8 Quality Control

8.1 Quality Control Steps and Items
8.2 Defects
8.3 Inspection of Raw Materials
8.4 Non-Destructive Evaluation

8.1 Quality Control Steps and Items

a. Receipt Checks
b. Revalidation
c. Physical Characteristics and Properties, Chemical and Mechanical Properties...

8.2 Defects

a. Surface Crazing
b. Pin hole
c. Color Variation
d. Wrinkles
e. Fabric texture surface
f. Pits
g. Foreing object

8.3 Inspection of Raw Materials

a. Viscosity
b. Gel time
c. Chemical Composition
d. Color number
e. Shrinking

The detection of cracks is a remote sensing problem; energy is directly into the structure,
allowed to sample the crack, and if suitably disturbed by the crack, the disturbance may be
analyzed to infer the location, size and orientation of the crack.

8.4 Non-Destructive Test (NDT)

8.4.1 Visual Inspection

Optical holography, including holographic interferometry, is another branch of visual inspection
of surface topography that can be applied to fiber reinforced materials.

8.4.2 Liquid Penetrants 

A coloured or fluorescent dye, when applied to a clean surface and allowed to dwell for 10 to 20 minutes, will be drawn into the discontinuity by capillary pressure. The capillary pressure is determined by the width of discontinuity, surface tension and contact angle of the dye on the surface.

The excess dye is then removed from the surface and a developer applied, The developer
has two functions to assist in drawing the dye back out to the surface, giving an indication to assist in seeing this indication by giving good visual contrast. After a time, usually a minimum
 of 10 minutes, the surfaces are visually inspected. White light is used for red dyes, ultra-violet light for fluorescent dyes.

Although fluorescent dyes do give a high contrast ratio that should make indications easier to see they do not always give the maximum chance of discontinuity detection. They are not suitable for components with rough or poor surface finishes as it is difficult to remove the excess dye, causing an overall fluorescence that masks discontinuities, preventing their detection.
They do however make seeing indications in internal bores, cored holes, etc. easier.

8.4.3 Ultrasonic Inspection

Ultrasonic inspection is the interrogation if materials or structures using ultrasonic waves,
which are also known as stress waves.

In ultrasonic testing we must inject stress waves into the material or component to be
examined and then monitored the transmitted or reflected beam.

8.4.3 Acoustic Emission

When a dynamic process such as cracking occurs in a material, some of the released
elastic strain energy can generate stress waves. These stress waves propagate through the
material and eventually reach the surface, so producing small temporary surface displacements.

In extreme cases, for example in the well known cracking of ice, the stress waves may be of
high amplitude and low frequency and consequently easily audible.

8.4.4 Acousto-Ultrasonic 

Acousto-ultrasonics utilizes pulsed ultra-sound stress wave stimulation in materials, as in
ultrasonics, combined with the sensing and measurement of the transmitted signal by acoustic
emission techniques.

8.4.5 Vibration Method

Honeycomb constructions can be difficult to inspect because the ultrasonic waves will only
propagate through the cell walls.

Low frequency vibration methods are classified as either global or local.

Global Methods

The measurement of the natural frequencies and/or damping of the whole component and
as such monitor the integrity of the whole component from single measurement.

Local Methods

Probably the oldest test for the inspection of laminated constructions is the " coin-tap " test.
This vibration requires an operator to tap the area of the structure to be investigated with a
coin and listen to the resulting sound.

8.4.6 Radiography

Base on the measurement of the attenuation of electromagnetic radiation after traveled
through the sample under test. The monitoring of materials and components by
radiography is based on the same principle as that for the detection of the fracture of bone,
namely, that the different attenuation as the radiation passes through the defect will be
sufficient to reveal the defect by the changes in the blackening of a photographic film.

8.4.7 Thermography 

Most thermal methods involve the measurement of stationary temperature fields such as
produced by variations in the insulation on a building.

In this thermal imaging picture; dark purple represents a cool area, and the temperature moves up through red, orange, yellow and white as it gets warmer. You can tell that it is a cool night by the colour of the ground, and likely early in the evening, as the concrete wall beside the driveway is still warm (concrete has what's known as Thermal Mass). You can see that the overhang on the house(purple) is properly insulated, as there is very little heat being lost through it. You can also see (on the wall next to it) where the insulation is between studs (red squares) and how much heat the studs are allowing to escape (orange). The first floor appears to contain only drywall, and no insulation.

8.4.8 Eddy Current
8.4.9 Holography NDT