T.O. 33B-1-1
5-63
5.4.1.3
Special Requirements.
a. Because of the many inspection configurations, each application must be examined in detail. The
advantages and limitations of each inspection method must be considered, and reference standards
(representative of the structure to be inspected) must be ultrasonically inspected to verify proposed
techniques. Scanning speeds must be identical on both the standard and the test part. Scan line
indexing must be no larger than half the width of the smallest rejectable discontinuity.
b. Complete information on the internal configuration of the bonded test part must be obtained by the
operator. Drawings should be reviewed; and, when necessary, radiographs should be taken.
Knowledge of details such as the location and boundaries of doublers, ribs, etc. is required for valid
interpretation of ultrasonic inspection results. The boundaries of internal details should be marked on
the test part using a grease pen or other easily removable marking.
c. This section does not include all the information required to establish techniques. Detailed techniques
for specific structures should be obtained from the applicable NDI manual or from the prime depot level
engineering activity. In addition, further information on the operation of specific instruments should be
obtained from the applicable equipment manuals.
5.4.2
Reference Standards.
5.4.2.1
Configuration.
Reference standards should:
a. Be similar to the test part with respect to material, geometry, and thickness. (This includes closure
members, core splices, stepped skins, and internal ribs similar to the test part if bonded areas over or
surrounding base details are to be inspected.)
b. Contain bond(s) of good quality except for controlled areas of unbond fabricated as explained below.
c. Be bonded using the adhesive and cure cycle prescribed for the test part.
The reference standard may be a duplicate of the test part except for the controlled areas of unbond. As an option,
simple test specimens which represent the respective different areas of the test part and contain controlled areas of
unbond may be used.
5.4.2.2
Defect Types.
Defects may be separated into five general types to represent the various areas of bonded sandwich and laminate
structures. The five general types are:
a. Type I: Unbonds or voids in an outer skin-to-adhesive interface.
b. Type II: Unbonds or voids at the adhesive-to-core interface.
c. Type III: Voids between layers of a laminate.
d. Type IV: Voids in foam adhesive or unbonds between the adhesive and a closure member at core-
closure member joints.
e. Type V: Water in the core.
