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Abstract Understanding the stress distribution within fiber‐reinforced polymers (FRPs) is critical to extending their operational lifespan. The integration of mechanoresponsive molecular force probes, referred to as mechanophores, presents a potential solution by enabling direct monitoring of stress concentrations. In this study, spiropyran (SP) mechanophores (MPs) are embedded within a polydimethylsiloxane (PDMS) matrix to visualize stress localization during loading within a single fiber‐reinforced framework. The SP mechanophore undergoes a transition from a non‐fluorescent state to an active state (merocyanine) through isomerization in response to mechanical forces. Using a single fiber mounted axially within the matrix, the fundamental failure modes observed in conventional fiber‐reinforced composites are replicated. Samples are strained under uniaxial tensile loading along the fiber direction and the localization of stresses is observed via MP activation. Stresses are concentrated in the matrix near the fiber region that gradually decreases away from the fiber surface. Confocal microscopy is used to visualize mechanophore activation and quantitatively assess fluorescence intensity. Finite element modeling is used to develop a calibration to quantify the stresses based on the observed fluorescence intensity. These outcomes underscore the viability of employing these mechanoresponsive molecules as a potential means to visualize real‐time stress distribution, thereby facilitating the design of high‐performance composites.
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Identifying Internal Stresses during Mechanophore Activation
Mechanophores (MPs) undergo chemical reactions to become fluorescent in response to a mechanical stimulus that reflects the magnitude and distribution of applied stress. MPs are an emerging technology for self‐reporting damage sensing applications in polymeric materials in the aeronautical, energy generation, and automotive industries. However, quantitative calibration of the MP response to local stresses remains an outstanding challenge. Herein, a method to calibrate the intensity of the MP fluorescent activation (I) with local hydrostatic stresses (σh) is presented. Uniaxial tension is applied to a simple composite comprised of a rigid sphere (silica) embedded in a MP‐functionalized elastomeric matrix (spiropyran (SPN) functionalized polydimethylsiloxane (PDMS)). By monitoring the fluorescence intensity with a confocal microscope while a quasi‐static deformation is applied, in situ observations of MP activation as a function of applied uniaxial strain are obtained. To calculate the associated stress fields, a finite element analysis (FEA) with cohesive zone elements is employed. By comparingσh, calculated through FEA with theIof the PDMS/SPN system, a linear relationship betweenIandσhis directly determined. The technique presented can be employed for many MP‐containing materials systems to calibrateItoσh.
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- PAR ID:
- 10306350
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Engineering Materials
- Volume:
- 24
- Issue:
- 4
- ISSN:
- 1438-1656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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