Award type：Award from international society, conference, symposium, etc. 

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Doctoral thesis   Publisher：Yamaguchi University  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science, Japan  

【Abstract】
Recently, carbon fiber reinforced plastics (CFRPs) have been used as high-pressure container materials for fuel cell vehicles and other applications. When used as structural components, carbon fibers in a CFRP are subjected to multiaxial loading. As is well known, multiaxial strength and fracture behavior are significantly different from those under uniaxial loading. However, research on the multiaxial strength evaluation of carbon fibers is insufficient. To date, there have been a few reports on studies under tension-torsion loading, but these have hardly clarified the fracture criterion. In this study, the tensile-torsional fracture strengths of PAN-based carbon fibers were obtained by proportional loading tests. As a result, it was found that the tensile strength along the fiber axis decreased largely with increasing shear stress at the fiber surface under tension-torsion loading. The changes in the experimental results were well explained by adding a correction term to Tsai-Hill criterion, the theory for anisotropic materials. Furthermore, since PAN-based carbon fibers showed extreme differences in strength between uniaxial tension and pure torsion, it was finally concluded that the carbon fibers follow the maximum principal stress theory when using normalized stresses.
【Keywords】
Brittle materials, CFRP, Multiaxial stress, Proportional loading, Tensile strength, Maximum principal stress criterion

DOI： 10.2472/jsms.73.379

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Received: 14 February 2024, Accepted: 14 March 2024, Published: 18 March 2024
Keywords: carbon fibers; epoxy resin; unidirectional laminate; biaxial test; fracture mode
Abstract: In order to clarify the fracture behavior of a unidirectional CFRP under proportional loading along the fiber (0°) and fiber vertical (90°) directions, a biaxial tensile test was carried out using a cruciform specimen with two symmetric flat indentations in the thickness direction. Three fracture modes were observed in the specimens after the test. The first mode was a transverse crack (TC), and the second was fiber breakage (FB). The third mode was a mixture mode of TC and FB (TC&FB). According to the measured fracture strains, regardless of the magnitude of the normal strain in the 0° direction, TC and TC&FB modes occurred when the normal strain in the 90° direction, εy, ranged from 0.08% to 1.26% (positive values), and the FB mode occurred when εy ranged from −0.19% to −0.79% (negative values). The TC&FB mode is a unique mode that does not appear as a failure mode under uniaxial tension; it only occurs under biaxial tensile loading. Biaxial tensile tests were also conducted under non-proportional loading. The result showed three fracture modes similarly to the proportional loading case, each of which was also determined by the positive or negative value of εy. Thus, this study reveals that the occurrence of each fracture mode in a unidirectional CFRP is characterized by only one parameter, namely εy.

DOI： 10.3390/ma17061387

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Materials Science, Japan  

Received : 12 September 2022, Accepted : 26 December 2022
【Keywords】Composite materials, Tensile strength, Stochastic process, Weibull distribution, Reliability model, Maximum likelihood estimation
【Abstract】The application of carbon fiber reinforced plastics (CFRP) has been expanding as large structural members, whereas there is a growing trend to expand its use to structural members of small devices such as “drones”. From such background, this study sampled strength data from tensile tests of micro-sized unidirectionally reinforced CFRP in diameter or thickness and discussed the damage and fracture process, as well as the number fiber-break points, nc up to fracture from the data. In our recent paper, the authors estimated the number of fiber-break points from previously obtained sampling data using an inverse analysis model of Markov processes. In this study, furthermore, another inverse analysis model, in which analytical solution can be obtained, was newly proposed. This model was in a good agreement with absorbing state probabilities and nc obtained from the previous model. However, it was also found that there was a data population for which the fracture probability was limited to less than one. This is because the estimation limit occurs when some of the data are somewhat far from the data population. This problem can be solved to some extent by using the maximum likelihood estimation method for complete or censored data.

DOI： 10.2472/jsms.72.180

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper, summary (international conference)   Publisher：JSMS Committee on Composite Materials, The Society of Material Science, Japan  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：English   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers, JSME  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Event date： 2024.8

Language：English  

Venue：Imadegawa campus, Doshisha University, Kyoto   Country：Japan  

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Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：National Institute of Technology(KOSEN), Numazu College, Shizuoka   Country：Japan  

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Event date： 2024.3

Presentation type：Oral presentation (general)  

Venue：Kyoto Terrsa, Kyoto   Country：Japan  

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Event date： 2023.12

Language：Japanese  

Venue：Kagawa University, Kagawa   Country：Japan  

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Event date： 2023.12

Language：English  

Venue：Kochi University of Technology, Kochi, Japan   Country：Japan  

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Audience： Teachers,　Researchesrs

Type：Lecture

Presenters:Mikiyasu Hashimoto, Tasuku Hitaka, Sho Takahashi, Daisuke Hayasaka

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