Criterion Sensitive Operating Point Selection in Passively Redundant Subsystems under Reliability and Tolerance Constraints

Passive redundancy can improve subsystem reliability without switching or reconfiguration, but its assessed effectiveness depends on how reliability gain is defined. This study examines that dependence for fixed passively redundant configurations subject to common reliability and tolerance constraints by comparing absolute and relative reliability‐gain criteria. Analytical stationary conditions are derived for both formulations and used to establish the ordering of their criterion‐optimal component reliabilities. Two configuration‐specific reliability boundaries are then obtained, separating fully criterion‐sensitive, constraint‐mediated, and criterion‐insensitive constrained regimes. Numerical verification over 149 non‐degenerate redundancy configurations confirms the analytical ordering and shows that the relative criterion selects a lower unconstrained component‐reliability operating point than the absolute criterion. The separation between the two solutions decreases markedly for configurations associated with more restrictive achievable tolerances. As the required subsystem reliability increases, the reliability constraint progressively overrides the unconstrained criterion optima; above the upper boundary, both criteria yield the same constrained operating point. The results therefore identify when criterion choice changes the selected operating point and when the reliability requirement makes that choice operationally immaterial.