Effects of Crystalline Anisotropy and Indenter Size on Nanoindentation by Multiscale Simulation

Nanoindentation processes in single crystal Ag thin film under different crystallographic orientations and various indenter widths are simulated by the quasicontinuum method. The nanoindentation deformation processes under influences of crystalline anisotropy and indenter size are investigated about hardness, load distribution, critical load for first dislocation emission and strain energy under the indenter. The simulation results are compared with previous experimental results and Rice-Thomson (R-T) dislocation model solution. It is shown that entirely different dislocation activities are presented under the effect of crystalline anisotropy during nanoindentation. The sharp load drops in the load–displacement curves are caused by the different dislocation activities. Both crystalline anisotropy and indenter size are found to have distinct effect on hardness, contact stress distribution, critical load for first dislocation emission and strain energy under the indenter. The above quantities are decreased at the indenter into Ag thin film along the crystal orientation with more favorable slip directions that easy trigger slip systems; whereas those will increase at the indenter into Ag thin film along the crystal orientation with less or without favorable slip directions that hard trigger slip systems. The results are shown to be in good agreement with experimental results and R-T dislocation model solution

Shock loading effect on the MHz-range amplitude-independent internal friction and elastic properties of the beta '(1) martensite phase in Cu-Al-Ni alloys

The internal friction spectrum at 5 MHz in the martensite beta'(1)-phase of CuAlNi alloys shows two prominent internal friction peaks at 270 and 170 K. Corresponding anomalies in the sound wave velocity-temperature dependence have been observed. Detailed analysis of the behaviour of the peaks in dependence on different levels of impact loading and gamma-irradiation points to dislocation-point defect interaction. It is assumed that grain boundary dislocations are responsible for the 270 K peak while lattice dislocation, existing within the martensite variants are responsible for the 170 K peak.status: publishe

Fatal haemorrhage and incomplete block to embryogenesis in mice locking coagulation factor V

COAGULATION factor V is a critical cofactor for the activation of prothrombin to thrombin, the penultimate step in the generation of a fibrin blood clot(1,2). Genetic deficiency of factor V results in a congenital bleeding disorder (parahaemophilia)(3), whereas inheritance of a mutation rendering factor V resistant to inactivation is an important risk factor for thrombosis(4,5). We report here that approximately half of homozygous embryos deficient in factor V (F upsilon(-/-)), which have been generated by gene targeting, die at embryonic day (E) 9-10, possibly as a result of an abnormality in the yolk-sac vasculature. The remaining F upsilon(-/-) mice progress normally to term, but die from massive haemorrhage within 2 hours or birth. Considered together with the milder phenotypes generally associated with deficiencies of other clotting factors(6,7), our findings demonstrate the primary role of the common coagulation pathway and the absolute requirement for functional factor V for prothrombinase activity. They also provide direct evidence for the existence of other critical haemostatic functions for thrombin in addition to fibrin clot formation, and identify a previously unrecognized role for the coagulation system in early mammalian development.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62813/1/384066a0.pd

Nanoindentation properties and the microstructure of grain boundary precipitate-free zones (PFZs) in an AlCuSiGe alloy

We have characterized the nanoscale mechanical properties of grain boundary precipitate-free zones (PFZ's) in an AlCuSiGe alloy, using combined nanoindentation and in-situ atomic force microscopy (AFM). These mechanical properties were then correlated to the composition, precipitate distribution and, indirectly, to the vacancy concentration within these regions, as analyzed by transmission electron microscopy and spectroscopy. Using these results we constructed a structure-zone map of the area adjacent to the grain boundary, which relates the reduced elastic modulus and nanoindentation hardness of the alloy to its graded microstructure. Our analysis indicates that the lowest hardness was found in the region where no precipitates are present at all, regardless of solute concentration. In regions where precipitation is different from that of the bulk, somewhat inferior mechanical properties are achieved.close2