PubMed · 14593386
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2003. Let there be light!. https://doi.org/10.1038/nmat1015
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The purpose of this study was to investigate the role of pores in the fracture of circular compacts and to predict compact properties and critical crack lengths. Four different particle size fractions of sucrose, ranging from 20 to 500 microm, were compressed into circular discs (i.e. flat tablets) and rectangular beam specimens of porosity between 30 and 14%. Modelling of the relationship between the tensile strength of the circular discs and the compact porosity indicated extensive fragmentation during compaction for particles in the size range of 250-500 microm, accompanied by a change in densification mechanism for very coarse particles (355-500 microm). When determining the critical stress intensity factor from rectangular single edge notched beam specimens by 3-point bending, an apparent influence of particle size on the values could be seen, whereby here the results indicated that the critical particle size for fragmentation to occur is about 20-40 microm. It was possible to predict the critical stress intensity factor of the compacts from the median pore size and the tensile strength of the circular disc specimens by interpolation of the critical crack length for propagation to occur. The results indicated that for sucrose compacts regardless of their porosity, the pores themselves acted as stress concentrators, not as sharp cracks. For sucrose compacts, crack propagation hence proceeds most likely along grain boundaries.
We present first principles molecular dynamics simulations of stretched siloxane oligomers in an environment representative of that present in single molecule atomic force microscopy experiments. We determine that the solvent used (hexamethyldisiloxane) does not influence the stretching of the siloxane in the high force regime or the rupture process, but trace amounts of water can induce rupture before the maximum siloxane extension has been attained. This would result in a significantly lower rupture force. The simulations show that the rupture of a covalent bond through a reaction with a molecule from the environment, which would not normally occur between the species when the polymer is not stressed, is possible, opening a route to mechanically induced chemical reactions. The attack of the normally hydrophobic siloxane by water when it is stretched has wider implications for the material failure under tensile stress, where trace amounts of water could induce tearing of the material.
A single aliquot protocol for the estimation of the natural dose in thermoluminescence dating (SATL) is presented that makes use of polymineral fine grains extracted from ceramic materials. The protocol is demonstrated using aliquots made from two Neolithic sherds and is compared with results from an additive dose polymineral technique. The results of both techniques are in close agreement and highlight the potential advantages of the new procedure, especially when sample availability is restricted, e.g. dating of small pottery fragments, or in cases of authenticity testing.