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- Non-destructive testing (6) (entfernen)
A new approach is discussed for characterizing the damage state of FRP with the appearance of micro cracking and its influence on the residual strength. For the quantitative analysis of micro cracking, X-ray refraction topography was used. Fatigue treatment of carbon fibre reinforced plastics (CFRP) laminates were performed to create defined damage states. With regard to real loading conditions of CFRP, studies on tube samples were performed to investigate two dimensional (tensiontorsion) loads. A rheological material model was presented which described the increase of micro cracking in ±45° CFRP laminates with a continuum mechanical approach. The correlation between the results of the X-ray refraction topography, the damage parameter of the rheological model and the decrease of residual strength were shown. The inter fibre fracture surface of the investigated CFRP materials was determined with tensiontorsion loaded tube specimens of 90°-laminate and a layer-wise strength analysis was done. Micro cracking occurs even at 50% inter-fibre fracture loading and can lead to a distinct strength reduction. The intralaminar fatigue effect itself seems to be an indication for the damage accumulation and the load history.
The low-strain pile integrity testing method is used for quality control of new piles as well as length and integrity check for old piles. If no other methods for calibration are available, the accuracy and reliability of the techniques depend on a good estimation of the elastic wave velocity. In practice it is assumed that piles can be tested 7 days after casting and that the velocity is almost constant in all piles of one kind in a construction project. Recent measurements at the BAM test site in Horstwalde, Germany, showed that the 7 day criterion is not generally applicable.
Impulse-thermography is an active method for quantitative investigations of the near surface region of various structures. It has recently been applied and optimised to applications in civil engineering. By using either an internal or external heat source, parts of the structure under investigation are heated up and the transient heat flux is observed by recording the temperature change at the surface as a function of time. This method is very well suited for the detection of voids and honeycombing in concrete, up to concrete covers of 10 cm as well as for the location of delaminations in multi-layered systems (e.g. plaster on concrete, CFRP-laminates on concrete, asphalt on concrete). Also safety relevant defects like voids in tendon ducts and cracks in concrete could be recognised.
Results of reconstructed and fused NDT-data measured in the laboratory and on-site at bridges
(2006)
Non-destructive testing (NDT) of concrete structures plays an increasing role in civil engineering. This paper presents the results of measurements carried out in the laboratory at BAM and on-site at several bridges using reconstructed and fused radar and ultrasonic echo data sets. In this context different scanning systems, developed for the on-site application of NDT-methods (e.g. reinforced concrete bridges) are introduced. The main object was the demonstration of the improved effectiveness of radar and ultrasonic pulse echo technique due to the automated measurements and the application of new software for the data processing and data visualisation. The results of these measurements show the high potential of reconstruction and data fusion for the improvement and simplification of the interpretability of large data sets measured with impulse-echo methods.