3.2Definitions of Terms Specific to This Standard:
3.2.1balanced laminate ,n —a continuous fiber-reinforced laminate in which each +u lamina,measured with respect to the laminate reference axis,is balanced by a –u lamina of the same material (for example,[0/+45/–45/+45/–45/0]).
3.2.2short-beam strength ,n —the shear stress as calculated in Eq 1,developed at the specimen mid-plane at the failure event specified in 11.6.
3.2.2.1Discussion —Although shear is the dominant applied loading in this test method,the internal stresses are complex and a variety of failure modes can occur.Elasticity solutions by Berg et al (1)7,Whitney (2),and Sullivan and Van Oene (3)have all demonstrated inadequacies in classical beam theory in defining the stress state in the short-beam configuration.These solutions show that the parabolic shear-stress distribution as predicted by Eq 1only occurs,and then not exactly,on planes midway between the loading nose and support points.Away from these planes,the stress distributions become skewed,with peak stresses occurring near the loading nose and support points.Of particular significance is the stress state local to the loading nose in which the severe shear-stress concentration combined with transverse and in-plane compressive stresses has been shown to initiate failure.However,for the more ductile matrices,plastic yielding may alleviate the situation under the loading nose (1)and allow other failure modes to occur such as bottom surface fiber tension (2).Conse
quently,unless mid-plane interlaminar failure has been clearly ob-served,the short-beam strength determined from this test method cannot be attributed to a shear property,and the use of Eq 1will not yield an accurate value for shear strength.
3.2.3symmetric laminate ,n —a continuous fiber-reinforced laminate in which each ply above the mid-plane is identically matched (in terms of position,orientation,and mechanical properties)with one below the mid-plane.
3.3Symbols :
b —specimen width.
CV —sample coefficient of variation (in percent).
F sbs —short-beam strength.
h —specimen thickness.
n —number of specimens.
P m —maximum load observed during the test.
x i —measured or derived property for an individual specimen from the sample population.
x ¯—sample mean (average).
4.Summary of Test Method
4.1The short-beam test specimens (Figs.1-4)are center-loaded as shown in Figs.5and 6.The specimen ends rest on two supports that allow lateral motion,the load being applied by means of a loading nose directly centered on the midpoint of the test specimen.
5.Significance and Use
5.1In most cases,because of the complexity of internal stresses and the variety of failure modes that can occur in this specimen,it is not generally possible to relate the short-beam strength to any one material property.However,failures are normally dominated by resin and interlaminar properties,and the test results have been found to be repeatable for a given specimen geometry,material system,and stacking sequence (4).5.2Short-beam strength determined by this test method can be used for quality control and process specification purposes.It can also be used for comparative testing of composite materials,provided that failures occur consistently in the same mode (5).5.3This test method is not limit
ed to specimens within the range specified in Section 8,but is limited to the use of a loading span length-to-specimen thickness ratio of 4.0and a minimum specimen thickness of 2.0mm [0.08in.].
6.Interferences 6.1Accurate reporting of observed failure modes is essen-tial for meaningful data interpretation,in particular,the detec-tion of initial damage modes.
7.Apparatus 7.1Testing Machine ,properly calibrated,which can be operated at a constant rate of crosshead motion,and which the error in the loading system shall not exceed 61%.The load-indicating mechanism shall be essentially free of inertia
7Boldface numbers in parentheses refer to the list of references at the end of this
standard.N OTE 1—Drawing interpretation per ANSI Y14.5-1982and ANSI/ASM B46.1-1986.N OTE 2—Ply orientation tolerance 60.5°relative to –B–.FIG.1Flat Specimen Configuration
(SI)
lag at the crosshead rate used.Inertia lag may not exceed 1%of the measured load.The accuracy of the testing machine shall be verified in accordance with Practices E 4.
7.2Loading Nose and Supports ,as shown in Figs.5and 6,shall be 6.00-mm (0.250-in.)and 3.00-mm (0.125-in.)diameter cylinders,respectively,with a hardness of 60to 62HRC,as specified in Test Methods E 18,and shall have finely ground surfaces free of indentation and burrs with all sharp edges relieved.
7.3Micrometers —For width and thickness measurements,the micrometers shall use a 4-to 5-mm (0.16-to 0.2-in.)nominal diameter ball interface on an irregular surface such as the bag side of a laminate and a flat anvil interface on machined edges or very smooth tooled surfaces.A micrometer or caliper with flat anvil faces shall be used to measure the length of the specimen.The accuracy of the instrument(s)shall be suitable for reading to within 1%of the sample dimensions.For typical section geometries,an instrument with an accuracy of 60.002mm (60.0001in.)is desirable for thickness and width mea-surement,while an instrument with an accuracy of 60.1mm (60.004in.)is adequate for length measurement.
7.4Conditioning Chamber ,when conditioning materials at nonlaboratory environments,a temperature/vapor-level-controlled environmental conditioning chamber is required that shall be capable of maintaining the required temperature to within 63°C (65°F)and the required vapor level to within 63%.Chamber conditions shall be monitored either on an automated continuous basis or on a manual basis at regular intervals.7.5Environmental Test Chamber ,an environmental test chamber is re
quired for test environments other than ambient testing laboratory conditions.This chamber shall be capable of maintaining the test specimen at the required test environment during the mechanical test method.8.Sampling and Test Specimens 8.1Sampling —Test at least five specimens per test condi-tion unless valid results can be gained through the use of fewer specimens,as in the case of a designed experiment.For statistically significant data,consult the procedures outlined in Practice E 122.Report the method of sampling.8.2Geometry :8.2.1Laminate Configurations —Both multidirectional and pure unidirectional laminates can be tested,provided that there are at least 10%0°fibers in the span direction of the beam (preferably well distributed through the thickness),and that the laminates are both balanced and symmetric with respect to the span direction of the beam.8.2.2Specimen Configurations —Typical configurations for the flat and curved specimens are shown in Figs.1-4.For specimen thicknesses other than those shown,the following geometries are recommended:Specimen length =thickness 36Specimen width,b =thickness 32.0N OTE 2—Analysis reported by Lewis and Adams (6)has shown that a width-to-thickness ratio of greater than 2.0can result in a significant width-wise shear-stress variation.8.2.2.1For curved beam specimens,it is recommended that the arc should not exceed 30°.Also,for these specimens,the specimen length is defined as the minimum chord length.8.3Specimen Preparation —Guide D 5687/D 5687M pro-vides recommended specimen preparation practices and should be followed where practical.8.3.1Laminate Fabrication —Laminates
editorially
may be hand-laid,filament-wound or tow-placed,and molded by any suitable laminating means,such as press,bag,autoclave,or resin transfer molding.8.3.2Machining Methods —Specimen preparation is impor-tant for these specimens.Take precautions when cutting specimens from the rings or plates to avoid notches,undercuts,rough or uneven surfaces,or delaminations as a result of inappropriate machining methods.Obtain final dimensions by water-lubricated precision sawing,milling,or grinding.The use of diamond tooling has been found to be extremely effective for many material systems.Edges should be flat and parallel within the specified tolerances.8.3.3Labeling —Label the specimens so that they will be distinct from each other and traceable back to the raw material,in a manner that will both be unaffected by the test method and not influence the test method.9.Calibration 9.1The accuracy of all measuring equipment shall have certified calibrations that are current at the time of use of the
equipment.
N OTE 1—Drawing interpretation per ANSI Y14.5-1982and ANSI/ASME B46.1-1986.
N OTE 2—Ply orientation tolerance 60.5°relative to –B–.
FIG.2Flat Specimen Configuration (Inch
Pound)
10.Conditioning
10.1Standard Conditioning Procedure —Unless a different environment is specified as part of the test method,condition the test specimens in accordance with Procedure C of Test Method D 5229/D 5229M,and store and test at standard laboratory atmosphere (2363°C (7365°F)and 50610%relative humidity).
11.Procedure
11.1Parameters to Be Specified Before Test :
11.1.1The specimen sampling method and coupon geom-etry.
11.1.2The material properties and data-reporting format desired.N OTE 3—Determine specific material property,accuracy,and data-reporting requirements before test for proper selection of instrumentation and data-recording equipment.Estimate operating stress levels to aid in calibration of equipment and determination of equipment settings.11.1.3The environmental conditioning test parameters.11.1.4If performed,the sampling test method,coupon geometry,and test parameters used to determine density and reinforcement volume.11.2General Instructions :11.2.1Report any deviations from this test method,whether intentional or inadvertent.11.2.2If specific gravity,density,reinforcement volume,or void volume are to be reported,then obtain these samples from the same panels as the test samples.Specific gravity
and
N OTE 1—Drawing interpretation per ANSI Y14.5-1982and ANSI/ASM B46.1-1986.N OTE 2—Ply orientation tolerance 60.5°relative to –A–.
FIG.3Curved Specimen Configuration
(SI)
density may be evaluated by means of Test Methods D 792.V olume percent of the constituents may be evaluated by one of the matrix digestion procedures of Test Method D 3171,or for certain reinforcement materials such as glass and ceramics,by the matrix burn-off technique of Test Method D 2584.V oid content may be evaluated from the equations of Test Method D 2734and are applicable to both Test Methods D 2584and D 3171.
11.2.3Condition the specimens as required.Store the speci-mens in the conditioned environment until test time,if the test environment is different from the conditioning environment.11.2.4Following final spe
cimen machining and any condi-tioning,but before testing,measure and record the specimen width and thickness at the specimen midsection and the
specimen length to the accuracy specified in 7.3.11.3Speed of Testing —Set the speed of testing at a rate of crosshead movement of 1.0mm (0.05in.)/min.11.4Test Environment —If possible,test the specimen under the same fluid exposure level as that used for conditioning.However,if the test temperature places too severe requirements upon the testing machine environmental chamber,test at a temperature with no fluid exposure control.In this case,a restriction must be placed upon the time from removal of the specimen from the conditioning chamber until test completion to inhibit nonrepresentative fluid loss from the specimen.Record any modifications to the test environment and specimen weight change after removal from conditioning until test completion.11.4.1Monitor the test temperature by placing an appropri-ate thermocouple at specimen mid-length to be located on
the N OTE 1—Drawing interpretation per ANSI Y14.5-1982and ANSI/ASME B46.1-1986.N OTE 2—Ply orientation tolerance 60.5°relative to –A–.
FIG.4Curved Specimen Configuration (Inch
Pound)

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