Platelet-shaped particles of similar size and shape were investigated as fillers for improving the thermal conductivity of polymer-ceramic composite materials. The conductivities of composites filled with hard, stiff ceramic particles exceeded 3.5 W⅐(m⅐K) ؊1 , or >20 times the conductivity of the polymer matrix, and were shown to be almost independent of the intrinsic filler conductivity range of 33-300 W⅐(m⅐K) ؊1 . In contrast, the thermal conductivity of composites filled with soft, platelet-shaped BN fillers reached over 13 W⅐(m⅐K) ؊1 . A mechanism is proposed whereby deformation of the soft filler particles provides improved particle-to-particle connectivity and allows greater packing density, resulting in the ability to achieve much higher conductivity than is possible for hard and stiff particles of similar initial morphology. Experimental results are discussed in light of various thermal conductivity prediction models in the literature.
The paper reviews the current state of art of the fracture of brittle ceramic materials. Typical loading situations (thermal shock, contact damage) are analysed and the resulting fracture modes are discussed. In focus of the paper are the brittle fracture and the resulting probabilistic aspects. The delayed failure of brittle materials (sub critical crack growth and cyclic fatigue) is also discussed.
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