Experimental Study On Ultrasonic Enhancement Methods Of Laser Ultrasonic Nondestructive Testing

Laser ultrasonic nondestructive testing technology is a non-contact new detection technology,which has the advantages of high sensitivity and good applicability,and has broad application prospects.But the technology also faces some problems to be solved,such as short propagation distance,acoustic wave loss and waveform distortion,and the main reason for these problems lies in the weak acoustic intensity.At present,laser ultrasonic nondestructive testing methods include surface processing technology,signal processing algorithm research and high-power power supply research,in which power supply is the main reason.The laser ultrasonic power from the laser ultrasonic nondestructive testing of the system,in order to improve the power supply output voltage of the sound wave is enhanced for the purpose of the design of Nd:YAG solid laser power model,experimental platform,and tested and verified in the experiment.In this paper,laser ultrasonic nondestructive testing methods for acoustic wave enhancement are analyzed,including surface processing,signal processing algorithms and high-power power supplies,especially laser ultrasonic acoustic wave power supply.Through the analysis of excitation and receiving mechanism of laser ultrasonic,the design principle of laser ultrasonic power were studied by pulse width modulation(PWM)inverter technology,design a series resonant voltage type inverter circuit,the constant current charging circuit;discharge circuit adopts LC single discharge form,its control circuit adopts the trigger chip control;simmer circuit and its control circuit adopts the half bridge circuit and chip control,realize constant current source precombustion high-voltage trigger circuit by multistage;transformer,to achieve a stable trigger;by using over-current and over-voltage protection circuit,the short circuit and overheating fault promptly cut off power supply.In order to meet the requirements of different laser power,this paper realizes the design of adjustable power discharge voltage,discharge voltage is 0 to 1400V,the discharge frequency of 10Hz,the maximum output power of 1.5kW and Q delay range 0?300 ?s,the output energy is 500mJ.The temporal power of the control requirements,the design of embedded system,embedded ARM+?C/OS-? system control scheme:CPU uses STM32 as the main control chip;?C/OS-? embedded multi task and real-time operating system.The discharge voltage is regulated by touch screen,and the peripheral circuit of CPU includes RS-232,serial debug,reset monitor chip and so on.The whole embedded system has realized the good control to the laser ultrasonic power supply,and the operation is more reliable.This paper on the electrical test on the experimental platform,through the analysis of the measuring instrument and experimental data,the use of digital oscilloscope waveform,the results show that the PWM waveform is stable and reliable,low electromagnetic interference;the power supply output voltage and power reliability,meet the requirements of Q delay effect,energy output value is higher,can receive the acoustic image accurate.The experimental results show that the circuit design and the embedded system design are stable,and the purpose of regulating display is achieved.By adjusting the discharge voltage of the power supply,different materials can be detected,and the laser induced thermoelastic mechanism and ablation mechanism can be realized,so that the purpose of acoustic wave enhancement can be achieved.