Department News
Size Effect of Hair-Size Structures - Experiments and Theory
Seminar Date
2003-06-14
Author
정기훈
Date
2003-06-14
Views
1648
1. 제 목 : Size Effect of Hair-Size Structures - Experiments and Theory
2. 연 사 : Prof. Pin Tong (Hong Kong University of Science and Technology)
3. 일 시 : 2003년 6월 20일 (금) 13:30 - 14:30
4. 장 소 : 서울대 신공학관(301동) 117호 세미나실
5. 내 용 :
The mechanical elastic properties of fine structures in micron and nanometer scales are size dependent. Experiments in bending of walled nanocarbon tubes have shown that the tube stiffness can increase by nearly ten times of conventional expectation when the size of the tube is decreased from 40 nanometers to 8 nanometers. The stiffness of micron-scaled epoxy beams has been shown to increase by three times when the beam thickness is reduced from 115 microns to below 20 microns. The stiffening has been attributed to the stiffening effects of strain gradients based on higher order elasticity theory. The higher order theory involves elastic material parameters in addition to the two in the classical theory for isotropic materials. Such mechanical behavior is important in micro- and nano-electromechanical systems and in optoelectronic applications.
Elasticity theories including the rotational gradients in the constitutive equations were developed in 1960s. Mindlin (1965) developed a general higher order stress theory to explain the size effect. Fleck and Hutchinson (1997) reformulated the theory and renamed it the strain gradient theory. We derived a modified strain gradient theory of elasticity with an alternate decomposition of the second order deformation gradient tensors. The additional material parameters of the higher order deformation theories manifest as the size effect.
We have established the beam bending and torsion solutions to identify the strain gradient contributions to the bending and torsion rigidities as a function of structural size. The size effect has been confirmed by experiments using epoxy. The confirmation of the significant elastic strain gradient effect by theory and experiments opens up a new frontier in the study of elasticity in micron- and nanometer-scaled structures.
6. 연구분야 :
Former President of the Far East and Oceanic Fracture Society
Former President of Hong Kong Society of Theoretical and Applied Mechanics
Former director of Asia Subregion Board, Region XIII, ASME International
Former or current editor of International Journal of Fracture, Int. J. of Computational Mechanics, Hong Kong Institution of Engineers Transaction, ACTA Mechanica Sinica, and International J. of Computer Modelling and Simulation in Engineering
Current research interests include fracture of piezoelectric materials, micron/nano-mechanics and biomechanics.
7. 문 의 : 기계항공공학부 김용협 교수 (☏ 880-7388)
2. 연 사 : Prof. Pin Tong (Hong Kong University of Science and Technology)
3. 일 시 : 2003년 6월 20일 (금) 13:30 - 14:30
4. 장 소 : 서울대 신공학관(301동) 117호 세미나실
5. 내 용 :
The mechanical elastic properties of fine structures in micron and nanometer scales are size dependent. Experiments in bending of walled nanocarbon tubes have shown that the tube stiffness can increase by nearly ten times of conventional expectation when the size of the tube is decreased from 40 nanometers to 8 nanometers. The stiffness of micron-scaled epoxy beams has been shown to increase by three times when the beam thickness is reduced from 115 microns to below 20 microns. The stiffening has been attributed to the stiffening effects of strain gradients based on higher order elasticity theory. The higher order theory involves elastic material parameters in addition to the two in the classical theory for isotropic materials. Such mechanical behavior is important in micro- and nano-electromechanical systems and in optoelectronic applications.
Elasticity theories including the rotational gradients in the constitutive equations were developed in 1960s. Mindlin (1965) developed a general higher order stress theory to explain the size effect. Fleck and Hutchinson (1997) reformulated the theory and renamed it the strain gradient theory. We derived a modified strain gradient theory of elasticity with an alternate decomposition of the second order deformation gradient tensors. The additional material parameters of the higher order deformation theories manifest as the size effect.
We have established the beam bending and torsion solutions to identify the strain gradient contributions to the bending and torsion rigidities as a function of structural size. The size effect has been confirmed by experiments using epoxy. The confirmation of the significant elastic strain gradient effect by theory and experiments opens up a new frontier in the study of elasticity in micron- and nanometer-scaled structures.
6. 연구분야 :
Former President of the Far East and Oceanic Fracture Society
Former President of Hong Kong Society of Theoretical and Applied Mechanics
Former director of Asia Subregion Board, Region XIII, ASME International
Former or current editor of International Journal of Fracture, Int. J. of Computational Mechanics, Hong Kong Institution of Engineers Transaction, ACTA Mechanica Sinica, and International J. of Computer Modelling and Simulation in Engineering
Current research interests include fracture of piezoelectric materials, micron/nano-mechanics and biomechanics.
7. 문 의 : 기계항공공학부 김용협 교수 (☏ 880-7388)
