compared. Effect of microstructure on the corrosion resistance of Nd-Fe-B magnets was also investigated. A neutral salt spray test (NSS) was performed for the different-processed magnets. The weight losses of the samples after the corrosion test were measured. The corrosion microstructures were observed using a scanning electron microscope. It shows that the corrosion resistance of hot deformed magnets is much better than that of the sintered ones because the grain size and the distribution of Nd-rich phases of the hot deformed magnets are much finer and more uniform than those of the sintered ones. The different microstructure between the sintered and the hot deformed magnets causes the different corrosion behavior.

New Compound Drill Bit for Damage Reduction in Drilling CFRP

Xinyi Qiu,Pengnan Li,Changping Li,Qiulin Niu,Anhua Chen,Puren Ouyang,Tae Jo Ko 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.1

This paper focuses on finding a suitable drill bit for drilling Carbon Fiber Reinforced Plastic (CFRP). The drilling characteristics of the dagger drill, the double point angle drill, and the candle stick drill are studied. The results show that the side edge has poor ability to remove burrs, and the tip structure of the outer corner of the candle stick drill can greatly reduce the entry damage. However, the outer corner small tip structure of the candle stick drill cannot effectively remove the uncut fiber around θ = 0° of hole exit. The long secondary cutting edge of the dagger drill makes a small thrust force at the drilling exit stage and reduces the dropping speed of the thrust force, leading a lower impact on the laminate bottom. Then, a new tool is developed for drilling CFRP based on the advantages of the three kinds of drill bits. The drill has a long secondary cutting edge, a small tip diameter and a small tip structure of the outer corner. And its drilling characteristics are analyzed. The result shows that the new compound drill bit can effectively remove fibers and reduce thrust force at the drilling exit stage, form burr-free and small delamination hole. The drill reduces the waste of CFRP in manufacturing process since the exit damage is reduced substantially, which is in line with the concept of green manufacturing.

Automated Breast Ultrasound: Interobserver Agreement, Diagnostic Value, and Associated Clinical Factors of Coronal-Plane Image Features

Guoxue Tang,Xin An,Huiling Xiang,Lixian Liu,Anhua Li,Xi Lin 대한영상의학회 2020 Korean Journal of Radiology Vol.21 No.5

Objective: To evaluate the interobserver agreement, diagnostic value, and associated clinical factors of automated breast ultrasound (ABUS) coronal features in differentiating breast lesions. Materials and Methods: This study enrolled 457 pathologically confirmed lesions in 387 female (age, 46.4 ± 10.3 years), including 377 masses and 80 non-mass lesions (NMLs). The unique coronal features, including retraction phenomenon, hyper- or hypoechoic rim (continuous or discontinuous), skipping sign, and white wall sign, were defined and recorded. The interobserver agreement on image type and coronal features was evaluated. Furthermore, clinical factors, including the lesion size, distance to the nipple or skin, palpability, and the histological grade were analyzed. Results: Among the 457 lesions, 296 were malignant and 161 were benign. The overall interobserver agreement for image type and all coronal features was moderate to good. For masses, the retraction phenomenon was significantly associated with malignancies (p < 0.001) and more frequently presented in small and superficial invasive carcinomas with a low histological grade (p = 0.027, 0.002, and < 0.001, respectively). Furthermore, continuous hyper- or hypoechoic rims were predictive of benign masses (p < 0.001), whereas discontinuous rims were predictive of malignancies (p < 0.001). A hyperechoic rim was more commonly detected in masses more distant from the nipple (p = 0.027), and a hypoechoic rim was more frequently found in large superficial masses (p < 0.001 for both). For NMLs, the skipping sign was a predictor of malignancies (p = 0.040). Conclusion: The coronal plane of ABUS may provide useful diagnostic value for breast lesions.

Inter‑diffusion Based Analytical Model for Growth Kinetics of IMC Layers at Roll Bonded Cu/Al Interface During Annealing Process

Fu‑an Hua,Hong‑wu Song,Tao Sun,Jian‑ping Li 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.3

A model based on inter-diffusion theory was established to predict growth kinetics of the intermetallic compounds (IMCs)formed in roll bonded Al/Cu sheets during annealing process. The model can give good prediction of both IMC layers growthkinetics and element concentration distribution at the interface of roll bonded Cu/Al sheets with different thickness underdifferent annealing conditions with certain roll reduction range. It is revealed that the calculated results of the proposedmodel are depended on the inter-diffusion coefficient of each components, which could be related to the interface bondingstate, i.e., bonding methods or rolling reductions for roll bonding. And there was big difference in inter-diffusion coefficientof Al and Cu matrix under different bonding state, while the inter-diffusion coefficient of IMCs changed slightly.