Aerospace
Primary structure, pressure boundaries, flight controls, engines, landing gear, interiors and systems demand low mass, fatigue resistance, vibration security, corrosion compatibility and configuration control.
SPI
Special Processes Institute
sp-i.org
Fastener Engineering Control Report
Aerospace, Defence & Space Fasteners
A comprehensive engineering knowledge, selection, manufacturing-control and installation-assurance app for bolts, screws, nuts, rivets, lockbolts, blind fasteners, pins, studs and inserts. Explore joint design, materials, coatings, special processes, quality requirements, counterfeit risk, installation controls and practical failure examples, then build and save a controlled fastener application record.
Engineering knowledge Selection assistant Torque & grip tools JSON / PDF report
Joint system
Fastener, parent materials, hole, finish, preload, locking and installation method must work together.
Traceability
Material heat, manufacturing lot, heat-treatment load, finish batch, test records and source.
Special processes
Heat treatment, plating, passivation, anodising, shot peening, lubricant and NDT.
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Fastener assessment completion
Why fasteners are safety and mission critical
A fastener is not merely a piece of hardware. Its performance depends on the complete joint: loads, stiffness, preload, grip, hole quality, parent materials, bearing and edge distances, surface condition, lubrication, environment, locking method, installation tooling and verification. An apparently correct part number can still produce an unsafe joint if any of these elements is uncontrolled.
Defence
Fasteners may also face shock, blast, extreme vibration, field maintenance, long storage, harsh climates, security restrictions, obsolescence and counterfeit or unauthorised-source risks.
Space
Launch loads, thermal cycling, vacuum, low outgassing, contamination control, non-repairable missions, preload retention and dissimilar-material effects make verification and mission assurance especially demanding.
Core fastener functions
Clamp
Preload compresses the joint and helps prevent separation, slip and fatigue cycling of the fastener.
Carry shear
Load may transfer through friction from preload, through shank bearing, or both. Threads should normally be kept out of critical shear planes where specified.
Locate
Close-tolerance bolts, interference-fit fasteners, pins and fitted shanks can control alignment and load distribution.
Seal / retain
Fasteners may contribute to pressure sealing, electrical bonding, panel retention, access, grounding or controlled breakaway.
Authority of data: Always use the current drawing, approved standard, manufacturer installation data, maintenance manual, customer specification and contract requirements. General engineering guidance must never override approved design data.
Fastener Selection Assistant
Select the application conditions to generate preliminary guidance.
Joint Design and Engineering Considerations
| Design topic | What must be controlled | Typical failure if ignored |
|---|---|---|
| Load path | Tension, shear, bending, prying, eccentricity, combined loading, fatigue spectrum and load sharing across the group. | Local overload, first-fastener failure, progressive joint failure. |
| Preload and stiffness | Target preload, proof/yield margin, fastener and joint stiffness, embedment, relaxation, thermal effects and scatter. | Separation, slip, fretting, fatigue or yielding. |
| Grip and thread position | Correct grip length, washer stack, protrusion, full nut engagement and avoidance of threads in critical shear planes. | Thread-root fatigue, bottoming, insufficient engagement or false torque. |
| Hole and geometry | Diameter, roundness, perpendicularity, countersink angle/depth, edge distance, pitch, bearing area, burrs and surface damage. | Bearing failure, tear-out, knife-edge, poor seating or crack initiation. |
| Materials and galvanic compatibility | Fastener/structure electrochemical compatibility, sealants, isolators, moisture traps, carbon-fibre contact and protective finishes. | Galvanic corrosion, loss of section, seizure or electrical degradation. |
| Temperature and environment | Differential thermal expansion, creep, oxidation, cryogenic behaviour, vacuum, radiation, fluids and fire zones. | Preload loss or excess, stress rupture, oxidation, outgassing contamination. |
| Locking | Positive locking, prevailing torque, locking compounds, safety wire, cotter pins, lockwashers only where approved. | Rotation, loosening, FOD or loss of retained item. |
| Maintainability | Tool access, inspectability, replacement criteria, single-use items, removal damage and life limits. | Incorrect installation, hidden damage or unauthorised reuse. |
Torque is an indirect control
Torque is mainly consumed by friction in threads and under the head or nut. Small changes in coating, lubricant, cleanliness, reuse or surface finish can create large preload variation.
Fatigue strategy
Maintain joint compression, minimise stress concentration, use controlled geometry and surface integrity, and consider rolled threads, generous under-head radii and interference fit where design-approved.
Composite structures
Control bearing/bypass loads, countersink quality, laminate damage, galvanic isolation from carbon fibre, clamp-up crushing and moisture sealing.
Quality Requirements Across the Lifecycle
Manufacturing Process Control
| Stage | Controls | Evidence / records |
|---|---|---|
| Raw material | Approved alloy and form, chemistry, cleanliness, source, heat identity, segregation and positive material identification where required. | Mill certificate, heat number, receipt inspection, PMI result. |
| Heading / forming / machining | Tool condition, grain flow, laps, seams, folds, under-head radius, concentricity, cold work and dimensional SPC. | Route card, tool-life record, first-off and in-process inspection. |
| Thread manufacture | Rolled or cut thread as specified, pitch diameter, lead, flank angle, root radius, incomplete threads, laps and gauge control. | Thread gauge results, optical inspection, SPC and tool records. |
| Heat treatment | Approved cycle, furnace qualification, loading, quench, atmosphere, hardness, tensile/shear properties and decarburisation control. | Furnace chart, load traceability, TUS/SAT status, test reports. |
| Surface treatment | Cleaning, activation, plating/coating thickness, coverage, adhesion, corrosion performance, lubricant, passivation and dimensional allowance. | Bath records, coating test, lot identity, process certification. |
| Hydrogen control | Material-strength applicability, pre-process cleaning method, bake start time, bake temperature/time, delay control and embrittlement testing where required. | Plating and bake timestamps, oven record, test specimen results. |
| NDT / surface integrity | Method applicability, qualified personnel, sensitivity, acceptance criteria, magnetic hygiene and post-cleaning. | NDT report, personnel approval, equipment checks. |
| Final acceptance | Dimensions, mechanical performance, finish, visual quality, marking, packaging, lot segregation and documentation review. | Inspection report, CoC, test certificate, release record. |
Counterfeit and substitution risk: Procure from approved and authorised sources wherever required. Verify manufacturer identity, lot traceability, packaging, marking, certification consistency and chain of custody. Quarantine suspect items; do not return them to a supply chain before disposition under the applicable procedure.
Installation Control
Before installation
- Verify part number, revision, lot and approved source.
- Confirm grip, length, material, finish and locking feature.
- Inspect holes, countersinks, threads and mating surfaces.
- Confirm sealant/lubricant and cleanliness state.
- Check tool calibration and programme/version.
During installation
- Use specified orientation, washer stack and tightening sequence.
- Prevent cross-threading, cocking and tool side-load.
- Control torque, angle, tension, swage or stem break as applicable.
- Observe run-down anomalies and seating.
- Protect adjacent structure and prevent FOD.
After installation
- Check head/collar seating, protrusion and locking.
- Verify recorded result and tool status.
- Apply witness mark only where specified.
- Inspect for damage, sealant coverage and gaps.
- Control rejected, removed and single-use fasteners.
Installation Method Comparison
| Method | Strength | Main controls | Limitations |
|---|---|---|---|
| Torque | Simple, familiar, productive. | Friction condition, K-factor validation, calibrated tool, smooth run-down. | Preload scatter can be high. |
| Torque-angle | Reduces some friction sensitivity after snug point. | Snug definition, angle control, joint stiffness and yielding limits. | Requires validated joint behaviour. |
| Direct tension / elongation | Measures preload more directly. | Access, datum, ultrasonic or mechanical measurement correlation. | More equipment and process complexity. |
| Break-off collar / lockbolt | Controlled installation by proprietary system. | Correct pin/collar, grip, tooling, anvil condition and completed swage. | System-specific inspection and removal. |
| Riveting | Light, reliable permanent joint. | Correct length, hole fit, driving force, bucking, shop-head geometry and damage. | Removal damages fastener and may enlarge hole. |
Failure Modes, Causes and Examples
Preliminary Torque–Preload Calculator
Uses the simplified relationship T = K × F × d. This is a preliminary engineering estimate only. Use validated joint-specific data for production.
Highly dependent on finish, lubricant and joint.
Enter values and calculate.
Grip and Protrusion Check
Enter drawing-specific values and check.
Standards and Reference Map
| Area | Examples of controlled references | Use |
|---|---|---|
| Quality management | AS9100 / EN 9100, contract quality clauses, customer supplier requirements. | Configuration, purchasing, special processes, inspection, traceability, nonconformance and records. |
| First article / production approval | AS9102; customer FAI, APQP or PPAP requirements where flowed down. | Demonstrate the production process can make the specified fastener or installed feature. |
| Fastener product definition | NAS, NASM, MS, AN, SAE AS, EN and ISO aerospace fastener standards; proprietary manufacturer standards. | Dimensions, materials, finish, performance, marking and acceptance. |
| Maintenance and repair | Approved aircraft maintenance manuals, structural repair manuals and FAA AC 43.13-1B only where applicable and not contrary to manufacturer data. | Selection, substitution limits, installation and repair. |
| Space engineering | Programme-specific NASA, ECSS, launch-provider and spacecraft workmanship requirements. | Preload, locking, contamination, vacuum compatibility, thermal cycling and verification. |
Fastener Application Assessment
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