Talbot-Lau grating interferometer XCT for the quantitative characterization of damage in polymers after impact and static tensile testing

X-ray imaging methods such as micro-computed tomography (XCT) are essential techniques to reveal and quantify internal defects in materials, particularly in polymers and composites. Conventional absorption-based contrast (AC) provides information on the attenuation of the X-ray beam intensity and is an invaluable tool in various domains, e.g. medicine and materials science. In the last decade however an important innovation in X-ray technology has emerged by the introduction of Talbot-Lau grating interferometer XCT. This method provides three complementary characteristics in a single scan of the specimen: a) the attenuation contrast, b) the differential phase contrast (DPC), and c) the dark-field contrast (DFC). DPC is related to the index of refraction and DFC reflects the total amount of radiation scattered at small angles, e.g. caused by microscopic inhomogeneities represented by cracks and pores. Using a novel Talbot-Lau grating interferometer XCT system (TLGI-XCT) for laboratory applications we visualize crack-like defects in carbon fiber reinforced laminates that were subjected to impact forces up to 20 Joules. Using DFC we were able to detect cracks in samples that were subject to low impact forces whereas these defects are merely detectable using AC. Specimens were scanned at isometric voxel sizes between 5.7 and 22.8 μm. TLGI-XCT results are compared to ultrasonic examinations. Secondly, we investigate polypropylene test specimens that were cyclically loaded in tensile testing experiments until final failure. Lower grey levels near the fracture surface in the AC and DPC images indicate pores. Due to increased scattering in these regions DFC images provide a high signal intensity even though the defects are smaller than the spatial resolution. For all samples high-resolution reference measurements were carried out using an industrial XCT system. Due to the fact that DFC delivers morphological information in the sub-pixel regime depending on the local scattering power, dark field imaging delivers information that may otherwise be inaccessible using conventional XCT. Using a Talbot-Lau XCT we show that dark field images