Seminar on composites

Development and characterization of polymer–ceramic continuous fibre reinforced functionally graded composites (FGC) for aerospace application

Topic

By-Tejveer PariharM. Tech Aerospace Engineering

I.I.T KHARAGPUR

AbstractFunctionally graded materials (FGMs) have continuous change in the composition across the thickness.

The FGMs as an an attractive material for aerospace applications.

So far the research focus has been on the functionally graded coatings and particulate reinforced functionally graded composites.

In this study, (FGCs) have been prepared using quartz fabric reinforcement for thermo-structural aerospace application.

Silicone resin and fused silica powder have been used to obtain graded matrix.

The FGC laminates have been characterized for mechanical and thermal properties.

The laminates were also evaluated for thermal shock resistance and thermal insulation properties by exposing to infra-red heating lamps under high heating rate of about 800 ◦ C/s and high heat flux of 0.6 W mm−2 for 70 s. FGC laminates did not de-laminate or charred.

Temperature drop across the laminate of 8 mm thickness was found to be 600 ◦ C

The concept of FGC fabrication process is demonstrated to fabricate scaled down typical airframe sections also.

Introduction

Advanced aerospace structures require materials capable of serving multi-functions.

(FGMs) has several contrasting functions are incorporated into a single material; like, toughness of the polymeric materials and temperature capability of the ceramics.

FGMs were developed first time by Japanese scientist Niino and coworkers in 1984 as a means of preparing thermal barrier materials for space structures, fusion reactors, space plane systems and turbine engines.

FRP as widely used structural material has temperature limitation and ceramics has strength limitation

In FGC by bonding ceramic and polymer layers and to avoid the large CTE mismatch between the polymer and ceramic these materials may be graded across the thickness keeping the two opposite surface layers as pure polymer and pure ceramic.

Toughness and mechanical strength be further enhanced by reinforcing with a suitable fibrous reinforcement to obtain (FGCs).

Silicone resins are capable of with-standing temperature up to 400 ◦ C and may provide good strength when reinforced with quartz fabric.

Quartz–silica (silica–silica) composites can with-stand temperature up to 1500 ◦ C in air without much degradation in mechanical properties

A suitably designed FGC may exploit mechanical strength of quartz–silicone composites and temperature capability of quartz–silica composites.

The matrix may be graded across the thickness of the FGC laminate by adding fused silica powder into silicone resin in an appropriate ratio.

AIM AND SCOPE

In this paper research efforts are made to fabricate quartz fibre reinforced FGC laminates and some typical shape scale down airframes.

The FGC laminates shall be tested for thermal and mechanical properties. Thermal shock and thermal insulation performance of the FGC laminates shall also be evaluated

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S. No. Material Strength Thermal conductivity Service temperature (MPa) (W /m K )

1. Quartz – silicone 250 – 300 0. 23 Up to 400 ? C

2. Quartz – silica 50– 70 1.0 Up to 1500 ? C

.

Fig. 1. Flow sheet for FGC preparation.

Table 1Thermo-structural properties of matrix materials being used for FGC preparation.

Fig. 2. Scheme of functionally graded composite

Experimental Preparation

Raw materials- As Reinforcement- Quartz fabric of twill weave textile pattern was used as reinforcement for FGC laminates

Matrix- Three components were used to obtain matrix system for the FGC laminates viz. (i) Dow Corning 4-3136 binding silicone resin; (ii) four micron sized fused silica powder; (iii) colloidal silica.

FGC laminate fabrication- -Prepreg prepration-Molding of FGC laminates(obtained fiber volume fraction in the range of 50–55%)-Impregnation of colloidal silica

Apart from FGC laminates, four other matrix compositions based laminates were also prepared for comparative study

Table 2 Matrix gradation scheme.

Reinforcement Fused silica Silicone resin (% w/w) (% w/w)

High temperature resistance Quartz fabric 100 0 Layer; Silica surface (Silica derived from

colloidal silica)

Graded matrix zone Quartz fabric 80 20 Quartz fabric 60 40 Quartz fabric 40 60 Quartz fabric 20 80

Structural layer; Silicone surface Quartz fabric 0 100

Characterization

Thermal Conductivity Test- Fused quartz was used as a reference material during the test (thermal conductivity of fused quartz = 1.0 W m−1 K−1).

Coe cient of thermal expansion (CTE) (alumina probe) ffiCTE = ( L /L)/_T ; where ( L/L)is the fractional change in length of the specimen due to the temperature change _T .

IR lamp (kinetic heating) testing (k type thermo couples)(70 s)(heat flux .6 wb mm^_2)

Flexural strength testing(UTM) (three point bending behaviour)

Fig. 3. Kinetic heating test setup.

Fig. 4. FGC shaped components.

Feasibility study to develop shaped FGC components was carried out successfully to demonstrate continuous fiber reinforced FGM

Results and Discussion

Laminate preparation- densities of silicone matrix and silica powder are 1.25 g/cc and 2.2 g/cc respectively

Density of the FGC laminates is higher than the density of laminates of category-II and IV but lower than the density of the laminates of category-V. Density of the FGC laminates was in the range of 1.95–2.0 g/cc

Thermal conductivity of the laminates of FGC, category-II and category-VI was found to be in the range of 0.435–0.458, 0.2–0.23 and 0.98–1.0 W m−1 K−1 respectively

Thermal conductivity-

Table 3 Thermal conductivity of FGC with temperature.

Temperature at silica surface, ◦ C 80 158.4 243.0 330.7 Temperature at silicone surface, ◦ C 39.6 71.3 106.7 138.1 Average temperature across the FGC 59.8 114.85 174.85 234.40

thickness (10 mm)

Thermal conductivity, W m−1 K−1 0.458 0.441 0.439 0.435

FGC composites have thermal conductivity in between the silicone resin and fused silica but dominated by the thermal conductivity of silicone resin due to the high thermal contact resistance of silicone resin and silica powder.

Fig. 5. CTE of quartz fabric reinforced silicone–silica powder matrix laminates.

Coe cient of thermal expansionffi

Fig. 6. (a) Temperature profile of category-II and VI laminates under kinetic heating test.

Kinetic heating test

(b) Temperature profile of FGC laminates under kinetic heating test

Fig. 7. Quartz–silicone laminate after kinetic heating test.

The surface of quartz–silicone facing the lamps was completely pyrolyzed and indicates that the composite of that category may not be suitable for repeated use under the tested conditions

Fig. 8. FGC laminate after kinetic heating test.

FGC plate did not show any physical change either in the form of de-lamination or pyrolysis

Fig. 9. Stress–strain curves for (1) quartz–silicone, (2) quartz–silica, and (3) FGC.

Flexural strength

Fig. 10. Stress–strain curves for FGC.

FGC laminate samples were tested in two modes; (i) silica face was under compression, (ii) when silica face was under tension; silicone resin face is under compression

Fig. 11. Three-point bend tested FGC specimen.

At the ultimate failure load the specimen failed in shear mode at the interface where composition of silica in the matrix is the highest

FGC does not fail catastrophically and continues to take load even after initiation of failure

Summary and conclusions

The FGC process technology has also been successfully demonstrated to fabricate shaped products.

The concept of FGM and functionally graded coating has been successfully extended to develop continuous fibre reinforced functionally graded composites

Quartz fabric reinforced polymer–ceramic FGM using grading of silicone resin and silica matrix across the thickness has been fabricated

The FGC laminates are tested for thermal conductivity, CTE, thermal shock and flexural properties.

The properties are found to be better than the pure polymer/ceramic matrices based composites.

The FGC laminates have shown very good thermo-structural capability under kinetic heating test and shown promising features for high temperature reusable structures.

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References

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