Curing processes of adhesives depend on application conditions such as temperature or humidity. Most of the time, manufacturer information like pot life and processing time are not directly transferrable to the actual application, so that large safety factors in the curing time are taken into account. They tie up resources such as production areas and delay subsequent process steps, which is accompanied by a significantly reduced added value. There are only a few non-destructive test methods that can be used to monitor the hardening processes of adhesives. Often laboratory methods are used which are not process-capable, have low penetration depths, high system costs and can only be applied to the adhesive itself and not to adhesive bonded component systems. As already shown in literature, air-coupled ultrasound overcomes these limitations. A corresponding test setup and an evaluation method for the determination of ultrasound parameters that allow conclusions to be drawn about the degree of curing are presented. There, the influence of a varying bonded sheet thickness and thus different wave modes, on the quality of the curing monitoring is described. The referencing is carried out by differential scanning calorimetry (DSC) investigations. The procedure is presented and discussed by means of adhesively bonded overlap joints.

In this paper we present a comparison between mono- and multifrequent lock-in shearography measurements of a carbon fiber reinforced plastics sample with artificial defects. In order to assess the differences in quality, required time and disc space, we take measurements at six different frequencies employing the monofrequent and the multifrequent technique. While both techniques are able to provide information about the depth position of defects, the monofrequent approach yields better results regarding the quality (signal-to-noise ratio, detectability of defects and reproducibility) of the outcome. In return, the multifrequent method is less time consuming and needs less storage space. Testing a frequency-weighting method to improve multifrequent shearography’s performance turns out to be only partially beneficial and on the whole counterproductive.

This paper presents possible means of reducing the computing time necessary for processing shearographic phase images obtained using a lock-in technique. The main steps to obtaining meaningful information from lock-in shearography data are filtering, unwrapping and Fourier-transformation, which can all be very time-consuming for large amounts of data. Using Matlab’s Parallel Computing Toolbox, we evaluated and compared the speed-up of processing times when using an optimized programming syntax, parallel CPU-computing or parallel GPU-computing. Coding in a time optimized syntax improved the processing time by a factor of about 10 compared with a simple syntax, employing 12 parallel computing threads leads to a time improvement factor of 29 and utilizing a GPU for computing resulted in a 116-fold speed-up. Optimized GPU-computing it thus recommended for processing large amounts of shearography data and can reduce the computation time for the data acquired by one lock-in measurement in a 5 MP resolution from about 10 hours to competitive 5 minutes.

A promising new technique in the field of non-destructive testing (NDT) is the multi-pulse thermography. With pulse thermography a test object is heated by short energetic flashes from an external source while the local- and time-dependent surface temperature is being measured by an infrared camera. The following paper gives an overview of multi-pulse thermography, its applications and its advantages against alternative thermographic methods. Furthermore the capability of this technique for coating thickness measurements is presented. For this purpose a periodic sequence of six flashes was applied. The thermographic response was evaluated at the respective frequency of the pulse sequence, which, due to the high-frequency character, allowed a resolution of the coating thickness on µm-scale. This technique, called pulsed lock-in thermography, combines advantages of both lock-in thermography and conventional pulse thermography.