Quality assessment of bonded primary CFRP structures by means of laser proof testing

The use of adhesive bonding as an assembly technology is still limited because of the absence of NDT method to assess the quality of the adhesion. This work evaluates the state-of-the-art of potential NDT technologies and focuses on laser proof test techniques. The theory of this approach aiming at debonding weak adhesive bond and leaving strong adhesive bond unaffected is introduced. A preparation technique and a characterization strategy for bonded CFRP specimens with defined adhesion levels is presented. Two laser proof test setups are then investigated experimentally. A first test focuses on the determination of threshold energy for debonding of the different adhesive bond states. Further tests (repetition of laser shocks, different laser energy levels, mechanical test after laser shock) are performed to evaluate the effects on the CFRP structures. The main objective is the evaluation of the NDT character of laser proof test. With both laser setups, a debonding intensity threshold was achieved, but not without affecting the CFRP substrates. Ultrasonic inspections and mechanical tests conducted before and after laser shocks are compared to analyze the role of each laser setting in the observations. This study shows the feasibility of the concept with a high potential of improvements for the laser technologies and for approaches towards the industrialization

Development of a laser shock adhesion test for the assessment of weak adhesive bonded CFRP structures

Adhesive bondin,g bas a great poœnlial far future ligbtweight bigb-loaded structures in the a.eronautic industiy. A preœquisite for sucb an application is dtat the bond quality of the adhesive joint can be assessed in a non-destructive way. However, the use of da.ssicaJ Non•DesiiUctive Techniques (NDT) does not aUow the evaluation of the adhesion stren,gt:h of an adhesive bond yet This paper pn!sents an investigation made on weak composite bonds in on!er to develop a laser shock wave adhesion test First, the procedure to produce controlled weak bonds is desaibed. CFRP bonded samples are pn!pared in a spedfic way and characterized by ultrasonic techniques to assess the absence of any detectable defect. 1ben, for sorne of the .samples, their bond streDgth is evaluated by mechanical destructive œsts and ether .samples are loaded by v.arious intensity lasers shocks. The obtained results help to understand the behavior of the composite bonds under Jaser shock loading:. thanks to two post-mortem techrùques. 1becorrelation between the laser parameterS and the induced damage is demon.strated, The potential of the laser shock. technique to dl.saiminate different bond quallties is shawn, and the need for the œst optinùzationlsdÛ(

A study of composite material damage induced by laser shock waves

A laser shock wave technique has been used to study the damage tolerance of T800/M21 CFRP (Carbon Fiber Reinforced Polymer) composite material with different lay_ups. Different levels of damage have been created according to various laser irradiation conditions. Several characterization methods such as Optical Microscopy, X-ray Radiography, or Interferometric Confocal Microscopy have been used to quantify these defects. The nature of the defects induced by the shock wave propagation has been studied. The sensitivity of the composite material damage to the shock conditions has been shown and quantified. Moreover, the experimental results gathered with each technique have been compared to each other and it leads to a better understanding of the CFRP behavior under high dynamic loading. These original results have enabled the definition of a specific damage criterion for CFRP under dynamic loading

Qualitätsbestimmung von geklebten primären CFK-Strukturen mittels Laser Proof Tests

The use of adhesive bonding as an assembly technology is still limited because of the absence of NDT method to assess the quality of the adhesion. This work evaluates the state-of-the-art of potential NDT technologies and focuses on laser proof test techniques. The theory of this approach aiming at debonding weak adhesive bond and leaving strong adhesive bond unaffected is introduced. A preparation technique and a characterization strategy for bonded CFRP specimens with defined adhesion levels is presented. Two laser proof test setups are then investigated experimentally. A first test focuses on the determination of threshold energy for debonding of the different adhesive bond states. Further tests (repetition of laser shocks, different laser energy levels, mechanical test after laser shock) are performed to evaluate the effects on the CFRP structures. The main objective is the evaluation of the NDT character of laser proof test. With both laser setups, a debonding intensity threshold was achieved, but not without affecting the CFRP substrates. Ultrasonic inspections and mechanical tests conducted before and after laser shocks are compared to analyze the role of each laser setting in the observations. This study shows the feasibility of the concept with a high potential of improvements for the laser technologies and for approaches towards the industrialization