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DOI：10.1186/s10033-020-00444-4

Numerical Investigation on Fracture Initiation Properties of Interface Crack in Dissimilar Steel Welded Joints

Longfei Zhao, Chendong Shao, Yasuhito Takashima, Fumiyoshi Minami & Fenggui Lu

Abstract：Fracture toughness property is of significant importance when evaluating structural safety. The current research of fracture toughness mainly focused on crack in homogeneous material and experimental results. When the crack is located in a welded joint with high-gradient microstructure and mechanical property distribution, it becomes difficult to evaluate the fracture toughness behavior since the stress distribution may be affected by various factors. In recent years, numerical method has become an ideal approach to reveal the essence and mechanism of fracture toughness behavior. This study focuses on the crack initiation behavior and driving force at different interfaces in dissimilar steel welded joints. The stress and strain fields around the crack tip lying at the interfaces of ductile-ductile, ductile-brittle and brittle-brittle materials are analyzed by the numerical simulation. For the interface of ductile-ductile materials, the strain concentration on the softer material side is responsible for ductile fracture initiation. For the ductile-brittle interface, the shielding effect of the ductile material plays an important role in decreasing the fracture driving force on the brittle material side. In the case of brittle-brittle interface, a careful matching is required, because the strength mismatch decreases the fracture driving force in one side, whereas the driving force in another side is increased. The results are deemed to offer support for the safety assessment of welded structures.

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https://cjme.springeropen.com/articles/10.1186/s10033-020-00444-4/figures/1

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Longfei Zhao, Chendong Shao, Yasuhito Takashima, et al. Numerical Investigation on Fracture Initiation Properties of Interface Crack in Dissimilar Steel Welded Joints. Chinese Journal of Mechanical Engineering, 2020, 33: 27.

DOI：10.1186/s10033-020-00443-5

Prediction of Leakage from an Axial Piston Pump Slipper with Circular Dimples Using Deep Neural Networks

Özkan Özmen, Cem Sinanoğlu, Abdullah Caliskan & Hasan Badem

Abstract：Oil leakage between the slipper and swash plate of an axial piston pump has a significant effect on the efficiency of the pump. Therefore, it is extremely important that any leakage can be predicted. This study investigates the leakage, oil film thickness, and pocket pressure values of a slipper with circular dimples under different working conditions. The results reveal that flat slippers suffer less leakage than those with textured surfaces. Also, a deep learning-based framework is proposed for modeling the slipper behavior. This framework is a long short-term memory-based deep neural network, which has been extremely successful in predicting time series. The model is compared with four conventional machine learning methods. In addition, statistical analyses and comparisons confirm the superiority of the proposed model.

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https://cjme.springeropen.com/articles/10.1186/s10033-020-00443-5

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Özkan Özmen, Cem Sinanoğlu, Abdullah Caliskan, et al. Prediction of Leakage from an Axial Piston Pump Slipper with Circular Dimples Using Deep Neural Networks. Chinese Journal of Mechanical Engineering, 2020, 33: 28.

DOI：10.1186/s10033-020-00442-6

An Overview of Bearing Candidates for the Next Generation of Reusable Liquid Rocket Turbopumps

Jimin Xu, Changhuan Li, Xusheng Miao, Cuiping Zhang & Xiaoyang Yuan

Abstract：There is a consensus in the aerospace field that the development of reusable liquid rockets can effectively reduce the launch expense. The pursuit of a long service life and reutilization highly depends on the bearing components. However, the rolling element bearings (REBs) used in the existing rocket turbopumps present obvious and increasing limitations due to their mechanical contacting mode. For REBs, high rotational speed and long service life are two performance indexes that mutually restrict each other. To go beyond the DN value (the product of the bearing bore and rotational speed) limit of REBs, the major space powers have conducted substantial explorations on the use of new types of bearings to replace the REB. This review discusses, first, the crucial role of bearings in rocket turbopumps and the related structural improvements of REBs. Then, with the prospect of application to the next generation of reusable liquid rocket turbopumps, the bearing candidates investigated by major space powers are summarized comprehensively. These promising alternatives to REBs include fluid-film, foil, and magnetic bearings, together with the novel superconducting compound bearings recently proposed by our team. Our more than ten years of relevant research on fluid-film and magnetic bearings are also introduced. This review is meaningful for the development of long-life and highly reliable bearings to be used in future reusable rocket turbopumps.

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https://cjme.springeropen.com/articles/10.1186/s10033-020-00442-6

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Jimin Xu, Changhuan Li, Xusheng Miao, et al. An Overview of Bearing Candidates for the Next Generation of Reusable Liquid Rocket Turbopumps. Chinese Journal of Mechanical Engineering, 2020, 33: 26.

DOI：10.1186/s10033-020-00441-7

Experimental Research on the Dynamic Lubricating Performance of Slipper/Swash Plate Interface in Axial Piston Pumps

Junjie Zhou, Jichen Zhou & Chongbo Jing

Abstract：The interface between the slipper/swash plate is one of the most important frication pairs in axial piston pumps. The test of this interface in a real pump is very challenging. In this paper, a novel pump prototype is designed and a test rig is set up to study the dynamic lubricating performance of the slipper/swash-plate interface in axial piston machines. Such an experimental setup can simulate the operating condition of a real axial piston pump without changing the relative motion relationship of the interfaces. Considering the lubricant oil film thickness as the main measurement parameter, the attitude of the slipper under the conditions of different load pressure, rotation speed and charge pressure are studied experimentally. After the test, the wear state of the swash plate is observed. According to the friction trace on the surface of the swash plate, the prediction for the attitude of the slipper and the zone easy to wear are verified.

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https://cjme.springeropen.com/articles/10.1186/s10033-020-00441-7

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Junjie Zhou, Jichen Zhou, Chongbo Jing. Experimental Research on the Dynamic Lubricating Performance of Slipper/Swash Plate Interface in Axial Piston Pumps. Chinese Journal of Mechanical Engineering, 2020, 33: 25.

DOI：10.1186/s10033-020-00440-8

Mass-Spring-Damping Theory Based Equivalent Mechanical Model for Cylindrical Lithium-ion Batteries under Mechanical Abuse

Wenwei Wang, Yiding Li, Cheng Lin & Sheng Yang

Abstract：An equivalent mechanical model with the equivalent physical meaning of mass-spring-damping is proposed for cylindrical lithium-ion batteries through experiments and theory. The equivalent mechanical model of a cylindrical lithium-ion battery consists of a spring-damping parallel unit. Therefore, a spring-damping parallel unit connecting a damping unit in series is selected to construct the constitutive characteristics of the battery under mechanical abuse. Comparison results show that the equivalent mechanical model can more effectively describe the mechanical properties of the batteries than most cubic fitting models, of which the average relative error of the equivalent mechanical model under different states-of-charge is less than 6.75%. Combined with the proposed equivalent mechanical model, the failure process of the batteries was simulated and analyzed using LS-Dyna and HyperWorks. Under rigid rod tests, failure occurred at the core and bottom of the batteries; under hemispherical punch tests, failure occurred at the core and top, consistent with the experimental results. The average prediction error for the failure displacement under different abuse conditions is less than 4% in the simulations. The equivalent mechanical model requires only a few parameters and can be recognized easily. In the future, the model can be used in safety warning devices based on mechanical penetration.

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https://cjme.springeropen.com/articles/10.1186/s10033-020-00440-8

引用本文

Wenwei Wang, Yiding Li, Cheng Lin, et al. Mass-Spring-Damping Theory Based Equivalent Mechanical Model for Cylindrical Lithium-ion Batteries under Mechanical Abuse. Chinese Journal of Mechanical Engineering, 2020, 33: 23

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