Designation:D695–02An American National Standard Standard Test Method for
Compressive Properties of Rigid Plastics1
This standard is issued under thefixed designation D695;the number immediately following the designation indicates the year of
original adoption or,in the ca of revision,the year of last revision.A number in parenthes indicates the year of last reapproval.A
superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
This standard has been approved for u by agencies of the Department of Defen.
1.Scope
1.1This test method covers the determination of the me-chanical properties of unreinforced and reinforced rigid plas-tics,including high-modulus composites,when loaded in compression at relatively low uniform rates of straining or loading.Test specimens of standard shape are employed.
1.2The values stated in SI units are to be regarded as the standard.The values in parenthes are for information only. N OTE1—For compressive properties of resin-matrix composites rein-forced with oriented continuous,discontinuous,or cross-ply reinforce-ments,tests may be made in accordance with Test Method D3410. 1.3This standard does not purport to address all of the safety concerns,if any,associated with its u.It is the responsibility of the ur of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to u.A specific precau-tionary statement is given in Note11.
N OTE2—This test method is technically equivalent to ISO604.
2.Referenced Documents
2.1ASTM Standards:
D618Practice for Conditioning Plastics for Testing2
D638Test Method for Tensile Properties of Plastics2
D3410Test Method for Compressive Properties of Poly-mer Matrix Composite Materials with Unsupported Gage Section by Shear Loading3
D4000Classification System for Specifying Plastic Mate-rials4
D4066Specification for Nylon Injection and Extrusion Materials4
E4Practices for Force Verification of Testing Machines5 E83Practice for Verification and Classification of Exten-someters5
E691Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method6
3.Terminology
3.1Definitions:
3.1.1compressive deformation—the decrea in length pro-duced in the gage length of the test specimen by a compressive load.It is expresd in units of length.
3.1.2compressive strain—the ratio of compressive defor-mation to the gage length of the test specimen,that is,the change in length per unit of original length along the longitu-dinal axis.It is expresd as a dimensionless ratio.
3.1.3compressive strength—the maximum compressive stress(nominal)carried by a test specimen during a compres-sion test.It may or may not be the compressive stress (nominal)carried by the specimen at the moment of rupture.
3.1.4compressive strength at failure(nominal)—the com-pressive stress(nominal)sustained at the moment of failure of the test specimen if shattering occurs.
3.1.5compressive stress(nominal)—the compressive load per unit area of minimum original cross ction within the gage boundaries,carried by the test specimen at any given moment. It is expresd in force per unit area.
3.1.5.1Discussion—The expression of compressive proper-ties in terms of the minimum original cros
s ction is almost universally ud.Under some circumstances the compressive properties have been expresd per unit of prevailing cross ction.The properties are called“true”compressive prop-erties.
3.1.6compressive stress-strain diagram—a diagram in which values of compressive stress are plotted as ordinates against corresponding values of compressive strain as abscis-sas.
3.1.7compressive yield point—thefirst point on the stress-strain diagram at which an increa in strain occurs without an increa in stress.
3.1.8compressive yield strength—normally the stress at the yield point(e also ction3.113.1.11).
3.1.9crushing load—the maximum compressive force ap-plied to the specimen,under the conditions of testing,that produces a designated degree of failure.
3.1.10modulus of elasticity—the ratio of stress(nominal)to
1This test method is under the jurisdiction of ASTM Committee D20on Plastics
and is the direct responsibility of Subcommittee D20.10on Mechanical Properties.
Current edition approved April10,2002.Published June2002.Originally
published as D695–42T.Last previous edition D695–96.
2Annual Book of ASTM Standards,V ol08.01.
3Annual Book of ASTM Standards,V ol15.03.
4Annual Book of ASTM Standards,V ol08.02.
5Annual Book of ASTM Standards,V ol03.01.
6Annual Book of ASTM Standards,V ol14.02.
1
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corresponding strain below the proportional limit of a material. It is expresd in force per unit area bad on the average initial cross-ctional area.
3.1.11offt compressive yield strength—the stress at which the stress-strain curve departs from linearity by a specified percent of deformation(offt).
3.1.12percent compressive strain—the compressive defor-mation of a test specimen expresd as a percent of the original gage length.
3.1.13proportional limit—the greatest stress that a material is capable of sustaining without any deviation from propor-tionality of stress to strain(Hooke’s law).It is expresd in force per unit area.
3.1.14slenderness ratio—the ratio of the length of a col-umn of uniform cross ction to its least radius of gyration.For specimens of uniform rectangular cross ction,the radius of gyration is0.289times the smaller cross-ctional dimension. For specimens of uniform circular cross ction,the radius of gyration is0.250times the diameter.
4.Significance and U
4.1Compression tests provide information about the com-pressive properties of plastics when employed under conditions approximating tho under which the tests are made.For many materials,there may be a specification that requires the u of this test method,but with some proced
ural modifications that take precedence when adhering to the specification.Therefore, it is advisable to refer to that material specification before using this test method.Table1in Classification D4000lists the ASTM materials standards that currently exist.
4.2Compressive properties include modulus of elasticity, yield stress,deformation beyond yield point,and compressive strength(unless the material merelyflattens but does not fracture).Materials posssing a low order of ductility may not exhibit a yield point.In the ca of a material that fails in compression by a shattering fracture,the compressive strength has a very definite value.In the ca of a material that does not fail in compression by a shattering fracture,the compressive strength is an arbitrary one depending upon the degree of distortion that is regarded as indicating complete failure of the material.Many plastic materials will continue to deform in compression until aflat disk is produced,the compressive stress(nominal)rising steadily in the process,without any well-defined fracture occurring.Compressive strength can have no real meaning in such cas.
4.3Compression tests provide a standard method of obtain-ing data for rearch and development,quality control,accep-tance or rejection under specifications,and special purpos. The tests cannot be considered significant for engineering design in applications differing widely from the load-time scale of the standard test.Such applications require additional tests such as impact,creep,
and fatigue.
4.4Before proceeding with this test method,reference should be made to the specification of the material being tested. Any test specimen preparation,conditioning,dimensions,and testing parameters covered in the materials specification shall take precedence over tho mentioned in this test method.If there is no material specification,then the default conditions apply.
5.Apparatus
5.1Testing Machine—Any suitable testing machine capable of control of constant-rate-of-crosshead movement and com-prising esntially the following:
5.1.1Drive Mechanism—A drive mechanism for imparting to the cross-head movable member,a uniform,controlled velocity with respect to the ba(fixed member),with this velocity to be regulated as specified in Section9.
5.1.2Load Indicator—A load-indicating mechanism ca-pable of showing the total compressive load carried by the test specimen.The mechanism shall be esntially free from inertia-lag at the specified rate of testing and shall indicate the load with an accuracy of61%of the maximum indicated value of t
he test(load).The accuracy of the testing machine shall be verified at least once a year in accordance with Practices E4.
5.2Compressometer—A suitable instrument for determin-ing the distance between twofixed points on the test specimen at any time during the test.It is desirable that this instrument automatically record this distance(or any change in it)as a function of the load on the test specimen.The instrument shall be esntially free of inertia-lag at the specified rate of loading and shall conform to the requirements for a Class B-2 extensometer as defined in Practice E83.
N OTE3—The requirements for extensometers cited herein apply to compressometers as well.
5.3Compression Tool—A compression tool for applying the load to the test specimen.This tool shall be so constructed that loading is axial within1:1000and applied through surfaces that areflat within0.025mm(0.001in.)and parallel to each other in a plane normal to the vertical loading axis.Examples of suitable compression tools are shown in Fig.1and Fig.2. 5.4Supporting Jig—A supporting jig for thin specimens is shown in Fig.3and Fig.4.
5.5Micrometers—Suitable micrometers,reading to0.01 mm or0.001in.for measuring the width,thickness,and length of the specimens.
6.Test Specimens
6.1Unless otherwi specified in the materials specifica-tions,the specimens described in6.2and6.7shall be ud. The specimens may be prepared by machining operations from materials in sheet,plate,rod,tube,or similar form,or they may be prepared by compression or injection molding of the material to be tested.All machining operations shall be done carefully so that smooth surfaces result.Great care shall be taken in machining the ends so that smooth,flat parallel surfaces and sharp,clean edges,to within0.025mm(0.001in.) perpendicular to the long axis of the specimen,result.
6.2The standard test specimen,except as indicated in 6.3-6.7,shall be in the form of a right cylinder or prism who length is twice its principal width or diameter.Preferred specimen sizes are12.7by12.7by25.4mm(0.50by0.50by 1in.)(prism),or12.7mm in diameter by25.4mm(cylinder). Where elastic modulus and offt yield-stress data are desired, the test specimen shall be of such dimensions that the slender-ness ratio is in the range from11to16:1.In this ca,preferred specimen sizes are12.7by12.7by50.8mm(0.50by0.50
by
2in.)(prism),or 12.7mm in diameter by 50.8mm (cylinder).6.3For rod material,the test specimen shall have a diameter equal to the diameter of the rod and a sufficient length to allow a specimen slenderness ratio in the range from 11to 16:1.6.4When testing tubes,the test specimen shall have a diameter equal to the diameter of the tube and a length of 25.4mm (1in.)(Note 4).For crushing-load determinations (at right angles to the longitudinal axis),the specimen size shall be the same,with the diameter becoming the height.
N OTE 4—This specimen can be ud for tubes with a wall thickness of
1mm (0.039in.)or over,to inside diameters of 6.4mm (0.25in.)or over,and to outside diameters of 50.8mm (2.0in.)or less.
6.5Where it is desired to test conventional high-pressure laminates in the form of sheets,the thickness of which is less than 25.4mm (1in.),a pile-up of sheets 25.4mm square,with a sufficient number of layers to produce a height of at least 25.4mm,may be ud.
6.6When testing material that may be suspected of anisot-ropy,duplicate ts of test specimens shall
be prepared having their long axis respectively parallel with and normal to the suspected direction of anisotropy.
6.7Reinforced Plastics,Including High-Strength Compos-ites and High-Strength Composites and Highly Orthotropic Laminates —The following specimens shall be ud for rein-forced materials,or for other materials when necessary to comply with the slenderness ratio requirements or to permit attachment of a deformation-measuring device.
6.7.1For materials 3.2mm (1⁄8in.)and over in thickness,a specimen shall consist of a prism having a cross ction of 12.7mm (1⁄2in.)by the thickness of the material and a length such that the slenderness ratio is in the range from 11to 16:1(Note 5).
6.7.2For materials under 3.2mm (1⁄8in.)thick,or where elastic modulus testing is required and the slenderness ratio does not provide for enough length for attachment of a compressometer or similar device,a specimen conforming to that shown in Fig.5shall be ud.The supporting jig shown in Fig.3and Fig.4shall be ud to support the specimen during testing (Note 6).
N OTE 5—If failure for materials in the thickness range of 3.2mm (1⁄8in.)is by delamination rather than by the desirable shear plane fracture,the material may be tested in accordance with 6.7.2.
N OTE 6—Round-robin tests have established that relatively satisfactory measurements of modulus of elasticity may be obtained by applying a compressometer to the edges of the jig-supported specimen.
6.8When testing syntactic foam,the standard test specimen shall be in the form of a right cylinder 25.4mm (1in.)in diameter by 50.8mm (2in.)in length.
7.Conditioning
7.1Conditioning —Condition the test specimens at 2362°C (73.463.6°F)and 5065%relative humidity for not less than 40h prior to test in accordance with Procedure A
of
N OTE 1—Devices similar to the one illustrated have been successfully ud in a number of different laboratories.Details of the device developed at the National Institute for Standards and Technology are given in the paper by Aitchinson,C.S.,and Miller,J.A.,“A Subpress for Compressive Tests,”National Advisory Committee for Aeronautics,Technical Note No.912,1943.
FIG.1Subpress for Compression
Tests
FIG.2Compression
Tool
FIG.3Support Jig for This
Specimen
Practice D 618unless otherwi specified by contract or the relevant ASTM material specification.Reference pre-test con-ditioning,to ttle disagreements,shall apply tolerances of 61°C (1.8°F)and 62%relative humidity.
7.2Test Conditions —Conduct the tests at 2362°C (73.463.6°F)and 5065%relative humidity unless otherwi specified by contract or the relevant ASTM material specifica-tion.Reference testing conditions,to ttle disagreements,shall apply tolerances of 61°C (1.8°F)and 62%relative humidity.
8.Number of Test Specimens
8.1At least five specimens shall be tested for each sample in the ca of isotropic materials.
8.2Ten specimens,five normal to and five parallel with the principal axis of anisotropy,shall be tested for each sample in the ca of anisotropic materials.
8.3Specimens that break at some obvious fortuitous flow shall be discarded and retests made,unless such flaws consti-tute a variable,the effect of which it is desired to study.
9.Speed of Testing
9.1Speed of testing shall be the relative rate of motion of the grips or test fixtures during the test.Rate of motion of the driven grip or fixture when the machine is running idle may be ud if it can be shown that the resulting speed of testing is within the limits of variation allowed.
9.2The standard speed of testing shall be 1.360.3mm (0.05060.010in.)/min,except as noted in 10.5.4.
10.Procedure
10.1Measure the width and thickness of the specimen to the nearest 0.01mm (0.001in.)at veral points along its length.Calculate and record the minimum value of the cross-ctional area.Measure the length of the specimen and record the value.10.2Place the test specimen between the surfaces of the compression tool,taking care to align the center line of its long axis with the center line of the plunger and to ensure that the ends of the specimen are parallel with the surface of the compression tool.Adjust the crosshead of the testing machine until it just contacts the top of the compression tool
plunger.
N OTE 1—Cold rolled steel.
N OTE 2—Furnished four steel machine screws and nuts,round head,slotted,length 31.75mm (11⁄4in.).N OTE 3—Grind surfaces denoted “Gr.”
FIG.4Support Jig,
Details
FIG.5Compression Test Specimen for Materials Less than 3.2mm
Thick
N OTE7—The compression tool may not be necessary for testing of lower modulus(for example,100000to500000psi)material if the loading surfaces are maintained smooth,flat,and parallel to the extent that buckling is not incurred.
10.3Place thin specimens in the jig(Fig.3and Fig.4)so that they areflush with the ba and centered(Note8).The nuts or screws on the jig shall befinger tight(Note9).Place the asmbly in the compression tool as described in5.3.
N OTE8—A round-robin test,designed to asss the influence of specimen positioning in the support
ing jig(that is,flush versus centered mounting),showed no significant effect on compressive strength due to this variable.However,flush mounting of the specimen with the ba of the jig is specified for convenience and ea of mounting.7
N OTE9—A round-robin test on the effect of lateral pressure at the supporting jig has established that reproducible data can be obtained with the tightness of the jig controlled as indicated.
10.4If only compressive strength or compressive yield strength,or both,are desired,proceed as follows:
10.4.1Set the speed control at1.3mm/min(0.050in./min) and start the machine.
10.4.2Record the maximum load carried by the specimen during the test(usually this will be the load at the moment of rupture).
10.5If stress-strain data are desired,proceed as follows: 10.5.1Attach compressometer.
10.5.2Set the speed control at1.3mm/min(0.050in./min) and start the machine.
10.5.3Record loads and corresponding compressive strain at appropriate intervals of strain or,if the t
est machine is equipped with an automatic recording device,record the complete load-deformation curve.
10.5.4After the yield point has been reached,it may be desirable to increa the speed from5to6mm/min(0.20to 0.25in./min)and allow the machine to run at this speed until the specimen breaks.This may be done only with relatively ductile materials and on a machine with a weighing system with respon rapid enough to produce accurate results. 11.Calculation
11.1Compressive Strength—Calculate the compressive strength by dividing the maximum compressive load carried by the specimen during the test by the original minimum cross-ctional area of the specimen.Express the result in megapas-cals or pounds-force per square inch and report to three significantfigures.
11.2Compressive Yield Strength—Calculate the compres-sive yield strength by dividing the load carried by the specimen at the yield point by the original minimum cross-ctional area of the specimen.Express the result in megapascals or pounds-force per square inch and report to three significantfigures.
11.3Offt Yield Strength—Calculate the offt yield strength by the method referred to in3.1.11.
11.4Modulus of Elasticity—Calculate the modulus of elas-ticity by drawing a tangent to the initial linear portion of the load deformation curve,lecting any point on this straight line portion,and dividing the compressive stress reprented by this point by the corresponding strain,measure from the point where the extended tangent line intercts the strain-axis. Express the result in gigapascals or pounds-force per square inch and report to three significantfigures(e Annex A1).
11.5For each ries of tests,calculate to three significant figures the arithmetic mean of all values obtained and report as the“average value”for the particular property in question. 11.6Calculate the standard deviation(estimated)as follows and report to two significantfigures:
s5=~(X22nX¯2!/~n21!(1) where:
s=estimated standard deviation,
X=value of single obrvation,
n=number of obrvations,and
X¯=arithmetic mean of the t of obrvations.
N OTE10—The method for determining the offt compressive yield strength is similar to that described in the Annex of Test Method D638.
12.Report
12.1Report the following information:
12.1.1Complete identification of the material tested,includ-ing type,source,manufacturer’s code number,form,principal dimensions,previous history,etc.,
12.1.2Method of preparing test specimens,
12.1.3Type of test specimen and dimensions,
12.1.4Conditioning procedure ud,
12.1.5Atmospheric conditions in test room,
12.1.6Number of specimens tested,
12.1.7Speed of testing,
12.1.8Compressive strength,average value,and standard deviation,
12.1.9Compressive yield strength and offt yield strength average value,and standard deviation,when of interest, 12.1.10Modulus of elasticity in compression(if required), average value,standard deviation,
12.1.11Date of test,and
12.1.12Date of test method.
13.Precision and Bias8
13.1Table1and Table2are bad on a round-robin test conducted in1987in accordance with Practice E691,involv-ing three materials tested by six laboratories for Test Method D695M.Since the test parameters overlap within tolerances and the test values are normalized,the same data are ud for both test methods.For each material,all of the samples were prepared at one source.Each test result was the average offive individual determinations.Each laboratory obtained two test results for each material.
N OTE11—Caution:The following explanations of r and R(13.2-13.2.3)are only intended to prent a
meaningful way of considering the approximate precision of this test method.The data in Table1and Table 2should not be rigorously applied to acceptance or rejection of material, as tho data are specific to the round robin and may not be reprentative
7Supporting data are available from ASTM Headquarters.Request RR:D20-1061.8Supporting data are available from ASTM Headquarters,Request RR:D20-
1150.
