The strength of an adhesive joint depends on many factors, the bonding strength between adhesive and adherends is the most important factor. However, the bond thickness is also important, and this is the main issue of this paper. If the interface is enough strong, the cohesive fracture will occur. In these cases, the strength of an adhesive joint depends on the bond thickness. The fracture of these adhesive joints caused from micro cracks in adhesive layers. Both of the energy release rate of a crack in an adhesive layer and the fracture toughness of adhesive depends on the bond thickness. The energy release rate of a crack in an adhesive layer is the driving force of the crack extension, and the fracture toughness is the resistance of adhesive from the crack extension. We need to consider to decrease the driving force and to increase the resistance separately for designing stronger adhesive structures. In the case of a butt adhesive joint of the same material under monotonic tensile stress, thinner adhesive layer shows stronger adhesive joint. However, in the case of large adhesive structures, thicker and soft adhesive layer have advantage. The fracture toughness decreases when the bond thickness being less than the size of the damage zone. We need to consider all factors depending on the bond thickness to design adhesive structures.
As of today, adhesives are essential material in architectural and civil engineering works. In the construction field, adhesives are used in various situations, from exterior to interior construction. Adhesives are utilized especially bonding different kinds of substrates due to diversification of the materials in construction. In constructions of civil engineering work, main materials are steel and concrete, then adhesives are used to bond these materials and also to different materials. In respond to large-scale disasters, the use of epoxy resin adhesives against seismic reinforcement, is increasing, and it has been contributing to secure reinforcement strength, shortening the construction period, saving labor and reducing weight. As the population declines, it is not high possibility to grow new housing market but repair and refurbishment market can be developing in the future.
For the practical application of carbon fiber reinforced thermoplastic（ CFRTP） using polypropylene（ PP） as a matrix, it is necessary to improve the poor interfacial adhesion between carbon fiber（ CF） and PP. In this work, we examined the effects of surface treatment on CF bundle and PP film utilizing microbubbles（ MB） containing ozone or nitrogen: the purpose was to observe the effects of oxidization from ozone gas and the treating capability of MB onto the surface of CF and PP. It was found that the MB treatments clearly increased the interfacial shear strengths（ IFSS） between CF and PP and the bending mechanical strengths of the CFRTP composite were also improved up to 55%. We concluded that the main processing mechanism depended on the degree of the introduction of polar groups onto CF and/or PP and on the anchoring effect originated from the roughened CF surface by the MB treatments.
The mechanical properties（ creep behavior） of poly（ butyl acrylate-acrylic acid） copolymers with different molecular weight distributions （PDI） and different molecular weights were studied. It was clarified that the PDI, especially the low molecular weight part in the PDI, greatly affected to the creep behavior. With decreasing PDI by living radical polymerization, creep compliance in a whole-time range decreased. Furthermore, the effect of the amount of cross-linking agent on the average molecular weight between effective network points （M） was determined from the creep compliance at a long-time region, using rubber elasticity theory. It was found that the M was also greatly affected from the PDI. In case of living radical polymer PSAs with narrow PDI, the calculated molecular weight between cross-linking points（ Mc） under assuming two of the four functional groups in the cross-linking agent contributed to the actual cross-link, was close value to the M determined from the creep compliance. On the other hand, in case of free radical polymer PSAs with wide PDI, the calculated results showed that less than one functional group contributed to the cross-link. The free-radical polymer PSAs contain a large amount of uncross-linked low molecular weight sol. Therefore, the apparent M increased because of the existence of slippage at the adhesion interface and flow in the bulk polymer.