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    ASTM D7249 / D7249M - 20

    Standard Test Method for Facesheet Properties of Sandwich Constructions by Long Beam Flexure

    Active Standard ASTM D7249 / D7249M | Developed by Subcommittee: D30.09

    Book of Standards Volume: 15.03

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    Significance and Use

    5.1 Flexure tests on flat sandwich construction may be conducted to determine the sandwich flexural stiffness, the core shear strength, and shear modulus, or the facesheets’ compressive and tensile strengths. Tests to evaluate core shear strength may also be used to evaluate core-to-facesheet bonds.

    5.2 This test method is limited to obtaining the strength and stiffness of the sandwich panel facesheets, and to obtaining load-deflection data for use in calculating sandwich beam flexural and shear stiffness using Practice D7250/D7250M. Due to the curvature of the flexural test specimen when loaded, facesheet compression strength from this test may not be equivalent to the facesheet compression strength of sandwich structures subjected to pure edgewise (in-plane) compression.

    5.3 Core shear strength and shear modulus are best determined in accordance with Test Method C273/C273M provided bare core material is available. Test Method C393/C393M may also be used to determine core shear strength. Practice D7250/D7250M may be used to calculate the flexural and shear stiffness of sandwich beams.

    5.4 This test method can be used to produce facesheet strength data for structural design allowables, material specifications, and research and development applications; it may also be used as a quality control test for bonded sandwich panels.

    5.5 Factors that influence the facesheet strength and shall therefore be reported include the following: facesheet material, core material, adhesive material, methods of material fabrication, facesheet stacking sequence and overall thickness, core geometry (cell size), core density, adhesive thickness, specimen geometry, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facesheet void content, adhesive void content, and facesheet volume percent reinforcement. Further, facesheet strength may be different between precured/bonded and co-cured facesheets of the same material.

    Note 2: Concentrated forces on beams with thin facesheets and low density cores can produce results that are difficult to interpret, especially close to the failure point. Wider loading blocks and rubber pressure pads may assist in distributing the forces.

    Note 3: To ensure that simple sandwich beam theory is valid, a good rule of thumb for the four-point bending test is the support span length divided by the sandwich thickness should be greater than 20 (S/d > 20) with the ratio of facesheet thickness to core thickness less than 0.1 (t/c < 0.1).

    1. Scope

    1.1 This test method covers determination of facesheet properties of flat sandwich constructions subjected to flexure in such a manner that the applied moments produce curvature of the sandwich facesheet planes and result in compressive and tensile forces in the facesheets. Permissible core material forms include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb).

    1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.

    1.2.1 Within the text, the inch-pound units are shown in brackets.

    1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

    Note 1: Alternate procedures for determining the compressive strength of unidirectional polymer matrix composites materials in a sandwich beam configuration may be found in Test Method D5467/D5467M.

    1.4 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.

    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    C273/C273M Test Method for Shear Properties of Sandwich Core Materials

    C393/C393M Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure

    D3410/D3410M Test Method for Compressive Properties of Polymer Matrix Composite Materials with Unsupported Gage Section by Shear Loading

    D3878 Terminology for Composite Materials

    D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials

    D5467/D5467M Test Method for Compressive Properties of Unidirectional Polymer Matrix Composite Materials Using a Sandwich Beam

    D7250/D7250M Practice for Determining Sandwich Beam Flexural and Shear Stiffness

    E4 Practices for Force Verification of Testing Machines

    E6 Terminology Relating to Methods of Mechanical Testing

    E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process

    E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

    E251 Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages

    E456 Terminology Relating to Quality and Statistics

    E1237 Guide for Installing Bonded Resistance Strain Gages

    ICS Code

    ICS Number Code 79.060.01 (Wood-based panels in general)

    UNSPSC Code

    UNSPSC Code

    Referencing This Standard
    Link Here
    Link to Active (This link will always route to the current Active version of the standard.)

    DOI: 10.1520/D7249_D7249M-20

    Citation Format

    ASTM D7249 / D7249M-20, Standard Test Method for Facesheet Properties of Sandwich Constructions by Long Beam Flexure, ASTM International, West Conshohocken, PA, 2020, www.astm.org

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