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Nondestructive Evaluation: USAF Perspectives on mapod. ... 1 Nondestructive Evaluation: USAF Perspectives on POD, Imaging, and Characterization Eric Lindgren Materials and Manufacturing

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  • 1

    Nondestructive Evaluation:

    USAF Perspectives on POD, Imaging,

    and Characterization

    E r i c L i n d g r e n

    M a t e r i a l s a n d M a n u f a c t u r i n g D i r e c t o r a t e , A i r F o r c e R e s e a r c h L a b o r a t o r y

    J u l y 1 3 , 2 0 1 9

    Distribution A, Unlimited Release. Case Number 88ABW-2019-3348

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    Outline

    • USAF Relevance

    • POD Refresher • MIL HDBK 1823A

    • Assumptions

    • Method (Math)

    • USAF Standardization • Why / How

    • Image based NDI • Implementation

    • POD Validation

    • Characterization • Background

    • Approach / Status

    • MAPOD

    • Summary

    Photograph by author

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    US Air Force Relevance

    • Nondestructive Inspection / Evaluation (NDI / NDE)

    key input to risk management in USAF

    • Aircraft Structural Integrity Program (ASIP)

    • Propulsion Systems Integrity Program (PSIP)

    • NDI / NDE used for new materials qualification

    • Polymer matrix composites: 100% inspection

    • Additive Manufacturing for critical parts

    • Probability of Detection (POD): capability validation

    • Facilitate with model-assisted POD (MAPOD)

    • Image-based NDE / NDI methods in use

    • Desired state: flaw / material characterization

    • Augments value of data from NDE

    • Accelerates decisions based on NDE

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    Example: USAF Approach for ASIP (MIL STD 1530Dc1)

    • First flight to 1950s: design to static strength • Wright brothers

    • Worked with finite use

    • 1950s: fatigue in metals leads to safe life • DeHavilland Comet

    • B-47 Stratofortress

    • 1970s: flaws at manufacturing leads to durability and damage tolerance

    • F-111

    • F-5

    • Commercial aviation uses variant of DADT

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    Durability and Damage Tolerance (DADT)

    • Tolerate defects for some inspection-free period of service usage:

    slow damage growth is USAF ASIP preferred approach

    • NDE at critical locations based on DADT analysis to protect safety

    How do we assess this value?

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    POD: A Key Factor in Risk Calculation

    *www.afgrow.net

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    POD Refresher

    Photograph by Author Distribution A, Unlimited Release. Case Number 88ABW-2019-3348

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    POD Introduction

    Probability of Detection:

    • Testing/evaluation procedures for assessing NDI capability

    • Validation of NDI procedure when performed as intended

    • Human factors affecting procedure

    • Not human factors affecting inspector

    • Objective: determine largest flaw missed during inspection

    • Capability study, not a sensitivity study

    • Improved sensitivity does not necessarily improve POD

    • Statistics to determine value

    • Must meet assumptions of math to be valid

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    MIL HDBK 1823A

    • Current title “NDE System

    Reliability Assessment”

    • Personal perspective: “system

    reliability” should be replaced by

    “procedure validation”

    • Provide guidance:

    • How to set up a POD Study

    • How to analyze the data

    • Assumptions that MUST be met

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    Design of the experiment

    • Includes all factors affecting detection

    • Measurement system

    • Probes, electrical noise, calibration

    procedure, and many more

    • Structure being assessed

    • Variance: manufacturing, maintenance,

    repair, modification, and use

    • Defect being detected

    • Geometry, morphology, and many more

    Attributes of the data

    • Independent samples

    • Response increases with flaw size

    • Linear models apply

    • Noise is normal

    • Constant variance

    If data is binary, use hit/miss analysis

    • Outcome: Probability that flaw of size

    “x” will be called by inspector

    Factors and Assumptions for Valid POD

    ≠ Find damage here Sensors

    Notch Plate

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    The Nature of Data

    𝜀 is a NORMAL

    random

    variable

    (noise)

    Parameters are

    ESTIMATED,

    not calculated

    Ideal Data

    Real POD

    Curve

    Ideal POD

    Curve

    Real Data

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    Confidence Bounds (Complex Math for Engineers)

    Requires:

    • Large data set

    • Symmetric

    distribution

    Determines:

    • Variance

    • Standard Normal

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    POD: Cautions

    Remember assumptions:

    • Independent samples

    • Response increases with flaw size

    • Linear models apply

    • Noise is normal

    • Constant variance

    Must have suitable data set to meet assumptions

    Size

    R e s p o n s e

    POD

    POD values can be calculated even if assumptions are

    NOT met, but these values are wrong Distribution A, Unlimited Release. Case Number 88ABW-2019-3348

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    Additional Challenges for SHM POD

    USAF definition: SHM is “a nondestructive inspection process or

    technique that uses in-situ sensing devices to detect damage”

    • Environment

    • Temperature, loads, etc.

    • Time variance in performance

    • Includes durability

    • Validation of Capability*

    • Required for ASIP driven applications

    • Qualification

    • Initial documents available**

    *Lindgren, et.al., “Demonstrating Capability Validation Protocol for in-situ Damage Detection,” presented at the 2011 ASIP Conference, San Antonio, TX

    **Brausch and Steffes, “Demonstration, Qualification, and Airworthiness Certification of Structural Damage Sensing (SDS) Systems for

    Air Force Applications, ” AFRL-RX-WP-TM-2013-0062

    Installation:

    • Qualification / certification

    • Training

    • Human factors

    Sustainment:

    • Training

    • Maintenance / Calibration

    • Durability

    • Repair / modification

    • Technical orders

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    Reminder: How USAF Uses POD for ASIP

    When to Inspect

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    Calculation of Risk

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    USAF Standardization

    Photograph by Author Distribution A, Unlimited Release. Case Number 88ABW-2019-3348

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    Need for Standardized Capability

    When critical to ensuring safety (i.e. risk)

    USAF structures challenge:

    • Large number of aircraft

    • High mobility of inspectors

    • Increased inspection requirements with aging fleet

    • Possible variance in capability as a function of weapon system

    USAF Solution:

    • Structures Bulletin EN-SB-08-012 • Baseline common procedures/equipment

    • Assumed capability for general classes of structural geometric features

    Inventory: 1017*

    *http://www.af.mil/AboutUs/FactSheets.aspx

    Inventory: 428*

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    Foundation of EN-SB-08-012

    Best Practices common inspection methods using standardized equipment

    • See "Recommended Processes and Best Practices for NDI of Safety-of-

    Flight Structures", AFRL-RX-WP-TR-2008-4373

    • Includes inspection implementation and capability estimation

    • Detection capability quantified for most standard practices

    • Part specific procedures reference appropriate standard practice

    Applicability

    • Detection capability assumptions based on standard equipment, training,

    and procedures across USAF programs

    • Not applicable for specialized equipment or procedures: they should have separate

    validation

    • Supersedes Table XXXII of JSSG 2006: Joint Services Specification Guide –

    Aircraft Structures

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    Content of EN-SB-08-012

    • Introduction

    • Members of USAF Capability Task Group

    • Description of assumptions in training, procedures, and

    assessments made in determining the capability values

    • Additional steps to be followed if alternative values of capability

    for specific inspections

    • Descriptio

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