تاثير افزودني هاي مختلف بر خواص مكانيكي، حرارتي و فداشونگي كامپوزيت هاي كربن/ فنوليك

THE EFFECT OF VARIOUS ADDITIVES ON THE MECHANICAL, THERMAL AND ABRASIVE CHARACTERISTICS OF ABLATIVE COMPOSITES

در اين تحقيق اثر پاراتولوين سولفونيك اسيد (PTSA) و پلي وينيل بوتيرال رزين (PVB) بر خواص بين لايه‌يي، حرارتي و ميرايي‌ ‌حرارتي كامپوزيت هاي كربن/فنوليك مورد بررسي قرار گرفته است. چهار دسته نمونه براي آزمايش فداشونگي حرارتي توسط مشعل پلاسما آماده شده است. براي مقايسه‌ي استحكام برشي بين لايه‌يي نمونه‌هاي كامپوزيتي، از آزمايش برش تير كوتاه استفاده شده است. نتايج نشان مي دهد كه افزودن 20درصد بوتيرال رزين به زمينه باعث كاهش 15درصدي نرخ سايش خطي كامپوزيت هاي كربن/فنوليك نسبت به ساير نمونه‌ها مي شود. همچنين استفاده از پاراتولوين سولفونيك اسيد در پخت نمونه‌ها، نرخ سايش وزني كامپوزيت هاي كربن/فنوليك را 35درصد كاهش مي‌دهد. بيشتر بودن شاخص عايق بودن نمونه‌هاي حاوي بوتيرال رزين باعث شده است كه اين كامپوزيت ها بهترين محافظ حرارتي در ميان كامپوزيت هاي مورد بررسي معرفي شوند. با توجه به نتايج حاصل از آزمايش برش تير كوتاه، استحكام برشي بين لايه يي كامپوزيت هاي حاوي پلي وينيل بوتيرال رزين 12درصد بيشتر از ساير نمونه‌هاست.

During atmospheric re-entry, a ballistic or space vehicle is subjected to severe aerodynamic heating and its successful return through the Earth’s atmosphere depends largely on the provision that is made for reducing aerodynamic heat transfer to its structure. For this purpose, an ablative heat shield is normally used, which undergoes physical, chemical, and mostly endothermal transformations. These transformations produce new liquid or gas phases, which are subsequently injected into the environment. The interfacial, thermal and ablation properties of carbon fiber/phenolic resin composites are evaluated in this study. Different materials, such as plain carbon fabrics, as reinforcement, resole type phenolic (IL800, Resitan Co.) as matrix, p-toluene sulfonic acid (PTSA) and polyvinyl Butyral resin (PVB) as additive, have been used in the synthesis of the composites. Four groups of samples were fabricated to be investigated by a plasma torch. In order to explore the interlaminar shear strength of the composites, short-beam shear tests were conducted. Short-beam shear tests indicate that the interlaminar shear strength of the C/P/PVB composite is 17% greater than that of the other samples. Observations show that 20% PVB has an important effect on proper adhesion between carbon fibers and the resole matrix of C/P composites, and on achieving improved interlaminar characteristics. The ablation test results reveal that composites with 20% polyvinyl butyral resin (C/P/PVB) have the highest ablation resistance, and the erosion rate (mm/s) of these specimens are 20% lower than other specimens. Additionally, the high insulation index of the C/P/PVB samples indicates that these composites are the best ablative materials in the present study. But, results show that the mass reduction percentage of C/P/PTSA/PVB samples is around 28% lower than C/P/PVB samples. According to Table 3, addition of PVB to C/P composites caused 70% improvement in the thermal conductivity of C/P/PVB composites. Regarding samples with 4-7 wt% PTSA, against our expectations, these samples, because of their porous structure, did not have appropriate ablative performance.