SiC optics have been considered for numerous optical applications for a long time. The fundamental
limitation of monolithic SiC is its, very low fracture toughness which greatly limits its reliability.
Long fiber, SiC-SiC composites are an excellent candidate for high end optical application. The selection of
the fiber and composite processing needs to address the intrinsic issues of modulus, strength, toughness,
thermal conductivity and CTE isotropy. The adaptability and flexibility of SiC-SiC composite
manufacturing renders the ability to fabricate very complex, closed-back structures. The fundamental issues
associated with uv optics is the ability to polish the substrate to ultra high quality in order to greatly reduce
the scattering.
SiC optics has been considered for a very long time. Today, there are a few military and commercial applications. Future imaging and energy transfer applications require robustness on a par with metallic systems. Intrinsic, low fracture toughness of several classes of monolithic SiC is the key impediment in these applications. A new form of SiC-SiC composite for optical applications has been developed. It features high modulus combined with high fracture toughness. This new, highly innovative technology offers the potential in demanding government applications, as well as large surveillance optics (increased toughness can translate into lower aerial density) and high energy commercial lasers. SiC-SIC is a novel technology for optical structures consisting of integrated composite materials and structures which exhibits excellent fracture toughness and homogeneous CTE.
SiC ceramics offer unique thermomechanical and optical characteristics. However, their practical application in optics is very limited. A novel approach was developed which combines carbon composites, carbon foam, Chemical Vapor Reaction (CVR)-Si and Chemical Vapor Deposition (CVD)-Si. This unique approach provided for a breakthrough in optical structures the elimination of the print-through at the rib section.
A novel technology to fabricate ultralightweight mirrors was demonstrated. High thermal conductivity C-C composite integrated honeycomb face sheets were fabricated using a tape layup. Chemical Vapor Deposition (CVR)-SiC was employed to produce a functionally graded transition in CTE from about 0 ppm/K to about 4.5 ppm/K. A crack free CVR-SiC surface was achieved which was subsequently polished. A 1 kg/m2 SiC mirror structure was demonstrated.
Currently, smart structures utilize both polymeric sensor and PZT-based actuators. Polymeric sensors based upon PVDF are limited to about 70 degrees C operating temperature, while PZT-based actuators are inflexible. This paper examines the use of PZT/polymer composites for smart materials applications. Both ferroelectric (VDF) and non- ferroelectric high temperatuer polymers were studied. High temperature composite sensors were fabricated exhibiting g31 values of 90 X 10-3 Vm/N compared to 110 X 10-3 Vm/N for PVDF combined with excellent compliance. On the other hand, 0-3 composite based actuators were fabricated with greatly enhanced d31 over PVDF. Piezo properties and dielectric properties of both sensor and actuators were studied as a function of temperature voltage. Processing-structure-properties relationship was established including key processing parameters such as PZT particle size, enhanced poling additives and polymer properties. Thermal dependence of the 0-3 composites piezoproperties was correlated with glass properties of the polymer. Applications of this new class of 0-3 concepts to cure monitoring of advanced composite systems will be discussed.
Currently, smart structures utilize both polymeric sensor and PZT-based actuators. The benefit of self-sensing calls for the development of integrated actuator/sensor composites. This paper addresses the development and properties of this new class of smart materials. Controlled porosity (amount, size, shape and distribution) were fabricated using sintering, blending and spin- on-disc. New flexible, thin polymer based composites were obtained. The optimization between d31 and g31 was performed to provide both actuator and sensing capabilities. It was found, that processing conditions including poling can be adjusted to provide the contribution from both PZT and VDF.
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