Some criteria for accepting defects in composites as applied to laminate cut with a water-jet
Andrzej Bełzowski*, Jan Stasieńko*, Bogumił Ziółkowski**, Anna Kamińska** *Politechnika Wrocławska, Wydział Mechaniczny, Wydziałowy Zakład Wytrzymałości Materiałów, ul. Smoluchowskiego 25, 50-370 Wrocław **Politechnika Wrocławska, Wydział Mechaniczny, Instytut Materiałoznawstwa i Mechaniki Technicznej, ul. Smoluchowskiego 25, 50-370 Wrocław
Annals 4 No. 12, 2004 pages 389-395
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abstract Structural components made of polymer composites may have built-in defects that have arisen during manufacturing operations. A list of such defects is presented along with two methodologies used in evaluating quality of a product. The first of them involves measurements of porosity (Figs. 1, 2) while the second one enables an inspector to assess type, size and severity of defects with a naked eye. An example is presented where porosity measurements failed to identify actual condition of a material. It was visual inspection that proved to be reliable in this case. Some manufacturing methods for composite components involve machining operations. Nowadays they are usually performed using hydrodynamic machining. The method was evaluated by the present author in preparing strength test specimens cut out from glass-epoxy plates. Figures 3 and 4 show typical images of resulting surfaces. The irregularities can be identified as single broken or pulled out fibres and debonding spots. The surface roughness height is comparable to that left by conventional cutting. Typical defects produced by a water jet can be seen in Figure 5 as the side ones and in Figures 6-8 as those arising in the bulk material. The defects of the two types served as a basis for putting forward a method of visual inspection for composite quality assessment. The method is flexible enough to take account of particular service conditions and durability/safety requirements set for a component to be fabricated. Key words: polymer-matrix composites, cutting of polymer composites, defects in composites