Fracture toughness of brittle materials determined with chevron notch specimens

The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail

Machinability of ZTA-TiC Ceramics by Electrical Discharge Drilling

AbstractElectric discharge machining of ceramics becomes principally feasible if the ceramic material has a sufficiently high electric conductivity. This can be achieved by adding transition metal carbides, borides or nitrides such as titanium carbide. In case of electric discharge drilling the small electrode dimensions lead to higher current densities compared to die sinking. In order to avoid bursting of the ceramics by thermal shock machining parameters have to be well adjusted and the material should have a high thermal conductivity. A parameter study was carried out to observe the removal behavior depending on machine parameters such as discharge energy, pulse form and flushing conditions

Integrating Service-Learning in the Public Speaking Course

This best-practices article endorses incorporating service-learning into the foundational public speaking course. The article explains connections between service-learning and the rhetorical tradition, highlights pedagogical approaches that would benefit from a service-learning component, and discusses the benefits of service-learning for community partners and students. The remainder of the article focuses on how to implement servicelearning in a public speaking course, including reflection and assessment recommendations