動機系邀請美國密西根大學機械系 Michael Thouless 教授蒞校進行專題演講。Thouless 教授為固體力學及材料接面破壞領域之權威，歡迎有興趣之師生踴躍參與。演講資訊如下，敬請參閱：

*演講時間：114/5/14（三）10:00-11:30
*演講地點：國立清華大學工程一館108演講廳
*演講者：Prof. Michael Thouless (Department of Mechanical Engineering ; Department of Materials Science & Engineering, University of Michigan)
*講題：The mechanics of adhesion and interfacial fracture - a cohesive-zone perspective

*Abstract：
Historically, the field of adhesion and interfacial fracture has evolved along three distinct routes in different communities. Linear-elastic fracture mechanics, as adapted for interfaces, tends to be used by mechanical engineers. The work of adhesion tends to be used by chemists and physicists.  Cohesive strengths are used by those who, perhaps, feel forces are more intuitively obvious than energies. However, all three approaches are valid and useful from different perspectives, and they can be coupled through a cohesive-zone perspective of fracture.

From a mechanical perspective, the role of an interface is to provide bonding between two materials. This bonding can be described by a traction-separation law that relates tractions [N/m2] to displacements [m] across the interface.  It is this traction-separation law that provides the physical basis for a cohesive-zone model, in which one thinks of the fracture process as being characterized by an energy density [J/m2] - the area under the traction-separation curve - and a cohesive length [m].

Linear-elastic fracture mechanics (LEFM), with its assumption of singular stresses described by a stress-intensity factor, follows from the assumption of Griffith that fracture can be described only by the energy density, and that the cohesive length can be neglected. While this assumption provides a powerful approach for design, it is valid only for a very limited set of conditions. Even in systems for which the crack is controlled by a stress-intensity factor, there are important fracture problems for which fracture can't be described from an LEFM perspective without introducing an arbitrary length scale into the description. A cohesive-zone perspective, with the cohesive length it brings naturally into the description of fracture, allows for a rational analysis of problems that are not amenable to an LEFM approach.

In this talk, the basic concepts of cohesive-zone models will be described, along with how they can be connected to LEFM approaches under appropriate conditions. Then a number of problems will be discussed for which a length scale missing from LEFM is needed. These examples include fracture from corners that don't contain cracks, fracture along bi-material interfaces, time-dependent fracture in creeping and visco-elastic materials, and crack deflection.