The most conventional manufacturing route for ceramic foams with open cells consists of coating reticulated polyurethane foams. The resulting material has well defined cell size, but suffers from low mechanical strength owing to the presence of hollow struts. As a result, the performance and utilisation of ceramic foams manufactured by this method are limited in certain applications. One solution to overcoming this inherent disadvantage is to use a stronger ceramic coating material and to ameliorate the wetting of the polyurethane template. Such a material is reaction bonded Al 2 O 3 (RBAO), which has high mechanical strength as a result of its fine grain structure, with less or even without glassy phases at the grain boundaries. The present work demonstrates the feasibility of producing strong ceramic foams by using a reaction bonded modified replica technique starting from polyurethane templates varying in both composition and cell size distribution.
This paper treats the ductile failure initiation in circumferentially-notched tension specimens and explores the local damage model that is able to represent the continuous degradation of the deforming material. With the aid of finite element calculations, the notched specimens have been simulated numerically and the whole strain-stress history for each geometry derived. This allows determination of the evolution of strain-stress fields until fracture occurs. Two damage models were evaluated: the Rice and Tracey cavity growth model and a model which combines the latter with the plastic strain work, to derive an intrinsic parameter called 'damage work'. These models could predict the location where the crack will initiate as well as the crack initiation step which is reached for a relatively constant value of the critical damage.
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