A deterministic lifetime assessment of alumina- porcelain insulators based on the mechanics of brittle materials has been built up within the research project "lifetime analysis of ceramic insulators" (LeKI). This uses a procedure based on fracture mechanics. Herein the stress is calculated, under which a given crack will propagate. This is exactly the failure mechanism of brittle materials, so fracture mechanics is in the case of brittle materials generally accepted as more accurate than the still common force balance. In addition fracture mechanics allows predicting sub-critical crack growth, which describes the gradual growth of cracks, until they reach critical condition and cause "sudden" failure. Two variants exist: static fatigue (stress corrosion cracking) and dynamic fatigue (vibrations). In this presentation static fatigue has been considered.

The present study aims to contribute a better understanding on the aging mechanisms of alumina porcelain long-rod insulators and provides the fundamentals for a life-time-model. Two different approaches are taken: On one hand long-rod insulators are investigated in a tensile test, after their use in high voltage grids, concerning a potential reduction in strength over their lifetime. On the other hand mechanical properties of glazed and unglazed C130 alumina porcelain are determined in a four-point-bending test.

Cracks terminating at free surfaces are affected by local stresses in the surface region. Under residual compression the crack front must retard compared with the crack contour in the absence of stresses. This effect can be used for an identification of residual stresses at glass surfaces. For an illustration of the procedure, Vickers indentation tests in soda-lime glass are considered. Specimens treated by ion exchange and chemically toughening showed reduced terminating angles compared with untreated glass.

Silicon carbide reinforced aluminum alloy matrix composites offer excellent thermo‐mechanical properties and are thus attractive for applications limited by thermal stresses. Open porous silicon carbide preforms are fabricated in this work using polymer wax as pore formers. Two different waxes with different particle size were used to fabricate preforms with different pore structures. Wax content was varied to introduce open porosities up to 64 vol%. Structural characterization was carried out using scanning electron microscopy and micro computed tomography, whereas ultrasound phase spectroscopy was used to determine three longitudinal and three shear elastic constants. The amount of porosity increases with the amount of total wax used. Uniaxial pressing prior to isostatic pressing flattens the pores and as a result the preforms behave transverse isotropically with respect to the press direction. For the same total wax content, while the mixture ratio of two waxes has a minor influence on total porosity, the mixture ratio strongly influences the elastic constants. Optimum elastic constants along all directions are obtained with a mixture of two wax types with a higher content of the larger wax particles.