# How does additive manufacturing combine with bio-inspiration for design innovation?

Julien Diperi, David Hernandez-Aristizabal, Santiago Arroyave-Tobón,
Jean-Marc Linares

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Julien Diperi, David Hernandez-Aristizabal, Santiago Arroyave-Tobón, Jean-Marc Linares. How does additive manufacturing combine with bio-inspiration for design innovation?. The 20th International Conference on Precision Engineering, Oct 2024, Sendai (JP), Japan. hal-04922934

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Submitted on 31 Jan 2025

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# How does additive manufacturing combine with bio-inspiration for design innovation?

Julien Diperi¹, David Hernandez-Aristizabal¹, Santiago Arroyave-Tobon¹,* and Jean-Marc Linares¹

1 Aix-Marseille Université, CNRS, ISM UMR 7287, 13288 Marseille, Cedex 09, France

*Corresponding Author: santiago.arroyave-tobon@univ-amu.fr

**Abstract:**

In the world context of the pursuit of sustainability, bio-inspiration and additive manufacturing could permit the generation of more efficient mechanical systems. In nature, segments of multibody systems (skeletons) are not created separately and then assembled, but they grow together in a functional environment. This in contrast with the classical manufacturing process of man-made systems, in which elementary parts are fabricated separately before assembly. Additive manufacturing makes it possible to produce bio-inspired joints that do not require an assembly process. This study focuses on the design, manufacture and wear resistance of a non-assembly pivot joint inspired by the elbow of a dorso-rigid mammalian. The wear characteristics of the joint were tested using finite element and experimental approaches, and compared with the performance of a conventional cylindrical joint. The results indicate that the bio-inspired design performs better in terms of wear distribution.

**Keywords:** Additive manufacturing, Bio-inspiration, Wear

## 1. Introduction

Biological joints have evolved to withstand mechanical loads. The functional advantages of these complex forms can be used to improve the performance of engineered mechanical joints. There are many works in the scientific literature on bio-inspired joints design. For example, there is work on bio-inspired lubrication [1], bio-inspired joint geometries [2] and bio-inspired generative design strategies [3].

In bio-inspired design, additive manufacturing (AM) plays a pivotal role in facilitating the development of intricate structures, such as assembly-free joints. Biological joints typically exhibit a self-locking configuration between the axis and the housing. Therefore, designs inspired by these geometries demand a manufacturing technique adapted to this self-locking attribute. For instance, in a prior investigation focusing on a bio-inspired joint [2], the housing was fabricated in two distinct components along the joint's axis. While this method streamlines the assembly process for self-locking configurations, it entails multiple production and assembly stages. An alternative approach involves producing the axe and the housing as a single job via AM, thereby allowing for the creation of joints without the need for assembly. The primary advantage of this method lies in its streamlined production process. A comprehensive review [4] highlights and consolidates notable advancements in the subject of assembly-free joints.

This work focuses on the design, manufacture and wear resistance of a pivot joint inspired by the elbow of a dorso-rigid mammalian. The biological model chosen for the study is a humerus of a *Camelus bactrianus*. The wear performance of the joint was tested using finite element and experimental approaches and compared with the performance of a conventional cylindrical joint. The results indicate that the bio-inspired design performs better in terms of wear distribution.

## 2. Materials and methods

The procedure for the joint design is depicted in Fig. 1. It starts with the scanning (GOM ATOS III, Germany) of a humerus of a *Camelus bactrianus* specimen of the collection of the national museum of natural history of Paris (ref: MNHN-ZM-AE-2007-1435). Afterward, the average generatrix profile was obtained through the intersection of the joint surface with equiangular planes that traverse the rotation axis. The final profile was constrained to be symmetric, and it was scaled to achieve an average radius of 15mm, adjusting to fit within the maximum fabrication volume permitted by the Powder Bed Fusion (PBF) machine. A clearance of 0.275mm was left between the housing and bearing parts (see Fig. 2). The joints were manufactured by metal printing with 17-4PH stainless steel with a PXM 300 (3D Systems, USA). The laser parameters were as follows: a travel speed of 1.045
m/s, a power of 184 W, a trap spacing of 59 µm and a defocus value of 4.8.

<figure><img src="image_2.png" /><figcaption>Fig. 1 Acquisition of geometrical data from the biological model</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Fig. Bio-inspired joint drawing (dimensions in mm).</figcaption></figure>

Archard's law (Eq. 1) was used to model wear in the joint:

$$ \frac{dh}{ds} = \kappa p_c \qquad (1) $$

With dh being the wear depth, ds the sliding distance, $p_c$ the contact pressure, and $\kappa$ a dimensional wear coefficient. This model was implemented into the finite-element software Code Aster (EDF, France) following the moving-node algorithm outlined in [12]. The material properties of 17-4PH steel were applied: E=203 GPa and v=0.3. The wear coefficient ($\kappa$ in Eq. 1) between the raw surfaces obtained by PBF was obtained with an experimental setup of the pin-on-disc type. A cylindrical track was used instead of the commonly used flat track under these conditions: a constant load of 30N, a steady slicing velocity of 0.6m/s, and a sliding distance of 2500m. The spherical pin had a radius of 8mm, while the cylindrical track measured 50mm in radius. The tests were performed with lubrication, specifically using Grindex 10 diluted to 8% in water (Blaser Swisslube, Switzerland).

The wear resistance of the fabricated joint was evaluated on a testing bench comprising an electric motor, a universal joint, a shaft, the bio-inspired joint, and two weights. The test involved maintaining a constant load of 45N and a consistent rotation speed of 400 rpm. It was conducted over a period of 7 hours under lubricated conditions. During the experiment, the weight of the joint was monitored to assess wear loss. The initial and final quality of the joint contact surfaces was measured on a three-dimensional optical measuring machine (Micromesure 2, STIL SA, France) and derived using MontainsMap software (Digital Surf, France). The filters used (according to ISO 16610-21) were $\lambda s=2.5\mu m$ and $\lambda c=$ None.

## 3. Results and discussion

A photo of the fabricated joint is shown in Fig. 3-a. While Fig3-b shows the joint after the wear test and after being cut and opened. The results of the finite element wear simulation are presented in Fig. 4. The simulation results underestimate the wear volume observed experimentally, presenting a deviation of 12 times. This may be linked to the non-compliant contact in the pin-on-disc experiment, unlike the conformal contact in the joint, which alters the conditions for heat

dissipation and elimination of wear debris. The results of the surface quality measure show an initial surface with good bearing capacity thanks to a negative asymmetry factor (Psk=-0.6707). This asymmetry tends to disappear at the end of the experiment (Psk_end=0.044). The evolution of the Pt (from 147.8 to 45.3) and Pa (from 29.2 to 6.4) values shows how the profile flattens under the effect of wear.

<figure><img src="image_4.png" /><figcaption>Fig. 3 (a) Fabricated non-assembly bio-inspired joint and (b) The joint after the wear test and being opened.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 4 Front and cut view (A and B) of the finite element wear simulation results. The lines in the boundary represent the wear in function of the time (see color bar).</figcaption></figure>

## 4. Conclusion

In this study, the operational performance of a bio-inspired non-assembly joint is assessed, providing insights into its design, manufacturing, and wear characteristics. The surface quality of the parts was not optimized in this work; future work is needed in this subject. This work underscores the capability of additive manufacturing to create functional joints in a single manufacturing job, employing geometries inspired by biological joints.

## ACKNOWLEDGEMENT

This research was supported by French Research National Agency (ANR) Grant No. ANR-20-CE10-0008.

## REFERENCES

1. Raske, N., Soltanahmadi, S., de Boer, G. N., Bryant, M., & Hewson, R. W. (2022). Finite element investigations of the fluid-solid behaviour in a bio-inspired porouselastic bearing. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 236(8), 1531-1544.

2. Sysaykeo, D., Mermoz, E., & Thouveny, T. (2020). Clearance and design optimization of bio-inspired bearings under off-center load. CIRP Annals, 69(1), 121-124.

3. Arroyave-Tobon, S., Marquez-Florez, K., Heymann, P., & Linares, J. M. (2022). Generative design of joint contact surfaces inspired by biological morphogenesis. CIRP Annals, 71(1), 125-128.

4. Lussenburg K, Sakes A, Breedveld P (2021) Design of non-assembly mechanisms: A state-of-the-art review. Addit. Manuf., 39:101846.