Mechanizm pękania materiałów kompozytowych na osnowie stopu AlSi9Mg umacnianych włóknami

Omówiono mechanikę pękania materiałów kompozytowych umacnianych włóknami „Saffil" poddanych jednoosiowemu rozciąganiu. Materiały wytworzone na osnowie stopu AK9 zawierały od 10 do 54% obj. włókien. Przeprowadzone badania mikroskopowe pokazały sposób powstawania przełomu oraz pozwoliły określić teoretyczny stan naprężeń. Zwrócono szczególną uwagę na role osnowy i defektów w niej występujących. Przedstawiono przykład propagacji pęknięcia oraz zaproponowano nowy model dekohezji materiałów kompozytowych umacnianych włóknami.

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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 intcrphases 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 unrcinforced 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 arc consistent with the simplified fibre agreement, driving force for crack extension in the composite can origin also from other places.