摘要
为掌握极端湿热环境下CFRP/钢界面性能的退化机理,用Sika‑30胶黏剂制作了12个CFRP/钢双搭接试件,并在70 ℃的模拟海水中浸泡不同时间后进行拉伸剪切试验. 结果表明:CFRP/钢双搭接试件的破坏模式受浸泡时长的影响较小;CFRP/钢界面平均抗剪强度随浸泡时长呈先上升后下降趋势;浸泡90 d后,CFRP/钢界面平均抗剪强度较未浸泡试件下降了35.6%.
碳纤维增强聚合物(CFRP)因其轻质、高强、耐腐蚀等优点被广泛用于加固结
Sika‑30胶黏剂由于其高强度和较高的Tg(62 ℃,该温度高于大多数环氧树脂胶的T
试验采用了型号为Q345B的钢板,以及Sika‑30胶黏剂和南京海拓公司生产的单向CFRP板.所有相关材料参数均由供应商提供,并详细列于
Material | Thickness/mm | Width/mm | Tensile strength/MPa | Elasticity/GPa | Elongation at break /% |
---|---|---|---|---|---|
Steel | 12.0 | 50 | 514.0 | 206.00 | - |
CFRP | 1.4 | 50 | 2 263.0 | 161.20 | 1.65 |
Sika-30 | - | 50 | 25.3 | 12.13 | 0.22 |
试件的设计(见

图1 CFRP/钢双搭接试件尺寸及应变片布置
Fig.1 Size of CFRP/steel double lap specimen and layout of strain gauges(size: mm)
Specimen | Ultimate bearing capacity /kN | Limit displacement/mm | Bond strength/MPa | Failure mode | |||
---|---|---|---|---|---|---|---|
Pult | Average | Dmax | Average | τ | Average | ||
25 ℃Sika30‑1 | 126.94 | 7.51 | 6.35 | a/b | |||
25 ℃Sika30‑2 | 106.32 | 111.76 | 7.42 | 7.32 | 5.31 | 5.59 | a |
25 ℃Sika30‑3 | 102.03 | 7.03 | 5.10 | a/b | |||
70 ℃‑30 d‑1 | 113.82 | 8.35 | 5.69 | a/b | |||
70 ℃‑30 d‑2 | 105.21 | 129.78 | 8.20 | 9.52 | 5.26 | 6.49 | a/b |
70 ℃‑30 d‑3 | 170.33 | 12.00 | 8.51 | a/b/c | |||
70 ℃‑60 d‑1 | 72.44 | 7.15 | 3.62 | a/b | |||
70 ℃‑60 d‑2 | 95.08 | 78.88 | 7.70 | 7.21 | 4.75 | 3.94 | a |
70 ℃‑60 d‑3 | 69.13 | 6.79 | 3.46 | a/b | |||
70 ℃‑90 d‑1 | 86.11 | 8.50 | 4.31 | a/b | |||
70 ℃‑90 d‑2 | 54.27 | 71.84 | 6.00 | 6.96 | 2.71 | 3.60 | a/b |
70 ℃‑90 d‑3 | 75.16 | 6.37 | 3.76 | a/b |
Note: Pult—indicates ultimate tensile capacity ; Dmax—indicates limit displacement; τ—indicates bond strength; a—indicates the CFRP layer failure; b—indicates the bond layer and steel interface stripping failure; c—indicates adhesive failure; ’*’/’*’or’*’/’*’/’*’—indicates two or more mixed failure modes.
为模拟海水环境,试验采用了5%的NaCl溶液,并将试件分为4组,即25 ℃下水浴0 d为1组,70 ℃下水浴30、60、90 d各1组,每组包含3个试件.
在试验开始前,对钢板和CFRP的表面进行抛光处理,确保钢板接触界面光滑,CFRP板结合界面无树脂基质,并用丙酮擦拭钢板与CFRP的接触界面.制作过程中,首先在一块CFRP板上涂抹Sika‑30结构胶,撒上直径为1 mm的钢球以控制结构胶层的厚度,然后对准粘贴钢板,再用相同方法粘贴另一块CFRP板.之后,试件被压重4 h以挤出多余的结构胶,并在常温下养护7 d.养护完成后,试件被分组放入70 ℃的水浴箱中.试件的尺寸、形状及CFRP板表面应变片的布置如
水浴结束后,对试件进行静力拉伸破坏试验,并对其荷载-位移曲线、剪切强度及破坏模式进行了分析,结果详见
为方便统计和分析,本文定义了3种破坏模式:当试件出现CFRP板层离破坏时,称为a型破坏;当试件黏结层与钢界面剥离破坏时,称为b型破坏;当黏合剂失效时,称为c型破坏.

图2 CFRP/钢界面破坏模式
Fig.2 Failure modes of CFRP/steel interface

图3 加载过程中CFRP/钢双搭接试件荷载位移曲线
Fig. 3 Load‑displacement curves for CFRP/steel double lap specimens during loading
对各组试件的平均极限荷载进行统计,结果分别为111.22(水浴0 d组)、129.78(水浴30 d组)、78.88(水浴60 d组)、71.84 kN(水浴90 d组).相较于水浴0 d组,水浴30 d组试件的极限荷载提升了17%,这可能是由于黏结剂的后固化作用增强了黏结强度.然而,随着水浴时间的进一步延长,水浴60、90 d组试件极的限荷载分别下降了29%和36%,显示出水浴对试件性能的负面影响.
在极限位移方面,4组试件的平均极限位移分别为7.48(水浴0 d组)、9.52(水浴30 d组)、7.21(水浴60 d组)、6.96 mm(水浴90 d组).与水浴0 d组相比,水浴30 d组试件的极限位移增加了27%,这可能与黏结剂后固化导致的性能提升有关.然而,水浴60、90 d组试件的极限位移分别下降了4%和7%,表明长时间的水浴处理对试件的变形能力也产生了不利影响.
综上所述,试件的极限荷载和极限位移随着水浴时间的增加呈现下降趋势,这可能与水分子对粘结剂和碳纤维板基体的侵蚀作用有关.尽管如此,在粘结剂后固化的影响下,水浴30 d组的试件在极限荷载和极限位移方面仍表现出一定程度的提升.
根据相邻2个应变片i、i‑1的正应变差值变化,算出i、i‑1两点之间的界面剪应
(1) |
式中:为相邻2个测点i、i‑1之间界面平均剪应力;为两相邻测点正应变的差值,即;分别是CFRP板的弹性模量和厚度;,即为应变片i、i‑1两点间距离.

图4 加载过程中CFRP/钢黏结界面剪应力分布
Fig. 4 Shear stress distribution of CFRP/steel bonding interfaces during loading
黏结滑移本构(剪应力-滑移曲线)能够反应界面局部受力及黏结失效过程.考虑到CFRP板与钢板的刚度差,假定试件的前端CFRP板与钢板黏结部分的端部滑移量为
(2) |
结合
(3) |
由

图5 CFRP/钢界面剪应力-滑移本构曲线
Fig.5 Bond‑slip constitutive curves for interfaces between CFRP and steel
峰值剪应力τf、刚度K、界面破坏能Gf及单元失效时极限滑移量δf常用于描述黏结滑移本构曲
(4) |
Gf是通过积分计算得出的精确解;是通过
Parameter | τf/MPa | δf/mm | K/(MPa·m | Gf/(MPa·mm) | /(MPa·mm) |
---|---|---|---|---|---|
25 ℃Sika30 | 12.9 | 0.215 | 64.100 | 1.935 | 1.387 |
70 ℃-30 d | 35.0 | 0.275 | 136.392 | 5.980 | 4.810 |
70 ℃-60 d | 17.0 | 0.120 | 146.665 | 2.210 | 1.020 |
70 ℃-90 d | 11.5 | 0.180 | 65.000 | 0.984 | 1.035 |
Xia
(4) |
其中,Gf满足经验值(即),故有:
(5) |
式中:bp为CFRP板宽度. Xia
(6) |
将Xia模型和Xia‑A模型计算的各组极限承载力与实测极限承载力进行对比,结果如
Specimen group | Test/kN | Xia model/kN | Xia model/Test | Xia model‑A/kN | Xia model‑A/Test |
---|---|---|---|---|---|
25 ℃Sika30 | 111.76 | 89.68 | 0.80 | 90.21 | 0.81 |
70 ℃-30 d | 129.78 | 146.58 | 1.13 | 148.04 | 1.15 |
70 ℃-60 d | 78.88 | 67.86 | 0.86 | 77.36 | 0.98 |
70 ℃-90 d | 71.84 | 68.34 | 0.95 | 77.92 | 1.08 |
如
综上所述,CFRP/钢试件的界面退化程度会随水浴时间的延长而加剧,同时失效模式也会随之变化.具体来说,水浴初期(0~30 d),黏结剂的后固化和界面退化现象并存,但后固化作用更为显著,从而提升了试件的极限承载力.此时的界面失效主要是由于黏结剂强度以及碳纤维束之间的黏结力不足.进入水浴中期(30~60 d),界面退化进一步加剧,后固化作用减弱或提升效果远不及退化速度,CFRP/钢试件的界面退化程度较初期更为严重.随着水浴时间的延长,水分子逐渐渗透进CFRP板材中,导致碳纤维束之间的黏结剂强度也逐渐退化.在此阶段,碳纤维束黏结剂强度的不足成为导致CFRP/钢试件界面失效的主要因素.到了水浴后期(60~90 d),碳纤维束之间的黏结剂强度退化更为严重,而界面黏结剂的退化则趋于稳定.由于界面黏结剂的强度大于碳纤维束之间的黏结剂强度,因此碳纤维束之间的黏结力不足最终导致了CFRP/钢试件的界面失效.
(1)极端湿热环境的时长对CFRP/钢双搭接试件的破坏模式影响较小,但对其界面抗剪承载力影响较大.试件平均抗剪强度从大到小的依次为9.52、7.32、7.21、6.96 MPa,对应的试件分别为70 ℃-30 d、25 ℃ sika30、70 ℃-60 d和70 ℃-90 d.
(2)在极端湿热环境下,CFRP/钢界面的黏结滑移本构关系随着水浴时间的延长而变化.水浴30 d试件组的峰值剪应力、极限滑移量、峰值剪应力对应的滑移量最大,并且随着水浴时间的增长,试件的峰值剪应力、极限滑移量有减小的趋势.
(3)在极端湿热环境下的CFRP/钢界面的抗剪承载力可采用Xia模型或Xia‑A模型来计算.
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