212 Effect of Damage on the Interlaminar Shear Properties of Hybrid Composite Laminates at Cryogenic Temperatures
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Three kinds of C/C composites with different matrix carbon were prepared, and then the ring-block sliding friction behavior was tested on M2000 tester against C/C ring with smooth lamination structure pyrocarbon matrix(SL).The results show that the coefficient of friction(COF) of the composite with SL(composite A) or resin carbon matrix(composite B) is lower than that of the composite with rough lamination structure pyrocarbon matrix(composite C). The COF of composite A and B decreases with the increase of load, while that of composite C increases at first and then decreases with the highest value of 0.145 at 100 N. The volume loss of composite A and B is close and remain stable when the load is higher than 80 N with the highest value is only 0.39 mm3. But the value loss of composite C increases up to the highest value of 1.47 mm3at 100 N and then remains some fluctuation. The COF of composite A can reach the stable value quickly while those of composite B and C still decrease after 5 hours' test. SEM images of worn surface show that some large film on composite A is peeled off, some dotted adhesive wear scar can be found on the worn surface of composite B. Abrasive worn is the main wear mechanism for tribological behavior of the three C/C composites.
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Abstract This study investigated the influence of carboxyl‐terminated butadiene acrylonitrile (CTBN) liquid rubbers on the microcracking response of polymeric composite materials to cryogenic cycling. Matrices of carbon fiber/epoxy prepregs were modified with different concentrations of two CTBN liquid rubbers. The glass transition temperature and the interlaminar shear strength of the laminate systems were depressed as a result of the presence of CTBN in the epoxy phase. An increase in total rubber concentration with the continuous phase was found to decrease and in some cases eliminate microcracking in laminates exposed to cryogenic cycling.
Cryogenic temperature
Nitrile rubber
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Experiments were conducted to establish a correlation between the weight loss of a polyimide (PMR- 15) matrix and graphite fibers and the in-plane shear properties of their unidirectional composites subjected to different isothermal aging times up to 1000 hr at 316 C. The role of fiber surface treatment on the composite degradation during the thermo-oxidative aging was investigated by using A4 graphite fibers with three surface modifications: untreated (AU-4), surface treated (AS-4), and surface treated and sized with an epoxy-compatible sizing (AS-4G). The weight loss of the matrix fibers, and composites was determined during the aging. The effect of thermal aging was seen in all the fiber samples in terms of weight loss and reduction in fiber diameter. Calculated values of weight loss fluxes for different surfaces of rectangular unidirectional composite plates showed that the largest weight loss occurred at those cut surfaces where fibers were perpendicular to the surface. Consequently, the largest amount of damage was also noted on these cut surfaces. Optical observation of the neat matrix and composite plates subjected to different aging times revealed that the degradation (such as matrix microcracking and void growth) occurred in a thin surface layer near the specimen edges. The in-plane shear modulus of the composites was unaffected by the fiber surface treatment and the thermal aging. The shear strength of the composites with the untreated fibers was the lowest and it decreased with aging. A fracture surface examination of the composites with untreated fibers suggested that the weak interface allowed the oxidation reaction to proceed along the interface and thus expose the inner material to further oxidation. The results indicated that the fiber-matrix interface affected the composite degradation process during its thermal aging and that the the weak interface accelerated the composite degradation.
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Evidence for existence of composite copper/oxygen vacancy nanofilaments is presented. The composite conductive nanofilment (CF) is a serial resistive connection of Cu and Vo CFs forming a composite Vo/Cu CF where the Cu filament segment is formed first and Vo filament completes the composite CF. A composite CF has been also formed in reverse order as Cu/Vo. Both composite CFs, Vo/Cu and Cu/Vo, display Vform at considerable lower voltages than monolithic CFs.
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Al₂O₃ particles were dispersed into carbon fiber reinforced epoxy composites to fabricate hybrid epoxy based composites. Interface behavior and mechanical properties of these hybrid composites were studied at room and liquid nitrogen temperature and the results were compared with those of carbon fiber reinforced composites to investigate their applicability at room and cryogenic temperature. Young's modulus in-perpendicular to fiber direction and interlaminar shear strength at room temperature and the thermal contraction down to cryogenic temperature were improved significantly by the addition of Al₂O₃ filler into the epoxy matrix. The effect of Al₂O₃ particle addition on mechanical properties were discussed.
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