Dissipation Energy Analysis And Life Prediction For Multiaxial Fatigue Process Of Adhesively Bonded Joints

Adhesively bonding technology has played an important role in many industrial fields with the advantages such as light weight and airtightness.In practical application,the adhesively bonded joints have been subjected to complex cyclic loads.Therefore,it is necessary to deeply understand the multiaxial fatigue failure behaviors and accurately predict the fatigue life of the adhesively bonded joints.In this study,uniaxial and multiaxial fatigue experiments were carried out on the DB527 sealant adhesively bonded hollow cylinder butt-joints.A method to identify the fatigue failure was proposed by observing and analyzing the evolution of dissipation energy during the multiaxial fatigue experiments of the adhesively bonded joints,and the effects of loading conditions on the dissipation energy and fatigue life in the process of multiaxial fatigue were discussed.Moreover,the stress-based and energy-based multiaxial fatigue life prediction models were proposed according to the multiaxial fatigue failure behavior of the adhesively bonded joints.The practicability and accuracy of the proposed models were evaluated by comparing the prediction results of the novel models with the test results and the prediction results of the existing energy-based model.The main research contents and results are as follows:(1)A series of stress-controlled multiaxial fatigue experiments were carried out on the adhesively bonded joints,and the effects of loading path,equivalent stress amplitude,equivalent mean stress and loading period on the dissipation energy and fatigue life were analyzed.An identification method of fatigue failure was proposed and applied to the fatigue failure analysis according to the actual failure situation and the evolution of the dissipation energy during the multiaxial fatigue process of the adhesively bonded joints.The experimental results proved that the dissipation energy increased with the increase of the number of cycles,and the mechanical behavior showed a typical cycle softening behavior.The non-proportional loading path had greater dissipation energy and shorter fatigue life than the proportional loading path.At the same time,the dissipation energy increased and the fatigue life decreased with the increase of equivalent stress amplitude and equivalent mean stress,and the decrease of loading period.(2)A novel stress-based fatigue life prediction model that collectively considered the effects of loading path,equivalent stress amplitude,equivalent mean stress and loading period on the multiaxial fatigue life of the adhesively bonded joints was proposed.The comparison of the predicted life and the experimental life indicated that the proposed stress-based fatigue life prediction model had good prediction ability for the multiaxial fatigue life of the adhesively bonded joints.(3)The multiaxial fatigue life of the adhesively bonded joints were predicted by the existing energy-based model that selected the energy dissipated in the first cycle,in the half-life cycle,in the end cycle,and the total dissipation energy as the parameters,respectively.The predicted results showed that the predicted fatigue life obtained by using the total dissipation energy as the parameter were the most accurate.(4)A novel energy-based fatigue life prediction model was proposed.This model only needed partial dissipation energy in the initial stage of the fatigue experiment as the parameters,and did not need to consider the influences of loading conditions.The novel energy-based model was applied to evaluate the multiaxial fatigue life of the adhesively bonded joints in view of the identification method of the fatigue failure.The comparison between the predicted results and the experimental results showed that the novel energy-based model had not only better prediction accuracy for the multiaxial fatigue life of the adhesively bonded joints,but also strong practicability in engineering applications.(5)The practicability and accuracy of the multiaxial fatigue life prediction models used in this paper were collectively evaluated.The results showed that the existing energy-based fatigue life prediction model had low accuracy and was difficult to apply in engineering.The novel stress-based fatigue life prediction model had high prediction accuracy.However,the calculation process of the novel stress-based model was complicated,and the model parameters that change with the loading conditions had significant effect on the prediction results.The novel energy-based fatigue life prediction model had not only high accuracy,but also simple calculation of model parameters.Therefore,the novel energy-based fatigue life prediction model was more suitable for the fatigue life prediction of the adhesively bonded joints.