Weakest-link failure prediction for ceramics IV : application of mixed-mode fracture criteria for multiaxial loading

Strength data obtained from uniaxial and biaxial bend tests on 2 alumina ceramics were analyzed by a weakest-link model with different mixed-mode fracture criteria and crack shapes. Taking the data from 3- and 4-point bend tests as a ref., strength predictions for the ball-on-ring and ring-on-ring biaxial tests were made, showing large differences in the predictions for the different fracture criteria. The best fitting models for the 2 aluminas cannot be interchanged, thus showing a marked difference in their shear stress sensitivity. Anal. shows that, in general, a combination of tests with a varying degree of stress multiaxiality is required to det. the best applicable mixed-mode fracture criterion. [on SciFinder (R)

Fractography of borosilicate glass tested in three- and four-point bending

Most studies dealing with fractog. anal. are based on the occurrence of features, such as mirror, mist and hackle zones, formed sym. around a defect. Calcns. are carried out. Polished borosilicate specimens, and ground, annealed and chamfered borosilicate glass specimens are used for fractog. Six defect types could be distinguished, of which four types deviate from symmetry. The strength data, obtained from three and four-point bending, are described by a Weibull probability d. function. Discontinuities present in the Weibull graphs were expected to be linked to the six defect populations. However, although glass is assumed to be an ideal and isotropic material, no such relationship has been found. [on SciFinder (R)

Fracture of alumino-borosilicate glass-aluminum joints

A no. of aluminoborosilicate glass-aluminum bonds were prepd. by thermocompression, resulting in fracture toughness values of 0.5-0.9 MPa.m1/2. Relatively high temp. and pressure have a pos. influence, while prolonged pressure time is unfavorable, due to the formation of a very thin reaction layer. Fracture energies, cor. for the amt. of nonbonded area, vary from 2-6 J/m2. An est. of the contributions to the measured fracture energy gives a difference of a factor 3-4 with the exptl. value. There is room, however, for considerable improvement in processing and modeling. [on SciFinder (R)