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Damage Tolerance for Engine Structures 4. Reliability and Quality Assurance

An AGARD meeting on the Damage Tolerance Concept (DTC) was held in San Antonio in
1985. One of the conclusions of this meeting was that DTC offers a way to improve
the integrity and efficient utilisation of critical aero engine components, in
particular those manufactured from the high strength materials which are required to
meet the design objectives set for high performance military engines. Following
this meeting, a series of workshops were arranged to investigate various aspects of
DTC.
The fourth workshop meeting is aimed at exploring reliability and quality assurance
issues in the Damage Tolerance approach. To this end, a series of papers are to be
given, following this introduction, to explore the implications on DTC of:
(a) Component material specifications and standards.
(b) Controls on manufacturing processes and procedures.
(c) Design systems and quality assurance.
The meeting will also explore the possibility of a common AGARD approach and
Database on quality and integrity—related issues which arise during aero engine
component life assessment.
The primary goal for Quality Aseurance is to provide Customer Satisfaction. From
the customer's viewpoint, this means that the product must meet the specification.
This is not the complete story, however; there must also be good communication
between the customer and the manufacturer. The aim here is to ensure that the
customer gives a clear, unambiguous specification of what is required and that the
manufacturer understands all aSpeCtS of this.
A good example of this is the definition of the mission profiles, mission mixes and
life requirements which the aero engine is designed to achieve. A simple
requirement that "the engine fracture critical parts must achieve an inspection
interval of x hours" is an insufficient definition, since the relationship between
cyclic life usage and time in Service depends on the types of mission flown.
profiles and mission mixes and then uses the engine for different profiles or mixes,
he must expect to see a consequent change in the lives achieved expressed in hours
and/or cycles. In the case of cyclic life—limited components, however, the life in
"equivalent cycles" should not change in these circumstances.