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strengthening-softening transition and maximum strength in Schwarz nanocrystals

Nano Materials Science 2024年第3期6卷 320-328页

作者： Hanzheng Xing Jiaxi Jiang Yujia Wang Yongpan Zeng Xiaoyan Li Center for Advanced Mechanics and Materials Applied Mechanics LaboratoryDepartment of Engineering MechanicsTsinghua UniversityBeijing100084China Institute of High Performance Computing(IHPC) Agency for ScienceTechnology and Research(A*STAR)Singapore138632Singapore

Recently,a Schwarz crystal structure with curved grain boundaries(GBs)constrained by twin-boundary(TB)networks was discovered in nanocrystalline Cu through experiments and atomistic *** Cu with nanosized Schwarz crystals exhibited high strength and excellent thermal ***,the grainsize effect and associated deformation mechanisms of Schwarz nanocrystals remain ***,we performed large-scale atomistic simulations to investigate the deformation behaviors and grain-size effect of nanocrystalline Cu with Schwarz *** simulations showed that similar to regular nanocrystals,Schwarz nanocrystals exhibit a strengthening-softening transition with decreasing grain *** critical grain size in Schwarz nanocrystals is smaller than that in regular nanocrystals,leading to a maximum strength higher than that of regular *** simulations revealed that the softening in Schwarz nanocrystals mainly originates from TB migration(or detwinning)and annihilation of GBs,rather than GB-mediated processes(including GB migration,sliding and diffusion)dominating the softening in regular *** analyses of simulation data further showed that compared with those in regular nanocrystals,the GB-mediated processes in Schwarz nanocrystals are suppressed,which is related to the low volume fraction of amorphous-like GBs and constraints of TB *** smaller critical grain size arises from the suppression of GB-mediated processes.

关键词： Schwarz nanocrystal Curved grain boundary Atomistic simulation Grain size effect maximum strength

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Microscopic Analysis of Cementitious Sand and Gravel Damming Materia

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Fluid Dynamics & Materials Processing 2024年第4期20卷 749-769页

作者： Ran Wang Aimin Gong Shanqing Shao Baoli Qu Jing Xu Fulai Wang Feipeng Liu College of Water Conservancy Yunnan Agricultural UniversityKunming650201China Tianqi Engineering Consulting Co. Ltd.Kunming650000China Institute of International Rivers and Ecological Security Yunnan UniversityKunming650500China

The mechanical properties of cementitious sand and gravel damming material have been experimentally determined by means of microscopic SEM(Scanning Electron Microscopy)image *** results show that the combination of fly ash and water can fill the voids in cemented sand and gravel test blocks because of the presence of hydrated calcium silicate and other substances;thereby,the compactness and mechanical properties of these materials can be greatly *** every 10 kg/m^(3) increase in the amount of cementitious material,the density increases by about 2%,and the water content decreases by 0.2%.The amount of cementitious material used in the sand and gravel in these tests was 80-110 kg/m^(3),the water-binder ratio was ***,the splitting tensile strength was 1/10 of the compressive strength,and the maximum strength was 7.42 MPa at 90 *** optimal mix ratio has been found to be 50 kg of cement,60 kg of fly ash and 120 kg of water(C50F60W120).The related dry density was 2.6 g/cm^(3),the water content was 6%,and the water-binder ratio was 1.09.

关键词： Cementitious sand gravel material scanning electron microscopy optimal mix ratio maximum strength

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Relationships Between Vertical Jump Metrics and Sprint Performance,and Qualities that Distinguish Between Faster and Slower Sprinters

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Journal of Science in Sport and Exercise 2022年第2期4卷 135-144页

作者： Jad Adrian Washif Lian-Yee Kok High-Performance Branch Sports Performance DivisionNational Sports Institute of MalaysiaNational Sports ComplexBukit Jalil57000 Kuala LumpurMalaysia Department of Sport Science Tunku Abdul Rahman University CollegeKuala LumpurMalaysia

Purpose This study aimed to investigate the relationships between vertical jump metrics and phases during a 60 m *** variances in strength qualities between sprinters of different ability levels were also *** Eighteen young male elite sprinters(age:18.1±1.3 years;stature:1.72±0.07 m;body mass:66.3±6.2 kg)were assessed for squat(SJ),countermovement(CMJ),drop(DJ),and standing long jumps,a maximal load back-squat,and a 60-m sprint from a *** relationships between sprint performances with all variables were analysed using correlation and multiple regression while discriminative parameters between fast(100 m time:~10.50 s)and slow(~11.00 s)sprint groups were assessed using independent *** Higher associations existed between vertical jumps and longer sprint distances,especially between SJ height and relative peak power with 10 m(r=−0.47 and−0.47,respectively),30 m(−0.71 and−0.74),60 m(−0.76 and−0.81),10-30 m(−0.80 and−0.86),and 30-60 m(−0.78 and−0.84)sprint ***,variables such as relative maximal-strength,relative SJ parameters(height,peak force,and peak power),relative CMJ peak power,and reactive strength index(DJ from 35 cm height)had significant discriminative ability and correlations(Pstrength during back-squat accounted for 75%of the variance in 60 m sprint *** Relative measures of multiple strength metrics may provide better insight regarding factors that enhance sprint *** maximal-strength,high explosive power,and reactive strength seem necessary to improve sprint performance in young male elite sprinters.

关键词： Acceleration Mechanical power maximum strength Neuromuscular abilities Reactive strength Track and field

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Peak Torque as an Indicator of Rapid Torque Production during Screening Examinations

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Journal of Sports Science 2016年第5期4卷 257-264页

作者： Roger Olen Kollock Nelson Cortes Eric Gresk James Onate Department of Kinesiology and Rehabilitative Sciences The University of Tulsa Tulsa OK 74104 U.S.A. Division of Health & Human Performance George Mason University Manassas VA 22030 U.S.A. Department of Exercise Science & Community Health University of West Florida Pensacola FL 32514 U.S.A. School of Health and Rehabilitation Sciences The Ohio State University Columbus OH 43210 U.S.A.

Although the ability to produce force rapidly is an indispensable characteristic of optimal health and performance, screening for this very critical parameter of strength is difficult because of clinician time constraints. The purpose this study was to investigate relationships between peak torque （PT） and rate of torque development （RTD） at 0-30, 0-50, 0-100, and 0-200 ms in female collegiate soccer athletes. Seventeen female collegiate soccer athletes were recruited. Isometric PT and RTD were collected at the hip abductors （AB）, hip adductors （AD）, knee extensors （KE） and knee flexors （KF）. The coefficients of determination were calculated to evaluate the association between PT and RTD. Normalized AB, AD and KF PT were significantly correlated to RTD at 0-30, 0-50, 0-100 and 0-200 ms, while KEPT was only significantly correlated to RTD at 0-100 and 0-200 ms. The results of this study indicate that PT is a viable, indirect indicator of early late phase RTD at separate time intervals at the AB, AD and KF. However, it is likely that other physiological factors coupled with PT are required to provide information on the rapid force production capabilities of the KFs and KEs based on the percent of common variance observed.

关键词： maximum strength hip strength preparticipation examination rate of force development.

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