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The application of lightweight materials for tanks for transportation appears promising. Besides saving weight and therefore transportation costs, new complex geometries that depart from common cylindrical shapes of steel tanks can be manufactured. For transportation of dangerous goods, fire and explosion safety must be maintained to prevent accidents with serious consequences. In this work the fire behavior of lightweight tanks made from glass fiber reinforced plastics (GFRP) with complex geometries is investigated. Pretests on intermediate scale GFRP plates are conducted to identify suitable fire protection systems and surface treatments for composite tanks. The fire resistance is shown to be improved by addition of fire protective coatings and integrated layers. Finally, a complex rectangular GFRP tank with a holding capacity of 1100 liters is fire protected with an intumescent fire coating. The tank is filled up to 80 % with water and burned under an engulfing fully developed fire. It was shown that the intumescent layer could expand before the decomposition of the resin occurred. Furthermore, the adhesion between tank surface and coating was maintained. The structure could withstand a fire for more than 20 min.
Defects in FRP structures may be introduced during the processing and fabrication of composite components and can initiate or grow in-service. In the context of this JRP, the term ‚defect‘ refers to imperfections introduced during manufacture/processing and/or secondary machining operations, as well as damage sustained during a component‘s service life. One of the challenges facing accurate and repeatable defect detection in FRP composites is the multitude of defect types that exist, each with characteristics that present different challenges to the NDE practitioner. In order for a particular NDE technique to achieve broad acceptance by industry, it is desirable for the technique to be able to detect a range of defect types with a high level of confidence. Project VITCEA (Validated Inspection Techniques for Composites in Energy Applications) is developing and validating traceable procedures for novel NDE techniques with contrasting detection capabilities, which will underpin the increased use of FRP composites for improved efficiency and reliability in energy related applications e.g. wind and marine turbine blades, nacelles, oil and gas flexible risers.
For assuring the safety and reliability of components and constructions in energy applications made of fiber reinforced polymers (e. g. blades of wind turbines and tidal power plants, engine chassis, flexible oil and gas pipelines) innovative non-destructive testing methods are required. Within the EMRP project VITCEA complementary methods (shearography, microwave, ultrasonics and thermography) are further developed and validated. Together with partners from the industry, test specimens were constructed and selected on-site containing different artificial and natural defect artefacts. As base materials, carbon and glass fibers in different orientations and layering embedded in different matrix materials (epoxy, polyamide) were considered.
In this contribution, the validation of different techniques of active thermography like flash, step heating and lock-in thermography to these testing problems is presented. Experimental data are compared to analytical and numerical models. Among others shows that although flash and lock-in thermography have the same detectability of flat bottom holes in the phase images, the detectability of delaminations is different. In another example, it is demonstrated that for GFRP, the transmissivity of the material has to be considered for the quantitative data analysis.
Thickness determination in active thermography for one and multilayer semitransparent materials
(2017)
Flash thermography is a well-known non-destructive testing technique and has proven to be a valuable tool to examine material defects and to determine thermal material parameters and the thickness of test specimens. However, its application to semitransparent materials is quite new and challenging, especially for semitransparent multilayer materials like glass fiber reinforced polymer (GFRP). Here, in order to deduce the thickness of coated and uncoated semitransparent specimens as well as the depth of defects in such specimens by means of flash thermography, we apply an analytical model based on the quadrupole method by Maillet et al. to calculate the temperature development during the flash thermography experiment.
The model considers semitransparency of the sample and thermal losses at its surface. It supports the use of an arbitrary temporal shape of the heating pulse to properly describe the measurement conditions for different heat sources. By fitting the results of the analytical model to experimental data it is possible to determine the thickness of the specimen, provided the thermal material parameters are known, e.g., by calibration experiments with samples of the same material with known thickness.
We will show that thickness determination of semitransparent test specimens is possible both for transmission and reflection configuration, with and without a blackened sample surface at either front or back side of the sample. As an example, Figure 1 shows the experimentally obtained temperature differences of the surface of a blackened GFRP sample in transmission configuration with the coating facing the flash lamp (usual configuration, (a)) or the infrared camera (unusual configuration, (b)). Using the proposed method, the thickness of the sample can be determined for both configurations.