An experimental study on mechanical response of single-lap bolted CFRP composite interference-fit joints

Hu, Junshan; Zhang, Kaifu; Yang, Qingda; Cheng, Hui; Liu, Ping; Yu, Yang

doi:10.1016/j.compstruct.2018.05.016

Cited by 70 publications

(20 citation statements)

References 35 publications

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“…As the interference-fit size increase from 0.5% to 2.1%, the corresponding frictional force grows from 597.6 N to 1608.9 N. The extruding behavior between bolt-shank and joint-hole is enhanced by the growth of interference-fit size, but the frictional forces are not proportional to the corresponding interference-fit percentages, indicating that the interfacial behavior is nonlinear and damage occurs on coupled interfaces as reported in the previous research. 31…”

Section: Resultsmentioning

confidence: 99%

“…30 But composite joints are heterogeneous structures with multiple materials where the interaction of fasteners and clamped parts should not be ignored. 31 In order to quantify the preload relaxation experimentally, the micrometer spindle, 21 strain-gauged bolt 32 and load washer 33 were employed to monitor the amount of preload loss over time. It is found that relaxation was determined predominantly by the viscoelastic creep response of the composite material and was affected by temperature, moisture and stress level.…”

Section: Introductionmentioning

confidence: 99%

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Mechanism of bolt pretightening and preload relaxation in composite interference-fit joints under thermal effects

Zhang

Cheng

et al. 2020

Journal of Composite Materials

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The present research investigates the mechanism of bolt pretightening and preload relaxation in composite interference-fit joint structures under thermal effects. In view of the dissimilar material properties and the interfacial friction in such joints, the mechanical behavior of bolt and composites during assembly can be regarded as immediate preload response which is described by a linear elastic model, whereas the long-term behavior of composites during preload relaxation in service is considered as delayed response which is characterized by a viscoelastic model. The clamping forces on both sides of joints were captured to evaluate the preload balanced by the frictional behavior. The preload relaxation of joints with various interference-fit sizes and tightening torques under thermal effects were monitored for 240 hours to calibrate and validate the proposed model. The research revealed that the interference-fit size determined the level of frictional force which resulted in a difference between clamping forces at two sides of the fasteners. The preload first increases slowly with the growth of temperature, then decreases sharply when it approaches to glass transition temperature of matrix. The interference-fit joint behaves better in terms of maintaining the stability of preload than clearance-fit joints.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanism of bolt pretightening and preload relaxation in composite interference-fit joints under thermal effects

Zhang

Cheng

et al. 2020

Journal of Composite Materials

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“…In the joint with an suitable interference-fit size, the bolt compacts the hole surface and acts as the cold expansion process, making the bolt-shank and joint-hole tightly coupled. 18 As aforementioned, the interface voids in the case of low interference-fit size (0%) and the hole damage caused by bolt inserting in the cases of high interference-fit percentages (0.8% and 1.2%) would reduce the effective bearing area and result in the decrease of the bearing strength by 8.2%, 6.8% and 8.1%, separately. The bolt torque improves bearing strength by producing sufficient friction force between CFRP coupons to transmit external load, whereas the excessive compressive preload through-thickness in the case of 12 N-m crushes the CFRP coupons and damages the joint structures, making the strength drop by 1.5%.…”

Section: Bearing Strength and Joint Stiffnessmentioning

confidence: 90%

“…17 However, in order to get an accurate prediction of load-displacement behavior in single-lap, singlebolted joint configuration, secondary bending effect must be considered with more detailed aspects. 18 The secondary bending can be described as the additional bending moment along with out-of-plane deformation induced by the eccentric loading path. This effect is an inherent feature of the single-lap structure that greatly affects the load-bearing performance.…”

Section: Introductionmentioning

confidence: 99%

Effect of secondary bending and bolt load on damage and strength of composite single-lap interference-fit bolted structures

Zhang

Zou³

et al. 2019

Journal of Composite Materials

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The single-lap interference-fit bolted joint is widely used in composite structures. In order to get an accurate prediction of bearing strength, secondary bending and bolt load effects are studied in the present research via combination of experimental and numerical methods. The joint specimens with four levels of interference-fit size ( I) and bolt torque ( T) were tested according to ASTM standard D5961 to evaluate the bearing behavior and joint stiffness. Meanwhile, a finite element model considering the shear nonlinearity is built to simulate the bearing strength and evolution of intralaminar damage and delamination. Results show that the bearing behavior of composite joints is more sensitive to bolt load than interference-fit size, and the optimal pattern is I = 0.4% and T = 8 N-m, which can effectively improve bearing performance and alleviate secondary bending effect. Matrix failure and fiber–matrix shear-out failure accompanied with delamination are commonly observed and localized on the bearing side of joint-holes, indicating the desired non-catastrophic failure modes.

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“…Zhang et al 22 identified the optimal interference-fit and torque by combing experimental and numerical methods; however, the research did not consider the impact of the preload imbalance. Hu et al 23,24 investigated the mechanism of bolt pre-tightening and preload relaxation in composite interference-fit joint structures, and identified a frictional force. This force resulted in a difference between clamping forces at two sides of the fastener.…”

Section: Introductionmentioning

confidence: 99%

Effect of imbalanced interface pre-tightening force on the bearing behavior of carbon fiber reinforced polymer interference-fit lap joint

Lai

Zou³

et al. 2021

Advances in Mechanical Engineering

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Interference-fit is attracting increasing attention in the aerospace field because of its excellent enhancement of the sealing and fatigue life of carbon fiber reinforced plastic (CFRP). However, it also induces imbalanced pre-tightening forces on the interface, and affects its mechanical behavior. A series of experiments were conducted to assess the imbalanced pre-tightening force of CFRP interference bolted joints and its effects. High-precision washer force sensors were used to measure the pre-tightening force between upper and lower surfaces at various interference-fit and torque. Strain gauges were used to estimate the varying effect on the imbalanced pre-tightening force during tensile tests. The effects of varying interference-fit and torque on pre-loaded transfer, surface strain distribution, tensile strength, and damage mode were identified. The results show that the synergy of interference-fit and torque induces an imbalanced pre-tightening force, which, in turn, changes the stress-strain evolution of the surface, and a special “transition regime” was identified in the evolution curves. Compared with clearance-fit, the ultimate strength and optimal torque of interference-fit joints could be significantly enhanced. In addition, the damage originates from fiber/matrix slipping to the upper surface with a low pre-tightening force and the formation of stack buckling, which then causes delamination fracture.

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An experimental study on mechanical response of single-lap bolted CFRP composite interference-fit joints

Cited by 70 publications

References 35 publications

Mechanism of bolt pretightening and preload relaxation in composite interference-fit joints under thermal effects

Mechanism of bolt pretightening and preload relaxation in composite interference-fit joints under thermal effects

Effect of secondary bending and bolt load on damage and strength of composite single-lap interference-fit bolted structures

Effect of imbalanced interface pre-tightening force on the bearing behavior of carbon fiber reinforced polymer interference-fit lap joint

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