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In this study, the effect of a tackifier on the viscoelastic and adhesion properties of acrylic pressure-sensitive adhesives (PSAs) was investigated. The intermediate products in the process of PSA synthesis, including an acrylate-based copolymer solution, a cross-linked copolymer, and the final product with a tackifier, were prepared and characterized using dynamic mechanical analysis (DMA). A significant increase in storage and loss moduli at high angular velocities was observed for the final product with the tackifier. The adhesion forces of the copolymer solution and the cross-linked copolymer measured by atomic force microscopy (AFM) were found to be almost independent of the release velocity, whereas that of the final product with the tackifier significantly increased at higher release velocities because of viscoelastic effects. Their fibrillations during the release process were also visualized using a charge-coupled device (CCD) camera installed on the cantilever holder. Although the contact area of the copolymer solution and the cross-linked copolymer with the probe surface decreased until detachment, the final product with the tackifier remained constant, with necking just below the probe surface. The increased storage and loss moduli were considered to resist the shrinkage of the contact area because the contact outline was subject to high shearing deformation, which led to localized high strain rates. Overall, the crucial role of the tackifier in maintaining the contact area for sufficient elongation during fibrillation was established.

This present study has been re-established to investigate failure mode and resistance characteristics of the PC/ABS blends and their ABS constituents under impact for a range of rubber contents. This present study has still been experimentally performed under an instrumented-drop weight impact test (DWIT) at a room temperature. It has been finally revealed that with a particular size of rubber particle, content of rubber significantly influenced impact failure modes and impact resistances of the PC/ABS blends and their ABS constituents as well. The test results showed that impact strength of the blends was improved about 23.22% and 155.33% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. There was also found that an increase in impact toughness of the blends for 57.48% and 239.23% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. Whilst, impact strength of the ABS was improved about 392.98% and 190.12% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. An increase in impact toughness of the ABS for 308.20% and 172.56% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively.

This study extensively investigates the fibrillation process of a pressure-sensitive adhesive (PSA) using a probe-tack test. It was conducted using a glass sphere at the millimeter scale for various thicknesses of PSA layers laminated on a glass substrate, on various contact areas. A sharp decrease in the adhesion force caused by cavity growth was confirmed in the case of large contact areas, whereas cavities were not generated in the case of small contact areas on the thick PSA layer. Furthermore, an atomic force microscopy (AFM) cantilever was used to conduct a probe-tack test on considerably smaller contact areas at the micrometer scale, to focus on the fibrillation process by avoiding the cavity-growth. The transition of the adhesion force during the release process by the AFM cantilever was confirmed to resemble the transition in the fibrillation process obtained using the glass sphere by the repeated tests using the probe without cleaning the surface. The fully adhesive failure was also confirmed by the tests at sufficiently high release velocity. A comparison of these tests at different scales revealed that the detachment force from the probe at the millimeter scale is proportional to the contact area, and determined using the release-strain rate through elongation of the entire thickness of the PSA layer. By contrast, the detachment force from the AFM cantilever is proportional to the contact radius and determined using the release velocity regardless of the PSA thickness.

This study evaluated the correlation between crystallite size and micromechanical characteristics of micrometer-sized monoclinic WO3 particles. To avoid the existence of other parameters in the measurement (such as impurities and porous structure in the particle), micrometer WO3 particles were prepared using a direct heat treatment of ultrapure micrometer-sized ammonium tungstate powders. The crystallite size was controlled independently in a constant WO3 particle outer diameters to obtain a precise measurement result. The mechanical properties, i.e., hardness and Young’s modulus, were measured by load-controlled nanoindentation test on the singular WO3 particles. The force and displacement relationship data was plotted and analyzed to obtain the correlation between crystallite size and mechanical properties. The results revealed that the micro-mechanical properties of WO3 particles were strongly dependent on the crystallite size. The hardness and Young’s modulus values increased more than 40 and 15 times, respectively, when increasing the crystallite size to about 40 nm. The study was completed with a proposed mechanism of crack propagation inside the particle due to static load. The study demonstrates the important role of crystallite size in determining the micro-mechanical characteristics of WO3 particles. The result is useful especially when utilizing WO3 microparticles for various processes involving extreme conditions, such as high pressure reaction.

This work investigates the influence of fiber surface profile and roughness to fiber–matrix interfacial properties. A series of the push-out test is performed using specimens with different fiber surface profile and roughness. Numerical simulation is then carried out by employing a finite element method to fit the experimental data. The model contains an indenter which pushes in a single fiber from the matrix, while the cohesive zone model is applied to represent the interface resulting in force–displacement curves. Our results suggest that continuous cavities formed in graphite-based fiber may not be beneficial to interfacial properties since it can accelerate a debonding process along with the interface. In contrast, scattered cavities on the fiber surface create strong mechanical locking, which increases the interfacial strength. These results broaden the understanding of the surface profile, which would shed light on a new perspective in designing composite structures.

Deformation induced by capillarity needs to be characterized appropriately to avoid unexpected collapse or to control self-assembly of fine structures. Nevertheless, even simple phenomena such as the pinching together of two plates require delicate instruments for observation. Our group proposed a simple experimental setup in which parallel plates separated by small gaps and fixed at their bottom ends were lowered into a liquid. Bending deformation of the plates caused by capillary rises between their inner surfaces was observed at the liquid surface. The experiments revealed that plates do not coalesce simultaneously, but in a sequence starting from pairs with the current smallest gap and with little influence of capillary rises in neighboring plates. After each pair of plates had coalesced, they behave as a single plate causing subsequent coalescences to occur in a similar manner. An analytical model based on this prescription is established to predict the deflection of plate pairs up until coalescence finishes. The effectiveness of the model was confirmed by accurately predicting the sequence of coalescence in multiple plates. Furthermore, it is presented that conditions required to avoid either coalescence in a pair of plates or complete coalescence of all plates can be determined by a non-dimensional parameter. [2018–0272]

Multilayer thin films polymer have been commonly used in a wide range of electronics applications, such as solar cells, photoconductors, semiconductors, and light-emitting diodes, in which failure due to delamination can occur. For evaluating and improving the quality of a multilayer thin-film product, the interfacial strength between its layers must be measured correctly and accurately. In this work, the interfacial strength of a multilayer thin-film polymer was quantified by measuring the interfacial energy release rate (interfacial fracture toughness), Gi , using the nanoindentation test technique. Three specimens of four-layer thin films were fabricated on a glass substrate. The top layer of each specimen was prepared with different thicknesses. The unloading curve technique introduced by Kozuki and Kishimoto (2010) was implemented to quantify the Gi of each specimen. Then, cross-sectional observation of the specimens was performed to confirm the layer thicknesses and to identify the delamination condition after the test. The measured Gi tended to increase as the range between the two unloading curves used to calculate the delamination energy widened. This phenomenon is believed to be caused by the plastic energy of the deformed films during the indentation process. Finally, an empirical method for eliminating the effect of the plastic energy on the measured Gi was proposed. Using this method, a pure Gi value can be effectively extracted; thus, the interfacial strength of multilayer thin-film polymers can be measured correctly and accurately.

In turbomachinery, such as turbine, pump, and valve, components damage caused by collapsing cavitation bubbles has been a critical issue that needs a proper solution. For this reason, investigation on the cavitation erosion behavior of materials as well as the life prediction techniques has been extensively conducted. Moreover, a number of repairing techniques, such as by a surface coating of polymeric materials, has been established. However, in real operation, cavitation is actually not the only load acquired by the components. Other external loads, such as centrifugal force and hydraulic pressure, may also affect the generation of damage. Therefore, its effect on the lifetime needs to be considered carefully. In this paper, the behavior of cavitation damage of epoxy resin specimens subjected to uniaxial tensile loading is reported. A self-developed testing device was used to conduct a cavitation test based on ASTM G32 while at the same time exerting a constant uniaxial tensile load to the specimen. Using this device, various levels of tensile stress effect on the cavitation damage was examined. As a result, besides erosion damage, we revealed that the specimens demonstrated fracture when a certain tensile load was applied. Furthermore, as the tensile load was increased, the time to fracture was shortened significantly, indicating the pronounced effect of tensile stress on the damage formation. The crack growth mechanism was then analyzed by fractography. The result indicated that the crack propagation under a mixed condition of cavitation and tensile loads was most likely driven by the combination of creep deformation and fatigue-like crack growth. Finally, a mathematical relationship between tensile stress and cavitation damage life was proposed. The relationship is important to enhancing the existing theory of cavitation damage evaluation in e.g. turbomachinery application.

To determine the fatigue limits of materials, fatigue testing, which is time-consuming and very expensive, is required. In order to overcome these shortcomings, estimating methods for fatigue limits based on temperature changes measured by IR camera have been proposed, and research and development of such methods have been widely conducted. In the current paper, a non-lock-in type, inexpensive IR camera was used for rotational bending fatigue testing to estimate the fatigue limit from temperature changes independent from loading signals. The results indicated that it is possible to estimate the fatigue limit from the time-temperature change curves measured under various stress conditions and converted stress amplitude-temperature change curves. The estimated results were sufficiently accurate and thus we confirmed that it is promising to estimate the fatigue limit by a non-lock-in type, inexpensive IR camera. The inflection point of a stress amplitude-temperature change curve can be determined by approximating a curve by two straight lines and finding the combination of the lines for which the sum of the residuals between the curve and the lines is the smallest. Although the temperature changes depended on the loading history (the number of loading cycles), the results of fatigue limit estimation changed little. Therefore, the proposed method is practically accurate as a simple estimation method. We also measured the behavior of stress-stroke for each loading history (the number of loading cycles) in tension-compression fatigue testing and confirmed that temperature changes during fatigue testing are associated with plastic strain energy.

This paper presents a finite element based method to investigate the hygrothermal effects on the transient dynamic response of delaminated composite pretwisted conical shells with initial twist impacted at arbitrary locations by multiple spherical impactors. An eight-noded shell element has been used in the present analysis based on the Mindlin’s theory. The generalized dynamic equilibrium equation is derived from Lagrange’s equation of motion neglecting Coriolis effect for moderate rotational speeds. The multi-point constraint algorithm has been incorporated to ensure the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front. The indentation laws as proposed by Hertz have been implemented to compute the contact force and displacement arising from each impact on specific locations of delaminated conical shells already prestressed by residual thermal or moisture strains. Results have been presented to depict the influence of important parameters like, twist angle, size and location of delamination, velocity and mass of the impactors and the time-delay between the impactors on the multiple impact response of delaminated composite conical shells in hygrothermal environment.

The adhesive force generated by a small short-term pressure, called tack, is measured by a probe tack test on pressure-sensitive adhesives (PSAs); the maximum force is evaluated by cavity growth at the interface between the PSA layer and the probe surface. As the PSA layer becomes thinner, it is more difficult to measure the tack with a cylindrical probe because of the uneven contact resulting from misalignment. A spherical probe is preferable to obtain reproducible contact on the PSA layer, but the contact area should be taken into account if the contact pressure affects the tack performance. Tack was measured on PSAs with various thicknesses in different contact areas to clarify their effect. The results showed that a larger contact area on a thinner PSA generated higher adhesive stress with larger strain. It was found that the maximum adhesive stress was not affected by the contact pressure, but it was strongly correlated to the contact radius divided by the PSA thickness. In addition, a video microscope observation showed that, in all of the experimental cases, the adhesive stress always reached the maximum when cavities were generated at the interface between the PSA and probe surface. Therefore, the criterion of cavity growth was introduced for the evaluation of the maximum adhesive stress. As a result, the experimental results, even at different release rates, were in good agreement with the estimation by considering the effect of confining a thin layer. Furthermore, the theoretical estimation indicated the ultimate value, which was not dependent upon the PSA thickness or contact area. It was defined as a material property, referred to as the "ultimate tack strength" of PSAs.

Adhesive properties of several serum proteins to the hemodialysis membrane surface previously studied by atomic force microscopy were compared with a more general case of adhesion/de-adhesion process of adhesive tapes and films. The three different tapes and film samples showed de-adhesion curves with different level of tack and flow properties. The two types of de-adhesion force curves of serum albumin from the hemodialysis membrane can be explained in terms of the difference in the physical process of de-adhesion and in a general perspective of self-cohesive force of the adhesives.

We have developed a new apparatus to dynamically generate supercritical CO 2 (scCO 2 ) bubbles in water using a water hammer facility by efficiently concentrating water energy. We measured the internal and external pressures of a CO 2 bubble covered with a rubber membrane using pressure transducers, and observed the bubble's oscillations by a high-speed video camera. We evaluated the maximum duration of the scCO 2 for conditions 60 μs in experiments. We performed numerical simulations using the Rayleigh–Plesset equation by substituting the experimental external pressure profiles of the bubble and confirmed that numerical results agreed with the experimental internal pressure. Moreover, in the minimum external pressure condition where we experimentally achieved the condition of scCO 2 in the bubble for 16 μs by water hammer, we obtained the maximum duration of scCO 2 conditions up to 55 μs by numerical simulations assuming isotropic compression.

In this study, we conducted water hammer experiments in the tube which was periodically supported by various numbers of clamps, named periodic structure, initiated by a projectile impact. The parts of the polycarbonate (PC) tube supported by 1-7 steel clamps make the tube stiffer and heavier than the original PC tube and are expected to cause a filtering effect of the frontal frequency components in the water hammer. According to our experimental observations, we confirmed that higher frequency components more than 1 kHz in the wave front were attenuated and the peak strains in circumferential direction of the tube were decreased 20% from the original PC tube. Moreover, we conducted numerical simulations of the water hammer wave similar to the experimental setup. Numerical results also revealed that frontal peak is attenuated 22% through periodic structure.

Our study focuses on the response of a water-filled polycarbonate tube under axial impact loading to the presence of a single large suspended particle. The particles, composed of steel, aluminum, and polycarbonate, were individually suspended by elastic string along the centerline of the tube. The impact of a free-fall piston initiated pressure waves in the water, called water hammer, and stress waves in the tube, especially at the level of the particle. Hoop strains were measured as impact responses; their distribution indicated that the maximum strains occurred around the particle. These maximum strains are narrowly confined and independent of particle composition. From measurements, hoop strain above the level of the particle become larger with increasing particle mass. We propose a theoretical model that assumes the particle to be a rigid body, and estimate tube responses from the change in area due to the particle’s presence rather than a dependence on particle material. With similar conditions as in experiments, numerical simulations, performed using the software AUTODYN, revealed that the particle motion initiated a reflected pressure wave and created another pressure wave underneath the particle. The transients propagating around the particle are independent of particle material, but composition does affect the attenuation of the reflected pressure wave above the particle.

In this paper, the resputtering technique without separated ion sources was used to improve the crystallization of alumina films during preparation at low temperature using reactive magnetron sputtering. The effects of the novel resputtering technique on the microstructural, mechanical and optical properties of alumina films were investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD), nanohardness measurements and Ultra/visible spectrometer. The AFM diagram indicated that the low root-mean-square (rms) roughness values of alumina films increased from 0.8 nm to 5.8 nm by the resputtering technique. The GIXRD patterns showed that with the resputtering technique, alumina thin films transformed from the amorphous phase into crystalline phase. The nanohardness of the films increased from 13.6 GPa to 15.6 GPa by the resputtering technique, which was only slightly smaller than that of the crystalline alumina films subjected to a post-annealing at 950 °C, about 16.6 GPa. Additionally, the crystalline alumina films deposited with resputtering technique also display good optical properties with higher refractive index, as compared to the amorphous films. The results suggest that the reactive magnetron sputtering with the resputtering technique is a simple, cheap and effective method of preparing crystalline alumina films at low temperature.

An important property of adhesive tapes is their tack performance, which relates to the adhesive force generated by a small short-term pressure on the tapes. Tack performance declines when an adhesive tape experiences tensile loading, but this influence has not been characterized well, especially for thin adhesive tapes. A testing apparatus is developed to quantitatively evaluate the influence of applied tensile loading on the tack performance of various thicknesses adhesive tapes. The apparatus allows microscopic observation of the adhered area during separation. The separation force of 15 μm and 5 μm thick adhesive tapes exhibit ductile behavior, while that of 1 μm thick adhesive exhibits brittle behavior. These separation behaviors relate to the generation of cavities in the adhesive, whose expansion is affected by adhesive thickness. Microscopic images show that the adhered area becomes smaller with increasing tensile loadings. The unified separation energy is defined and calculated for adhesive tapes, to simultaneously evaluate the tack performance for different adhesive thicknesses and applied tensile loadings. The separation energy decreases with increasing tensile loading, but the separation energy per unit area remains largely constant, regardless of the applied tension. The effect of separation speed on separation behavior is investigated, with a change from ductile to brittle separation observed with increasing separation speed. Separation speed is also reflected in the unified separation energy.

In this paper, thermal buckling properties of a nanoplate with small-scale effects are studied. Based on the nonlocal continuum theory, critical temperatures for the nonlocal Kirchhoff and Mindlin plate theories are derived. The thermal buckling characteristics are presented with different models. The influences of the scale coefficients, half-wave numbers, width ratios, and the ratios of the width to the thickness are discussed. From this work, it can be observed that the small-scale effects are significant for the thermal buckling properties. Both the half-wave number and width ratio have influence. The nonlocal Kirchhoff plate theory is valid for the thin nanoplate, and the nonlocal Mindlin plate theory is more appropriate for simulating the mechanical behaviors of the thick nanoplate.

The variable substitution and power-series techniques are used for the asymptotic analytical derivation of the governing equation of a transverse surface wave. The results reveal that the transverse wave can propagate along the surface of a functionally graded infinite half space in various modes, and that their dispersion relations are normal. For certain cases, energy is concentrated on the surface region to a depth of several wavelengths. A new theoretical foundation based on the transverse surface wave can be provided for graded-material characterization by experimental measurement. Some phenomena of seismic wave propagation may also be explained.

The elastic behavior of aluminum alloy foam under uniaxial loading and bending conditions is studied by experimental investigations and theoretical analyses. It is found from the experiments that the elastic moduli measured from three- and four-point bending tests as well as flexural vibration tests are significantly larger than the corresponding elastic moduli measured from uniaxial compression tests. This discrepancy cannot be described by the well-known elastic modulus equation introduced by Gibson and Ashby for foam materials. Theoretical analyses are carried out to explain the discrepancy and to improve the elastic modulus equation of Gibson and Ashby. In the analyses, unit-cell models are proposed, and elastic modulus equations for both uniaxial loading and bending conditions are derived. The derived equations offer a good description of the discrepancy as well as reveal the prominent role of cell local deformation under bending condition. Furthermore, the present work offers clear evidence that the classical continuum theories, such as Bernoulli–Euler beam theory, are inadequate for describing the elastic bending behavior of metal foams.