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This paper presents the progress of successful location of grouting faults in tendon ducts with ultrasonic imaging. The examples were obtained in the research group FOR 384 funded by DFG (German Research Foundation). The co-operation of experimental research and modeling allowed imaging and identification of grouted and ungrouted areas of tendon ducts (including strands) in a large test specimen (40 m²). In addition to the criteria for indicating grouting faults in post-tensioned ducts known until now the phase evaluation of reflected ultrasonic pulses is described. Experiments and modeling of wave propagation are presented for reflections at metal plates in concrete (thickness range 0.5 mm to 40 mm) and for tendon ducts including strands.
The main part of the progress was achieved by automated measurements using dry contact transducers, 3D-SAFT reconstruction including phase evaluation and modeling considering wave propagation for typical elastic parameters and exact experimental site conditions. The results for shear waves as well as for pressure waves are compared in the frequency range from 50 kHz to 120 kHz.
3D structural investigations are described by X-ray laminography studies of sandwich shell segments, made of a PVC foam core, covered by non-crimp fabric glass fibre composite lay-ups processed by vacuum assisted resin infusion of epoxy. The specific scope of this study is to image transversal flaws within the foam core (joints) and of single ply overlaps. Test flaws were purposely implemented in order to simulate typical failure under cyclic load. In a dedicated test rig for shell structures, the flaw evolution/propagation is monitored by thermography and optical 3D inspection of deformation. Due to the unfavourable preconditions for classical computed tomography as of large aspect ratio, the samples were investigated by coplanar translational laminography. Its limited range of observation angles of ± 45°, results in anisotropic artefacts about the normal to the sample surface, but the typical flaws are well visualized in the as-prepared state, in a state of early damage, and in the repaired state.