Along with the selection of various materials for use on the structure, it is essential that a control system be established.  Ehert [1979] describes such a system as including the areas of source selection, usage, evaluation, documentation, and tracking of all materials.  The establishment of material control specifications is necessary to achieve the desired end result.  It is suggested that a rating system be established for each material based on the expected usage. Ehert [1979] suggests a five-level system (A, B, C, U, X) which may be defined as:

·        A - Acceptable for Usage

·        B - Acceptable with Specific Controls

·        C - Acceptable with Demonstration Evaluation

·        U - Not Evaluated for a Given Usage

·        X - Not Acceptable

The development of a material selection list includes all properties that are required for each material usage.  A pre-release material approval is suggested as a screening device.  This would be by a material review board that would pass on all selected materials.

After the approval of all selected materials, the next step is to assure that only approved materials are actually used and that they meet the requirements.  An accountability procedure must be implemented.  As a minimum, this system must do the following:

1.      Identify the part

2.      List all material data required

3.      List all supplemental data related to part;

a.)    Test Data

b.)    Change Notices

c.)    Deviations

d.)    Process Specifications

e.)    Inspection Reports

f.)      Rework Required

 

This system should be easily accessible and usable throughout the design, manufacturing, and usage phases of the aircraft life cycle.  It would provide the information necessary to solve any future problems and will be the basis for the next design.  This system is directed toward fracture critical parts, but it is evident that such material control is necessary for all parts.  If such is the case, then fracture critical parts can be easily identified and tracked as part of the total aircraft design and development.

As a part of this system, it is necessary to establish a material quality control program.  Sample testing of all material which is identified for fracture critical parts should include verification of crack growth rate and toughness properties.  Special handling instructions for this material to preserve initial quality should be implemented.  Non-destructive testing techniques must be developed and incorporated into the manufacturing process to insure that manufacturing quality is maintained.

While such systems of material control are easily established by a prime contractor, it is also necessary to extend them to subcontractors and parts vendors who furnish fracture critical parts.  All procurement specifications for such parts must include the same requirements for incorporation and maintenance of quality as practiced by the prime.  Figure 10.2.3 from Ehert [1979] illustrates how such vendor interfaces can be achieved.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 10.2.3.  Fracture Control System for Subcontractors [Ehert, 1979]