Nanoindentation mapping of mechanical properties of cement paste and natural rocks

Vertically aligned carbon nanotube (CNT) ‘forest’ microstructures fabricated by chemical vapor deposition (CVD) using patterned catalyst films typically have a low CNT density per unit area. As a result, CNT forests have poor bulk properties and are too fragile for integration with microfabrication processing. We introduce a new self-directed capillary densification method where a liquid is controllably condensed onto and evaporated from the CNT forests. Compared to prior approaches, where the substrate with CNTs is immersed in a liquid, our condensation approach gives significantly more uniform structures and enables precise control of the CNT packing density. We present a set of design rules and parametric studies of CNT micropillar densification by self-directed capillary action, and show that self-directed capillary densification enhances Young’s modulus and electrical conductivity of CNT micropillars by more than three orders of magnitude. Owing to the outstanding properties of CNTs, this scalable process will be useful for the integration of CNTs as a functional material in microfabricated devices for mechanical, electrical, thermal and biomedical applications. (Some figures in this article are in colour only in the electronic version)

/pdf/fabrication-and-electrical-integration-of-robust-carbon-1gqkgo1mll.pdf

Fabrication and electrical integration of robust carbon nanotube micropillars by self-directed elastocapillary densification

Overcoming the brittleness of metal–organic frameworks (MOFs) is a challenge for industrial applications. To increase the mechanical strength, MOFs have been blended with polymers to form composites. However, this also brings challenges, such as integration and integrity of MOF in the composite, which can hamper the selectivity of gas separations. In this report, an “all MOF” material with mechanical flexibility has been prepared by covalent cross-linking of metal–organic polyhedra (MOPs). The ubiquitous Cu24 isophthalate MOP has been decorated with a long alkyl chain having terminal alkene functionalities so that MOPs can be cross-linked via olefin metathesis using Grubbs second generation catalyst. Different degrees of cross-linked MOP materials have been obtained by varying the amount of catalyst in the reaction. Rheology of these structures with varying number of cross-links was performed to assess the cross-link density and its homogeneity throughout the sample. The mechanical properties were further...

Mechanical Properties of a Metal-Organic Framework formed by Covalent Cross-Linking of Metal-Organic Polyhedra.

Vertically-aligned carbon nanotube (CNT) "forest" microstructures fabricated by chemical vapor deposition (CVD) using patterned catalyst films typically have a low CNT density per unit area. As a result, CNT forests have poor bulk properties and are too fragile for integration with microfabrication processing. We introduce a new self-directed capillary densification method where a liquid is controllably condensed onto and evaporated from CNT forests. Compared to prior approaches, where the substrate with CNTs is immersed in a liquid, our condensation approach gives significantly more uniform structures and enables precise control of the CNT packing density and pillar cross-sectional shape. We present a set of design rules and parametric studies of CNT micropillar densification by this method, and show that self-directed capillary densification enhances the Young's modulus and electrical conductivity of CNT micropillars by more than three orders of magnitude. Owing to the outstanding properties of CNTs, this scalable process will be useful for the integration of CNTs as functional material in microfabricated devices for mechanical, electrical, thermal, and biomedical applications.

/pdf/fabrication-and-electrical-integration-of-robust-carbon-1utglzsotl.pdf

Microstructure evolution and mechanical behavior of severe shot peened commercially pure titanium

Calculating the elastic modulus from nanoindentation and microindentation reload curves

A major factor in calibrating a depth-sensing indentation tester is to determine its load-frame compliance. In this work a simplified theoretical approach and a computerized iterative method were developed to calculate the load-frame compliance of our laboratory commercial instrumented indentation tester. In addition, this research discusses many of the problems associated with the calibration of this type of testing machine. Three materials were used for the load-unload tests: fused silica, 6066-O aluminum and electrolytic copper. A value of load-frame compliance of 0,23 nm/mN was obtained with fused silica. This value was considered acceptable because the calculated elastic modulus for fused silica was comparable to those found by other researchers using a similar strategy of unload curve analysis. This calculated load-frame compliance is in the range found in literature for other instrumented indentation testers. The load-frame compliance values obtained with the two metals were unacceptable because of errors probably associated with pile-up and strain hardening.

Determination of the compliance of an instrumented indentation testing machine

It is desirable to measure the hardness of individual grains and microconstituents to have control over the mechanical properties of materials. An ultra-micro or nanoindenter is required to make indents small enough to fit inside a single grain or phases that is smaller than 10 mm diameter. Because the indents are too small for an optical microscope an atomic force microscope was used to view the location and measure the contact area. Measuring the contact area of indents from an atomic force microscope image is unreliable because it is difficult to manually locate the indent edge. To solve this problem computerized image analysis software called NanoMc was used to measure the residual indent contact area. This software digitally reconstructed the residual indent back into the fully loaded indentation shape and then measures the contact area and depth. This method avoids the complicated tip rounding and load-frame compliance problems. As an example this method was used to measure the hardness of pearlite and ferrite microconstituents in SAE 1020 steel.

David J. Shuman

Papers

Calculating the elastic modulus from nanoindentation and microindentation reload curves

Determination of the compliance of an instrumented indentation testing machine

Using new atomic force microscope software to measure the hardness of grains and microconstituents