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SSRN 2024年

作者： He, Zongkai Zheng, Gang Luo, Quantian Li, Qing Sun, Guangyong State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Hunan University Changsha410082 China School of Aerospace Mechanical and Mechatronic Engineering The University of Sydney SydneyNSW2006 Australia

In order to promote adhesive connection in primary load-bearing structures for engineering applications, fatigue damage tolerance signifies a critical parameter in line with the guidance of FAA AC 20-107B. This study aims to investigate this issue from four aspects, namely, fatigue crack statistics, residual performance, critical point for fatigue damage tolerance, and adhesive property degradation. Joints subjected to pre-fatigue loading were first tested, in which the specimens with different degrees of fatigue damage were selected through the real-time stiffness monitoring. Their residual strengths under different temperatures were then studied. The degradation mechanisms of joint strength were further evaluated quantitatively in terms of degradation factors by using pre-fatigue crack and cohesive zone model (CZM). It is shown that for million cycle condition, the adhesive property will degrade to around 50% of its initial value, which generally counts for 60% of reduction in the fatigue strength. A short-term high-temperature environment can cause comparable degradation effect to a long-term fatigue cyclic load. For sake of service safety, it is recommended to take the normalized stiffness of 92% as the critical point. This study revealed that a reliable management for residual fatigue performance can be achieved. It is anticipated to provide an effective guide for damage-tolerant design, reliable safety monitoring and repair of adhesive *** order to promote adhesive connection in primary load-bearing structures for engineering applications, fatigue damage tolerance signifies a critical parameter in line with the guidance of FAA AC 20-107B. This study aims to investigate this issue from four aspects, namely, fatigue crack statistics, residual performance, critical point for fatigue damage tolerance, and adhesive property degradation. Joints subjected to pre-fatigue loading were first tested, in which the specimens with different degrees of fatigue damag

关键词： Fatigue damage

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Quantitatively regulated and recognized dual-precipitates of Mg-5Sn alloy through an improved twinning-aging-detwinning and strengthening mechanisms

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Journal of Magnesium and Alloys 2025年

作者： Fu, Ruihao Zeng, Ying Wan, Yangjie Qian, Xiaoying Xu, Shiwei Yin, Dongdi Key Laboratory of Advanced Technologies of Materials Ministry of Education School of Material Science and Engineering Southwest Jiaotong University Chengdu610031 China National Engineering Research Center for Magnesium Alloys Chongqing University Chongqing400044 China State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Hunan University Changsha410082 China

The orientation of precipitates was regulated by an improved twinning-aging-detwinning (TAD) process in Mg-Sn sheets. A structure with specific proportions of dual-precipitates was regulated, significantly enhancing the material's strength. The formation mechanism of the dual-precipitates was investigated, and the evolution of precipitate orientation was confirmed. A combined SEM, EBSD and TEM method was developed to identify the coupling relationship between complex grain orientation and precipitate orientation. The orientation relationship between precipitates and the matrix could be quantitatively analyzed in the same region. Subsequently, the Orowan model was refined to quantify the strength enhancement effect following the orientation regulation of precipitates. The TAD sample containing dual-precipitates exhibited a 99.1 % increase in TYS, equivalent to an increase of 108 MPa, compared to unregulated samples A. According to Orowan calculations, the theoretical strength increment from the three strengthening mechanisms was 113 MPa, closely matching the experimental increment of 108 MPa. Notably, the materials with a specific proportion of the dual-precipitates showed a substantial increase in strength. © 2025

关键词： Precipitates

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Research on Cracking Mechanism of Aero-Engine Thermocouple Bearing Ring Under High-Temperature Creep Test

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SSRN 2024年

作者： Wang, Songjun He, Jianjun Gong, Zhihui Cai, Yuhui Yao, Biqing Xiao, Tingyi School of Energy and Power Engineering Changsha University of Science and Technology Changsha410114 China State Key Laboratory of Advanced Design and Manufacture for Vehicle Body Hunan University Changsha40082 China

The thermocouple bearing ring in aero-engine have prematurely cracked during service, posing a significant safety hazard. This paper analyzes the microstructure and fracture behavior of K4169 high-temperature superalloy specimens under thermomechanical loading considering this phenomenon. The results revealed that a small amount of needle-like δ-phases and an increased number of Laves phases accumulated around the grain boundaries after direct aging treatment. After solution treatment followed by aging, more twinning features were observed at the grain boundaries, and the Laves phase was diffusely distributed. No needle-like δ-phases were found at 710°C, indicating that the heat treatment was optimal. At 650°C, the alloy demonstrated excellent creep resistance, characterized by distinct stages of constant velocity and accelerated creep. On the specimen's surface, twins and a few dislocations appeared, while the Laves phase precipitated and partially aggregated at the grain boundaries, accompanied by the formation of small voids. As the temperature increases, the Laves phase content increases along with the formation of voids. These Laves phases were accompanied by needle-like δ phases, forming 'bands' that facilitated crack initiation, primarily along the grain boundaries. At 650°C, secondary cracks appeared at the fracture, indicative of predominantly ductile fracture behavior. With an increase in temperature to 710°C, precipitation of the second phase increased significantly, leading to pronounced stress concentration. Consequently, the fracture mode transitioned from ductile fracture to a ductile-brittle mixed fracture. © 2024, The Authors. All rights reserved.

关键词： Grain boundaries

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On Interlaminar Fracture of Tensile-Compressive Asymmetry Plain Weave Cfrp: Accurate Calibration and Simulation with Cohesive Zone Models

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SSRN 2024年

作者： Sun, Guangyong Luo, Junjie Luo, Quantian Li, Qing State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Hunan University Changsha410082 China School of Aerospace Mechanical and Mechatronic Engineering The University of Sydney SydneyNSW2006 Australia

Interlaminar fracture is a crucial factor influencing the structural integrity of plain weave carbon fiber reinforced polymer (PW-CFRP) composites, which is often modeled by cohesive zone models (CZM). While laminar tensile-compressive asymmetry (TC-A) in PW-CFRP is widely accepted, its effect has not been well considered in the modeling of interlaminar fracture using CZM. In this study, double cantilever beam (DCB) for mode I, end-notched flexure (ENF) for mode II, and single leg bending (SLB) for mixed-mode I+II tests were conducted on PW-CFRP. The interlaminar R-curve was calibrated using commonly-used analytical approaches. Since mixed-mode ratio (MMR) varied during damage evolution of mixed-mode in CZM, contrary to a constant MMR assumed in linear elastic fracture mechanics (LEFM), a high-fidelity finite element method (HiFEM) based on TC-A model was developed in this study to account for the MMR at local crack tip in CZM. Experimental and numerical results unveiled that the TC-A model significantly improved the prediction accuracy of stiffness and delamination process in DCB, ENF and SLB tests as compared to the conventional tensile-compressive symmetric (TC-S) model. Furthermore, adoption of R-curves rather than constant fracture toughness has proven essential for capturing the peak force and nonlinear responses in DCB, ENF, and SLB. The validity of HiFEM was demonstrated in accurately decoupling the mixed-mode energy release rates (ERRs) with different interlaminar strengths and stiffnesses, thus correcting the energy dissipation in CZM and enabling to accurately model the mixed-mode delamination. This study provides a reliable approach for better modeling interlaminar fracture effectively. © 2024, The Authors. All rights reserved.

关键词： Crack tips

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Inverse Janus design of two-dimensional Rashba semiconductors

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Physical Review B 2023年第11期108卷 115130-115130页

作者： Qikun Tian Puxuan Li Jinghui Wei Ziyu Xing Guangzhao Qin Zhenzhen Qin International Laboratory for Quantum Functional Materials of Henan and School of Physics and Microelectronics Zhengzhou University Zhengzhou 450001 People's Republic of China National Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle College of Mechanical and Vehicle Engineering Hunan University Changsha 410082 People's Republic of China

The search for optimal Rashba semiconductors with large Rashba constants, strong electric field responses, and potential thermoelectric properties is pivotal for spin field-effect transistors (SFETs) and Rashba thermoelectric devices. Herein, we employ first-principles calculations to explore the intrinsic Rashba spin splitting in a series of two-dimensional (2D) XYZ2 (X, Y=Si, Ge, Sn; X≠Y; Z=P, As, Sb, Bi) monolayers via unnatural inverse Janus structural design. Instead of common Janus-type Rashba systems, the SiSnSb2 and GeSnSb2 monolayers within inverse Janus structures are first predicted as ideal Rashba systems with isolated spin-splitting bands near the Fermi level, and the Rashba constants αR are calculated as 0.94 and 1.27eVÅ, respectively. More importantly, the Rashba effect in such SiSnSb2 and GeSnSb2 monolayers can be more efficiently modulated by the external electric field compared to the biaxial or uniaxial strain, especially with GeSnSb2 monolayer exhibiting a strong electric field response rate of 1.34eÅ2, leading to a short channel length, L=64nm. Additionally, owing to the inapplicability of work function and potential energy in assessing built-in electric field (Ein) in inverse Janus SiSnSb2 and GeSnSb2 structures, we further propose an effective method to characterize Ein through a view of fundamental charge transfer to approximately quantize the αR and its variation under an external electric field. Our work not only proposes the GeSnSb2 monolayer acting as a promising multifunctional material for potential applications in SFETs and Rashba thermoelectric devices but also inspires future research to introduce Rashba spin splitting in 2D materials through inverse Janus design.

关键词： Electronic structure Rashba coupling Spin-orbit coupling 2-dimensional systems Density functional calculations

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Fatigue Crack Blunting Enabled by High Work Hardening in a High-Entropy Alloy at Intermediate Temperature

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SSRN 2024年

作者： Li, Weipeng Tan, Fusheng Li, Xuepan He, Binbin Jiang, Chao State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body College of Mechanical and Vehicle Engineering Hunan University Changsha410082 China China Academy of Safety Science and Technology Beijing100012 China Applied Mechanics Laboratory Department of Engineering Mechanics School of Aerospace Engineering Tsinghua University Beijing100084 China Department of Mechanical and Energy Engineering Southern University of Science and Technology Shenzhen518055 China

High-temperature fatigue service performances of metallic materials are very important for integrity of engineering structures. This study investigates the fatigue crack growth behavior and fatigue resistance of a CoCrFeNiMn high-entropy alloy (HEA) at an intermediate temperature of 673 K. High work hardening of HEA enabled fatigue crack blunting, leading to a unique sharpening–blunting–resharpening mechanism. Notably, it reduced the crack growth driving force and was responsible for the sudden decrease in fatigue crack growth rate. Many dislocations were further revealed to exist at the blunting crack tip. We believe that intense thermal activation instead of severe lattice distortion in the alloy results in sufficient dislocations at 673 K that facilitate crack growth relaxation and blunting. © 2024, The Authors. All rights reserved.

关键词： Entropy

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Concurrent Topology Optimization of Sandwich Structures with Multi-Configuration and Variable-Diameter Lattice Infill

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SSRN 2024年

作者： Ji, Wei Bai, Yingchun Jiang, Chao Liu, Jianhua Yan, Qingdong Han, Xu School of Mechanical Engineering Beijing Institute of Technology Beijing100081 China State Key Laboratory of Advance Design and Manufacturing for Vehicles Hunan University Changsha410082 China State Key Laboratory of Reliability and Intelligence of Electrical Equipment School of Mechanical Engineering Hebei University of Technology Tianjin300401 China

The superior stiffness-to-weight and strength-to-weight mechanical advantages of sandwich structures can be fully exploited through concurrent design of entire topology, infill configuration and density, where the high-performance yet complicated structure can be fabricated through additive manufacturing. However, the emerging design challenges are concurrent design updating related to sandwich topology, infill configuration and density, which is a design problem with continuous and discrete variables mathematically. In this paper, a concurrent topology optimization is proposed for sandwich structures with multi-configuration and variable-diameter lattice infill. Three design variable fields are employed to describe the fundamental topology considering sandwich structural topology, infill configuration and density simultaneously. Corresponding material interpolation model is developed by combining DSP-based shell-infill description and multi-response latent-variable surrogate model based effective material property calculation. Two-stage design model is formulated as a rough design model considering all design variables followed by a refined design model with only infill density variables, which is developed to strictly satisfy the material allowance constraint due to the mapping between discrete infill configuration variables and continuous latent configuration variables. Corresponding sensitivities of compliance and mass with respect to the structural topology, infill configuration and density variables are derived, and the method of moving asymptotes (MMA) is employed to solve the design model efficiently. Several numerical examples are present to systematically demonstrate the effectiveness of the proposed approach. © 2024, The Authors. All rights reserved.

关键词： Sandwich structures

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A Finite Element Human Body Model of Chinese Midsize Male for Pedestrian safety Analysis

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SSRN 2024年

作者： Mo, Fuhao Liang, Ziyang Tian, Tengfei Li, Guibing Luo, Dian Xiao, Zhi Xiao, Sen State Key Laboratory of Advanced Design and Manufacture for Vehicle Hunan University Changsha410082 China Department of Orthopedics The Second Xiangya Hospital of Central South University Changsha410011 China Tianjin Key Laboratory of Power Transmission and Safety Technology for New Energy Vehicles Hebei University of Technology Tianjin300401 China School of Mechanical Engineering Hunan University of Science and Technology Xiangtan411201 China Hunan University of Science and Technology China

The most commonly used numerical human body models and anthropomorphic test devices (ATDs) in vehicle safety analysis are in the anthropometry of Western European or North American. However, the anthropometric differences between European/American and Chinese population are remarkable and have significant influences on pedestrian kinematics and injury response in vehicle crashes. Therefore, the current study aims to develop and validate a finite element (FE) human body model representing the anthropometry of Chinese 50th% adult male for pedestrian safety analysis and development of Chinese ATDs. Firstly, a human body pedestrian model, named as C-HBM (Chinese Human Body Model), was developed based on the medical image data of a volunteer selected according to both anthropometry and anatomy characteristics of 50th% Chinese adult male. Then, the biofidelity of the C-HBM pedestrian model was validated against cadaver impact test data reported in the literature at the segment and full-body level. Finally, the validated C-HBM pedestrian model was employed to predict Chinese pedestrian injuries in real world vehicle crashes. The results indicate that the C-HBM pedestrian model has a good capability in predicting human body mechanical response in cadaver tests and Chinese pedestrian leg and thorax injuries in real world vehicle crashes. Kinematic analysis shows that the C-HBM pedestrian model has less sliding on the hood surface, shorter movement in the horizontal direction, and higher pelvis displacement in the vertical direction than cadavers and the pedestrian model in the anthropometry of westerner due to anthropometric differences in the lower limbs. This implies that anthropometric differences between different ethnic groups should be considered in applications of numerical human body models and ATDs. The currently developed C-HBM pedestrian model provides a basic tool for vehicle safety design and evaluation in China market, and for development of Chinese ATDs. © 202

关键词： Pedestrian safety

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Experimental demonstration of a space-time modulated airborne acoustic circulator

arXiv

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arXiv 2024年

作者： Chen, Tinggui Malléjac, Matthieu Bi, Chuanxing Xia, Baizhan Fleury, Romain Institute of Sound and Vibration Research Hefei University of Technology Hefei230009 China Laboratory of Wave Engineering School of Electrical Engineering EPFL Lausanne Switzerland State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Hunan University Changsha410082 China

Achieving strongly nonreciprocal scattering in compact linear acoustic devices is a challenging task. One possible solution is the use of time-modulated resonators, however, their implementation in the realm of audible airborne acoustics is typically hindered by the difficulty to obtain large modulation depth and speeds while managing noise issues. Here, we propose a practical and cost-efficient route to realize simple modulated resonators and observe experimentally the strong nonreciprocal behavior of an acoustic circulator. We propose to modulate the neck cross-section areas of three coupled Helmholtz resonators using rotating circular plates actuated by an electrical motor, and control their phase difference via meshed gears, thereby implementing a modulation scheme with broken time-reversal symmetry that effectively imparts angular momentum to the system. We experimentally demonstrate tunable nonreciprocal behavior with a high nonreciprocal isolation of 34 dB and reflection as low as -9 dB, with insertion losses of 5 dB and parasitic signals below -20 dB. All the experimental results agree well with theoretical and numerical predictions. Copyright © 2024, The Authors. All rights reserved.

关键词： Acoustic resonators

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Emergence of instability-driven domains in soft stratified materials

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npj Computational Materials 2022年第1期8卷 931-936页

作者： Jian Li Viacheslav Slesarenko Stephan Rudykh Key Laboratory of Traffic Safety on Track of Ministry of Education School of Traffic&Transportation EngineeringCentral South UniversityChangshaHunan410075China Joint International Research Laboratory of Key Technology for Rail Traffic Safety Central South UniversityChangsha410075China National&Local Joint Engineering Research Center of Safety Technology for Rail Traffic Vehicle Central South UniversityChangsha410075China Cluster of Excellence livMatS@FIT–Freiburg Center for Interactive Materials and Bioinspired Technologies University of FreiburgGeorges-Köhler-Allee 105D-79110FreiburgGermany Department of Mechanical Engineering University of Wisconsin—MadisonMadisonWI53706USA School of Mathematical&Statistical Sciences National University of Ireland GalwayUniversity RoadGalwayIreland

Nature frequently employs the buckling phenomenon to facilitate the formation of complicated patterns across *** knowledge,however,is limited to a small set of buckling-induced microstructure transformations in soft composites;and the pattern formation phenomenon remains largely unknown for a vast pool of material ***,we investigate the unexplored rich domain of soft heterogeneous *** experimentally observe the formation of instability-driven domains in stratified composites with a non-dilute stiff *** illustrate that the discovered domain patterns are energetically favorable over ***,we introduce a closed-form analytical expression allowing us to predict the evolution of the patterns in the post-buckling ***,we show that various patterns can be pre-designed via altering material *** findings can help advance our understanding of the mechanisms governing pattern formations in soft biological tissues,and potentially enable the platform for mechanical metamaterials.

关键词： composites buckling stratified

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