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Development and practical application of a stairclimbing wheelchair in Nagasaki
Murray J Lawn,Toshihide Sakai,Megumu Kuroiwa,Takakazu Ishimatsu 한국과학기술원 인간친화 복지 로봇 시스템 연구센터 2001 International Journal of Assistive Robotics and Me Vol.2 No.2
In the field of providing mobility for the elderly or disabled the aspect of dealing with stairs continues largely unresolved. This paper focuses on presenting continued development of the "Nagasaki Stairclimber", a duel section tracked wheelchair capable of negotiating the large number of twisting and irregular stairs typically encounted by the residents living on the slopes that surround the Nagasaki harbor. Recent developments include an auto guidance system, auto leveling of the chair angle and active control of the front-rear track angle.
Fatigue and debris generation at indentation-induced cracks in silicon
Bhowmick, Sanjit,Cha, Hyunmin,Jung, Yeon-Gil,Lawn, Brian R. Elsevier 2009 ACTA MATERIALIA Vol.57 No.2
<P><B>Abstract</B></P><P>The nature of fatigue in bulk silicon subjected to cyclic loading is considered. Indentation tests with hard spheres of millimeter-scale radius are used to generate fractures principally in {100} silicon surfaces, but also in selected {111} silicon, polycrystalline silicon and {100} monocrystalline germanium surfaces. Pronounced damage accumulation is observed with progressive indenter cycling, as ejection of slabs and particles onto the specimen surfaces. It is argued that the fatigue arises from sliding at friction points within the crack interfaces, with consequent production of debris outside and (ultimately) within the contact. Section views through the indentation sites provide clues as to the material ejection process, involving coalescence of secondary cracks into a primary ring crack to create the slabs. Ejection is facilitated by linkage between adjacent ring cracks, leading ultimately to mass removal.</P>
Hertzian Crack Suppression and Damage Tolerance of Silicon Nitride Bilayer
Lee, Kee-Sung,Kim, Do-Kyung,Lee, Seung-Kun,Lawn, Brian R. The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.4
Hertzian crack suppression phenomena and relatively high damage tolerance were investigated in hard/soft silicon nitride ($Si_3N_4$) bilayers. Coarse $\alpha}-Si_3N_4$ powder was wsed for the hard coating layer and fine $\alpha}-Si_3N_4$ powder was used for the soft substrate layer. The two layers were designed with a strong interface. Hertzian indentation was used to investigate contact fracture and damage tolerance property. Hertzian crack suppression has occurred with increasing applied load and decreasing coating thickness. The crack suppression contributed strength improvement, especially in the bilayers with thinner coatings. Ultimately, the combination of hard coating with soft but tough underlayer improved the damage tolerance of brittle $Si_3N_4$ ceramics.