The sound absorption performance of porous asphalt concrete (PAC) is inseparable from the sizes of voids, as different sizes of voids have different absorption effects on noise in different frequency bands. However, the relationship between the two is not clear. In this study, the equivalent diameter of voids was obtained by the proposed image segmentation algorithm based on the square area, then grey entropy method was used to analyze the effect of different equivalent diameter of voids on the sound absorption performance of PAC in the frequency range of traffic noise. The results show that with the increase of air voids, the peak and average sound absorption coefficient of PAC increase, the sound absorption performance of PAC is improved; and the sound absorption performance of PAC is mainly affected by the equivalent diameter of voids of 3-4mm.

To account for the adverse effects of white spot defects onto the performance of gear wheel, physicochemical properties are studied based on the conducted surface carbonization experiment. Further, the geneses for white spot defects are discussed and the solutions to this problem are also clarified. It is found from the physicochemical analysis that the white spot defects occurred on gear surface can be classified into two parts: a) the ‘single white spot’, which originates from the sick point produced during the carbonization process, and b) the ‘multiple continuous spots’, which are produced by either the non-uniformity surface carbonization or the grinding burn or otherwise the micro ecarbonization caused by overheat on gear surface. For different white spot defects, different strategies should be employed: ultrasonic cleaning technique should be performed for the single white spot case, while for the ‘multiple white spot’ case, not only should the vacuum carburizing technique be employed to avoid surface non-uniformity of carbonization, but also vacuum oil quenching are needed to clear up the defects induced by micro decarbonization.