This work presents an experimental and numerical study of the failure behavior of planar lightwave circuit (PLC) optical splitters under uniaxial tensile loading. Based on the experimental results, ...the specific fracture position, ultimate failure load (Pm), failure mode and load-displacement behavior of the PLC optical splitter under uniaxial tensile loading were determined. In order to numerically simulate the real fracture behavior and stress distribution of adhesively bonded joints, a three-dimensional (3-D) explicit finite element analysis method based on material constitutive and tiebreak contact algorithm was proposed, which treats cohesive failure and adhesive/interfacial failure separately. The Pm predicted by the numerical simulation agrees well with the experimentally obtained Pm with a relative error of ∼4.3%, and the predicted failure mode is also similar to the experimentally observed mixed failure mode, which proves the accuracy and rationality of the adopted finite element method and model. This study can provide useful references for the reliability design and optimization of PLC optical splitters.
There is a lack of understanding on the damage tolerant design of bonded scarf joints, specifically when an existing bondline flaw affects the performance. This paper presents an improved progressive ...damage modelling methodology for assessing the damage tolerant performance of composite scarf joints containing artificial flaws in the bondline. The developed methodology is validated using an experimental study investigating the influences of design parameters on the strength of scarf joints under quasi-static tensile loading. The presented work gives excellent predictions of joint strength, and significant insight into the initiation, interaction and progression of damage. A new damage tolerant design approach is subsequently proposed for the application of bonded composite scarf joints, particularly in primary aerospace structures. The proposed design approach assesses the state of the stress at the failure-critical regions of adhesive and adherend to inform on damage-tolerant safe design loads, thus improving the future application of bonded composite scarf joints.
Hybrid joints formed by combining two or more joining methods, including spot welding and adhesive bonding, are relatively new joints designed especially for use in the automotive industry. The aim ...of this work is to study numerically the static and fatigue behavior of ultrasonically spot-welded, adhesively bonded and hybrid spot welded – adhesive bonded joints. The Virtual Crack Closure Technique was used to model the experimental static and fatigue tests for single lap joints reported in the literature. By introducing a short fictitious initial crack, in static loading the simulations matched the experimental results, characterized by a higher stiffness and static strength of the bonded and hybrid joints compared to the just spot-welded ones, and by an approximately similar static strength of the bonded and the hybrid joints. By the same method, a good match between the numerical and the experimental fatigue strengths was found, with the hybrid joints providing higher strength compared to the just spot-welded joints at 0.1 load ratio. According to the numerical analyses, S–N curves of bonded joints are expected to be statistically similar to those of the hybrid joints. This indicates that the adhesive plays the major role in the fatigue behaviour of the hybrid joint. Finally, the fatigue strength of hybrid joints was simulated at 0.3 load ratio. It was found a reasonable agreement between the experimental and numerical observations at 0.3 load ratio. The VCCT proved to be capable of simulating the static and the fatigue behaviour of the hybrid joints, thus proving to be a tool useful for the interpretation of the results and for the design of other hybrid joint configurations.
•Prolonged exposure (30 min) of the dogbones at 85 °C and subsequent cooling showed a decay of the adhesive mechanical performance in terms of ultimate strength and stiffness.•Tensile tests after ...curing under laboratory conditions (T0) showed that EPX1 exhibited the best performance in terms of stiffness and ultimate load.•Tensile tests (T1-85) after a heating (85 °C) and cooling (20 °C) cycle showed a positive effect on the mechanical performance of the joints.•The cyclic loading/unloading tests (T10-85) after each heating (85 °C) and cooling (20 °C) process - up to ten repetitions – showed an increase in the joint ductility, due to the ageing under the heating and cooling cycles.•A short exposure (T1-85) to high temperatures (85 °C) improves the failure modes observed.
The present paper illustrates an experimental investigation on double-lap adhesive joints between glass and aluminium adherends. Four different commercial structural adhesives (three epoxies and one urethane) are selected for tensile tests on adhesive joints subjected to different loading conditions (i.e. quasi-static and cyclic) and high temperature exposures (85 °C). The main objective is to verify the mechanical performance and the applicability of the joint in the field of civil engineering.
The results show - after curing under laboratory conditions (20 ± 1 °C/50 ± 5% RH) - a good adhesion between the tested materials. A suitable mechanical behaviour for the assembly of building components with adhesive technology is observed. The first epoxy adhesive shows the best performance both in terms of stiffness and ultimate load, which is due to a better and complete catalysis of the two components of the epoxy adhesive. Exposure to a heating (85 °C) and cooling (20 °C) cycle shows a positive effect on the mechanical performance of the joints. An increase in stiffness and ultimate loads is observed for the first and second epoxy and urethane adhesives. Cyclic loading/unloading tests performed after each heating (85 °C) and cooling (20 °C) process - up to ten repetitions - show a nonlinear trend of displacements and stiffnesses. However, at the end of each loading/unloading cycle, an increase in the ductility of the joint is observed. Moreover, a short exposure of the joints to high temperatures (85 °C) leads to an improvement in the failure modes: mixed failure modes are observed, with CF and GF failure rates coexisting with adhesive failures. Prolonged exposure to high temperatures has a negative effect on the failure modes of the joints and leads to an increase in the percentage of adhesive failures.
In this paper, the use of polymer additive manufacturing technology, also called 3D printing, for imparting texture to bond regions in adhesively bonded joints is explored. An improvement in the ...apparent shear strength values of adhesively bonded single lap joints is achieved by fusing structural reinforcements to the adherents through fused deposition modeling (FDM) additive technique. Towards that, computational models were first developed to simulate stress distribution along the overlap region of single lap shear joints, and four models that performed the best were chosen for physical testing. Pure adhesive (PA) joints were manufactured first, followed by the fabrication of 3D-printed adhesive (3D-PA) joints. Peak loads, shear stresses, and failure types were compared between these models. PA joints failed mainly adhesively, resulting in low peak loads and shear strength, whereas, 3D-PA joints registered higher average peak loads and shear strengths (increased by up to ≈832 %) with predominantly cohesive failure. 3D printed reinforcements appear to have imparted higher shear resistance against failure at the bond regions. Overall, using a combined computational and experimental approach, it is established that the 3D printed reinforcements have the potential to drastically improve the apparent shear strength of adhesively bonded single lap joints.
A cohesive zone model adequate for simulating the behaviour of adhesively bonded joints subjected to high-cycle fatigue and pure mode I loading is presented. The bilinear cohesive zone law with ...linear softening relationship was considered. The main advantage of the proposed formulation is the use of a unique damage parameter accounting for cumulative damage resulting from static and fatigue loading. The method was implemented in a user subroutine of the commercial finite element software Abaqus®. Two-dimensional numerical simulations of the double cantilever beam test using different representative combinations of the modified Paris law coefficients were performed. It was verified that the results of the model simulate with excellent agreement the several Paris laws used as input, thus demonstrating the good performance of the method as a predictive tool.
In the present work, a specific three-point bending test is applied to evaluate how the roughness can impact the bond strength (adherence) and the mechanism of interfacial failure initiation. The ...study is conducted using an aluminum alloy 2024-T3 as substrate and the DGEBA (polyepoxide bisphenol A diglycidyl ether) /DETA (diethylenetriamine) as adhesive, considering different abrasive surface treatments. An optimal roughness is reached to maximize the critical force during failure initiation; besides, the roughness impacted the failure propagation mechanism and the failure initiation area for each abrasive treatment. A power-law regression is considered to correlate the critical force and the failure initiation area, considering different average roughness. Local assessment using a mechanical profilometer and Scanning Electron Microscope (SEM) with Focused Ion Beam (FIB) are applied to measure the residual adhesive thickness at failure initiation and failure propagation zones as well as the initiation-to-propagation transitions. It is constated that the residual adhesive thickness is dependent on the average roughness of the substrate. Finally, Weibull's analysis is undertaken to demonstrate that the mechanism of failure initiation for all substrate groups is essentially the same, although the failure propagation mechanism can be different.
This work presents an approach for lifetime calculation of adhesively bonded joints under proportional and non-proportional multiaxial fatigue loads. In-phase and out-of-phase fatigue data with ...varying stress ratio (R = 0.1 and −1.0) from several joint geometries (butt, scarf, thick adherend shear test and butt-bonded double pipe joints) was employed. The approach is based on the stress-life concept and the Theory of Critical Distances (TCD) considering point and line methods. Stresses were calculated using 2D-FEA with linear-elastic and elastoplastic adhesive behaviours. Non-proportional stresses were addressed by the Maximum Rectangular Hull method. Three failure criteria were investigated: Drucker-Prager (DPC): an invariant-based equivalent stress criterion; Findley (FC): a critical plane stress-based criterion; (c) Fatemi-Socie (FSC): a critical plane stress-strain-based criterion. The material parameter of each failure criterion was iteratively calibrated using fatigue data. The FSC had the worst prediction performance. The DPC presented good agreement with in-phase data, but less robust as the variation of its material parameter changed considerably the prediction accuracy. For both DPC and FC, the line method and linear-elastic models were capable of providing good predictions. The FC yielded the best predictions considering a normal sensitivity b
F
> 1.0 for different stress ratios, in-phase and out-of-phase loads.
The fatigue life evaluation of adhesively bonded joints has attracted more and more attention with its extensive application. Here, the fatigue experiments under various loading conditions were ...carried out to understand the stress amplitude, mean stress, cycle period, and loading path related to the fatigue life of the adhesively bonded tubular butt-joints. The experimental results showed that the fatigue life of the adhesively bonded butt-joint decreased with the increase of stress amplitude and mean stress, and the influence of cycle period on the fatigue life was more obvious since the mechanical property of the selected adhesive was rate dependent. Meanwhile, the fatigue life of the adhesively bonded butt-joint was influenced by the loading path under multiaxial loading conditions. In addition, the relationship between the damage parameters and fatigue life was characterized based on the experimental observations. Accordingly, a stress-based fatigue life prediction model was developed which can simultaneously consider multiple damage parameters related to fatigue life of the adhesively bonded joint. The predicted results indicated that the predicted life correlated well with the experimental data of the adhesively bonded joints.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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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