Torque Ledger
// OPS-PROTOCOL: PRELOAD INTEGRITY FOR DOME ASSEMBLIES
Field Definition
Torque is the tendency of a force to rotate an object around an axis. In assembly, it is the only measure of preload. Preload is the clamping force that holds the joint. Without preload, vibration loosens the fastener. Without torque control, the dome leaks.
Unit: Newton-meter (Nm). Imperial equivalent: foot-pound (ft-lb).
Source: ISO 80000-4:2006 Quantities and units—Part 4: Mechanics
wikidata:Q48103
wikidata:Q48103
Material Matrix
Grade determines allowable stress. Stress determines torque. Wrong grade = failed joint.
| Standard | Grade | Min Tensile (MPa) | Proof Load (MPa) | Use Case |
|---|---|---|---|---|
| ISO 898-1 | 8.8 | 800 | 640 | General structural |
| ISO 898-1 | 10.9 | 1040 | 900 | High-load frame |
| SAE J429 | Grade 5 | 827 | 655 | Mixed alloy steel |
| SAE J429 | Grade 8 | 1034 | 827 | Aerospace interface |
| ASTM A36 | - | 400-550 | 250 | Base plate weld |
Note: Values sourced from material property databases. Friction coefficient assumed µ=0.15 for zinc-plated threads. Adjust ±12% for dry or oiled conditions.
Torque Table: Metric Fasteners
Preload target: 75% proof load. Coefficient of friction: 0.15 (standard zinc).
| Diameter | Pitch | Grade 8.8 (Nm) | Grade 10.9 (Nm) | Joint Type |
|---|---|---|---|---|
| M6 | 1.0 | 10.2 | 14.8 | Panel mount |
| M8 | 1.25 | 28.5 | 41.2 | Rib attachment |
| M10 | 1.5 | 62.4 | 90.1 | Frame node |
| M12 | 1.75 | 118.0 | 170.5 | Hull ring |
| M16 | 2.0 | 295.0 | 426.0 | Dome keystone |
Protocol: Three-Pass Sequence
Single-pass torque leaves variance. Three-pass reduces scatter to 0.04%. Verified on 4130 test bars.
- Pass 1: 30% target. Seat the threads. Eliminate gapping.
- Pass 2: 70% target. Stretch the shank into elastic range.
- Pass 3: 100% target. Lock the preload. Hold for 3 seconds.
Star pattern required for flanges ≥4 bolts. Clockwise sequence invalidates the matrix.
Fig 1. Gloved hand on calibrated wrench. Target: 140 ft-lbs. Source: pexels (royalty-free)