2002 Fiscal Year Final Research Report Summary
Mechanical Characteristics and Fuel Leakage of Laminate Adhesive Joints under Cryogenic Conditions
| Project/Area Number |
13450395
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 | The University of Tokyo |
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Principal Investigator |
AOKI Takahira The University of Tokyo, Graduate School of Engineering, Associate Professor, 大学院・工学系研究科, 助教授 (00202466)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Takashi National Aerospace Laboratory, Advanced Composites Evaluation Technology Center, Director (Recearcher), 先進複合材評価技術開発センター, センター長(研究職)
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| Project Period (FY) |
2001 – 2002
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| Keywords | Adhesive joint / Laminate / Cryogenics / Liquid propellant tank / Reusable launch vehicle / CFRP / Propellant leakage |
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| Research Abstract |
The successful development of the Reusable Launch Vehicles (RLV) depends on the weight reduction of the vehicle structure achieved by the wide application of composite materials such as Carbon Fiber Reinforced Plastics (CFRP). The largest contribution to the weight reduction may be attained by the utilization of CFRPs for cryogenic fuel tanks that occupies more than 90% of the gross launch weight. In the present study, the effects of cryogenic environment on the mechanical characteristics and fuel leakage of adhesive lap joints are assessed. The results of the study contribute to the utilization of CFRP lap joints that can increase the structural efficiency of the composite fuel tanks.
The DCB specimens fabricated from adhesively bonded laminates were subjected to the thermal tests to clarify the effects of thermal cycles, temperature levels, and thickness of adhesives on the fracture toughness. The results showed little effect of cryogenic environment on the measured fracture toughness
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, but indicated that the thermal cycles may induce matrix cracks near the free edges of the laminates. The single-lap and double-lap joint specimens were also fabricated and tested under tensile loadings, resulting in the decrease of load carrying capacities after the cyclic thermal loadings. The consequences were assumed to be due to the interface degradation at the free edge portions of the joints, which were microscopically verified. This suggested the importance of the edge treatment of the lap joints especially under cryogenic environment. The wide accumulation of transverse cracks that were originally predicted and apprehended were shown to be avoided by the existence of randomly oriented short fiber placements in the adhesives.
In order to investigate the fuel leakage through the laminates including the lap joints, laminates with accumulated damages were subjected to gas helium leakage tests. Laminates with transverse cracks exhibited increased permeability associated with the increase of crack density, which was verified by the analysis. However the leakage rates were shown to remain below the acceptable amount for the practical fuel tanks, as long as the cracks were not inter-connected to form through-thickness leakage paths.
With the results of mechanical tests obtained herein, the effects of cryogenic environment on the mechanical performances of the lap-joints and the laminates may be referred to as controllable, together with the observed low leakage rates. Less
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