Modeling progressive damage accumulation in cortical bone from human ribs using acoustic emission data

This work investigates how progressive microdamage accumulates in intact human fourth ribs under bending loads and how acoustic emission (AE) signals reflect that deterioration. Twenty-four ex vivo ribs (eighteen under quasi-static ( < 0.0004 s − 1 ) and six under dynamic (0.012– 0.042 s − 1 ) ) were subjected to three-point bending while AE sensors recorded microcrack activity near regions of peak tensile stress. To accommodate large deformations and complex geometry, we applied finite strain theory and described the mechanical response with an orthotropic continuum damage model. Damage growth followed a Weibull distribution, and stiffness degradation closely tracked the damage variable. We then correlated AE event counts with damage progression by fitting an empirical relationship that captures both the gradual accumulation of low-damage events and the abrupt increases in events near failure. Our analyses reveal three key outcomes. First, the Hild–Lemaître quasi-brittle damage model provides an excellent fit to stress-strain data across all strain-rate regimes. Second, cumulative AE counts increase monotonically with internal damage, confirming AE as a reliable real-time proxy for microcrack evolution. Third, AE-damage curves differ qualitatively with strain rate: quasi-static tests produce strongly convex profiles culminating in a near-vertical asymptote, whereas dynamic tests exhibit an initial concave segment followed by a more linear trend before ultimate failure. Furthermore, it was observed that increasing strain rate elevates both ultimate and damage strains, whereas subject age is associated with reductions in ultimate stress and stiffness. In contrast, BMI exerts only minor effects. Finally, b -value analysis did not yield predictive insight for human cortical bone fracture, unlike in concrete. Together, these findings establish AE monitoring coupled with continuum damage mechanics as a powerful framework for characterizing rate-dependent failure in rib cortical bone, which could inform real-time clinical monitoring during high-risk procedures.