EVALUATION OF K_II USING A COPPER FOIL WHEN ASSESSING FRICTIONAL FORCES ON CRACK SURFACES

Abstract

The relation is examined between the strain sensitivity and the grain size of a grown copper foil gauge which has a preferred orientation to slip. We adopted this gauge to evaluate the mode II stress intensity factor K,, of a through-thickness crack in a plate subjected to cyclic torsion. The K , values obtained are lower than the calculated values because of the frictional force on the crack surfaces. By using the experimentally determined K, value for torsion and the calculated K , values for plane bending, the threshold condition for crack propagation under the combination of bending and torsion is predicted on the basis of the strain energy density criterion. NOMENCLATURE a =half crack length r = length from crack tip N = number of cycles z , , = maximum shearing stress zo = nominal shearing stress zp = critical shearing stress zPth = threshold stress of T~ T~,, = threshold stress for crack propagation YeX, Yw = correction factor for the stress intensity factor (experimental and calculated values)

Pressure and friction dependent mechanical strength – cracks and plastic flow

“…A similar explanation for the brittle to ductile transition in rock with increasing pressure is given by Paterson, 1970. The results in the low pressure range can be understood on the basis of a crack friction model developed by Dienes, 1983 andDienes, 2005. Other authors have also considered the effect of friction on the mechanical properties of materials (McClintock and Walsh, 1962;Mavko, 1979;Comninou and Dundurs, 1980;TianHu and Weishen, 1993;Egami and Kitaoka, 1996;Kovtunenko, 1998. Dienes, 1983and Zuo and Dienes, 2005 have applied the concept of coulomb friction forces between closed shear crack surfaces as resisting crack growth (Ward and Hadley, 1993).…”

Elasto-plastic bond mechanics of embedded fiber optic sensors in concrete under uniaxial tension with strain localization

“…Fiber optic sensors have been employed for sensing and measurement of engineering parameters in a wide spectrum of disciplines [1][2][3][4][5][6]. These sensors offer an advantage over conventional foil strain gages in sensing large-strain regimes with crack development [7,8]. Sensing and measurement of internal strains in concrete structures is an area where optical fibers provide superior measurement capabilities [9,10].…”