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Shear Band Formation in AISI 4340 Steel Under Dynamic Impact Loads:Modeling and Experiment

Acta Metallurgica Sinica(English Letters) 2013年第4期26卷 378-384页

作者： Daniel Odoh Gbadebo Owolabi Akindele Odeshi horace whitworth Department of Mechanical Engineering Howard University Department of Mechanical Engineering University of Saskatchewan57 Campus DriveSaskatoonSKS7N 5A9Canada

In this study, the occurrence of the adiabatic shear bands in AISI 4340 steel under high velocity impact loading was investigated using finite element analysis and experimental tests. The cylindrical specimen subjected to the impact load was divided into different regions separated by nodes using finite element method in ABAQUS environment with boundary conditions specified. The material properties were assumed to be lower in the region where the probability of strain localization is high based on prior experimental results in order to initialize the formation of the adiabatic shear bands. The finite element model was used to determine the maximum flow stress, the strain hardening, the thermal softening, and the time to reach the critical strain for the formation of adiabatic shear bands. Experimental results show that deformed bands were formed at low strain rates and there was a minimum strain rate required for the formation of the transformed band in the alloy and the cracks were initiated and propagated along the transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by the strain-rates and the initial material microstructure. The simulation results obtained were compared with the experimental results obtained from the AISI 4340 steel under high strain-rate loading in compression using split impact Hopkinson bars. A good agreement between the experimental and simulation results was obtained.

关键词： Adiabatic shear bands Finite element model Strain hardening Thermal softening Johnson-Cook model AISI 4340 steel

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Occurrence of Dynamic Shear Bands in AISI 4340 Steel under Impact Loads

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World Journal of Mechanics 2013年第2期3卷 139-145页

作者： Gbadebo Owolabi Daniel Odoh Akindele Odeshi horace whitworth Department of Mechanical Engineering Howard University Washington DC USA Department of Mechanical Engineering University of Saskatchewan Saskatoon Canada

In this study, occurrence of adiabatic shear bands in AISI 4340 steel under high velocity impact loads is investigated using finite element analysis and experimental tests. The cylindrical steel specimen subjected to impact load was divided into different sections separated by nodes using finite element method in ABAQUS environment with boundary conditions specified. The material properties were assumed to be lower at the section where the adiabatic shear bands are expected to initialize. The finite element model was used to determine the maximum flow stress, the strain hardening, the thermal softening, and the critical strain for the formation of adiabatic shear bands. Experimental results show that deformed bands were formed at low strain rates and there was a minimum strain rate required for formation of transformed band in the alloy. The experimental results also show that cracks were initiated and propagated along transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by strain-rates. The simulation results obtained were compared with experimental results obtained for the AISI 4340 steel under high strain-rate loading in compression using split impact Hopkinson bars. A good agreement between the experimental and simulation results was obtained.

关键词： Adiabatic Shear Band Finite Element Model Strain Hardening Thermal Softening Johnson-Cook Model AISI 4340 Steel

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Measurement of the Deformation of Aluminum Alloys under High Strain Rates Using High Speed Digital Cameras

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World Journal of Mechanics 2013年第2期3卷 112-121页

作者： Gbadebo Owolabi Daniel Odoh Alex Peterson Akindele Odeshi horace whitworth Department of Mechanical Engineering Howard University Washington DC USA Department of Mechanical Engineering University of Saskatchewan Saskatoon Canada

Aluminum alloys exhibit an attractive combination of mechanical and physical properties such as high stiffness and low density, which favors their utilization in many structural applications. Thus, increasing the structural applications of aluminum alloy is the driving force for the need to adequately understand its deformation and failure mechanisms under various types of dynamic loading conditions. In this study, full field plastic deformation of AA6061-T6 aluminum alloy at high strain-rates under compressive and torsion loads are measured using split Hopkinson compression, torsion Kolsky bars, and a high speed digital image correlation system. The stress-strain curves obtained using the high speed digital cameras are compared with results obtained from the elastic waves in the compression and torsion bars. A post deformation analysis of the specimen also shows strain localization along narrow adiabatic shear bands in the AA6061-T6 alloy.

关键词： Split Hopkinson Pressure Bar Torsion Kolsky Bar Digital Image Correlation System Adiabatic Shear Band Post Deformation Analysis

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Microstructure and Quasi-Static Mechanical Behavior of Cryoforged AA2519 Alloy

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Materials Sciences and Applications 2019年第2期10卷 137-149页

作者： Amin Azimi Gbadebo Moses Owolabi Hamid Fallahdoost Nikhil Kumar horace whitworth Department of Mechanical Engineering Howard University Washington DC USA Department of Mechanical Engineering Materials Science and Engineering Program Binghamton University (SUNY) Binghamton NY USA

In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-static loading were investigated to determine the influence of cryogenic forging on alloys’ subgrains dimensions, grain boundaries interactions, strength, ductility and toughness. In addition, the failure mechanisms at the tensile rupture surfaces were characterized using scanning electron micro-scope (SEM). The results show significant improvements in the strength, ductility and toughness of the alloy as a result of the cryogenic MAF process. The formation of nanoscale crystallite microstructure, heavily deformed grains with high density of grain boundaries and second phase breakage to finer particles were characterized as the main reasons for the increase in the mechanical properties of the cryogenic forged samples. The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles MAF when compared with the materials processed at ambient temperature. The fractography analysis on the tested materials shows a substantial ductility improvement in the cryoforged (CF) samples when compared to the room temperature forged (RTF) samples which is in alignment with their stress-strain profiles. However, extended forging at higher cycles than 2 cycles led only to increase in strength at the expense of ductility for both the CF and RTF samples.

关键词： AA2519 Aluminum Alloy Cryogenic Forging Quasi-Static Mechanical Behavior Microstructure Investigation Fractography Analysis

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Fatigue Responses of Three AA 2000 Series Aluminum Alloys

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Journal of Materials Science and Chemical Engineering 2019年第3期7卷 32-48页

作者： Gbadebo Moses Owolabi Mark Thom Olusegun Ajide Nikhil Kumar Amin Azimi horace whitworth Grant Warner Department of Mechanical Engineering Howard University Washington DC USA Department of Mechanical Engineering University of Ibadan Ibadan Nigeria

In this paper, smooth specimens of three aluminum alloys: AA 2219-T8, AA 2519-T8 and AA 2624-T351, were subjected to the same level of uniaxial (tension/compression) fatigue loading to compare their fatigue responses. Fractographic investigations of the failed specimens after fatigue loading was also conducted using a scanning electron microscope. The fatigue test results showed considerable differences in the fatigue lives of the three investigated alloys with AA 2219-T8 having the shortest fatigue life and AA 2624-T351 the longest fatigue life. The fractographic analysis showed that coalescence of micropores, microvoids, particles cleavage and microcracks are the predominant features in the fracture surface of AA 2219-T8. The fracture surface features of AA 2519-T8 revealed higher resistance to fatigue cracks nucleation and growth when compared to AA 2219-T8. The features depicted mainly partly ductile and partly brittle fracture. The AA 2624-T351 fracture surface features revealed noteworthy ductile failure mechanism. The results suggest a strong correlation between the surface fractographic features and the fatigue lives of the alloys. It is also observed that in addition to the yield strengths and ultimate tensile strengths, the total strain energy densities (SED) may provide a reasonable indication of the relative fatigue performance of the three alloys. AA 2219-T8 had the lowest SED and the lowest fatigue life, while AA 2624-T351 had the highest SED and the highest fatigue life. Thus, AA 2624-T351 would be the most suitable materials for components subjected to fatigue loading.

关键词： Fatigue Life Aluminum Alloy Strain Energy Density Fractography

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基于协同神经网络的仿射不变性检索相似性度量方法(英文)

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红外与毫米波学报 2002年第5期21卷 327-331页

作者：戚飞虎赵同 horace HSIp 上海交通大学计算机科学与工程系 Image Computing Group Department of Computer Science City University of Hong Kong 200030 Hong Kong

根据协同神经网络 ,提出了一种新的控制参数———序矢量 ,并着重研究了其在图像检索方面的相关性质 .在此基础上 ,针对商标图像检索 ,提出了一种高效的基于元素的仿射不变性度量方法 .实验表明 ,该检索算法抗噪、抗缺损能力强 ,同时对... 详细信息

根据协同神经网络 ,提出了一种新的控制参数———序矢量 ,并着重研究了其在图像检索方面的相关性质 .在此基础上 ,针对商标图像检索 ,提出了一种高效的基于元素的仿射不变性度量方法 .实验表明 ,该检索算法抗噪、抗缺损能力强 ,同时对于平移、旋转、缩放具有不变性 .

关键词：图像检索相似性度量仿射不变性协同神经网络

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SPLENOMEGALY IN THE FOOCHOW AREA WITH SPECIAL REFERENCE TO SCHISTOSOMIASIS, AND ITS RELATIONSHIP TO CRYPTOGENETIC SPLENOMEGALY (BANTI’S DISEASE) A PRELIMINARY REPORT

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Chinese Medical Journal 1936年第11期50卷 1561-1576页

作者： horace EMERSON CAMPBELL M.D. Foochow Christian Union Hospital Foochow Fukien

1. We have records of something like 200 cases of splenomegaly in the majority of which the only diagnosis we could reach was splenic anemia (Banti’s disease).2. During the period from November 1934 to January 1936 thirteen cases were operated upon with the diagnosis of splenic anemia. The spleen was removed in twelve, it was firmly fixed and irremovable in the other. 3. Liver biopsy was performed in four cases, and in two other cases not biopsied, liver was obtained at autopsy. In three of these six livers, the ova of S. Japonicum were discovered.4. Of the splenectomized patients, two died of hemorrhage from the liver or diaphragm, and one died after two weeks from mesenteric thrombosis, a mortality of 25 per cent.5. Two of the three fatal cases were those with marked ascites. The nine other splenectomized cases were all improved, some of them strikingly so.6. The belief is expressed that most of the so-called Banti’s disease of the Orient is actually schistosomiasis.7. It is suggested that prior to operation the spleen be vigorously manipulated with comparison of the platelet count before and after manipulation, in an effort to recognize those cases which will be complicated by thromboses in the post-operative period.8. It is suggested that platelet counts be done at operation, and if the count rises greatly after delivery of the spleen, that the spleen be not removed but the splenic artery merely ligated.

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Proteins in DNA methylation and their role in neural stem cell proliferation and differentiation

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Cell Regeneration 2021年第1期10卷 64-75页

作者： Jiaqi Sun Junzheng Yang Xiaoli Miao horace HLoh Duanqing Pei Hui Zheng Bioland Laboratory(Guangzhou Regenerative Medicine and Health Guangdong Laboratory) #188 Kaiyuan Ave.Science CityHuangpu DistrictGuangzhou 510700China CAS Key Laboratory of Regenerative Biology Guangzhou Institutes of Biomedicine and HealthChinese Academy of SciencesGuangzhou 510530China Guangdong Provincial Key Laboratory of Stem Cell and Regenerative Medicine Guangzhou 510530China Institutes for Stem Cell and Regeneration Chinese Academy of SciencesBeijing 100101China School of Life Science Westlake UniversityHangzhou 310024China

Background:Epigenetic modifications,namely non-coding RNAs,DNA methylation,and histone modifications such as methylation,phosphorylation,acetylation,ubiquitylation,and sumoylation play a significant role in brain *** methyltransferases,methyl-CpG binding proteins,and ten-eleven translocation proteins facilitate the maintenance,interpretation,and removal of DNA methylation,*** forms of methylation,including 5-methylcytosine,5-hydroxymethylcytosine,and other oxidized forms,have been detected by recently developed sequencing *** evidence suggests that the diversity of DNA methylation patterns in the brain plays a key role in fine-tuning and coordinating gene expression in the development,plasticity,and disorders of the mammalian central nervous *** stem cells(NSCs),originating from the neuroepithelium,generate neurons and glial cells in the central nervous system and contribute to brain plasticity in the adult mammalian *** body:Here,we summarized recent research in proteins responsible for the establishment,maintenance,interpretation,and removal of DNA methylation and those involved in the regulation of the proliferation and differentiation of *** addition,we discussed the interactions of chemicals with epigenetic pathways to regulate NSCs as well as the connections between proteins involved in DNA methylation and human ***:Understanding the interplay between DNA methylation and NSCs in a broad biological context can facilitate the related studies and reduce potential misunderstanding.

关键词： DNA methylation Neural stem cells DNA methyltransferases Methyl-CpG binding proteins Ten-eleven translocations Vitamin C

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Shepherding Public Discourse Practices： Homiletic Form Aligned to the Logic Operative in Racial Rhetoric and Public Theological Discourse for Secular Liberal Democracies

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Cultural and Religious Studies 2016年第9期4卷 576-588页

作者： Maury Jackson horace Crogman La Sierra University HMS Richards Divinity School Riverside USA The Institute of Effective Thinking Riverside USA College of the Desert Palm Spring USA

Given that preaching is the primary mode of public theological discourse for most Christian ministers, an intellectual virtue of verbal restraint is required when practicing public theology and it is wise to address the ways that homilies can shepherd public discourse practices. A theology of rhetoric includes the homilist＇s moral purpose. Homilies either enhance public discourse or pervert it. This essay sketches a pattern of sermon movement that respects the logic operative in public theology, given the social context of America. Homilies can help cultivate the pastoral care of public rhetoric by modeling discourse that nurtures the politics of accountability. While many call for a public ethos where divergent moral voices engage each other in highly contested arenas, a precondition to practicing effective public theology requires that one exercises discourse in a way that respects the social limits on the free exercise of religion. It is important that a public theology of rhetoric clarifies the original social agreement for acceptable religious discourse in the public arena. Homiletics, as a dimension of practical theology, can teach preachers methods of pastoral care for public discourse. The social agreement in liberal democracies to contain the combative nature of religious discourse assumes a logic that is circumscribed by commitments to （1） religious pluralism, （2） theological agnosticism, and （3） epistemological pragmatism. Here we propose that a sermon＇s form, which implicitly touches upon these commitments, can tap into the basic modes of persuasion in secular liberal societies. This respects the moral purposes previously agreed upon and expected of partisans during highly contestable times. This calls for incarnational humility on the part of the Christian public theologian and it guides her/his practice.

关键词： homiletics liberal democracy secularization Bonhoeffer radical theology rhetoric

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BRICS Bank Challenges the Exorbitant Privilege of the U.S. Dollar

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China International Business 2014年第8期 32-37页

作者： horace G. CAMPBELL

At the end of the sixth Brazil, Russia, India, China and South Africa （BRICS） summit in Fortaleza,Brazil on July 16, 2014, the leaders announced the Fortaleza Action Plan. This was in the context of the Fortaleza Declaration＇ where the leaders reinforced their position that BRICS would be an international force in challenging the neo-liberal policies of the Washington Consensus. Touching on areas of major destabilization in the world - from Syria to Sudan and from Ukraine to Iraq - the leaders spelt out the need for new paths to peace and for strengthening the United Nations to resolve the outstanding questions of war and insecurity.

关键词：金砖特权过度美元银行新自由主义领导人俄罗斯

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