ASTM F3601-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F3601 − 23
Standard Practice for
Structural Finite Element Model Verification and Validation
This standard is issued under the fixed designation F3601; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice provides guidance for verification and
responsibility of the user of this standard to establish appro-
validation of structural finite element models (FEMs) that are
priate safety, health, and environmental practices and deter-
used to support showings of compliance with Civil Aviation
mine the applicability of regulatory limitations prior to use.
Authority (CAA) regulations. This encompasses FEM predic-
1.7 This international standard was developed in accor-
tions of internal loads, displacements, strains, stresses,
dance with internationally recognized principles on standard-
stability, and post-buckling loads.
ization established in the Decision on Principles for the
1.2 This practice applies to normal category aeroplanes with
Development of International Standards, Guides and Recom-
a certified maximum take-off weight of 19 000 lb (8618 kg) or
mendations issued by the World Trade Organization Technical
less and a passenger seating configuration of up to 19. Use of
Barriers to Trade (TBT) Committee.
the term aircraft throughout this specification is intended to
allow the relevant CAA(s) to accept this practice as a means of 2. Referenced Documents
compliance for other aircraft as they determine appropriate.
2.1 ASTM Standards:
1.3 Code verification for FEM software is not included in F3060 Terminology for Aircraft
the scope of this practice. It is expected, however, that the F3114 Specification for Structures
developer of software that is used to support showings of 2.2 Federal Standard:
14 CFR Part 23 Airworthiness Standards: Normal, Utility,
compliance has applied appropriate software quality assurance
and numerical algorithm verification processes, including Acrobatic, and Commuter Category Airplanes
benchmark cases, to verify the accuracy and consistency of the
3. Terminology
solutions. Evidence of these activities should be recorded and
documented and made available to the applicant and CAA
3.1 Definitions— The following definitions are a selection
upon request. of relevant terms. See Terminology F3060 for more definitions
and abbreviations.
1.4 The applicant for a design approval should verify CAA
3.1.1 external loads, n—loads, external from the structure or
acceptance of this practice before using it to support showings
what is being modeled, that are applied to the structure or finite
of compliance. For information on which CAA regulatory
element model (FEM) as a real-life event or part of a load
bodies have accepted this practice (in whole or in part) as a
condition (see 3.1.6).
means of compliance to airworthiness standards: normal cat-
3.1.2 finite element model, FEM, n—mathematical approxi-
egory aeroplanes (hereinafter referred to as “the Rules”), refer
mate representation of a real structure.
to the ASTM F44 webpage (www.ASTM.org/COMMITTEE/
3.1.2.1 Discussion—The structural stiffness of the part or
F44.htm), which includes CAA website links.
parts are represented as an equivalent stiffness matrix. A
1.5 The values stated in inch-pound units are to be regarded
numerical solution is performed on the FEM to determine
as standard. The values given in parentheses are mathematical
output given imposed loads, displacements, and boundary
conversions to SI units that are provided for information only
conditions.
and are not considered standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This practice is under the jurisdiction of ASTM Committee F44 on General contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Aviation Aircraft and is the direct responsibility of Subcommittee F44.30 on Standards volume information, refer to the standard’s Document Summary page on
Structures. the ASTM website.
Current edition approved March 1, 2023. Published April 2023. DOI: 10.1520/ Available from Federal Aviation Administration (FAA), 800 Independence
F3601-23. Ave., SW, Washington, DC 20591, http://www.faa.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F3601 − 23
3.1.3 finite element model (FEM) validation, n—task of verification checks for any variations of the FEM (including
demonstrating that the FEM predicted internal loads or defor- variations to match validation testing). Include the following
mations or both match or conservatively predict the real information and/or other applicable information:
structure internal loads or deformations or both as measured in 6.2.1 Listing of type design data (including materials) to
a test article or as predicted by other analytical means within an which the FEM conforms along with discussion of simplifica-
acceptable range of accuracy. tions or other deviations of the FEM from the type design data;
6.2.2 Listing of material data sources used in the FEM
3.1.4 finite element model (FEM) verification, n—task of
[Materials Properties Development and Standardization
demonstrating that the FEM represents the engineering defined
(MMPDS) Handbook-10, company tests, and so forth];
structure that is being analyzed to the degree necessary to
6.2.3 Figure(s) of overall FEM;
obtain the desired results.
6.2.4 Figure(s) of loads and constraints, including rigid
3.1.4.1 Discussion—This includes ensuring the FEM solver
elements, with descriptions;
does not produce errors based on the input. The errors could be
6.2.5 Listing(s) of materials and properties;
computer “run errors” or errors from improper or incorrect
6.2.6 Figure(s) of fastened joint representations;
modeling. The input includes all items defined by the user, such
6.2.7 Figure(s) of overall deformation for critical load
as the node and element definitions, material properties, loads,
conditions;
boundary conditions, and so forth. The verification should
6.2.8 Figure(s) of buckling mode shapes for critical load
include any variations of the FEM (including variations to
conditions;
match validation testing).
6.2.9 Figure(s) of post-buckling deformation for critical
3.1.5 internal loads, n—loads (forces and moments), inter-
load conditions;
nal to a structural element regardless whether that element is a
6.2.10 Figure(s) of stresses, strains, deformations, and/or
part of the FEM or the real structure.
internal loads for critical load conditions; and
3.1.5.1 Discussion—This is terminology commonly used by
6.2.11 Checklist(s) of pre- and post-processing checks listed
a stress analyst to distinguish from external loads (such as
in 6.3 and 6.4.
aerodynamic pressures, actuation loads, temperatures, and so
forth). 6.3 Preprocessing Checks—Complete the following checks
and/or other applicable checks before running a FEM.
3.1.6 load condition, n—set of external loads (forces,
6.3.1 All nodes are correctly located.
moments, pressures, temperatures, and so forth) applied to a
6.3.2 No nodes are free.
FEM or real structure to simulate a real-life event, for example,
6.3.3 No nodes are coincident with other nodes (unless
a vertical gust or maneuver.
intentional).
4. Significance and Use
6.3.4 All elements are connected to correct nodes.
6.3.5 All elements are of acceptable sizes, types, and
4.1 This practice provides guidance for verification and
validation of structural FEMs that are used to support showings quality.
of compliance with CAA regulations. 6.3.6 All elements have correct offsets.
6.3.7 All elements have correct and consistent normals, or
4.2 This practice is a companion to Specification F3114.
orientations, or both.
5. General
6.3.8 All elements have correct first-edge directions.
6.3.9 All elements have correct material directions.
5.1 Experience has shown the finite element technique, in a
6.3.10 All elements have correct properties (matching as-
general sense, to be a reliable method of internal loads analysis
tested values or design values as appropriate).
for aircraft structures.
6.3.11 No elements are coincident with other elements
5.2 Experience has also shown that each specific FEM
(unless intentional).
should be sufficiently verified and validated to ensure that the
6.3.12 All multipoint constraints (rigid elements) have cor-
results obtained from it are within acceptable accuracy for use
rect degrees of freedom.
in showings of compliance.
6.3.13 No multipoint constraints (rigid elements) are the
5.3 Before using a FEM to support a showing of compliance
sole connection to a node unless it is a load application node.
with CAA regulations, complete the verification checks in
6.3.14 All properties have correct materials.
Section 6 and the validation checks in Section 7.
6.3.15 All properties have correct material directions.
6.3.16 All properties have correct dimensions (thickness, I1,
6. Verification
I2, and so forth).
6.1 Perform verification checks before using a FEM to
6.3.17 All laminate properties have correct materials, stack-
support a showing of compliance with CAA regulations. The
ing sequence, orientations, thicknesses, and interlaminar values
verification process outlined in 6.2 – 6.4 serves as a baseline
or have correct layups (if used).
for a linear static solution and should be adjusted, as
applicable, depending on the type and complexity of the FEM
and its intended use.
Metallic Materials Properties Development and Standardization (MMPDS)
6.2 Document Verification Checks—Document verification
Handbook-10, available from SAE International, https://www.sae.org/publications/
checks in the applicable compliance document(s). Include books/content/b-980/.
F3601 − 23
6.3.18 All layups (if used) have correct materials, stacking 7.2.6 Figure(s) and table(s) of strain and deformation results
sequence, orientations, thicknesses, and interlaminar values. and correlation,
6.3.19 All materials have correct stiffness values.
7.2.7 Figure(s) and table(s) of buckling load results and
6.3.20 All part connections (such as fasteners) are correctly
correlation, and
modeled (with proper transverse, axial, and bending
7.2.8 Justifications for correlation exceedances that are
stiffnesses, and continuities across layers, as applicable).
deemed acceptable (see 7.5).
6.3.21 All load location
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