Yu Sekiguchi 교수

ABSTRACTThe 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

With an increasing demand for adhesives, the durability of joints has become highly important. The fatigue resistance of adhesives has been investigated mainly for epoxies, but in recent years many other resins have been adopted for structural adhesives. Therefore, understanding the fatigue characteristics of these resins is also important. In this study, the cyclic fatigue behavior of a two-part acrylic-based adhesive used for structural bonding was investigated using a fracture-mechanics appro

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 length and strain during the crack propagation are obtained, and the effect of the traction–separation profile on the DCB test results is investigated. The fracture energy is given by the area under the traction–separation curve and is not affected by the curve profile. However, the crack length of the DCB

Understanding the changes in the adhesive properties with the temperature and loading rate is important, particularly for designing adhesively bonded joints in structural applications. The viscoelastic behavior of adhesives is widely known to be based on the time–temperature superposition principle. In the case of the elastoplastic behavior, the stress–strain relationship is significantly affected by the external conditions, particularly for ductile adhesives. Similarly, the fracture behavior is

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

Abstract Conducting displacement‐controlled fatigue double cantilever beam tests of a structural acrylic adhesive, two different slopes were observed in the fatigue crack growth (FCG) relationship of the FCG rate versus the strain energy release rate (SERR) parameters depending on the loading conditions. Because fatigue is a two‐parameter problem where stress waveforms contain cyclic and monotonic terms, the contribution of each term toward FCG needs to be clarified. Therefore, each slope was ex

Abstract Adhesive joints are degraded when exposed to moist conditions, making it essential to assess the permeation distance of absorbed moisture. However, monitoring the water penetration in the adhesive layer is challenging because the adhesive layer is sandwiched between the adherends. To overcome this difficulty, we proposed a new monitoring system using fiber‐type near‐infrared spectroscopy (NIRS), and the moisture distribution at the joint was successfully observed by introducing quartz g

Double cantilever beam joints were manufactured from spring steel substrates bonded together using a twopartepoxy adhesive, a two-component type second-generation acrylic adhesive, and a one-part polyurethaneadhesive. Rheological behavior of the adhesives was measured with a dynamic mechanical analyzer. Mode Ifracture behavior of the joints was investigated with a tensile test machine and a falling-wedge impact test machinechanging opening speeds from 8.33 × 10-5 m/s to about 1.9 m/s. Although s

An adhesion model of an oblique structure with an adhesive tip is proposed by considering a limiting stress for adhesion to describe the detachment mechanism of gecko foot hairs. When a force is applied to the root of the oblique structure, normal and shear stresses are generated at contact and the adhesive tip is detached from the surface when reaching the limiting stress. An adhesion criterion that considers both the normal and shear stresses is introduced, and the asymmetric detachment of the

Double cantilever beam (DCB) tests were conducted by immersing the specimens in temperature-controlled water while applying a creep load using a spring. By introducing a data reduction scheme to the spring-loaded DCB test method, it was confirmed that only a single parameter measurement was sufficient to calculate the energy release rate (ERR). Aluminum alloy substrates bonded with an epoxy adhesive were used, and DCB tests were performed by changing the initial load values, spring constants, an

In this study, we used near-infrared spectroscopy to measure the moisture penetration in epoxy adhesives and investigated the difference in the diffusion coefficients between the bulk and the adhesive layer. Moisture diffusion was evaluated under 100% RH and water immersion conditions. First, the effects of the curing agents and additives on moisture diffusion in the bulk were gravimetrically evaluated using epoxy-coated quartz glass plates. Different diffusion behaviors were observed depending