Dynamic Crack Propagation in Particle Reinforced Nanocomposites and Graded Materials

Abstract

An experimental investigation has been conducted to evaluate the mechanical properties of novel materials fabricated using nano and micron sized particles in polymer matrix. Experiments were also conducted to investigate the dynamic crack propagation in theses particle reinforced materials. High-speed digital imaging was employed along with dynamic photoelasticity to obtain real time, full-field quantification of the dynamic fracture process. Birefringent coatings were used to conduct the photoelastic study due to the opaqueness of these materials [1].Unsaturated polyester resin specimens embedded with small loadings of 36 nm average diameter TiO 2 particles were fabricated using a direct ultrasonification method to study the effects of nanosized particles on nanocomposite bulk mechanical properties [2]. The ultrasonification method employed produced nanocomposites with excellent particle dispersion as verified by TEM. The presence of the particles had the greatest effect on fracture toughness. Both static and dynamic fracture toughness showed marked improvements with addition of small volume fractions (up to 1%)of nano particles. Dynamic fracture experiments were conducted with various specimen geometries to study the complete history of dynamic crack propagation from initiation to crack branching. Results from several of these experiments were compiled in order to establish a relationship between dynamic stress intensity factor, K I , and crack tip velocity, , and the behavior of the nanocomposites is compared with that of the virgin polyester matrix. This relationship is shown in Fig. 1. The specimens used in this study and the nano-particle distribution is also shown in the figure. Crack arrest toughness increased by 64% in the nanocomposite relative to the virgin polyester. Also, Crack propagation velocities in nanocomposites were found to be 50% greater than those in the virgin polyester A detailed analytical and experimental investigation has also been conducted to understand the behavior of a rapidly moving crack-tip in functionally graded materials (FGMs). First, an a