Load-bearing mechanism and full-process response characterization of a GFRP square tube bonded-bolted sleeve connection
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摘要: 纤维增强复合材料(FRP)构件的接头部分是结构的潜在薄弱环节,在结构尺度计算中准确反映接头的全过程行为是FRP组合结构的设计难点。本文以压缩工况下拼装式玻璃纤维增强复合材料(GFRP)格构柱为结构背景,以拉挤GFRP方管型材的胶栓混合套管连接接头为研究对象,设计制备了4个胶栓混合连接试件和2个纯螺栓连接试件,开展了轴压静载试验,并建立了考虑胶层失效行为的实体有限元模型。结果表明:该连接形式具有二次承载特性,其整体力学行为源于胶层剪切传力机制和螺栓剪切传力机制的叠加结果;对于本文试件,二次极值荷载达到了首次极值荷载的92%,挤压破坏荷载相较于纯螺栓连接试件平均提升了49%。针对胶栓混合套管连接,提出了一种简化建模方法,并基于连续损伤模型和塑性势理论建立了以力和位移表述的宏观本构,提炼出了具有明确物理意义的本构参数,可在结构尺度计算中以较小的计算成本准确考虑接头的全过程行为。宏观本构模型的唯象属性使得简化建模方法对于接头的力学行为描述较为准确,计算成本较小,能够适用于压缩工况下拼装式GFRP格构柱的结构尺度计算分析。Abstract: The connection region of fiber reinforced polymer (FRP) components is a potential weak link in structures. Accurately reflecting the full-process behavior of the joint in structural scale calculations is a challenging aspect in the design of FRP composite structures. In this study, assembled glass fiber reinforced polymer (GFRP) lattice columns subject to compression loads were used as the structural background, and the focus was on the research of bonded-bolted sleeve connections for pultruded GFRP square tubes. Four hybrid joint specimens and two pure bolted joint specimens were designed and prepared. Axial compression static load tests were conducted, and a solid finite element (FE) model considering the failure behavior of the adhesive layer was established. The results indicate that the connection form exhibits a secondary load-carrying characteristic, and the overall mechanical behavior is derived from the superposition of the adhesive shear and bolt shear load transmitting mechanisms; Regarding specimens in this paper, the secondary peak load reaches 92% of the first, and the bearing failure load is on average increased by 49% compared to pure bolted connection specimens. For the bonded-bolted sleeve connection, a simplified modeling approach is proposed. Based on the continuous damage model and the plastic potential theory, a macroscopic constitutive model in terms of force and displacement is established. This model distills constitutive parameters with clear physical meanings, enabling an accurate consideration of the full-process behavior of the joint in structural-scale calculations at a relatively low computational cost. The phenomenological nature of the macroscopic constitutive model leads to a relatively accurate description of the mechanical behavior of the joint, and the computational cost is small, making it suitable for structural scale calculation analysis of assembled GFRP latticed columns subject to compression loads.
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图 4 胶栓混合套管连接实体有限元(FE)模型
Figure 4. Solid finite element (FE) model for the bonded-bolted sleeve connection
σII,max—Mode II shear strength; GII—Mode II fracture energy; KII—Mode II stiffness; uII,0—Mode II separation at zero stress; uII,ini—Mode II separation at damage initiation; uII,f—Mode II separation at complete failure
图 9 胶栓混合连接传力机制示意图
Figure 9. Schematic diagram for the load transmitting mechanism of bonded-bolted connections
*—Original photo without annotations is taken from reference [31]
图 12 两种受力机制的本构关系曲线示意图
Figure 12. Schematic diagram of the constitutional relationship curves of the two load transmitting mechanisms
NI—Axial load at damage initiation; NS—Axial load at shear failure; NB—Axial load at bearing failure; NR—Initial load of the second load stage; Nresi—Axial load contributed by adhesive residual strength; uI—Deformation at damage initiation; uR—Initial deformation of the second load stage; ufa—Deformation at complete adhesive failure; uB—Deformation at bearing failure; uS—Deformation at shear failure; uF—Deformation at complete joint failure; NS,b—Axial load contributed by BSD at shear failure; NB,b—Axial load contributed by BSD at bearing failure; NR,b—Axial load contributed by BSD at the initiation of the second load stage
表 1 材料参数
Table 1. Material properties
Component Modulus/GPa Strength (Yield strength)/MPa Poisson's ratio Pultruded GFRP Longitudinal 29.7 429-456 0.3 Transverse 7.55 64.91 In-plane shear* 3.0 27 Transverse shear* 3.0 33.54 Steel sleeve 210.0 345.0 0.3 M8 through-bolts* 235.0 1043 0.42 Sikadur-330CN Tensile 3.5 41.2 0.28 Shear 1.37 26.6 Note: * data taken from Qiu et al[20]. 表 2 BBSC和BSC试件试验结果汇总
Table 2. Summary of the experiment results of BBSC and BSC specimens
Specimen label Aa/mm2 ${N_{{\text{i,exp}}}}$/kN $\overline {{N_{{\text{i,exp}}}}} $/kN ${N_{{\text{i,FEM}}}}$/kN ${N_{{\text{B,exp}}}}$/kN $\overline {{N_{{\text{B,exp}}}}} $/kN ${N_{{\text{S,exp}}}}$/kN $\overline {{N_{{\text{S,exp}}}}} $/kN $\overline {{K_{{\text{a,exp}}}}} $/
(kN·mm−1)${K_{{\text{a,FEM}}}}$/
(kN·mm−1)BBSC1 4×48 mm×
150 mm132.6 114.6 144.1 82.5 96.4 94.4 105.7 142.63 117.7 BBSC2 105.9 107.5 116.1 BBSC3 118.8 90.0 103.4 BBSC4 101.2 105.5 108.8 BSC1 0 — — — 51.1 49.2 — — 30.7 — BSC2 — 47.3 — Notes: Subscript exp and FEM denote experiment value and 3D FEM value, respectively; Variables with an overline $ \mathit{\overline{N_{\text{x}}}} $ means average value of Nx; Aa—Adhesive bond area; ${N_{\text{i}}}$—Load at bond failure; ${N_{\text{B}}}$—Load at bearing failure; ${N_{\text{S}}}$—Load at shear failure; ${K_{\text{a}}}$—Axial compression stiffness of the joint. 表 3 BBSC1简化模型宏观本构参数
Table 3. Macroscopic constitutive parameters for the simplified model of BBSC1
Adhesive shear dominated behavior Bolt shear dominated behavior NI 132.60 kN NR 44.77 kN uI 0.89 mm NB 82.50 kN uR 0.97 mm uB 1.94 mm Nresi 42.31 kN NS 94.40 kN — — uS 3.59 mm 表 4 BBSC1荷载-位移曲线关键位置数据
Table 4. Key position data of the BBSC1's load-displacement curve
First loading stage Second loading stage NI,exp 132.60 kN NR,exp 44.77 kN uI,exp 1.45 mm uR,exp 1.53 mm $ K_{{\text{a,exp}}}^{{\text{BBSC}}} $ 149.1 kN/mm NB,exp 82.50 kN $ K_{{\text{a,exp}}}^{{\text{BSC}}} $ 30.7 kN/mm uB,exp 2.50 mm — — NS,exp 94.40 kN — — uS,exp 4.15 mm Notes: (uI,exp, NI,exp), (uB,exp, NB,exp), and (uS,exp, NS,exp) correspond to the bond failure, bearing failure, and shear failure points in Fig. 5, respectively; (uR,exp, NR,exp) corresponds to the start point of the second loading stage; $ K_{{\text{a,exp}}}^{{\text{BBSC}}} $ and $ K_{{\text{a,exp}}}^{{\text{BSC}}} $ are the compression stiffness of the BBSC and BSC joint, respectively. 表 5 文献[30]中胶栓混合搭接接头简化模型宏观本构参数
Table 5. Macroscopic constitutive parameters for the simplified model of the bonded-bolted lap joint from the reference [30]
Adhesive shear dominated behavior Bolt shear dominated behavior NI 11.29 kN NR 6.37 kN uI 0.3636 mmNB 16.78 kN uR 0.4064 mmuB 1.0695 mmNresi 0 kN NS 19.01 kN — — uS 1.4759 mm -
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