Chapter 9:Predicting Thermooxidative Degradation 383 Dark-field microscopy [95]is used to monitor the oxidation pro- pagation rates in both the axial direction(along the fiber)and the trans- verse direction (transverse to the fibers)of unidirectional G30-500/PMR-15 composites aged in air at 288C.Test specimens are removed from the aging oven at specified times,and a small cross section of the specimen is cut off and mounted in an epoxy plug for polishing,as illustrated in Fig.9.7.The original specimen is then placed back into the oven until the next specified aging time. Figure 9.16 shows (a)the original stitched micrograph and (b)an enhanced micrograph that clearly distinguishes the white oxidized material from the black unoxidized material.The oxidation layer appears as a frame around the composite specimen just as seen in aged neat resin PMR-15 samples in Fig.9.8.The specimen aged for 197 h is shown to have only minimal oxidation transverse to the fibers,but has moderate oxidation development in the axial direction.The method of enhancing the micro- graph consists of constructing (using Adobe Photoshop 7.0)a complete image of the entire composite by stitching together individual micrographs using standard light microscopy in the grayscale mode.Once the image is constructed,the apparent light-oxidized region is best fit in the lab mode to a pure white,specified as having a lightness value of 100,while the remaining unoxidized regions of the image are given a lightness value of zero.Thus,this image processing creates exactly two distinct grayscale colors:black and white. (a) (b) Fig.9.16.(a)Array of eight stitched photomicrographs of oxidized specimen cross section and(b)enhanced micrograph of the specimen cross sectionDark-field microscopy [95] is used to monitor the oxidation pro￾pagation rates in both the axial direction (along the fiber) and the trans￾verse direction (transverse to the fibers) of unidirectional G30-500/PMR-15 composites aged in air at 288°C. Test specimens are removed from the aging oven at specified times, and a small cross section of the specimen is cut off and mounted in an epoxy plug for polishing, as illustrated in Fig. 9.7. The original specimen is then placed back into the oven until the next specified aging time. Figure 9.16 shows (a) the original stitched micrograph and (b) an enhanced micrograph that clearly distinguishes the white oxidized material from the black unoxidized material. The oxidation layer appears as a frame around the composite specimen just as seen in aged neat resin PMR-15 samples in Fig. 9.8. The specimen aged for 197 h is shown to have only minimal oxidation transverse to the fibers, but has moderate oxidation development in the axial direction. The method of enhancing the micro￾graph consists of constructing (using Adobe Photoshop® 7.0) a complete image of the entire composite by stitching together individual micrographs using standard light microscopy in the grayscale mode. Once the image is constructed, the apparent light-oxidized region is best fit in the lab mode to a pure white, specified as having a lightness value of 100, while the remaining unoxidized regions of the image are given a lightness value of zero. Thus, this image processing creates exactly two distinct grayscale colors: black and white. Fig. 9.16. (a) Array of eight stitched photomicrographs of oxidized specimen cross section and (b) enhanced micrograph of the specimen cross section (a) (b) Chapter 9: Predicting Thermooxidative Degradation 383