One of the key strengths of the planned TRR on the topic of forecasting and adaptability in mechanical joining technology is therefore its interdisciplinary research approach, which goes beyond a purely production-oriented approach. By involving scientists from the fields of materials engineering, design, mechanics, measurement technology, and lightweight construction, the topic of joinability can be explored academically from various angles. In addition to gaining in-depth knowledge, a holistic understanding of the problem will be developed in the participating departments and locations. This will also enable efficient knowledge transfer into technical practice in the future through the involvement of students and scientific staff. At the same time, it is foreseeable that the subprojects on joining technology will provide new impetus. In order to achieve the previously set goals, a fundamental, scientific investigation of joinability is required, whereby a holistic description of the three subject areas of joinability, join reliability, and joinability is necessary. These three subject areas reflect the three central project areas of the planned TRR, which are supplemented by cross-cutting topics in five working groups. The figure shows the project areas, working groups, and possible assignment of the subprojects of the planned TRR.

In order to establish networking between the research centers, a number of meetings will be held as required. These will take place more frequently at the beginning of the funding period, but at least twice a year. A central PLM system will be set up for data exchange. In the following, the individual focal points of the TRR initiative are divided into the three project areas of joining suitability, joining feasibility, and joining reliability, and described in order to briefly present the subprojects planned within them. The project areas each have a cross-location function, as there are subprojects from all locations as well as networking of the subprojects across locations.

Project area A investigates the suitability of materials and components for joining. During the first funding period, the focus will be on material-related and mechanical issues. This project area also conducts basic scientific research into casting materials tailored to the joining process. Prof. Meschut, the Paderborn site spokesperson, will act as spokesperson for sub-area A. In addition to the chemical composition and physical properties of the material, the history of the unjoined structure will also be taken into account. Sub-projects A01, A02, A03, A04, and A05 will work closely together to develop alternative solutions for a fundamental understanding of materials. In Paderborn, subproject A01 aims to achieve complete predictability of joinability. To this end, a comprehensive methodology is being developed that maps the entire product life cycle of a mixed-material joint, from the joining material to production and operation of the joint, primarily incorporating the results of the subprojects involved and the interfaces between the project areas. In subproject A02, the correlation between manufacturing process conditions and the mechanical joinability of the material is being established. To this end, cast aluminum components with improved joinability are being developed and produced in order to implement the required mixed construction concept. Subproject A03 in Dresden determines the process-induced material structure phenomena in continuous fiber-reinforced plastics during and after joining using cross-scale calculation methods. The combination of findings from the micro-level analysis between individual fibers and matrix and the meso-level analysis to account for permeability provides a comprehensive macro-level understanding of the joining process-induced processes of thermoformed FRP-metal fasteners. The calculation methodology is validated using in situ CT analysis. In TP A04, bonding mechanisms based on energies are primarily investigated in order to describe the physical properties of the joint as a function of the bonding mechanisms using a suitable modeling approach. This should enable targeted control and utilization of the energy supplied by the joining process. The goal of TP A05 in Erlangen is the nonlinear, geometrically accurate modeling of the inelastic material behavior of the materials involved in the joining process. The challenges here are the coupling of plasticity and damage, their physically motivated regularization, and the algorithmic implementation, taking into account accuracy, robustness, and efficiency. The material models developed are incorporated into the process simulation. In the TRR, basic scientific research into the central question of mechanical joining suitability is also carried out on a selection of materials, including in combination, which also has a high implementation potential for the joinability of adaptable process chains.

The focus of the work in Project Area B, with subprojects from all locations, is on issues relating to the development of methods for the design and layout of joining processes and joints. This involves researching the necessary design methodology and service life prediction for mechanical joints, including under the influence of corrosion. The spokesperson for sub-area B is Prof. Brosius, spokesperson for the TU Dresden site. The cross-site TP B01 in Dresden and Paderborn has the overarching task of designing the joints in a load- and property-based manner, both numerically and experimentally, in such a way that, in conjunction with A01, not only the pure joint load capacity but also the preceding process steps are taken into account. The long-term goal is to use detailed FEA to prevent any weakening of the joint before component failure occurs. In Dresden, TP B02 is developing methods for evaluating the reliability of joined connections. The focus here is primarily on the still unknown interaction mechanism between the joining process and subsequent cyclic or corrosive loading and the resulting failure mechanisms. Therefore, a test strategy is to isolate the influencing factors and thus create a basis for design. Also in Dresden, TP B03 is primarily investigating the influence of joining process-induced pre-damage on diffusion processes during corrosion in a numerical model under cyclic loading. In addition to identifying corrosion phenomena that occur, the descriptive mechanical damage is supplemented by the effects of corrosion and other material degradation. In Paderborn, TP B04 is expanding the design focus to include the continuous evaluation and simulation of crack growth using fracture mechanics. The first step is to classify the types of crack stress and determine fracture mechanical material properties for the joined materials. In addition, it will be necessary to determine which fracture mechanics concepts can be applied or need to be expanded or newly developed in order to understand the cause-and-effect relationships from a fracture mechanics perspective. In TP B05 in Erlangen, the structural design of the joint is being investigated and concrete analytical design formulas are being derived from this. After sensitivity analysis of the process parameters, the identified relevant parameters will be validated using T-joint demonstrators. From this, the relationships will be abstracted and translated into generally valid and transferable forms and formulations for novel and convertible mechanical joints.
 

Project area C investigates the relevant process-related issues. The work focuses on the investigation of different joining process technologies, their in situ analysis, and the mechanisms involved in forming the joints. The description of the joining option focuses on the selection of the process, the production sequence, and the necessary comprehensive pre- and post-treatment of the joint. Therefore, existing joining processes and measurement methods are being researched in subprojects C01, C02, C03, C04, and C05. Prof. Merklein, based in Erlangen, is the spokesperson for this manufacturing technology project area. In a joint project in Erlangen, TP C01 is conducting fundamental scientific research into a novel joining process for multi-material systems that does not require auxiliary joining parts. The flexible manufacturing process is created by means of press-fit and caulking pin structures and local material accumulations. In the cross-location TP C02, research is being conducted in Paderborn and Erlangen into the flexibilization and in situ process control of the semi-tubular blind riveting process with the aim of compensating for process-related fluctuations. In addition to identifying suitable measures for adapting the auxiliary joining part, a central issue is the control of the joining process through extended tool kinematics such as wobbling movements and the associated connection properties. Also in Paderborn, TP C03 is researching a new joining process with customized auxiliary joining parts, whose needs-based, process-integrated manufacture opens up the greatest possible flexibility for this joining technology. In the joint project C04 in Dresden, the in situ testing methodology for joining connections is being implemented. In situ CT analysis can primarily map the mechanisms of the joint characteristics, taking into account the induced damage. Analysis using vibration excitation should also enable the load-bearing capacity of the joint to be derived. Since the shape of mechanically joined joints and joining process-induced damage are currently primarily recorded destructively, non-destructive measurement methods for quality assurance are being developed and investigated in TP C05 in Erlangen. The focus here will be on X-ray computed tomography and the associated surface and boundary detection of components and structures, as well as high-resolution optical topography measurements. Furthermore, for the in-process measurement of joining process parameters using conventional sensor technology, the measurement data acquisition and evaluation will be optimized by means of measurement uncertainty analyses, and dynamic measurements of the process variables will be improved on the basis of a Bayesian approach.