Influence of loading course on failure stress of glass fabric reinforced polycarbonate composite
Danuta Witemberg-Perzyk*, Anna Boczkowska**, Zbigniew Pakieła** *Warsaw University of Technology, Institute of Mechanics and Design, Narbutta 85, 02-524 Warsaw, Poland **Warsaw University of Technology, Faculty of Materials Science and Engineering, Wołoska 141, 02-507 Warsaw, Poland
Quarterly No. 1, 2005 pages 51-55
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abstract Tensile strength of woven glass reinforced composites with polycarbonate matrix was investigated. Several types of loading programs were examined: monotonic with different strain rates, monotonic with preceding loading up to different values of the stress and subsequent unloading, creep at several constant load levels preceded by fast monotonic loading. Additionally, the composite matrix structural changes at the composite failure were monitored through measurements of the degree of whiteness (fogging) occurring in the matrix material. The experimental results have pointed out the basic types of the course of loading or deformation in which the history effect on failure stress is significant for the examined material. It was found that unloading, i.e. stress relief, has no remarkable influence. Significantly lower failure stresses were obtained for the loading programs which included creep at constant load, compared to all other cases, which revealed similar failure stress values. In particular, the change of strain rate, within the limits of two orders of magnitude in simple monotonic loading tests, had practically no influence on failure stress. The degree of whiteness of the matrix in creep tests was significantly higher compared to both fast and low rate monotonic loading tests, however no regularity was observed for the tests which included unloading. It is concluded that the phenomena associated with matrix damage may significantly influence the strength of the investigated composite. A further research, aimed at explanation of the creep effect on the composite failure stress, is necessary. Key words: glass fabric-polycarbonate matrix composite, failure stress, loading program