Research On The Interlaminar Damage Mechanism Of Aerospace Vehicle Composite Laminate Plates Based On The LBI Method

Structural integrity is vital for the safe operation of aerospace vehicles.A key concern is the potential weakness in the interlaminar bonds of composite materials,which can cause delamination under demanding service conditions,thereby jeopardizing the safety and reliability of the equipment’s structure.The innovative method of laser shock wave bonding strength detection uses the mechanical effects of laser-induced shock waves to non-destructively assess the internal bond strength of these composites.This paper focuses on understanding the dynamic behavior of composite materials when subjected to high strain rates induced by laser shock waves.It includes the development of a three-dimensional model that accounts for the strain rate effects on laser-shocked composite laminates.The research delves into the dynamics of stress wave propagation,reflection,and interaction within the material.It further examines the dynamic response of laser-shocked resin-based,fiber-reinforced composite laminates,elucidating how impact loads affect interfacial damage.The primary findings and conclusions of this study are as follows:1.Experimental Platform Setup and Scheme Design for Laser Shock Testing on Composite LaminatesInnovation was employed by adopting a structure of fiber seed source + waveform modulator + power amplifier laser,amplifying the nJ-level energy output from the seed source to 20 mJ through the first three stages of Nd:YLF amplifiers,and further to 50 J through the subsequent six stages of Nd:Glass amplifiers,achieving a laser output with an adjustable pulse width of 10ns～400 ns,and a maximum energy of 50 J.The setup encompasses a main control system,a tri-axis dynamic movement optical system,fixture and optical systems,water constraint absorption layers,and energy protection layer application system.In conjunction with the laser and PDV(Photonic Doppler Velocimetry)velocity measurement system,a complete composite material laser shock testing platform was formed.Experiments were designed to laser shock composite laminates and establish the relationships between laser parameters such as pulse width,beam spot,energy and material layer cracking.Utilizing the controlled variable method,under a fixed parameter,composite laminates of two thicknesses 1.5/3 mm were shocked with different power densities within a large beam spot of 5-10 mm,and small energy of 0.5-5J.The impact of thickness on shock wave propagation patterns was discussed,and on this basis,the size of energy loss when interface damage occurs was analyzed,and damage thresholds were estimated.2.Analysis of Layer Cracking Characteristics in Laser-Shocked Composite LaminatesThrough multidimensional and multi-angle auxiliary experiments,the characteristics of delamination damage under different laser shock parameters were analyzed in terms of the size of the layer cracking damage,the depth of cracking,and the morphology of cracking on composite laminates.On the basis of summarizing the layer cracking characteristics,an in-depth analysis of the potential mapping relationship between layer cracking features and laser parameters was conducted.The precision of layer cracking depth characterization in PDV signals was validated through ultrasonic B-scans,establishing the correlation between pulse width and layer cracking depth;the accuracy of cumulative damage area characterization of layer cracking in PDV signals was validated through ultrasonic water immersion C-scans,establishing the relationship between energy magnitude and the extent of layer cracking;the effectiveness and rationality of characterization methods were validated through industrial CT,establishing the mapping relationship between laser shock parameters and material damage type,damage size,and damage depth.3.Construction of Laser Shock Constitutive Model for Composite Materials Considering Strain Rate EffectsA constitutive model for laser-shocked composite laminates considering strain rate effects was established,based on the orthogonal anisotropic constitutive relationships,introducing Dynamic Increase Factors(DIF)in three directions for constitutive parameter adjustments.Finite iteration computational methods and domain adaptive fitting models were employed,using PDV(Photonic Doppler Velocimetry)data for result matching,and after multiple iterative computations,an adaptive matching model considering high strain rate conditions was derived for dynamic increase factors.Further,through transfer learning methods,a deep feature extraction was conducted on simulation data and actual measurements to obtain realistic DIF adjustment parameters,thereby determining an effective material constitutive relationship under strain rate effects.This model facilitated the analysis of the influence of different laser parameters on layer cracking characteristics,the degree of interlaminar delamination and the extent of layer cracking within the laminates,studying the stress-strain response,failure thresholds,and failure characteristics of composites under laser shock wave effects.4.Propagation patterns and response mechanisms of laser-induced shock waves in multi-layer interface structuresBased on the model,the propagation and coupling laws of shock waves within the laminates were studied,identifying the mechanism of delamination damage response in regions with high tensile stress.It was shown that during the propagation process through multi-layer interface structures,shock waves present a parallel form of shock loading wave and sparse unloading wave,manifesting as an alternating distribution of tensile and compressive stresses;the magnitude of the coupled tensile stress determines whether layer cracking occurs.Both laser energy and beam spot size jointly affect the stress levels,propagation cycles,and the possibility of multi-layer cracking states during the shock wave propagation process;laser pulse width affects the formation moment of sparse unloading waves,influencing the depth of layer cracking.A larger pulse width extends the action time of laser-induced shock waves,delaying the generation moment of sparse unloading waves,and consequently,the action moment of reflected waves is delayed,causing the tensile stress coupling moment to lag.Subsequently,the position of coupled tensile stress is closer to the shock surface.This study’s findings and theoretical framework clarify the coupling dynamics of shock wave propagation and material response in composites.These insights provide a theoretical basis for using laser-induced shock waves to assess bonding strength in composite material interfaces.