POM Path-Memory Bimodal Basin Test

Hidden Assumption

Path independence: polyoxymethylene (POM) parts that meet standard mechanical acceptance criteria are molecularly equivalent; prior thermal microhistory cannot create distinct, stable internal basins that alter functional behavior.

Why This Assumption Persists

ASTM and ISO qualification workflows treat tensile outcomes and visual inspection as sufficient proxies for material equivalence. Thermal microhistory is operationally difficult to track and is assumed to average out if parts remain within tensile tolerances and show no visible damage. Functional drift at low stress is rarely attributed to hidden molecular state when primary acceptance tests still pass.

Minimal Falsification Experiment

1. Mold 60 POM tensile bars from a single production lot under identical processing conditions. Randomly assign into 6 groups (n = 10 per group).
2. Apply thermal history treatments:
   • Microcycle groups: 0, 10, 50, 100, 300 cycles between 25 °C and 140 °C, ~2 min dwell per step.
   • Reference group: 120 °C anneal × 24 h, slow cool.
3. Condition all samples identically for 48 h at ambient laboratory conditions.
4. Mechanical indistinguishability gate: tensile test 5 bars per group.
   • Yield stress and UTS within ±3% of 0-cycle mean
   • Modulus and elongation within ±5%
   • No whitening, cracking, or necking anomalies
   Any group failing this gate is excluded.
5. Functional proxy — low-stress creep: on remaining 5 bars per group, apply constant stress at 10–20% of baseline yield stress for 60 min at room temperature. Record strain at 5 min, 60 min, unload, then record residual strain after 10 min recovery.
6. Molecular proxy — DSC: run identical DSC programs on tested bars or matched coupons. Record crystallization temperature (Tc), crystallization enthalpy (cooling), and melting enthalpy (heating).
7. Degradation discriminator: run oxidation induction time (DSC) or FTIR oxidation index on 0-cycle vs 300-cycle material to rule out simple oxidative aging.
8. Reversibility (reset) test: select the first diverged microcycle group and the 0-cycle control. Apply standardized reset anneal (120 °C × 24 h, slow cool), condition 48 h, then repeat DSC and low-stress creep testing.

Primary Readout

Paired divergence in mechanically indistinguishable samples:

• Emergence of bimodal or threshold-shifted Tc and/or crystallization enthalpy
• Discontinuous increase in low-stress creep compliance and residual strain
• Persistence or collapse of divergence after standardized reset anneal

Pass / Fail Threshold

The assumption fails if any microcycle group:

• Passes mechanical indistinguishability gates
• Shows ≥5 °C Tc separation or ≥10% enthalpy separation, including bimodality
• Shows ≥25% higher creep strain at 60 min or ≥2× residual strain after recovery vs 0-cycle group
• Retains ≥3 °C Tc or ≥1.5× residual creep divergence after reset anneal
• While oxidation metrics do not explain the divergence

Embarrassing Flip Condition

Discovery of a sharp thermal microcycle threshold where POM remains tensile-spec compliant yet occupies a reset-resistant molecular basin forces revision of acceptance logic: thermal microhistory must be treated as a first-class state variable, and mechanical qualification alone can no longer certify interchangeability for dimensional stability or long-term performance.

This experiment is fixed at publication and revised only by explicit versioning to preserve epistemic continuity.

← Back to Edge of Practice Index