Failure analysis of the HVAC centrifugal blower wheel for commercial vehicles
Evans, Phillip C.
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The object of this study is to evaluate the cause of the failure of a plastic 20% glass fiber-reinforced polypropylene blower wheel. The blower wheel plays an integral part in the forced distribution of the airflow in the heating, ventilating, and air conditioning system of commercial vehicles. Therefore, it is essential that the blower wheel be highly dependable. This is especially true for commercial vehicles where long warranty requirements and high reliability are required. Several test and analysis methods were employed to understand the cause of the failure of the blower wheel. Initially, the high-speed burst test was used to expose the effects of temperature and imbalance on the part. Experimental vibration analysis was performed on the blower wheel to show the characteristic natural frequencies. This was compared to the numerical natural frequencies found with a finite element analysis (FEA) software package. The experimental stress values were compared to the numerical stress values. The material analysis showed the material was not degraded during the injection molding process and it was not always meeting specifications for the glass coupling agent. Finally, the failures were compared to the S-N fatigue life curves for 25% glass fiber-reinforced polypropylene and 20% glass fiber-reinforced polypropylene material. The study found the root cause of the failures to be a combination of resonance, material issues and fatigue that cause the inlet top ring to break on the blower wheel. Improvements in design, process, and testing are recommended for the blower wheel.