Calorimetric Measurements of The Heat Generated by The Peel Adhesion Test

The peel test is a simple mechanical test commonly used to measure the adhesion of flexible films bonded to rigid substrates. When the film is deformed elastically during peeling, the peel force is a direct measure of the strength of the interface. However, when plastic deformation takes place, the work of detachment is much larger than the thermodynamic work of forming the fracture surfaces. Simultaneous mechanical and calorimetric measurements of the work of detachment and the heat generated during the peeling of polymeric films from metal substrates and metal films from polymeric substrates have been made. An energy balance for peeling has been proposed. Most of the work of peeling was consumed by plastic deformation. The peeled polymer dissipated approximately one half of the work of peeling as heat and most of the remainder was stored in the peeled material. The peeled metal dissipated most of the work of peeling as heat.     

Peeling of Elastic Tapes: Effects of Large Deformations,Pre-Straining,and of a Peel-Zone Model

A peel model for non-linear elastic tapes is presented which accounts for large deformations and for pre-straining. The large deformation setting is a new feature of modelling, which would be of interest for applications related to soft polymers and tissues. The conditions for having quasistatic-steady debonding or dynamic catastrophic debonding are determined in terms of the loading variables (peel angle and peeling force). The decohesion energy associated with a given process-zone model is included in the formulation of the peeling model. The predictions of various decohesion laws are discussed with respect to experimental results in the literature. Finally, the adhesion of a gecko is analysed and the maximum adhesion force of a single spatula is evaluated. The result correlates well with the maximum experimental pulling force reported in the literature for a gecko's seta.     

Adhesion between side surface of an elastic beam and flat surface of a rigid body

A theory of adhesion between an elastic beam and a rigid body is proposed using linear beam theory. Normalized force between the elastic beam and the rigid body considering adhesion of the side surface of the elastic beam is investigated theoretically. Adhesion of an elastic beam is important to analyze gecko adhesion, and peeling mechanism of an adhered film. This adhesion is also important in design of grip-and-release devices. The force between an elastic beam and a rigid body is investigated by considering shear force and total energy, and is obtained as a function of the displacement of the elastic beam. The proposed theory is different from Kendall’s thin-film peeling theory in terms of the elastic energy. The proposed theory considers bending elastic energy, whereas Kendall’s theory considers extension elastic energy. Two different contacts, line contact and area contact, are taken into account to discuss the loading and unloading processes in terms of the relation between the force and the displacement. Non-dimensional parameter, which relates to the work of adhesion and the specifications of the elastic beam, is introduced to explain the normalized maximum tensile force.     

In situ Measurement of the Adhesion Strength and Effective Elastic Stiffness of Single Soft Micropillar

We report the deformation behavior and mechanical properties of a polymeric micropillar, which measures approximately 10 μm by 30 μm in size by measuring the loading/unloading response using an in situ force measurement system. When the single poly(dimethylsiloxane) (PDMS) micropillar was subjected to compression, we observed a periodic wrinkle and global (Euler) buckling at the sidewall. During unloading, we found the pull-off force (adhesion force) to increase for higher values of preloading and also for lower loading/unloading rates. From the slope of the load–displacement curves measured in situ, we calculated the effective elastic stiffness of the PDMS micropillar to be about 2.03 MPa. In addition to the current work, we report that this method can be used more broadly for in situ measurement of the intrinsic mechanical and adhesion properties of polymers and other relatively soft materials.     

Experimental determination of the peel adhesion strength for metallic foils

This work addresses the problem of experimental measurement of peel adhesion in cases where a non-recoverable (plastic) deformation energy of the peeled foil, plus frictional losses, constitutes a significant portion of the total peel energy. In standard tests, when the true adhesion strength is desired, the plastic energy has to be calculated and deducted from the total energy. Several studies have been dedicated to the modelling and calculation of the energy dissipated through plastic deformation so that the net adhesion energy could be deduced. These calculations are cumbersome and impractical for general use. A simple experimental technique for the determination of the net adhesion strength is proposed. Experimental results with ～ 0.1 mm thick foils of stainless steel, nickel, and titanium confirm the theoretical predictions regarding the energy balance during peeling. Using the proposed methodology, there is no need to calculate or otherwise determine the deformation energy losses of the peeled foil or the frictional dissipation. The method is not limited to a particular material and can be used successfully for strain hardening plastic as well as metallic foils. Peel tests on adhesively bonded specimens of stainless steel and nickel and of a thermal spray-coated Ti alloy foil were carried out to demonstrate the applicability of the proposed method.     

On using a penalty-based cohesive-zone finite element approach,Part II: Inelastic peeling of an epoxy-bonded aluminum strip

Previous work has demonstrated the use of a penalty methodology for enhancing the use of cohesive-zone elements to simulate double cantilever beam (DCB) and flexible-arm peeling problems, both involving elastic arm deformation. This approach is extended to the general case of inelastic peel arm deformations. Refinements to the original penalty selection methodology are included to account for the influence of plasticity in the peel arms. Accuracy of the method is demonstrated by comparing simulation results to experimental data of epoxy-bonded aluminum arms being peeled at different angles from a rigid substrate. This work addresses significant complexities in the analysis that arise due to the inelastic deformation of the aluminum peel arms.     

Adhesion of Pure and CaCO3 Filled Latex Films on Poly(ethylene terephthalate)

Adhesion to poly(ethylene terephthalate) of carboxylated styrene-butadiene latex films, filled with calcium carbonate particles, was studied in this work. The acid content (2, 4 or 6 wt%) the degree of crosslinking (25, 50 or 75 wt% of insoluble polymer) of the latex particles, and the percentage of filler (0, 20, 40, 60, 80 or 90wt%) were varied. A peel test at 180° was used.

It was shown that, for the lowest filler percentages (up to 60 wt%), the films were non-porous and adhesion decreased when the peel rate, the percentage of filler, the degree of crosslinking and the acid content increased. Failure was always localized at the film-support interface (except at very low peel rate). At low peel rate, stick-slip was observed. The adhesion lowering can be explained by a decrease of the energy dissipation during peeling due to a reduced mobility of the polymeric chains. At high filler percentage (80 or 90 wt%), the films became porous and the level of adhesion very low. Failure occurred in the bulk of the latex film. The peel rate dependence was reversed; adhesion increased at higher speed. Owing to its marked importance in this system, the mechanism of the stick-slip phenomenon is especially discussed.     

Silicone-based release agents for polyurethane: a general assessment of the importance of interface structure and morphology

This paper describes an evaluation of various silicone-based materials as mould release agents for a polyurethane/smooth stainless steel interface. The release properties of these materials have been characterized by the use of a blister test and data are provided for peeling energies over a range of peeling velocities. Three types of silicone system were studied: silicone fluid, silicone resin, and a combination of fluids and resins. All these materials provide a reduction in the peeling work compared with a virgin interface although some systems are significantly more effective than others in reducing the peeling work. The lowest adhesion energies were obtained with certain combinations of per-methyl silicone resins and silicone fluids. In these systems there is indirect evidence for the formation of friable, marginally bonded particle based structures which are sufficiently durable to . withstand the polymerization process but are readily ruptured or fractured during the subsequent peeling of interface.     

A Practical Criterion for Rheological Modeling of the Peeling of Pressure Sensitive Adhesives

The transient extensional viscosity of non-crosslinked pressure sensitive adhesives (PSA's) and physically-crosslinked PSA's is measured and compared with theoretical predictions based on the linear viscoelastic (LVE) properties of the PSA's and the use of linear and quasi-linear constitutive equations. Based on a previously-derived expression for the relative contributions of individual relaxation modes of a polymeric material to its transient extensional viscosity, a criterion for whether large extensional deformations can be modeled on the basis of the LVE spectrum is proposed and evaluated for each PSA. The relevance to adhesion is demonstrated in peel tests, where the deformation of adhesive is quantified in images of the peel front under the assumption of uniaxial elongation and used to obtain theoretical peel forces in excellent agreement with measurements. This demonstrates the applicability of the criterion to the peeling process.     

The Mechanisms of Peeling of Uncross-Linked Pressure Sensitive Adhesives

We analyze the peeling properties of an uncross-linked pressure sensitive adhesive. 90° peeling master curves on Pyrex^TM and PMMA (polymethylmetacrylate) are constructed The shift coefficients a_T are compared with the ones obtained from rheometrical shear tests.

With our machine, the peeling front is kept fixed, enabling us to observe the mechanisms of deformation of the adhesive. We count four different mechanisms of peeling in cohesive failure, and three in interfacial peeling (the last being unstable); they correspond to various slopes that we identify. The flow patterns at slow reduced velocities are two-dimensional. Then they undergo transitions to three-dimensional periodic complex flows, due to instabilities in the flow of thin adhesives. Interpretation of these peeling master curves are discussed in terms of rheology and physico-chemistry. It appears necessary to take into account the elongational properties of the adhesive, as well as the surface energy properties, to predict adhesion.     

A Practical Criterion for Rheological Modeling of the Peeling of Pressure Sensitive Adhesives

The transient extensional viscosity of non-crosslinked pressure sensitive adhesives (PSA's) and physically-crosslinked PSA's is measured and compared with theoretical predictions based on the linear viscoelastic (LVE) properties of the PSA's and the use of linear and quasi-linear constitutive equations. Based on a previously-derived expression for the relative contributions of individual relaxation modes of a polymeric material to its transient extensional viscosity, a criterion for whether large extensional deformations can be modeled on the basis of the LVE spectrum is proposed and evaluated for each PSA. The relevance to adhesion is demonstrated in peel tests, where the deformation of adhesive is quantified in images of the peel front under the assumption of uniaxial elongation and used to obtain theoretical peel forces in excellent agreement with measurements. This demonstrates the applicability of the criterion to the peeling process.     

An Elasto-Plastic Investigation of the Peel Test

This work outlines an elasto-plastic investigation of two common peel tests which use high and low yield strength aluminium adherends. An elastic, large-displacement, finite element program has been extended to include elasto-plastic material behaviour. This has been used to analyse both peel tests. The adhesive stresses near the crack tip have been shown to be finite while the corresponding strains remain singular. A failure criterion based on a maximum adhesive strain has been used to predict the relative strengths of the peel test. The amount of energy dissipated in the plastic deformation of the peeling adherends has been assessed by a series of tests and has been shown to be a considerable amount of the total energy supplied to the peeling system. Further, although the two aluminium alloys considered have grossly different yield strengths the energies dissipated in plastic deformation are similar. Material data for the finite element analysis and the plastic work calculations have been obtained from uniaxial tensile tests of both the adherends and the adhesive and actual peel strengths have been measured in a series of peel tests.     

Numerical simulations of the normal impact of adhesive microparticles with a rigid substrate

The rebound behavior of elastic and elastoplastic microspheres impacting normally with a rigid wall is studied using the finite element method. The interfacial adhesion forces are introduced by adding piecewise-linear spring elements with a particular constitutive relation characterizing the adhesion property. The effect of adhesion hysteresis is taken into account by assuming that the adhesion work during the incident stage is smaller than that during rebounding. The influences of the interfacial adhesion parameters, the constitutive relations, size, and incident velocity of the particle on the coefficient of restitution (COR) are all examined. We also analyze the changing tendency of the kinetic energy, elastic strain energy, adhesion work, and their interchange during impact. It is found that besides interfacial adhesion and plastic dissipation, the residual stress field caused by incompatible plastic deformation has a considerable influence on the impact behavior of the sphere as well. For smaller impact velocities, interfacial adhesion plays a dominant role in the impact process, while for higher incident velocities, the COR depends mainly on plastic deformation. In addition, the COR shows a distinct dependence on the particle size. Finally, our numerical results are compared with the relevant experimental results.     

An Elasto-Plastic Investigation of the Peel Test

This work outlines an elasto-plastic investigation of two common peel tests which use high and low yield strength aluminium adherends. An elastic, large-displacement, finite element program has been extended to include elasto-plastic material behaviour. This has been used to analyse both peel tests. The adhesive stresses near the crack tip have been shown to be finite while the corresponding strains remain singular. A failure criterion based on a maximum adhesive strain has been used to predict the relative strengths of the peel test. The amount of energy dissipated in the plastic deformation of the peeling adherends has been assessed by a series of tests and has been shown to be a considerable amount of the total energy supplied to the peeling system. Further, although the two aluminium alloys considered have grossly different yield strengths the energies dissipated in plastic deformation are similar. Material data for the finite element analysis and the plastic work calculations have been obtained from uniaxial tensile tests of both the adherends and the adhesive and actual peel strengths have been measured in a series of peel tests.     

Deformation and fracture characterization of inelastic composite materials using potentials

An approach using strain energy-like potentials to characterize deformation and fracture of inelastic, nonlinear composite materials is described. The inelasticity may be due to various causes, including microcracking, microslipping, and rate processes responsible for fading memory (viscoelasticity). The concept of work potentials is introduced first, and then arguments are given for their existence for inelastic materials. Emphasis in the paper is on elastic composite materials with changing or constant states of distributed damage. Experimental results on polymeric composites are subsequently presented to illustrate this approach to deformation and fracture characterization. Finally, extension to viscoelastic behavior is discussed.     

Failure mechanisms in peeling of pressure-sensitive adhesive tape

Studies on the peel behavior of pressure-sensitive tape comprising a polyester backing and polyacrylate adhesive have shown that, in peeling from a plane glass surface, three fundamentally different modes of peeling may be distinguished, depending upon the rate of pulling. At low rates, deformation by flow of the adhesive appears to determine the peel behavior and the peel force is strongly rate dependent. At high rates, little or no viscous deformation of the adhesive occurs and the peel force is independent of rate. At intermediate pulling rates, cyclical instability of made of failure involving alternate storage and dissipation of elastic energy in the backing, results in the phenomenon of “slip-stick” peeling, in which failure is jerky and regular. Results have been obtained which show how the pulling rates at which transitions from one mode of peel to another occur, and the peel force values for a given type of failure, depend upon such factors as molecular weight of adhesive, thickness of backing film, and angle of peeling.     

A Novel Technique for Evaluating the Work of Adhesion

One of the basic problems which one encounters in bonding dissimilar materials such as glass and polymers is the development of internal stresses. These stresses arise primarily as a result of the difference in their thermal coefficients of expansion. Other stresses may also occur due to the processing history of the polymer, swelling of the polymer due to the absorption of gases in the environment or internal reaction products, and/or the loss of absorption of solvent from the adhesive. As a result, it is obvious that techniques designed to evaluate adhesion must evaluate the effects of these intrinsic stresses without modification by the external imposed stresses of the test. For example, Ahagon and Gent evaluate a work of detachment from the time average of the 180° peel force per unit width of the detaching layer.¹ However, Gent and Hamed have recently shown that this mode of peeling involves deformation of the detaching layer due to bending.² Similar problems are encountered in other techniques used to measure adhesion.     

Influence of the interfacial composition on the adhesion between aggregates and bitumen: Investigations by EDX, XPS and peel tests

The study of the adhesion between aggregates and bitumen is necessary to enhance the lifetime of the roads. The purpose of this work concerns the interaction between the mineralogy of the aggregates and the adhesion force measured at the interface between bitumen and aggregate. The adhesion of bitumen was studied according to the mineralogy of the aggregates, which were made of dolomite rock or granite. A method was developed to measure the fracture energy during the peeling of the bitumen layer from the aggregate surface. The specific manufacturing of the samples ensured reproducible measurements using a constant thickness of the bitumen layer and by introducing a strengthened and flexible membrane into the bulk of bitumen. The peeling results demonstrated that the locus of the failure varied according to the mineralogy of the aggregate. The failure was cohesive during the peeling of the dolomite/bitumen system while the failure was partly interfacial concerning the granite/bitumen system. The interface between bitumen and minerals was characterized, before and after peeling. In case of the granite, the detection of sulfur by X-ray Photoelectron Spectroscopy (XPS) highlighted only the bitumen residues and allowed identifying the mineral compounds that weaken the interface between bitumen and granite. Finally, XPS analyses showed that the alkali feldspars of the granite induced a weak interface with bitumen.     

The effect of flexible substrates on pressure-sensitive adhesive performance

The adhesive fracture energy (fracture toughness) of tapes during globally elastic unpeeling is often calculated from the relation “G=P/b(1−cos θ)”. We show that while this expression is correct for elastic peeling from rigid substrates, it gives misleading results when peeling from reversible flexible substrates. A two-dimensional analysis is presented for peeling from non-linear elastic substrates that give consistent fracture energies from experimental data.     

Influence of the degree of crosslinking on the stringiness of crosslinked polyacrylic pressure‐sensitive adhesives

The stringiness of crosslinked polyacrylic pressure‐sensitive adhesive (PSA) was observed during 90° peeling under the constant peel load. The random copolymer of butyl acrylate with 5 wt % acrylic acid crosslinked by N,N,N′,N′‐tetraglycidyl‐m‐xylenediamine was used as PSA. All observed stringiness upon peeling was sawtooth‐shaped, but it could be classified into three types dependent on the degree of crosslinking. The typical sawtooth‐shaped stringiness with interfacial failure was observed at the relatively higher crosslinker content ranging from 0.008 to 0.016 chemical equivalents (Eq.), where the PSA has high cohesive strength and low interfacial adhesion. The frame formed at the front end of stringiness at the content ranging from 0.002 to 0.004 Eq. Sufficient interfacial adhesion and deformability generate large internal deformation of the PSA layer. Internal deformation occurred preferentially over peeling as a result of front frame formation. The mode of peeling was changed from cohesive failure to interfacial failure in this range of crosslinker content. The sawtooth‐shaped with cohesive failure was observed at the lower content ranging from 0 to 0.001 Eq. The PSA has high interfacial adhesion and low cohesive strength, and thus exhibited cohesive failure. The PSA after peeling remained in the shape of belts. It was found that the shape of stringiness is strongly dependent on the balance between the interfacial adhesion and the cohesive strength of PSA. When the sawtooth‐shaped stringiness with frame formed, the peeling rate was lowest. This means the peel strength should be the maximum in this shape of stringiness. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40336.