Jun Takahashi

Possibility of closed loop material recycling for fiber reinforced thermoplastic composites

It becomes significantly important to preserve ecological balance of the earth and protect the environment from getting worse. One of the urgent issues to be tackled will be to develop and establish recycling technology for polymeric composite materials. The expression of recycling technology in this case is that after the life of industrial products of fiber reinforced thermoplastic (FRTP) is completed, instead of being thrown away as wastes, they are reused as a raw material for new applications. An additional goal is that of saving valuable resources and not consuming further energy. This paper deals with a possibility of closed-loop recycling technologies for FRTP. The key factor is the fiber length which is expected to reduce in each recycling step. Materials tested here are continuous FRTPs, long FRTPs, short FRTPs, and powder reinforced plastics. The effect of fiber length on the reinforcing mechanism is first examined. The correlation between outdoor exposure test and accelerated weathering test is the second subject to covered. The third subject is to make clear the influence of crushing and heat history which are inevitable during each recycling stage. Throughout the above investigation, the concept of closed-loop recycling technologies has been established, although it is still in a preliminary stage.

Fracture mechanism of cross-ply carbon/carbon composites

Mode I fracture toughness tests were carried out on (0/90) cross-ply carbon/carbon composite laminates in order to investigate the applicability of the concept of the fracture toughness based on linear elastic fracture mechanics. Tests were carried out by using both compact tension (CT) and single edge notched beam (SENB) specimens. Effect of the root radius of the starter notch was also investigated in order to find out its sensitivity on the fracture behavior. Although the load-displacement relation showed nonlinear behavior, the relation between the specimen compliance calculated by the straight line from the origin of the load-displacement axis and the measured crack length followed the polynomial equations based on the linear elastic fracture mechanics. Fracture toughness values were calculated by using the stress intensity factor. The relation between the fracture toughness and the increment of crack length (R-curve) was independent of the specimen shapes, the starter notch lengths, and the root rad...

Development of ultra-high temperature testing equipment and some mechanical and thermal properties of advanced carbon/carbon composites

Advanced carbon fiber reinforced carbon (C/C) composites are one of candidate materials for leading success of a space plane program in the 21st century. Though ultra-high temperature experimental studies for C/C composites have been performed, the effect of neither temperature nor heating/cooling speed on material properties have been fully made clear yet. In this paper, highfrequency induction heating material testing system developed by us is presented first; the main advantage of this system is the capability of quite fast heating and cooling speed. After verifying the temperature distribution of the specimen, some experimental studies are performed for two types of non-oxidation-protected C/C composites whose heat treatment temperatures are 1600 and 3000° C. Obtained results are summarized as follows; (1) Only tensile strength tends to decrease when cooling speed becomes fast although heating speed does not have an influence upon both thermal and mechanical properties of C/C composites. This phenomen...

Bearing failure in plain woven C_C composites

Abstracts are not published in this journal

Observation on Bearing Damage Propagation of Plain Weave C/C Composites.

Bearing strength tests either with or without lateral constraint were performed for plain weave C/C composites. The tests were conducted with reference to JIS K 7080 which standardized the testing methods for bearing strength of carbon-fiber reinforced plastics. The bearing damage propagation was observed by a soft X-ray and an optical microscopy. Shear cracks were initiated and propagated rapidly at the maximum load when tests were performed without lateral constraint. Tests being performed with lateral constraint, shear cracks were initiated at the relative displacement of 4% of the pin diameter and followed by the stable crack propagation. At the maximum load the crack reached the edge of collar which constrained the specimen laterally. Then the load dropped abruptly. The loads for evaluating bearing strength which are standardized in JIS K 7080 would correspond to the shear crack initiation.

Closed-Form Expressions of the Compliance due to the Presence of Crack for SEN Specimens under Tension and Bending.

Closed-form expressions of the stress intensity factor are so useful in fracture mechanics analysis that a number of expressions have been obtained for various kinds of cracked specimens. However, most of actual structures are statically indeterminate, and stress intensity factors for such statically indeterminate cracked structures cannot be estimated only in terms of the above expressions. Such crack problems in statically indeterminate structures were systematically discussed by Okamura et al., and stress intensity factors for statically indeterminate cracked structures were shown to be estimated in terms of the crack compliance, i. e., the variation of compliance due to the presence of cracks. In this paper, an estimation scheme of closed-form expressions for crack compliance is presented. First, asymptotic properties of the crack compliance are obtained for single edge notched (SEN) specimens under both tension and bending. Then, closed-form expressions are estimated based on the asymptotic properties. The obtained expressions are shown to be quite accurate and useful for not only engineering discussion but also theoretical study.