Damage detection and removal

Types of damage

Holes and punctures, delaminations, disbonds, core damage, resin damage, water ingression or intrusion, lighning fire and heat damage

Holes and punctures

Most common, usually caused by high or medium level impacts(tools being dropped), easily detected

Delaminating

Marinate separating from core, usually caused by low energy impacts, can be visible if near the surface, can be caused by manufacturing defects, resin starvation in a laminate and moisture ingression(can be left after it is builder after a repair)

Disbands

Disbonds indicate adhesive failure between dissimilar metals

Core damage

Improper vacuum bagging or handling damage from manufacturing, impacts in service, fluid ingress(freeze/thaw cycle)

Resin damage

Fire or excessive heat, UV rays, paint stripper, impacts. Degrades tensile strength and compressive strength(but not as much)

Water ingression or instrusion

Causes weight gain, corrosion in aluminum honeycomb, Disbonds

Lightning, fire and heat damage

Fire or excessive heat may char or burn resin and/or fibers, difficult to determine how badly damaged or how deep the damage extends

Where do burn associated delaminations show up visibly

There is a burn mark, but the damage itself normally goes beyond what is visible

What are the levels of damage impact

High, medium, and low level impacts. High and medium are easier to detect

What type of NDT requires knowledge of the underlying structure

Tap testing

What is X-ray best used for

Aramid fiber and fiberglass. Not carbon fiber

What is herbal imaging not very good at

Finding disbonds and delaminations

What are the different types of ultrasonic

Pulse echo, through transmission, phased array UT

When is laser shearogrpahy used

In production and during maintenance inspections. Uses image

What is holographic laser interferometry(HLI)

Non-contact optical technique that provides visual representation of out-of-plane deformations

What is pulse echo good at detecting

Thin film inclusions in composites

What cannot determine the depth of a defect

Through transmission

What is best at detecting defects in multilayered structures and in quantifying porosity

Through transmission

What is phased array UT

Excellent detection of small defects, ability to determine both depth and location of defects, sound waves can be focused which examines depth, sound waves can be steered which examines left, right, at an angle, etc. uses multiples transducers in a single housing

How should you make a repair compared to the original

As close as you can to the original

What should you match when making a repair

Material, fiber orientation, stacking sequence, nesting, curing temp, sealing of original part

What must be considered when making a repair

Matrix resins, fibers/fabrics, core materials, lightning strike materials, sealants

What are the methods of paint removal

Chemical stripping, hand sanding, media blasting(sandblasting, aluminum oxide blasting, plastic media blasting), bio based media blasting

Plastic media blasting

Cleaning process designed to remove paint chips and solid matter, plastic particles become dull with reuse

What should you be mindful of when using media blasting

Contaminants, leftover metal, etc.

What are the methods of skin removal

Cutting and peeling, routing, grinding

What are the methods of core removal

Cutting and peeling or chiseling, routing and grinding

What should you never do for cutting a repair

Never cut a square repair, corners wont be strong, will have stress risers

Contamination

Contaminated surfaces must be removed and treated in a way that will allow the resin and adhesives of repair to bond

Drying

All moisture affected composite materials must be dry prior to repair. Drying cycles are specified in repair manuals.

What s the preffered/most common temperature for drying

150-170 degrees F

What must the drying temp be below

Glass transition temp

What is the perfect repair

Replacement part

What it's he design goal of a repair

To return the structure to its original strength, stiffness, shape, and surface finish

Primary structure

Heavily loaded or safety of flight. WING SPAR, WING

Secondary structure

Intermediate in load and safety criteria. AERODYNAMIC FAIRING

Tertiary structure

Lightly loaded or non-critical structures. INTERIOR SIDEWALL PANEL, RAYDOME.

Cosmetic repair

Superficial, non structural, export based filler

Resin injection

Not recommended, used for very limited delaminations at edge of composite part, only in tertiary panels

Mechanically fastened composite doubler

Bolted titanium patches used on thick carbon fiber solid laminate structures. Easily matches strength and stiffness required, no galvanic corrosion, limits to size and location, can be permanent or temporary

Patches are always beveled or chamfered

True

Structural adhesively bonded double repairs

Lightly loaded thin laminate structures

Flush structural repairs

Restores full structural properties by forming a joint between the prepared repair area and the repair patch

Resin infusion repairs

Preferred over resin injection, vacuum pressure to pull liquid resin into dry reinforcements

Common sandwich panel used in commercial aircraft

Nomes honeycomb, film adhesive, graphite fabric, Kevlar fabric, fiberglass fabric, primer paint, polyurethane paint