Theoretical study based on 2D assumptions of the influence of small pores on crack initiation in adhesively bonded joints

Purpose Adhesively bonded joints are gaining importance in the structural joining processes competing against welding and bolting processes. However, long-term behaviour of adhesively bonded joints is still an open question. Due to the increasing interest in adhesively bonded joints, mainly in the transports industry, there is a need to deep the knowledge about the fatigue behaviour of adhesive joints with metallic substrates allowing the development of reliable joints to resist cyclic loadings. The paper aims to discuss these issues. Design/methodology/approach An experimental research aiming at characterizing the fatigue behaviour of adhesively bonded aluminium substrates is presented in this paper, covering both fatigue crack propagation and global S-N behaviours. Double cantilever beam (DCB), end notch flexure (ENF) and double lap joints (DLJ) specimens built using the AA6061T651 substrate and epoxy adhesive were used to evaluate the pure modes I and II fatigue crack propagation rates and the S-N fatigue behaviours. Findings DCB and ENF specimens allowed the formulation of pure modes I and II fatigue crack propagation laws including the propagation thresholds. DLJs showed higher static shear strength than recommended by the manufacturer for aluminium substrates, but fatigue resistance of the DLJs was lower than suggested by the manufacturer. The fatigue damage process in the DLJs was dominated by a fatigue crack initiation process. Originality/value A consistent fatigue research on adhesively bonded aluminium substrates is presented covering in the same study aspects of fatigue crack propagation and fatigue crack initiation. Data reduction schemes involving both numerical and analytical procedures were followed. Proposed work constitutes a rigorous basis for future fatigue prediction models developments.

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Development of an integrated sacrificial sensor for damage detection and monitoring in composite materials and adhesively bonded joints

Structural Health Monitoring ◽

10.1177/1475921721989041 ◽

2021 ◽

pp. 147592172198904

Author(s):

G Ólafsson ◽

RC Tighe ◽

SW Boyd ◽

JM Dulieu-Barton

Keyword(s):

Crack Initiation ◽

Electrical Resistance ◽

Electrical Response ◽

Lap Joints ◽

Structural Performance ◽

Bonded Joints ◽

Adhesively Bonded ◽

Adhesively Bonded Joints ◽

Wide Range ◽

Adhesively Bonded Joint

Quality assurance of adhesively bonded joints is of vital importance if their benefits are to be exploited across a wide range of industrial applications. A novel lightweight, low-cost, non-invasive embedded sacrificial sensor is proposed, capable of detecting damage within an adhesively bonded joint, which could also be used in a laminated composite structure. The sensor operation uses changes in electrical resistance, increasing as the sensing material area diminishes with damage progression. Initial tests prove the sensor concept by showing that the electrical resistance of the sensor increases proportionally with material removal, mimicking the sensor operation. Thermography is used to verify the current flow through the sensor and that any localised heating caused by the sensor is minimal. Short beam interlaminar shear strength (ILSS) tests show that embedding sensors in a composite laminates did not cause a reduction in material interfacial structural performance. Finally, the in situ performance of the sensor is demonstrated in quasi-static tensile tests to failure of adhesively bonded single lap joints (SLJs) with sensors embedded in the bond line. Prior to crack initiation, an electrical response occurs that correlates with increasing applied load, suggesting scope for secondary uses of the sensor for load monitoring and cycle counting. Crack initiation is accompanied by a rapid increase in electrical resistance, providing an indication of failure ahead of crack propagation and an opportunity for timely repair. As the crack damage propagated, the electrical response of the sensor increased proportionally. The effect of the sensor on the overall structural performance was assessed by comparing the failure load of joints with and without the embedded sensor with no measurable difference in ultimate strength. The research presented in the article serves as an important first step in developing a simple yet promising new technology for structural health monitoring with numerous potential applications.

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Nonlinear Viscoelastic Finite Element Analysis of Adhesive Joints

Tire Science and Technology ◽

10.2346/1.2148803 ◽

1988 ◽

Vol 16 (3) ◽

pp. 146-170 ◽

Cited By ~ 4

Author(s):

S. Roy ◽

J. N. Reddy

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Viscoelastic Behavior ◽

Bonded Joints ◽

Adhesively Bonded ◽

Element Analysis ◽

Adhesively Bonded Joints ◽

Nonlinear Viscoelastic ◽

Structural Failures ◽

Updated Lagrangian

Abstract A good understanding of the process of adhesion from the mechanics viewpoint and the predictive capability for structural failures associated with adhesively bonded joints require a realistic modeling (both constitutive and kinematic) of the constituent materials. The present investigation deals with the development of an Updated Lagrangian formulation and the associated finite element analysis of adhesively bonded joints. The formulation accounts for the geometric nonlinearity of the adherends and the nonlinear viscoelastic behavior of the adhesive. Sample numerical problems are presented to show the stress and strain distributions in bonded joints.

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