Stability Analysis of a Nonlinear Blister Test

The Griffith and stability criteria for the blister test have been derived from thermodynamic arguments. The Griffith criterion includes the stored energy in the blister as well as the interfacial energy change associated with debonding. Based on these criteria an analysis is given of a blister test with a neo-Hookian overlayer debonding from a rigid substrate. A closed analytic form for the strain energy release rate, G, is obtained valid for large elastic deformation of a thin circular film. The criteria derived indicate that quasi-static debonding of the blister is always stable, independent of the interfacial energies and the extent of blister deformation.     

Dissipative Processes in Interfacial Failure

An investigation of the failure behavior of pressure sensitive adhesive tape was performed utilizing the constrained blister test. The constrained blister test was designed to measure the energy of interfacial adhesion of thin polymeric coatings. A constant energy of interfacial adhesion of 1.8J/m² was determined for a rubber based pressure sensitive adhesive on a copper substrate. An active zone was visualized through the transparent backing. The deformation within the active zone was found to consist of cavitation and deformation of ligaments. Fracture of the ligaments causes the detachment front to advance. It was proposed that the rate of energy dissipation, D, reflects the resistance of the bond to time dependent deformation, and therefore dictates the lifetime for this particular specimen geometry. A direct relationship was established between lifetime and the inverse of the rate of energy dissipation in the active zone, D.     

Confocal scanning laser microscopy of polymer coatings

A new nondestructive technique, confocal scanning laser microscopy (CSLM), is described that is used to characterize the topography and morphology of polymer coatings. The topography of the coating can be determined even when the coating is completely opaque. When the coating is not completely opaque, CSLM has the distinct advantage of also being able to distinguish between the coating surface and the substrate, thus enabling coating thickness to be determined over a wide range of areas. In this study CSLM was successfully applied to poly(2-vinylpyridine) coatings formed on mild steel substrates by in situ electropolymerization. Satisfactory morphological details were obtained for areas ranging from 200 × 200 μm to 4 × 4 mm. Quantitative measurements of the coating thickness and the surface roughness distribution were also carried out. Although several other nondestructive techniques for coating morphological analyses are available, CSLM has unique advantages in being able to provide simultaneous qualitative and quantitative information on coating surfaces as well as measurements over a wide range of surface areas. A comparison of CSLM with other popularly used methods is provided and the characteristics and limitations of the various techniques are discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 149–158, 1998     

A spectroscopic technique for in situ measurement of water at the coating/metal interface

A technique was developed based on Fourier transform infrared spectroscopy in the multiple internal reflection mode (FTIR-MIR) for measuring in situ water at the coating/metal interface. The technique requires a direct application of a transparent or opaque polymer coating of any thickness to a Ge internal reflection element (IRE). A water chamber was attached to the polymer-coated IRE and water was introduced through the chamber inlet. FTIR-MIR spectra were taken automatically at specified time intervals without realignment or readjustment of the ATR accessory and without disturbing the specimens or the conditions of the experiment. The intensities of the water bands increased and those of the coating bands decreased initially and then leveled off as the exposure times increased. Calculations are presented to demonstrate that the technique can provide information on water at the coating/metal interface. The method may also provide a convenient means for measuring the diffusion of water in polymer coatings on metals.     

In situ measurement of water at the organic coating/substrate interface

In situ and quantitative information on the water layer at the organic coating/substrate interface is crucial for understanding and preventing the failure of organic coating systems. A technique, based on a two-layer model derived rigorously from internal reflection theory, has been developed for measuring in situ the thickness and amount of the water layer at the organic coating/substrate interface. The technique gives new insight into the processes by which water degrades the coating/substrate bonds. In this technique, a transparent or an opaque organic coating of sufficient thickness is applied to an internal reflection element (IRE) with or without a thin metallic film, which is used as the substrate. A water chamber is attached to the organic-coated specimen. After adding water to the chamber, Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectra are taken automatically at specified time intervals without disturbing the specimens or the instrument. Water uptake in the coating and FTIR-MIR spectra of water on the coating-free substrate are also used for the analysis. Examples of clear and pigmented coatings on untreated and treated substrate surfaces are given to demonstrate the technique. Results of water accumulation at the coating/iron interface with and without applied electrical potentials are given. In addition to measuring water at the coating/substrate interface, the technique provides a means for studying the transport of water through a coating adhered to a substrate. Information on water at the interface and its transport properties through coatings applied to a substrate is valuable for interpreting corrosion, blistering and delamination of organic coating systems, and for developing models for use in predicting the serivce lives of protective coatings.     

Effect of interlayer deformation on blister test

The effect of interlayer deformation on blister test for measuring adhesive strength was analyzed by modeling the interlayer as a Winkler foundation. Critical load for the initiation of debonding along the interface between the interlayer and an elastic thin film was obtained as a function of the adhesive strength, interlayer deformation, elastic modulus of Winkler foundation, and blister size. The critical pressure increases with increasing the elastic modulus of Winkler foundation. The propagation of debonding was discussed, and the arrest of debonding was observed for the condition of constant deflection. The results provide a rational for characterizing the effect of interlayer deformation on the measurement of adhesive strength from a blister test.     

压延机自动划泡装置

为解决压延过程中因胶片含有过多气泡而产生的胶帘布压摞质量问题,设计安装了压延机自动划泡装置。该装置主要由上划泡装置,下刈泡装置,主动辊和链轮等组成,主动辊由压延帘布带动,上划泡装置和下划泡装置由主动辊右边的双排链轮链条带动,划泡装置上与上辊和中辊相触的钢针有规律地划破上胶睡和下胶处事的气泡,彻底消除胶片中的气泡。     

Dissipative Processes in Interfacial Failure

An investigation of the failure behavior of pressure sensitive adhesive tape was performed utilizing the constrained blister test. The constrained blister test was designed to measure the energy of interfacial adhesion of thin polymeric coatings. A constant energy of interfacial adhesion of 1.8J/m² was determined for a rubber based pressure sensitive adhesive on a copper substrate. An active zone was visualized through the transparent backing. The deformation within the active zone was found to consist of cavitation and deformation of ligaments. Fracture of the ligaments causes the detachment front to advance. It was proposed that the rate of energy dissipation, D, reflects the resistance of the bond to time dependent deformation, and therefore dictates the lifetime for this particular specimen geometry. A direct relationship was established between lifetime and the inverse of the rate of energy dissipation in the active zone, D.     

Analysis of Critical Debonding Pressures of Stressed Thin Films in the Blister Test

This paper reports a model for the relationship between critical debonding pressures and the work of adhesion of thin films in the blister test. Previous models have neglected the possible role of residual stresses in the film on the critical pressure. The model reported here shows that these stresses may have a large effect on the relation between the critical pressure and the work of adhesion. A similar model is developed for an alternative blister geometry, the annular or “island” blister. It is shown that films which cannot be peeled using the standard blister test (due to exceeding the tensile strength limit of the film before initiating a debond) can be peeled by varying the geometric parameters of the island blister.     

Electrochemical approach to evaluate the interlayer adhesion of organic coatings

In this work we used the electrochemical impedance spectroscopy (EIS) to quantify the interlayer adhesion of coatings. Different automotive basecoat/clearcoat systems were tested on their interlayer adhesion with EIS. For EIS measurements, two thin electrode stripes of an electroconductive ink were applied between two coating layers. The impedance measurements were conducted to find out the effect of moisture on the interlayer adhesion. The data obtained show a strong sensitivity of the interlayer impedance on the outer air humidity and point out at the possibility of following the water accumulation in the interlayer and the formation of the conductive paths. Such phenomena lead to the adhesion loss and delamination between the coating layers. We found that the interlayer adhesion loss follows the same trend as the changes of the activation energy of the ion mobility, which can be derived from the interlayer resistance, measured with EIS.

For the verification of EIS measurements blister test measurements were carried out. With this method, it is possible to evaluate directly the interlayer adhesion of coatings. A good correlation was found between EIS and blister test data.     

The constrained blister test for the energy of interfacial adhesion

The constrained blister test (CBT) was designed to measure the energy of interfacial adhesion ( y) of polymeric films and coatings. Theoretical analysis of the CBT established a relationship between blister growth and interfacial parameters of the form A(t) A(t₀)=exp[βp²h ph-γ (t- t₀)] where A(t) is the blister area at time t, p is the applied pressure, h is the spacer height, y is the energy of interfacial adhesion, and β is a dissipative coefficient which is also related to geometric factors. The validity of the theoretical model was tested using a rubber-based pressure sensitive adhesive (PSA) tape. The PSA tape was investigated as a function of the applied pressure and the spacer height. A value of 44 J/m² was determined for the energy of interfacial adhesion. The dissipative coefficient, β, was found to vary with the applied pressure and the spacer height.     

Gas permeation and temperature effects in laser-induced delamination

Laser-induced delamination (LID) is a technique aimed at measuring the work of adhesion of thin polymer coatings on metal substrates. A laser pulse is used to create a blister that initiates delamination of the film under pressure. The stress fields in the blister wall and the work of adhesion of the interface are determined using a linear elastic model.In this paper we discuss validity of the LID results addressing permeation of gas through the blister wall and the initial high temperature of the substrate. A procedure to account for the effect of gas permeation in the calculations of the work of adhesion is proposed. Permeation of gas is also considered under compressive and tensile in-plane stresses. Modeling of the permeation process demonstrates a good agreement with the experiment.At early stage of the blister formation the metal substrate and the blister gas experience high temperatures. The time scales of the cooling processes are estimated. Possible effects of the high temperatures on the permeation of gas and on the process of delamination are discussed.     

Thermodynamics of a Stable Blister Delamination at Elevated Temperature

A new blister test using thermal expansion of an internal working gas trapped at a dissimilar interface between a thin polymer coating and a rigid adherend is developed to measure the adhesive strength at elevated temperature. The blister dimensions are measured by a thermomechanical analyser (TMA) and an optical microscope as a function of temperature. The thermodynamics is presented based on both linear elastic fracture mechanics and the ideal gas law.     

Evaluation of the weathering performance of basecoat/clearcoat automotive paint systems by electrochemical properties measurements

The aim of the present study was to investigate the possibility of evaluating the weathering performance of a basecoat/clearcoat automotive paint system through the determination of its electrochemical properties. To this end, the electrochemical properties of a basecoat/clearcoat automotive paint in a 3.5% solution of NaCl in deionized water were measured at different weathering exposure times. A constant phase element (CPE) was used for describing the electrochemical behavior of the coatings under test. The values of the CPE parameters, i.e. Y₀ (the CPE constant) and n (the CPE power) were subsequently correlated to the extent of photo-oxidation (as measured by appearance, surface roughness, FTIR, surface tension and adhesion measurements) of clearcoat at the surface, in the bulk and at the interface between the basecoat and the clearcoat. The result showed that the electrochemical parameters Y₀ and n provide ready means for comparing the weathering performances of basecoat/clearcoat automotive paint systems. Increases in the value of Y₀ together with decreases in the value of n with increasing weathering exposure times suggest increased possibilities for the onset of cracking in the clearcoat itself in addition to its propagation towards the basecoat. Additionally, sudden variations in the values of Y₀ and n are indicative of increases for the clearcoat to peel off.     

A Fracture Mechanics Approach to Characterizing Cyclic Debonding of Varied Thickness Adhesive Joints to Electroprimed Steel Surfaces

Applications of adhesive bonding for automotive structures have been increasing in recent years due to improvements in the types of adhesives available and in improved knowledge of bonding procedures. Consequently, there exists a demand for design techniques to assess the influence of bondline thickness on adhesive joint strength. One design approach currently being used is based on limiting shear stresses in the adhesive while designing to eliminate peel stresses. Another design approach is based on fracture mechanics and accounts for shear and peel stresses and both static and fatigue modes of failure. The present study applies fracture mechanics to investigate the mixed-mode response of cracked-lap-shear (CLS) joints bonded with unprimed and electroprimed steel surfaces. Three bondline thicknesses equal to 0.254, 0.813, and 1.27 mm were evaluated for unprimed and primed bondlines. For the experimental portion of the study, debond growth rates (da/dN) were measured using a remote imaging system over a range of applied cyclic loads. Corresponding changes in the strain release rates (ΔG) were calculated, through finite element analyses, as a function of debond length and applied load level. The computations for ΔG applied a finite element formulation to determine both the peel component, ΔG_i, and the shear component, ΔG_ii. When computed ΔG values were plotted against the measured debond growth rates, da/dN, the results showed a power law relationship which characterizes the debond behavior of a given material system and bondline thickness.     

The role of basecoat pigmentation on the biological resistance of an automotive clearcoat

This work aims to study the effect of various natural and artificial biological compounds on an automotive acrylic/melamine clearcoat applied over silver and black basecoats containing pigments. The visual performance of the coating system was evaluated at different aging conditions. To this end, analytical techniques including optical microscopy, scanning electron microscopy, gonio-spectrophotometery, gloss measurement, ATR-FTIR spectroscopy, and DMTA analysis were utilized to investigate the optical and mechanical response of the system upon exposure to the biological materials. Results indicated different effects produced by gums and bird droppings on both silver and black systems at all aging processes. In addition, a more severe effect of biological attacks was observed on the clearcoat samples applied on the black basecoat which had experienced postaging conditions. However, it was found that pancreatin and bird droppings influence the coating systems more severely compared to the natural and synthetic Arabic gums.     

水性吸塑油的研究

在对水性光油研究的基础上,对吸塑包装的工艺、原理进行了深入的分析,考察了吸塑剂、渗透剂、Tg对水性吸塑油使用性能的影响,得到了满足下列使用条件的水性吸塑油:(1)泡壳基材为PVC或PET;(2)纸卡材料为白版纸、白卡纸或铜版纸;(3)热封方式可采用电加热或高周波吸塑热合工艺。该水性吸塑油已经通过工业化生产并上机验证,可满足吸塑粘合要求。     

双循环流化床混合颗粒流率实验研究与核极限学习机模型预测

两床间颗粒循环流率是保证双循环流化床正常运行的关键。在自行设计的双循环流化床（DCFB）实验系统上进行循环流率（G _s,mix）与各控制参数（气化室风速、提升管风速、初始床层物料量、混合物料中石英砂粒径以及稻壳质量分数）变化关系的研究，并对循环物料中稻壳质量分数（X _r）变化进行分析。此外，根据实验测量数据，建立核极限学习机（KELM）模型并进行G _s,mix和循环物料中X _r的预测，同时与极限学习机（ELM）模型进行比较，发现KELM模型具有更小的预测平均绝对值误差和均方根误差且预测所需时间较短，表明该模型可实现各控制参数下DCFB系统中G _s,mix和X _r的良好预测，为DCFB系统及类似气化系统的数据模型研究提供一种新方法。     

Use of the Blister Test to Study the Adhesion of Brittle Materials. Part II. Application

Using a modified form of the blister test, where the adhesive layer was between the substrate and a massive base, instead of as a continuous sheet on top of the substrate, we determined the interfacial fracture energy F for a series of interfaces where a brittle material (ice) was adhering to various substrates. Fracture energies obtained were compared with work of adhesion values measured for water on the same substrates. Fracture energy, which contains within it both a reversible contribution due to intermolecular interactions across the interface (work of adhesion) and an irreversible contribution due to collective dissipative processes, was found to rise rapidly with modest increases in work of adhesion. The observed relation suggests that the irreversible contribution to fracture energy is influenced strongly by the intermolecular interactions at the interface.     

Measurement of charge distribution in polymer electrets by a new pressure-pulse method

Summary The charge distribution in the thickness direction of 10 to 100 m thick polymer electrets can be determined with a new method utilizing a <1 ns laser pulse to launch a pressure pulse in the sample. Propagation of the pressure pulse through the film causes electrode currents which yield the charge distribution. The method has been applied to electron-beam charged PETP and FEP samples.