学术报告会通知
题目1：COHESIVE ZONE MODELING OF MATERIALS FRACTURE
题目2：thermal fracture of advanced materials:
I: Effect of Interfacial Thermal Resistance on Surface Crackingin a Coating Layer Bonded to a Substrate
II: A Matricity-Based Thermal Conductivity Model with Application toThermal Fracture of Interpenetrating Phase Composites
报告人：Professor Zhihe Jin (University of Maine,USA)
时 间：2018年6月25日(周一)上午10:00
地 点：9号楼506会议室
主办单位：国际合作处，航空宇航学院，机械结构力学及控制国家重点实验室
报告1简介：The first part of this seminar is concerned with the equivalency between the cohesive zone modeling and continuum fracture mechanics approaches by considering the influence of the cohesive zone on the crack tip stress field in elastic-plastic materials. A mode III crack with a cohesive zone in an elastic power-law hardening material is studied under the small scale yielding conditions. The cohesive law follows a softening path with the peak traction at the start of separation. The stress and strain fields in the plastic zone, and the cohesive traction and separation displacement in the cohesive zone are obtained using the Hodograph transform technique. It is found that for a modest hardening material with a hardening exponent N = 0.3, the stress distribution in a large portion of the plastic zone is significantly altered with the introduction of the cohesive zone if the peak cohesive traction is less than two times yield stress, which implies the disparity in terms of the fracture prediction between the conventional elastic-plastic fracture mechanics and the cohesive zone approach. The stress distributions with and without the cohesive zone converge when the peak cohesive traction becomes infinitely large. The implications of these results to the medium and large scale yielding are that the peak cohesive traction should be greater than about 2.5 times yield stress to fulfill the requirement of the stress distribution match so that the cohesive zone approach and elastic-plastic fracture mechanics produce similar predictions on fracture.
The second part of this seminar is concerned with crack growth resistance simulation in a ceramic/metal functionally graded material (FGM) using a cohesive zone approach. The plasticity in the background (bulk) material follows J2 flow theory with the flow properties determined by a volume fraction based, elastic–plastic model (extension of the original Tamura–Tomota–Ozawa model). A phenomenological, cohesive zone model with six material-dependent parameters (the cohesive energy densities and the peak cohesive tractions of the ceramic and metal phases, respectively, and two cohesive gradation parameters) describes the constitutive response of the cohesive zone. The crack growth resistance of the FGM is characterized by a rising J-integral with crack extension (averaged over the specimen thickness) computed using a domain integral (DI) formulation. The 3-D analyses are performed using WARP3D, a fracture mechanics research finite element code, which incorporates solid elements with graded elastic and plastic properties and interface–cohesive elements coupled with the functionally graded cohesive zone model. The numerical results for a TiB/Ti FGM SE(B) specimen show that the FGM exhibits significant crack growth resistance behavior when the crack grows from the ceramic-rich region into the metal-rich region. Under these conditions, the J-integral is generally higher than the cohesive energy density at the crack tip even when the background material response remains linearly elastic, which contrasts with the case for homogeneous materials wherein the J-integral equals the cohesive energy density for a quasi-statically growing crack.
报告2简介：The first part of this seminar is concerned with the thermal fracture of bonded dissimilar materials considering interfacial thermal resistance. It is known that thermal resistance exists at interfaces in bonded dissimilar materials due to imperfect mechanical and chemical bonding as well as phonon scattering at the interface. This thermal resistance influences the temperature distribution as well as thermal stresses in the bonded materials. We consider an edge crack in the coating layer that is bonded to a substrate. The thermal stress intensity factor for the edge crack considering the thermal resistance at the coating-substrate interface is calculated using an integral transform/integral equation method. The numerical results for an Al2O3 coating on a Si3N4 substrate show that the thermal stress field deviates from that for the coating/substrate system without considering interfacial thermal resistance. The thermal stress intensity factor is increased by the interfacial thermal resistance, which indicates that the thermal shock resistance of the coating/substrate system can be degraded by the presence of thermal resistance at the interface between the coating and substrate.
The second part of this seminar is concerned with thermal fracture of interpenetrating phase composites (IPCs) using a matricity-based thermal conductivity model. A matricity-based thermal conductivity model for IPCs is first developed. The model employs the formulas of effective thermal conductivities for particulate composites together with the so-called matricities of the constituent phases. The model is then applied to investigate a double edge cracked plate of a ceramic/metal IPC under a thermal shock. The numerical results for an Al2O3/aluminum IPC show that both the peak tensile thermal stress and the peak thermal stress intensity factor (TSIF) are significantly lower than those for the corresponding aluminum particulate Al2O3-matrix composite.
报告人简介：Dr. Zhihe Jin is a Professor in the Department of Mechanical Engineering at the University of Maine. He received his B.S. in Mechanics from Lanzhou University in 1982, and his Master’s and Doctoral degrees in Engineering Mechanics from Tsinghua University in 1985 and 1988, respectively. He worked at Northern Jiaotong University, Shizuoka University, University of Sydney, Virginia Tech, University of Illinois and Purdue University before joining the University of Maine in 2005. Dr. Jin is a Fellow of ASME, and was a JSPS Invitation Fellow in 2016. He has published more than 100 refereed journal papers and a book on fracture mechanics.