Romain Ecault

Hybrid Ray-FDTD Model for the Simulation of the Ultrasonic Inspection of CFRP Parts

Carbon Fiber Reinforced Polymers (CFRP) are commonly used in structural parts in the aeronautic industry, to reduce the weight of aircraft while maintaining high mechanical performances. Simulation of the ultrasonic inspections of these parts has to face the highly heterogeneous and anisotropic characteristics of these materials. To model the propagation of ultrasound in these composite structures, we propose two complementary approaches. The first one is based on a ray model predicting the propagation of the ultrasound in an anisotropic effective medium obtained from a homogenization of the material. The ray model is designed to deal with possibly curved parts and subsequent continuously varying anisotropic orientations. The second approach is based on the coupling of the ray model, and a finite difference scheme in time domain (FDTD). The ray model handles the ultrasonic propagation between the transducer and the FDTD computation zone that surrounds the composite part. In this way, the computational eff...

Evaluation of adhesively bonded composites by nondestructive techniques

Composite materials are commonly used in many branches of industry. One method to join or repair CFRP parts is by the use adhesive bonding. There is a search of effective methods for pre-bond assessment of bonded parts and post-bond inspection. Research reported here focuses on post-bond inspection of bonded CFRP plates. In this paper we reported results of two methods. We used noncontact ultrasonic testing (UT) technique as reference method. Ultrasonic testing was made in an immersion tank using phased-array probes. The second method was the electromechanical impedance (EMI). A piezoelectric sensors were surface mounted on each of the samples. Due to piezoelectric effect the electrical response of the sensor is related to mechanical response of the structure to which the sensors is bonded to. Measurements were conducted using HIOKI Impedance Analyzer IM3570. In order to perform a detailed study three samples of each kind were tested. There were three reference samples. The samples with modified adhesive bonds had three levels of severity, so there were three samples with each level of modification. The ultrasonic testing was focused on C-scan analysis taking into consideration the amplitude and time of flight (TOF). Two probes were used, one with 5 MHz frequency, second with 10 MHz. The EMI spectra were gathered up to 5 MHz and they were processed with signal processing algorithms in order to extract differences between reference samples and samples with modified bonds. The UT results provided relevant information about the investigated samples, while the EMI showed sensitivity to the level of adhesive bond modification.

Study of CFRP adhesive bonds influenced by factors encountered during aircraft operations

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.

Study of CFRP adhesive bonds influenced by manufacturing-related contaminations

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.