Feb_March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 8 1 2 BREAKING DOWN HOW COMPOSITES BREAK After some 400 computer simula­ tions, scientists at Rice University, Houston, developed a model to de­ code how naturally occurring layered platelet-matrix composite materials respond to fracture events to stave off catastrophic failure. These composites, such as mother of pearl, tooth enam­ el, and bamboo, consist of nanoscale arrangements of strong, hard, overlap­ ping platelets connected by a flexible matrix that distributes stress through­ out the material. They exhibit two kinds of toughening: before crack propaga­ tion, when the platelets slide against each other to relieve stress; and after­ ward, when the crack may be rerout­ ed several times between layers into a long, complex trajectory that requires much more energy to drive it than a short, straight crack would. The new compu- ter model allows four parameters to be ad­ justed in each simu- lation: characteristic platelet length, ma-trix plasticity, platelet dissimilarity ratio, and platelet overlap offset. These characteristics are integrated to com­ pute the composite’s strength, toughness, stiffness, and frac­ ture strain, allowing users to arrive at the optimal psi, a quantification of a com­ posite’s ability to avoid catastrophic failure. The model demonstrates that platelet length may be the strongest contributor to optimal psi, which can be achieved with platelet lengths that distribute the fracture evenly and allow maximum crack growth. rice.edu . MATERIALS SYNTHESIS METHOD IS A KNOCKOUT Researchers at Hokkaido Universi­ ty, Japan, developed a novel materials synthesis method that uses protons to drive ions out of a source materi­ al—the way a cue ball knocks billiard balls out of formation—for insertion into a host material. In the liquid-free process called proton-driven ion intro- duction, several kilovolts are applied to a needle-shaped anode placed in atmospheric hydrogen, triggering elec­ trolytic disassociation of the hydrogen and generating protons. These protons Illustration of proton-driven ion introduction. Protons generated by electric disassociation of hydrogen are shot into the supply source of the desired ions. The ions are then forced out of the source to be introduced into the host material. Courtesy of M. Fujioka/ Hokkaido University. EMERGING TECHNOLOGY Oliver Myers, associate professor of mechanical engineering, Clemson University, S.C., received a grant for $993,492 from the U.S. Army Research Laboratory to create a smart material for military vehicles that can detect and report component damage to a central computer. Myers will lead the project to develop a magnetostrictive composite lam­ inate, which could extend the service times of vehicle parts by allowing them to be replaced on an as-needed basis instead of on a schedule. clemson.edu , arl.army.mil . BRIEF Model platelet-matrix composite in the foreground with nacre in the background. Researchers developed com­ puter simulations to decode natural materials to guide research into synthetic multifunctional composites. Cour­ tesy of Multiscale Materials Laboratory/Rice University. migrate along the electric field and are shot into the ion source. Because the source must maintain electric neutrali­ ty, ions are driven out and intercalated into a nanoscale gap in the host materi­ al, creating the new substance. The team homogenously intro­ duced ions of lithium, sodium, potas­ sium, copper, and silver into tantalum (IV) sulfide (TaS 2 ), a layered material, while maintaining its crystallinity. Re­ searchers also substituted sodium ions of Na 3 V 2 (PO 4 ) 3 with potassium, produc­ ing a thermodynamically metastable material that cannot be obtained us­ ing a conventional solid-state reaction method. www .global.hokudai.ac.jp.