A DIC-Based Study on Fatigue Damage Evolution in Pre-Corroded Aluminum Alloy 2024-T4.

This paper investigates the fatigue damage and cracking behavior of aluminum alloy 2024-T4 with different levels of prior corrosion. Damage evolution, crack initiation and propagation were experimentally analyzed by digital image correlation, scanning electron microscopy and damage curves. Prior corrosion is shown to cause accelerated damage accumulation, inducing premature fatigue crack initiation, and affecting crack nucleation location, crack orientation and fracture path. For the pre-corrosion condition, although multiple cracks were observed, only one corrosion-initiated primary crack dominates the failure process, in contrast to the plain fatigue cases, where multiple cracks propagated simultaneously leading to final coalescence and fracture. Based on the experimental observations, a mixed-mode fracture model is proposed and shown to successfully predict fatigue crack growth and failure from the single dominant localized corrosion region.

Experimental characterisation for micromechanical modelling of CoCr stent fatigue.

Fatigue of CoCr alloy stents has become a major concern in recent times, owing to cases of premature fracture, often driven by microstructural phenomena. This work presents the development of a micromechanical framework for fatigue design, based on experimental characterisation of a biomedical grade CoCr alloy, including both microscopy and mechanical testing. Fatigue indicator parameters (FIPs) within the micromechanical framework are calibrated for the prediction of microstructure-sensitive fatigue crack initiation (FCI). A multi-scale CoCr stent model is developed, including a 3D global J2 continuum stent-artery model and a 2D micromechanical sub-model. Several microstructure realizations for the stent sub-model allow assessment of the effect of crystallographic orientations on stent fatigue crack initiation predictions. Predictions of FCI are compared with traditional Basquin-Goodman total life predictions, revealing more realistic scatter of data for the microstructure-based FIP approach. Comparison of stent predictions with performance of a 316L stent for the same generic design exposes the design as over-conservative for the CoCr alloy. In response, the micromechanical framework is used to modify the stent design for the CoCr alloy, improving design efficiency.

Optimizing the design of a bioabsorbable metal stent using computer simulation methods.

Computer simulation is used extensively in the design of permanent stents. In order to address new challenges that arise in the design of absorbable metal stents (AMSs), such as corrosion and the limited mechanical properties of bioabsorbable alloys, new simulation and design techniques are needed. In this study a new method for simulating AMS corrosion is developed to study the effects of corrosion on the mechanical performance of a range of stent designs. The corrosion model is combined with an optimization strategy to identify AMS features that give optimal corrosion performance in the body. It is found that strut width is the predominant geometrical factor in determining long-term AMS scaffolding performance. An AMS with superior scaffolding performance to a commercial design is identified, based on deployment and corrosion simulations in stenosed vessels. These simulation and design techniques give new insights into in-vivo AMS performance and the role of device geometry in determining long-term scaffolding performance.