Performance of laminated natural rubber bearing used for 30 years in seismic isolation building was evaluated. Horizontal stiffness increased by 14.6% and vertical stiffness increased by 5.9% for 30 years. It was confirmed from rubber physical property tests that change in physical properties with age remained within a limited range from the surface of the laminated rubber bearing. Moreover, these results were compared with other research results, and the validity of the rate of change in performance of laminated rubber bearing was verified.

Rubber industries utilize many kinds of soft matter, polymer, colloids, surfactants etc. They are complex materials, but they all obey the law of physics, and their complex behaviors can be understood in terms of physics. In this series of lectures, I will try to explain the principles of physics which governs the complex behavior of these materials. In this first chapter, I will discuss the elasticity of rubbers: where does the unique elasticity of rubber come from, and how to understand the strange behaviors of rubber balloons.

The effect of filler silica particle size on the flexural strength and the fracture toughness (K_IC) of silica particle-filled epoxy composite was investigated. As the particle size increased the flexural strength decreased and the K_IC increased. The large filler acts as the defect which causes fracture initiation for the flexural strength. On the other hand, the stress relaxation by the branching, the making a detour and the debonding of interface caused by the large filler developed the K_IC. In order to raise both strength and K_IC, the following interface of filler/resin considered to be ideal: the interface having the adhesion strength which is sufficient for the required mechanical strength of composite, whereas when the applied stress exceeds a threshold value, the debonding of the interface occurs and causes the stress relaxation.