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Effects of thermal cycles on the mechanical response of pultruded GFRP profiles used in civil engineering applications

机译：热循环对拉挤玻璃纤维增​​强型材在土木工程应用中的机械响应的影响

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This paper presents a literature review and results of an experimental study about the effects of thermal cycles on the physical and mechanical properties of pultruded glass fibre reinforced polymer (GFRP) profiles used in civil engineering structural applications. The GFRP profiles used in this study present similar fibre architecture, differing only in their matrix nature: unsaturated polyester and vinylester. Small-scale coupons obtained from both types of GFRP profiles were exposed to a Mediterranean range of thermal variations (-5 ℃ to 40 ℃) for up to 190 cycles in a dry condition. The effects of such exposure on the physical and mechanical response of the GFRP materials were assessed and compared using the following experimental techniques: (a) dynamic mechanical analyses (DMA) to assess the viscoelastic behaviour; (b) tensile, flexural and interlaminar shear tests, to evaluate the mechanical properties; and (c) scanning electron microscopy (SEM), to monitor the potential changes in the microstructure due to the degradation (if any) caused by the thermal cycles, as well as the possible changes into the main mechanisms of fracture. After exposure to thermal cycles, the viscoelastic behaviour of the GFRP profiles presented only slight changes, indicating no significant degradation, neither in the matrix structure nor at the fibre-matrix interphase. In terms of mechanical properties, both types of GFRP materials suffered slight changes regarding tensile and interlaminar shear properties. Flexural properties were more affected, particularly the flexural modulus, especially in the first cycles, as degradation tended to stabilize for increasing cycles. The GFRP profile made of vinylester resin presented better overall performance than the one made of polyester, especially regarding the tensile properties. SEM observations of the surfaces of fracture of mechanically tested pultruded specimens showed two main mechanisms of crack propagation: cohesive rupture (matrix cracking), where the crack propagates inside the matrix, and adhesive rupture (fibre-matrix debonding), where the crack propagates at the interface fibre-matrix. Degradation of the polyester matrix caused by the thermal cycles is evidenced by extensive matrix microcracking and increased fibre-matrix debonding. The vinylester matrix resists better to such degradation as fibre-matrix debonding occurs in less extent, and matrix microcracking is scarcely present.
机译：本文介绍了有关热循环对在土木工程结构应用中使用的拉挤玻璃纤维增​​强聚合物（GFRP）型材的物理和机械性能的影响的文献综述和实验研究的结果。这项研究中使用的GFRP轮廓具有相似的纤维结构，仅在基质性质上有所不同：不饱和聚酯和乙烯基酯。从两种类型的GFRP型材获得的小型试样均在干燥条件下暴露于地中海范围的热变化范围（-5℃至40℃），最多可进行190个循环。使用以下实验技术评估并比较了此类暴露对GFRP材料的物理和机械响应的影响：（a）动态力学分析（DMA）以评估粘弹性行为； （b）拉伸，弯曲和层间剪切试验，以评估机械性能； （c）扫描电子显微镜（SEM），以监测由于热循环引起的退化（如果有的话）引起的微观结构的潜在变化，以及断裂的主要机理可能发生的变化。暴露于热循环后，GFRP轮廓的粘弹性行为仅表现出轻微变化，表明在基质结构和纤维-基体间相中都没有明显的降解。在机械性能方面，两种类型的GFRP材料在拉伸和层间剪切性能方面均发生了细微变化。弯曲特性受到的影响更大，尤其是在最初的循环中，尤其是在最初的循环中，因为降解趋于稳定。由乙烯基酯树脂制成的GFRP型材比由聚酯制成的GFRP型材具有更好的整体性能，尤其是在拉伸性能方面。 SEM对机械测试的拉挤试样的断裂表面的SEM观察显示出裂纹扩展的两个主要机理：内聚破裂（基体开裂），其中裂纹在基体内传播；粘合剂断裂（纤维基体脱粘），裂纹在基体中传播。接口光纤矩阵。由热循环引起的聚酯基体的降解可以通过广泛的基体微裂纹和增加的纤维-基体剥离力来证明。乙烯基酯基体可以更好地抵抗这种降解，因为纤维基体的脱粘程度较小，并且几乎不存在基体微裂纹。

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