Composite Repair Patch Testing — PatSnap Eureka
Destructive vs. Non-Destructive Testing for Composite Repair Patches in Aircraft
Qualifying composite repair patches demands two complementary testing paradigms. Understanding when to apply destructive methods and when NDT takes over is critical for R&D engineers, MRO specialists, and IP professionals working in aerospace structural repair.
Why Both Testing Paradigms Are Needed
Composite repair patches applied to aircraft primary and secondary structures must be substantiated before return to service. The qualification process draws on two fundamentally different categories of evidence: destructive testing, which physically breaks specimens to establish material and bond-strength allowables, and non-destructive testing (NDT), which interrogates installed repairs without causing any damage.
Destructive methods — including FAA-recognised lap shear, flatwise tension, and peel tests — are applied to witness coupons or sacrificial test panels manufactured under the same process conditions as the repair. They yield the quantitative strength data that underpin design allowables. Because they consume the specimen, they cannot be used on the aircraft itself.
NDT methods such as ultrasonic inspection, infrared thermography, and shearography fill that gap. They are applied directly to the bonded repair on the aircraft, verifying that the installed patch is free from disbonds, delaminations, voids, and other defects that would reduce its structural contribution. Regulatory frameworks from EASA and the FAA require both categories of evidence for a complete substantiation package.
For MRO engineers and R&D teams, understanding which method targets which failure mode — and how the two paradigms complement each other — is essential for designing efficient qualification programmes. PatSnap's life sciences and engineering intelligence tools can help teams map the patent landscape around both testing methodologies.
Breaking Specimens to Build Confidence
Destructive tests are the foundation of composite repair qualification. They measure the mechanical properties and bond integrity that NDT methods later verify in service.
Lap Shear Test
The lap shear test measures the shear strength of the adhesive bond-line between the repair patch and the parent structure. Two overlapping coupons — one representing the patch, one the substrate — are pulled apart in tension, causing the bond-line to fail in shear. The result, expressed in MPa, establishes the shear allowable used in repair design calculations. It is among the most commonly specified tests in FAA Advisory Circulars for bonded composite repairs.
Result: Bond shear strength (MPa)Flatwise Tension Test
The flatwise tension test applies a tensile load perpendicular to the laminate plane, pulling the repair patch away from the substrate. This reveals the through-thickness tensile strength of the bond and the laminate itself — a critical property for repairs on curved or pressurised structures where peel-mode loading is significant. Failure modes observed (cohesive, adhesive, or substrate) inform both design allowables and process quality.
Result: Through-thickness tensile strengthPeel Test
Peel tests — including climbing drum and T-peel variants — measure the energy required to progressively separate the repair patch from the substrate at a defined peel angle. Results are expressed in N/mm of width and characterise the adhesive's resistance to crack propagation along the bond-line. Peel tests are particularly relevant for thin-skin repairs and for evaluating the effect of surface preparation quality on bond durability under environmental exposure.
Result: Peel resistance (N/mm)Short Beam Shear Test
The short beam shear (SBS) test loads a short, thick specimen in three-point bending at a span-to-depth ratio designed to induce interlaminar shear failure rather than flexural failure. It measures interlaminar shear strength (ILSS) in MPa and is widely used to assess cure state, fibre-matrix adhesion, and the effect of moisture absorption on the repair laminate. SBS results are sensitive to processing variables, making them useful as process control indicators alongside structural allowables.
Result: Interlaminar shear strength (MPa)Comparing NDT Method Capabilities
Each non-destructive testing method has a distinct detection profile. Understanding which defect type each method targets helps engineers design an efficient inspection programme for composite repair patches.
NDT Method Detection Capability by Defect Type
Ultrasonic inspection and thermography offer the broadest defect coverage for composite repair patch inspection; shearography excels at near-surface disbonds.
Destructive Test Methods: Properties Measured
Four primary destructive test types cover the key mechanical property domains required for composite repair patch design allowables.
Inspecting Installed Repairs Without Damage
NDT methods verify that each installed composite repair patch meets the quality standards established by the destructive qualification programme. Each technique targets a different class of defect.
Ultrasonic Inspection
Ultrasonic methods — both pulse-echo (single-sided) and through-transmission (requiring access to both surfaces) — propagate high-frequency sound waves through the repair laminate and bond-line. Disbonds, delaminations, and porosity reflect or attenuate the ultrasonic beam, creating detectable signal anomalies. Pulse-echo is preferred for in-situ inspection where only one surface is accessible. Automated scanning systems can produce C-scan images showing the spatial distribution of defects across large repair areas. Recognised by FAA Advisory Circulars as a primary method for bonded repair inspection.
Infrared Thermography
Thermography measures the surface temperature distribution of the repair patch after a controlled thermal stimulus (flash lamp, heat gun, or lock-in excitation). Defects such as voids, kissing bonds, and disbonds impede heat conduction through the laminate, creating thermal contrast at the surface that is captured by an infrared camera. Flash thermography is particularly effective for large-area scanning and can be performed rapidly without contact. It is sensitive to near-surface defects and has been adopted in aerospace MRO for both composite and bonded metallic repairs, with guidance referenced in EASA AMC materials.
How FAA and EASA Define the Testing Requirements
Regulatory bodies specify which test methods are recognised, what defect detection thresholds are required, and how repairs must be documented. Aligning your testing programme with these standards is essential for airworthiness approval.
| Test Category | Method | Primary Target | Regulatory Reference | Applied To |
|---|---|---|---|---|
| Destructive | Lap Shear | Bond shear strength allowable | FAA AC 21-26 / ASTM D1002 | Witness coupons / process qualification panels |
| Destructive | Flatwise Tension | Through-thickness tensile strength | FAA AC 43.13-1B / ASTM D7291 | Witness coupons |
| Destructive | Peel Test | Adhesive peel resistance | EASA AMC 20-29 / ASTM D1876 | Witness coupons |
| Destructive | Short Beam Shear | Interlaminar shear strength / cure state | FAA AC 21-26 / ASTM D2344 | Process control coupons |
| NDT | Ultrasonic (pulse-echo) | Disbonds, delaminations | FAA AC 43.13-1B Section 4 | Installed repair on aircraft |
| NDT | Infrared Thermography | Voids, kissing bonds | EASA AMC 20-29 / NAS 410 | Installed repair on aircraft |
Map the IP Landscape Around Composite Repair Qualification
Use PatSnap Eureka to find patents filed by aerospace OEMs and MRO providers covering testing and qualification methods for bonded composite repairs.
Accelerate Your Composite Repair Testing Research
R&D engineers and MRO specialists working on composite repair patch qualification face a dual challenge: staying current with evolving NDT technology and understanding the competitive patent landscape around qualification methods. PatSnap Eureka addresses both by combining AI-powered patent search with scientific literature analysis across more than 2 billion data points.
With Eureka, teams can rapidly identify which assignees hold key patents in ultrasonic inspection for bonded composite repairs, track innovation trends in thermographic inspection systems, and map white spaces in shearography and digital radiography for aerospace MRO. The platform's AI assistant can answer technical questions about test methods and surface relevant prior art in seconds.
For IP professionals, Eureka provides the landscape analysis needed to assess freedom-to-operate for new NDT system designs, identify licensing opportunities, and monitor competitor filing activity. PatSnap's IP analytics tools complement Eureka with portfolio benchmarking and citation analysis for deeper competitive intelligence.
Eureka also integrates with PatSnap's open API for teams that need to embed patent intelligence into their own R&D workflows or MRO management systems. Explore how PatSnap customers in aerospace and advanced materials are using the platform to reduce research time and strengthen their IP positions.
Composite Repair Patch Testing — key questions answered
Destructive testing methods such as lap shear, flatwise tension, and peel tests physically damage or consume the test specimen to measure bond strength and material properties, making them unsuitable for in-service components. Non-destructive testing methods such as ultrasonic inspection, thermography, and shearography evaluate the repair patch integrity without damaging the structure, allowing inspection of installed repairs on operational aircraft.
The most widely referenced NDT methods for composite repair patch qualification in aerospace MRO include ultrasonic inspection (both pulse-echo and through-transmission), infrared thermography, and shearography. Each method targets different defect types: ultrasonics detect delaminations and disbonds, thermography reveals heat-flow anomalies indicating voids, and shearography identifies subsurface strain concentrations.
Composite repair patches involve bonded interfaces between dissimilar or similar materials under complex load paths. Qualification must address bond-line integrity, fiber orientation, cure state, and environmental degradation. Regulatory frameworks from bodies such as the FAA and EASA require substantiation of both the repair design and the inspection method used to verify it, creating a dual qualification burden for MRO engineers.
In current aerospace practice, NDT cannot fully replace destructive testing for initial qualification. Destructive tests are used to establish baseline material properties, bond strength allowables, and process qualification data. NDT is then used to verify conformance of each installed repair against those baselines. Regulatory guidance from the FAA and EASA requires both categories of evidence for a complete substantiation package.
Regulatory bodies including the FAA (via Advisory Circulars) and EASA (via AMC materials) define the acceptable means of compliance for composite repair substantiation. They specify which test methods are recognised, what defect detection thresholds are required, and how repairs must be documented. Engineers and MRO specialists must align their testing programmes with these standards to achieve airworthiness approval.
Shearography is an optical interferometric technique that detects subsurface anomalies by measuring surface strain gradients under applied stress or thermal load. It is particularly sensitive to delaminations and disbonds near the surface. Thermography, by contrast, measures heat flow through the material: defects such as voids and kissing bonds impede heat conduction, creating thermal contrast detectable by an infrared camera. Both methods are non-contact and suitable for large-area scanning.
Still have questions? Let PatSnap Eureka search the patent and literature evidence for you.
Ask Eureka About Composite Repair Testing →Accelerate Your Composite Repair R&D with AI-Powered Patent Intelligence
Join 18,000+ innovators already using PatSnap Eureka to accelerate their R&D and stay ahead of the IP landscape in aerospace structural repair.
References
- Federal Aviation Administration (FAA) — Advisory Circulars on Composite Repair Substantiation (AC 43.13-1B, AC 21-26)
- European Union Aviation Safety Agency (EASA) — Acceptable Means of Compliance: AMC 20-29, Composite Aircraft Structure
- World Intellectual Property Organization (WIPO) — Global Patent Database: Composite Repair and NDT Method Filings
- ASTM International — Standards D1002 (Lap Shear), D7291 (Flatwise Tension), D1876 (Peel), D2344 (Short Beam Shear)
- American Institute of Aeronautics and Astronautics (AIAA) — Journal of Aircraft: Bonded Composite Repair Certification Methods
- Elsevier — NDT&E International and Composites Part B: Engineering — Peer-reviewed research on composite repair NDT methods
All data and statistics on this page are sourced from the references above and from PatSnap's proprietary innovation intelligence platform. Regulatory citations are indicative; always verify against the current version of applicable Advisory Circulars and AMC documents before use in a substantiation programme.
PatSnap Eureka searches patents and research to answer instantly.