REDIPhE Project Methodology

The main method used in REDIPhE Project to confirm and extend the validity of the results shown in the figures above was FEM simulation. We as well carried out experimental tests for material characterization and finite element model validation for the polymeric material in its printed form. The experimental tests were modelled virtually by means of a FE software in order to develop a validated finite element model of the hierarchical structure.

The validated constitutive material model was used to develop the hierarchical lattice liner, which was inserted in the model of a commercially available helmet, provided by Dainese. In the first development phase head-form models were coupled with the helmet prototypes. A numerical method was adopted for topology optimization of the lattice structure according to two criteria:

1)         The first objective function for performing the optimization was the minimization of the linear acceleration in virtual tests reproducing the standard tests.

2)         The second objective function for performing the optimization was the minimization of the rotational acceleration in virtual tests similar to those currently proposed for motorcycle helmets [9].

The performance of the optimized liner was compared with that of an existing state of the art liner of equal mass to verify that the hierarchical lattice structure can improve the performance of existing liners. After some optimisation it was expected that the newly designed helmets would have performed much better than their commercial counterpart in standard tests.

Finally, once all above steps had been satisfactorily performed, the optimized structure was assessed by making use of the very detailed human head models (as shown in figure) described above. All head models, for man, woman and teenager, were coupled with helmet models of the relevant size and for each of them the maximum values of the Green-Lagrange strain tensor and the maximum values of the total time derivative of the Green-Lagrange strain tensor that each element experienced during the simulation were determined.

Schematic drawing showing the head of the commercially available human body model THUMS equipped with a simplified version of a safety helmet in which the liner is a hierarchical lattice structure. Our research will not use the simplistic THUMS head model, but we will develop very detailed and bio-faithful head models. We will use as well models of commercially available safety helmets.

All selected impact cases, representing meaningful impact configurations, were simulated with both the innovative liner and with the state of the art currently adopted liner and the injury measure values of the two cases were compared.

Finally the two most promising prototypes of innovative helmets will be manufactured and tested experimentally with the help of the Dainese company.

The main scientific results of the research will be published, whereas the improved protective devices will be the object of patent applications.