Fabrication of Chitin Nanofiber-Reinforced PLA Nanocomposites by an Environmentally Friendly Process

Polylactic acid (PLA) reinforced with chitin nanofibers was produced from a mixture of a colloidal suspension of PLA particles with chitin nanofiber suspension. The dispersion medium was solely water, which was removed by filtration and drying. Nanocomposites were obtained by compression molding of the filtrates. Static tensile test and dynamic mechanical analysis were performed to evaluate the reinforcement as a function of nanofiber content. Chitin nanofibers delivered reinforcement similar to cellulose nanofibers, being especially effective at up to 70 wt% fiber load. The ultimate tensile modulus and strength reached 7.7 GPa and 110 MPa, respectively, at a nanofiber content of 70 wt%

Slip in twinned copper crystals

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31974/1/0000016.pd

New constitutive analysis of microstructural evolution: hot compression of gamma iron

Oral Presentation - SteelsWork hardening evolution during deformation is typically examined quasi-statically by quenching-in the deformed structure. However quenching of gamma-Fe results in a complex martensitic structure and hence the presumed typical deformation of a face-centred cubic metal can not be easily validated. A recent derivation of constitutive relation can replicate the dynamic stress-strain curve from which the microstructure parameters can be determined (Saimoto and Van Houtte, Acta Mater., 2010 in press). In this determination the mean slip distance is quantitatively derived from the measured curve and correlated to the resolved stress and strain at that point. The plot of shear stress versus inverse mean slip distance reveals that initially the mean slip distance decreases and then increases with strain. At some point a change of slope is observed and this point has been attributed to the matching of the increasing slip distance to that of the decreasing cell size. This analysis have been applied to two low carbon steels, one with 0.002 wt %C and the other with 0.052%C as reported by M. Huang et al. (Scripta Mater, 61, 2009). The results from the compression tests over three-decades of strain rates and temperatures ranging from 920 to 1050°C for these two cases will be compared and discussed.link_to_OA_fulltex

Constitutive relation based on Taylor slip analysis to replicate work-hardening evolution

A constitutive relation based on crystal plasticity was derived by equating the energy of dislocations required to generate the imposed incremental strain with that which was stored as determined from the flow stress. The dynamic annihilation of created dislocations was accounted for by using a factor to balance the equation. The specific case of Taylor's parabolic relation was reproduced and microstructure-based parameters were explicitly formulated in the proportionality constant usually attributed as empirical in the Hollomon relation. The nearly precise replication of the stress-strain relation using at least two curve-fits for aluminum and its alloys validates the quantitative determination of the mean slip distance. The intersection of the two fits appears to be analogous to Stage II to III transition, which was confirmed by analysis of [1 1 1] and [1 0 0] single-crystal studies taken from the literature. The correlation of the flow stress with inverse mean slip distance and deformation cell size, together with the measured stored work, permitted an insight into this Stage II to III transition. The analysis suggests that dynamic-recovery effect in Stage III may be attributed to the change in mean slip distance pattern due to the evolution of cells.status: publishe