Visualizing fiber end geometry effects on stress distribution in composites using mechanophores

Area of Science:

• Materials Science
• Polymer Science
• Mechanical Engineering

Background:

• Localized stress concentrations at fiber ends in short fiber-reinforced polymer composites (SFRCs) significantly impact mechanical properties.
• Understanding and mitigating these stress concentrations is crucial for enhancing composite performance and durability.

Purpose of the Study:

• To visualize and quantify stress distributions at fiber ends in SFRCs using embedded nitro-spiropyran (SPN) mechanophores.
• To investigate the influence of different fiber end geometries on stress distribution and failure mechanisms.
• To correlate experimental observations with finite element analysis (FEA) for a comprehensive understanding of stress behavior.

Main Methods:

• Embedding SPN mechanophores into the polymer matrix of SFRCs.
• Utilizing confocal fluorescence microscopy to detect SPN color changes, indicating stress levels.
• Performing single fiber pull-out tests with varying fiber end geometries (flat, cone, round, sharp).
• Combining experimental stress visualization with FEA for quantitative stress analysis.

Main Results:

• SPN mechanophores successfully visualized and quantified localized stress distributions at fiber ends.
• Mechanophore activation intensity varied significantly with fiber end geometry and pull-out displacement.
• Round fiber ends demonstrated more gradual stress transfer, leading to improved stress distribution.
• Distinct fiber end geometries resulted in different failure mechanisms.

Conclusions:

• Fiber end geometry is a critical factor in managing stress distribution within SFRCs.
• The integration of mechanophores provides a powerful tool for real-time stress visualization and quantification in composites.
• Optimizing fiber end geometry can enhance the reliability and performance of SFRCs in practical applications.