Using additive manufacturing to generate a polymer–metal structure offers the potential to achieve a complex customized polymer structure joined to a metal base of high stiffness and strength. A tool to evaluate the generated interface during the process is of fundamental interest, as the sequential deposition of the polymer as well as temperature gradients within the substrate lead to local variations in adhesion depending on the local processing conditions. On preheated aluminum substrates, 0.3 and 0.6 mm high traces of polylactic acid (PLA) were deposited. Based on differential scanning calorimetry (DSC) and rheometry measurements, the substrate temperature was varied in between 150 and 200 °C to identify an optimized manufacturing process. Decreasing the layer height and increasing the substrate temperature promoted wetting and improved the adhesion interface performance as measured in a single lap shear test (up to 7 MPa). Thermographic monitoring was conducted at an angle of 25° with respect to the substrate surface and allowed a thermal evaluation of the process at any position on the substrate. Based on the thermographic information acquired during the first second after extrusion and the preset shape of the polymer trace, the resulting wetting and shear strength were estimated.

A method to calculate an emissivity image out of two thermographic images taken at different wavelengths has been developed. Main part is a thermal pixel to pixel calibration to make measurements physically comparable. The new image shows enhanced contrast in several nondestructive testing situations and reveals details that could not be accessed in the input images. Examples for passive and active thermography are presented using an infrared dual-band camera working simultaneously in the MWIR and LWIR band. Reflection characteristics of CFRP and its components apparent in thermography have been compared with reflectance spectroscopy measurements.

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In this paper a new metal - CFRP (Carbon Fibre Reinforced Polymer) hybrid concept is introduced. The new aspect of this hybrid is a thermoplastic polymer component inserted between the metal and CFRP structure to reduce the gap of the different stiffnesses in each structure. To characterise defects in the hybrid, both destructive and nondestructive testing (NDT) approaches are shown. Especially the interface between the metal structure and the thermoplastic polymer component as well as the interface between the thermoplastic polymer component and the CFRP structure, where is most-likely the starting point for cracks, are investigated. An additional probability of detection (POD) approach enables to connect fracture mechanics with crack values of NDT. In consequence it is possible to achieve the assessment of defect-caused damage progress, so called effects of defects.