# Aging-Feature-Extraction Method Based on the Short-Axis Diameter Ratio of Serviced Rubber Strips

## TL;DR

This paper introduces a new method to assess rubber aging in hydropower units by measuring the short-axis diameter ratio of used rubber strips.

## Contribution

A novel quantitative aging-feature-extraction technique based on the short-axis diameter ratio (b/D) of rubber strips is proposed.

## Key findings

- The short-axis diameter ratio (b/D) shows a linear relationship with dimensionless yield stress (σs/E) and a quadratic relationship with dimensionless reaction force (F/ED).
- Measured data from fluororubber (FKM) and nitrile rubber (NBR) specimens align well with Qi’s empirical formula for modulus estimation.
- The b/D method enables rapid and accurate rubber aging assessment suitable for hydropower unit maintenance.

## Abstract

In this paper, aiming at the aging problem of rubber sealing strips in key parts of hydropower units under long-term load, this study proposes a quantitative aging-feature-extraction technique centered on the ratio of the short-axis length to the original diameter (b/D) of serviced rubber strips. Through a systematic approach combining theoretical analysis, numerical simulation, and measured data calculations, the research first derives from energy principles that the elastic modulus (E) and yield stress (σs) are key physical parameters characterizing rubber aging, reflecting the material’s energy storage capacity and irreversible deformation threshold, respectively. Based on this, a radial compression simulation model of rubber strips is established, focusing on the cross-sectional deformation laws under 25% and 30% compression ratios in serviced conditions. It is found that the short-axis diameter ratio b/D exhibits a significant linear relationship with the dimensionless yield stress (σs/E), and a quadratic relationship with the dimensionless unit-length reaction force (F/ED). Using measured data, fluororubber (FKM) and nitrile rubber (NBR) specimens after 17 years of service are selected for radial compression experiments to extract the elastic modulus. The calculated results are compared with elasticity modulus estimates based on hardness empirical formulas (Gent’s and Qi’s formulas), showing consistency, particularly with Qi’s formula for NBR. This method enables rapid and accurate assessment of rubber aging, demonstrating the effectiveness and practicality of using b/D as a feature parameter. The study provides a quantitative and convenient tool for condition monitoring and life prediction of industrial equipment seals, especially suitable for the operation and maintenance of rubber components in complex environments such as hydropower units.