دانلود رایگان مقاله تحلیل شکست یک پیش برنده گریز از مرکز پلیمر

ABSTRACT

A failure analysis investigation was performed on a fractured polymer impeller used in a respiratory blower. Light microscopy, scanning electron microscopy and finite element analysis techniques were utilized to characterize the mode(s) of failure and fracture surfaces. A radial split down the impeller center was observed with symmetric fracture faces about the impeller bore. Fractographic analysis revealed brittle fracture features including Wallner lines, mirror, mist and hackle features stemming from the impeller bore, emanating radially outward. Crazed fibrils and faint fatigue striations suggest that intermittent load cycling led to initiation, and rapid propagation of multiple crack fronts originating along the impeller lip. Finite element analysis revealed a flexural condition induces localized stresses along the impeller lip. Significant wear features were also observed within the impeller bore, which may have contributed to premature failure of the impeller. The brittle fracture morphology and defects within the impeller bore suggest that premature failure occurred because of multiple interacting factors including: intermittently high centrifugal velocities, imbalance bore and shaft conditions, defects within the bore caused by machining, and stress concentrations along the circumference of the impeller lip.

5. Conclusion A failed, centrifugal polyetherimide impeller was analyzed using light microscopy, scanning electron microscopy and finite element analysis to provide insight on causes for premature failure. The investigation showed symmetric brittle fracture features which include Wallner lines, mirror, mist, and hackle zones that emanated from an origin near the base and bore of the impeller, and additionally showed signs of fretting damage that may have contributed to premature failure due to defect growth. Slow drawn fibrils were observed on the left half face of the fracture origin, while faint fatigue striations were observed near the right half face of the fracture suggesting that the right half was the primary fracture, and the left half fracture failed in a secondary fashion, with separation of the impeller into two halves creating drawn fibrils. Finite element analysis showed that centrifugal loads produced a stress concentration along the impeller lip where the fracture initiated. To increase service life and reduce the potential for premature failure, the fretting wear defects (caused by reaming) need to be minimized.