Dynamic crack propagation in nano-composite thin plates under multi-axial cyclic loading

Abstract

The main cause of failure in structural mechanics is Fatigue, because of cyclic loading which effects on the crack growth, so in this research, the dynamic crack growth for thin plates subjected to multi-axial cyclic loading (non –proportional) have been studied. The material of plates are pure Copper and reinforced with two types of CNTs with 6 vol %, Single Wall Carbon Nano Tubes Carboxylic (SWCNTs-COOH) and Multi-Wall Carbon Nano Tubes Carboxylic MWCNTs-COOH. It was used an efficient way for producing a Nano-composite material, with perfect dispersions of CNTs, to enhance the mechanical properties of copper and getting a homogeneous mixture of Copper and CNTs. For fracture mechanics part will consider firstly, the theoretical model by using the fracture mechanics modeling to predict the enhancement, reliability and operating life of materials and finding a-N curve. Secondly, in the experimental work, a new apparatus was designed to apply the cyclic shear load (repeated and zero based) and constant tension, Also we will find the critical stress intensity factor Kc for mode I and II experimentally, and all the parameter of Paris Law (c & m Paris Law’s constants), (ΔK the change in stress intensity factor) and (da/dN crack growth per cycle), to insert it in ABAQUS program to simulate the model and compare the results to verify this work. The speed of the crack propagation also found experimentally and analytically at the secondary stage of the crack life, for pure copper experimentally crack speed 0.0.0940 mm/min and 0.1248 mm/min analytically, For MWCNTs + Cu 0.083 mm/min experimentally and 0.08809 mm/min analytically, for SWCNTs + Cu 0.1217 mm/min experimentally and 0.135 mm/min analytically, but also it can be seen the difference between the three material in the crack initiation, where the crack starts in the pure copper earlier than MWCNTs + Cu and at last SWCNTs + Cu’s crack will start. So it’s seen that the life of copper was increased around 10% with MWCNTs-COOH and 18% with SWCNTs-COOH.