tailieunhanh - Encyclopedia of Smart Materials (Vols 1 and 2) - M. Schwartz (2002) WW Part 11

Tham khảo tài liệu 'encyclopedia of smart materials (vols 1 and 2) - m. schwartz (2002) ww part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Figure 29. Transverse strain along the stretchii as a function of driving electric field at differei measured for stretched P VDF-TrFE 68 32 mol irradiated at 100 C with 70 Mrad dose using that are isotropic in the plane perpendicular field the strain component in the plane is the strains along the chain positive and pe the chain negative and is in general positi For electrostrictive materials the elec coupling factor kij has been derived by Ho on the consideration of electrical and mecha generated in the material under external fi Figure 28. a Electric field induced strain along the thickness direction longitudinal strain S3 versus electric field measured at room temperature and 1 Hz b change in longitudinal strain S3 with square of polarization P and c temperature dependence of longitudinal strain induced under 14 MV m and 1 Hz driving electric field of unstretched P VDF-TrFE 68 32 mol copolymer films irradiated at 105 C with 70 Mrad dose using 1 MeV electrons. 2 _ kS2 k j .D Pl Ps Pe VpuA sij pE Hip p ps ln 1 ps pE ỵ where j 1 or 3 correspond to the transve dinal direction . k31 is the transverse c and SjD is the elastic compliance under cons tion Sj and Pe are the strain and polarizat respectively for the material under an elec The coupling factor depends on E the elec In Eq. 13 it is assumed that the polarizat relationship follows approximately Pe Ps tanh k E where Ps is the saturation polarization and 1 It is found that Eq. 14 describes the P-E the irradiated copolymers studied here quit The electromechanical coupling factors ated copolymers have been determined bas on the field-induced strain the elastic mod and polarization. Presented in Fig. 31 are stretched sample and k31 for the stretched the drawing direction. Near room temperat an electric field of 80 MV m k33 can reach which is comparable to that obtained in a P VDF-TrFE copolymer 81 . More intere can be obtained in a stretched copoly 20 30 40 50 60 70 T C Figure 30. Temperature dependence

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