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3D Printed Surfboard: Researchers Test Different Bio-Inspired Core Structures

Just as a New Zealand-based surfer was inspired by the humpback whale and the microgrooves of shark skin when creating his surfboard fins, so too was a team of international researchers inspired by the natural world in their structure study of an on-water sports board. In their recently published paper, “3D Printing On-Water Sports Boards with Bio-Inspired Core Designs,” they explain their work advancing the board by using 3D printing and different bio-inspired core structures, such as the honeycomb.

“Modeling and analyzing the sports equipment for injury prevention, reduction in cost, and performance enhancement have gained considerable attention in the sports engineering community. In this regard, the structure study of on-water sports board (surfboard, kiteboard, and skimboard) is vital due to its close relation with environmental and human health as well as performance and safety of the board,” the researchers wrote.

(a) A natural honeycomb structure; (b) the designed honeycomb core inspired by nature.

3D printing has often been used in the sports field, but in previous studies about 3D printed boards, researchers mainly focused on the geometry, only making small modifications to the equipment. This research team actually introduced different patterns to use as the board’s internal core structure. FDM technology and PLA materials were used to make the first sample board, featuring a uniform honeycomb structure that was created with the help of CATIA V5 software.

Most modern boards feature a sandwich structure, where a thin outer shell covers an inner core made of foam, which allows for increased buoyancy and stability, less weight, and improved bending resistance. These structures typically feature a top shell, the lightweight core, and a bottom shell, but this board merged the bottom shell with the core.

“A smaller scale version of a real on-water sports board was designed,” the researchers wrote. “The board had a 48 mm width and 144 mm length with a 357 mm radius curvature at two sides. A bottom curvature of 600 mm was considered, resulting in a model closer to the real one. The hexagonal honeycomb structure formed the core of the board, and was repeated across the specimen.”

The honeycombs were 3 mm wide, and patterned with 1 mm thick walls, while the bottom and top shells had thicknesses of 5 and 1.5 mm, respectively. The team used an XYZprinting da Vinci 1.0 Pro 3D printer to make the sample board with a uniform honeycomb structure.

(a) Two separate 3D printed parts of the board; (b) two parts glued together with strong adhesive.

Surfboard fractures frequently happen between the surfer’s feet, in the board’s middle section. Usually, this occurs because the lip of the wave impacts in the middle and rips it into two parts after the surfer falls into the water, or because the surfer’s feet get too close together and concentrate their body’s pressure in the middle.

“In both of these circumstances, an immense force acts upon the middle portion of the board, causing large bending stress that may result in breakage,” the researchers explained.

“As both of these breakages are caused by bending stresses, a mechanical three-point bending test could be employed to determine the strength of the board in such loading.”

The board with a uniform honeycomb structure core under three-point bending test.

The team tested the honeycomb board under 3-point loading, though they had to change the grippers for the test.

“The test with the strain rate of 0.001 s−1 was carried out at room temperature with an 80 mm distance between two supports. A displacement-controlled test was conducted to get a maximum deflection of 4 mm in the elastic range.”

I-shaped beam and the board with equivalent sections shown with orange lines.

In order to validate these results, and model the structure’s deformation under the test, the researchers developed a “geometrically linear analytical method,” using an equivalent I-shaped section with geometrical stiffness varied along the X-axis, to simulate the honeycomb structure. Then, a geometrically non-linear finite element method, based on ABAQUS software, simulated the boards with a variety of different core structures under the three-point bending test.

Boundary conditions of the finite element method model.

A bending test was simulated to validate the FEM model, and the team performed a mesh sensitivity analysis to make sure the numerical results were accurate. Then, they applied the same test to the sample board with the honeycomb core for a 4 mm maximum deflection. The maximum stress of ∼40 MPa, found in the middle of the board, was low enough to keep the board “in the desired elastic region.” For comparison, the PLA had a yield test level of 60 MPa.

Von Mises stress contour of the board with the uniform honeycomb core.

“The force–deflection curve for the experimental, geometrically non-linear numerical, and geometrically linear analytical results are plotted and compared to each other in Figure 13,” the researchers explained. “The preliminary conclusion drawn from this figure is the fact that the PLA board shows a linear elastic deformation up to 300 N force, beyond which the material yields, followed by plastic deformation that is manifested as a plateau after 500 N.”

Comparison of the experimental, numerical, and analytical load–deflection curves for the three-point bending test of the honeycomb and fully-filled boards.

Once the team had validated the geometrically non-linear FEM model for the board with the honeycomb core structure, they simulated other patterns for the bottom shell’s core. Performing the three-point bending test with the geometrically non-linear FEM software package ABAQUS, while the board’s total volume was kept constant, helped them find the structure with the maximal bending resistance. The different structures they tested were:

  • Hexagonal-Rhomic (HR) Structure
  • Triangular Honeycomb Structure
  • Hexagonal Carbon Lattice
  • Pine Cone and Sunflower-Inspired Patterns
  • Spiderweb-Inspired Pattern
  • Functionally Graded (FG) Honeycomb Structure

“For all of the structures, the mesh convergence study was conducted and the appropriate number of elements for the FEM model was selected,” the researchers wrote. “Furthermore, the maximum stresses of all boards with various core structures were figured to have shown a maximum stress lower than the yield stress of the PLA material.”

(a) A pinecone with two 8-number and 13-number opposite directional spirals; (b) Sunflower with Fibonacci spiral; (c) Pinecone-inspired structure designed using Fibonacci spirals.

They found that the board with the FG honeycomb structure had the best bending performance – 31% better, in fact, than the board with the uniform honeycomb structure at 500 N force. This means that it can tolerate maximum forces, as opposed to an intermediate force like the rest of the structures.

“Due to the absence of similar designs and results in the literature, this paper is expected to advance the state of the art of on-water sports boards and provide designers with structures that could enhance the performance of sports equipment,” the researchers concluded.

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RMIT proves 3D printed titanium alloys can be enhanced by addition of copper

Researchers at Royal Melbourne Institute of Technology (RMIT) in Australia have trialled a new material for metal 3D printing that combines titanium alloy with copper.  Developed by RMIT’s School of Engineering, titanium-copper alloys were created in a bid to prevent cracking and distortion that can affect titanium when 3D printing. RMIT states that the material […]
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3D Printed Cellular Fingers Offer Material Balance Required for Modern Robotics

In ‘Toward a Smart Compliant Robotic Gripper Equipped with 3D-Designed Cellular Fingers,’ authors Manpreet Kaur and Woo Soo Kim delve into the world of combining 3D printing and robotics. Their recently published paper focuses on the design of a robotic structure with deformable cellular structures that are easy to fabricate.

The conventional metal robot or robotic components are increasingly being upstaged by softer materials that offer more versatility for industrial applications. Not only that, many of these new materials are able to morph to their environment, affected by environments such as temperature or moisture. Kaur and Kim remind us that many of these innovations are originally inspired by nature, such as the movement of and the frictional properties of the snake.

Design and fabrication of multi‐material auxetic structure: A) 2D sketch of the re‐entrant honeycomb unit cell with defined parameters. B) Schematic demonstration of filament extrusion–based multi‐material 3D printing. C) Different designs of auxetic unit cells with two important parameters, α (the ratio of length of vertical strut h by re‐entrant strut l) and θ (the re‐entrant angle), defined in the sketch (A). D) The CAD image of the 3D re‐entrant honeycomb structure made by joining two 2D structures at 90°. The single tone gray color indicates the usage of a single material that is a TPU‐based flexible material. E) A dual‐material‐based auxetic unit cell where the re‐entrant struts (red) made of flexible material and the vertical struts (gray) made of rigid material. F) Different designs of dual‐material‐based auxetic unit cell, where the joints (gray) are made of flexible material and the rest of the portion of the struts (blue) are printed with the combination of both flexible and rigid material with equal proportion.

In creating soft robotics, however, there is the challenge of finding a balance between flexibility and structural stiffness and incorporating electronics which usually consist of a variety of different bulky systems. The cellular finger noted in this research can be made with embedded sensors in the fingertips, allowing for a significant gripping force of 16N, and the ability to pick up numerous objects—and acting as an example of more complex architectures for better functionality and performance overall.

“Stretching‐dominated cellular solids, such as octet, octahedral, and so on, show higher initial yield strength compared with bending‐dominated foamed materials, which is due to their different layout of structural components and makes them better alternatives for lightweight structural applications. One such unique spatially arranged structure produces a negative Poisson’s ratio (NPR); these are called auxetics. Like other types of mechanical metamaterials, the NPR of auxetics is generally a direct consequence of the topology, where the joints rotate to move the structure,” state the researchers.

Characterization of 3D printed auxetic structures: A) Compressed samples from the design with α = 1.5 and θ = −20°. Three different material distributions in the unit cell (single, dual 1, and dual 2 designs) are studied. Images were captured for each sample at 0%, 20%, and 40% strains. B) Stress–strain graph of three samples with different combinations of α = 1.5, 2 and θ = −20°, −30 ° for designs (single, dual 1, and dual 2). The legends read as “a” for alpha, “t” for theta, and S, D1, D2 for single, dual 1, and dual 2, respectively. C) Finite element analysis (FEA) simulation analysis of compressed auxetic unit cell to study the different stress distributions in the elastic region for the three different designs. The color code is kept constant and is defined next to each image. The corresponding elastic curves from experiment and simulation are compared for each case. D) The cellular finger is designed using the rigid stretching‐dominated octet structure for the main body and using chosen auxetic structure (α = 1.5 and θ = −20°) with dual 2 designs for the joints.

NPR materials are also able to deform and show ‘compliant-bending behavior.’ In this research project, Kaur and Kim used honeycomb structures—again, inspired by nature—examining their ability to absorb energy and bend. These re-entrant structures are more easily translated to the 3D realm and allowed the authors to experiment regarding parameters and resulting cell properties. The end goal was to achieve deformity, along with suitable durability and energy efficiency.

With the use of porous cellular materials meant to meet the balance of both softness and flexibility and the need for firmness also, the researchers were able to roll their knowledge of materials, manufacturing, and robotics into one—along with 3D printing and the use of triple materials. The robotic gripper finger was made up of the following lightweight parts:

  • Three octet segments
  • Two auxetic joints (mimicking human bones and joints)
  • Integrated pressure sensor on the fingertip

The following materials were used for 3D printing the single, dual 1, and dual 2 designs: SemiFlex, PLA, and carbon fiber reinforced PLA (CFRPLA). The porosity level allowed for the sought-after balance in a lightweight structure as well as offering the proper rigidity for various gripping functions. The overall design was also responsible for the system of fingers able to deform as needed, in tune with objects and their specific shapes—while the fingertip sensors monitoring the environment.

Mechanical properties of the samples from compression test

“Our architectured robotic finger is a starting point of cellular design concept. Therefore, there is a lot of room for further research in this topic. Design of other mechanical metamaterials has lots of opportunities, so other lattice structures can be investigated to tune additional mechanical deformation functionality in the robotic finger,” concluded the researchers.

“The optimization of sensor design and addition of other sensors can also be investigated to achieve its ubiquitous performance. This compliant robotic design with metamaterial body can prove to enhance the functionality and durability of robotic bodies for prosthetic or industrial applications, thus developing new generation of robotic systems with better performance and greater adaptability in a variety of tasks.”

Robotics and 3D printing are paired up often these days, in projects ranging from uses in furniture manufacturing to soft robotics, and more. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Auxetic unit cell designs based on different α and θ parameters

[Source / Images: ‘Toward a Smart Compliant Robotic Gripper Equipped with 3D-Designed Cellular Fingers’]

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Researchers Inspired by Nature to Develop Recyclable Liquid Crystal Polymers for FDM 3D Printing

While it’s possibly to quickly manufacture complex parts at a low cost using fused deposition modeling (FDM) 3D printing, the readily available polymers are fairly weak, and the completed 3D prints have poor adhesion. According to an ETH Zürich research group that specializes in 3D printing complex materials, this one of the reasons why FDM is not used successfully to fabricate commercial products.

Polymer performance has been traditionally increased by adding strong, stiff, continuous fibers into the material, like glass or carbon, but it takes a lot of time, effort, and expensive equipment to develop these composite materials, which are also difficult to recycle. But the researchers have developed a bio-inspired approach to 3D print recyclable liquid crystal polymer (LCP) materials using desktop FDM systems.

According to a press release, “For the first time, researchers from the Complex Materials group and the Soft Materials group at ETH Zürich, were able to print objects from a single recyclable material with mechanical  properties that surpass all other available printable polymers and can compete even with fibre-reinforced composites.”

During development, the team was inspired by two materials found in nature: wood and spider silk, the latter of which has inspired other 3D printing innovations in the past. The material’s silk proteins have a high degree of molecular alignment along the fiber directions, which gives spider silk its “unrivalled mechanical properties.”

3D printed samples of specimens with print lines following the stress lines and the biological inspiration represented by a wood knot.

The researchers were able to duplicate this high alignment during extrusion by using an LCP as FDM feedstock material. This gave the material excellent mechanical properties in the deposition direction. In addition, its anisotropic fiber properties were put to good use by “tailoring the local orientation of the print path according to the specific loading conditions imposed by the environment,” which was inspired by how living tissue, like wood, can arrange fibers along its stress lines while it grows and adapts to its surrounding environment.

The team published a paper on their work with 3D printing strong LCPs, titled “Three-dimensional printing of hierarchical liquid-crystal-polymer structures,” in the Nature journal.

Loop test of 3D printed LCPs.

The abstract reads, “Fibre-reinforced polymer structures are often used when stiff lightweight materials are required, such as in aircraft, vehicles and biomedical implants. Despite their very high stiffness and strength, such lightweight materials require energy- and labour-intensive fabrication processes, exhibit typically brittle fracture and are difficult to shape and recycle. This is in stark contrast to lightweight biological materials such as bone, silk and wood, which form by directed self-assembly into complex, hierarchically structured shapes with outstanding mechanical properties, and are circularly integrated into the environment. Here we demonstrate a three-dimensional (3D) printing approach to generate recyclable lightweight structures with hierarchical architectures, complex geometries and unprecedented stiffness and toughness. Their features arise from the self-assembly of liquid-crystal polymer molecules into highly oriented domains during extrusion of the molten feedstock material. By orienting the molecular domains with the print path, we are able to reinforce the polymer structure according to the expected mechanical stresses, leading to stiffness, strength and toughness that outperform state-of-the-art 3D-printed polymers by an order of magnitude and are comparable with the highest-performance lightweight composites. The ability to combine the top-down shaping freedom of 3D printing with bottom-up molecular control over polymer orientation opens up the possibility to freely design and realize structures without the typical restrictions of current manufacturing processes.”

The team’s materials, in addition to being more easily recyclable, are far stronger than typical 3D printed composite polymers, and are not nearly as difficult to fabricate. This means that it should now be possible to 3D print FDM structures for industry use as lightweight, structural parts.

Example 3D prints made with LCPs

“Because the research has been conducted using a readily available polymer and a commercial desktop printer, it should be easy for the broader additive manufacturing and open source communities to adopt this new material and digitally design and fabricate strong and complex lightweight objects from LCPs,” the ETH Zürich press release states. “Thus, the technology is expected to be a game-changer in several structural, biomedical and energy-harvesting applications and finally enable complex FDM printed parts that mimic natural structural designs to be manufactured for the mass market.”

Co-authors of the paper are Silvan Gantenbein, Kunal Masania, Wilhelm Woigk, Jens P. W. Sesseg, Theo A. Tervoort, and André R. Studart.

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