In Situ Observation on Rate-Dependent Strain Localization of Thermo-Induced Shape Memory Polyurethane

In situ monotonic tensile experiments of thermo-induced shape memory polyurethane (SMPU) at different loading rates were carried out by the digital image correlation (DIC) method and infrared camera FLIR®-A655sc in natural convection (NC) and forced convection (FC) conditions, respectively. The multiform strain localization of SMPU was observed by the DIC method, and the influence of thermo–mechanical coupling on the strain localization was analyzed by using the FLIR to measure the temperature field caused by the internal heat generation. The experimental results show that the strain localization mode strongly depends on the strain rate and convection condition, and the strain localization mode can be transformed by changing the convection condition from NC to FC. The competition mechanism between the strain hardening induced by the increasing loading rate and strain softening induced by the internal heat generation is indicated, the transition modes of strain localization are clarified, and the influences of thermo–mechanical coupling on shape memory effect are discussed.

Convection Condition Variation Analysis on Thermal Dissipation of High Power Single Chip LED

High power light emitting diodes (LEDs) characteristics in terms of efficiency, long operating life and reliability which has lead to its application as lighting systems. However, the high power LEDs are subjected to thermal challenges due to it high input power. This work reports simulation analysis on a single chip high power LED to where thermal performances of the LED package were evaluated under varied convection condition. The simulation was carried out using Ansys version 11. The heat dissipation evaluated and compared in terms of junction temperature, von Mises stress and thermal resistance at each respective convection condition with constant input power of 1 W.