MECHANICAL PROPERTIES OF CARBON/SILICON CARBIDE COMPOSITES MATERIALS BOLTS
Donglin Zhao, Litong Zhang, Laifei Cheng, Xiang Chen
Science and Technology on Thermostructural Composite Materials Laboratory, Northwestern Polytechnical University,127 Youyixi Road, Xi'an Shaanxi, P.R.China
Xi'an Golden-mountain Ceramic Composites Co., Ltd, NO.2 Lantian Road, Yanliang Investment of Xi'an, Shaanxi, P.R.China
ABSTRACT
With the extensive use of carbon/silicon carbide composite materials(C/SiC) in aerospace fields, the bolting of C/SiC materials is important in structure of aircraft and spacecraft. However, there is a problem of the heat matching with the use of metal bolts. Now it can be solved by the development of C/SiC bolts. The C/SiC bolts were prepared by chemical vapor infiltration (CVI). The carbon fabric preform was fabricated with the three dimension needling method. The mechanical properties of C/SiC bolts were investigated. The results indicated that the average tensile strength of C/SiC bolts was 114.71 MPa and the average shear strength of C/SiC bolts was 71.34 MPa. These results are helpful for the design of C/SiC materials bolting in Aerospace Structures.
INTRODUCTION
Carbon/silicon carbide composite materials have been widely used in aerospace fields because of their lightweight,excellent high temperature properties and heat resistant properties. The C/SiC components of aircraft and spacecraft are increasingly becoming larger and more complex, such as bay section, rudder and body flap etc. These components cannot be manufactured without connection technology of composite materials. NASA proposed using the Carbon/Silicon Carbide (C/SiC) Ruddervator Subcomponent Test Article (RSTA) as a test structure to support research objectives within the Hypersonics Materials & Structures (M&S) program. C/SiC fasteners were designed, fabricated in the C/SiC RSTA, but never tested. The C/SiC fasteners designed and fabricated by Northwestern Polytechnical University (NWPU) are simple, lower-cost and standardization. They have been widely used in many C/SiC components such as body flap, rudder etc. some of them have successful passed the flight test. In this paper, the mechanical properties of C/SiC bolts developed by NWPU were tested, that can provide the basic data for connection design of C/SiC components.
TEST
Preparation of Test Specimens
A three-dimensional needled C/SiC composite was fabricated by CVI. The C/SiC composite was processed into M8 C/SiC bolts as shown in Figure 1. The density of C/SiC bolts for finally test was 2.00 g/cm3.
Figure 1. M8 C/SiC bolts
Tests of Mechanical Properties
Tests were performed in INSTRON 3369 testing machine by the self-designed toolings. Figure 2 for self-designed toolings.
(a) tooling for tensile test (b) tooling for shear test
Figure 2. Self-designed toolings for test
Strength Calculation
Formula of Tensile strength is given by eq.(1).
s
F
A
σ=
(1)
Formula of Tensile strength is given by eq.(2).
3
s
F
A
τ=
(2)
2
23
(
)42
s d d A π+=
(3)
310.8666P
d d =-
(4)
F —load
As — Stress area d 1— minor diameter d 2— pitch diameter P —crest
RESULTS
Tensile Strength of C/SiC Bolts
The specimens were clamped in the testing machine by the self-designed tooling as shown in Figure 3. The loading rate of testing machine was 0.5 mm/min. Table I for tensile test results, Figure 4 for tensile curve.
Figure 3. Tensile strength test
Figure 4. Tensile test load-displacement curve of M8 C/SiC bolts
Shear Strength of C/SiC Bolts
The specimens were clamped in the testing machine by the self-designed tooling as shown in Figure 5. The loading rate of testing machine was 0.5 mm/min. Table II for shear test results, Figure 6 for shear curve.
Figure 5. Shear strength test
Displacement (mm)
L o a d (N )
Figure 6. Shear test load-displacement curve of M8 C/SiC bolts
CONCLUSIONS
C/SiC bolts designed and fabricated by NWPU were tested, the average tensile strength of C/SiC bolts was 114.71 MPa and the average shear strength of C/SiC bolts was 71.34 MPa. C/SiC bolts showed good mechanical properties.
REFERENCE 1
Hudson, Larry, Stephens, Craig, Aeronautics Research Mission Directorate Hypersonics Material and Structures Carbon-Silicon Carbide Ruddervator Subcomponent Test and Analysis Task, Dryden Flight Research Center, August 2007.
2Dogigli, M, Froehlich, A, Koeberle, H, Sygulla, D, Hypersonic Air Intake Ramp - A Complex Hot CMC-Structure, ESA International Conference on Spacecraft Structures, Materials and Mechanical Testing, Noordwijk, Netherlands, 27-29 Mar. 1996. 3
Wulz, Hans G, Joining Fastening and Sealing of Hot CMC Structures, AIAA Thermophysics Conference 33rd, Norfolk, VA, United States, 28 June-1 July 1999.
Displacement (mm)
L o a d (N )