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Optical components are often adjusted to maintain their alignment along the optical axis. They are fixed at their optimal positions particularly using ultraviolet (UV) ray-curable adhesives. To ach...

The plastic zone at the crack front of an adhesively bonded double cantilever beam (DCB) specimen is analytically expressed considering the deformation of the adhesive layer. The plastic zone lengt...

Although adhesive-adherend interfaces play an important role in improving adhesive joint strength, their observation is a challenging task. If the adhesive and adherend can be clearly separ...

A method to prevent substrate damage in a double cantilever beam (DCB) test was experimentally investigated by changing bond-line width. Highly toughened adhesives are developed due to an increase in the demand for structural adhesives. Furthermore, structural materials that are lightweight and excellent in mechanical properties but have limitations in thickness are developed. In contrast, plastic deformation of the substrates is expected when the DCB test is performed with conventional DCB specimens using the aforementioned adhesives and materials. The reduction in the maximum stress on the substrate surface by narrowing a bond-line width is a practical method to prevent plastic deformation when a substrate possesses limited thickness. In this study, the influence of the bond-line width on an adhesive fracture energy in mode I was experimentally investigated by manufacturing DCB specimens in which the bond-line width is narrower than the substrate width. Additionally, the maximum bond-line width ...

A method for fabricating adhesively bonded joints with graded properties along the bond-line was proposed. By utilizing two types of acrylic adhesives, one hard and the other soft, the properties of the mixture were changed by controlling the mixing ratio. An applicator for the adhesives was developed and used for the experiments, in which property-graded adhesive layers were actually produced. The properties, i.e., stress-strain curves at various points of the property-graded adhesive layer, were experimentally measured, and the validity of the proposed method was confirmed. The Young’s moduli at multiple points of the adhesive layer changed from 34.7 MPa to 634 MPa by changing the mixing ratio of the adhesives.

The expansion characteristics of thermally expandable microcapsules (TEMs) under hydrostatic pressure or in resin were experimentally investigated. For the experiments, the expansion of the microcapsules was observed in high-pressure nitrogen at high temperature utilizing optical microscopy with a digital camera installed. The TEMs used for the experiments were expanded by heating under hydrostatic pressure up to 3 MPa, but the expansion degree decreased with increasing pressure. A cured bulk specimen of epoxy resin containing the microcapsules was made, and the expansion of the microcapsules was again observed with the microscope. It was found that the expansion of the microcapsules in the resin was saturated at a certain temperature. The stress distribution in the resin produced by the expansion of the microcapsules was calculated by the finite-element method. It was found that normal stress occurred, but it was mainly compressive. Tensile stress was also generated, although the maximum value wa...

The separation characteristics of an electrically dismantlable adhesive, ElectRelease, were experimentally investigated. The adhesive has a strength that decreases by applying voltage. The residual strengths of cylindrical butt joints bonded with the adhesive were measured after voltage application. Various experiments were carried out in order to investigate the influences of the bonding area and the type of adherend materials on the residual strength by changing the dimensions and material of the adherends. The influence of constant voltage and current applications was also examined. As a result, it was confirmed that the residual strength of a joint does not depend significantly on the bonding area but on the type of adherend material. The residual strength was able to be determined and predicted by using an areal density of the total charge passing through the bonding area. Higher applied voltage was able to accelerate the decay of the residual strength and shorten the time for a given decreas...

Thermal effects on welded joints between fiber-reinforced thermoplastics (FRTPs) and metals have been investigated theoretically and experimentally. Because FRTPs use thermoplastics as the matrix resin, they have advantages over fiber-reinforced thermoset plastics (FRPs or FRSPs), including the ability to be welded. When dissimilar materials are welded together, however, thermal stress occurs due to the different thermal expansions of the materials and affects the energy release rate of the joint. Therefore, a method for evaluating the true energy release rate, including the effect of thermal stress, is necessary for strength evaluation tests. Although several theories that compensate for the thermal stress and evaluate the true energy release rate have already been proposed, they require parameters that are difficult to measure. Therefore, it is difficult to apply them in experimental investigations. In this article, a theoretical method with easily measurable parameters is proposed to calculate the ener...

The Mode I fracture energy of a polyurethane adhesive with low Young’s modulus was investigated. Metal adherends in standardized double cantilever beam (DCB) tests are typically too stiff for soft adhesives, making it difficult to measure the fracture energy accurately. However, soft adhesives, such as a single-component polyurethane adhesive tested in this paper, are in high demand in the automobile industry. Thus, accurate measurement techniques must be established. Flexible substrates composed of spring steel were used for the DCB tests to accommodate the deformation of the adhesive layer. First, the applicability of the flexible substrates was discussed using specimens bonded with an epoxy adhesive. For soft adhesives, however, the deformation of the adhesive layer must be considered in the calculation methods of the fracture energy. Although the deformation effect on the DCB tests has been discussed with Winkler’s elastic foundation, the crack length must be measured along with the load and d...