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Grant AFOSR-F49620-99-1-0275 20(151024 090 ,,,- SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S)12. DISTRIBUTION I AVAILABILITY STATEMENT ApPiiov•d ta f or ]att e Iaeltestio, SUPPLEMENTARY NOTES14. ABSTRACTAn elevated temperature fiber pushout apparatus has been built and used to test the interfacial shear strenght and frictional shear stress at various temperatures in Ti matrix composites. The pushout apparatus, coupled with thermal aging studies, was used to investigate the influence of temperature and thermal exposure on tangential interfacial shear strength and frictional shear stress. Additionally, the effect of variation of processing conditions, including variation of fiber volume fraction and of the time-temperature-pressure profile during consolidation, has been examined using concentric cylinder numerical mode, and compared to experimental test results. Using interface properties, composite failure maps have been established for this material that describe the dominant failure mode as a function of the temperature and stress intensity factor during loading.Furthermore, iInterface debonding behavior, in terms of the cohesive zone model parameters of maximum traction, maximum separation and cohesive energy, in both the normal and tangential direction, has been established for the MMC composite system SCS-6/Timetal-21S, for temperatures from 23 to 650 °C ABSTRACTThe high temperature interfacial properties, in the tangential and normal direction, of a continuous SiC fiber reinforced Ti matrix composites, primarily SCS-6/Timetal-21S, have been examined in this experimental/numerical study. An elevated temperature fiber pushout apparatus has been built and used to test the interfacial shear strenght and frictional shear stress at various temperatures. It was found that as temperature increases, both interface properties decrease, but the debonding behavior changes for test temperatures above 400 TC. Additionally, transverse loading tests have shown a similar decrease in normal separation stress with increasing temperature. The pushout apparatus, coupled with thermal aging studies, was used to investigate the influence of temperature and thermal exposure on tangential interfacial shear strength and frictional shear stress. It was found that thermal exposure under vacuum for temperatures up to 650 TC conditions results in no noticeable increase in the interphase size, composition, or interphase strength properties. Aging in air causes a degradation of the interphase, resulting in deterioration of interphase properties, particularly at higher temperatures. The effect of variation of processing conditions, including variation of fiber volume fraction and of the time-temperature-pressure profile during consolidation, has been examined using concentric cylinder numerical mode, and compared to experimental test results. It was found that the processing conditions required for full consolidation of the material allow little variation in th...

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A series of fiber pushout tests on thin-slice samples of a SCS-6/Timetal-21S composite were carried out to determine the load values at which partial and full debonding occurs. Finite element calculations of the stress field in the specimen were employed to assess the interphase strength of the composite as function of temperature. In these calculations, the semi-infinite thickness and the traction-free surface effects of the thin-slice samples on the corresponding stress field are considered. For each of these specimens, the distribution of shear stress along the fiber/matrix interface is determined in order to identify a region of stress localization which is taken in this study to be a measure of the interphase shear strength. This strength is then identified as the balance of forces at this localized field due to the traction-free surface of the composite section. Both contributions from process-induced residual stress and geometry-induced constraint of the traction-free surface to the strength are considered. The results of this study showed that the interphase shear strength decreases with an increase in temperature and processing-related residual stress contributes about 35 % to the interphase shear strength at room temperature. Furthermore, the interphase shear strength as calculated in this paper was found to be larger than that determined by considering uniformly distributed shear stress along a pushout fiber.