106 Y Gong, Z-G. Yang/Composites: Part B 53(2013)103-11 46007°C4849%L055 48043°C4988%Loss Fig 3. TGA results of the failed pedal arm(a)pedal, and (b)frame. marked by the red rectangular was the stress concentration area, and cracks while shown in Fig. 10d, some of them were twisted. Thus must be the initiation site of fracture. Thus, special attention was in order to identify what such foreign fibers exactly were, subse- then paid to it in Fig. 6b. Two black areas with no glass fibers quently their chemical compositions were analyzed by Eds (marked by the red arrows)were observed around it, which verified According to Fig. 10e-g and table 2, compared with the normal the uneven distribution of the glass fibers again. glass fibers that possessed high contents of inorganic elements, Meanwhile, other distinct flaws besides the uneven distribution the foreign fibers were predominantly composed of carbon and of glass fibers were also detected on areas away from the corner, oxygen elements on the contrary, indicating they were organic fi- including voids(Fig. 7a) and curly foreign fibers(Fig. 7b)within bers instead! As for their concrete constituents, it's not difficult the matrix, which would definitely affect the comprehensive per- to infer they were polypropylene too, but were probably the recy- ormances of the pedal arms too led ones mingled in processing. Actually, this was exactly the effi- On basis of the microscopic observation above, further investi- cient way to decrease cost, and would not have negative effects ations especially into those flaws would then be conducted under chemically. However, just like in Fig. 10a and c, if some extraordi- SEM. As shown in Fig 8, on the convex(right )of the stress concen- narily long fibers existed, they would possibly block the flow of tration corner there were nearly no glass fibers, while on the con- melted GF/PP pellets, and would finally result in voids around, ave (left) although there existed some fibers, their alignments influencing the comprehensive strength of the pedal arms. ere parallel rather than perpendicular to the fracture surface. All these phenomena clearly demonstrated the strength of the 3.6.2. Unused sample stress concentration corner, i.e. the potential fracture initiation For purpose of comparison, the fracture surfaces of the unused site, seemed not to be sufficiently qualified. pedal arm were then observed too. Totally speaking, the glass fi- On other areas, large-scale glass fibers parallel to the fracture bers distributed more evenly than the previous failed sample, seen surface also existed, seen in Fig. 9a; and meanwhile, the flaws of in Fig. 1la. But in some area( Fig. 11b), agglomerated glass fibers voids in size of multi-hundred microns were also observed, seen (marked by the red circle)and foreign fibers (marked by the red ar- Fig 9b. row)could also be detected If only focus on the most significant It must be particularly pointed out that abnormal foreign fibers area, i. e the stress concentration corner, lots of pulled-out glass fi that were in shape of extraordinarily long curls were detected bers perpendicular to the fracture surfaces could be observed obvi well by SEM, seen in Fig. 10a and c As shown in Fig. 10b, compared ously, seen in Fig. 12a. After magnified ( Fig. 12b), the localized with erect and smooth glass fibers, these curly fibers exhibited concave (left) was still covered with glass fibers, and the area with- rough surface morphologies, and were even embedded with micro- out glass fibers on the convex (right) was only 0.5 0.5 mmmarked by the red rectangular was the stress concentration area, and must be the initiation site of fracture. Thus, special attention was then paid to it in Fig. 6b. Two black areas with no glass fibers (marked by the red arrows) were observed around it, which verified the uneven distribution of the glass fibers again. Meanwhile, other distinct flaws besides the uneven distribution of glass fibers were also detected on areas away from the corner, including voids (Fig. 7a) and curly foreign fibers (Fig. 7b) within the matrix, which would definitely affect the comprehensive per￾formances of the pedal arms too. On basis of the microscopic observation above, further investi￾gations especially into those flaws would then be conducted under SEM. As shown in Fig. 8, on the convex (right) of the stress concen￾tration corner there were nearly no glass fibers, while on the con￾cave (left) although there existed some fibers, their alignments were parallel rather than perpendicular to the fracture surface. All these phenomena clearly demonstrated the strength of the stress concentration corner, i.e. the potential fracture initiation site, seemed not to be sufficiently qualified. On other areas, large-scale glass fibers parallel to the fracture surface also existed, seen in Fig. 9a; and meanwhile, the flaws of voids in size of multi-hundred microns were also observed, seen in Fig. 9b. It must be particularly pointed out that abnormal foreign fibers that were in shape of extraordinarily long curls were detected as well by SEM, seen in Fig. 10a and c. As shown in Fig. 10b, compared with erect and smooth glass fibers, these curly fibers exhibited rough surface morphologies, and were even embedded with micro￾cracks; while shown in Fig. 10d, some of them were twisted. Thus in order to identify what such foreign fibers exactly were, subse￾quently their chemical compositions were analyzed by EDS. According to Fig. 10e–g and Table 2, compared with the normal glass fibers that possessed high contents of inorganic elements, the foreign fibers were predominantly composed of carbon and oxygen elements on the contrary, indicating they were organic fi- bers instead! As for their concrete constituents, it’s not difficult to infer they were polypropylene too, but were probably the recy￾cled ones mingled in processing. Actually, this was exactly the effi- cient way to decrease cost, and would not have negative effects chemically. However, just like in Fig. 10a and c, if some extraordi￾narily long fibers existed, they would possibly block the flow of melted GF/PP pellets, and would finally result in voids around, influencing the comprehensive strength of the pedal arms. 3.6.2. Unused sample For purpose of comparison, the fracture surfaces of the unused pedal arm were then observed too. Totally speaking, the glass fi- bers distributed more evenly than the previous failed sample, seen in Fig. 11a. But in some area (Fig. 11b), agglomerated glass fibers (marked by the red circle) and foreign fibers (marked by the red ar￾row) could also be detected. If only focus on the most significant area, i.e. the stress concentration corner, lots of pulled-out glass fi- bers perpendicular to the fracture surfaces could be observed obvi￾ously, seen in Fig. 12a. After magnified (Fig. 12b), the localized concave (left) was still covered with glass fibers, and the area with￾out glass fibers on the convex (right) was only 0.5 0.5 mm, Fig. 3. TGA results of the failed pedal arm (a) pedal, and (b) frame. 106 Y. Gong, Z.-G. Yang / Composites: Part B 53 (2013) 103–111