Blister Test Research Articles

Numerical investigation on adhesion properties of graphene nanofilm debonding from substrate

The adhesion properties of graphene nanofilm are studied by finite element simulation according to an approach of blister test. The critical debonding load and debonding deflection are calculated, and their dependence on the geometrical dimensions of the graphene nanofilm is analysed when the graphene nanofilm begins to debond from the substrate. The results of simulation show a good agreement with the theoretical results as well as the corresponding experiment results. Furthermore, the influence of adhesion energy and graphene thickness on the debonding behaviour of graphene nanofilm is also investigated, and the results show that there exist an obvious size effects for the critical debonding load and debonding deflection.

Closed-form Formulas for Adhesion Energy of Blister Tests Under Pressure and Point Load

Based on the nonlinear finite element analysis results and the known theoretical equations for the two extreme regimes of bending plate and stretching membrane, we propose two new closed-form formulas for determining the adhesion energy or interfacial energy release rate for pressurized and point-loaded blister tests. A comparison with existing experimental data shows that the present formulas can predict energy release rate well in the full range of all parameters, covering all three regimes of bending plate, transition from plate to membrane, and stretching membrane, for both pressurized and point-loaded blister tests.

All-Optical Blister Test of Suspended Graphene Using Micro-Raman Spectroscopy

We report a comprehensive micro-Raman study of a pressurized suspended graphene membrane that hermetically seals a circular pit, etched in a Si/SiO$_2$ substrate. Placing the sample under a uniform pressure load results in bulging of the graphene membrane and subsequent softening of the main Raman features, due to tensile strain. In such a microcavity, the intensity of the Raman features depends very sensitively on the distance between the graphene membrane and the Si substrate, which acts as the bottom mirror of the cavity. Thus, a spatially resolved analysis of the intensity of the G- and 2D-mode features as a function of the pressure load permits a direct reconstruction of the blister profile. An average strain is then deduced at each pressure load, and Gr\"{u}neisen parameters of $1.8\pm0.2$ and $2.4\pm0.2$ are determined for the Raman G and 2D modes, respectively. In addition, the measured blister height is proportional to the cubic root of the pressure load, as predicted theoretically. The validation of this scaling provides a direct and accurate determination the Young's modulus of graphene with a purely optical, hence contactless and minimally invasive, approach. We find a Young's modulus of $(1.05\pm 0.10) \rm TPa$ for monolayer graphene, in a perfect match with previous nanoindentation measurements. This all-optical methodology opens avenues for pressure sensing using graphene and could readily be adapted to other emerging two-dimensional materials and nanoresonators.

Adhesion and Puncture Strength of Polyurethane Coating Used to Mitigate Tin Whisker Growth

Reliability of conformal coatings used to mitigate tin whisker growth depends on their ability to contain tin whiskers. Two key material properties required to assess the reliability of a polyurethane coating are documented experimentally: adhesion strength and puncture strength. A modified blister test using a predefined blister area is employed to assess the adhesion strength and a puncture test is employed to evaluate the puncture strength of the coating. After measuring the properties at time zero, the coatings are subjected to accelerated testing conditions (high temperature/humidity storage and temperature cycling) and the degradations of the coating properties are documented.

Effects of Pretreatments on the Adhesion of Acetoacetate to AA2024-T3 Using the Blister Test

The blister test was used to assess the effect of various pre-treatments, including chromate conversion coatings, non-chromium process conversion coatings, and trivalent chromium process coatings, ...

Theoretical study on shaft-loaded blister test technique: Synchronous characterization of surface and interfacial mechanical properties

In this paper, the existing shaft-loaded blister test technique was improved and a theoretical study on synchronous characterization of mechanical properties of coating thin-film and film/substrate interface was presented. Problems considered include the exact analytical solution to the problem of axisymmetric deformation of a blistering film and the theoretical derivation of expressions to determine Poisson׳s ratios, Young׳s modulus, the work done by the applied external load, the elastic energy stored in a blistering film, and energy release rate. Some relative issues such as how to control the blistering film as free as possible from plastic yielding and the influence of changing the loading-shaft radius on the membrane stress distribution were discussed. Moreover, an experiment was conducted to verify the presented theoretical work.

A blister test for interfacial adhesion of large-scale transferred graphene

A blister test and associated analysis was developed to characterize the interfacial adhesion between graphene and substrates to which it has been transferred. In this study, chemical vapor deposition grown graphene had been transferred to a highly polished copper substrate from its seed foil. The graphene/photoresist composite film was pressurized with deionized water through a nominally 1-mm hole in the copper and the deflection of the membrane was measured by a full field interference method. The deflection profiles compared well with those obtained from a linear plate model that accounted for the initial strain in the membrane and a relaxed boundary condition at the edge of the blister. This was used to calculate the energy release rate as a function of delamination growth to obtain fracture resistance curves for the graphene/copper interface. To the best of our knowledge, these are the first measurements of fracture resistance curves for adhesive interactions between transferred graphene and a copper substrate. The delamination path of the graphene/photoresist sample was confirmed by Raman spectroscopy. The measured adhesion energy for the graphene/copper interface was higher than that of a photoresist/copper interface, but slightly lower than previous measurements for as-grown graphene on copper foil.

Applications of Squeeze Casting for Automobile Parts

With an increasing pressure on automotive weight reduction, the demand on the lighter weight automotive components continues to increase. In recent years, squeeze casting processes have been used with different aluminium alloys to produce high integrity automotive parts. In this study, the indirect squeeze casting processes is adopted to cast a motorcycles component originally produced by a high pressure die casting process using aluminium alloy ADC12. To minimize amount of gas porosity inside squeeze casts, concepts of (1) minimization of ingate velocity along with (2) bottom filling pattern during the die filling, and (3) maximization of intensifications casting pressure are applied. Then parts are casted with both conventional high pressure die casting and indirect squeeze casting processes. Comparative evaluation of mechanical properties was made between HPDC casts and squeeze casts both in as-cast and heat treated conditions. Results from the experiment have shown that squeeze casts can pass the blister test at 490 °C for 2.5 hours. Then, squeeze casts are heat treated by solution treatment at 484 °C for 20 minutes and artificial age at 190 °C for 2.5 hours, respectively. This improves UTS of the heat treated squeeze cast to 254.14 MPa with 1.84% of elongation, while the UTS of as cast condition from both processes is not significantly different.

Effect of Roughness and Surface Topography on Adhesion of PVB to AA2024-T3 using the Blister Test

Corrosion protection through protective coatings depends on the adhesion of the coating system to the base metal, which is controlled by surface treatments. Measuring adhesion strength is a challenging task. However, the Blister Test (BT) is a quantitative and reproducible technique not exploited in the corrosion field. In this investigation, the effect of roughness and surface topography is studied using this technique. Samples were abraded using SiC paper up to 120, 180, 600 and 1200 in a randomly or aligned manner to obtain different topographies and roughness levels in the range of 0.026 to 1.324μm. The surfaces were characterized using Optical Profilometry before polyvinyl butyral (PVB) coating was applied. Then the adhesion strength was determined using the BT. The substrates abraded randomly presented lower average roughness than the ones abraded in an aligned manner due to continual cross abrasion of grooves. The adhesion strength results from the BT were reproducible and could rank different mechanical treatments. Roughness degree and surface topography were found to be very important factors for adhesion strength. Adhesion strength was found to increase with roughness for both abrasion methods; however the random samples exhibited the highest adhesion strength at similar roughness values. The groove peaks were found to be stronger barriers than the groove valleys as a result of a higher peeling angle needed for delamination to take place, increasing the energy used for plastic deformation and therefore decreasing the energy available for blister growth. An adhesion strength indicator (AS) was defined based on peeling rate and found to be effective in sensing adhesion strength.

Determination of interfacial adhesive properties for polymeric film by blister test

The interfacial adhesive properties of polypropylene/stainless steel were studied by the blister test. The polypropylene film with a squared free-standing window was pressured by oil from one side of film. The corresponding deformation field was observed by a digital speckle correlation method. The experimental results show that the squared film deforms and debonds from stainless steel with the increase of pressure. The debonding of the squared film in initiates from the center of edge and extends to the corner, and then the deformation of film evolves from square to circle shape. The interfacial adhesive energy of polypropylene/stainless steel is (22.60±1.55) J/m2, which is in agreement with that measured by film with a circular window.

Measurement of the mechanical properties of nickel film based on the full-field deformation: An improved blister method

To characterize the mechanical properties of thin films, an improved blister method is proposed, which combines a digital speckle correlation method with the blister test. Based on this method, an experimental setup is developed to measure Young's modulus, residual stress, and interfacial adhesion energy of an electroplated nickel film. The results show that the improved blister method has the advantage of a high accuracy full-field measurement with the simple operation and low requirement on environments, which can be used to characterize the mechanical properties of films with various scales from laboratorial to industrial applications.

Effects of carbon nanotube content on adhesion strength and wear and corrosion resistance of epoxy composite coatings on AA2024-T3

The effects of multiwalled carbon nanotube (MWCNT) content on the adhesion strength and wear and corrosion resistance of the epoxy composite coatings prepared on aluminum alloy (AA) 2024-T3 substrates were evaluated using atomic force microscopy (AFM), blister test, ball-on-disk micro-tribological test and electrochemical impedance spectroscopy (EIS). The adhesion strength of the epoxy composite coatings improved with increasing MWCNT content. Increased MWCNT content also decreased the friction coefficient and increased the wear resistance of the epoxy composite coatings due to improved solid lubricating and rolling effects of the MWCNTs and the improved load bearing capacity of the composite coatings. Finally, EIS indicated that increased MWCNT content increased the coating pore resistance due to a decreased porosity density, which resulted in an increase in the total impedance of the coated samples.

Adhesive blister propagation under an orthotropic bituminous waterproofing membrane

In most countries, waterproofing systems used on concrete bridge decks or roofs of buildings are generally based on orthotropic bituminous membranes; amongst these, styrene–butadiene–styrene copolymer (SBS) and atactic polypropylene (APP) polymer modified bituminous membranes are being used in most applications. One of the main technical concerns is the formation of blisters under the membrane caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. This paper intends to contribute in understanding this mechanism by mechanical elastic modeling and experimental investigation. In order to study the material properties of SBS membranes under the in-plane complex stress state, the orthotropic mechanical behavior of a polymer modified bitumen membrane (PBM) was determined from biaxial test data. Hence, the measured stress–strain data were analyzed using the orthotropic equation to find the material properties in the longitudinal and transversal direction. Finally, blister tests were performed on concrete plates for studying adhesive blister propagation by applying controlled pressure between the PBM and the concrete plates. It was found that the ratio of the longitudinal to transversal adhesive blister propagation is comparable to the ratio of the modulus of elasticity in the longitudinal to transversal direction. Due to the orthotropic material property of the PBM, elliptical adhesive blister propagation was observed and a new model proposed for determining the energy for elliptical adhesive blister propagation.

Characterization of flow behavior of semi-solid slurries containing low solid fractions in high-pressure die casting

Understanding the flow behavior of semi-solid slurries containing low solid fractions is key to the success in applying this process in the die casting industry. With these low initial solid fractions, the flow behavior of semi-solid slurries is quite complicated, making it difficult to model accurately. This present work developed and studied characterization methods for the flow behavior of semi-solid slurries at low solid fractions in high-pressure die casting. A new parameter, the ratio of gate speed to initial solid fraction (Vg/fs), was proposed to be correlated to the normalized flow interface length, blister area and tensile properties. Results from the flow pattern analysis suggest that the flow behavior can be controlled to achieve laminar flow by varying the initial solid fraction. Blister test results show the trend that slurry die casting conditions with high Vg/fs values exhibit high blister areas. Die casting conditions with excessively high gate speeds and insufficient solid fractions result in turbulent flow patterns and high levels of blister defect. The results of tensile test and fracture surface analysis are consistent with other analysis results. The samples formed by liquid die casting and slurry die casting with high Vg/fs values have gas porosity due to turbulent flow pattern during die filling. On the other hand, the samples formed by slurry die casting with too low Vg/fs values contain shrinkage porosity. This is because of insufficient time for shrinkage feeding due to a combination of a high solid fraction and a low gate speed. This study has demonstrated that die casting with slurries containing low initial solid fractions gives die casters another process parameter to adjust, which can help reduce and control the gas and shrinkage porosities.

A comparative study of the bonding energy in adhesive wafer bonding

Adhesion energies are determined for three different polymers currently used in adhesive wafer bonding of silicon wafers. The adhesion energies of the polymer off-stoichiometry thiol-ene-epoxy OSTE+ and the nano-imprint resist mr-I 9150XP are determined. The results are compared to the adhesion energies of wafers bonded with benzocyclobutene, both with and without adhesion promoter. The adhesion energies of the bonds are studied by blister tests, consisting of delaminating silicon lids bonded to silicon dies with etched circular cavities, using compressed nitrogen gas. The critical pressure needed for delamination is converted into an estimate of the bond adhesion energy. The fabrication of test dies and the evaluation method are described in detail. The mean bond energies of OSTE+ were determined to be 2.1 and 20 J m−2 depending on the choice of the epoxy used. A mean bond energy of 1.5 J m−2 was measured for mr-I 9150XP.

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.

Mechanics of Adhered, Pressurized Graphene Blisters

We study the mechanics of pressurized graphene membranes using an experimental configuration that allows the determination of the elasticity of graphene and the adhesion energy between a substrate and a graphene (or other two-dimensional solid) membrane. The test consists of a monolayer graphene membrane adhered to a substrate by surface forces. The substrate is patterned with etched microcavities of a prescribed volume and, when they are covered with the graphene monolayer, it traps a fixed number (N) of gas molecules in the microchamber. By lowering the ambient pressure and thus changing the pressure difference across the graphene membrane, the membrane can be made to bulge and delaminate in a stable manner from the substrate. This is in contrast to the more common scenario of a constant pressure membrane blister test, where membrane delamination is unstable, and so this is not an appealing test to determine adhesion energy. Here, we describe the analysis of the membrane/substrate as a thermodynamic system and explore the behavior of the system over representative experimentally accessible geometry and loading parameters. We carry out companion experiments and compare them to the theoretical predictions and then use the theory and experiments together to determine the adhesion energy of graphene/SiO2 interfaces. We find an average adhesion energy of 0.24 J/m2, which is lower but in line with our previously reported values. We assert that this test—which we call the constant N blister test—is a valuable approach to determine the adhesion energy between two-dimensional solid membranes and a substrate, which is an important but not well-understood aspect of behavior. The test also provides valuable information that can serve as the basis for subsequent research to understand the mechanisms contributing to the observed adhesion energy. Finally, we show how, in the limit of a large microcavity, the constant N test approaches the behavior observed in a constant pressure blister test, and we provide an experimental observation that suggests this behavior.

Theoretical study of adhesion energy measurement for film/substrate interface using pressurized blister test: Energy release rate

In this paper, a new loading method able to subtly control the crack driving force for pressurized blister test was proposed. A theoretical study of the adhesion energy measurement for film/substrate interface using this loading method was presented. Problems considered include solving the exact volume under a circular blister and the elastic strain energy stored in a thin blistering film, determining the work done by the poured colored liquid as external force to the system and the elastic strain energy stored in the compressed air. A new formula of energy release rate was finally presented. A comparison between the work presented here and the existing work was made.

Characterization of thin film adhesion by MEMS shaft-loading blister testing

A new microelectromechanical system shaft-loaded blister test was developed and demonstrated to provide stability, repeatability, and simultaneous quantitative measurements of adhesion between thin films deposited on a silicon substrate. The authors assessed adhesion of sputtered platinum, copper, and chromium/copper (300 nm) to underlaying atomic layer deposited (ALD) aluminum oxide. The average adhesion energies for thin films on ALD aluminum oxide were found to be 1.15 ± 0.1 J/m2 for platinum thin films, 1.4 J/m2 for copper thin films, and 1.75 J/m2 for chromium/copper.

Selective molecular sieving through porous graphene

Membranes act as selective barriers and play an important role in processes such as cellular compartmentalization and industrial-scale chemical and gas purification. The ideal membrane should be as thin as possible to maximize flux, mechanically robust to prevent fracture, and have well-defined pore sizes to increase selectivity. Graphene is an excellent starting point for developing size-selective membranes because of its atomic thickness, high mechanical strength, relative inertness and impermeability to all standard gases. However, pores that can exclude larger molecules but allow smaller molecules to pass through would have to be introduced into the material. Here, we show that ultraviolet-induced oxidative etching can create pores in micrometre-sized graphene membranes, and the resulting membranes can be used as molecular sieves. A pressurized blister test and mechanical resonance are used to measure the transport of a range of gases (H(2), CO(2), Ar, N(2), CH(4) and SF(6)) through the pores. The experimentally measured leak rate, separation factors and Raman spectrum agree well with models based on effusion through a small number of ångstrom-sized pores.