Biological materials: Structure and mechanical properties

Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Deformation twinning in nanocrystalline materials

Twinning-induced plasticity (TWIP) steels

Spider silk is extraordinarily strong, mollusk shells and bone are tough, and porcupine quills and feathers resist buckling How are these notable properties achieved? The building blocks of the materials listed above are primarily minerals and biopolymers, mostly in combination; the first weak in tension and the second weak in compression The intricate and ingenious hierarchical structures are responsible for the outstanding performance of each material Toughness is conferred by the presence of controlled interfacial features (friction, hydrogen bonds, chain straightening and stretching); buckling resistance can be achieved by filling a slender column with a lightweight foam Here, we present and interpret selected examples of these and other biological materials Structural bio-inspired materials design makes use of the biological structures by inserting synthetic materials and processes that augment the structures' capability while retaining their essential features In this Review, we explain this idea through some unusual concepts

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Structural Biological Materials: Critical Mechanics-Materials Connections

http://newmaeweb.ucsd.edu/~vlubarda/research/pdfpapers/am-04.pdf

Void growth by dislocation emission

http://meyersgroup.ucsd.edu/papers/journals/Meyers%20240.pdf

Laser-induced shock compression of monocrystalline copper: characterization and analysis

http://www.meyersgroup.ucsd.edu/papers/journals/Meyers%20265.pdf

Structure and mechanical behavior of a toucan beak

Solid state experiments at extreme pressures (102100 GPa) and strain rates (10 6 –10 8 s 21 )a re being developed on high energy laser facilities, and offer the possibility for exploring new regimes of materials science. These extreme solid state conditions can be accessed with either shock loading or with a quasi-isentropic ramped pressure drive. Velocity interferometer measurements establish the high pressure conditions. Constitutive models for solid state strength under these conditions are tested by comparing 2D continuum simulations with experiments measuring perturbation growth from the Rayleigh–Taylor instability in solid state samples. Lattice compression, phase and temperature are deduced from extended X-ray absorption fine structure (EXAFS) measurements, from which the shock induced a2v phase transition in Ti and the a2e phase transition in Fe, are inferred to occur on subnanosec time scales. Time resolved lattice response and phase can also be measured with dynamic X-ray diffraction measurements, where the elastic– plastic (1D–3D) lattice relaxation in shocked Cu is shown to occur promptly (,1 ns). Subsequent large scale molecular dynamics (MD) simulations elucidate the microscopic dislocation dynamics that underlies this 1D–3D lattice relaxation. Deformation mechanisms are identified by examining the residual microstructure in recovered samples. The slip-twinning threshold in single crystal Cu shocked along the [001] direction is shown to occur at shock strengths of ,20 GPa, whereas the corresponding transition for Cu shocked along the [134] direction occurs at higher shock strengths. This slip twinning threshold also depends on the stacking fault energy (SFE), being lower for low SFE materials. Designs have been developed for achieving much higher pressures, P.1000 GPa, in the solid state on the National Ignition Facility (NIF) laser.

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Material dynamics under extreme conditions of pressure and strain rate

Nonequilibrium molecular-dynamics (MD) simulations show that shock-induced void collapse in copper occurs by emission of shear loops. These loops carry away the vacancies which comprise the void. The growth of the loops continues even after they collide and form sessile junctions, creating a hardened region around the collapsing void. The scenario seen in our simulations differs from current models that assume that prismatic loop emission is responsible for void collapse. We propose a dislocation-based model that gives excellent agreement with the stress threshold found in the MD simulations for void collapse as a function of void radius.

/pdf/atomistic-modeling-of-shock-induced-void-collapse-in-copper-1dzw4uf25j.pdf

M. S. Schneider

Papers

Void growth by dislocation emission

Laser-induced shock compression of monocrystalline copper: characterization and analysis

Structure and mechanical behavior of a toucan beak

Material dynamics under extreme conditions of pressure and strain rate

Atomistic modeling of shock-induced void collapse in copper