O.N. Grigoriev et aL./Composites: Part B 37(2006)530-541 604B91自 01p304560;:9:0z2 33 01203045060708090100Z2 aaea3n405060790地2 Fig. 2. Distribution of principal stresses o11, 022. 33(aHc)as well as o1(d)in laminated composites SiC/SiC-TiB2/TiB2 rgent. One of such alternative methods is optic-polarization Since, the magnitude of the signal is defined by phase traditionally used in crystallography to study transparent changes of a light wave reflected from a sample it provides materials and for simulation of the mechanic behavior a very high sensitivity for stress measurements. It was (polymers, glasses)[27] shown [30], that changes of anisotropic dielectric properties In the present work the polarization-modulation method is caused by stresses are comparable in magnitude with considered for study of internal stresses in composite materials. anisotropy of properties changes caused by the deformation It is suitable for research of transparent materials in of sample by its own weight due to gravity forces. The distribution of tensile residual stresses with a spatial resolution 10% atati, E transmittance mode and for opaque materials in reflection relative anisotropy of refractive index, arising from such mode. With this method it is possible to obtain local gravitational deformation in silicon crystal, does not exceed In this case the phase difference between two orthogonal polarized components of light with wavelength The optical scheme of experimental setup is shown in a of I cm is about 2X10 which corresponds approxi Fig. 3. The scheme performed as a Michelson interferometer mately one angular second however its peculiarity is the measurement of the phase In the case of polycrystalline ceramics the reflected beam polarized light wave cause by An=nx-y and arising at its result of interaction of reflections from 1 to 100 crystalgrana changes between two orthogonal components of linearly from accident beam of a diameter about 10 um is formed as a transmission (or reflection) through the sample. For this The state of polarization of the reflected light wave will be purpose the photoelastic modulator(PM)[28] is added into characterized by some average effective parameters of the scheme. This element represents a dynamic phase plate The alternating mechanical load of a suitable frequency of wo was applied to plate. During the period of one vibration the plate becomes the quarter wave or half wave plate depending on the magnitude of load. In the first case the linearly polarized light wave after passing through the plate is transformed in LG.126 circular polarized light, and in the second case it is transformed in linear orthogonally polarized light The principle of setup operation consists in the followin [29]. Radiation of the laser LG-126 (rad 0.63 or 1.15 um), polarized at the angle of 45 to the axis Y in the plane Xor equally divided on two light beams by the splitter. One of them is directed to a anisotropic reflector(), and another one is focused on a sample(S)by the lens(O1). The beams reflected from the reflector(R)and the sample are combined together and directed to the photodetector(PD)through the photoelastic Fig. 3. Optical scheme of polarization-modulated setup: LG-126-He-Ne modulator(PM) and polarizer(P). In the transmittance mode laser, S, sample: R, anisotropic reflector; PM, photoelastic modulator: the mirror is places behind the sample darizer pdurgent. One of such alternative methods is optic-polarization traditionally used in crystallography to study transparent materials and for simulation of the mechanic behavior (polymers, glasses) [27]. In the present work the polarization-modulation method is considered for study of internal stresses in composite materials. It is suitable for research of transparent materials in transmittance mode and for opaque materials in reflection mode. With this method it is possible to obtain local distribution of tensile residual stresses with a spatial resolution of about 3 mm. The optical scheme of experimental setup is shown in a Fig. 3. The scheme performed as a Michelson interferometer however its peculiarity is the measurement of the phase changes between two orthogonal components of linearly polarized light wave cause by DnZnxKny and arising at its transmission (or reflection) through the sample. For this purpose the photoelastic modulator (PM) [28] is added into the scheme. This element represents a dynamic phase plate. The alternating mechanical load of a suitable frequency of u0 was applied to plate. During the period of one vibration the plate becomes the quarter wave or half wave plate depending on the magnitude of load. In the first case the linearly polarized light wave after passing through the plate is transformed in circular polarized light, and in the second case it is transformed in linear orthogonally polarized light. The principle of setup operation consists in the following [29]. Radiation of the laser LG-126 (lrad 0.63 or 1.15 mm), polarized at the angle of 458 to the axis Y in the plane XOY equally divided on two light beams by the splitter. One of them is directed to a anisotropic reflector (R), and another one is focused on a sample (S) by the lens (O1). The beams reflected from the reflector (R) and the sample are combined together and directed to the photodetector (PD) through the photoelastic modulator (PM) and polarizer (P). In the transmittance mode the mirror is places behind the sample. Since, the magnitude of the signal is defined by phase changes of a light wave reflected from a sample it provides a very high sensitivity for stress measurements. It was shown [30], that changes of anisotropic dielectric properties caused by stresses are comparable in magnitude with anisotropy of properties changes caused by the deformation of sample by its own weight due to gravity forces. The relative anisotropy of refractive index, arising from such gravitational deformation in silicon crystal, does not exceed 10K10. In this case the phase difference between two orthogonal polarized components of light with wavelength of 1 cm is about 2p!10K6 which corresponds approxi￾mately one angular second. In the case of polycrystalline ceramics the reflected beam from accident beam of a diameter about 10 mm is formed as a result of interaction of reflections from 1 to 100 crystal grains. The state of polarization of the reflected light wave will be characterized by some average effective parameters of Fig. 3. Optical scheme of polarization-modulated setup: LG-126—He–Ne laser; S, sample; R, anisotropic reflector; PM, photoelastic modulator; P, polarizer; PD, photodiode. Fig. 2. Distribution of principal stresses s11, s22, s33 (a)–(c) as well as s12 (d) in laminated composites SiC/SiC–TiB2/TiB2. O.N. Grigoriev et al. / Composites: Part B 37 (2006) 530–541 533