•The effect of surface treatment/preparation techniques on the adherend surface characteristics was discussed.•Mode-I and Mode-II delamination resistance of adhesively bonded CF/PEKK composite joints ...were investigated for different surface treatment methods.•Atmospheric plasma treatment significantly improved both Mode-I and Mode-II fracture toughness values of the bonded joints.•The failure modes and damage propagations in the joints were detected using acoustic emission (AE).•Fracture surface morphological examinations and AE findings suggested that cohesive failure was more predominantly observed in APA-treated SLJs.
This study aims to assess the influence of peel-ply (PP), mechanical abrasion (MA), and atmospheric plasma activation (APA) treatments on Mode-I and Mode-II fracture toughness of carbon fiber/ poly-ether-ketone-ketone (CF/PEKK) composite joints. A comprehensive examination of the topography and wettability of the adherend surfaces is conducted using various methods. The CF/PEKK adherends are produced through an automated fiber placement (AFP) process, and the CF/PEKK bonded joints are prepared using two different structural adhesive films, one of which has a lower strength, while the other has a higher strength. To evaluate their fracture toughness properties, double cantilever beam (DCB) and end-notched flexure (ENF) tests are carried out in accordance with ASTM standards. Acoustic emission sensors are used to monitor the test specimens during DCB tests, allowing for an in-depth evaluation of the failure modes and damage propagations in the joints. The results show that the GIC and GIIC values of the APA-treated CF/PEKK bonded joints are remarkably higher than those of the untreated ones, with a range of improvement of 34.0–84.8 times and 7.5–17.4 times, respectively. Adhesive failure is the dominant failure mode on the surfaces of non-treated (NT) and PP samples, while cohesive failure is more prominent in those treated with MA and APA. The failure modes of the treated samples varied depending on the adhesive used, with APA-treated samples always exhibiting a cohesive failure. It is observed that the AE counts increase more slowly in APA-treated samples compared to MA-treated joints as delamination progresses more slowly with cohesive failure dominant, which leads to a lower release of AE energy.
Continuing interest and more developments in recent years indicated that it would be useful to update Banea and da Silva paper entitled “Adhesively bonded joints in composite materials: an overview”. ...This paper presents an updated review of adhesively bonded joints in composite materials, which covers articles published from 2009 to 2016. The main parameters that affect the performance of bonded joints such as surface treatment, joint configuration, geometric and material parameters, failure mode etc. are discussed. The environmental factors such as pre-bond moisture, moisture and temperature are also discussed in detail and how they affect the durability of adhesive joints. Lots of shortcomings were resolved during the last years by developing new materials, new methods and models. However, there is still a potential to evaluate and identify the best possible combination of parameters which would give the best performance of composite bonded joints.
•A new CE formulation is presented to model the response of adhesives in mode I.•The CE is enriched to account for the mechanical state of the adhesive and its viscoelasticity.•Good correlation is ...found when comparing with a hybrid approach.•This CE formulation allows to reduce greatly the computational effort.
This paper presents the formulation of an enriched cohesive element (CE) accounting for the confinement and the viscoelasticity of the adhesive layer under pure mode I solicitation. This formulation follows the structure of the hybrid approach, which combines the use of solid bulk elements (BEs) and CEs. This leads to define the enriched CE as a zero-thickness interface core embedded within two solid bulk adhesive regions. The interface is modelled with a spring whose stiffness is degraded by a damage variable. The bulk adhesive regions are modelled with a standard linear solid (SLS) model with one Maxwell arm. This formulation is implemented using the ABAQUS finite element (FE) software through a custom UMAT material routine, and applied to a single enriched CE as well as to a double cantilever beam (DCB) bonded joint. It is also evaluated numerically against the respective equivalent hybrid models.
Recently, fiber metal laminates (FMLs) have attracted considerable application in many industries due to their outstanding properties. FMLs are hybrid materials that are fabricated by adhesion of ...thin layers of metals and fiber-reinforced composites. It should be noted that the reinforcing mechanisms of nanoparticles on the polymeric composites have been well-established, but there is limited literature regarding the influence of nanoparticles on the mechanical behavior of FMLs and adhesively bonded joints (ABJs) between metal sheets and polymeric composites. To date, various nanofillers including carbon nanotubes, graphene nanoplatelets, clay nanoparticles and oxide nanoparticles have been used for improving the mechanical properties of FMLs, and ABJs. The performed studies revealed that the efficiency of nanoparticles in improving the properties of FMLs and ABJs mainly dependent on various factors such as surface treatment of metal sheets, type of nanoparticles, the morphology of nanoparticles, the size of samples, fabrication parameters, etc. However, the effects of parameters on the properties of FMLs and ABJs reinforced with nanoparticles have not considerably discussed in the literature. This review paper aims to review the existing related papers regarding the effects of nanoparticles on the mechanical properties of FMLs and ABJs in the term of adhesion between metal sheets and polymers.
The mechanical behavior of adhesively bonded plain-woven-composite (PWC) joints has been investigated using a multiscale modeling approach. Microscale and mesoscale representative volume elements ...(RVEs) have been constructed using the hierarchical architectures of PWCs. Based on the local homogenization of the mesoscale RVE model, an equivalent cross-ply laminate (ECPL) cell is developed to represent the woven architecture. It enables not only to accurately compute the effective properties of PWCs, but also to efficiently retain the local behavior within each ply. The macroscale models of single-lap joints (SLJs) and double-lap joints (DLJs) fabricated with PWCs, are constructed by topologically arraying the ECPL cells. Combined with continuum damage mechanics (CDM) and cohesive zone model, the mechanical behaviors are predicted for the SLJs and DLJs subjected to tensile loads. Moreover, experimental tensile tests have been performed on the corresponding SLJ structures, which confirm the reliability of the proposed multiscale models. A parametric study of the overlap length and width, as well as the bondline thickness has been numerically carried out to further analyze their effect on the joining performance. It reveals that, the dominant damage mechanisms mainly depend on the overlap length. When the overlap length is less than a critical value, the main damage mode is identified as the debonding of the bondlines. Otherwise, the delamination and matrix-tensile damages within the composite adherends are considered as the dominant damage modes.
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•A multiscale modeling approach is proposed for adhesively bonded PWC joints.•An ECPL cell is used to simplify the woven structure based on local homogenization.•The proposed approach is validated by tensile tests on different single-lap joints.•The effect on the joining performance is analyzed for various design parameters.•The damage mechanisms are identified for SLJs and DLJs using multiscale modeling.
A long-term study was conducted on double-lap spruce wood-concrete joints to investigate their shear strength and stiffness over a 12-month period. These joints were manufactured using both wet and ...dry processes, each incorporating two adhesive types for bonding the wood to the concrete: a brittle epoxy and a ductile polyurethane (PUR). The experimental design exposed the joints to three specific long-term environments: (1) outdoor exposure, (2) indoor conditions with applied load, and (3) outdoor conditions with applied load. The wood-concrete joints exposed to outdoor conditions were subjected to destructive shear testing at intervals of 0 (serving as the reference sample), 2, 4, 6, and 12 months, respectively. For joints subjected to both indoor and outdoor conditions with shear loading, the shear deformation of joints was monitored continuously over the 12 months before performing the destructive tests. A gradual reduction in the shear stiffness and strength of dry joints (produced using the dry bond method) exposed to outdoor conditions was observed over a 12-month period, primarily due to bond failure at the concrete-adhesive interface. The wet joints exhibited no degradation in shear stiffness and strength across long-term conditions over the same period. The bond failure observed in dry joints was predominantly associated with stresses arising from dimensional changes in the wood. No degradation was found in the cross-linking density of the adhesive or in the concrete's compressive stiffness and strength.
•Long-term durability study was performed on adhesive bonded timber-concrete composite joints.•Different long-term environmental conditions were considered and their effects were evaluated.•Wet bonded joints exhibited no degradation in shear stiffness and strength.
Progressive damage analysis (PDA) is used to explain experimentally observed differences in failure modes and levels of strength in sandwich panels joined with double lap adhesively bonded joints ...(ABJ). Experimental data indicates that nominally identical ABJ failed in different failure modes, including facesheet delamination, and a combination of facesheet delamination and doubler net section failure, with joint strengths ranging from 26.8 MPa to 33.3 MPa. A finite element model for the ABJ considers different possible failure modes in the multidirectional facesheet, woven doubler, honeycomb core, and adhesive. PDA predictions by a pristine model agree with the average experimental peak load, strain in the joint, and post-mortem damage states. Material defects are incorporated into an ABJ model that includes simulation of pre-existing matrix damage, local adhesive porosity, and uniform modification of adhesive properties. Analysis of the defect effects suggests existence of structure–property relationships that explain variability in ABJ behavior observed experimentally.
Compared with mechanical fastening, adhesive bonding offers numerous advantages in the joining of pultruded glass fiber reinforced polymer (GFRP) sections. However, one critical issue associated with ...bonded joints is the assessment of their mechanical behavior considering bondline defects. This paper presents the results of an experimental investigation of the damage tolerance of adhesively bonded pultruded GFRP joints considering bondline defects. Double-strap specimens with and without bondline defects were prepared and tested in tension until failure. The location (five different locations in the bond length and width directions), size (10%, 20%, and 30% of the total bonded area in both the bond length and width directions), shape (triangular, rectangular, square, circular, and elliptical), and number (between 1 and 8) of defects within the bondline were considered as variable parameters. This paper reports and discusses the observed failure modes, load–displacement curves, and joint capacities, considering the effects of bondline defects. Interface debonding was observed in regions neighboring the bondline defects, and delamination was observed in other bonded areas. All joints exhibited a linear elastic load–displacement response with sudden and brittle failure, regardless of the presence of bondline defects. The observed capacity reduction of up to 33% could be significant if the defects were located at the edges of the bonded area. Defects of different shapes resulted in similar reductions in joint capacity (21%). Furthermore, the joint was found to be more sensitive to irregularly shaped (e.g., triangular) defects, and reducing the number of defects was more effective in mitigating the reduction in joint capacity than reducing the total defect area was.
•Experimental study on manufacturing parameters of a bi-material bonded joint.•Tougher adhesive more likely results in adhesive or adherend failure.•Secondary and co-bonded specimen show different ...fracture due to surface treatment.•Surface treatment of composite plays key role in effect of manufacturing method.
In this paper, effects of adhesive, titanium surface roughness and manufacturing method on the fracture behaviors of composite-titanium adhesively bonded structures under mode Ⅰ loading were studied. Experimental results showed that the maximum GⅠc obtained from specimen bonded with tougher adhesive was approximately 276% higher than another adhesive. Higher flatwise tensile strength and roller peel strength of tougher adhesive resulted in stronger resistance for crack growth in tougher adhesive itself, leading to adhesive or adherend fracture mode. The titanium surface roughness only affected the fracture performance of specimen with cohesive fracture, and the GⅠc of specimen with higher surface roughness was improved by 20%. As for manufacturing method, due to the surface treatment of composite, the secondary and co-bonded specimen presented fiber pull-out and matrix failure, respectively. As a result, the lower fracture energy required for fiber pull-out failure resulted that the secondary bonded specimen present nearly 50% smaller GⅠc than co-bonded specimen. The findings can provide detailed reference for design of composite-titanium bonded structures.
The tension-tension fatigue behavior of ductile adhesively-bonded double-lap FRP joints was experimentally investigated. An acrylic adhesive, which was in the rubbery state at ambient temperature, ...provided the joint ductility. The fatigue degradation of the joints was characterized by the cyclic energy dissipation, cyclic stiffness, cyclic creep displacement and self-generated temperature. The effects of elevated temperature on the joints’ static tensile and pure creep behaviors were also investigated. All joints failed in the adhesive layer at almost the same failure displacement, independent of the loading history (static, creep, fatigue, and temperature loading) due to the stretching of the adhesive’s molecular chains until the primary bonds failed. Fatigue failure was driven by cyclic creep; the cyclic creep displacements were accelerated mainly by the damage caused by fatigue at high load levels and by the damage caused by creep and self-generated temperature at low load levels.
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