Finite element analysis of sandwich structures with viscoelastic foam cores for mechanical applications

Polyurethane foams are used nowadays for vibration attenuation and energy absorption during impact applications. They are widely used in aerospace and automotive field due to its light weight and good energy absorption capabilities. Therefore, it is interesting to analyze these materials from the point of view of vibration attenuation and impact absorption properties. Polyurethane foam consists of two types, i.e., flexible polyurethane foam and rigid polyurethane foam. Further, they are divided into open type and closed type. The mechanical properties of foam materials depend on the initial density as these materials are porous. Moreover, these materials are compressible and exhibits the property of viscoelasticity. The viscoelasticity property is represented by the Prony series, which shows the linear viscoelasticity. The compressible behavior of the foams is captured by using other models such as Blatz-Ko, Ogden foam etc. Among all the models the Ogden foam is popular and have been used widely in the literature. In this thesis, the impact analysis of different configuration of beams are simulated in the Ansys software V19.1 student license. The beam configuration can be found in different mechanical applications such as turbine blades, wing of an aero-plane, industrial robotic arms and front bumper beam of cars. In this analysis the beam dimensions and loading is simulated by keeping in view the front bumper beam of vehicles and the objective is to minimize the deformations, accelerations of the body and the reaction forces at the support which ultimately causes the reduction in the acceleration experienced by the passengers during impact. The rigid body is considered to collide (impact) the beam fixed at both ends, with a velocity of 15 m/s (54 km/h) and the effects are studied. The hollow beam is then replaced by the foam sandwich beam in which Polyurethane foam is considered as a core material. Both the contact type in which the foam is bonded and non-bonded with a coefficient of friction is analyzed and the differences in the behavior of the beam are studied. In this analysis, two types of geometry are considered for beams. One is simple hollow beam and the other is two-channel hollow beam. Similarly, two types of foam-sandwich beams are considered. The one is simple foam sandwich beam while the other is two-channel foam sandwich beam. Furthermore, two different densities, i.e., 40kg/m3 and 93kg/m3 of the flexible polyurethane foam are analyzed in order to see the differences and dependence of results on foam density. Moreover, a rigid polyurethane foam of density 93kg/m3 is also analyzed and compared with the flexible polyurethane foam of the same density. In the literature, viscoelasticity of the polyurethane foam is modelled through Prony series parameters as well as different scholars have shown the P-alpha model captures the response of the material to a high degree of accuracy, therefore, in the analysis this model will be used which is also supported in Ansys. The rigid polyurethane foam is modelled through P-alpha model and Hugoniot shock data. Different results after impact such as maximum deformations, reaction force-time history, and the acceleration attenuation of the beams are evaluated. The comparison is made between the hollow beams and the foam sandwich beams. The results show that the foam sandwich beam is better choice than the hollow beam in all respect.