An innovative methodology for the efficient numerical simulation of adhesive joints subjected to ultrasonic very-high-cycle fatigue tests

In the last decades, the use of adhesives has significantly grown in several applications (e.g., automotive and aerospace) to substitute fasteners, rivets and welds in lightweight structural components. A common feature for in-service components is the presence of time varying loads in the range of high frequency vibrations which are usually source of detrimental effects for the global/local structural integrity. In this context adhesive joints, during their in-service life, can experience loading cycles in the Very-High-Cycle Fatigue (VHCF) region, beyond 10^8 cycles. Our research group recently designed and implemented an innovative testing technique for performing accelerated fully reversed tension‐compression VHCF tests on adhesive butt‐joints, based on ultrasonic excitation. Early results have been obtained on a cyanoacrylate and then on a structural epoxy. Thanks to this experimental configuration, results from tests up to 109 cycles were obtained in suitable laboratory time. A remaining issue is the assessment of the stress state in the joint specimen during the test. This presentation describes the development of an innovative, efficient and reliable procedure to simulate the stress state in an adhesive layer subjected to ultrasonic fully reversed tension-compression VHCF tests. The proposed methodology consists of few numerical steps based on: i) creation of an FE model in Ansys; ii) exportation of condensed mass and stiffness matrices in Matlab environment; iii) application of the Harmonic Balance Method in the frequency domain to identify the stress-strain fields in the adhesive layer. The results obtained with the proposed approach are finally compared to those achievable in Ansys, in terms of identified stress-strain fields and computational time required to solve the model. The comparison proves the robustness and the efficiency of the proposed approach, that can be usefully adopted to reduce computational time and increase simulation accuracy when modelling adhesive joints subjected to ultrasonic VHCF.