ASTM_D_7956_-_D_7956M_-_16.pdf

Designation:D7956/D7956M16Standard Practice forCompressive Testing of Thin Damaged Laminates Using aSandwich Long Beam Flexure Specimen1This standard is issued under the fixed designation D7956/D7956M;the number immediately following the designation indicates theyear of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of lastreapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers an approach for compressive test-ing thin damaged multidirectional polymer matrix compositelaminates reinforced by high-modulus fibers using a sandwichlong beam flexure specimen.It provides a test configuration inwhich the core does not constrain any protruding back sidedamage.It is limited to testing of monolithic solid laminateswhich are too thin to be tested using typical anti-bucklingfixtures.It does not cover compressive testing of damagedsandwich panel facings.The composite material forms arelimited to continuous-fiber or discontinuous-fiber(tape orfabric,or both)reinforced composites in which the laminate isbalanced and symmetric with respect to the test direction1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard.The values stated ineach system may not be exact equivalents;therefore,eachsystem shall be used independently of the other.Combiningvalues from the two systems may result in non-conformancewith the standard.1.2.1 Within the text the inch-pound units are shown inbrackets.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD3878 Terminology for Composite MaterialsD3410 Test Method for Compressive Properties of PolymerMatrix Composite Materials with Unsupported Gage Sec-tion by Shear LoadingD6264/D6264M Test Method for Measuring the DamageResistance of a Fiber-Reinforced Polymer-Matrix Com-posite to a Concentrated Quasi-Static Indentation ForceD7136/D7136M Test Method for Measuring the DamageResistance of a Fiber-Reinforced Polymer Matrix Com-posite to a Drop-Weight Impact EventD7137/D7137M Test Method for Compressive ResidualStrength Properties of Damaged Polymer Matrix Compos-ite PlatesD7249/D7249M Test Method for Facing Properties of Sand-wich Constructions by Long Beam FlexureE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate,WithSpecified Precision,the Average for a Characteristic of aLot or ProcessE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE456 Terminology Relating to Quality and Statistics3.Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites,as well as termsrelating to sandwich constructions.Terminology D883 definesterms relating to plastics.Terminology E6 defines termsrelating to mechanical testing.Terminology E456 and PracticeE177 define terms relating to statistics.In the event of aconflict between terms,Terminology D3878 shall have prece-dence over the other terminologies.4.Summary of Practice4.1 This practice consists of fabricating a compositelaminate,damaging the laminate using either Test MethodD6264/D6264M or Test Method D7136/D7136M,bonding theimpacted or indented side of the laminate onto core and a backside facing to form a sandwich panel,and testing the damagedlaminate in compression using Test Method D7249/D7249M.5.Significance and Use5.1 This practice provides a standard method of testingdamaged composite laminates which are too thin to be tested1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved Sept.1,2016.Published September 2016.Originallyapproved in 2014.Last previous edition approved in 2014 as-14.DOI:10.1520/D7956_D7956M-16.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 using typical anti-buckling fixtures,such as those used in TestMethod D7137/D7137M.The laminate is first impacted orindented in order to produce a damage state representative ofactual monolithic solid laminate structure.Impacting or staticindentation is not performed on an assembled sandwich panel,as the damage state is altered by energy absorption in the coreand by support of the core during the impact or indentationevent.After damaging,the laminate is bond