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We present the results of extended non-destructive testing (ENDT) methods for bond line quality assessment in adhesive joints. The results presented were derived for important application scenarios with regards to aircraft manufacturing and the in-service repair of composite structures. The electromechanical impedance (EMI), laser shock adhesion testing (LASAT), and nonlinear ultrasound scanning (NUS) were used on flat coupon samples, scarfed samples, and curved samples. The EMI method applied to the flat coupons showed some relation of the frequency shift to the level of contamination. For the curved samples, there was insufficient sensitivity to differentiate distinct levels of contamination, while for scarfed samples in most cases both detection and distinction were possible. The LASAT method gave good results for the coupon samples, which were also in accordance with the results of the $${\text{G}}_{\text{IC}}$$ G IC and $${\text{G}}_{\text{IIC}}$$ G IIC tests. For coupon samples with multiple contaminations, we obtained results with varying significance. In the case of NUS, the measurements revealed an increase in nonlinearity affected by contamination at the interphase between the CFRP adherend and the adhesive layer for the majority of scenarios comprising single contamination of flat coupons and scarfed samples. The effect of multiple contaminations was a decrease in nonlinearity for the curved samples.

This chapter highlights two advances towards a higher maturity of versatile extended non-destructive testing (ENDT) procedures. Full-scale demonstration tests are presented in realistic user application cases that involve typical production or repair scenarios. Subsequently, the investigations used to assess the probability of detection (POD) are detailed for the respective ENDT processes and application-relevant scenarios in a realistic environment. Although some results indicated that some additional in-depth investigations would be even more enlightening, these demonstrations still clearly showed that developments and progress described in the previous chapters have enabled some of the technologies to achieve a maturity that is sufficient to proceed towards industrial implementation. Some ENDT techniques revealed the presence of contaminants on real structural parts with unknown contaminant amounts. For the first time, POD results obtained for ENDT investigations are presented. Some ENDT procedures permitted POD results to be obtained for several scenarios, while others showed technologically relevant POD only for certain scenarios. For two ENDT techniques, determining the POD helped to enhance the respective testing and evaluation procedures. In most of the cases, it was possible to estimate a preliminary quantification of POD by giving the POD90/95. For some techniques, this value was below the lowest contamination degree.

International audience; This study aims to assess the capability of the LAser Shock Adhesion Test to detect weak bonds in assemblies made of carbon fibre reinforced polymer laminates as well as understand the behaviour of different bonded composite structure under a shock load. A specific setup based on symmetrical laser shocks has been used. After each test, ultrasounds are used to determine if the bond has been damaged or not. At first, samples with two contaminants - de-icing fluid and finger prints - were studied. Then, the bond quality of two partially contaminated aircraft parts were investigated. These original results demonstrate the efficiency of the symmetrical laser shocks method as a Non-Destructive Test for bonded carbon fibre reinforced polymer assemblies.

Composite materials are commonly used in many branches of industry. One of the effective methods to join CFRP parts is the adhesive bonding. There is a search of effective methods for quality assurance of bonded parts. There is a need for pre- and post-bond inspection to ensure proper bonding and verify its quality. Research reported here focuses on post-bond inspection of bonded CFRP parts. In this paper we report investigations of samples that were modified with contamination that can be encountered during the manufacturing process of the CFRP parts. The contaminations were introduced before adhesive bonding, and the effect of the contamination on the quality bond is studied. First of the investigated cases was release agent contamination prepared by dip-coating of clean CFRP plates. The release agent is used during the production of composite elements and can contaminate the surface to be bonded. The second case was the moisture contamination. It was obtained by conditioning of the samples in humid conditions. Moisture contamination can be gained from water-coupled ultrasonics or during transportation of unprotected parts. The third type of contamination had more local character. It simulated fingerprints. Artificial sweat was used. The fingerprint contamination can be caused by improper handling of the parts. Apart from single contamination, also mixed contamination cases were studied, as well as curved samples. The samples were studied in non-destructive approach. It was shown that for some of the cases the detection is possible.

Composite materials are commonly used in many branches of industry. One of the effective methods to join CFRP parts is to use adhesives. There is a search of effective methods for quality assurance of bonded parts. There is a need for pre- and post-bond inspection to ensure proper bonding and verify its quality. Research reported here focuses on post-bond inspection of bonded CFRP parts. In this paper we report investigations of samples that were modified in order to simulate the conditions that can be encountered during the bonding repair processes. The modifications were made before adhesive bonding, and their effect on the quality of the bond is studied. The first case was the thermal treatment. It was made by exposure of samples to elevated temperatures. This case accounts for parts that may be exposed to external heat source or lightening impact. Second of the investigated cases was deicing fluid contamination prepared by dip-coating of clean CFRP plates. When cleaning the aircraft for a repair this fluid can be transported to bonding areas and weaken the joint. The third type of modification was faulty curing of the adhesive. It was prepared by local pre-curing of the adhesive. Pre-curing causes irregularities in the curing of the adhesive joint. Apart from single modifications, also mixed cases were studied, as well as scarf bonding. The samples were studied in non-destructive approach. It was shown that for some of the cases the detection is possible.

This paper presents the LAser Shock Adhesion Test (LASAT) using symmetrical laser shocks. The study is part of ComBoNDT European project that develops new Non-Destructive Tests (NDT) to assess adherence properties of bonded composite structures. The technique, its principle, and the experimental setup are first presented. To evaluate the technology, a various contaminated CFRP assemblies are tested using the LASAT. For each case, their bonding strength is discriminated from a reference bonding strength. If the results are promising, they also rise a lot of questions concerning the state of the material post laser shot. A series of photomicrographs of tested areas are performed showing how the contamination impacts the crack propagation pattern. The study concludes on the technology capability to differentiate a correct assembly from a contaminated one.

International audience