Long-term mechanical properties of carbon fiber reinforced vinyl resin composites in hygrothermal environment
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摘要: 碳纤维增强聚合物基复合材料(CFRP)因其耐腐蚀、轻质高强等特点被广泛应用于海洋环境,进而长期遭受湿热环境的考验。为了解湿热环境和极端温度对碳纤维增强乙烯基树脂复合材料的影响,测试了湿热老化前后和不同温度下CFRP的压缩性能、面内剪切性能和层间剪切强度变化。FTIR和SEM结果表明:纯树脂试样在湿热环境中发生了水解,使试样表面的微裂纹和孔隙不断扩展并向试样内部渗透;碳纤维的埋入抑制了水的扩散和水解,因而CFRP的吸湿曲线与Fickian模型高度吻合;纯树脂由于水解反应影响了吸湿通道使吸湿曲线偏离Fickian模型。力学性能表明:湿热老化90天后压缩强度和层间剪切强度分别降低7.6%、12.3%;试样在高温(70℃)下的压缩强度、面内剪切强度、层间剪切强度分别急剧降低36.2%、26.9%、37.4%,且高温对试样力学性能的影响具有部分可逆性。Abstract: Carbon fiber reinforced polymers (CFRP) were widely used in marine environments due to their corrosion resistance, light weight and high strength, and thus were subjected to hygrothermal environment for a long time. To understand the effects of hygrothermal environment and extreme temperatures on carbon fiber reinforced vinyl resin composites, the changes of compression properties, in-plane shear properties and interlaminar shear strength of CFRP before and after hygrothermal aging and at different testing temperatures were determined. The results of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) show that the pure resin specimens undergo hydrolysis in the hygrothermal environment, which cause the microcracks and pores on the surfaces of the specimens to expand and penetrate into the interior of the specimens. The moisture absorption curve of CFRP is in high agreement with Fickian model, while the moisture absorption curve of pure resin deviated from Fickian model because the hydrolysis reaction affected the moisture absorption channels. Meanwhile, the measurement on mechanical properties reveals that the compressive strength and interlaminar shear strength decrease by 7.6% and 12.3%, respectively, after hygrothermal aging for 90 days, and the compressive strength, in-plane shear strength, and interlaminar shear strength of the specimens at elevated temperature (70℃) decrease sharply by 36.2%, 26.9% and 37.4%, respectively. Meanwhile, it can be concluded that the effect of elevated tempera-ture on the mechanical properties of the specimens is partially reversible.
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图 9 CFRP试样压缩试验典型破坏模式
Figure 9. Typical failure modes of compression test for CFRP specimens
Failure identification codes (such as HAT) consisting of 3 characters marked describe the failure mode, failure area and failure location respectively; Failure mode: B—Brooming; D—Delamination; H—Thyrough-thickness; M(xyz)—Multi-mode; Failure area: A—At grip/tab; G—Gage; Failure location: T—Top; M—Middle; V—Various
图 15 CFRP面内剪切试验可接受的典型破坏模式
Figure 15. Typical acceptable failure modes of in-plane shear test for CFRP
Failure identification codes (such as VGN) consisting of three characters marked describe the failure mode, failure area and failure location respectively; Failure mode: H—Horizontal cracking; V—Vertical cracking; Failure area: G—Gage; Failure location: N—Between notches
表 1 CFRP和纯树脂的老化环境
Table 1. Ageing environment for CFRP and pure resin
Environment Hygrothermal environment Medium Deionized water Material CFRP, pure resin Temperature/℃ 70 Ageing time/d 7, 14, 90 表 2 CFRP的测试环境
Table 2. Testing environment for CFRP
Testing environments Testing temperature/℃ Ageing time/d Specimen conditions RTD 20±5 0 Dry ETD 70 0 Dry RTW 20±5 7, 14, 90 Wet ETW 70 90 Wet Notes: RTD—Room temperature dry condition; ETD—Elevated temperature dry condition; RTW—Room temperature wet condition; ETW—Elevated temperature wet condition. -
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