The engineers developed a new method to more accurately predict the strength of lightweight 3D-printed objects. Their goal was to create more robust, reliable components by controlling strength when creating plastic components. Potential applications include automotive, aerospace and medical device products.

Philip Bean, Ph.D., an ASCC research engineer, and his colleagues applied advanced computer modeling with physical experiments to provide a more comprehensive understanding of how small printed parts perform under stress.

They focused on gyroid infill, an intricate, repeating internal structure commonly employed in additive manufacturing to minimize weight while preserving structural integrity. By utilizing computer simulations to analyze the gyroid’s response to various forces, Bean and his colleagues validated their predictions through experiments on prototype parts.

“Infill is the internal structure inside a 3D-printed part,” explains Bean. “Different infill patterns have different tradeoffs, but gyroids are especially attractive. They are strong, quick to print, and unlike most patterns behave isotropically, meaning their properties are the same in all directions. This makes analysis and design much simpler.

“Our research focused on characterizing the mechanical behavior of gyroid infills, which we see as a crucial step toward enabling engineers to design stronger, more efficient lightweight components,” says Bean.

“Until now, little work has been done to rigorously characterize 3D-printed infill structures,” claims Bean. “Our study provides a simple relationship between gyroid density and its mechanical properties, making it possible to predict performance more accurately.”

According to Bean, additive manufacturing has several advantages over traditional subtractive manufacturing methods. For instance, the ability to mass-produce lightweight parts that have an external skin and sparse internal infill decreases weight and the amount of material required to manufacture the part.

“This skin-infill structure [enables] a part to have a prescribed external geometry while varying the placement of material internally to optimize stiffness or strength,” explains Bean. “To design a part which takes full advantage of the skin-infill structure, however, it is first necessary to characterize the structural properties of the infill.”

A variety of infills are commonly used in additive manufacturing. Each has benefits and drawbacks.

The most common type are 2D infills, such as rectilinear infill, which are generated using the same pattern for every layer. These infills have the advantage of simplicity, which makes them quick and reliable to manufacture. However, the infill geometry results in highly anisotropic structural properties.

Another variety are 3D infills, such as cubic infills, which consist of a structure that spatially repeats in all three directions. Many of these exhibit cubic symmetry, which more closely approximates isotropic behavior. This benefit, however, comes at the cost of added complexity, which can cause issues with manufacturing reliability.

“One such infill that is particularly promising for future design work is the gyroid, a 3D infill based on a mathematical construct known as a triply periodic minimal surface,” says Bean. “This infill is nearly isotropic, is manufactured rapidly and is generally considered to be stronger than other infill patterns.

“All of these properties are useful for manufacturing parts, but very little data is available on which to base structural designs,” notes Bean.

The final category of infills is the least well defined. It consists of those infills that don’t fall into either of the previous categories due to their nonperiodic nature, which often arises from optimization processes.

“These can take several forms, including using graded infills, internal structures containing voids, or internal structures with repeating optimized lattice structures, which can be tuned to have specific elastic properties or graded to have spatially varying properties,” explains Bean. “These repeating structures often take the form of standard rectangular, rhombic or hexagonal infill patterns.

“Our specimens were simple rectangular shapes,” says Bean. “For compression testing, we used specimens measuring 2-by-2-by-6 inches. For shear testing, we used composite sandwich panels measuring 4.8-by-9.6-by-1 inches.

“Our study was not aimed at improving a particular part, but at developing tools for engineers,” Bean points out. “By characterizing how gyroid infill behaves across different print densities, we [created] a foundation that allows designers to optimize strength and weight in their own applications.

“Because engineers can now link density to strength, they can confidently vary gyroid density within a part and still know how the structure will behave.,” claims Bean. “This enables lighter components without sacrificing reliability.

“By providing predictive models for gyroids, our method allows engineers to design optimized parts that use less material while maintaining or even improving performance,” says Bean. “This has potential benefits anywhere plastic parts are used.”

The ASCC’s results are based primarily on finite element simulations, which Bean and his colleagues validated using standard compression (ASTM D695) and shear (ASTM C393) tests.

“The findings offer insights into how this complex internal pattern contributes to a part’s overall performance, a factor often not possible with conventional analytical methods,” notes Bean.

“This work allows us to design 3D-printed parts with greater confidence and efficiency,” adds Bean. “By understanding the precise strength of these gyroid-infilled structures, we can reduce material use and improve performance across industries.”