Takayuki Shimoda

Applicability of CFRP materials to the cryogenic propellant tank for reusable launch vehicle (RLV)

It is essential to utilize carbon fiber reinforced plastics (CFRP) for main structural materials of cryogenic propellant tanks in order to realize the drastic weight reduction needed for efficient reusable space transportation systems. Recently developed toughened CFRP materials, which are expected to show good cryogenic properties, are considered promising candidates for these kinds of applications. The present study investigates cryogenic properties of candidate materials and structural elements, including Y-joint structural models. 300 mm diameter filament wound tank and 600 mm diameter lay up tanks were fabricated and tested. Based on these experimental data, the feasibility of a CFRP cryogenic tank is discussed and future research tasks are proposed. This research is being conducted under the cooperation contract between NASDA and NAL.

Pressurization test on CFRP liner-less tanks at liquefied nitrogen temperature

Two liner-less CFRP concept tanks were prepared for internal pressurization tests at liquefied nitrogen (LN2) temperature. The tanks were designed in two patterns of eight-ply UD quasi-isotropic lay-up, in the shape as a cylinder of 600 mm in diameter and 1200 mm in length, covered with an aluminum flange at one end and with a CFRP hemisphere dome at the other. The maximum strain was applied as the damage onset condition so that the internal pressurization at LN2 temperature did not damage them up to 1.1 MPa. Damage onsets, such as transverse cracking and leak path formation, were monitored during the tests using helium flow detection, acoustic emission, and pressure-strain monitoring. The CFRP concept tanks showed no damage in the 1.1 mm thick cylindrical gauge section under pressurization up to 1.1 MPa at LN2 temperature. The design was thus shown to be successful in keeping the CFRP tanks intact.

Pressurizing Test of CFRP Model Tank in Cryogenic Temperature

The authors present in this study an approach demonstrating the performance of a toughened epoxy CFRP concept tank under internal pressure at a cryogenic temperature. Three tanks were prepared with eight-ply unidirectional (UD) quasi-isotropic lay-ups of two different patterns and cloth lay-up. Each tank was cylindrical with a diameter of 600mm and length of 1200mm, covered with an aluminum flange at one end and a 600mm hemispherical CFRP dome at the other. The gauge length used was the central 300mm of the cylindrical section with a wall thickness of I.imm and made from IM600/#133 toughened epoxy CFRP. Each of the tanks was installed into a metallic chamber with the outside being under vacuum in order to preserve the cryogenic condition. The inside of the tank was pressurized with liquid nitrogen (LN2) together with gaseous helium (GHe) with the aim of detecting the onset of damage from the GHe leakage. The experiments were performed as follows. Firstly, helium gas leakage was measured and indicated no damage resulting from a water pressure of 1 MPa at room temperature (R.T.). Secondly, LN2 storage was performed without pressurization in order to evaluate any damage onsets due to the cryogenic condition. Following LN2 storage, no damage was detected within the gauge section of the tank. Thirdly, the tank was pressurized with LN2 and GHe to 0.98 MPa at gauge pressure (MPaG) and indicated the gauge section to has kept intact. Therefore, it was concluded that the materials and concept CFRP tank structure were successfully demonstrated under pressurization in cryogenic conditions. Although technical steps remain regarding engineering structures, CFRP appears to be a promising candidate for the realization of lightweight pressure vessels such as launch vehicle cryogenic tanks.

A Fundamental Study of Detecting Delaminations in Composite Tanks by Using Lamb Waves

Abstract. The lined filament-wound (FW) CFRP tank is supposed to be used for future space transportation vehicles such as GX-launch-vehicle which is under development by a group of private enterprises in Japan. In order to prevent buckling of inner-liner of tanks, it is essential to detect delaminations between outer-CFRP and inner-aluminum-liner. Traditional pulse-echo ultrasonic inspection method is used for detecting these delaminations at the work side, although, this method takes long time for inspecting whole parts of the tank wall. In this study, in order to shorten inspection-time, we examined new inspection method that uses lamb-waves (plate-waves). Lamb-waves were induced by transducer on the specimen surface and detected by small sensor on the same surface at 50 mm far from the generating points. A CFRP plate with aluminum liner, which consists of 30mm-width artificial delamination zone, was used for evaluating inspection ability. Three types of signals (pulse, burst and sweep) were put into the transducer and characteristics of generating lamb waves were compared. A new inspection method, which uses sweep input-signals combined with FFT analysis, was proposed. The proposed method was effective method for shortening inspecting time was found.

Design of 'KIBO' structure and verification

Japanese Experiment Module (JEM, which is so called “KIBO”) was completed and assembled as a part of the International Space Station (ISS) on orbit in July, 2009. The JEM is a payload of Space Shuttle at lift off and also it is a part of ISS on orbit. JEM structure is required to be compatible with Space Shuttle Flight and ISS. This paper shows the activities to evaluate and validate the structural compatibility.

Test of filament wound CFRP prototype for cryogenic propellant tank of space plane

National Space Development Agency of Japan (NASDA) is conducting a feasibility study of applying CFRP to the cryogenic propellant tank of a reusable vehicle system. As a part of the feasibility study, we are now conducting tests of small filament winding (FW) tanks with 300mm diameter to study the possibility of the filament winding method for manufacturing. The first phase test of a FW tank was conducted in 1999. We analyzed the weak points of the first FW tank and conducted the second phase tank test under the collaboration works with Italian Aerospace Research Centre (CIRA). The design and manufacturing processes of the second phase test were improved, and the first tank was completed with half surface of the cylinder good (healthy surface) and another half no good with large wrinkles produced in the curing process. Leakage occurred in the first pressurization test at 0.3MPa at room temperature along a large wrinkle. After the leak points were repaired, the tank was used for waterproof testing at 1.0MPa and 1.5MPa and the strain data was obtained. Finally, we conducted a pressurization test at liquid nitrogen (LN2) temperature at 1.5MPa, 1.9MPa, and 2.0MPa. The healthy surface of the tank cylinder remained healthy even at 1.9MPa and there were no leaks occurred. The first leak occurred at 2.0MPa in the healthy area at LN2 temperature. This is a promising result for the next series for realizing a perfect tank.