Dummy structures from additive manufacturing

Surrogate and model development of rib bone

© PRIMUS breakable dummy by crashtest-service.com GmbH
Full view of the interior structure of the PRIMUS dummy.

How does the human thorax behave under the impact of dynamic loads? This question is of crucial importance for many areas of research. Be it in the development of new safety technologies in the automotive sector or the testing of new protective clothing in defense research. Researchers at Fraunhofer EMI are working on methods to make the results of such tests more accurate and meaningful.


The further development of dummies by means of additive manufacturing

This goal is achieved through the further development of a new, innovative dummy the bone structures of which are based as closely as possible on the human body. Marcin Jenerowicz from the Human Body Dynamics working group and other scientists from the Additive Design and Manufacturing group at the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut. EMI, are taking on the challenge of producing rib bone surrogates using 3D printing processes. The surrogates are intended to provide information about when and under which forces structures of the human thorax undergo damage.

The PRIMUS breakable dummy of the Crash Test Service GmbH (CTS) company is already used in various fields as an anthropomorphic test device (ATD). The CTS dummy (50-percentile male surrogate, M50) is able to represent authentic vehicle damage as well as damage to its own structural components in order to find a match between dummy damage and injury probability. However, to date, only crash validation tests have been conducted to represent the validity and global structural behavior (trajectory, damage to internal and external structures) of the dummy for specific accident outcomes.

Skeletal structure of the thorax of the PRIMUS dummy. © PRIMUS breakable dummy by crashtest-service.com GmbH

The objective of the current research is to directly compare surrogates of the 5th rib of the CTS-PRIMUS dummy and the rib surrogates additively manufactured at Fraunhofer EMI with material properties from post-mortem human subjects (PMHS) data from the literature in order to improve the assessment of the validation of the individual structures.

In addition, tests from experimental ballistics will be conducted to investigate the highly dynamic properties of the structures.

© Fraunhofer EMI
Rib surrogate additively manufactured by Fraunhofer EMI (left) and rib surrogate from the CTS PRIMUS breakable dummy (right).

Ribs alone are not sufficient to create a dummy

The Bundeswehr Technical Center for Protective and Special Technologies (Wehrtechnische Dienststelle für Schutz- und Sondertechnik, WTD 52), which has the task of ensuring the protection of the troops and their facilities, has therefore commissioned the Helmut Schmidt University of the Bundeswehr (HSU) in Hamburg to develop a thorax surrogate for ballistic tests. This should provide better information about the effects of the forces applied to the human body. The soft tissue and other relevant components for the thorax model are being developed mainly by the HSU. The development of the bone surrogates and the execution of highly dynamic tests with different materials are carried out by Fraunhofer EMI.

Exemplary 3D digital image correlation recording of the engineering strain of a CTS PRIMUS rib to determine the fracture strain and the strain field over the visible surface. © Fraunhofer EMI

The current research progress

Previously, dynamic tests were carried out with several materials in order to reproduce the structural behavior of rib bones. The rib model developed at EMI is new in this form, as it reproduces the geometry (outer contour and cross-sectional areas) of the human rib (M50) one-to-one. By using additive manufacturing (laser beam melting), it is possible to reproduce this highly complex structure realistically. The advantages of the manufacturing process include high precision and the direct adjustability of the material properties by varying the process parameters.


Future development

With the help of new testing equipment, the next step will be to carry out tests with different strain and impact rates. A corresponding pendulum impact system is currently being developed. The materials will be further developed and tested. The aim is to achieve the characteristic values of real human ribs, known from the literature, as accurately as possible. The results so far were presented in a paper (“Comparison of rib bone surrogates from additive manufacturing, cast material and PMHS data under dynamic loading”) by Marcin Jenerowicz at the last IRCOBI 2022 Europe (International Research Council on Biomechanics of Injury).

In addition, as part of Marcin Jenerowicz’s same-named doctoral thesis, mesomechanical simulation methods for the predictive analysis of bone surrogates are being developed, which are comparable to human bone in their damage and failure behavior and should provide a better validation basis for the ballistic experiments.