Pulse Fatigue Endurance Curve Library (ISO 6803 Annex B)
The Pulse Fatigue Endurance Curve Library (ISO 6803 Annex B) is a standardized set of empirically derived S–N (stress–cycles-to-failure) curves that quantify the fatigue life of hydraulic hoses under repeated pressure pulsation. It provides design engineers with data to estimate hose service life based on operating pressure amplitude, frequency, and temperature. These curves are derived from controlled laboratory testing per ISO 6803 and serve as a critical reference for validating hose selection in dynamic hydraulic systems.
📖 Overview
📑 Key Components
🎯 Applications
- ✓ Hydraulic hose life prediction in mobile equipment (e.g., excavators, agricultural machinery)
- ✓ Validation of hose routing and bend radius against dynamic fatigue limits
- ✓ Design margin assessment for pulsating systems (e.g., piston pump circuits, accumulator-supplied lines)
📐 Key Formulas
Modified Miner’s Rule (Cumulative Damage)
Σ(n_i / N_i) ≥ 1 → failure
Estimates cumulative fatigue damage when operating across multiple pressure amplitude/frequency regimes; n_i is cycles at stress level i, N_i is cycles to failure at that level per Annex B curve
Frequency Scaling Factor (ISO 6803 Annex B)
N_{corr} = N × (f / f_{ref})^k
Adjusts baseline endurance curve (tested at reference frequency f_ref, typically 0.5–2 Hz) to actual operating frequency f; k is an empirical exponent (typically −0.15 to −0.3) dependent on hose construction
Temperature Derating Factor
ΔP_{allow} = ΔP_{base} × e^{−α(T − T_{ref})}
Reduces allowable pressure amplitude ΔP_base at reference temperature T_ref (e.g., 23°C) based on elevated fluid/ambient temperature T; α is material-specific thermal degradation coefficient