Paint thickness measurement on CFRP and similar substrates

2012

Carbon fiber reinforced plastics (CFRP) are more and more used in aerospace applications because of their potential to considerably reduce the weight. Using CFRP, however, the problem occurs that at painted parts the paint thickness has to be measured non-destructively. Traditional procedures come to their limits because the substrate is only medium conducting and furthermore anisotropic. Therefore a mobile paint thickness meter had been developed to measure the paint thickness on plane samples of CFRP, CFRP with copper mesh, and metal. The present paper extends this development to measurements on curved surfaces. This method consists of two steps. In a first step the average liftoff is determined, which occurs when the plane probe is placed on the curved surface. This first step is also performed with the paint thickness meter. In a second step the paint thickness measurement is performed as on plane surfaces. This gives raw data, from which the average liftoff has to be subtracted...

Journal of Nondestructive Evaluation, 2016

A portable automated scanner for non-destructive testing (NDT) of carbon-fibre-reinforced polymer (CFRP) composites has been developed. Measurement head has been equipped with an array of newly developed radio-frequency (RF) inductive sensors mounted on a flexible arm, which allows the measurement of curved CFRP samples. The scanner is also equipped with vacuum sucks providing mechanical stability. RF sensors operate in a frequency range spanning from 10 up to 300 MHz, where the largest sensitivity to defects buried below the front CFRP surface is expected. Unlike to ultrasonic testing (UT), which will be used for reference, the proposed technique does not require additional couplants. Moreover, negligible cost and high repeatability of inductive sensors allows developing large scanning arrays, thus, substantially speeding up the measurements of large surfaces. The objective will be to present the results of an extensive measurement campaign undertaken for both planar and curved large CFRP samples, pointing out major achievements and potential challenges that still have to be addressed.

4th National Conference of Telecommunication Technology, 2003. NCTT 2003 Proceedings.

Microwave nondestructive testing (MNDT) techniques are applied to evaluate quality of anti-corrosive protective coatings and paints on metal surfaces. A tree-space microwave measurement (FSMM) system is used for MNDT of protective coatings. The FSMM system consists of transmit and receive spotfocusing horn lens antennas, a vector network analyzer, mode transitions and a computer. Diffraction effects at the edges of the sample are minimized by using spot-focusing horn lens antennas. Errors due to multiple reflections between antennas are corrected by using free-space LRL (line, reflect, line) calibration technique. We have measured complex reflection coefficient of polyurethane based paint which is coated on brass plates.

2020

Microwave non-destructive testing (MNDT) methods represent an effective solution in detecting defects within composite structures with relatively low electrical conductivity. They offer the advantage to overcome the problems of traditional NDT techniques such as coupling, danger coming from ionizing radiation, limited depth of operation, large wavelengths, time consuming post processing. Near-field microwave and millimetre non-invasive inspections have been successfully used for detecting defects such as disbond and delamination in complex structures. In dielectric materials, they can be used for dielectric properties characterization, degree of porosity evaluation, degree of ageing, anisotropy, dielectric mixture constituents determination, state of cure. When it comes to the analysis of carbon fibre reinforced polymers (CFRPs), the use of these non-destructive techniques is restricted by the composite relatively high conductivity of about 10 S/m. In this paper, the investigation o...

2018

The standard method to measure wall thicknesses is based on ultrasonics. In certain cases, however, there may be drawbacks and limitations given by the need of a coupling medium, a temperature dependent sound velocity, a high sound attenuation, and an extra needed manual data evaluation. If the walls are from dielectric, i.e. nonconducting material, a microwave based gauge may be advantageous. Following the basic ideas of the successful development of a microwave based thickness gauge for paint on carbon composites, a method has been developed to measure non-destructively dielectric wall thicknesses.

Inspection of carbon fiber reinforced polymer (CFRP) composites is very important in the aeronautical and transportation industries. Many nondestructive testing (NDT) techniques have been applied for health monitoring including ultrasound, thermography, etc. Although thermography has been widely used for this purpose, it often requires powerful heat lamps which may increase the risk of (thermal) damage to the structure under test. Thus, hybrid NDT methods have also been developed. Recently, the integration of microwave heating and thermography, herein referred to as Active Microwave Thermography (AMT), has also been considered as a potential health monitoring tool for infrastructure. This hybrid method uses microwave energy to heat a structure of interest, and subsequently the thermal surface profile is measured using a thermal camera. This paper investigates the potential of AMT for inspection of CFRP-rehabilitated airframes. Preliminary simulations and measurements indicate that AMT has the potential to detect disbonds under carbon fiber patches bonded to aluminum.

Coatings, 2023

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Designs, 2019

Additive manufacturing (AM) has become more important and common in recent years. Advantages of AM include the ability to rapidly design and fabricate samples much faster than traditional manufacturing processes and to create complex internal geometries. Materials are crucial components of microwave systems and proper and accurate measurement of their dielectric properties is important to aid a high level of accuracy in design. There are numerous measurement techniques and finding the most appropriate method is important and requires consideration of all different factors and limitations. One limitation of sample preparation is that the sample size needs to fit in the measurement method. By utilizing the advantage of additive manufacturing, the material can be characterized using different measurement methods. In this paper, the additive manufacturing process and dielectric measurement methods have been critically reviewed. The test specimens for measuring dielectric properties were...

AIRCC, 2020

Fiber reinforced polymer (FRP) composites are employed in various applications of aerospace and defence industry. FRP composites are preferred as major structural parts due to their high stiffness strength and light weight.Non-destructive evaluation (NDE) plays an important role in assessing the quality and health monitoring of FRP composite structures during their manufacturing and in-service period.Different NDE techniques, such as ultrasonics, thermography, X-ray radiography, etc are employed for evaluating the quality of the composite structures.Microwave non-destructive evaluation (MWNDE) is an emerging NDE technique for characterizing and inspecting dielectric structures. Microwave NDE finds application in the areas of dielectric material characterization, determining thickness variation, defect detection and bond quality inspection.Inspection of profiled FRP composite structures by near-field reflection microwave NDE technique is presented in this paper. Application of Microwave NDE for bond quality inspection of FRP composite structures and thickness variation of composite structures is discussed. Results of inspected profiled composite structures by swept frequency reflection microwave NDE technique in the frequency range of X-band and Ku-band respectively are presented. KEYWORDS Microwave NDE, near-field reflection method, bond quality inspection, defect detection and swept frequency NDE technique

NDT & E international, 2019

The paper exploits the possibility of extracting the geometric properties of a polymeric coating of periodic metal layers used in industrial products from non-contact microwave backscattering measurements. Specifically, a flexible pipe having a periodically corrugated metal profile coated with a thick Polivinylidenedifluoride (PVDF) layer, suitable for oil industry applications, has been considered. The combined use of magnitude and phase of the reflected signal, acquired on a wide relative frequency band (∼15%), allows calculating the dielectric filling level and the period of each corrugation with accuracy better than 1/100 of the period length, 21 mm in our case. The results of an experimental campaign, carried out to estimate the accuracy achievable in the operational environment, are also shown.