Tsuyoshi Matsuo

Investigation about the fracture behavior and strength in a curved section of CF/PP composite by a thin-curved beam specimen

A curved beam specimen with a curved section bent at a right angle and straight arms is an efficient experimental method to evaluate the interlaminar tensile strength of a composite laminate. This paper describes a technique to apply such a test method to determining the fracture behavior and strength in a curved section of a thin laminate. The proposed technique is capable of estimating appropriately the compressive or tensile strength as well as the interlaminar tensile strength at failure in a thin-curved section, especially targeting thermoplastic composite materials. The significant point of the proposed technique is a modified calculating method of the stress distribution in a curved section by taking into account the large deformation of the specimen because of thin laminate.

Effects of curvature on strength and damage modes of L-shaped carbon fiber-reinforced polypropylene

Curved section is regarded as the weak point of composite structures because of the delamination caused by the stress concentration. In the present work, L-shaped specimens made of randomly oriented short fiber-reinforced polypropylene were prepared to investigate the effect of the radius of the curved section of composite structures on the strength and the damage modes. The results of tensile tests and finite element analysis indicated that the radius greatly affects on the stress distribution and the damage modes, and showed good agreement with former researches using different composites. The strengths of the materials were extrapolated from the results of tensile tests and finite element analysis in this research. Finally, allowable radii of the curved section of the composite structures of two kinds of materials were given respectively.

Prediction of fiber-directional flexural strength of carbon fiber-reinforced polypropylene based on time–temperature superposition principle

This study verified that the time–temperature superposition principle for fiber-directional flexural strength can be applied to thermoplastic composites undergoing instantaneous fast phenomena such as impact failure and long-term phenomena such as creep failure, by constructing the time- and temperature-dependent master curve of relaxation modulus of thermoplastic resin. The master curve could be transformed to another master curve that predicts fiber-directional flexural strength of carbon fiber-reinforced thermoplastic composites based on the micro-buckling failure theory expressed mainly by the resin’s elastic modulus. The experimental results obtained from high-speed bending test, static bending test at various temperatures, and creep bending test demonstrated that kink band failure occurred on the compressive surface of the specimen at every test condition. This validation and verification related to thermoplastic composites made it possible to predict static and dynamic flexural strengths at arbitrary temperature and creep flexural strength.

Acoustic emission and elastic wave measurements by using a new fiber-optic (DEFEW) sensor

A new fiber-optic acoustic/vibration sensor has been developed. The sensor is based on Doppler effect in flexible and expandable light-waveguide (DEFEW). The DEFEW sensor has extremely high sensitivity in wide band of frequency range. The sensing technology is applied to high speed phenomena, for examples, breakage of carbon fiber in matrix resin and elastic wave propagation impacted by electrical discharge. The demonstrated results show that the DEFEW sensor is applicable to nondestructive damage detection for structural health monitoring.

Development of Smart Composite Panel with Optical Fiber Sensors

We have developed a novel fiber-optic vibration sensors and applied commercially available strain and temperature sensors to health monitoring of composite structures. In this study, we constructed an optical fiber network integrating four types of optical fiber sensor into a carbon reinforced plastic (CFRP) panel. These four sensors were the vibration sensor developed by our laboratory, two distributed sensors based on Brillouin and Raman backscattering and Fiber Bragg Grating (FBG) sensors. By dealing the data obtained from the measurement systems corresponding to these four sensors, strain/stress and temperature distributions throughout the panel can be monitored. Vibration and elastic waves transmitting on the panel are also detected at several sensing points. Furthermore, we will be able to determine damage locations and modes by processing the wave signals. To make the panel with the optical fiber sensor network more sensitive and smarter, we are developing some techniques that can improve the performance of the sensors and can assess the structural integrity by analyzing measurement results. In this paper, the development of the first generation of our smart composite panel with the optical fiber sensors is described and the techniques making the panel more sensitive and smarter are also described.