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Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30–50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus–low density and high modulus–high damping material structures. A nanoscale tube-in-tube sandwich structure is generated by a two-step templating-pyrolysis process, which strengthens the log-pile carbon architecture and slows down the decrease of stiffness with decreasing density.

We show for the first time that amorphous soda-lime glass undergoes polymorphic transformation to its densest crystalline stishovite phase at only ~5 GPa of pressure and room temperature, by uniaxially compressing the soda-lime glass nanopillars of 500 nm diameter and observing the post-deformed pillars under transmission electron microscopy. This contrasts with the recent shock-compression experiments of amorphous fused silica glass plates which report a pressure threshold of 34 GPa for stishovite formation. Our findings support recent dislocation dynamics simulations on W pillars which show that small domain size acts as a proxy for high temperature, thereby reducing the pressure threshold.

Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30-50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus-low density and high modulus-high damping material structures.

The mechanical behavior of nano-scale metallic glasses was investigated by in situ compression tests in a scanning electron microscope. Platinum-based metallic glass nano-pillars were fabricated by thermoplastic forming. The nano-pillars and corresponding bulk substrate were tested in compression over the range of room temperature to glass transition. Stress–strain curves of the nano-pillars were obtained along with in situ observation of their deformation behavior. The bulk substrate as well as nano-pillars showed an increase in elastic modulus with temperature which is explained by diffusive rearrangement of atomic-scale viscoelastic units.

Mechanically guided 3D microassembly with controlled compressive buckling represents a promising emerging route to 3D mesostructures in a broad range of advanced materials, including single-crystalline silicon (Si), of direct relevance to microelectronic devices. During practical applications, the assembled 3D mesostructures and microdevices usually undergo external mechanical loading such as out-of-plane compression, which can induce damage in or failure of the structures/devices. Here, the mechanical responses of a few mechanically assembled 3D kirigami mesostructures under flat-punch compression are studied through combined experiment and finite element analyses. These 3D kirigami mesostructures consisting of a bilayer of Si and SU-8 epoxy are formed through integration of patterned 2D precursors with a prestretched elastomeric substrate at predefined bonding sites to allow controlled buckling that transforms them into desired 3D configurations. In situ scanning electron microscopy measurement enables detailed studies of the mechanical behavior of these structures. Analysis of the load-displacement curves allows the measurement of the effective stiffness and elastic recovery of various 3D structures. The compression experiments indicate distinct regimes in the compressive force/displacement curves and reveals different geometry-dependent deformation for the structures. Complementary computational modeling supports the experimental findings and further explains the geometry-dependent deformation.

A unique nanoheterostructure, a boron-filled hybrid carbon nanotube (BHCNT), has been synthesized using a one-step chemical vapor deposition process. The BHCNTs can be considered to be a novel form of boron carbide consisting of boron doped, distorted multiwalled carbon nanotubes (MWCNTs) encapsulating boron nanowires. These MWCNTs were found to be insulating in spite of their graphitic layered outer structures. While conventional MWCNTs have great axial strength, they have weak radial compressive strength and do not bond well to one another or to other materials. In contrast, BHCNTs are shown to be up to 31% stiffer and 233% stronger than conventional MWCNTs in radial compression and have excellent mechanical properties at elevated temperatures. The corrugated surface of BHCNTs enables them to bond easily to themselves and other materials, in contrast to carbon nanotubes (CNTs). BHCNTs can, therefore, be used to make nanocomposites, nanopaper sheets and bundles that are stronger than those made with CNTs.

This paper demonstrates the direct observation of crack initiation, crack propagation, and interfacial delamination events during in-situ microbeam bending tests of FIB milled BEOL structures. The elastic modulus and the critical force of fracture of the BEOL beam samples were compared for beams of different length and width. ispartof: Applied Physics Letters vol:105 issue:21 status: published