1998 Fiscal Year Final Research Report Summary
Studies of the Fatigue Failure Mechanism for Composite Laminates.
| Project/Area Number |
08405062
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Aerospace engineering
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
KUNOO Kazuo Kyushu University, Faculty of Engineering, Professor, 工学部, 教授 (90128009)
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| Co-Investigator(Kenkyū-buntansha) |
SAKAI Masahiro Muroran Institute of Technology, Department of Mechanical Systems Engineering, A, 工学部, 助手 (20301963)
ONO Kousei Kyushu University, Faculty of Engineering, Assistant Professor, 工学部, 助手 (90038092)
UDA Nobuhide Kyushu University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (20160260)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Composite Meterials / Fatigue / Delaminations / ultrasonic NDT / Failure / Failure mode / PEEK matrix / Epoxy matrix |
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| Research Abstract |
We found that the maximum accumulated strain for PEEK matrix composite laminates [+30/-30] _<4s> subjected to zero-tension cyclic loadings, 85%, 80% and 75% of static strength was about 3.9% at failure. From the experimental results, S-N, (Stress-Number of Cycles) relations can be expressed by linearity in log-log coordinates. The static strength of [+30/-30] _<4s> was about two times that of [+304/-304] _s in the case of PEEK.The difference comes from failure modes in fatigue tests.
We clarified the fatigue failure mechanisms of quasi-isotropic composite laminates subjected to cyclic loadings in several different directions or different matrices. In the case of angle-ply laminates subjected to zero-tension cyclic loadings, the stress-strain relations showed accumulation of strains, so called a mechanical ratchet phenomenon. Fatigue failure was observed as delaminations among laminae by ultrasonic NDT.The progress of fatigue failure is dependent on stacking sequences, for example, the failure of [+theta/-theta]_<4s>. advanced gradually, and the failure of [+theta_4/-theta_4]_5 progressed rapidly. We derived the constitutive relations of mechanical ratchet phenomenon and showed their satisfactory agreement with experimental results. We also investigated the fatigue failure processes of quasi-isotropic laminates, [+30/-30/90]_s, [+30_2/-30_2/90_2]_s, [-45/+45/0/90]_s, [-45_2/+45_2/0_2/90_2]_s and [-45_3/+45_3/0_3/90]_s under cyclic loadings.
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