Yoshiki Morino

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.

Pressurization of CF/Epoxy Model Tank at LN2 Temperature and Identification of Leak Path Formation in Tank Wall

A review of six years research project for accumulation of basic knowledge about cryogenic composite tank of future RLV conducted in NAL/ NASDA will be given first. An emphasis is placed on the final part of pressurization of the model tank made of CF/Epoxy at liquid nitrogen temperature. Some typical results of preliminary steps in the research route will be also given. In the final cryogenic pressurization, an advantage of the difference in the matrix crack initiation strain levels at room temperature and at LN2 temperature played a key role to conduct the present test possible under safety requirements. The matrix crack free strain (stress) levels were obtained for the same composites as used for the tanks in the research programs conducted in NAL/University of Tokyo in parallel to this program. In the present cryogenic pressurization, leak path formation was detected at real time by nonlinear gas pressure – strain behavior and by sudden rise in gas pressure in the vacuum chamber. Later, the exact locations of the leak path were identified by a sniffer scan using a helium leak detector and by snoop tests using leak check solvent. Finally, the strain level of the leak path formation was compared with the matrix crack formation and evolution strain levels obtained by coupon tests. It is clarified that the leak path formation strain level coincides well with the strain level of matrix crack propagation in coupon detected by AE sensors, almost identical to the matrix crack initiation strain of tubular specimens. This conclusion seems to be appropriate if we notice that the present composite model tanks have no edges.

VIBRATION TEST OF 1/5 SCALE H-11 LAUNCH VEHICLE

In order to predict dynamic loads on the newly designed Japanese H-11 launch vehicle, adequacy of prediction methods has been assessed by the dynamic scale model testing. The three dimensional dynamic model was used in the analysis to express coupling effects among axial, lateral (pitch and yaw) and torsional vibrations. Liquid/tank interaction was considered by use of boundary element method. The 1/5 scale model of H-I1 launch vehicle was designed to simulate stiffness and mass properties of important structural parts, such as core/SRB junctions, first and second stage Lox tanks and engine mount structures. Modal excitation of the test vehicle were accomplished with 100-1000 N shakers which produced random or sinusoidal vibration forces. Vibration response of the test vehicle were measured at various locations with accelerometers and pressure sensors. In the lower frequency range, correspondence between analysis and experiment were generally good. The basic procedures in analysis seem to be adequate so far, but some improvements in mathematical modeling are suggested by comparison of test and analysis.

EVALUATION OF CRYOGENIC SHEAR PERFORMANCE OF CFRP LAMINATES

oC). Experimental evaluations using the v-notched specimens (Iosipescu shear test) to determine the in-plane and out-of-plane (inter-laminar) shear properties (modulus and strength) of CFRP laminates were conducted at three different temperatures (room temperature, -70 o C and –160 o C). Epoxy-toughened BESFIGHT IM600/#133 CFRP prepreg sheets were used as the material system for experimental investigation. Different correction factors of the v–notched specimens for in-plane and inter-laminar shear modulus determinations at different temperatures were obtained from analytical simulations and they were used to modify the experimental results of shear modulus. It concluded that the cryogenic shear modulus of CFRP laminates for both in-plane and inter-laminar shear becomes about twice of that at room temperature. Failure mechanisms of the in-plane and inter-laminar specimens at different temperatures were also discussed from the experimentally obtained rupture strength. We concluded that the failure strength of inter-laminar specimens becomes higher as the temperature decreases to cryogenic temperatures.

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.

Oxidation Characteristics of High Purity CVD-SiC under Low Pressure Conditions

Much research has been conducted on the erosion mechanism of Carbon/Carbon (C/C) materials to develop thermal protection technologies for atmospheric re-entry vehicles. The erosion and oxidation phenomena of the Chemical Vapor Deposition (CVD)-SiC thermal protection coatings are important factors in thermal protection technologies. High purity CVD-SiC materials were selected to evaluate the oxidation phenomena by comparison with those of C/C samples. (1)-(3) Results of previous research indicated that the experimental methods should be improved to investigate the phenomena more precisely. This paper describes the latest outcomes, including the re-analysis of the previously acquired results.

OVERVIEW OF BASIC RESEARCH ACTIVITIES ON CRYOGENIC COMPOSITE PROPELLANT TANKS IN JAPAN

Extensive application of composite materials is one of the major technical challenges for drastic reduction of structural weight of the planned space planes and reusable launch vehicles (RLV). Propellant tanks are the dominating structural components of the vehicle structure and thus the application of carbon fiber reinforced plastics (CFRP) to these components is one of the most promising but challenging technologies for achieving the goal of weight reduction. The overview of current activities on basic research related to the application of CFRP to cryogenic propellant tanks in Japan is given. These research projects indicate that the load-carrying performance of the state-of-the-art material systems is at the sufficient level to be used in the CFRP tanks, leaving the problems related to permeability, durability and fabrication yet to be extensively investigated. The preliminary evaluations of thermal insulation materials and adhesive materials are also under way at NASDA. The research project led by NAL-Kakuda also exhibits the promising results of the CFRP components.