Lamb wave modes repulsion in multi-layered structures II (LaWaMoRe II)

• Applicants: Professor Dr.-Ing. Bernd Henning; Dr. Jens Prager
• Subject Area: Mechanics ; Measurement Systems
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449607253

The LaWaMoRe II project aims to develop an innovative non-destructive testing (NDT) method based on Lamb wave propagation to quantify the adhesion strength of adhesively bonded plates. This quantification is of great interest, especially for adhesive bonds used in lightweight construction such as in the aerospace and automotive industry. In the first phase of this project (LaWaMoRe), it was demonstrated that the adhesion strength is related to the coupling strength between the inherent Lamb wave modes of two individual plates. When Lamb wave modes are coupled (the plates are bonded), certain coupling features called mode repulsion regions (MRRs) emerge in the dispersion diagram. In these regions, the modes seem to repel each other after converging to a frequency difference, Δf. For weakly coupled modes, this difference can be very small whereas for a stronger coupling it is significantly larger. Therefore, in this second phase of the project, the correlation between the coupling strength (represented with a coupling parameter such as Δf and the adhesion strength will be determined and applied to industry-relevant samples. The project is a two-step-process: First, an accurate numerical coupling model in the form of a cohesive rheological model will be developed to account for varying adhesion strengths and material combinations. Selective excitation of Lamb waves, destructive testing (DT)) as well as an inverse parameter identification process, will serve to validate the coupling model and confirm its accuracy. Once the coupling model is validated, it will be used to extract the coupling parameter from the MRRs. This coupling parameter will then be directly correlated with the adhesion strength (from DT) representing the second step of this project. The goal is to develop a model that is able to robustly quantify the adhesion strength by this coupling parameter alone, without the need of the numerical coupling model. The LaWaMoRe II project can be an important contribution to existing NDT methods for adhesive joints, possibly complement them and gives new insights to the nature of coupled Lamb wave modes.

• DFG Programme: Research Grants