讲座题目：Role of Inclusion Stiffness and Interfacial Strength on Dynamic Matrix Crack Growth: An Optical Study Using DIC and High-speed Photography

报告人：Professor Hareesh Tippur  

时 间：5月13日（周五）下午2:30~4:30 
地 点：力学楼434会议室
主持人：方岱宁（教授）

报告内容摘要：
     This presentation deals with experimental simulation of dynamic crack growth past embedded inclusions of two different elastic moduli, stiff (glass) and compliant (polyurethane) relative to the matrix (epoxy) in a 2D setting. Full-field surface deformations are mapped optically in the crack-inclusion vicinity using 2D DIC method.The crack growth behavior as a function of inclusion-matrix interfacial strength and the inclusion location relative to the crack is studied. An ultra high-speed rotating mirror-type multi-sensor digital camera is used to record random speckle patterns in the crack-inclusion vicinity at rates of 150,000-300,000 fps. The crack-tip deformation histories from the time of impact until complete fracture are mapped and fracture parameters are extracted.The crack arrest duration at a strongly bonded compliant inclusion is longer than the one for the weakly bonded counterpart. On the other hand, the crack is deflected away for the stiff and attracted by the compliant inclusion for a strong interface when the inclusion is located eccentrically. The compliant inclusion cases show higher fracture toughness than the stiff inclusion cases. The measured crack-tip mode-mixities correlate well with the observed crack attraction and repulsion mechanisms. The examination of fracture surfaces reveals much higher surface roughness and ruggedness after crack-inclusion interaction for compliant inclusion than the stiff one. Implications of these observations to dynamic fracture behavior of particle-filled polymer composites are enunciated.

报告人简介：
     Hareesh V. Tippur is currently a McWane Endowed Chair Professor and Graduate Program Chair of Mechanical Engineering at Auburn University, Alabama. He has worked extensively in the overlapping areas of optical metrology and failure mechanics of solids. He was responsible for the development of the Coherent Gradient Sensing (CGS) method and for initiating dynamic interfacial fracture mechanics work during his tenure at Caltech. At Auburn his research has focussed on development of visible and infrared interferometers for fracture mechanics, dynamic fracture behavior of dissimilar material interfaces and functionally graded materials, extension of Digital Image Correlation (DIC) method for dynamic fracture problems and failure characterization of novel interpenetrating phase composites and foams.To date his research has resulted in over 150 publications in archival journals, books and conference proceedings. Several agencies including the US National Science Foundation, Army Research Office, NASA and Air Force Office of Scientific Research have sponsored his research work over the years.He has received several recognitions including Hetènyi Award from the Society for Experimental Mechanics, Beer-Johnston Mechanics Educator Award from the American Society for Engineering Education, elected Fellow of the American Society of Mechanical Engineers and the Society for Experimental Mechanics, Fylde Electronics Prize from the British Society for Strain Measurement. Currently he serves on the editorial boards of Experimental Mechanics and Optics and Lasers in Engineering. After serving as an Associate Editor of Experimental Mechanics since 2001, he has recently taken up the responsibility as its Editor-in-Chief. His other past professional society contributions include chairing ASME-AMD Technical Committee on Fracture Mechanics and SEM Technical Division on Fracture and Fatigue.