Damage processes in glass fiber reinforced plastic composites have been examined extensively by many analytical and experimental methods, including acoustic emission. While damage phenomena in mezo- and macro-scale are well described, the subtle mechanisms in micro-scale are still under discussion. The goal of this work was to apply the acoustic emission to examine damage initiation in fiber reinforced epoxy resin composites with different continuous glass-fiber architectures. Basic lay-ups were used: unidirectional, cross-ply and angle-ply, each with varying fiber volume content in epoxy matrix. Detection of fine micro-cracks was possible owing to merging the mechanical monotonic and step-load tests in 4-point bending with acoustic emission monitoring and detailed scanning electron microscopy observations. Clear images of macroscopically undamaged samples after interruption of step-loading cycles revealed the initiation of micro-cracks by debonding of fiber-matrix interfaces, in agreement with acoustic emission signal analyses, featuring use of historic index and rise time/amplitude ratio.

中文翻译：

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玻璃-环氧复合材料弯曲过程中声发射与断口的相关性

玻璃纤维增​​强塑料复合材料的损伤过程已经通过许多分析和实验方法进行了广泛的研究，包括声发射。虽然中尺度和宏观尺度的损伤现象得到了很好的描述，但微观尺度的微妙机制仍在讨论中。这项工作的目标是应用声发射来检查具有不同连续玻璃纤维结构的纤维增强环氧树脂复合材料的损伤起始。使用了基本的叠层：单向、交叉层和角层，每种在环氧树脂基体中都有不同的纤维体积含量。由于将 4 点弯曲中的机械单调和阶跃载荷测试与声发射监测和详细的扫描电子显微镜观察相结合，可以检测到细微裂纹。