日本複合材料学会誌

Natural fibers used for reinforcement in green composites fail due to cyclic loading, but the effects of various factors on fatigue strength of natural fibers have not been clarified. In this study, the effects of cyclic frequency and time-dependent fracture on fatigue strength of jute monofilament were investigated. Fatigue tests were conducted at a cyclic frequency of 1 Hz and 10 Hz. The results indicated that there is no significant difference between fatigue strengths of both frequencies. Then, constant loading tests of jute monofilaments were conducted, and the results revealed that a jute monofilament fails after a period of constant loading. Life predictions based on a linear cumulative damage rule results implies that the time-dependent fracture mode has much less effect on the fatigue life of jute monofilament than the cyclic-dependent fracture mode.

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One of the authors has already proposed the method to analyze electric current density of carbon fiber reinforced plastics (CFRP) laminates using the anisotropic electric potential function. The effectiveness of the method was verified by comparisons with FEM analyses. The method is based on the assumption that CFRP laminates are homogeneous orthotropic materials. Actual CFRP laminates are, however, heterogeneous materials: the actual CFRP has resin rich layers and carbon fiber layers. In the present study, an electric conductance is calculated on the assumption that CFRP laminates are homogeneous by using an electric resistance measured by a four-probe method, and the measured values are used for an electric current analysis. To investigate electric current distribution of CFRP laminates experimentally, a newly designed specimen is proposed. The results of an electric current tell us that the analysis method gives us the accurate result of electric current density of actual CFRP laminates. This shows that the assumption that CFRP laminates are homogeneous orthotropic material in case of electric current analysis was verified experimentally.

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