Bone structure complexity and the strong inter-dependence between mechanical properties and its meso and micro-architecture are particularly visible in the human femur, especially in presence of diseases such as osteoporosis and osteoarthritis. The present work is focused on the micro-scale, where a detailed knowledge of damage mechanisms is missing, being influenced by the presence of lacunae, cement lines and toughening mechanisms. For this purpose, a portable micro-compressive device and synchrotron imaging has been used to map bone local mechanical properties, evaluate cracks propagation mechanisms, and measure fracture mechanics parameters that could characterize damage patterns’ differences. Analyzing four healthy and four osteoporotic femoral heads, intra-patients variability shows increased resistance to compression in the proximal sub-region, close to the acetabulum, where loads are transmitted from the hip to the femur. Furthermore, it has been measured values of crack tip opening displacement (CTOD) around 3-4 µm, K of the order of 10^(−2)-10^(−1) MPa√m and crack propagation velocities around 10-20 µm/min, with a preferential propagation along Z-direction in osteoporotic samples.
La complessità della struttura ossea e la forte interdipendenza fra proprietà meccaniche e la sua meso e micro-architettura sono particolarmente visibili nel femore umano, specialmente in presenza di malattie quali osteoporosi ed osteoartrite. Il presente lavoro si concentra sulla microscala, per la quale non si ha ancora una conoscenza dettagliata dei meccanismi di danneggiamento, poiché influenzata dalla presenza di lacune, linee cementizie e dal verificarsi di fenomeni tenacizzanti. A tal proposito, si è sfruttato un set up di prova coniugato con l’imaging al sincrotrone per mappare le proprietà locali dell’osso, osservarne l’avanzamento delle cricche e misurare alcuni parametri di meccanica della frattura che possano caratterizzarne il comportamento a frattura. Analizzando quattro teste femorali sane e quattro osteoporotiche, la variabilità intra-paziente mostra maggiore resistenza a compressione nelle sub-zone prossimali, vicine all’acetabolo, dove i carichi vengono trasmessi dal bacino al femore. Inoltre sono stati misurati per le cricche valori di crack tip opening displacement (CTOD) attorno ai 3-4 µm, K dell’ordine di 10^(−2)-10^(−1) MPa√m e velocità di propagazione sui 10-20 µm/min, con direzione preferenziale di propagazione lungo la direzione Z nei campioni osteoporotici.
Micro-compressive testing and synchrotron-based damage analysis of human trabecular bone
Zilioli, Sara;RENOLFI, FEDERICO
2020/2021
Abstract
Bone structure complexity and the strong inter-dependence between mechanical properties and its meso and micro-architecture are particularly visible in the human femur, especially in presence of diseases such as osteoporosis and osteoarthritis. The present work is focused on the micro-scale, where a detailed knowledge of damage mechanisms is missing, being influenced by the presence of lacunae, cement lines and toughening mechanisms. For this purpose, a portable micro-compressive device and synchrotron imaging has been used to map bone local mechanical properties, evaluate cracks propagation mechanisms, and measure fracture mechanics parameters that could characterize damage patterns’ differences. Analyzing four healthy and four osteoporotic femoral heads, intra-patients variability shows increased resistance to compression in the proximal sub-region, close to the acetabulum, where loads are transmitted from the hip to the femur. Furthermore, it has been measured values of crack tip opening displacement (CTOD) around 3-4 µm, K of the order of 10^(−2)-10^(−1) MPa√m and crack propagation velocities around 10-20 µm/min, with a preferential propagation along Z-direction in osteoporotic samples.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/184157