Low cycle fatigue of bolted connections in composites for arctic applications

Abstract

Nowadays composite materials are a very interesting research field. They show an extraordinary performance due to their high stiffness and low density. They are applied in high advance technology industries such as aerospace or defense. But their use is becoming more and more popular in energetic industries, particularly in wind and tidal energy their use is increasing because of the concern of the global warming problem. Wind and tidal companies have planed the construction of wind farms in offshore that means that the materials will be exposed to rough environmental conditions. Many studies have remarked the good mechanical performance of composites at low temperatures under static loads but still the behavior of the composites under dynamic conditions is unexplored. The aim of this report is to give a start point for the fatigue characterization of composites under low temperature conditions.

To achieve this purpose a FEM has been developed and in parallel some tests have been developed to confirm the model predictions. While working with this project, many difficulties appeared and to solve them it was required to have a background in composite materials theory as well as basic knowledge of the numerical program used. For this reason a composite course was made and also many hours behind the computer to understand all the numerical convergence problems caused when running simulations.

Basically the work focuses on the development of a model capable of predicting the stresses under static and dynamic loads. If the model is able to calculate stress fields and progressive material failure properly, it will be ready for predicting the performance of the material at low temperatures only making a few changes. At least in theory because as it can be seen while reading this report some inconvenients appear while simulating materials at low temperature that invalidate partially the results obtained and require new lines of investigation. That is the contact problem created by changing low temperatures that cannot be solved by the direct cyclic method. But the objective of the work has been achieved and recommendations for further work are established.