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Numerical modeling of adhesion and adhesive failure during unidirectional contact between metallic surfaces

Friction 2016年第3期4卷 217-227页

作者： Eleir M.BORTOLETO Erika F.PRADOS Vanessa SERIACOPI Newton K.fukumasu Luiz G.D.B.da S.LIMA Izabel F.MACHADO Roberto M.SOUZA Surface Phenomena Laboratory Department of Mechanical Engineering Polytechnic School of the University of S(a)o Paulo Av.Prof.Mello Moraes 2231 S(a)o Paulo 05508-900 Brazil Federal University of ABC-UFABC Santo André 09210-170 Brazil

In this work, we developed a finite element modeling approach to study adhesion during unidirectional contact between a two-dimensional plane-strain square and a flat slab. The surfaces were metallic or ceramic, and we analyzed different pairs of materials and their adhesion intensity using a FORTRAN subroutine (DLOAD) connected to a commercial finite element code Abaqus, which provided the surface attractive forces based on the Lennard-Jones interatomic potential using Hamaker constants. We considered adhesive loads during both the approach and separation of the surfaces. During the separation step, we modeled the material transfer between surfaces due to adhesion with respect to damage initiation and propagation at the flat slab. The parameters considered in the simulations include normal load, chemical affinity, and system size, and we analyzed different conditions by comparing the interaction forces during approach and withdrawal. This work also presents: (i) a description of the evolution of energy dissipation due to adhesion hysteresis, (ii) the formation–growth–breakage process of the adhesive junctions and the material transfer between surfaces, and (iii) an adhesive wear map based on a proposed novel equation that correlates the material parameters and material loss due to adhesion. The results indicate that the chemical affinity between bodies in contact is more related to adhesion than the applied load. In addition, the ratio between the material strength and elastic modulus seems to be an important factor in reducing adhesive wear.

关键词： adhesion adhesive failure finite element model interatomic potentials Hamaker constants

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Circulating leptin and its muscle gene expression in Nellore cattle with divergent feed efficiency

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Journal of Animal Science and Biotechnology 2018年第1期9卷 228-232页

作者： Lúcio Flávio Macedo Mota Cristina Moreira Bonafé Pamela Almeida Alexandre Miguel henrique Santana Francisco JoséNovais Erika Toriyama Aldrin Vieira Pires Saulo da Luz Silva Paulo Roberto Leme JoséBento Sterman Ferraz he.dge.fukumasu Departmento de Zootecnia Universidade Federal dos Vales do Jequitinhonha e MucuriDiamantinaMG 39100 000Brazil Faculdade de Ciencias Agrarias e Veterinarias Universidade Estadual Paulista JaboticabalSP 14884 900Brazil Departamento de Medicina Veterinaria Faculdade de Zootecnia e Encjenharia de AlimentosUniversidade de Sao PauloAM.Duque de Caxias Norte n225Pirassununcja 13635 900SPBrazil Departmento de Zootecnia e Desenvolvimento Acjrossocioambiental Sustentavel Faculdade de VeterinariaUniversidade Federal FluminenseNiteroiRJ 24230 340Brazil Departamento de Zootecnia Faculdade de Zootecnia e Engenharia de AlimentosUniversidade de Sao PauloPirassununga 13635-900SPBrazil

Background： Leptin has a strong relation to important traits in animal production, such as carcass composition,feed intake, and reproduction. It is mainly produced by adipose cells and acts predominantly in the *** this study, circulating leptin and its gene expression in muscle were evaluated in two groups of young Nellore bulls with divergent feed efficiency. Individual dry matter intake（DMI） and average daily gain（ADG） of 98 Nellore bulls were evaluated in feedlot for 70 d to determinate the residual feed intake（RFI） and select 20 animals for the high feed efficient（LRFI） and 20 for the low feed efficient（HRFI） groups. Blood samples were collected on d 56 and at slaughter（80 d） to determine circulating plasma leptin. Samples of Longissimus dorsi were taken at slaughter for leptin gene expression ***： DMI and RFI were different between groups and LRFI animals showed less back fat and rump fat thickness,as well as less pelvic and kidney fat weight. Circulating leptin increased over time in all animals. Plasma leptin was greater in LRFI on 56 d and at slaughter（P = 0.0049）. Gene expression of leptin were greater in LRFI animals（P = 0.0022） in accordance with the plasma levels. The animals of the LRFI group were leaner, ate less, and had more circulating leptin and its gene ***： These findings demonstrated that leptin plays its physiological role in young Nellore bulls, probably controlling food intake because feed efficient animals have more leptin and lower residual feed intake.

关键词： Beef cattle Energy homeostasis Fat depositon Residual feed intake

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