Stress Relaxation: How it differs from Compression Set.

Stress Relaxation vs. Compression Set: Root Cause Analysis for High-Temperature Seals

Problem Statement

Hydraulic seals in EV battery cooling systems failed after 500 hours at 175°C. Initial diagnosis suggested compression set failure, but SEM imaging revealed polymer chain scission—a stress relaxation mechanism.

Material Science Analysis

• FKM (Standard Grade): Loses 40% sealing force at 150°C due to backbone depolymerization. Fluorine content below 66% accelerates degradation.
• RubberQ’s Custom FKM-70: 70% fluorine, peroxide-cured. Maintains 85% stress retention at 200°C via crosslink density optimization (ASTM D6147).

Technical Specifications

Parameter	FKM-70 (RubberQ)	Standard FKM	HNBR
Shore A Hardness	75 ±2	75 ±5	80 ±3
Tensile Strength (MPa)	22.4	18.7	25.1
Elongation at Break (%)	210	250	190
Compression Set (22h @ 200°C)	12%	35%	18%
Stress Relaxation (500h @ 175°C)	15% force loss	60% force loss	25% force loss

Key Differentiators

• Stress Relaxation: Time-dependent decrease in sealing force under constant strain (ASTM D6147). Governed by polymer chain mobility.
• Compression Set: Permanent deformation after force removal. Indicates irreversible network breakdown (ASTM D395).

IATF 16949 Process Controls

Every batch undergoes:

• FTIR spectroscopy for fluorine content verification (±1%)
• Rheometer testing for cure kinetics (t90 ±3 seconds)
• Post-cure oven profiling (ISO 188, Method B)

For custom material compound development or IATF 16949 documentation, consult RubberQ’s engineering department.