Eric Hintsala

A Sinusoidally Architected Helicoidal Biocomposite.

A fibrous herringbone-modified helicoidal architecture is identified within the exocuticle of an impact-resistant crustacean appendage. This previously unreported composite microstructure, which features highly textured apatite mineral templated by an alpha-chitin matrix, provides enhanced stress redistribution and energy absorption over the traditional helicoidal design under compressive loading. Nanoscale toughening mechanisms are also identified using high-load nanoindentation and in situ transmission electron microscopy picoindentation.

Review Article: Case studies in future trends of computational and experimental nanomechanics

With rapidly increasing numbers of studies of new and exotic material uses for perovskites and quasicrystals, these demand newer instrumentation and simulation developments to resolve the revealed complexities. One such set of observational mechanics at the nanoscale is presented here for somewhat simpler material systems. The expectation is that these approaches will assist those materials scientists and physicists needing to verify atomistic potentials appropriate to the nanomechanical understanding of increasingly complex solids. The five following segments from nine University, National and Industrial Laboratories both review and forecast where some of the important approaches will allow a confirming of how in situ mechanics and nanometric visualization might unravel complex phenomena. These address two-dimensional structures, temporal models for the nanoscale, atomistic and multiscale friction fundamentals, nanoparticle surfaces and interfaces and nanomechanical fracture measurements, all coupled to in situ observational techniques. Rapid future advances in the applicability of such materials science solutions appear guaranteed.

Linking Nanoscales and Dislocation Shielding to the Ductile–Brittle Transition of Silicon

The ductile–brittle transition of nano/microscale silicon is explored at low-temperature, high stress conditions. A pathway to eventual mechanism maps describing this ductile–brittle transition behavior using sample size, strain rate, and temperature is outlined. First, a discussion of variables controlling the BDT in silicon is given and discussed in the context of development of eventual modeling that could simultaneously incorporate all their effects. For description of energy dissipation by dislocation nucleation from a crack tip, three critical input parameters are identified: the effective stress, activation volume, and activation energy for dislocation motion. These are discussed individually relating to the controlling variables for the BDT. Lastly, possibilities for measuring these parameters experimentally are also described.

Extreme Ductility at the Nanoscale in Fe-based Alloys

A novel method for preparing and testing bending specimens in-situ the TEM has been developed. This method provides high visibility of the crack front and its associated plastic zone. This is significant because energy release rates can now be calculated at many points throughout the test based on crack tip opening displacement (CTOD), crack opening angle (COA), and crack advance. Further refinement of testing methods to do dark field imaging of dislocations would allow estimation of dislocation content vs. time and may provide insights into dislocation behavior.

Optimization of a dissimilar platinum to niobium microresistance weld: a structure–processing–property study

Dissimilar metal resistance spot welds, critical to the manufacture of medical devices, typically form brittle intermetallic compounds that are prone to failure. Here, a case study of biocompatible metals platinum and niobium using advanced analytical techniques is presented. It describes the variation of properties and microstructure using microresistance spot welding under four conditions, including a legacy process and processing conditions optimized by design of experiments. Adjustments to the electrode force, welding current, surface roughness, and pulse duration and exchanging the platinum anode contact for a cathode result in a joint with less porosity and greater uniformity in the thickness, chemistry, and microstructure of the fusion zone. The optimized microstructure contains fewer defects, with increased plasticity under deformation and a more uniform microstructure reducing the propensity for failure and variability between welds. Extensive analysis with optical, scanning electron, transmission electron microscopy coupled with nano- and micromechanical testing (such as micropillar compression) was used to characterize the weld zone.

Correlated EBSD and High Speed Nanoindentation Mapping

Nanoindentation techniques have long had an important role in evaluating the mechanical properties of microstructural features. In recent years, high speed nanoindentation mapping techniques have been under development and have recently achieved speeds up to 6 indents/second. This gives speed, resolution and scan size comparable to that of electron backscatter diffraction (EBSD), allowing for oneto-one correlation techniques with corresponding large data sets for statistical analysis. This correlation can produce high resolution structure-property (EBSD: structure, nanoindentation:property) relationships which can be mapped over length scales of several microns to several hundreds of microns. This has numerous potential applications, from evaluation of microstructural evolution during processing [1], quality control testing of weld zones [2], evaluation of sub-surface damage gradients [3] (wear, corrosion, irradiation), composite material interfaces [4] and more.

Temperature Dependence of Fracture Initiation in Silicon from In-situ SEM

Silicon has a rich history of technological importance, as well as serving as an ideal model material for studying mechanical behavior in semi-metallic materials. Of particular interest is the rapid transition in deformation mechanisms as a function of scale and temperature, where such concepts as dislocation character1, nucleation/propagation control2 and possible core structure3 changes may contribute. The result is that under certain loading conditions, sizes, temperatures and doping, silicon can display a wide variety of response from highly brittle cleavage to over 50% plastic strain4.

X-Ray Mapping of an Impact-Resistant Crustacean-Derived Biocomposite

1. Materials Science & Engineering, University of California, Riverside, Riverside, California, USA 2. Lyles School of Civil Engineering, Purdue University, West Lafayette, Indiana, USA 3. Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, USA 4. Hysitron Inc., Minneapolis, Minnesota, USA 5. School of Computing, Engineering and Mathematics, Western Sydney University, Penrith, Australia 6. Advanced Materials Characterization Facility, Western Sydney University, Penrith, Australia 7. Chemical and Environmental Engineering, University of California, Riverside, California, USA

Strength and Plasticity of H- and Oxide- Terminated Cubic Si Nanocrystals

Greater understanding of the structure-property relationships contributing to exceptional strength and plasticity in nanoscale materials is vital for the continued miniaturization of electron and MEMS devices [1]. Recent innovations have enabled in-situ investigations of mechanical properties in the TEM at a size scale where a material’s defect density can approach zero, allowing intrinsic material properties to be studied. Silicon, being a ubiquitous component of micro-devices, has been studied extensively via ex-situ [2,3] and in-situ [4,5] mechanical testing. However, direct observation of the dynamic processes under deformation has not been scaled beyond 50 to 100 nm. Here, we investigate the elastic-plastic response of 25 to 40 nm cubic Si nanocrystals (NCs) under [001] compression.