Development of a friction energy capacity approach to predict the surface coating endurance under complex oscillating sliding conditions

In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent catastrophic consequences. In this study, a model based on local dissipated energy is developed and related to the friction process. Indeed, the friction dissipated energy is a unique parameter that takes into account the major loading variables which are the pressure, sliding distance and the friction coefficient. To illustrate the approach a sphere/plane (Alumina/TiC) contact is studied under gross slip fretting regime. Considering the contact area extension, the wear depth evolution can be predicted from the cumulated dissipated energy density. Nevertheless, some difference is observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter, the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The surface treatment lifetime is then simply deduced from an energy ratio between this specific energy capacity and a mean energy density dissipated per fretting cycle. The stability of this approach has been validated under constant and variable sliding conditions and illustrated through an Energy Density–Coating Endurance char

On the in vitro fatigue behavior of human dentin with implications for life prediction

Although human dentin is known to be susceptible to failure under repetitive cyclic fatigue loading, there are few reports in the literature that reliably quantify this phenomenon

Microstructural and biochemical characterization of the nanoporous sucker rings from Dosidicus gigas

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Advanced Materials 21 (2009): 401-406, doi:10.1002/adma.200801197.Recent interest in the development of environmentally benign routes to the synthesis of novel multifunctional materials has resulted in numerous investigations into structure-function relationships of a wide range of biological systems at the ultrastructural, micromechanical, and biochemical levels. While much of this research has concentrated on mineralized structures such as bone, mollusk shells sponge spicules and echinoderm ossicles, there is an equally broad range of animals whose skeletal structures are devoid of mineral components.One such group, the squids (Mollusca: Cephalopoda: Teuthoidea), are remarkable in several aspects. In addition to having an exceptionally well developed brain, sensory systems and skin (for adaptive coloration), these swift agile predators have eight flexible strong arms, two fast extensible tentacles, and strong malleable suckers, all of which are muscular hydrostats.We gratefully acknowledge funding from the Swiss National Science Foundation (AM, PA002–113176 / 1), NIH 5 R01 DE 014672, DANSYNC for supporting the synchrotron experiments, and the Danish Research Councils, as well as partial support (RTH) by DARPA DSO BioDynotics Program (Project N66001-03-C-8043)

Variations in human DEJ scallop size with tooth type

OBJECTIVE: Recent literature suggests that the scalloped structure of the dentino-enamel junction (DEJ) is critical for DEJ stability. Aim of our study was to see if there are differences in scallop size and shape with tooth type. METHODS: Enamel of extracted permanent human teeth was demineralised using EDTA. After fixation and dehydration the scallops of the DEJ were investigated in a scanning electron microscope. Scallop area and shape (circularity) were measured for molars, premolars, canines and incisors. RESULTS: Scallop area showed main effects for tooth type and specimen, while, due to high variability in third molars, there was also an interaction effect (repeated measures two-way ANOVA, p < 0.05). Differences between tooth types were statistically significant, suggesting that posterior teeth showed larger scallops compared to anterior teeth. Differences in shape (circularity) were not statistically significant. CONCLUSION: Our results suggest that teeth which are subject to higher masticatory loads (posterior teeth) show larger and more pronounced scallops. These findings might be of interest for improving other interfaces joining dissimilar materials

Enamel-like apatite crown covering amorphous mineral in a crayfish mandible

Carbonated hydroxyapatite is the mineral found in vertebrate bones and teeth, whereas invertebrates utilize calcium carbonate in their mineralized organs. In particular, stable amorphous calcium carbonate is found in many crustaceans. Here we report on an unusual, crystalline enamel-like apatite layer found in the mandibles of the arthropod Cherax quadricarinatus (freshwater crayfish). Despite their very different thermodynamic stabilities, amorphous calcium carbonate, amorphous calcium phosphate, calcite and fluorapatite coexist in well-defined functional layers in close proximity within the mandible. The softer amorphous minerals are found primarily in the bulk of the mandible whereas apatite, the harder and less soluble mineral, forms a wear-resistant, enamel-like coating of the molar tooth. Our findings suggest a unique case of convergent evolution, where similar functional challenges of mastication led to independent developments of structurally and mechanically similar, apatite-based layers in the teeth of genetically remote phyla: vertebrates and crustaceans