Performance evolution of carbon fiber composites under moisture absorption coupled four-point bending load
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摘要: 为研究吸湿耦合四点弯曲载荷条件下碳纤维增强环氧树脂基复合材料的性能演变规律,通过自行设计的夹具施加四点弯曲载荷,并耦合5倍浓度模拟海水吸湿环境以模拟复合材料承载结构在海水中的服役条件。通过裂纹观测系统原位监测复合材料在力学实验过程中的损伤萌生与扩展,对比分析不同预处理条件对复合材料剩余力学性能及损伤模式的影响,分别通过四点弯曲、三点弯曲及短梁剪切力学试验,对预处理中复合材料的加载区域、等弯矩段进行评估。结果表明,预处理后复合材料的四点弯曲性能降低,一端加载处出现损伤破坏后,随之继续发生多次载荷下降直至最终失效发生;复合材料的等弯矩段短梁剪切性能无明显变化,三点弯曲力学试验结果表明预处理条件对等弯矩段的应力集中作用不显著。从而,预处理条件对加载区域影响显著,使其在失效过程中呈现出多断口扩展,伴随有层间裂纹扩展现象,而对等弯矩段无显著影响。Abstract: In order to study the performance evolution of carbon fiber reinforced epoxy composites under moisture absorption coupling four-point bending load, a four-point bending loading fixture was self-designed to provide the load condition, and 5 times concentration of seawater simulating moisture environment was coupled to simulate the service condition. The damage initiation and propagation process of composite under mechanical loading were monitored in situ by self-designed crack observation system. The effects of different pretreatment conditions on mechanical properties and damage modes were compared and analyzed. The loading area and equal bending moment area of composite under four-point bending pretreatment conditions were evaluated by four-point bending, three-point bending and short beam shearing test, respectively. The results show that the four-point bending property is decreased after pretreatment, the composite is damaged at one end of the loading at first, and then the load continues to decline for several times until the final failure occurs. There is no obvious change in the short beam shearing performance of the equal bending moment section. The three-point bending mechanical test results show that the pretreatment has no significant stress concentration effect on the equal bending moment area. Thus, the pretreatment conditions had a significant effect on the loading area but insignificant on the equal bending moment area. Multiple fracture propagation was observed on the loading area during the failure process, accompanied by interlayer crack propagation.
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Key words:
- carbon fiber composite /
- four-point bending /
- simulated seawater /
- moisture absorption /
- damage mode
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图 1 (a)自行设计的四点弯曲夹具载荷施加实验;(b)吸湿耦合四点弯曲载荷条件预处理实验;(c)四点弯曲力学实验;(d)原位裂纹观测实验
Figure 1. (a)Self-designed four-point bending fixture loading experiment; (b)Moisture absorption coupling four-point bending loading pretreatment experiment; (c)Four-point bending mechanical experiment; (d)In-situ crack observation experiment
图 8 T800级碳纤维复合材料层合板的四点弯曲载荷位移对比图:(a)未经预处理、(b)预处理7天后、(c)预处理14天后、(d)预处理21天后
Figure 8. Comparison of four-point bending load displacement of T800 carbon fiber composite laminate: (a) without pretreatment, (b) with pretreatment for 7 days, (c) with pretreatment for 14 days, (d) with pretreatment for 21 days.
图 9 5倍盐水+60%四点弯曲载荷条件下处理7天,T800级碳纤维复合材料层合板四点失效形貌特征(a)左侧加载处,(b)右侧加载处
Figure 9. Four-point failure morphology characteristics of T800 carbon fiber composite laminate after 7 days pretreatment under 5 times seawater moisture coupled with 60% four-point bending load (a)the left loading position, (b)the right loading position
图 10 5倍盐水+60%四点弯曲载荷条件下处理14天,T800级碳纤维复合材料层合板四点失效形貌特征(a)左侧加载处,(b)右侧加载处
Figure 10. Four-point failure morphology characteristics of T800 carbon fiber composite laminate after 14 days pretreatment under 5 times seawater moisture coupled with 60% four-point bending load (a)the left loading position, (b)the right loading position
图 11 5倍盐水+60%四点弯曲载荷条件下处理21天,T800级碳纤维复合材料层合板四点失效形貌特征(a)左侧加载处,(b)等弯矩段,(c)右侧加载处
Figure 11. Four-point failure morphology characteristics of T800 carbon fiber composite laminate after 21 days pretreatment under 5 times seawater moisture coupled with 60% four-point bending load (a)the left loading position, (b) the equal bending moment area, (c)the right loading position
表 1 未经预处理,T800级碳纤维复合材料层合板四点弯曲性能
Table 1. Four-point bending properties of untreated T800 carbon fiber composite laminate
Width/
mmThickness/
mmBending
load/NBending
strength/MPaBending
modulus/GPa13.1 1.95 1197 1441 223 -
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