Peel Angle Research Articles

Analytical Model and Experimental Verification of the Interfacial Peeling Strength of Electrodes

The interfacial peeling strength of lithium-ion battery electrodes is a very important mechanical property that significantly affects the electrochemical performance of battery cells. To characterize the interfacial peeling strength of an electrode, an analytical model based on the energy balance principle is established by considering the state of charge (SOC), the energy release rate, the tensile stiffness, and the peeling angle. Uniaxial tensile tests and 180-degree peeling tests are conducted to determine the Young’s modulus and the interfacial peeling strengths of electrodes at different SOCs, respectively. The experimental data serve as a validation of the accuracy of the analytical model. The interfacial peeling strength of the electrode shows a strong reliance on many factors. Specifically, the interfacial peeling strength increases with the SOC and the energy release, and decreases with the peeling angle. When the tensile stiffness of the active layer equals that of the current collector, the interfacial peeling strength has a maximum value. By comparing with experimental data of the 180-degree peeling test, the model prediction shows excellent agreement at different SOCs, and the analytical model established in this paper can be used to guide and assess the interfacial properties of electrodes for industry.

On the presence of a critical detachment angle in gecko spatula peeling - a numerical investigation using an adhesive friction model

ABSTRACT A continuum-based computational contact model is employed to study coupled adhesion and friction in gecko spatulae. Nonlinear finite element analysis is carried out to simulate spatula peeling from a rigid substrate. It is shown that the “frictional adhesion” behavior, until now only observed from seta to toe levels, is also present at the spatula level. It is shown that for sufficiently small spatula pad thickness, the spatula detaches at a constant angle known as the critical detachment angle irrespective of the peeling and shaft angles. The spatula reaches the same energy states at the jump-off contact point, which directly relates to the invariance of the critical detachment angle. This study also reveals that there is an optimum pad thickness associated with the invariance of the critical detachment angle. It is further observed that the sliding of the spatula pad is essential for the invariance of the critical detachment angle. Further, it is found that the invariance of the critical detachment angle is unaffected for a wide range of spatula shaft lengths.

Investigating the normal and tangential peeling behaviour of gecko spatulae using a coupled adhesion-friction model

ABSTRACT The present work investigates the normal and tangential peeling behaviour of a gecko spatula using a coupled adhesion-friction model. The objective is to explain the strong attachment and easy detachment behaviour of the spatulae as well as to understand the influence of various parameters on the pull-off forces. Using nonlinear finite element computations, it is shown that during tangentially-constrained peeling the partial sliding of the spatula pad near the peeling front stretches the spatula, thus increasing the strain energy and leading to high pull-off forces. The model is used to investigate the influence of various parameters on the pull-off forces – such as the peeling angle, spatula shaft angle, strip thickness, and material stiffness. The model shows that increasing the spatula pad thickness beyond a certain level does not lead to a significant increase in the attachment forces. Further, the easy detachment behaviour of geckos is studied under tangentially-free peeling conditions. It is found that the spatulae readily detach from the substrate by changing their shaft angle and eventually peel vertically like a tape. Since the present computational model is not limited by geometrical, kinematical, and material restrictions, it can be employed to analyse similar biological adhesive systems.

Dynamics of graphene/Al interfaces using COMB3 potentials

This work describes the development of a third-generation charge optimized many-body (COMB3) potential for Al-C and its application to the investigation of aluminum/graphene nanostructures. In particular, the new COMB3 potential was used to investigate the interactions of aluminum surfaces with pristine and defective graphene sheets. Classical molecular dynamics simulations were performed at temperatures of 300-900K to investigate the structural evolution of these interfaces. The results indicate that although the interfaces between Al and graphene are mostly weakly bonded, aluminum carbide can form under the right conditions, including the presence of vacancy defects in graphene, undercoordinated Al in surface regions with sharp boundaries, and at high temperatures. COMB3 potentials were further used to examine a new method to transfer graphene between Al surfaces as well as between Al and Cu surfaces by controlling the angle of the graphene between the two surfaces. The findings indicate that by controlling the peeling angles it is possible to transfer graphene without any damage from the surface having greater graphene/surface adhesion to another surface with less adhesion.

Competition between delamination and tearing in multiple peeling problems.

Adhesive attachment systems consisting of multiple tapes or strands are commonly found in nature, for example in spider web anchorages or in mussel byssal threads, and their structure has been found to be ingeniously architected in order to optimize mechanical properties: in particular, to maximize dissipated energy before full detachment. These properties emerge from the complex interplay between mechanical and geometric parameters, including tape stiffness, adhesive energy, attached and detached lengths and peeling angles, which determine the occurrence of three main mechanisms: elastic deformation, interface delamination and tape fracture. In this paper, we introduce a formalism to evaluate the mechanical performance of multiple tape attachments in different parameter ranges, where an optimal (not maximal) adhesion energy emerges. We also introduce a numerical model to simulate the multiple peeling behaviour of complex structures, illustrating its predictions in the case of the staple-pin architecture. Finally, we present a proof-of-principle experiment to illustrate the predicted behaviour. We expect the presented formalism and the numerical model to provide important tools for the design of bioinspired adhesive systems with tuneable or optimized detachment properties.

Characterizing the Structural Integrity of Endotracheal Tube Taping Techniques: A Simulation Study

Endotracheal tubes (ETTs) are commonly secured with tape to prevent undesirable tube migration. Many methods of taping have been described, although little has been published comparing various methods of taping to one another. In this study, we evaluated several methods for securing ETTs with tape. We hypothesized a difference in mean peak forces between the methods studied during forced extubation. Five methods of securing an ETT with tape were studied in a variety of contexts including cadaver and simulation lab settings. Testing included measurement of peak force (Newton [N]) during forced extubation, durability of taping following mechanical stress, effects of tape length-width variation, and characterization of failure mechanisms. We found several significant differences in mean peak extubation forces between the 5 methods of taping, with mean peak forces during forced extubation ranging from 20 N to 156 N. In separate tests, we found an association between mean peak forces and total surface area as well as geometric configuration of tape on the face. Long thin strips of tape appeared to provide surprising durability against forced extubation, a phenomenon that was associated with minimization of the "peel angle" as tape was removed. We found evidence of differential structural integrity between the 5 taping methods studied. More generally, we found that increased peak extubation forces were associated with increased total surface area of tape and that minimization of the "peel angle" by lateral application of tape is associated with surprisingly high relative peak extubation forces.

Bending to Kinetic Energy Transfer in Adhesive Peel Front Microinstability.

We report an extensive experimental study of a detachment front dynamics instability, appearing at microscopic scales during the peeling of adhesive tapes. The amplitude of this instability scales with its period as A_{mss}∝T_{mss}^{1/3}, with a prefactor evolving slightly with the peel angle θ, and increasing systematically with the bending modulus B of the tape backing. Establishing a local energy budget of the detachment process during one period of this microinstability, our theoretical model shows that the elastic bending energy stored in the portion of tape to be peeled is converted into kinetic energy, providing a quantitative description of the experimental scaling law.

Contact splitting in dry adhesion and friction: reducing the influence of roughness

Splitting a large contact area into finer, sub-contact areas is thought to result in higher adaptability to rough surfaces, stronger adhesion, and a more uniform stress distribution with higher tolerance to defects. However, while it is widely believed that contact splitting helps to mitigate the negative effects of roughness on adhesion- and friction-based attachment, no decisive experimental validation of this hypothesis has been performed so far for thin-film-based adhesives. To this end, we report on the behavior of original and split, wall-shaped adhesive microstructures on different surfaces ranging across four orders of magnitude in roughness. Our results clearly demonstrate that the adhesion- and friction-driven attachment of the wall-shaped microstructure degrades, regardless of the surface waviness, when the surface roughness increases. Second, splitting the wall-shaped microstructure indeed helps to mitigate the negative effect of the increasing surface unevenness by allowing the split microstructure to adapt more easily to the surface waviness and by reducing the effective average peeling angle. These findings can be used to guide the development of biomimetic shear-actuated adhesives suitable for operation not only on smooth but also on rough surfaces.

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.

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.

Quantitative Prediction of the Whole Peeling Process of an Elastic Film on a Rigid Substrate

The whole peeling behavior of thin films on substrates attract lots of research interests due to the wide application of film-substrate systems, which was well modeled theoretically by introducing Lennard–Jones (L-J) potential to describe the interface in Peng and Chen (2015, Effect of Bending Stiffness on the Peeling Behavior of an Elastic Thin Film on a Rigid Substrate,” Phys. Rev. E, 91(4), p. 042401). However, it is difficult for real applications because the parameters in the L-J potential are difficult to determine experimentally. In this paper, with the help of the peeling test and combining the constitutive relation of a cohesive zone model (CZM) with the L-J potential, we establish a new method to find the parameters in the L-J potential. The whole peeling process can then be analyzed quantitatively. Both the theoretical prediction and the experimental result agree well with each other. Finite element simulations of the whole peeling process are carried out subsequently. Quantitative agreements among the theoretical prediction, numerical calculation, and the experiment measurement further demonstrate the feasibility of the method. Effects of not only the interface strength but also the interface toughness on the whole peeling behavior are analyzed. It is found that the peeling force at a peeling angle of 90 deg during the steady-state stage is affected only by the interface toughness, while the peeling force before the steady-state stage would be influenced significantly by the interface toughness, interface strength, and bending stiffness of the film. All the present results should be helpful for deep understanding and theoretical prediction of the interface behavior of film-substrate systems in real applications.

Synergistic effect of Fe and Al2O3 layers on the growth of vertically aligned carbon nanotubes for gecko-inspired adhesive applications

This study focused on the application of vertically aligned carbon nanotubes (VACNTs) grown by thermal chemical vapor deposition as a gecko-inspired dry adhesive material. The adhesive properties of VACNTs comprising Fe and Al2O3 layers of different thicknesses were evaluated by scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and atomic force microscopy. Owing to the surface energy difference between metallic Fe and alumina, the wetting influence of the latter enabled the conversion of the iron film into metal islands (nanoparticles) at high temperature. The bionic morphological characteristics of the produced VACNTs (e.g., alignment, density, diameter, growth rate, and defects) and thus their adhesive properties were determined by the size and distribution of the catalyst particles. With respect to variable adhesion test angles, VACNTs were sensitive to peeling angles and showed high tangential but low normal adhesion strength, thereby providing controlled strong adhesion characteristics in combination with easy peel-off.

Single fiber peel test to assess ultra high molecular weight polyethylene fiber mesostructure interactions

ABSTRACTIn this work, a variable angle, single fiber peel test is developed to analyze the effects of fiber structure on the mixed mode failure within ultra high molecular weight polyethylene fibers. The Mode I and Mode II peel energy release rates are quantified and the effects of fiber meso/nanostructure on these modes are examined. Comparison of the load‐extension curves from the peel test with in‐situ video, and post‐mortem analysis using high‐resolution microscopy techniques indicates that Mode I and Mode II splitting are both significantly influenced by the deformation of nanoscale fibrils within a mesoscale network. The fibrils in the network are placed in tension across the peel/shear interface resulting in elevated values of peel energy release rates with an increasing number of engaged fibrils. The number of engaged fibrils is shown to increase with decreasing peel angle and increasing Mode II failure contribution. A bi‐linear mixed‐mode failure criterion is established. The results, and analysis of the fiber structure are discussed in context of their implications for load pathways in the fiber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46156.

Numerical models of delamination behavior in 2G HTS tapes under transverse tension and peel

In extreme operating environments, delamination in 2G HTS tapes occurs within and/or near the superconductor layer from high transverse tensile stresses caused by fabrication, Lorentz forces and thermal mismatch, etc. Generally, transverse opening and peeling off are the main delamination modes, and are always studied in anvil and peel tests, respectively. Numerical models of these modes for 2G HTS tape are presented wherein the mixed-mode traction-separation law at the interface of the silver and superconductor layers is considered. Plastic deformations of copper, silver, and Hastelloy® in the HTS tape are taken into account. The results obtained from the transverse opening model show that the maximum average tensile stress is smaller than the delamination tensile strength because delamination is asynchronous in the tape. When a crack appears in the tape, only a small stress ( ≤ 1 MPa) is required to expand the crack to other stress free areas through peeling. Using the peeling model, the dependency of the peel strength on peeling angle is investigated under constant fracture toughness. Peel strength decreases with the peeling angle until the minimum value is reached at 150°, and thereafter increases slightly. Other results indicate that peel strength depends strongly on delamination strength, fracture toughness, and thickness of copper layer. The fracture toughness of the delamination interface, which is difficult to obtain by experiment, can be extracted using the present model.

Long-Term Stability Evaluation and Pillar Design Criterion for Room-and-Pillar Mines

The collapse of abandoned room-and-pillar mines is often violent and unpredictable. Safety concerns often resulted in mine closures with no post-mining stability evaluations. As a result, large amounts of land resources over room-and-pillar mines are wasted. This paper attempts to establish an understanding of the long-term stability issues of goafs (abandoned mines). Considering progressive pillar failures and the effect of single pillar failure on surrounding pillars, this paper proposes a pillar peeling model to evaluate the long-term stability of coal mines and the associated criteria for evaluating the long-term stability of room-and-pillar mines. The validity of the peeling model was verified by numerical simulation, and field data from 500 pillar cases from China, South Africa, and India. It is found that the damage level of pillar peeling is affected by the peel angle and pillar height and is controlled by the pillar width–height ratio.

Finite Element Modeling for Debonding of FRP-to-Concrete Interfaces Subjected to Mixed-Mode Loading.

This paper presents finite element (FE) modeling of the debonding behavior of fiber reinforced polymer (FRP)-to-concrete interfaces subject to mixed-mode loading, which is realized through a peeling test of FRP composites externally bonded onto a concrete substrate. A cohesive zone model (CZM) is implemented into the FE model to represent the behavior of the FRP-to-concrete interface. Two element schemes (orthotropic plane stress element and beam element) were employed to simulate the behavior of FRP composite plate in the peeling test. The orthotropic plane stress element scheme, bearing a clear physical background and with an easy definition of the material property parameters following the composite mechanics, is found to be superior to the beam element scheme, and thus is utilized to conduct parametric studies. The influences of the peeling angle, the interfacial parameters (i.e., the configuration of the cohesive zone models, the interfacial damage initiation law (DIL), the interfacial damage evolution law (DEL), the coupling of mode-I and mode-II components), on the mixed-mode failure of the FRP-concrete-interface are carefully investigated. The results showed that the mode I component plays a critical role in the debonding failure of FRP-to-concrete interfaces even when the peeling angle is very small. The failure of FRP-to-concrete interface transits promptly from a mode II-dominated one to a mode I-dominated one when the peeling angle increases to a relatively small value (e.g., 4 degree) and subsequently the peeling force (i.e., the debonding strength of FRP) decreases dramatically. Such mixity of the mode I and mode II components should be appropriately considered for refining the analysis of FRP-strengthened RC beams and the FRP debonding strength design, for which a pure mode II interfacial failure was usually assumed.

A theoretical analysis of peeling behavior between nanowires and substrates in the ambient condition with high relative humidity

At micro/nano scale in the ambient condition, both capillary force and van der Waals (vdW) force dominate adhesive forces of micro- and nano-electrodevices. In this study, the peeling behavior between nanowires and substrates in the ambient condition with high relative humidity is analyzed using continuum modeling under the combined effect of capillary force and vdW force. The capillary force is obtained by solving both the Kelvin equation and the Young–Laplace equation in the thermodynamic equilibrium state, while it is derived by solving both the Young–Laplace equation and the volume equation in the thermodynamic nonequilibrium state. The vdW force is derived from the first derivative of the cohesive energy versus distance. Our analytical results from the modified Kendall model show that the peeling behavior between the nanowire and the substrate strongly depends on the peeling angle, the pre-tension, the radius, and the Young's modulus of the nanowire. In particular, both the effects of the liquid bridge position relative to the nanowire and the bending stiffness of the nanowire on the peeling force are considered by the modified Kendall model. The present solution should be of great help for understanding the structural stability of nanodevices and designing nanoelectromechanical systems.

A practical fabrication method of the gecko-inspired easy-removal skin adhesives

Abstract Easy-removal skin adhesives require a robust reversible adhesion. This requirement is addressed in this study with the fabrication of PDMS micro-patterned surfaces that inspired by gecko feet. The design of these gecko-inspired structures were aimed to maximize the ratio between pull-off strength and peel strength. They were fabricated using the laser cutting technology which is typically used for industrial manufacturing applications. Several kinds of PDMS specimens in triangular, square and hexagonal patterns, as well as triangular, square, diamond and circular cross-sections were made. The wetting properties of the gecko-inspired surfaces were evaluated by contact angle measurements. Pull-off strength and peel strength measurements were performed against a silicon skin substitute. Multiple attachments were achieved on a range of preloads. The averaged pull-off strength under a preload 10 N for 10 s can reach up to approximately five times of peel strength when the peel angle is 30 degree. Also compared with conventional Band-Aids, a slight enhancement in attachment ability and a significant decrease in peel strength between the skin and the adhesives were consistently observed. Therefore, the fabrication of the gecko-inspired structures on the micro-molding of PDMS appeared to offer a near-practical way for manufacturing an easy-removal skin adhesives, albeit in its present form with a comparable adhesion strength and a decreased peel strength. The originality of this work is the reverse de-molding approach based on the combination of the cost- and time-efficient laser cutting methods and the Teflon film as the mold material, which avoid the limitation caused by taking PDMS structure out of the molds, so that provide more variations of the tip geometry. As such, a further development of this fabrication method might be of significant interest in a number of practical applications in skin tissue industrial design.

Influence of Channel Shape on Wave-Generated Parameters by a Pressure Source in Shallow Water

The present work is a numerical investigation into the waves generated by a pressure source moving in straight channels with a nonrectangular cross-channel depth profile. Wave fields generated by the moving pressure source are described, and the effects of channel bathymetry on the generated wave characteristics of wave height, wave-breaking location, wave-breaking type and intensity, and peel angle are presented. Four different channel cross-section shapes were investigated, and the results were analyzed. It was concluded that the maximum wave height depended primarily on pressure-source parameters and that the investigated channel shapes did not have a significant effect on the maximum wave height. All four investigated channels were able to generate plunging-shaped breaking waves. In addition, wave-breaking intensity and barrel shape could be controlled by beach-slope shape; however, beach slope did not have a considerable effect on the wave-breaking location. The width of the deep section of the channel had a significant effect on the breaking location. Widening the deep section of the channel moved the breaking point farther from the pressure source. According to the simulation results, it is possible to generate waves for an intermediate or expert surfer only by changing the pressure-source speed. According to the results, by changing the pressure-source speed, the peel angle changes, which is the best way to change the required skill level for surfing. In addition, changing the channel shape did not have a significant effect on the required skill level for surfing.

Adhesion performance test and trajectory optimization for gecko-inspired footpad under simulated micro-gravity environment

The extraordinary locomotory abilities of geckos are attributed to striking adhesive setae segmented into scansors or pads on the undersides of the toes or legs, have been well-known for many centuries due to van der waals force. The outstanding climbing performances of the animal inspired the engineers and researchers for the design of artificial systems, such as adhesive materials, which in turn enabled the construction of climbing robots that are capable of climbing smooth walls and ceiling. The robot based on van der waals force has a wide prospect for execution space task application. Legged climbing robot involves the controlled application of forces during the leg-substrate contact and release, in order to propel the body forwards. The achievement of strong attachment and easy removal of the adhesive is the critical issues, when we apply the adhesive to the robot’s footpad. Here, by using a custom-built force platform, adhesion performance of the bio-inspired adhesive which directly apply to the footpad were investigated. The effect of footpad stiffness, contact area and trajectory on adhesion force and real contact area is investigated. Results show that normal force and shear force increased as stiffness increase up to 68.9 N/m. After that, normal force and shear force decrease as stiffness increase. Both normal force and shear force increase as real contact area increase, but not increase linearly. Additionally, different attaching trajectories are applied to explore the adhesion characteristic of the footpad. The result indicates that for the robot, the footpad of this kind does not need much load control: the pad just needs to contact the surface, in order to produce substantial adhesion force and meet the requirement of the attaching phase. This characteristic of footpad is extremely beneficial for applying it at zero gravity, when the robot cannot rely on gravity to load the adhesive pad. Furthermore, normal force and shear of the footpad during one cycle are tested. The force is compared with the frictional-adhesion model. Stable adhesion region under different conditions can be obtained by adjust peeling angle and effective real contact area. Finally, optimized footpad stiffness, area and trajectory are selected and stable adhesion region is analyzed. By using gravity compensation method to simulate micro-gravity environment and designing attachment and detachment trajectory, the robot can climb stably under zero gravity environment up to 1 cm/s. This paper presents adhesion performance test and trajectory optimization of gecko-inspired footpad under simulated micro-gravity environment. The experimental tests demonstrated that the robot can climb under mimic zero gravity at the velocity of up to 1 cm/s. The major contribution of this work is the application of the biological principle of footpad to the legged robot, and the demonstration of the feasibility and reliability of this design. To the best of our knowledge, the legged robot, climbing under nearly zero gravity, is demonstrated here for the first time. We also explore the effect of the stiffness, contact area and attaching trajectory on the reliability of the robot locomotion. This research could be a basis for the space application of micro-adhesion robot.