Macroscopically-Zoned Grandite from the Garnetite Skarn of Meka Presedla(Kopaonik Mountain,Serbia)

The macroscopically-zoned grandite from the garnetite skarn of Meka Presedla （Kopaonik Mountain, Serbia） was studied with optical microscopy, electron microprobe analysis （EMPA）, Fourier transform infra-red （FT-IR）, and Raman methods. The EMPA results indicate that the main core-rim compositional variations （Ca2.93-2.97Mn0.05-0.06Mg0.00-0.01AI1.14-L26 Fe0.72-0.83 Ti0.00-0.02Si2.97-3.02012） slightly differ along the zones, showing evidence for a quasi-cyclic alternation of the oscillatory zoning nature. Among this, considerable variation is observed only by the AI-Fe3＋ substitutions in the octahedral site. The EMPA also indicate that the grandite zones compositionally vary, mostly within ＋1 and ±2 mol% of the homogeneity level range, that is, Grs64±1Adra36±1SpS2 （A）, Grs62±1Adra38±1Sps2 （B）, Grs59±2Adr40±2Sps2 （C）, Grs58±2Adr41±2Sps2 （D）, and Grss±1Adr41±1Sps2 （E）. Therefore, the investigated garnet can be considered as relatively highly homogeneous. The majority of compositions lie within the narrow miscibility region of 0.58±2〈XGrs〈0.64±1, without gaps, and with only three outliers near the zone boundaries of approximately 0.38〈XGrs〈0.52. FT-IR and Raman bands are almost constant within the zones and adequate to the chemical compositions. All of the zones should be considered as anhydrous. From the results, formation temperatures between -600 and 720℃ and pressures 0f-2-3 kbars, are derived. Among five possible causes for the slightly optical anisotropy of grandite, three were reconsidered, and consequently rejected.

MICROMECHANICS OF ROUGH SURFACE ADHESION:A HOMOGENIZED PROJECTION METHOD

A quasistatic homogenized projection is made to characterize the effective cohesive zone behavior for rough-surface adhesion. In the context of the homogenized projection, the traction versus separation relation for the homogenized cohesive zone （HCZ） of a rough interface can be highly oscillatory due to instabilities during microscopic adhesion and decohesion processes. The instabilities are found to occur not only individually but also collectively among the adhesive micro-asperity contacts, leading to extensive energy dissipation. Based on the behaviors of the HCZ relations, a framework for describing instability-induced energy dissipation in rough-surface adhesion is proposed to elucidate the effect of roughness on apparent interface adhesion. Two non- dimensional parameters, α related to roughness morphology and n related to flaw distribution, are identified to be most crucial for controlling the energy dissipation. For an interface with a shallow roughness and a strong intrinsic adhesive strength, the interface adhesion can be stronger if we make it rougher （reducing α） or lower its flaw density （increasing n）. The HCZ projection method can be potentially extended and employed to bridge the apparent adhesion from intrinsic adhesion properties for engineering surfaces with multi-scale shallow roughness.