Research On The Dynamic Response Characteristics Of Laser Shock On Aircraft Skin Laminated Structures

As a crucial transportation tool,the structural safety and reliability of airplanes are focal points in the field of transportation engineering.Currently,fiber-reinforced resin matrix composites are widely used in load-bearing structures such as aircraft skins.However,traditional connection methods like riveting and bolting can cause fiber breakage,matrix cracking,and delamination,which reduce structural integrity and load-bearing safety.Therefore,adhesive bonding is commonly used in skin structures for fiber-reinforced resin matrix composites.However,factors such as interface contamination,uneven adhesive application,and adhesive aging during manufacturing and service can lead to insufficient or no bonding,posing serious structural safety risks.Traditional non-destructive testing methods also find it difficult to detect these issues.Evaluating the interface bonding strength of skin structures is an important indicator of aircraft structural safety performance,directly affecting the service safety of the aircraft.The laser shock wave interface bonding strength detection technology,which uses the mechanical effect of laser-induced shock waves to evaluate the bonding strength of composite material interfaces,is a new technology that offers unique advantages in addressing the issue of undetectable"kiss bonds"and"weak bonds"by current non-destructive testing technologies.However,the complex reflection and coupling reactions of shock waves during propagation through multiple interfaces,along with limitations in structural profile and signal strength during testing,make engineering applications challenging and lack detection criteria.Therefore,to address the issues of laser shock wave regulation and interface bonding strength detection,it is crucial to study the coupling mechanism of stress wave propagation within composite materials and the transient stress wave mechanism induced by lasers.Supported by the preliminary research program of the Equipment Development Department of the Central Military Commission and the National Natural Science Foundation,this paper conducts research on the dynamic response characteristics of laser shock wave on laminated panels of aircraft skin structures.The main conclusions and innovations are as follows:1.The pressure characteristics of shock waves induced by nanosecond pulse lasers were obtained,revealing the propagation and coupling mechanisms of laser-induced shock longitudinal waves within the laminated panels of aircraft skin structures.This allows for accurate prediction of stress wave coupling positions and stress magnitudes.Traditional PDV signal processing methods cannot accurately characterize the dynamic response process of composite materials to microsecond-level transient pulse laser shocks,and are limited by experimental fitting parameters,making direct stress prediction impossible.A method was proposed to characterize low signal-to-noise ratio signals and weak echo signals during laser shock testing.By dynamically monitoring the mechanical behavior of stress waves propagating through materials,the variation of backface particle velocity over time under different impact load conditions was precisely described.Using shock wave pressure as the dynamic load boundary condition,the coupling mechanism of shock wave longitudinal waves within materials was revealed,identifying the coupling positions of incident waves and rarefaction waves.The interlayer bonding strength calculation formula was revised,achieving accurate prediction of maximum tensile stress positions and magnitudes.2.A calculation model for the damage value R of laminated panels/adhesive joints of aircraft skin structures was constructed,establishing a mapping relationship between laser parameters and damage stages,achieving quantitative evaluation of damage thresholds for laminated panels/adhesive joints of aircraft skin structures.Existing research cannot determine material damage states based solely on PDV signals,and laser intensity is constrained by material damage thresholds,making it difficult to balance signal strength and material threshold relationships.A new damage characterization parameter R was constructed to represent the relationship between laser parameters and damage degree,allowing determination of material damage stages based solely on PDV signals.The established damage threshold model avoids issues of low photoacoustic energy conversion efficiency and weak ultrasonic signals,enabling the matching of ideal impact parameters with higher signal strength while ensuring no damage to the material.Results show that the model error is within 8.71%,and it can search for impact parameters with the highest signal strength within the threshold range.3.The mechanism of laser-excited Lamb waves in laminated panels of aircraft skin structures was revealed,elucidating the dispersive response characteristics of low-order modes in various propagation directions and the displacement distribution patterns in non-principal directions,achieving optimized selection of impact modes.The traditional"front impact-back reception"detection method is limited by the detection requirements of different structural profiles and spatial positions,and the unclear mechanism of laser-excited Lamb waves in composite material panels prevents engineering applications.An orthotropic thermoelastic equation,dispersion response equation,and heat conduction equation were established directly using laser characteristic functions as inputs,revealing the mechanism of laser-excited Lamb waves in composite material panels,achieving"front impact-front reception."The dispersive characteristics and displacement characteristics of low-order A₀ modes were analyzed.Results show that the A₀ mode has a longer propagation distance,lower attenuation,easier signal identification,only 4.8%propagation error,and 1.11 times the signal amplitude of the S₀mode,making it a suitable detection criterion.This research provides a theoretical foundation,analytical methods,and means for the engineering application of laser shock wave interface bonding strength detection technology to improve the interface performance of large aircraft skin structural components.