{"id":13981,"date":"2023-02-08T06:05:48","date_gmt":"2023-02-08T12:05:48","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=13981"},"modified":"2023-04-26T13:44:17","modified_gmt":"2023-04-26T19:44:17","slug":"pe-programmable-materials-changing-shapes-at-the-push-of-a-button","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/13981\/pe-programmable-materials-changing-shapes-at-the-push-of-a-button\/","title":{"rendered":"Programmable Materials – Changing Shapes at the Push of a Button"},"content":{"rendered":"
\"Stiffness
Stiffness and shape change can be locally adjusted by patterning a film.<\/center><\/figcaption><\/figure>\n

Materials for applications requiring specific changes to stiffness or shape are being developed in Germany by researchers from Fraunhofer CPM. Essentially, there are two key areas where adjustments can be made: the base material \u2013 thermoplastic polymers or metallic alloys (including shape memory alloys) \u2013 and, more specifically, the microstructure. The arrangement of thousands of cells into a unit offers the most options for the design of programmable materials.<\/p>\n

These materials consist of three-dimensional arrays of cubic cells. Each unit cell exhibits a non-linear mechanical behavior and multiple stable states. A range of these “unit cells” are being developed, researched, manufactured and tested at Fraunhofer IWM.<\/p>\n

In this way, a single piece of material can take the place of entire systems of sensors, regulators and actuators. The goal is to reduce the complexity of systems by integrating their functionalities into the material.<\/p>\n

\u201cThe microstructure of these metamaterials is made up of unit cells that consist of structural elements such as small beams and thin shells,\u201d explains Dr Heiko Andr\u00e4, of the Fraunhofer Institute for Industrial Mathematics ITWM, one of the Fraunhofer CPM core institutes. “While the size of each unit cell and its structural elements in conventional cellular materials, like foams, vary randomly, the cells in the programmable materials are also variable \u2013 but can be precisely defined – ‘programmed’. This programming can be made in such a way that a force applied in a particular position will result in specific dimensional changes in other regions.”<\/p>\n

This approach is very well suited to new manufacturing methods, such as 3D printing (additive manufacturing), which make it possible not only to design the outer shape, but to faithfully reproduce the internal microstructures in the micron range. It would be possible to define multiple states for such microstructures and apply external stimuli to switch between them.<\/p>\n

\"Unit
Left Unit cell made up of structural elements; Center Material structure comprised of multiple cells; Right 3D-printed demonstrator<\/center><\/figcaption><\/figure>\n

Mechanical effects can be affected that do not exist in the naturally occurring material. Examples include auxetic cells, which expand under tension in a direction orthogonal to the applied force – they become thicker when stretched and thinner when compressed. Another example is a structure of pentamode cells which generates solids with properties similar to those of liquids.<\/p>\n

The change in shape that the material exhibits and the stimuli to which it reacts – mechanical stress, heat, moisture or even an electric or magnetic field \u2013 is determined by the choice of material and its microstructure. Piezoelectric and thermo-mechanical effects are also being studied as possible alternative trigger mechanisms.<\/p>\n

\"Auxetic
Auxetic cell in compound with angle alpha<\/center><\/figcaption><\/figure>\n

\u201cProgrammable materials make it possible to adapt products to a specific application or person so that they are more multifunctional than before,” says Franziska Wenz, from the Fraunhofer Institute for Mechanics of Materials IWM, another core institute of Fraunhofer CPM. “We always have industrial products in mind when developing programmable materials. As such, we take mass production processes into account, amongst other things.<\/p>\n

Unit cells algorithm<\/h2>\n

Software has been developed that generates the optimum shape and arrangement of cells, depending on the requirements. It includes a graphical user design interface. A database stores all necessary information about unit cells. At the end of the cell design phase, the calculated structures are directly forwarded as input for 3D printing.<\/p>\n

Potential applications<\/h2>\n

Initial pilot projects with industry partners are already underway. The research team expects that initially, programmable materials will act as replacements for components in existing systems or be used in special applications such as medical mattresses, comfortable chairs, variable damping shoe soles and protective clothing. \u201cGradually, the proportion of programmable materials used will increase,\u201d says Andr\u00e4. Ultimately, they could be used everywhere \u2013 from medicine and sporting goods to soft robotics and even space research.”<\/p>\n

One early application is to make comfy chairs or mattresses that prevent bedsores using materials that can be programmed to entirely adapt their form and mechanical properties. To produce these, the support is formed in such a way that the contact surface is large which, as a result, lowers the pressure on parts of the body.<\/p>\n

\"Final
Final result of an optimization procedure: material forms the desired bulge after vertical tension<\/center><\/figcaption><\/figure>\n

For example, the body support of the mattress can be adjusted in any given area at the push of a button. Furthermore, the support layer is formed in such a way that strong pressure on one point can be distributed across a wider area. Areas of the bed where pressure is applied are automatically made softer and more elastic. Carers can also adjust the ergonomic lying position to best fit their patient.<\/p>\n

In another application, filter membranes can be made from thermally activated shape memory polymers, that can remember their previous form. They can change form at the time of cleaning and make the process more effective. The aim is to achieve a deformation of the pore geometry on the micro-scale and thus to change the material permeability (porosity). In this case, the membrane geometries are produced by laser irradiation and the required adaptive filtration is achieved through deliberate deformation.<\/p>\n

One project is studying membranes with additional surface structuring for applications with cross-flow filtration. Such structuring can delay the onset of fouling, by keeping bacteria away from the membrane. Chemo-selective membranes have permeability which can change, depending on the presence of certain chemicals, making it possible to block pollutants.<\/p>\n

References<\/strong><\/p>\n