Cracks are the major vehicle for material failure and often exhibit complex dynamics. In spite of the fact that the laws that govern their motion have been intensively investigated for nearly a century, several fundamental issues in dynamic fracture remain poorly understood. A major stumbling block in making progress in this problem is that it involves the coupling between widely separated scales; fast fracture, which is ultimately driven by the release of (linear) elastic energy slowly stored on large scales, is affected by the rapid, non-linear and dissipative processes taking place in the very small scales near the front of a moving crack. In this talk, I will describe some of the major challenges in this field and review recent experimental and theoretical advances, highlighting basic properties of the recently developed “Weakly Nonlinear Theory of Dynamic Fracture” and its success in explaining various experimental observations, including a high-speed crack instability.

Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery, without which most of the sensor network may be impossible. The piezoelectric nanogenerators developed by us have the potential to serve as self-sufficient power sources for mico/nano-systems. For Wurtzite structures that have non-central symmetry, such as ZnO, GaN and InN, a piezoelectric potential (piezopotential) is created in the crystal by applying a strain. The nanogenerator is invented by using the piezopotential as the driving force for electrons to flow in responding to a dynamic straining of piezoelectric nanowires. A gentle straining can produce an output voltage of up to 20-40 V from an integrated nanogenerator. Furthermore, piezopotential in the wurtzite structure can serve as a “gate” voltage that can effectively tune/control the charge transport across an interface/junction; electronics fabricated based on such a mechanism is coined as piezotronics, with applications in force/pressure triggered/controlled electronic devices, sensors, logic units and memory. By using the piezotronic effect, we show that the optoelectronc devices fabricated using wurtzite materials can have superior performance as solar cell, photon detector and light emitting diode. Piezotronic is likely to serve as a “mechanosensation” for directly interfacing biomechanical action with silicon based technology and active flexible electronics.