Autonomous damage indication in coatings has been achieved via encapsulated AIE luminogens [5, 6]. AIE is the only
proven method that does not rely on auxiliary material constituents—an advantage attributable to the unique properties of AIE
molecules. In solution, AIE luminogens can relax absorbed photon energy non-radiatively due to their vibrational and
rotational modes. Upon capsule rupture and solvent evaporation, aggregation of these AIE luminogens restricts the intramolecular motions required to relax the absorbed photon energy and triggers localized photoluminescence [5]. In this work, we
successfully incorporate microencapsulated AIE luminogens into fiber reinforced composites.
1.3 Results
Composite self-healing and self-reporting capabilities were assessed separately before combining both functionalities into one
material system. Self-healing composites were fabricated by incorporating solvent-only microcapsules into a cross-ply CFRP
with a thermoplastic-toughened epoxy matrix. The composite layup was hot-pressed at 120
C under 0.3 MPa for 3 h,
followed by 180
C under 0.3 MPa for 1 h with a temperature ramp rate of 1
C/min between steps. After cooling to room
temperature, the panel was post-cured in an oven at 180
C for 1 h. SEM was used to estimate capsule volume fraction in the
composite and to also confirm that the microcapsules survived both pre-pregging and hot-pressing. Final composites had a
fiber volume fraction of 51%, estimated capsule volume fraction of 1%, and T g of 172
C. Tensile specimens were cut from
processed panels with dimensions of 1.2 Â 2.5 Â 15 mm and the cross-section was polished. Specimens were loaded in
transverse tension in a xyz load frame mounted under a digital optical microscope (Keyence VHX-5000). DIC was performed
on these specimens during loading and a representative strain field is shown in Fig. 1.1. Healing is assessed by comparing the
stress-strain response of the damaged composites pre- and post-healing.
Self-reporting composites were produced by incorporating AIE-doped solvent microcapsules into a cross-ply CFRP with
an Araldite LY 8605 epoxy matrix (no thermoplastic phase). Self-reporting composite layups were hot-pressed at room
temperature for 24 h under 0.3 MPa, followed by 2 h at 121
C under 0.3 MPa, and a final 3 h at 177
C under 0.3 MPa. As
described above, capsule volume fraction and capsule survival were evaluated by SEM. Final self-reporting composites had a
fiber volume fraction of 53%, estimated capsule volume fraction of 1%, and T g of 150
C. Self-reporting FRP tensile
specimens were loaded in transverse tension until crack saturation occurred. Optical microscopy was used to characterize
localized fluorescence near the cracked regions.
1.4 Conclusion
Autonomous healing and reporting were demonstrated separately in CFRPs. Self-healing and self-reporting composites were
fabricated with a 54% fiber volume fraction and estimated capsule volume fraction of 1%. The microcapsules survived the
cure cycle and were shown to rupture under transverse tensile loading. Tensile tests with DIC were successfully performed on
self-healing samples and found to have a 4% local strain to failure before healing. Successful damage indication was
demonstrated in neat epoxy specimens. Future tests are planned to assess local post-healing mechanical properties. We also
plan to assess simultaneous self-healing and self-reporting by correlating local fluorescence with local recovery in mechanical
properties.
Fig. 1.1 Surface strain map of a carbon-fiber specimen with two transverse cracks. Surface strain field is determined via DIC
2
K. M. Chang and N. R. Sottos
proven method that does not rely on auxiliary material constituents—an advantage attributable to the unique properties of AIE
molecules. In solution, AIE luminogens can relax absorbed photon energy non-radiatively due to their vibrational and
rotational modes. Upon capsule rupture and solvent evaporation, aggregation of these AIE luminogens restricts the intramolecular motions required to relax the absorbed photon energy and triggers localized photoluminescence [5]. In this work, we
successfully incorporate microencapsulated AIE luminogens into fiber reinforced composites.
1.3 Results
Composite self-healing and self-reporting capabilities were assessed separately before combining both functionalities into one
material system. Self-healing composites were fabricated by incorporating solvent-only microcapsules into a cross-ply CFRP
with a thermoplastic-toughened epoxy matrix. The composite layup was hot-pressed at 120
C under 0.3 MPa for 3 h,
followed by 180
C under 0.3 MPa for 1 h with a temperature ramp rate of 1
C/min between steps. After cooling to room
temperature, the panel was post-cured in an oven at 180
C for 1 h. SEM was used to estimate capsule volume fraction in the
composite and to also confirm that the microcapsules survived both pre-pregging and hot-pressing. Final composites had a
fiber volume fraction of 51%, estimated capsule volume fraction of 1%, and T g of 172
C. Tensile specimens were cut from
processed panels with dimensions of 1.2 Â 2.5 Â 15 mm and the cross-section was polished. Specimens were loaded in
transverse tension in a xyz load frame mounted under a digital optical microscope (Keyence VHX-5000). DIC was performed
on these specimens during loading and a representative strain field is shown in Fig. 1.1. Healing is assessed by comparing the
stress-strain response of the damaged composites pre- and post-healing.
Self-reporting composites were produced by incorporating AIE-doped solvent microcapsules into a cross-ply CFRP with
an Araldite LY 8605 epoxy matrix (no thermoplastic phase). Self-reporting composite layups were hot-pressed at room
temperature for 24 h under 0.3 MPa, followed by 2 h at 121
C under 0.3 MPa, and a final 3 h at 177
C under 0.3 MPa. As
described above, capsule volume fraction and capsule survival were evaluated by SEM. Final self-reporting composites had a
fiber volume fraction of 53%, estimated capsule volume fraction of 1%, and T g of 150
C. Self-reporting FRP tensile
specimens were loaded in transverse tension until crack saturation occurred. Optical microscopy was used to characterize
localized fluorescence near the cracked regions.
1.4 Conclusion
Autonomous healing and reporting were demonstrated separately in CFRPs. Self-healing and self-reporting composites were
fabricated with a 54% fiber volume fraction and estimated capsule volume fraction of 1%. The microcapsules survived the
cure cycle and were shown to rupture under transverse tensile loading. Tensile tests with DIC were successfully performed on
self-healing samples and found to have a 4% local strain to failure before healing. Successful damage indication was
demonstrated in neat epoxy specimens. Future tests are planned to assess local post-healing mechanical properties. We also
plan to assess simultaneous self-healing and self-reporting by correlating local fluorescence with local recovery in mechanical
properties.
Fig. 1.1 Surface strain map of a carbon-fiber specimen with two transverse cracks. Surface strain field is determined via DIC
2
K. M. Chang and N. R. Sottos