Quantification of human bone microarchitecture damage in press-fit femoral knee implantation using HR-pQCT and digital volume correlation

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Time-elapsed microstructural imaging of failure of the reverse shoulder implant

Abstract Background Reverse Shoulder Arthroplasties (RSA) have become a primary choice for improving shoulder function and pain. However, the biomechanical failure mechanism of the humeral component is still unclear. The present study reports a novel protocol for microstructural imaging of the entire humerus implant under load before and after fracture. Methods A humerus specimen was obtained from a 75-year-old male donor. An expert surgeon implanted the specimen with a commonly used RSA implant (Aequalis reversed II, Stryker Orthopaedics, USA) and surgical procedure. The physiological glenohumeral contact force that maximized the distal implant migration was selected from a public repository ( orthoload.com ). Imaging and concomitant mechanical testing were performed using a large-volume micro-CT scanner (Nikon XT H 225 ST) and a custom-made compressive stage. Both when intact and once implanted, the specimen was tested under a pre-load and by imposing a constant deformation causing a physiological reaction load (650 N, 10 degrees adducted). The deformation of the implanted specimen was then increased up to fracture, which was identified by a sudden drop of the reaction force, and the specimen was then re-scanned. Results The specimen’s stiffness decreased from 874 N/mm to 464 N/mm after implantation, producing movements of the bone-implant interface consistent with the implant’s long-term stability reported in the literature. The micro-CT images displayed fracture of the tuberosity, caused by a combined compression and circumferential tension, induced by the distal migration of the implant. Conclusion The developed protocol offers detailed information on implant mechanics under load relative to intact conditions and fracture, providing insights into the failure mechanics of RSA implants. This protocol can be used to inform future implant design and surgical technique improvements

X-ray micro-computed tomography of porosities in large-volume 3D-printed Ti–6Al–4V components using laser powder-bed fusion and their tensile properties

Characterization of defects in large 3D printed metals is critical but challenging. This study reports on the X-ray micro-computed tomography (micro-CT) examination of porosities in large-volume 3D-printed and heat-treated titanium (Ti–6Al–4V) alloys, together with their tensile properties and failure mechanisms. Titanium alloy powders were analyzed using scanning electron microscopy (SEM). Laser powder bed fusion (L-PBF) was used to print titanium alloy specimens vertically and horizontally, followed by stress-relieved heat treatment. Micro-CT imaging was performed on printed specimens of 10 × 20 mm3 (diameter × length) to determine their porosities, pore locations and size distributions using an industrial micro-CT system and relevant imaging software. Tensile testing of the processed specimens was conducted to determine their mechanical properties. Optical microscopy and SEM were used to examine the tension-induced failure mechanisms. The results show that porosities, pore sizes and locations were influenced by the build direction, resulting in different mechanical properties. Horizontal printing achieved higher tensile modulus, strength, ductility, resilience and toughness than vertical printing. Heat treatment did not change porosities in horizontally built specimens, but slightly reduced porosities for vertically built ones by 10%. This led to most mechanical properties nearly unchanged for the horizontally printed specimens but remarkably increased yield and tensile strength, and resilience, for the vertically printed ones. All tension-induced fractured surfaces contained pores, possible indicators of failure origins, which should be diminished in advanced processes for higher mechanical reliability

Dissimilar Weld Failure: A Forensic Analysis to Determine Primary Failure Mechanisms

Solar receivers are an integral part of a concentrated solar power plant and commonly utilise tubular structures to absorb solar energy and transfer the heat into a heat transfer fluid. These systems often contain dissimilar materials joined through welds which are exposed to cyclic temperatures, which can be a locus of failure. A systematic forensic analysis was carried out on a low-pressure CO2 receiver that had developed extensive cracking. Microstructural characterisation using micro-computed tomography was performed to understand the failure mechanism in an area adjacent to a welded section of the two dissimilar alloys Haynes 230 and 253 MA. An electrolytical oxalic acid etch showed grain boundary damage from oxidation. Grain boundary damage through oxidation was confirmed with SEM and energy dispersive X-ray spectroscopy (EDX) analysis as the likely metallurgical degradation mechanism which, combined with thermally induced stress cycles led to the failure of the weaker stainless-steel tube adjacent to the weld.</p