The deformation and damage phenomena that occur during the manufacture and loading of mechanical joints cannot yet be directly observed and characterised in detail due to the limited accessibility of the joint. Instead, a joint must first be unloaded and elaborately prepared and analysed, generally destructively. During this ex-situ analysis, elastic deformations reset as a result of the unloading, whereby cracks that have been introduced can potentially close. Thus these cracks cannot be detected or can only be detected to a limited extent.
The overall objective of this sub-project is the development and implementation of two complementary experimental methods for the non-destructive in-situ analysis of joints. The two methods to be developed complement each other in such a way that they enable a spatially and temporally highly resolved analysis of the joint both during its formation and under load. For the development and adaptation of the two measurement procedures as well as the phenomenological allocation of the test data, a method-based procedure for the interpretation of the temporally and spatially resolved measurement information is to be developed. The sub-project makes a significant contribution to achieving the goal of versatility in mechanical joining technology, as both the joint production and the joint load can be subjected to a detailed analysis that has not been possible so far and thus the cause-effect relationships of both life phases can be investigated.
A novel in-situ procedure using X-ray computed tomography (in-situ CT) is to be developed for local high-resolution analysis, with which the joining zone can be recorded three-dimensionally during the joining process or stress. CT as a tool for evaluating the quality of joints in larger assemblies can only be used to a limited extent due to the limited measuring volume. This is where the second method to be developed, the transient dynamic analysis (TDA), comes in. It is based on the introduction of ultrasonic waves into the joint and on the recording of the response depending on the energy contributions transmitted through the joint. The dissipated energy contributions as a result of material damage or an inadequate joint can be distinguished on the basis of their characteristics via frequency and amplitude. By introducing the ultrasonic waves, changes in the response behaviour and thus a change in the characteristic profile can be detected with high temporal resolution. Thus, the detailed CT images enable a clear assignment of the measured characteristic TDA response profiles to particular damage characteristics in the material.