An experimental-numerical method for measuring dynamic crack propagating velocities under stress wave loading is established in this paper. The experiments of the three-point bend specimen are done on the improved Hopkinson bar. Deflection of loading point, dynamic load and instantaneous crack length are measured, then crack propagating velocities are calculated. Experiments on 40Cr steel show that the results given by this method have a good agreement with that obtained by the resistance fracture gage method. Therefore this method is feasible for measuring crack propagating velocities under high loading rate and will have wide application. 相似文献
The flow field is a pivotal part to manage the transport of water and gas in proton exchange membrane fuel cell. However, the reported water measurement methods (e.g., X-ray and electrochemical impedance spectroscopy (EIS)) cannot give a comprehensive understanding water distribution in the flow field, resulting in challenges in optimizing the channel design and enhancing fuel cell performance. Therefore, we propose a water measurement method combining the X-ray radiography with EIS to investigate the effect of different operating conditions on the growth law and distribution of liquid water in parallel and serpentine flow fields. The attenuation coefficient of liquid water to X-ray is calibrated with constant tube-current and tube-voltage of X-ray generator. Besides, the parallel flow field with hydrophobic treatment is studied. The results show that the water accumulation of the parallel flow field is far more than the serpentine flow field, and the water content of the middle region is higher than that of other regions in the parallel flow field. Furthermore, operating conditions (cathode inlet gas flow rate, inlet gas humidity, and back pressure) have little effect on the liquid water content of the middle region in the parallel flow field. The polarization curve, EIS result, and X-ray radiography show that the performance and water drainage capacity of the hydrophobic parallel flow field are better than the normal one.
Journal of Inorganic and Organometallic Polymers and Materials - The original version of this article unfortunately contained mistakes. In line 9 of the abstract, 5% should read as 2%. The... 相似文献
