Mechanisms of cracking in a fibre reinforced metal matrix composite
Krzysztof Naplocha, Zdzisław Samsonowicz Politechnika Wrocławska, Instytut Technologii Maszyn i Automatyzacji, ul. Łukasiewicza 3/5, 50-371 Wrocław
Annals 2 No. 4, 2002 pages 238-241
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abstract The crack growth of no directional, fibre reinforced metal matrix composite have been discussing and the results compared with model prediction. Composite materials were produced by squeeze casting method. Heated porous preforms were placed in the heated die, then pouring of overheated molten AlSi9Mg alloy into the die and pressing it in order to infiltrate the porous preforms with the molten alloy. Microscopic investigations revealed homogeneous distribution of ceramic fibres in the matrix. Composite fractures after tensile tests revealed good bonding at the interphases and no pull-out of fibres (Fig. 2). The present observations have been used to assess the failure of composite. During matrix dissolution, the fracture fibres were not removed (Fig. 3). Many developments in the field of composite crack have revealed extend of fibre failure due to leak bonding between fibre and matrix. In this study microscopic observations showed events of longitudinal splits of the fibres, which might prove a considerable strength of the link. Sometimes cracks growth in the unreinforced matrix, crossing fibres and further extend (Fig. 4). It might prove that the first step of crack take place in matrix by defect derived from manufacturing process. Load is bored by the layer with the fibres and leaded to matrix. Stress require for initiate matrix cracking in terms of component geometry and various constituent properties delivers energy needed to its extend. Between fibres may occur particular stress state (Fig. 5) that the cracks propagate along the matrix. These observations are consistent with the simplified fibre agreement, driving force for crack extension in the composite can origin also from other places.