The noncollagenous interfibrillar interface in bone provides the critical function of transferring loads among collagen fibrils and their bundles, with adhesive mechanisms at this site thus significantly contributing to the mechanical properties of bone. Motivated by the experimental observations and hypotheses, a computational study is presented to elucidate the critical roles of two major proteins at the nanoscale interfibrillar interface, that is, osteopontin (OPN) and osteocalcin (OC) in bone. This study reveals the extremely high interfacial toughness of the OPN/OC composite. The previously proposed hypothesis of sacrificial bonds in the extracellular organic matrix is tested, and the remarkable mechanical properties of the nanoscale bone interface are attributed to the collaborative interactions between the OPN and OC proteins.
Nanotwinned metals (nt-metals) show larger ductility and strength compared to nanocrystalline metals facilitated by their special microstructure containing arrays of parallel twin boundaries. The recently-introduced localized pulsed electrodeposition (L-PED) enables 3D printing of nt-metals in complex geometries. Herein, the first computational model incorporating all the involved physics (i.e. electrodeposition, evaporation, fluid flow, and heat transfer) in the L-PED process is presented. The model reveals the critical rules of the pulsed signal and evaporation-driven convection flux in the mass transport mechanism, ion concentration, current density, and printing rate in the L-PED process. Notably, the simulation results predict a very high peak current density (∼130 times of the average current density) during the short (∼ms) ON-time. This high current density in a short period of ON-time results in high deposition rate, of possibly a metal with high internal stress. This prediction may explain the current hypotheses in the literature on formation of nt-metals by stress relaxation during the OFF-time.
Noncollagenous proteins at nanoscale interfaces in bone are less than 2–3% of bone content by weight, while they contribute more than 30% to fracture toughness. Major gaps in quantitative understanding of noncollagenous proteins’ role in the interfibrillar interfaces, largely because of the limitation of probing their nanoscale dimension, have resulted in ongoing controversies and several outstanding hypotheses on their role and function, arguably going back to centuries ago to the original work from Galileo. Our results from the first detailed computational model of the nano-interface in the bone reveal “synergistic” deformation mechanism of a “double-part” natural glue, that is, noncollagenous osteopontin and osteocalcin at the interfibrillar interface. Specifically, through strong anchoring and formation of dynamic binding sites on mineral nanoplatelets, the nano-interface can sustain a large nonlinear deformation with ductility approaching 5000%. This large deformation results in an outstanding specific energy to failure exceeding ∼350 J/g, which is larger than the most known tough materials (such as Kevlar, spider silk, and so forth.).
Tonpilz acoustic transducer is a device for detecting objects under the water and measuring their properties. The Tonpilz includes a stack of piezoelectric actuators polarized across their thickness. The range of pressure level on the working frequency band and the sound pressure level at the resonance frequency are two crucial factors determining the performance of the transducer. A large number of structural and material attributes makes the design process of Tonpilz difficult. This study aims to improve the performance of a Tonpilz by using the optimization to find the globally optimum design variable set. A multi-objective function is introduced based on transducer performance measures. Furthermore, the problem of mixed-integer programming is addressed. Based on the geometrical and operational limits, a series of constraints were introduced in the optimization problem. The results show that optimizing the design variables greatly enhances performance.
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