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Christopher M Magazzeni

Publications and source records attributed to Christopher M Magazzeni.

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Bayesian Optimised Collection Strategies for Fatigue Strength Testing

A statistical framework is presented enabling optimal sampling and analysis of constant life fatigue data. Protocols using Bayesian maximum entropy sampling are built based on conventional staircase and stress step methods, reducing the requirement of prior knowledge for data collection. The Bayesian Staircase method shows improved parameter estimation efficiency, and the Bayesian Stress Step method shows equal accuracy to the standard method at larger step size allowing experimentalists to lessen concerns of loading history. Statistical methods for determining model suitability are shown, highlighting the influence of protocol. Experimental validation is performed, showing the applicability of the methods in laboratory testing.

cond-mat.mtrl-sci

Cold Creep of Titanium: Analysis of stress relaxation using synchrotron diffraction and crystal plasticity simulations

There is a long standing technological problem in which a stress dwell during cyclic loading at room temperature in Ti causes a significant fatigue life reduction. It is thought that localised time dependent plasticity in soft grains oriented for easy plastic slip leads to load shedding and an increase in stress within a neighbouring hard grain poorly oriented for easy slip. Quantifying this time dependent plasticity process is key to successfully predicting the complex cold dwell fatigue problem. This work uses a novel approach of in situ synchrotron X-ray diffraction during stress relaxation tests, to quantify the time dependent plasticity. Measured lattice strains from multiple lattice families (21 diffraction rings) were compared with simulated lattice strains from crystal plasticity finite element (CPFE) simulations. The prism slip parameters were found to show stronger strain rate sensitivity compared to basal slip, and this has a significant effect on stress redistribution to hard grain orientations during cold creep.

cond-mat.mtrl-sci