First Microscopic Analysis of Aeronautical Shape Memory Composites

First microscopic analysis of shape-memory aeronautical composites

In a study published in the journal Materials Today Communications, an analysis was conducted on shape memory polymer composites (SMPC) made from industrial substances previously used in aerospace. The results helped identify microscopic-level retrieval processes crucial to macro-level shape-memory abilities.

Study: Microscopic testing of carbon fiber laminates with shape memory epoxy interlayer. Image credit: Bellisario, D., et al (2022)

Shape Memory Polymers – A pillar in the future of several industries

Shape-memory polymer composites (SMPCs) belong to a class of smart material architectures that can deform and restore their original shape when stimulated.

In thermally stimulated architectures, the glass transition temperature (Tg) can be used to adjust the fixing phase and the recovery qualities of the original shape. Interest in these smart materials is high in various industries, including biomedical and aerospace, where the use of actuation is essential.

Shape memory behavior – No one does it like polymers

Shape memory (SM) response in carbon fiber is often achieved by adding a polymer structure with SM characteristics. Shape-memory polymers (SMP) can withstand greater deformations than shape-memory alloys (SMA), even when a lower actuation force is required to return to the baseline undeformed state.

Depending on the function required, an appropriate polymer structure can be used. Generally, thermosetting resins have superior shape memory characteristics than thermoplastics, and epoxy resins often provide the best performance.

Epoxies have exceptional thermal and mechanical qualities and are widely used in all production techniques used in high impact sectors such as aerospace and automotive.

Main objective of the study

Using thermomechanical cycling to measure SM qualities is a common approach to assess the shape memory behavior of SMP.

The shape memory behavior and the interactions of the distinct layers at the nanoscale have not yet been studied. This research aims to analyze in depth these smart materials at the microscopic and macroscopic level, with a particular focus on the resulting mesostructures.

a) Diagram of SMPC structures and b) procedure for manufacturing SMPC samples. © Bellisario, D., et al (2022)

Research Methodology

This work used compression molding of industrially accessible materials to create two distinct shape-memory polymer composite structures suitable for aeronautical use. A large carbon fiber blanket made from commercially available thermoset aerospace “prepregs” was first evaluated for microscale shape-memory behavior analysis.

The contribution of the shape memory spacer through its architecture has been examined at the microscopic level. The suggested composite laminations coupled the architectural properties of carbon laminations with the functionality of SMPs. The shape memory layer sandwiched between the two shape memory polymer composite structures differed such that one had a thin coating of shape memory epoxy resin, while the second contained an epoxy shape memory foam .

Both systems were built to test the suitability of an aerospace molding method, such as compression molding, in producing intelligent aircraft architectures. This was a significant achievement for research, as most new shape memory polymer composite materials suggested in the existing literature could not be classified as aerospace-grade materials.

Micro-CT scan and analysis of SMPC in a) cross-section, b) side view and c) scan of SMPC with epoxy powder interlayer and d) cross-section, e) side view and f) scan of SMPC with thin layer of epoxy foam. © Bellisario, D., et al (2022)

Main results of the study

MicroCT and SEM imaging demonstrated a strong bond between the carbon fiber reinforced prepreg (CFRP) layer and the epoxy spacer, either in the form of a thin layer of foam or a thin film. The homogeneity of the thin interlayer of shape memory polymer created during compound lamination was highlighted by SEM imaging, with a very low level of porosity in the CFRP layer indicated by MicroCT evaluation.

DMA studies have revealed that shape memory interlayers influence the transition region, which shrinks further when shape memory resin is used. Nano-instrumented indentations and micro-indentations have been used to analyze shape-restoring behavior at the microscopic and nanoscale.

It was the first time that the nano-instrumented approach was applied to this type of shape memory polymer composites, allowing to calculate the temperature for the SM response over a small region for both SMPC shapes.

The SM behavior of shape memory polymer composite structures has been confirmed at the macro scale using pressure-increasing thermomechanical cycles and numerous thermomechanical cycles.

The SM polymer composite with the thin epoxy foam sheet exhibited better shape memory capabilities, as expected, given the foam architecture. The SM polymer composite with epoxy powder interlayer, on the other hand, showed inferior but impressive shape memory characteristics.

The recurring thermomechanical cycles influenced the behavior of the SM while maintaining the architectural integrity of the smart materials generated. Also, proper design of type and quantity of shape memory epoxy spacers could significantly improve the shape memory behavior.

Reference

Bellisario, D., Quadrini, F. et al. (2022). Microscopic testing of carbon fiber laminates with shape memory epoxy interlayer. Materials Today Communications. Available at: https://doi.org/10.1016/j.mtcomm.2022.103854

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#microscopic #analysis #shapememory #aeronautical #composites

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