Finite Element Analysis Of A Flat-tubes Heat Exchanger’s Die-less Bending By Using A Cohesive Zone Damage Model

Heat-exchangers manufacturing cost is of first importance for HVAC units manufacturers.These systems assembly is traditionally carried out using brazing techniques.Yet,they show a lot of disadvantages which can greatly impact the producing cost: brazing requires considerable ovens,and hence a big amount of energy.In consequence of being heated,heat-exchanger systems need to be constituted of materials able to not being deformed during the process.More and more used in high tech industries such as automotive or aero-spatial industry,the use of adhesive joints had proven it efficiency in robustly assembling complex systems formed of different materials and overrides most of welding-related issues.This research work investigated the bending formability of a new flat-tube heat exchanger system assembled using toughened epoxy adhesive usually used in automotive industry,bent using a dieless bending process.A finite element analysis by using the explicit solver LS-Dyna is carried out to study the adhesive layer behavior during the bending process.A cohesive zone damage model is used to model the adhesive layer elastic and plastic behavior in mode I and mode II delamination.The adhesive is characterized in these two modes by carrying out double cantilever beam and end notched flexure tests.From these tests,mode I and II fracture behaviors are modeled and used in the numerical damage model.The numerical results of the heat-exchanger bending show that the adhesive used is strong enough to support the die-less bending process.Indeed adhesive layers were not damaged during the bending process despite plastic deformation.Moreover the use of an adhesive layer can greatly limit the buckling during the bending.Some bending experiments were carried out,but having to use a different adhesive,and at bending angles of 70° and 90°.For both angles,similar observations were made: for half specimens,tubes were subjected to large deformation leading to a very localized adhesive joint failure in the bending portion,while on the other half,only light wrinkling occurred in the same region,and without any adhesive joint failure.Yet,more experiment should be carried out to precisely characterize the adhesive material as well and bending experiments using the same adhesive should be carried out in order to confirm bending numerical predictions.