Peel Angles Research Articles

ON THE AFFERRANTE-CARBONE THEORY OF ULTRATOUGH TAPE PEELING

In a simple and interesting theory of ultratough peeling of an elastic tape from a viscoelastic substrate, Afferrante and Carbone find that there are conditions for which the load for steady state peeling could be arbitrarily large in steady state peeling, at low angles of peeling - what they call "ultratough" peeling (Afferrante, L., Carbone, G., 2016, The ultratough peeling of elastic tapes from viscoelastic substrates, Journal of the Mechanics and Physics of Solids, 96, pp.223-234). Surprisingly, this seems to lead to toughness enhancement higher than the limit value observed in a very large crack in an infinite viscoelastic body, possibly even considering a limit on the stress transmitted. The Afferrante-Carbone theory seems to be a quite approximate, qualitative theory and many aspects and features of this "ultratough" peeling (e.g. conformity with the Rivlin result at low peel angles) are obtained also through other mechanisms (Begley, M.R., Collino, R.R., Israelachvili, J.N., McMeeking, R.M., 2013, Peeling of a tape with large deformations and frictional sliding, Journal of the Mechanics and Physics of Solids, 61(5), pp. 1265-1279) although not at “critical velocities”. Experimental and/or numerical verification would be most useful.

Effects of prolonged saline water exposure on the peel strength of polyurea/monel 400 interface

ABSTRACT This study investigates changes in the peel strength of polyurea/monel 400 interfaces after prolonged exposure to saline water. The monel family of alloys is extensively used on marine structures due to its resistance to corrosion, and polyurea has shown considerable promise as a coating material for marine structures to mitigate the damage from blast loading and provide corrosion resistance. In the present work, polyurea was cast on sandblasted and chemically treated Monel 400 bars, which were subsequently immersed in saline water at 70°C for 2, 5 and 8 weeks, respectively, to accelerate the aging process. This high-temperature exposure corresponded to 19, 48 and 76 weeks in the real-life service environment. The peel strengths of the interfaces were measured using the fixed arm peel test at two angles: 90° and 180°. The adhesive energy was computed from the experimentally determined peel strength using models developed by Kendall and Rivlin. The surfaces exposed by peeling were analyzed with the use of an optical microscope to determine the different failure modes at the interfaces. Finally, employing degradation kinetics, a degradation model was established and used to calculate long-term adhesive energy and the degradation rate of the interface. Results showed that prolonged exposure to saline water leads to a drop in the peel strength. For 180° peel test, an 83% decrease in the peel strength of the polyurea/monel 400 interface was observed after 8 weeks of exposure at 70°C. Both peel angles gave similar adhesive energies for the same exposure durations indicating the independence of the adhesive energy on the testing angle. The elastic term contribution to the adhesive energy for all experiments was less than 5.5%. Lastly, the exposure time dependence on the adhesive energy followed first-order degradation kinetics.

Development of miniaturized peel experiments to quantify interfacial adhesion between 2D monolayers and viscoelastic polymers

ABSTRACT In this work, a miniaturized peel-testing setup capable of performing peel tests for viscoelastic polymer strips attached to rigid substrate at different peel rates (20 nm/s–20 µm/s) and at constant peel angles (45°–135°) was developed. A mathematical framework accounting for competition between the delamination from rigid substrate as well as bending and extension of the peel arm during the peel test was employed for modeling the viscoelastic response of the soft polymeric strips attached to a rigid substrate. The efficacy of the novel miniaturized peel-testing setup was evaluated for linear elastic and viscoelastic peel arms attached to rigid substrates. The adhesion measurements for the linear elastic peel arms were found to be insensitive to peel angles and the values were in great agreement with standardized macroscale adhesion measurements for the same interface. The peel tests revealed that the interfacial adhesion measurements for the viscoelastic PDMS peel arms were highly sensitive to the nominal peel rates. An elaborate specimen fabrication process was developed to evaluate the interfacial adhesion between large area 2D materials and soft polymer substrates. A series of peel-testing experiments were performed to ensure that the developed fabrication process does not adverse effects on the interfacial adhesion measurements. The peel-testing methodology was then employed to quantify the interfacial adhesion between graphene monolayers and PDMS substrates. Due to the weak van der Waals interactions associated with the graphene/PDMS interface, the interfacial adhesion measurements for this interface was significantly lower than the adhesion values for a PDMS/PDMS interface.

Peeling of metal foil from a compliant substrate

ABSTRACT Large displacement peel was studied for cases where a compliant substrate leads to a large value of the root rotation. An existing simplified beam model to calculate the peel fracture energy was modified to allow for a kinematic hardening beam model of the foil. The steady-state peel force and the root rotation were used as input data to the resulting analytical beam model. Test results from the literature were analysed. A more elaborate finite element model was also studied, using cohesive elements for the interface layer between the foil and the substrate. The cohesive zone parameters used were the fracture energy, the cohesive strength and a shape parameter. An optimization scheme for the cohesive zone parameters was developed and optimized against experimental steady-state peel force and root rotation. The optimization scheme was effective to characterize the cohesive parameters. The method yields similar values of fracture energy for the two peel angles, with the one for being slightly higher than for . The difference in fracture energies for different peel angles suggests that the fracture energy can be mode dependent.

Unsteady peeling accompanied by oscillations of adhesive tape from a soft adherend.

Peel angle dependence of the peel force was investigated using cross-linked polydimethylsiloxane (PDMS) covered with a pressure-sensitive adhesive tape. In our previous report, the peeling behavior at peel angles below 90° was discussed. The study revealed that an unsteady peeling occurs due to the extreme effects of the shear force on the adhered portion of the tape before the peeling starts. In this paper, we studied the peeling behavior and unsteady peeling accompanied by oscillations at peel angles higher than 90°, which is different from unsteady peeling at peel angles lower than 90°. The appearance of unsteady peeling accompanied by oscillations depended on the experimental conditions and material properties. Specifically, unsteady peeling was observed when the peel velocity, peel angle, and the thickness of PDMS were increased. Additionally, a decrease in the degree of cross-linking in PDMS also resulted in unsteady peeling. The periodic length of the oscillation was obtained from the peel force curves, which depended on the thickness and elasticity of the adherend. This unsteady peeling resulted from the large deformation of the adherend and the buckling of the tape due to the shear and compressive forces. In this paper, the mechanism of unsteady peeling was discussed on the basis of the classical models of mechanics.

Spring Contact Model of Tape Peeling: A Combination of the Peel-Zone Approach and the Kendall Approach

Energy-based and force-based approaches are two basic ways to establish an adhesion model. For the adhesion of tape-like thin films, the Kendall equation considers the overall energy balance but inherently contains little information of the peel zone geometry and stress distribution. The peel zone model provides an empirical approximate of the peel front from the approach of a force description and coincides well with experimental results for a wide range of peel angles. However, the peel-zone model itself has not been unified with the Kendall equation yet. We propose a two-layer spring contact tape peeling model which considers the balance between the stretching force of the backing layer and the adhesive force transferred through the adhesive layer. The model provides an analytic shape description of the curved bifurcation region of the peel front. An approximate analytic solution of the peel force reduces to the Kendall equation by considering a Kendall-like energy conservation critical criterion, which further supports the proposed model. Further analysis of the relationship between the length of the peel zone and the adhesive force provides insight into the validity of the peel zone model. The proposed model provides a new insight in the tape peeling process and mathematically builds a potential bridge between the Kendall model and the peel-zone model.

Interface strength analysis of the corrugated anode-electrolyte interface in solid oxide fuel cell characterized by peel force

The interface delamination will directly lead to mechanical failure of solid oxide fuel cells (SOFCs), so improving interface strength is essential to ensure the stability of cell. A novel fundamental theoretical model for half-cell of corrugated SOFC is employed to analyze the interface strength of corrugated anode-electrolyte interface of which interfacial morphology is characterized by parabolic function. Based on potential energy principle and first variation theory of half-cell system, the analytical solution of peel force under different peel angles is derived and agrees well with the previous research result. The results show that introducing the corrugated interface can improve the interface strength. The extreme values of peel force described by parabolic function are compared with that by sinusoidal function under different peel angles. The ultimate peel strength and allowable peel strength corresponding to two shape functions are preferable in different ranges of amplitude-wavelength ratio. In addition, the corresponding peel angle and amplitude-wavelength ratio are also determined and discussed for when peel angle is less than inclination angle of corrugated film. The research provides guidance for optimizing the interfacial morphology and enhancing the interface strength.

Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

Many arthropods and small vertebrates use adhesive pads for climbing. These biological adhesives have to meet conflicting demands: attachment must be strong and reliable, yet detachment should be fast and effortless. Climbing animals can rapidly and reversibly control their pads' adhesive strength by shear forces, but the mechanisms underlying this coupling have remained unclear. Here, we show that adhesive forces of stick insect pads closely followed the predictions from tape peeling models when shear forces were small, but strongly exceeded them when shear forces were large, resulting in an approximately linear increase of adhesion with friction. Adhesion sharply increased at peel angles less than ca 30°, allowing a rapid switch between attachment and detachment. The departure from classic peeling theory coincided with the appearance of pad sliding, which dramatically increased the peel force via a combination of two mechanisms. First, partial sliding pre-stretched the pads, so that they were effectively stiffer upon detachment and peeled increasingly like inextensible tape. Second, pad sliding reduces the thickness of the fluid layer in the contact zone, thereby increasing the stress levels required for peeling. In combination, these effects can explain the coupling between adhesion and friction that is fundamental to adhesion control across all climbing animals. Our results highlight that control of adhesion is not solely achieved by direction-dependence and morphological anisotropy, suggesting promising new routes for the development of controllable bio-inspired adhesives.

Modeling the effect of rate and geometry on peeling and tack of pressure-sensitive adhesives

A model is developed for predicting separation along interfaces of pressure sensitive adhesives. Many authors have used the cohesive zone approach to solve such problems but the parameter calibration of such models remains uncertain. This study reports a novel method for determining such parameters. In addition, it provides crucial evidence for the suitability of the cohesive zone model approach in modelling interface fractures.Peel tests were performed at various rates using specimens which consisted of a polyester backing membrane supporting an acrylic pressure-sensitive adhesive (PSA) adhered to a polyethylene substrate. Interfacial separation of the PSA from the polyethylene substrate was observed. Finite element (FE) peeling simulations were conducted which modeled the backing-membrane as an elasto-plastic power-law material, the adhesive as a viscoelastic material and the interfacial properties with a cohesive zone model (CZM). The material properties of the backing membrane and the pressure-sensitive adhesive were measured from tensile and stress relaxation experiments. The rate-dependent CZM parameters were measured directly from poker-chip probe-tack tests which were performed at pull-off speeds which corresponded to the rates employed for the peel tests. The effect of the PSA thickness and test rate on both tack and peel was investigated experimentally, as well as modeled numerically. Good agreement was found between the experimentally measured and numerically predicted peel forces for different peel angles, speeds and PSA thicknesses. In addition, it was proven that the rate dependence observed in the peel and probe-tack data was dominated by the rate dependence of the interface properties, i.e. the time dependence of the two CZM parameters of maximum stress and fracture energy, rather than the time-dependent bulk viscoelasticity of the PSA peel arm.

Peeling condition analysis of biomimetic adhesive structure – a finite element study

Gecko and many insects have nanoscale fibrillary structures on their feet serving as adhesive devices. In recent years, van der Waals interaction has been proven to be the primary molecular origin for this kind of phenomena. However, the peeling zone and the cohesive zone both play significant roles in the peeling process while the peeling zone can be described by van der Waals force and the cohesive zone is dependent of molecular interaction. In this reported work, the case of peeling of two elastic bodies, in which the pull-off force depends linearly on the cohesive stress and is independent of the work of adhesion is considered. The adhesion interaction and peeling condition between a single biomimetic adhesive structure and a substrate is simulated as an axisymmetric geometries model, by encoding van der Waals force and molecular interaction in COMSOL software. The simulation takes theoretical fundamental equations as inputs, and by varying relative peel angles, functional variables are built to estimate peeling processes of the biomimetic adhesive structure in various conditions. The results show that the maximum pull-off force of the structure with different materials and pull-off force is decreasing in the peeling process but the cohesive force immediately raises while the contact area becomes smaller. Stress concentration occurs both on the top and at the base of the structure during the peeling process. The simulation results demonstrate that an optimal shape of the adhesive structure can be achieved by examining the simulated pull-off forces. To avoid failure occurring during the peeling process, the structure with a large base can decrease the stress concentrate at the bottom. Based on the analysis, the adhesive structure with an optimised half-hourglass shape is proposed.

Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

To live and clamber about in an arboreal habitat, tree frogs have evolved adhesive pads on their toes. In addition, they often have long and slender legs to facilitate not only long jumps, but also to bridge gaps between leaves when climbing. Both adhesive pads and long limbs are used in conjunction, as we will show in this study. Previous research has shown that tree frogs change from a crouched posture (where the limbs are close to the body) to a sprawled posture with extended limbs when clinging on to steeper inclines such as vertical or overhanging slopes. We investigated this change in posture in White's tree frogs (Litoria caerulea) by challenging the frogs to cling onto a tiltable platform. The platform consisted of an array of 24 three-dimensional force transducers, which allowed us to measure the ground reaction forces of the frogs during a tilt. Starting from a crouched resting position, the normal forces on the forelimbs changed sign and became increasingly negative with increasing slope angle of the platform. At about 106° ± 12°, tilt of the platform the frogs reacted by extending one or two of their limbs outwards. At a steeper angle (131° ± 11°), the frogs spread out all their limbs sideways, with the hindlimbs stretched out to their maximum reach. Although the extension was strongest in the lateral direction, limbs were significantly extended in the fore-aft direction as well. With the extension of the limbs, the lateral forces increased relative to the normal forces. The large contribution of the in-plane forces helped to keep the angle between the force vector and the platform small. The Kendall theory for the peeling of adhesive tape predicts that smaller peel angles lead to higher attachment forces. We compare our data with the predictions of the Kendall model and discuss possible implications of the sliding of the pads on the surface. The forces were indeed much larger for smaller angles and thus can be explained by peeling theory.

The Extended Peel Zone Model: Effect of Peeling Velocity

According to the peel zone model proposed by Pesika et al. [8], the peel strength of an adhesive tape is proportional to the length of the peel zone or the bifurcation region at the peeling front between the tape backing and the substrate. In this study, the effects of the peel angle and peel velocity on the shape of the peel zone and the peel strength are further investigated theoretically and experimentally. The theoretical analysis on the angle at the edge of the peel zone, θ0, and the peel strengths at different peel velocities and angles was compared with experimental tests using three different commercial tapes. The experimental results are in good agreement with the extended peel zone model, which provides a simple approach to predict the peel strength of adhesive tapes with different physical properties at different peel angles and velocities.

フィルムドレッシング材の適切な剥離方法に関する検討

The application of film-dressings to the skin rarely causes dermal irritation. It is important to reduce the damage of the skin when they are removed from the skin. Several methods of removing film-dressings have been recommended. However, only the peel angle has been studied. Therefore, we examined the best method of removing film-dressings by studying the peel rate, peel angle, and the effect of draw, in which the skin was drawn by hand in the opposite direction in order to keep the film-dressing in a stationary position, using two kinds of film-dressings.With an increase in peel rate, the number of stripped corneocytes significantly increased. The number of stripped corneocytes and the pain at 0 degree peel angle (i.e., removal by stretching the film-dressing parallel to the skin) were slightly less than those at other peel angles. When the skin was drawn by hand in order to keep the film-dressing in a stationary position, the pain decreased slightly. It was most important that film-dressings were removed from the skin as slowly as possible.

Determination of interfacial mechanical parameters for an Al/Epoxy/Al 2o 3 system by using peel test simulations

Peel test measurements and simulations of the interfacial mechanical parameters for the Al/Epoxy/Al2O3 system are performed in the present investigation. A series of Al film thicknesses between 20 and 250 microns and three peel angles of 90, 135 and 180 degrees are considered. Two types of epoxy adhesives are adopted to obtain both strong and weak interface adhesions. A finite element model with cohesive zone elements is used to identify the interfacial parameters and simulate the peel test process. By simulating and recording normal stress near the crack tip, the separation strength is obtained. Furthermore, the cohesive energy is identified by comparing the simulated steady-state peel force and the experimental result. It is found from the research that both the cohesive energy and the separation strength can be taken as the intrinsic interfacial parameters which are dependent on the thickness of the adhesive layer and independent of the film thickness and peel angle.

Determination of interfacial properties between metal film and ceramic substrate with an adhesive layer

Peel test measurements and inverse analysis to determine the interfacial mechanical parameters for the metal film/ceramic system are performed, considering that there exist an epoxy interface layer between film and ceramic. In the present investigation, Al films with a series of thicknesses between 20 and 250 μm and three peel angles of 90, 135 and 180° are considered. A finite element model with the cohesive zone elements is used to simulate the peel test process. The finite element results are taken as the training data of a neural network in the inverse analysis. The interfacial cohesive energy and the separation strength can be determined based on the inverse analysis and peel experimental result.

Inverse analysis determining interfacial properties between metal film and ceramic substrate with an adhesive layer

In the present study, peel tests and inverse analysis were performed to determine the interfacial mechanical parameters for the metal film/ceramic system with an epoxy interface layer between film and ceramic. Al films with a series of thicknesses between 20 and 250 mu m and three peel angles of 90 degrees, 135 degrees and 180 degrees were considered. A finite element model with the cohesive zone elements was used to simulate the peeling process. The finite element results were taken as the training data of a neural network in the inverse analysis. The interfacial cohesive energy and the separation strength can be determined based on the inverse analysis and peel experimental result.

Peel Behaviour of Aircraft Fuel Tank Sealants: the Effect of Peel Angle, Sealant Layer Thickness and Peel Rate

The peel performance of two aircraft fuel tank sealants was comprehensively investigated by means of a modified peel specimen previously developed. Experiments were carried out at five different peel angles in the range from 90 to 180° using seven sealant layer thicknesses in the range from 0.1 to 5 mm. The effect of the peel rate was also investigated at a fixed peel angle and sealant layer thickness. The results were analysed in terms of the peel energy. Both peel angle and sealant layer thickness were found to affect significantly the measured peel energy of the sealants in a coupled way. In particular, it was found that the peel energy increased linearly with the sealant layer thickness, for the range considered in this study, and the rate of this increase was also found to increase as the peel angle was varied from 90 to 180°. For very small sealant layer thicknesses (0.1 mm) there was no effect of the peel angle on the measured peel energy. The results were explained in terms of the amount of energy these materials dissipated upon deformation up to fracture and a relationship for the prediction of the peel energy was proposed. The peel rate was found to affect only slightly the measured peel energy, in the range studied.

Peel of an adhesive tape from a temperature-gradient surface

The peel force of a pressure sensitive adhesive (PSA) tape is measured on a surface that varied linearly in temperature. As the tape is peeled from the surface, the adhesive is peeled from the surface at a different temperature. Since the peel force varies with temperature, the measurement allows the temperature dependence of the peel force to be determined with one peel test. By this method, the temperature of the transition from cohesive to interfacial failure can be easily identified, not only by the relative peak in the peel force, but also by the clearly visible adhesive layer that remains on the stainless steel plate during cohesive failure. Peel forces are measured at 90° and 180° peel angles and peel rates between 0.05 and 15 mm/s. The peel forces measured on a temperature-gradient surface are similar in magnitude to peel forces measured on the same surface but at constant temperature and averaged over longer peel lengths.

The use of a modified peel specimen to assess the peel resistance of aircraft fuel tank sealants

The aim of this study was to comprehensively review the traditional peel specimen for assessing adhesion of aircraft fuel tank sealants. A modified peel specimen was proposed that overcomes the inherent problems of the traditional test, which are associated with inaccurate geometry definition and clamping, and avoids any subjective interaction during testing from the knife cuts used to re-initiate the crack at the metallic interface. Artificial defects, which are easy to apply consistently, were introduced during manufacturing of the peel specimens and it was shown that these can act as precise knife cuts during testing. Two aircraft fuel tank sealants were tested using two different peel angles (135° and 180°), several sealant layer thicknesses (1.5, 2, 3 and 4 mm), various substrates (aluminium and mild steel) and chromate epoxy primers (low and conventional VOC). For those specimens that failed cohesively, the peel resistance increased significantly with the peel angle and the sealant layer thickness. On the other hand, the use of chromate epoxy primers did not affect either the peel resistance of the sealants or the failure mode.

Peel-Zone Model of Tape Peeling Based on the Gecko Adhesive System

A tape-peeling model based on the geometry of the peel zone (PZ) is derived to predict the peeling behavior of adhesive tapes at peel angles less than or equal to 90°. The PZ model adds an angle-dependent multiplier to the Kendall equation that takes into account the geometrical changes within the peel zone. The model is compared with experimental measurements of the peel force at different angles for a model tape and two commercial tapes, each with different bending moduli, stretch moduli, and adhesive strengths. Good agreement is found for a wide range of peel angles. The PZ model is also applied to the gecko adhesive system and predicts a spatula peel angle of 18.4° to achieve the adhesion forces reported for single setae. The PZ model captures the fact that adhesive forces can be significantly enhanced by peeling at an angle, thereby exploiting high friction forces between the detaching material and the substrate.