SOW_Attachment_E_--_Analysis_Requirements_for_Non-Conformances_MRB_Process.pdf

T-38 -33 WING PRODUCTION PROGRAM

ANALYSIS REQUIREMENTS AND GUIDELINES FOR

NON-CONFORMANCE CONDITIONS

1 August 2018

DISTRIBUTION D. Distribution authorized to U.S. Government agencies and their contractors for administrative or operational use (date of determination, 1 August 2018). Other requests for this document shall be referred to the T-38 Program Office.

WARNING – This document contains technical data whose export control is restricted by the Arms Export Control Act (Title 22, U.S.C., Sec 2751, et seq.) or the Export Administration Act of 1979 (Title 50, U.S.C., App. 2401 et seq.) as amended. Violations of these export laws are subject to severe criminal penalties.

Disseminate in accordance with provisions of DoD Directive 5230.25.

DESTRUCTION NOTICE – Destroy by any method that will prevent disclosure of contents or reconstruction of the document.

T - 3 8 - 3 3 W i n g P r o d u c t i o n P r o g r a m :

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1 Introduction

This document defines the analysis requirements that will be used to provide engineering support for non-conformance conditions encountered during the T-38 -33 Wing Production Program. It discusses the guidelines set out by the program and the United States Air Force (USAF) that govern the selection of analysis methods and tools. It also includes a list of appropriate reference sources and analysis methods to be used, as well as a list of appropriate software tools. Repair dispositions and the related analysis will be reviewed and approved through the Material Review Board (MRB) process.

2 Analysis Requirements

This section outlines the analysis requirements for non-conformance conditions, and associated repair dispositions, encountered during the -33 Wing Production Program.

1. Analysis will be performed on the blueprint and non-conformance condition

2. The following minimum requirements must be met for a disposition to be considered for approval:

a. Static Strength: Margin of safety (MS) > 0

b. Damage Tolerance (DT critical parts only*): Initial and recurring inspections must be equal to or exceed the intervals in T.O. 1T-38C-6 (assume IFF usage)

c. Durability (durability critical regions only†): Durability life > 10,000 hours

(assuming IFF usage and using fracture mechanics based approach)

d. Corrosion Resistance: Non-conformance is equivalent to or better than the blueprint condition

e. If one or more of the above requirements cannot be met, a disposition may be approved by utilizing one of the following approaches

i. Equivalence approach: show that the repair is equivalent to or better than the blueprint condition

ii. Worse Case approach: show that there is a “worse case” in close proximity to the repair; the repair is equivalent to or better than an adjacent detail on the same part (adjacent detail must be in close proximity to the damage and have similar functionality)

3. Durability and damage tolerance analyses will assume IFF usage

4. All non-conformance dispositions need to assess the down-stream impact to maintainability and inspectability

* DT critical parts are defined here as parts with fatigue critical locations (FCLs) and which are managed through regular T.O. inspections – P/N 3-23502 (lower wing skin) and 3-23279 (66% spar) † Durability critical regions are defined where the cyclic loading is dominated by tension (i.e.

geometrically located below the neutral axis of the wing)

The above analysis requirements are incorporated into the Engineering Process Flow for -33 Wing MRBs that is shown in Figure 1.

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Figure 1: Engineering Process Flow

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3 Guidelines

This section provides general guidelines that govern the analysis tools and processes that are allowed for the -33 Wing Production Program. MRB guidelines are provided for situations where the contractor may not need to perform formal static or durability analysis.

3.1 Guidelines for Analysis Tools, Processes, and Reporting

1. All wing non-conformances which require analysis must be formally documented using an approved analysis report template

2. The analysis report will contain enough detail that USAF Engineering could reproduce the analytical results

3. All analysis results must be fully visible and printable

4. All tools must produce engineering that is reproducible by USAF (acceptable software tools are identified in Section 5)

a. They must have a license for the software which is used to perform the engineering, or

b. The analysis code must be adequately documented that its analysis can be reproduced

5. No proprietary materials or tools may be used; analysis will be performed using the underlying methods and alternate, non-proprietary sources

6. No proprietary stamps will be applied to analysis reports

3.2 Guidelines for Exceptions to Analysis Requirements for MRBs

For specific scenarios, USAF may not require formal analysis reporting for MRB non-conformances. Guidelines are defined for both hole and non-hole details as well as low-stress criteria for static strength and durability analyses. The guidelines and criteria are presented in Appendix A.

The hole criteria shown on page A-3 to waive formal analysis reporting cannot be applied to damage tolerant critical parts (lower wing skin, 3-23502 and 66% spar, 3-23282). Meeting the criteria presented in Appendix A does not guarantee USAF concurrence. USAF may require formal analysis upon review of a specific MRB disposition.

4 References for Methods and Allowables

This section outlines the references that are appropriate for analysis methods and allowables for the -33 Wing Production Program. It also describes those references that are inappropriate for this program.

4.1 Appropriate Analysis Method References

All analysis method references for the -33 Wing Production Program must be in the public domain, or the data must be available to USAF so that all engineering is reproducible. The following is a list of T-38 documents, textbooks, and reports which may be used to perform engineering work on the -33 Wing Production Program. This list is not all-inclusive. Additional open sources may be identified as the program develops.

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1. T-38 Specific Guidelines Documents

a. USAF, T-38 Guidelines for Durability and Damage Tolerance Analysis – AFGROW, Rev B, October 2015

i. Durability and damage tolerance analyses must use the appropriate

T-38 stress spectra provided by USAF

b. USAF, Methodology for Stress Scale Factor Determination, Rev. B, October 2015

c. USAF, T-38 Crippling Analysis Guidelines, July 2014

2. Textbooks – Including, but not limited to:

a. Bruhn, Analysis and Design of Flight Vehicle Structures, June 1973

b. McCombs, Supplement to Analysis and Design of Flight Vehicle Structures

(Bruhn), January 2004

c. Niu, Airframe Stress Analysis and Sizing, 2nd edition

d. Peterson, Stress Concentration Factors, 1974

e. Roark and Young, Roark’s Formulas for Stress and Strain, 5th edition, 1975

f. Timoshenko, any of his textbooks, appropriate reference required with detail analysis

g. Young, Roark’s Formulas for Stress and Strain, 6th edition, 1989

h. Stress Memo No. 1e, Static Strength Analysis of Lugs and Shear Pins, Lockheed, September, 1972

i. Other textbooks may be referenced but will require prior approval by USAF; full reference must be provided with analysis report

3. T-38 Reports

a. T-38C Stress Analysis Reports – Volume 2: Wing, Section B: T-38C -33 Wing Analysis, September 2017

b. T-38 Durability and Damage Tolerance Analysis Report, September 2017

4.2 Appropriate Material Allowable References

All material allowable references for the -33 Wing Production Program must be in the public domain or the data must be available to USAF so that all engineering is reproducible. The following is a list of references which shall be used to perform engineering analysis on the -33 Wing Production Program. Use of other references must have USAF approval.

1. Static Strength and Corrosion Resistance

a. DOT/FAA/AR-MMPDS-01, Metallic Materials Properties Development and

Standardization, January 2003

b. Fastener specifications (i.e. PLT, HL, etc)

2. Durability and Damage Tolerance

a. Material files provided by USAF (AFGROW format)

i. Crack growth rate, fracture toughness, etc

ii. Die Forging 7050-T74.lkp

iii. Plate 7475-T7351.lkp

iv. Others available, upon request to USAF

b. Stress spectra provided by USAF (AFGROW format)

i. Stress spectra are specific to each fatigue critical location (FCL)

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ii. Example filename for FCL A-1-33

1. 33 Wing, IFF Moody (2007), A-1-33_V1_AFG.SP3 (main spectrum file)

2. 33 Wing, IFF Moody (2007), A-1-33_V1_AFG.sub (sub spectrum file)

4.3 Inappropriate References

References that contain either proprietary information or data that are not available to USAF are not appropriate and shall not be used for engineering work on the -33 Wing Production Program.

5 Analysis Software Tools

This section outlines appropriate and inappropriate analysis tools for use on the -33 Wing Production Program.

5.1 Appropriate Analysis Software Tools

These tools may be used to perform analysis work on the -33 Wing Production Program.

1. AFGROW (Crack growth analysis software)

a. Version 5.3.2.22 or greater

2. MSC Patran / MSC Nastran (Finite element analysis software)

a. Version 2010 or greater

b. -33 Wing finite element model (FEM) will be provided by USAF

i. Design and fatigue load cases

3. StressCheck (Finite element analysis software)

a. Version 10.2 or greater

4. Microsoft Excel

a. Version 2013 or greater

b. Document all equations outside of cells – no hidden equations

5. Section analysis tools – section properties are considered a repeatable, obvious analysis so they can be generated from any code without providing program documentation or providing a program license to USAF

a. Solid modeling software (e.g. Unigraphics, etc)

b. Excel – Section property analysis

5.2 Inappropriate Analysis Tools

Analysis tools that are not listed in Section 5.1 shall not be used for engineering work on the -33 Wing Production Program.

6 Conclusion

This document has provided an overview of the Analysis Requirements, Guidelines, References, and Tools that are permissible for use on the -33 Wing Production Program to substantiate repair dispositions for non-conforming conditions.

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Appendix A: Guidelines for Exceptions to Analysis Requirements for MRBs

The purpose of Appendix A is to provide MRB guidelines for non-conforming conditions and subsequent repairs for which the contractor does not need to perform formal analysis (static, damage tolerance, or durability analysis). Guidelines are defined for both hole and non-hole details as well as low-stress criteria for static strength and durability analyses.

A.1 Holes

If all the following criteria are met for a non-conforming fastener hole, then formal analysis support is not required.*

Edge distance > 1.75 × Diameter

Pitch distance > 3.5 × Diameter (average of 2 adjacent holes)

Countersink depth < 2/3 × part thickness

Diameter ≤ 1/32” oversize from blueprint

Non-conforming hole must have at least 2 adjacent fasteners in the same load path

Non-conforming hole will not intersect any fillets, steps, or other geometric entities

No more than 20% of the holes in any row or group may be non-conforming

*These criteria cannot be applied to damage tolerant critical parts (lower wing skin, 3-23502 and 66% spar, 3-23282). Meeting the above hole criteria does not guarantee USAF concurrence.

USAF reserves the right to require formal analysis upon review of a specific MRB disposition.

The static strength low stress criterion (see Section A.2) cannot be applied to non-conforming holes. Static analysis of holes generally involved fastener loads, not a “far-field” stress. The influence of fastener loads may not be adequately captured by a stress fringe plot from the T-38 wing FEM. For example: A “high” load can exist at an end fastener (which would require static analysis) even though the “far-field” stress is below 15 ksi.

A.2 Non-Hole Details (Low Stress Criterion)

A formal analysis report of non-conforming non-hole details may not be required if the ultimate stress for the critical load case is less than 15 ksi (in the area of the non-conformance). A static strength positive margin by inspection is acceptable. The contractor should provide a screenshot of the ultimate stress for the critical load case from the T-38 FEM with the MRB documentation for USAF review.

Meeting the static low stress criterion (less than 15 ksi) does not guarantee USAF concurrence.

USAF reserves the right to require formal analysis upon review of a specific MRB disposition.

A.3 Durability Analysis (Low Stress Criterion)

For durability analysis, a formal analysis report may not be required if the scaled maximum spectrum stress for IFF usage is less than 7 ksi in the area of the non-conformance. The development of a stress scale factor (using the FEM fatigue load cases) shall be provided with the MRB documentation for USAF review.

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Meeting the durability low stress criterion (less than 7 ksi) does not guarantee USAF concurrence. USAF reserves the right to require formal analysis upon review of a specific MRB disposition.