Experimental Study on Fatigue Behavior of Adhesive & Bolted Hybrid FRP Joints

doi:10.12141/j.issn.1000-565X.220105

Abstract

Abstract:

FRP adhesive & bolted hybrid joint has the combined advantages of adhesive joints and bolted joints, which behave enhanced static performance, but its fatigue failure mechanism still needs to be studied. In order to study the fatigue performance of hybrid FRP joints under various working conditions, this study designed and manufactured single-lap hybrid FRP joints specimens. Firstly, the static load tests under axial tension loads and four side shear loads were carried out, and the corresponding failure modes and ultimate bearing capacity were obtained. Then, high cycle fatigue tests under two working conditions were carried out, and the damage process of the adhesive layer was measured by acoustic emission (AE) technology. The fatigue failure mode, characteristic fatigue life and stiffness degradation of the specimen were obtained, and the fatigue life prediction method was proposed. The results indicate that the anti- -fatigue performance of hybrid FRP joints is mainly controlled by bolted-connection, and its fatigue failure process can be divided into four stages: adhesive layer cumulative damage, adhesive layer failure, FRP cumulative damage, and FRP failure. Among them, the AE characteristic parameters of adhesive layer failure stage and FRP failure stage change significantly, and this can be used as the basis for identifying the failure occurrence. When the number of bolts is small, two working condition show the similar failure mode of the nut squeezing into the FRP plate. When the number of bolts is large, for tensile specimens, the tensile-shear failure mainly occurs at the hole of the FRP plate; for shear specimens, the failure mode is overall shear failure of FRP plate. The increase of the number of bolts can significantly improve the characteristic fatigue life of tensile specimens, and effectively inhibit the stiffness degradation during fatigue loads, but the improvement of fatigue performance of shear specimens is not obvious with the increasing number of bolts. The S-N curve of two working conditions obtained based on the test data can provide a reference for the fatigue life calculation of hybrid FRP joints, and help the application of such joints in bridges and other structures that mainly bear repeated loads.

Key words: FRP joint, adhesive &, bolted hybrid connection, fatigue behavior, axial tensile test, fatigue failure mode, characteristic fatigue life, acoustic emission

CLC Number:

TU399

WANG Jinxiao, LI Sida, CHENG Bin, et al. Experimental Study on Fatigue Behavior of Adhesive & Bolted Hybrid FRP Joints[J]. Journal of South China University of Technology(Natural Science Edition), 2022, 50(11): 95-106.

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材性	值	材性	值
E₁₁/GPa	26.8	X_T/MPa	727.31
E₂₂/GPa	4.0	X_C/MPa	727.31
G₁₂/GPa	4.5	Y_T/MPa	70.98
S₁₂/MPa	35	Y_C/MPa	142

工况	试件编号	螺栓数量	单块板尺寸/（mm×mm×mm）	纤维铺层	加载方式
拉伸	HT1-1	1	480×160×20	［（0/0/+45/-45/90/0/90/0）₂］_S	静力
	HT1-2，HT1-3	1			疲劳
	HT4-1	4			静力
	HT4-2，HT4-3	4			疲劳
	HT9-1	9			静力
	HT9-2，HT9-3	9			疲劳
剪切	HS1-1	1	330×330×20	［（-45/+45/0/90/+45/-45/0/90）₂］_S	静力
	HS1-2，HS1-3	1			疲劳
	HS4-1	4			静力
	HS4-2，HS4-3	4			疲劳
	HS9-1	9			静力
	HS9-2，HS9-3	9			疲劳

工况	试件编号	静力加载		疲劳加载
		胶层破坏荷载/kN	极限荷载/kN	胶层破坏			FRP破坏
		胶层破坏荷载/kN	极限荷载/kN	最小荷载/kN	最大荷载/kN	疲劳寿命N₁	最小荷载/kN	最大荷载/kN	疲劳寿命N₂- N₁
拉伸	HT1-1	62	100	—	—	—	—	—	—
	HT1-2	—	—	4.8	48	—	4.8	48	150
	HT1-3	—	—	2.2	22	8 339	3	30	226 609
	HT4-1	60	270	—	—	—	—	—	—
	HT4-2	—	—	4	40	31 303	5.8	58	136 949
	HT4-3	—	—	5.8	58	21 827	52	122	85 488
	HT9-1	130	460	—	—	—	—	—	—
	HT9-2	—	—	8	58	275 230	40	210	3 152
	HT9-3	—	—	54	124	157 541	90	160	44 052
剪切	HS1-1	44	400	—	—	—	—	—	—
	HS1-2	—	—	2	20	—	140	310	248 037
	HS1-3	—	—	4.1	41	101 799	100	300	219 898
	HS4-1	79	458	—	—	—	—	—	—
	HS4-2	—	—	30	50	79 921	280	380	641 000
	HS4-3	—	—	14	58	58 504	110	270	469 120
	HS9-1	89	492	—	—	—	—	—	—
	HS9-2	—	—	7	70	53 904	140	300	173 532
	HS9-3	—	—	7	87	39 436	100	300	20 415

阶段	能量/eu	振铃计数	峰值频率/kHz	损伤类型
Ⅰ	0~1×10⁸	0~5×10⁵	90~160	胶层开裂，少量基体开裂和分层
Ⅱ	2×10¹⁰~3×10¹⁰	2×10⁶~4×10⁶	50~80，80~180	胶层开裂，少量基体开裂和分层
Ⅲ	0~1×10⁹	0~1×10⁶	50~80， 80~200	基体开裂，分层，纤维断裂/纤维抽拔
Ⅳ	3×10⁹~4×10⁹	2×10⁶~6×10⁶	50~80， 120~180，300~360	基体开裂，分层，纤维断裂/纤维抽拔

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