Masahiro Nagai

The study on Charpy impact testing method of CFRP

The Charpy impact test method has been widely used to investigate impact resistance of fiber reinforced composites because of its simplicity. However, when laminated composites such as CFRPs are to be tested, each specimen may have different thickness without a notch. This may result in incorrect material evaluation for impact resistance. In this paper, an instrumented Charpy impact tester was introduced in order to determine a proper Charpy impact test method for CFRPs and to investigate the effect of the ratio of the support-span length to thickness l/t on impact characteristics for both unidirectional and fabric CFRPs. Energy per unit volume u increases rapidly along with l/t in the range of l/t < 20 and l/t < 16 for unidirectional CFRPs and fabric CFRPs, respectively, both of which are influenced by interlaminar separation. However, the u values become almost constant over 20 l/t 40 for the unidirectional CFRPs and over 16 l/t 40 for the fabric CFRPs. It is found that those ranges are the proper range...

Shock absorption performance of full-face rider helmets

Full-face rider helmets are widely used these days, but the shock absorption and safety performance of them have not been discussed yet. So we examined the shock absorption performance and the safety of three full-face rider helmets (samples A, B, and C) of which the laminated constitutions of the FRP shell part were respectively different. The effect of the hybrid lamination, composed of aramid and glass fabrics, on the shock absorption performance has been discussed also. Testing was performed twice for the same impact site of a helmet hit flat and with semi-spherical anvils, according to the JIS-C shock absorption test method. The following results were obtained: The acceleration waveform measured at the forehead part of Helmet-A, which was hit on a semi-spherical anvil, behaved flatly while the part on the left side of the head behaved parabolically. In the case of Helmets-B and -C, which have an aramid fabric layer, they behaved conversely, such that a flat waveform was observed on the part on the le...

Application to thinning palatal area of upper complete denture base by CF-cloth reinforcement

The acrylic resin denture base is used more than the usual metal denture base because of its low cost, ease of manufacture and ease of rebasing. Because the resin base is weaker than the metal base, the upper resin denture base is three to four times as thick as the metal denture base. So, a study was made to make the upper complete resin denture base thinner while maintaining the strength of the resin denture base currently in use. To make the palatal area of the denture base thinner carbon fiber (CF) cloth reinforcement was used. The resin denture base reinforced by the CF cloth was 0.7 mm thick and was evaluated for the mechanical properties of bending. As a result, it was found that both the stiffness and strength were improved by 10% or more compared with those of the ordinary resin denture bases.

Flexural Fracture and Mechanical Properties of Nonsymmetrical Sandwich Construction

Sandwich construction is composed of hard polyurethane foam(PUF) as core and glass-mat FRP(GRP) and aluminium(Al) as facing. The flexural fracture and mechanical properties of this nonsymmetrical sandwich construction are examined. The behaviors of flexural fracture of GRP/PUF/Al sandwich construction, which is loaded with GRP on tension side, are examined for flexural stress, strain etc. to consider the elasto-plastic deformation of GRP, and are numerically analyzed using a flexural load-deflection diagram of this sandwich construction. The flexural experiment has been made for comparing with the results of theoretical analysis on the mechanical properties of this sandwich construction. And this analytical method applied to the process of flexural fracture can be practical enough for the estimation of flexural strength and theoretical flexural load-deflection diagram.

A Study on the Reinforced Properties of Dental Plastics with Hybrid Construction

Acrylic resin is widely used as the denture base material, but a failure of the upper complete denture often happens during its use. Therefore, the denture base made of acrylic resin should be reinforced by something else. So, the authors have thought of improving the strength and rigidity by laminating the organic fiber reinforced plastics on the palatal surface of the denture base, which is called the canape construction. In this paper, the flexural strength, fatigue strength and the modulus of elasticity in bending of the canape construction were investigated as basic experiment. As the result, the flexural and fatigue strengths have been improved to 160% and 130% of the denture base acrylic resin, respectively. And the modulus of elasticity in bending has been improved 80%. Therefore, it seems that this new combination of materials using the canape construction might be applied well enough to the denture base.