[Paper Review] 3D Fluorescent Mapping of Invisible Molecular Damage after Cavi-tation in Hydrogen Exposed Elastomers

Xavier Morelle, Gabriel E. Sanoja+2 more|arXiv (Cornell University)|Jan 3, 2021

Soft Robotics and Applications48 references35 citations

TL;DR

The paper presents a non-destructive 3D fluorescent mapping method to visualize molecular damage in a hydrogen-exposed elastomer after cavitation, revealing flower-like crack patterns and discontinuous fracture behavior.

ABSTRACT

Elastomers saturated with gas at high pressure suffer from cavity nucleation, inflation, and deflation upon rapid or explosive de-compression. Although this process often results in undetectable changes in appearance, it causes internal damage, hampers func-tionality (e.g., permeability), and shortens lifetime. Here, we tag a model poly(ethyl acrylate) elastomer with {\\pi}-extended anthracene-maleimide adducts that fluoresce upon polymer chain scission, and map in 3D the internal damage present after a cycle of gas satu-ration and rapid decompression. Interestingly, we observe that each cavity observable during the decompression results in a dam-aged region, the shape of which reveals a fracture locus of randomly oriented penny-shape cracks (i.e., with a flower-like morpholo-gy) that contain crack arrest lines. Thus, cavity growth likely proceeds discontinuously (i.e., non-steadily) through the stable and unstable fracture of numerous 2D crack planes. This non-destructive methodology to visualize in 3D molecular damage in polymer networks is novel and serves to understand how fracture occurs under complex 3D loads, predict mechanical aging of pristine look-ing elastomers, and holds potential to optimize cavitation-resistant materials.

Motivation & Objective

• Motivate the need to detect internal damage in elastomers after gas cavitation when surface appearance remains unchanged.
• Develop a non-destructive imaging method to map 3D molecular damage in polymer networks after gas saturation and rapid decompression.
• Understand the fracture mechanisms and crack geometry underlying cavitation in elastomers to predict aging and guide material design.

Proposed method

• Tag a poly(ethyl acrylate) elastomer with pi-extended anthracene-maleimide adducts that fluoresce upon polymer chain scission.
• Perform 3D fluorescence mapping to visualize internal molecular damage after a cycle of gas saturation and rapid decompression.
• Analyze the spatial pattern of damage to infer fracture loci and crack geometry.
• Interpret observed damage patterns as evidence for fracture processes across multiple randomly oriented penny-shaped cracks with crack arrest lines.

Experimental results

Research questions

• RQ1 How does 3D fluorescence mapping reveal internal molecular damage after cavitation in hydrogen-exposed elastomers?
• RQ2 What is the geometry and organization of fracture patterns associated with cavitation-induced damage?
• RQ3 Does cavity growth proceed in a continuous or discontinuous manner, and how do crack planes contribute to damage localization?

Key findings

• Each observable cavity during decompression corresponds to a damaged region in the surrounding material.
• Damage patterns form a flower-like morphology consisting of randomly oriented penny-shaped cracks with arrest lines.
• Cavity growth appears to be discontinuous, driven by the stable and unstable fracture of multiple 2D crack planes.
• The method provides a non-destructive way to visualize 3D molecular damage and offers insights into fracture under complex 3D loads.