Seminars

Interfaces abound in many technologically important applications that range from primary structural adhesively bonded joints in aerospace, naval and automo- tive structures to the multiple interfaces that are common in microelectronics devices and packaging. Over the years, cohesive zone modelling has emerged as the natural successor to the classical linear elastic fracture mechanics. Cohesive zone modeling relies on the accurate description of the damage zone through the traction-separation relations relating the e!ective tractions due to damage to the e!ective crack tip sep- arations, which makes the accurate and reliable extraction of the traction-separation relations important for precise modeling. While there are multiple techniques to ex- tract the the traction-separation relations, their direct extraction from delaminating beams loaded with dual actuators provides a comprehensive and efficient approach to extracting normal and shear interactions over the complete range of fracture mode mixes.
The first part of this work deals with the development of an analytic beam on elastic foundation model that accounts for linear interactions in tension and shear with finite strengths and toughness values that vary with mode-mix. It is used to dif- ferentiate between various loading configurations and shows that rotation-controlled loading is more favorable than displacement-controlled loading, when considering sta ble crack growth options. The di!erence between these loading modalities is also brought forth through numerical studies which contrast the nature of self-similarity of beam opening profiles and has consequences on the analysis of heterogeneous inter- faces. Accordingly, a dual actuator, rotation-controlled device has been designed and developed. A wide range of mode-mix is accessed by independently controlling each servo motor. Experiments are conducted on a Aluminum/Epoxy interface under var- ious mode-mixes and the traction-separation relations are extracted. The extracted traction-separation relations show unique characteristics, which are missed by the commonly assumed analytical models. More brittle substrates, such as Silicon, need to be reinforced, otherwise they have a tendency to break before delamination. Steel is used as a reinforcement material as we demonstrate that the same approach can be used to extract traction-separation relations for brittle substrates as well.
The experimentally extracted traction-separation relations obtained so far are entirely phenomenological. Thus, the focus of the second part of this dissertation is on the development of an ab-initio model that provides a more mechanistic un- derstanding of scission and healing of polymer chains. We describe a ‘weak bond’ model which accounts for the fact that a polymer chain will dissociate once one of its bonds breaks. While force-controlled stretching of a single bond has been ex- tensively studied, we perform a study controlled-displacements where we show that reversible bond scission and healing can be understood through the same framework. Such an approach can be integrated into network polymer models in order to provide physics-informed cohesive laws.