Henrik Jackman

Bio: Henrik Jackman is an academic researcher from Karlstad University. The author has contributed to research in topics: Carbon nanotube & Bending stiffness. The author has an hindex of 5, co-authored 8 publications receiving 52 citations.

Measurements of the critical strain for rippling in carbon nanotubes

Abstract: We report measurements of the bending stiffness in free standing carbon nanotubes, using atomic force microscopy inside a scanning electron microscope. Two regimes with different bending stiffness were observed, indicative of a rippling deformation at high curvatures. The observed critical strains for rippling were in the order of a few percent and comparable to previous modeling predictions. We have also found indications that the presence of defects can give a higher critical strain value and a concomitant reduction in Young’s modulus.

Mechanical behavior of carbon nanotubes in the rippled and buckled phase

Abstract: We have studied the mechanical behavior of multi-walled carbon nanotubes for bending strains beyond the onset for rippling and buckling. We found a characteristic drop in the bending stiffness at the rippling and buckling onset and the relative retained stiffness was dependent on the nanotube dimensions and crystallinity. Thin tubes are more prone to buckle, where some lose all of their bending stiffness, while thicker tubes are more prone to ripple and on average retain about 20% of their bending stiffness. In defect rich tubes, the bending stiffness is very low prior to rippling, but these tubes retain up to 70% of their initial bending stiffness.

Large variations in the onset of rippling in concentric nanotubes

Abstract: We present a detailed experimental study of the onset of rippling in highly crystalline carbon nanotubes. Modeling has shown that there should be a material constant, called the critical length, describing the dependence of the critical strain on the nanotube outer radius. Surprisingly, we have found very large variations, by a factor of three, in the critical length. We attribute this to a supporting effect from the inner walls in multiwalled concentric nanotubes. We provide an analytical expression for the maximum deflection prior to rippling, which is an important design consideration in nanoelectromechanical systems utilizing nanotubes.

Direct measurement of bending stiffness and estimation of Young's modulus of vertically aligned carbon nanofibers

Abstract: The bending stiffness of individual, as-grown, vertically aligned carbon nanofibers was measured using a custom-built atomic force microscope placed inside a scanning electron microscope. The internal structure of the nanofiber was best modeled as dual-phase, composed of an inner graphitic core covered with a tapered amorphous carbon shell. It was found that the fibers have a relatively low bending stiffness, with Young's modulus values of about 10 GPa for the inner core and 65 GPa for the outer shell. The low Young's modulus of the inner core is attributed to a non-zero angle between the graphitic sheets and the nanofiber axis. The weak shear modulus between graphitic sheets thereby dominates the mechanical behaviour of the fibers.

Towards a review of the EC Recommendation for a definition of the term "nanomaterial"Part 2: Assessment of collected information concerning the experience with the defintion

Abstract: This report provides the JRC assessment of feedback on the experiences of stakeholders with the EC nanomaterial definition, published in 2011 (EC Recommendation 2011/696/EU). The report is a follow-up report of the previous JRC report (EUR 26567 EN, 2014), which compiled feedback collected by JRC in 2013 and early 2014, partly through a dedicated survey. Based on the current report, JRC will prepare a set of recommendations for the revision of the EC nanomaterial definition, as part of the review process foreseen in the 2011 EC Recommendation. JRC Scientific and Policy Report Towards a review of the EC Recommendation for a definition of the term "nanomaterial" Part 2: Assessment of collected information concerning the experience with the definition

Thin boron nitride nanotubes with exceptionally high strength and toughness

Abstract: Bending manipulation and direct force measurements of ultrathin boron nitride nanotubes (BNNTs) were performed inside a transmission electron microscope. Our results demonstrate an obvious transition in mechanics of BNNTs when the external diameters of nanotubes are in the range of 10 nm or less. During in situ transmission electron microscopy bending tests, characteristic "hollow" ripple-like structures formed in the bent ultrathin BNNTs with diameters of sub-10 nm. This peculiar buckling/bending mode makes the ultrathin BNNTs hold very high post-buckling loads which significantly exceed their initial buckling forces. Exceptional compressive/bending strength as high as approximately 1210 MPa was observed. Moreover, the analysis of reversible bending force curves of such ultrathin nanotubes indicates that they may store/adsorb strain energy at a density of ~400 x 10(6) J m(-3). Such nanotubes are thus very promising for strengthening and toughening of structural ceramics and may find potential applications as effective energy-absorbing materials like armor.