Notch stress/strain estimation techniques and fatigue life modeling for asymmetric materials

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The global automotive industry is under intense pressure to meet fuel economy standards that will nearly double the fuel efficiency of mass-market passenger vehicles by 2025. Vehicle weight reduction strategies are critical to meeting these targets, and have triggered a worldwide search for lightweight materials that can feasibly be applied to component structures while maintaining the highest safety and performance standards. Magnesium alloys are 75% lighter than steel, 35% lighter than aluminum, and demonstrate promising fatigue performance by comparison with these heavier metals. In fact, magnesium alloys (AZ31B and ZK60) were found to match or outperform aluminum alloys (A356 or AA6082) in terms of fatigue behavior, and are thus considered among the most promising replacement materials for non-crash-critical automotive components. Before magnesium can be applied to automotive parts, manufacturers must develop the ability to design notched members. Most of the parts would either have weld nuggets, connection holes, or geometrical discontinuities which are sources of stress gradients and are identified as notches.Due to limited slip systems, magnesium structures demonstrate twinning, which is a deformation mechanism that results in different yield and hardening in tension and compression, known as asymmetric behaviour. To date there is no comprehensive methodology for notch analysis in asymmetric materials.The ability to accurately model the influence of asymmetry on the notch during fatigue performance of an automotive notched part represents a major advancement. Such knowledge is non-existing and will be tackled for the first time through the work proposed in this project.