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Notes: Abstract Two archeological ceramic sherds in a single quartz aliquot form have been dated success-fully for the first time, by the newly developed method of optical stimulated luminescence (OSL) with green light-emitting diodes (LED). Comparison with the conventional thermoluminescence (TL) method provided ages of the same order of magnitude. The ceramics come from two recently excavated sites at “Hellenikon” and “Ligourio” in Argolid, Peloponnese, Greece. One sherd dates from the end of 4th millenium B.C., while the other is classified around 7th c. B.C.. The new method of nuclear dating is described in the paper and appropriately evaluated.

Notes: Abstract While it has been established that the elastic moduli and compliances of anisotropic and isotropic materials should be positive for thermodynamic reasons, no condition related to the values of Poisson's ratio has yet been established. However, it is generally accepted that for isotropic materials Poisson's ratio should vary between — 1.0 and 0.5, whereas for orthotropic materials various conditions have been introduced relating the different components of the anisotropic Poisson's ratio with the remaining elastic constants of the material. In this paper, limits for Poisson's ratio of body-centred cubic (bcc) polycrystalline materials are determined, based on the modes of deformation of a typical unit cell of the material subjected to a uniform external loading arbitrarily oriented relative to the principal axes of the crystal. It is shown that the values of Poisson's ratio thus established correlate satisfactorily with experimental values of this constant. The procedure can be readily applied to other structural units of polycrystalline bodies.

Notes: Summary Woven fabric undirectional laminae in the form of plain weave present an important advantage over typical fiber reinforced laminae, which consists that, at the strong weave plane, their failure locus approaches very close to a circle, thus suggesting that the failure mode on this plane is invariant and independent of the orientation of the fiber direction [1]. While this property appears when the loading axis coincides with the principal stress directions in the isotropic plane, it is of interest to study the failure locus in this isotropic plane of weave for off-axis modes of loading. It is the purpose of this paper to study the general case of failure mode in the isotropic strong-plane of a woven fabric composite when the loading direction of the lamina subtends an arbitrary angle with the principal material directions. Interesting results were derived indicating that for an angle of off-axis loading of the order of ϕ=±15° this quasi-isotropy is maintained. However, for larger angles of off-axis loadings varying between ϕ=±15° and ϕ=±(90−15)° the discepancies from isotropy are mild with the highest at ϕ=±45°. The study was based on the principles holding for the elliptic paraboloid failure surface [2]. A comparison with the results derived from the same tensor polynomial criterion with the assumption of validity of the Tsai-Hahn relationship indicated significant discrepancies between the two criteria. However, the type of anisotropy valid for such woven-fabric materials, whose eigenangle ω approaches values close to the respective isotropic value, suggests the validity of the simple relationshipH 33=2H 11 for the tensor coefficients, which results to the particular value forH 12=0. Thus, for such materials the (EPFS)-criterion and (FTP)-criterion with the assumption thatH 12=0 give similar results. Finally, it is derived that the failure loci for woven-fabric composites in the (σ1, σ2) isotropic plane present, in general, a weak resistance to failure in the compression-compression quadrant and a strong one in the tension-tension quadrant, where, also, the discrepancies between the results of the (EPFS)- and the Tsai-Hahn criteria are stronger. This suggests a convenient way to test the validity of these criteria by simple biaxial tests, which are easy to perform and may give a decisive answer about the superiority of any of the as yet suggested different versions of failure tensor criteria.