V. Vinogradov

The Pair Distribution Function for an Array of Screw Dislocations: Implications for Gradient Plasticity

The problem of spatial correlation within an array of dislocations in a two-dimensional crystalline solid is addressed. A system of equations for joint probability densities is derived based on the assumption that the force on each dislocation remains finite. For arrays of screw dislocations moving on several slip planes the equations are consistent with balanced positive and negative dislocations forming dipoles or mutually cancelling, leaving geometrically necessary dislocations to interact and correlate. The resulting pair distribution function for the geometrically necessary screw dislocations is found, and used to demonstrate the strain gradient correction emerging in the case of micro-scale plasticity.

Advancements in fail safe response with bistable composite structures

Cars have dent resistant side panels, crumple zones and composite bumpers to absorb and disperse impact energy protecting occupants. Each of these improvements share a common feature: once activated or deformed, their load carrying capacity is diminished. A bistable structure is such that, once activated, it has a second stronger phase which has the ability to sustain higher loads. This allows for a better distribution of damage, and in addition the structure keeps its integrity for a longer time. Initial tests have verified this concept proving that a bistable structure under tensile loading has the capacity of absorbing more energy than a similar monolithic structure under the same load conditions. Bistable structure behavior has also been shown for a system composed of advanced fiber reinforced composites, which has the potential of being a break-through for applications where energy absorption is sought.Copyright