The appearance and accumulation of internal impact damage seriously influence overall performance of carbon fiber reinforced plastic(CFRP).Thus,this study evaluates the change in impact damage number by using linear a...The appearance and accumulation of internal impact damage seriously influence overall performance of carbon fiber reinforced plastic(CFRP).Thus,this study evaluates the change in impact damage number by using linear and nonlinear ultrasonic Lamb wave detection methods,and compares these two detection results.An ultrasonic wave simulation model for composite structure with impact damage is established using the finite element method,and the interaction between impact damage and the ultrasonic wave is simulated.Simulation results demonstrate that the ultrasonic amplitude linearly decreases,and the relative nonlinear parameter linearly increases in proportion to the impact number,respectively.The linear-fitting slope of nonlinear parameter is 0.38 per impact number at an input frequency of 1.0 MHz.It is far higher than that of the linear ultrasonic amplitude,which is only-0.12.However,with the increase of impact damage,the linear growth of nonlinear parameters mainly depends on the decrease in ultrasonic amplitude rather than the accumulation of second harmonic amplitude.In the linear ultrasonic amplitude detection,the linear fitting slope at 1.1 MHz is-0.14,which is lower than those at 0.9 MHz and 1.0 MHz.Meanwhile,in the nonlinear ultrasonic parameter detection,the linear fitting slope at 1.1 MHz is 0.92,which is higher than those at 0.9 MHz and 1.0 MHz.The results show that higher frequencies lead to greater attenuation of ultrasonic amplitude and a larger increase in nonlinear parameters,which can enhance the sensitivity of both linear and nonlinear ultrasonic detections.The accuracy of simulation results is demonstrated through the low-velocity impact and ultrasonic experiments.The results show that compared with nonlinear ultrasonic technology,the linear ultrasonic technology is more suitable for impact damage assessment of carbon fiber reinforced plastic because of its simpler detection process and higher sensitivity.展开更多
To study the lung injury caused by segmented shock waves. Methods: A total of 60 rabbits and 20 rats were used in this study. The process of transmission of shock waves was divided into three phases, i.e., the recompr...To study the lung injury caused by segmented shock waves. Methods: A total of 60 rabbits and 20 rats were used in this study. The process of transmission of shock waves was divided into three phases, i.e., the recompression phase (RP), the decompression phase (DP) and the underpressure phase (UP). And the recompression wave (RW), the decompression wave (DW) and the underpressure wave (UW) simulated the three phases, respectively, generated by the equipment designed by us. The RW test, DW test and UW test were respectively applied to the animals. And lung injuries caused by segmented shock waves were discussed. Results: Under the experimental conditions, the RW did not cause obvious lung injury, but the DW could cause different severities of lung injuries. The greater the decompression ranged and the shorter the decompression duration was adopted, the more severe the lung injury was observed. The UW, to some extent, could cause obvious lung injury. Conclusions: It suggests that lung injury under shock waves probably occurs during the DP primarily. It probably does not cause direct obvious lung injury during the RP, but significantly influences the capability of causing lung injury during the DP.展开更多
基金supported by the Na⁃tional Natural Science Foundation of China(No.11972016)the Natural Science Foundation of the Jiangsu Higher Educa⁃tion Institutions of China(No.23KJD460005)Scientif⁃ic Research Foundation for the Introduction of Talent in Nan⁃jing Vocational University of Industry Technology(No.YK21-04-02).
文摘The appearance and accumulation of internal impact damage seriously influence overall performance of carbon fiber reinforced plastic(CFRP).Thus,this study evaluates the change in impact damage number by using linear and nonlinear ultrasonic Lamb wave detection methods,and compares these two detection results.An ultrasonic wave simulation model for composite structure with impact damage is established using the finite element method,and the interaction between impact damage and the ultrasonic wave is simulated.Simulation results demonstrate that the ultrasonic amplitude linearly decreases,and the relative nonlinear parameter linearly increases in proportion to the impact number,respectively.The linear-fitting slope of nonlinear parameter is 0.38 per impact number at an input frequency of 1.0 MHz.It is far higher than that of the linear ultrasonic amplitude,which is only-0.12.However,with the increase of impact damage,the linear growth of nonlinear parameters mainly depends on the decrease in ultrasonic amplitude rather than the accumulation of second harmonic amplitude.In the linear ultrasonic amplitude detection,the linear fitting slope at 1.1 MHz is-0.14,which is lower than those at 0.9 MHz and 1.0 MHz.Meanwhile,in the nonlinear ultrasonic parameter detection,the linear fitting slope at 1.1 MHz is 0.92,which is higher than those at 0.9 MHz and 1.0 MHz.The results show that higher frequencies lead to greater attenuation of ultrasonic amplitude and a larger increase in nonlinear parameters,which can enhance the sensitivity of both linear and nonlinear ultrasonic detections.The accuracy of simulation results is demonstrated through the low-velocity impact and ultrasonic experiments.The results show that compared with nonlinear ultrasonic technology,the linear ultrasonic technology is more suitable for impact damage assessment of carbon fiber reinforced plastic because of its simpler detection process and higher sensitivity.
基金Thisworkwassupportedby"theNinth 5 YearPlan"InstructiveProjectofPLA (No .96L0 40 )
文摘To study the lung injury caused by segmented shock waves. Methods: A total of 60 rabbits and 20 rats were used in this study. The process of transmission of shock waves was divided into three phases, i.e., the recompression phase (RP), the decompression phase (DP) and the underpressure phase (UP). And the recompression wave (RW), the decompression wave (DW) and the underpressure wave (UW) simulated the three phases, respectively, generated by the equipment designed by us. The RW test, DW test and UW test were respectively applied to the animals. And lung injuries caused by segmented shock waves were discussed. Results: Under the experimental conditions, the RW did not cause obvious lung injury, but the DW could cause different severities of lung injuries. The greater the decompression ranged and the shorter the decompression duration was adopted, the more severe the lung injury was observed. The UW, to some extent, could cause obvious lung injury. Conclusions: It suggests that lung injury under shock waves probably occurs during the DP primarily. It probably does not cause direct obvious lung injury during the RP, but significantly influences the capability of causing lung injury during the DP.
