Material Review Board – MRB Stress Analysis

Material Review Board (MRB)

The Material Review Board (MRB) is one of the critical teams in an aerospace OEM or PMA (parts manufacturing authority) company. In this post we will learn more about the role of a stress engineer as part of the material review board.

1. 14 CFR Subpart C Section 25-603: Materials
2. 14 CFR Subpart C Section 25-605: Fabrication Methods
3. 14 CFR Subpart C Section 25-607: Fasteners
4. 14 CFR Subpart C Section 25-609: Structure Protection
5. 14 CFR Subpart C Section 25-613: Strength of Materials

(a) What is a Material Review Board (MRB)?

The Material Review Board (MRB) team generally consists of subject matter experts (SMEs) from various fields such as quality, design, stress, manufacturing, planning etc. This type of a team is called a cross functional team. The role of the Material Review Board (MRB) team is to generally meet on a regular basis (weekly or monthly).

They go through each critical deviation that cannot be dispositioned outside the MRB board. Such deviations do not conform to a standard or specification that a particular part, assembly or their associated materials are required to conform to. Then the team decides what to do with that non conformity. These kinds of deviations are generally documented in a tracking document called the Non Conformity Report (NCR), each such deviation may have its own NCR that needs to be approved for the product to move through.

Once the team analyzes the NCR, a suitable disposition is made to proceed further, common dispositions are listed below:

Typical Material Review Board (MRB) Dispositions:

• Use As Is: Use the part or material in its current state of deviation without any change
  • This disposition is only made after confirming that the form fit or function of the component or assembly is not affected by the NCR discrepancy
  • Example: A part's critical dimension was undersized by the technician or machinist, for example a radius feature, but the feature is in a remote non critical location as assessed by stress
• Repair or Rework: The component can be reworked or repaired to bring it into a conforming state
  • This disposition is only made after sufficient stress analysis is conducted so that the reworked component is adequate to comply with all applicable regulations and applied loading
  • Example: A vendor component was received with a larger fillet radius than required on the face of a drawing. This component can be reworked to conform to the drawing so it can be used in the production line
• Scrap: The part has to be scrapped or discarded
  • This is typically done when the component includes a critical flaw in a critical area that is insufficient and cannot be reworked
  • Example: A composite part is received with a crack at a critical bend radius that is highly loaded
    • Note that such gross deviations are generally not common when dealing with reputable part manufacturers as there are strict quality control practices in place to prevent slipping of such a part out to a customer, so this case was only provided as an example
  • Other examples may include a part made from an inferior material than required, a feature too thin, a hole too large , an edge distance too small, a defect too large that affects life limits etc.

A good link that explains further and also points out the subtleties of repair vs rework: Click Here

(b) Stress Material Review Board: Other Duties

In addition to what we discussed above, a stress engineer who is part of a material review board (MRB) is also called into action for other related activities.

Materials and Process Specifications (MP&S) Support:

Generally speaking, at least as far as I know, there is either a separate department or a separate SME that deals with MP&S activities. However, there may be situations where the MP&S SME may need stress support. Sometimes a material specification may not be available and an alternate specification may be suggested by a vendor with inferior strength properties. As a member of the Material Review Board, a stress engineer would support him or her with appropriate stress analysis as required by the MP&S SME to disposition a specific materials related MRB issue.

Field Support:

More often than not, there will be issues that come up from field service of an aircraft. These issues are generally related to corrosion, cracking, repairs etc. Again, the stress engineer is the go to person to support the repair reports and substantiation.

Production Support:

As the product is moving through the production line, inevitably some technician is bound to oversize a fastener hole, or mess up a dimension on a critical part etc. The stress engineer is critical in these situations to support that NCR and move things forward.

Aircraft on Ground (AOG):

This is similar to field support, except that the aircraft is now inoperable due to the issue that requires immediate attention. This can be a repair that is critical for flight safety. The stress engineer is generally expected to give top priority to AOG issues as the customer is waiting for the issue to be resolved immediately.

Conclusion:

As you know, a development environment is a bit different than an MRB type environment in terms of stress engineering. Generally there is a little more time in a development environment. But as we can see from the above situations, MRB engineers are typically under greater stress, aggressive deadlines and pressure. But for someone that enjoys this kind of stuff it can be a rewarding experience, because guess what, you are someone that can save the day in rough waters for the company.

So that is all for now folks, what did you think about this post? Comment below the post....

Cheers...

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