Adhesive Fracture Energy Research Articles

Regulation interfacial energy by reducing the Young’s modulus of perovskite film in carbon-based HTM free MAPbI3 perovskite solar cell

In ambient air, a long-chain dodecafluorosuberic acid (DFSA) with lower Young’s modulus was introduced to improve the mechanical compatibility of perovskite/carbon interface. Firstly, the carbonyl groups CO and F– in DFSA can passivate the intrinsic defects of perovskite, the DFSA effectively reduces the Young’s modulus of the perovskite and mitigates residual stress generated during perovskite annealing procedure. Most importantly, DFSA significantly enhances the Young’s modulus compatible degree between DFSA-CH3NH3PbI3 (DFSA-MAPbI3, 35.8 GPa) and carbon (6.3 GPa), alleviating the interfacial stress concentration. Based on quantitatively analysis, interfical crack driving energy (Gd) is reduced from 0.63 to 0.43 J m−2, while the adhesive fracture energy (Ga) is increased from 0.47 to 0.54 J m−2, which reduces the probability of crack propagation and ductile delamination, and is conducive to the extraction and transmission of photogenerated carrior. This was also verified in finite element simulations. Finally, the photoelectric conversion efficiency (PCE) of the organic-inorganic hybrid perovskite (MAPbI3) PSC device is improved from 10.27 % to optimal 14.12 %. After service at room temperature with relative humidity (RH) of 50–55 % and high temperature of 85 °C for 720 h, the original efficiency is maintained at 72 % and 89 %, respectively.

An enhanced surface treatment for effective bonding of 7075-T6 aluminium alloys

ABSTRACT This study research focuses on optimising adhesion through surface treatments on 7075-T6 aluminium alloy substrates using a chromium-free protocol. The treatment involves acetone degreasing, NaOH etching, and sulphuric acid-based solution etching. Wettability analysis and scanning electron microscopy were used to characterise the treated surfaces, highlighting the effectiveness of the proposed protocol. The proposed etching protocol was then applied to aluminium alloy substrates, and fracture surfaces corresponding to each treatment were compared. Mechanical testing, specifically double cantilever beam (DCB) experiments, assesses the fracture energy of bonded assemblies in mode I. The results demonstrate that the sulphuric acid-based treatment significantly improves the surface characteristics, leading to enhanced adhesion and optimal fracture energy in bonded aluminium assemblies.

Fracture energy and cohesive law analysis of adhesives using a recently developed SCB joint: The influence of joint geometry and mode mixity

In a prior study, the current authors proposed the utilization of semi-circular bend (SCB) specimens for analyzing the fracture energy of adhesive materials. However, similar to standard fracture test specimens, the geometry and size of the joint can impact the measured fracture energy when using SCB samples. Therefore, the objective of this research is to investigate the influence of adhesive layer thickness, substrate thickness, and disk radius of SCB specimens on cohesive law parameters and fracture energy of the adhesive. The study examines the fracture energy under different loading conditions, including pure mode I, pure mode II, and two mixed-mode conditions. By employing an inverse data reduction method, the cohesive law parameters of the tested adhesive are determined for various joint geometries. The results demonstrate that the disk radius does not affect the cohesive law of the joint. Furthermore, it is observed that bondline thicknesses of 0.2 mm and 0.4 mm lead to similar cohesive laws, whereas an adhesive thickness of 1 mm results in lower initial stiffness but higher fracture energy and damage initiation traction. Moreover, the study reveals that an increase in substrate thickness reduces the final fracture separation, indicating a more brittle fracture behavior. This can be attributed to a smaller fracture process zone caused by the plane strain load distribution in the adhesive layer.

Inverse estimation of mode I fracture energies for structural adhesives from impact wedge peel tests

This work presents a practical approach to estimate mode I fracture energy of structural adhesives at high strain rates from impact wedge peel (IWP) tests. For this purpose, an inverse estimation approach is used which requires relevant input quantities for the associated IWP simulations, e.g., primarily the dynamic friction coefficient between the wedge and the fractured adhesive and the adhesive strength. We describe two new impact-pendulum-based test devices to measure these unknown parameters. These parameters serve as input for the IWP simulation from which the remaining unknown fracture energy of the structural adhesive is estimated by an efficient regression scheme. An uncertainty quantification approach is used to approximate the statistical deviation of the generated material parameters based on the deviation of the measured input parameters. Experimental IWP test results are matched to IWP simulation results for three different substrates. The entire workflow is tested and validated for two different structural adhesives.

Strengthened Interficial Adhesive Fracture Energy by Young's Modulus Matching Degree Strategy in Carbon-Based HTM Free MAPbI3 Perovskite Solar Cell with Enhanced Mechanical Compatibility.

Carbon-based hole transport layer-free perovskite solar cells (PSCs) based on methylammonium lead triiodide (MAPbI3 ) have become one of the research focus due to low cost, easy preparation, and good optoelectronic properties. However, instability of perovskite under vacancy defects and stress-strain makes it difficult to achieve high-efficiency and stable power output. Here, a soft-structured long-chain 2D pentanamine iodide (abbreviated as "PI") is used to improve perovskite quality and interfacial mechanical compatibility. PI containing CH3 (CH2 )4 NH3 + and I- ions not only passivate defects at grain boundaries, but also effectively alleviate residual stress during high temperature annealing via decreasing Young's modulus of perovskite film. Most importantly, PI effectively increases matching degree of Young's modulus between MAPbI3 (47.1GPa) and carbon (6.7GPa), and strengthens adhesive fracture energy (Gc ) between perovskite and carbon, which is helpful for outward release of nascent interfacial stress generated under service conditions. Consequently, photoelectric conversion efficiency (PCE) of optimal device is enhanced from 10.85% to 13.76% and operational stability is also significantly improved. 83.1% output is maintained after aging for 720h at room temperature and 25-60% relative humidity (RH). This strategy of regulation from chemistry and physics provides a strategy for efficient and stable carbon-based PSCs.

Characterizing the Adhesion Between Thin Films and Rigid Substrates Using Digital Image Correlation-Informed Inverse Finite Elements and the Blister Test

Abstract Characterizing the adhesion between thin films and rigid substrates is crucial in engineering applications. Still, existing standard methods suffer from issues such as poor reproducibility, difficulties in quantifying adhesion parameters, or overestimation of adhesion strength and fracture energy. Recent studies have shown that the blister test (BT) is a superior method for characterizing adhesion, as it provides a quantifiable measurement of mix-mode fracture energy, and it is highly reproducible. In this paper, we present a novel method to characterize mechanical mix-mode adhesion between thin films and rigid substrates using the BT. Our method combines the full triaxial displacement field obtained through digital image correlation with inverse finite element method simulations using cohesive zone elements. This approach eliminates the need for making any mechanistic or kinematic assumptions of the blister formation and allows the characterization of the full traction-separation law governing the adhesion between the film and the substrate. To demonstrate the efficacy of this methodology, we conducted a case study analyzing the adhesion mechanics of a polymeric pressure-sensitive adhesive on an aluminum substrate. Our results indicate that the proposed technique is a reliable and effective method for characterizing the mix-mode traction-separation law governing the mechanical behavior of the adhesive interface and could have broad applications in the field of materials science and engineering. Also, by providing a comprehensive understanding of the adhesion mechanics between thin films and rigid substrates, our method can aid in the design and optimization of adhesively bonded structures.

A new technique to measure shear fracture toughness of adhesives using tensile load

The end notched flexure (ENF) test is the most common method for measuring the mode II fracture energy of adhesives which provides reliable results but has some inherent problems. The shear fracture energy calculated using ENF for brittle adhesives is often based on a single data point (corresponding to the fracture load) obtained from the test where the crack grows catastrophically and the results are significantly sensitive to pre-crack tip conditions. The aim of the current study is to introduce a new pure mode II fracture test suitable for measuring the shear fracture energy of adhesives. A new technique for measuring the mode II critical strain energy release rate (SERR) of brittle adhesives is proposed based on the central cut ply (CCP) configuration. Fracture tests were carried out on adhesively bonded steel CCP specimens. It is shown that the crack growth in CCP joints is more stable, and the failure develops in multiple steps that generates more experimental data point during the crack propagation. The mode II fracture energy of a brittle epoxy-based adhesive is extracted using CCP method and is compared with the shear fracture energy obtained from the ENF tests. The effect of adhesive thickness on the obtained fracture energies is also analyzed. The CCP technique can be used to find both the crack initiation and crack propagation toughness values whereas the ENF method only provides the crack initiation fracture energy.

Influence of Date Palm Tree Fibers on the Tensile Fracture Energy of an Epoxy-based Adhesive

ABSTRACT In the previous study, the effect of date palm fibers on the shear strength of adhesively bonded joints has been investigated by the same authors. Nevertheless, the role of these bio-based fibers on the fracture energy of adhesives has not been explored. The current study was conducted to comprehend the influences of date palm fibers on mode I fracture energy (GIc ) of adhesives. To this aim, the fibers were collected from four different parts of a date palm tree (Bunch, Rachis, Petiole, and Mesh). After an alkalization treatment, they were cut into 0.5 to 2 mm and added to the adhesive in three various weight ratios (2, 5, and 10%). The fracture energy of the neat and reinforced adhesively bonded double cantilever beam (DCB) was then experimentally analyzed utilizing a compliance-based method. The outcomes prove the outstanding potential of the date palm fibers in enhancing the tensile fracture energy of adhesives. The highest improvement in GIc was achieved by 10 wt% Rachis fibers where the fracture energy of the enhanced adhesive was 7.6 times higher than the neat adhesive. The microscopic images of fracture surfaces revealed the significant roles of the considered fibers in the improvement of the GIc of the adhesive.

Measurement and FEM of ice adhesion to the downstream pipe of an air cycle machine

Ice accretion on the downstream pipe of an air cycle machine can lead to pipe blockage and turbine blade damage, and therefore de-icing is needed. Most previous studies focused on ice shedding from flat surfaces, and average interface shear strength rather than the true shear strength was usually reported. Here, the debonding of the interface between ice and cylindric surfaces of an aluminium pipe (2024-T3) was studied trying to understand the mechanism of interface fracture and to obtain the true adhesive shear strength and fracture energy. Average adhesive strength was measured first in the scrape test and the result was used to calibrate the finite element analysis. A cohesive zone model (CZM) with bilinear traction-separation law was used to simulate the interface delamination. The true shear strength σcs and mode-II energy release rate Gcs were determined by matching the numerically predicted critical force to the measured force. The influence of shear strength and shear energy release rate on the critical force was also investigated. At the interface, both the damage factor and the peak shear stress were found progressing away from the edge as the pushing force increased. Parametric studies on the influence of the length of the interface was performed. The critical force first increased and then stabilised with the increase of the length, showing the same trend as that of a theoretical model which ignored the mode-I fracture.

Effect of temperature and loading rate on the mode I fracture energy of structural acrylic adhesives

Understanding the changes in the adhesive properties with the temperature and loading rate is important, particularly for designing adhesively bonded joints in structural applications. The viscoelastic behavior of adhesives is widely known to be based on the time–temperature superposition principle. In the case of the elastoplastic behavior, the stress–strain relationship is significantly affected by the external conditions, particularly for ductile adhesives. Similarly, the fracture behavior is expected to exhibit a temperature–loading rate dependence; however, few studies have focused on them, especially for structural acrylic adhesives.In this study, the impact of the temperature and test speed on the fracture energy of structural acrylic adhesives was investigated. Bulk tensile tests and double cantilever beam (DCB) tests were performed at different temperatures and test speeds. Bulk behavior showed an increase in the maximum stress and a decrease in the elongation at lower temperatures and higher loading rates. Conversely, the fracture toughness increased with a combination of higher temperatures and loading rates when the crack stably propagated. The mode I fracture energies of the test speed of 500 mm/min at 60°C increased by approximately 1.5–2 times that of 0.05 mm/min at room temperature. In addition, stick-slip crack propagation was observed at lower temperatures or higher loading rates.

Effects of core–shell and reactive liquid rubbers incorporation on practical adhesion and fracture energy of epoxy adhesives

Effects of core–shell and reactive liquid rubbers incorporation on practical adhesion and fracture energy of epoxy adhesives

Influence of Manufacturing Process in Structural Health Monitoring and Mechanical Behaviour of CNT Reinforced CFRP and Ti6Al4V Multi-Material Joints.

Co-cured multi-material metal–polymer composites joints are recent interesting structural materials for locally reinforcing a structure in specific areas of high structural requirements, in fibre metal laminates and lightweight high-performance structures. The influence of manufacturing processes on the morphological quality and their mechanical behaviour has been analysed on joints constituted by sol-gel treated Ti6Al4V and carbon fibre reinforced composites (CFRP). In addition, carbon nanotubes (CNT) have been added to an epoxy matrix to develop multiscale CNT reinforced CFRP, increasing their electrical conductivity and allowing their structural health monitoring (SHM). Mechanical behaviour of manufactured multi-material joints is analysed by the measurement of lap shear strength (LSS) and Mode I adhesive fracture energy (GIC) using double cantilever beam specimens (DCB). It has been proven that the addition of MWCNT improves the conductivity of the multi-material joints, even including surface treatment with sol-gel, allowing structural health monitoring (SHM). Moreover, it has been proven that the manufacturing process affects the polymer interface thickness and the porosity, which strongly influence the mechanical and SHM behaviour. On the one hand, the increase in the adhesive layer thickness leads to a great improvement in mode I fracture energy. On the other hand, a lower interface thickness enhances the SHM sensibility due to the proximity between MWCNT and layers of conductive substrates, carbon woven and titanium alloy.

Effect of creep on the mode II residual fracture energy of adhesives

AbstractViscous flow that often occurs in adhesive materials leads to a permanent deformation when adhesives are subjected to creep loading. Creep loading has a significant influence on the strength of bonded structures. Due to the viscous behavior, the fracture energy also may change with time for joints that experience creep loading in service. In this work the effects of two creep parameters (creep load and time) on the residual mode II fracture energy of an adhesive was investigated using end notched flexure (ENF) specimens. To achieve this, ENF samples were subjected to different creep loading levels at different creep times followed by quasi static tests to obtain the residual shear fracture energy of the adhesive. Experimental results showed that pre‐creep loading of the bonded structures can significantly improve the fracture energy and the static strength of the joints.

A Compact Icing Research Tunnel for Ice Adhesion Characterization

A compact icing facility is developed to allow the measurement of ice adhesion tensile stress and fracture energy of aerospace impact ice, in coordination with thermal measurements, to ensure a well-characterized thermal environment. The facility was 1.5 m wide, 1.5 m long, and 2.1 m tall, and the tunnel is equipped with a single MOD-1 spray nozzle to produce a cloud of supercooled droplets at the targeted mean volumetric diameter for a liquid water content range from 2 to . The compact icing research tunnel (CIRT) was used to generate ice accretion on an aluminum test specimen, which was then measured to determine the ice tensile adhesion strength for two conditions: impact ice and static ice. The static ice was made by freezing motionless deionized water on the aluminum test specimen, whereas impact ice was obtained as a result of water droplets freezing after impacting the specimen at the velocity of about , with air and surface temperature both at . It was found that the substrate temperature increased significantly through the accretion process, to about 5°C for static ice and 7°C for impact ice (where the latter includes a significant increase in humidity).

Measuring fracture energy of interfaces under mode I loading with the wedge driven test

The wedge driven test is a valuable tool to determine the mode I fracture energy (GIc) of adhesives or interfaces in composites. At first glance, the test is simple enough (introduction of a wedge into the specimen midplane to progagate a crack) to be a good alternative to the standard method, the DCB test. However, friction between the wedge and the specimen’s arms is not properly dealt in existing studies and, consequently, there is still a need for a reliable test procedure. In this work, we present a test methodology and its associated data reduction procedure to obtain GIc. The test does not need to measure the crack length and the friction coefficient is determined as the wedge is introduced in between the specimen’s arms. The new testing methodology is validated experimentally comparing the GIc obtained from the wedge driven and the DCB tests. A very close agreement is obtained between them.

Mixed mode I/III fracture behavior of adhesive joints

In this paper, the mixed mode (I/III) fracture behavior of an epoxy based adhesive is investigated using a modified mixed mode I/III apparatus. The fracture tests are performed on adhesively bonded aluminum rectangular specimens with different adhesive thicknesses. Based on the obtained experimental data, the critical stress intensity factors (SIFs) of the adhesive are calculated by performing a 3D finite element analysis (FEA). Then, the fracture energy of modes I and III of the adhesive were extracted using SIFs. To verify the obtained fracture energy, an extended finite element model (XFEM) was employed. The obtained numerical results were in good agreement with the experimental data. It shows that the proposed apparatus can be applied for measuring the mixed mode I/III fracture energy of brittle or semi brittle adhesives where a small scale yielding around the crack tip is observed. The crack propagation path was also analyzed and the out-of-plane angle of crack propagation in the adhesive layer was estimated using XFEM. By comparing the experimental fracture surfaces with the crack propagation path obtained out of the numerical results, it is observed that the XFEM can provide an appropriate estimation of the crack propagation path in adhesive joints under mixed I/III loading.

Graphite modified epoxy-based adhesive for joining of aluminium and PP/graphite composites

ABSTRACTA graphite-modified adhesive was developed in order to simultaneously enhance the thermal conductivity and the strength of an adhesive joint. The thermal conductivity through the joint was investigated by using highly filled PP/graphite composite substrates, which were joined with an epoxy adhesive of different layer thicknesses. Similar measurements were carried out with a constant adhesive layer thickness, whilst applying an epoxy adhesive modified with expanded graphite (EG) (6, 10, and 20 wt%). By reducing the adhesive layer thickness or modifying the adhesive with conductive fillers, a significant increase of the thermal conductivity through the joint was achieved. The examination of the mechanical properties of the modified adhesives was carried out by tensile tests (adhesive only), lap-shear tests, and fracture energy tests (mode 1) with aluminium substrates. Modification of the adhesive with EG led to an increase of the tensile lap-shear strength and the adhesive fracture energy (mode 1) of the joint. In addition, burst pressure tests were performed to determine the strength of the joint in a complex component. The strength of the joint increased with the graphite content in the PP substrate and in the epoxy adhesive.

Multiphysics analysis of backsheet blistering in photovoltaic modules

Backsheet blistering in photovoltaic modules is frequently reported but not yet thoroughly described. Visual inspection only identifies the presence of bubbles, while physical mechanisms leading to their occurrence need further theoretical investigation. To evaluate the effect of external (temperature, humidity) and internal (manufacturing defects) causes of blistering, we propose a semi-analytic model to describe this phenomenon in poly(ethylene-co-vinyl acetate)-based modules. The blistering occurrence is triggered by pressure exerted by partially vaporized moisture in existing defects. Vapor pressure in such defects, originated during module manufacturing, is related to moisture concentration profiles, governed by external conditions. Moisture also affects the adhesive fracture energy which plays a fundamental role in blistering activation. The proposed model predicts the critical pressure and the critical size of the initial defects causing blistering. This work represents an important step for the long-term reliability prediction of photovoltaic modules.

Effect of notch length and pre-crack size on mode II fracture energy of brittle adhesives

In this study, the effects of notch length and pre-crack size on mode II fracture energy of brittle adhesives are investigated. These effects are not considered by the direct beam theory (DBT) and the compliance-based beam method (CBBM) for the end-notched flexure (ENF) specimens. The sum of the lengths of the notch and the pre-crack are known as the pre-crack size in common data reduction schemes. In the current work, experiments were performed on ENF adhesive joints using digital image correlation (DIC) technique. Then, the fracture energy was obtained experimentally based on the J-integral method, the classic beam theory, and the compliance-based beam method. Numerical analyses were carried out to measure the stress distribution ahead of the pre-crack tip. Based on the obtained results, it is shown that there is a specific pre-crack length and notch size in which the pure mode II condition in an ENF test is obtained. Other combinations of the notch to pre-crake size ratio result in mixed mode conditions where the obtained fracture energy significantly changes.

The role of T-stress and stress triaxiality combined with the geometry on tensile fracture energy of brittle adhesives

In this study, a new semi-empirical evaluation method is proposed to take into account the effects of substrate stiffness and bondline thickness on the tensile fracture behavior of brittle adhesives. To this end, combined experimental-numerical analyses are conducted on double cantilever beams with various geometries. Two different data reduction approaches including the simple beam theory and the J-integral technique are employed to obtain the fracture energy of the tested joints. The experimental fracture energy and the corresponding numerical results are used to analyze the considered configurations based on the proposed relation. The new parameter is a function of the tensile fracture energy (GIC), the first non-singular stress term of William's series expansion (T-stress), the amount of stress triaxiality and the bondline thickness (t). Based on the proposed method, the role of each factor in the mode I fracture energy of brittle systems is specified. It is found that the T-stress has a critical impact on the GIC obtained by adhesively bonded double cantilever beams (DCBs) where the adhesive bondline is different. It is also shown that the effect of stress triaxiality is less significant but it should be taken into account. The results also show that the new relation can predict the effect of the substrate stiffness on the GIC of the considered adhesives very well. The optimum bondline thickness of DCBs corresponding to the maximum GIC is also predicted based on the proposed relation. Further validations are also performed by applying the method to experimental data previously published in the literature.