ASTM D7248/D7248M-12(2017)
(Test Method)Standard Test Method for Bearing/Bypass Interaction Response of Polymer Matrix Composite Laminates Using 2-Fastener Specimens
Standard Test Method for Bearing/Bypass Interaction Response of Polymer Matrix Composite Laminates Using 2-Fastener Specimens
SIGNIFICANCE AND USE
5.1 This test method is designed to produce bearing/bypass interaction response data for research and development, and for structural design and analysis. The standard configuration for each procedure is very specific and is intended as a baseline configuration for developing structural design data.
5.1.1 Procedure A, the bypass/high bearing double-shear configuration is recommended for developing data for specific applications which involve double shear joints.
5.1.2 Procedure B, the bypass/high bearing single-shear configuration is more useful in the evaluation of typical joint configurations. The specimen may be tested in either an unstabilized (no support fixture) or stabilized configuration. The unstabilized configuration is intended for tensile loading and the stabilized configuration is intended for compressive loading. These configurations, particularly the stabilized configuration, have been extensively used in the development of design allowables data. The variants of either procedure provide flexibility in the conduct of the test, allowing adaptation of the test setup to a specific application. However, the flexibility of test parameters allowed by the variants makes meaningful comparison between datasets difficult if the datasets were not tested using identical test parameters.
5.1.3 Procedure C, the bypass/low bearing double-shear hardpoint configuration is recommended for determining the effect of low bearing stress levels on bypass strength. While a similar single-shear configuration could be tested, there is insufficient experience with a single-shear configuration to recommend its use at this time.
5.2 General factors that influence the mechanical response of composite laminates and should therefore be reported include the following: material, methods of material preparation and lay-up, specimen stacking sequence, specimen preparation, specimen conditioning, environment of testing, specimen alignment and gripping, speed of testing, ti...
SCOPE
1.1 This test method determines the uniaxial bearing/bypass interaction response of multi-directional polymer matrix composite laminates reinforced by high-modulus fibers by either double-shear tensile loading (Procedures A and C) or single-shear tensile or compressive loading (Procedure B) of a two-fastener specimen. The scope of this test method is limited to net section (bypass) failure modes. Standard specimen configurations using fixed values of test parameters are described for each procedure. A number of test parameters may be varied within the scope of the standard, provided that the parameters are fully documented in the test report. The composite material forms are limited to continuous-fiber or discontinuous-fiber (tape or fabric, or both) reinforced composites for which the laminate is balanced and symmetric with respect to the test direction. The range of acceptable test laminates and thicknesses are described in 8.2.1.
1.2 This test method is consistent with the recommendations of MIL-HDBK-17, which describes the desirable attributes of a bearing/bypass interaction response test method.
1.3 The two-fastener test configurations described in this test method are similar to those in Test Method D5961/D5961M as well as those used by industry to investigate the bearing portion of the bearing/bypass interaction response for bolted joints, where the specimen may produce either a bearing failure mode or a bypass failure mode. Should the test specimen fail in a bearing failure mode rather than the desired bypass mode, then the test should be considered to be a bearing dominated bearing/bypass test, and the data reduction and reporting procedures of Test Method D5961/D5961M should be used instead of those given in this standard.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each...
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Designation: D7248/D7248M − 12 (Reapproved 2017)
Standard Test Method for
Bearing/Bypass Interaction Response of Polymer Matrix
Composite Laminates Using 2-Fastener Specimens
This standard is issued under the fixed designation D7248/D7248M; 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 system shall be used independently of the other. Combining
values from the two systems may result in non-conformance
1.1 Thistestmethoddeterminestheuniaxialbearing/bypass
with the standard.
interaction response of multi-directional polymer matrix com-
1.4.1 Within the text the inch-pound units are shown in
posite laminates reinforced by high-modulus fibers by either
brackets.
double-shear tensile loading (Procedures A and C) or single-
1.5 This standard does not purport to address all of the
shear tensile or compressive loading (Procedure B) of a
safety concerns, if any, associated with its use. It is the
two-fastenerspecimen.Thescopeofthistestmethodislimited
responsibility of the user of this standard to establish appro-
to net section (bypass) failure modes. Standard specimen
priate safety and health practices and determine the applica-
configurations using fixed values of test parameters are de-
bility of regulatory limitations prior to use.
scribed for each procedure. A number of test parameters may
1.6 This international standard was developed in accor-
be varied within the scope of the standard, provided that the
dance with internationally recognized principles on standard-
parameters are fully documented in the test report. The
ization established in the Decision on Principles for the
composite material forms are limited to continuous-fiber or
Development of International Standards, Guides and Recom-
discontinuous-fiber (tape or fabric, or both) reinforced com-
mendations issued by the World Trade Organization Technical
posites for which the laminate is balanced and symmetric with
Barriers to Trade (TBT) Committee.
respect to the test direction. The range of acceptable test
laminates and thicknesses are described in 8.2.1.
2. Referenced Documents
1.2 Thistestmethodisconsistentwiththerecommendations
2.1 ASTM Standards:
of MIL-HDBK-17, which describes the desirable attributes of
D792Test Methods for Density and Specific Gravity (Rela-
a bearing/bypass interaction response test method.
tive Density) of Plastics by Displacement
1.3 The two-fastener test configurations described in this D883Terminology Relating to Plastics
test method are similar to those in Test Method D5961/
D2584Test Method for Ignition Loss of Cured Reinforced
D5961M as well as those used by industry to investigate the Resins
bearing portion of the bearing/bypass interaction response for
D2734TestMethodsforVoidContentofReinforcedPlastics
boltedjoints,wherethespecimenmayproduceeitherabearing
D3171Test Methods for Constituent Content of Composite
failure mode or a bypass failure mode. Should the test
Materials
specimen fail in a bearing failure mode rather than the desired
D3878Terminology for Composite Materials
bypassmode,thenthetestshouldbeconsideredtobeabearing
D5229/D5229MTestMethodforMoistureAbsorptionProp-
dominated bearing/bypass test, and the data reduction and
erties and Equilibrium Conditioning of Polymer Matrix
reporting procedures of Test Method D5961/D5961M should
Composite Materials
be used instead of those given in this standard.
D5687/D5687MGuide for Preparation of Flat Composite
Panels with Processing Guidelines for Specimen Prepara-
1.4 The values stated in either SI units or inch-pound units
tion
are to be regarded separately as standard. The values stated in
D5766/D5766M Test Method for Open-Hole Tensile
each system may not be exact equivalents; therefore, each
Strength of Polymer Matrix Composite Laminates
D5961/D5961MTestMethodforBearingResponseofPoly-
mer Matrix Composite Laminates
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.05 on
Structural Test Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Aug. 1, 2017. Published May 2017. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2007. Last previous edition approved in 2012 as D7248/D7248M-12. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7248_D7248M-12R17. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7248/D7248M − 12 (2017)
(since for the compressive loading case the bearing stress reaction is on
D6484/D6484MTest Method for Open-Hole Compressive
the same side of the fastener as the applied force, the force reacted in
Strength of Polymer Matrix Composite Laminates
bearing does not bypass the fastener hole).
D6742/D6742MPractice for Filled-Hole Tension and Com-
NOTE 3—Several alternate definitions for gross and net bypass stress
pressionTesting of Polymer Matrix Composite Laminates
have been used historically in the aerospace industry. Comparison of data
E4Practices for Force Verification of Testing Machines
from tests conforming to this standard with historical data may need to
E6Terminology Relating to Methods of Mechanical Testing account for differences in the bypass definitions.
E83Practice for Verification and Classification of Exten-
3.2.3 bearing area, [L ],n—the area of that portion of a
someter Systems
specimen used to normalize applied loading into an effective
E122PracticeforCalculatingSampleSizetoEstimate,With
bearing stress; equal to the diameter of the fastener multiplied
Specified Precision, the Average for a Characteristic of a
by the thickness of the specimen.
Lot or Process
br
3.2.4 bearing chord stiffness, E [ML-1T-2],n—the chord
E177Practice for Use of the Terms Precision and Bias in
stiffness between two specific bearing stress or bearing strain
ASTM Test Methods
points in the linear portion of the bearing stress/bearing strain
E251Test Methods for Performance Characteristics of Me-
curve.
tallic Bonded Resistance Strain Gages
E456Terminology Relating to Quality and Statistics
3.2.5 bearing force, P [MLT ],n—the in-plane force trans-
E1237Guide for Installing Bonded Resistance Strain Gages
mitted by a fastener to a specimen at the fastener hole.
E1309 Guide for Identification of Fiber-Reinforced
br
3.2.6 bearing strain, ε, [nd],n—the normalized hole de-
Polymer-Matrix Composite Materials in Databases (With-
formation in a specimen, equal to the deformation of the
drawn 2015)
bearing hole in the direction of the bearing force, divided by
E1434Guide for Recording Mechanical Test Data of Fiber-
the diameter of the hole.
ReinforcedCompositeMaterialsinDatabases(Withdrawn
br_byp
3.2.7 bearing strength, F [ML-1T-2],n—the value of
2015)
x
bearing stress occurring at the point of bypass (net section)
2.2 Other Document:
failure.
MIL-HDBK-17 Polymer Matrix Composites, Vol 1, Sec-
br
tion7
3.2.8 bearing stress, σ [ML-1T-2],n—the bearing force
divided by the bearing area.
3. Terminology
3.2.9 diameter to thickness ratio, D/h [nd], n— in a bearing
3.1 Definitions—Terminology D3878 defines terms relating
specimen, the ratio of the hole diameter to the specimen
to high-modulus fibers and their composites. Terminology
thickness.
D883definestermsrelatingtoplastics.TerminologyE6defines
3.2.9.1 Discussion—The diameter to thickness ratio may be
terms relating to mechanical testing. Terminology E456 and
eitheranominalvaluedeterminedfromnominaldimensionsor
Practice E177 define terms relating to statistics. In the event of
an actual value determined from measured dimensions.
a conflict between terms, Terminology D3878 shall have
precedence over the other documents.
3.2.10 edge distance ratio, e/D [nd], n— in a bearing
specimen, the ratio of the distance between the center of the
NOTE 1—If the term represents a physical quantity, its analytical
hole and the specimen end to the hole diameter.
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
fundamental dimension form, using the following ASTM standard sym-
3.2.10.1 Discussion—The edge distance ratio may be either
bology for fundamental dimensions, shown within square brackets: [M]
a nominal value determined from nominal dimensions or an
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
actual value determined from measured dimensions.
and[nd]fornon-dimensionalquantities.Useofthesesymbolsisrestricted
to analytical dimensions when used with square brackets, as the symbols
3.2.11 nominal value, n—a value, existing in name only,
may have other definitions when used without the brackets.
assigned to a measurable quantity for the purpose of conve-
3.2 Definitions of Terms Specific to This Standard:
nient designation. Tolerances may be applied to a nominal
gr_byp
3.2.1 gross bypass stress, f [ML-1T-2],n—the gross
value to define an acceptable range for the quantity.
bypass stress for tensile loadings is calculated from the total
bro
3.2.12 offset bearing strength, F [ML-1T-2],n—the
x
force bypassing the fastener hole.
value of bearing stress, in the direction specified by the
net_byp
3.2.2 netbypassstress,f [ML-1T-2],n—thenetbypass
subscript, at the point where a bearing chord stiffness line,
stressfortensileloadingiscalculatedfromtheforcebypassing
offsetalongthebearingstrainaxisbyaspecifiedbearingstrain
the fastener hole minus the force reacted in bearing at the
value, intersects the bearing stress/bearing strain curve.
fastener.
3.2.12.1 Discussion—Unless otherwise specified, an offset
NOTE2—Forcompressiveloadingsthegrossandnetbypassstressesare bearing strain of 2% is to be used in this test method.
equal and are calculated using the force that bypasses the fastener hole
3.2.13 width to diameter ratio, w/D [nd], n— in a bearing
specimen, the ratio of specimen width to hole diameter.
The last approved version of this historical standard is referenced on
3.2.13.1 Discussion—The width to diameter ratio may be
www.astm.org.
eitheranominalvaluedeterminedfromnominaldimensionsor
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
an actual value, determined as the ratio of the actual specimen
Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
dodssp.daps.dla.mil. width to the actual hole diameter.
D7248/D7248M − 12 (2017)
bru gr_byp_t
3.2.14 ultimate bearing strength, F [ML-1T-2],n—the F =ultimate tensile gross bypass strength in the test
x x
value of bearing stress, in the direction specified by the direction specified by the subscript
net_byp_c
subscript, at the maximum force capability of a bearing
F =ultimate compressive net bypass strength in the
x
specimen. test direction specified by the subscript
net_byp_t
gr_byp
F =ultimate tensile net bypass strength in the test
3.2.15 ultimate gross bypass strength, F [ML-1T-2], x
x
direction specified by the subscript
n—the value of gross bypass stress, in the direction specified
g=distance, perpendicular to applied force, from hole edge
by the subscript, at the maximum force capability of the
to shortest edge of specimen
specimen.
net_byp h=specimen thickness
3.2.16 ultimate net bypass strength, F [ML-1T-2],
x
k=calculation factor used in bearing equations to distin-
n—the value of net bypass stress, in the direction specified by
guish single-fastener tests from double-fastener tests
thesubscript,atthemaximumforcecapabilityofthespecimen.
L =extensometer gage length
g
3.3 Symbols:
n=number of specimens per sample population
A=cross-sectional area of a specimen
P=force carried by test specimen
CV=coefficient of variation statistic of a sample population
f
P =force carried by test specimen at failure
for a given property (in percent)
max
P =maximum force carried by test specimen prior to
d=fastener or pin diameter
failure
D=specimen hole diameter
s =standard deviation statistic of a sample population for
n-1
e=distance, parallel to applied force, from hole center to
a given property
end of specimen; the edge distance
br w=specimen width
E =bearing chord stiffness in the test direction specified
x
x =test result for an individual specimen from the sample
i
by the subscript
population for a given property
f=distance, parallel to applied force, from hole edge to end
x¯ =mean or average (estimate of mean) of a sample
of specimen
br_byp population for a given property
F =bearing stress at the ultimate bypass strength in
x
δ=extensional displacement
the test direction specified by the subscript
gr_byp_c
F =ultimate compressive gross bypass strength in ε=generalsymbolforstrain,whethernormalstrainorshear
x
the test direction specified by the subscript strain
FIG. 1 Illustration of FHT, FHC, Bearing and Bearing/Bypass Bolted Joints Data and Bearing/Bypass Interaction Diagram (Refs 1-3)
D7248/D7248M − 12 (2017)
br
NOTE 4—Should the test specimen fail in a bearing failure mode rather
ε =bearing strain
br
than the desired bypass (net tension or compression) mode, then the test
σ =bearing stress
should be considered to be a bearing dominated bearing/bypass test, and
w=specimen width
the data reduction and reporting procedures of Test Method D5961/
d =countersink depth
csk D5961M should be used instead of those given in this standard.
d =countersink flushness (depth or protrusion of the fas-
fl
4.2.3 The standard test configuration for this procedure has
tener in a countersunk hole)
defined values for the major test parameters. However, the
following variations in configuration are allowed and can be
4. Summary of Test Method
consideredasbeinginaccordancewiththistestmethodaslong
4.1 Bearing/Bypass Procedures—Definition of the uniaxial
as the values of all variant test parameters are prominently
bearing/bypass interaction response requires data for varying
documented with the results.
amounts of bearing and bypass forces at a fastener hole. Fig. 1
Parameter Standard Variation
shows a typical composite laminate bearing/bypass interaction
Loading condition double-shear none
Loading type tensile none
diagram (Refs 1-3), along with illustrative data from various
Mating material steel fixture any, if documented
test types. Data from Practice D6742/D6742M and Test
Number of holes 2 3
Method D5961/D5961M define the 100% bypass and bearing
Countersink none none
Hole fit tight any, if documented
ends of the interaction diagram. Rationale for the baseline
F
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7248/D7248M − 12 D7248/D7248M − 12 (Reapproved 2017)
Standard Test Method for
Bearing/Bypass Interaction Response of Polymer Matrix
Composite Laminates Using 2-Fastener Specimens
This standard is issued under the fixed designation D7248/D7248M; 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
1.1 This test method determines the uniaxial bearing/bypass interaction response of multi-directional polymer matrix composite
laminates reinforced by high-modulus fibers by either double-shear tensile loading (Procedures A and C) or single-shear tensile
or compressive loading (Procedure B) of a two-fastener specimen. The scope of this test method is limited to net section (bypass)
failure modes. Standard specimen configurations using fixed values of test parameters are described for each procedure. A number
of test parameters may be varied within the scope of the standard, provided that the parameters are fully documented in the test
report. The composite material forms are limited to continuous-fiber or discontinuous-fiber (tape or fabric, or both) reinforced
composites for which the laminate is balanced and symmetric with respect to the test direction. The range of acceptable test
laminates and thicknesses are described in 8.2.1.
1.2 This test method is consistent with the recommendations of MIL-HDBK-17, which describes the desirable attributes of a
bearing/bypass interaction response test method.
1.3 The two-fastener test configurations described in this test method are similar to those in Test Method D5961/D5961M as
well as those used by industry to investigate the bearing portion of the bearing/bypass interaction response for bolted joints, where
the specimen may produce either a bearing failure mode or a bypass failure mode. Should the test specimen fail in a bearing failure
mode rather than the desired bypass mode, then the test should be considered to be a bearing dominated bearing/bypass test, and
the data reduction and reporting procedures of Test Method D5961/D5961M should be used instead of those given in this standard.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.4.1 Within the text the inch-pound units are shown in brackets.
1.5 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 and health practices and determine the applicability of regulatory
limitations prior to use.
1.6 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
2.1 ASTM Standards:
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D883 Terminology Relating to Plastics
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
D2734 Test Methods for Void Content of Reinforced Plastics
D3171 Test Methods for Constituent Content of Composite Materials
D3878 Terminology for Composite Materials
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.05 on Structural Test
Methods.
Current edition approved April 1, 2012Aug. 1, 2017. Published May 2012May 2017. Originally approved in 2007. Last previous edition approved in 20082012 as
D7248/D7248M-08.-12. DOI: 10.1520/D7248_D7248M-12.10.1520/D7248_D7248M-12R17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7248/D7248M − 12 (2017)
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite
Materials
D5687/D5687M Guide for Preparation of Flat Composite Panels with Processing Guidelines for Specimen Preparation
D5766/D5766M Test Method for Open-Hole Tensile Strength of Polymer Matrix Composite Laminates
D5961/D5961M Test Method for Bearing Response of Polymer Matrix Composite Laminates
D6484/D6484M Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
D6742/D6742M Practice for Filled-Hole Tension and Compression Testing of Polymer Matrix Composite Laminates
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E83 Practice for Verification and Classification of Extensometer Systems
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
E1309 Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in Databases (Withdrawn 2015)
E1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases (Withdrawn 2015)
2.2 Other Document:
MIL-HDBK-17 Polymer Matrix Composites, Vol 1, Section 7
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology D883
defines terms relating to plastics. Terminology E6 defines terms relating to mechanical testing. Terminology E456 and Practice
E177 define terms relating to statistics. In the event of a conflict between terms, Terminology D3878 shall have precedence over
the other documents.
NOTE 1—If the term represents a physical quantity, its analytical dimensions are stated immediately following the term (or letter symbol) in
fundamental dimension form, using the following ASTM standard symbology for fundamental dimensions, shown within square brackets: [M] for mass,
[L] for length, [T] for time, [θ] for thermodynamic temperature, and [nd] for non-dimensional quantities. Use of these symbols is restricted to analytical
dimensions when used with square brackets, as the symbols may have other definitions when used without the brackets.
3.2 Definitions of Terms Specific to This Standard:
gr_byp
3.2.1 gross bypass stress, f [ML-1T-2],n—the gross bypass stress for tensile loadings is calculated from the total force
bypassing the fastener hole.
net_byp
3.2.2 net bypass stress, f [ML-1T-2],n—the net bypass stress for tensile loading is calculated from the force bypassing the
fastener hole minus the force reacted in bearing at the fastener.
NOTE 2—For compressive loadings the gross and net bypass stresses are equal and are calculated using the force that bypasses the fastener hole (since
for the compressive loading case the bearing stress reaction is on the same side of the fastener as the applied force, the force reacted in bearing does not
bypass the fastener hole).
NOTE 3—Several alternate definitions for gross and net bypass stress have been used historically in the aerospace industry. Comparison of data from
tests conforming to this standard with historical data may need to account for differences in the bypass definitions.
3.2.3 bearing area, [L ],n—the area of that portion of a specimen used to normalize applied loading into an effective bearing
stress; equal to the diameter of the fastener multiplied by the thickness of the specimen.
br
3.2.4 bearing chord stiffness, E [ML-1T-2],n—the chord stiffness between two specific bearing stress or bearing strain points
in the linear portion of the bearing stress/bearing strain curve.
3.2.5 bearing force, P [MLT ],n—the in-plane force transmitted by a fastener to a specimen at the fastener hole.
br
3.2.6 bearing strain, ε, [nd],n—the normalized hole deformation in a specimen, equal to the deformation of the bearing hole
in the direction of the bearing force, divided by the diameter of the hole.
br_byp
3.2.7 bearing strength, F [ML-1T-2],n—the value of bearing stress occurring at the point of bypass (net section) failure.
x
br
3.2.8 bearing stress, σ [ML-1T-2],n—the bearing force divided by the bearing area.
3.2.9 diameter to thickness ratio, D/h [nd],n— in a bearing specimen, the ratio of the hole diameter to the specimen thickness.
The last approved version of this historical standard is referenced on www.astm.org.
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://dodssp.daps.dla.mil.
3.2.9.1 Discussion—
D7248/D7248M − 12 (2017)
The diameter to thickness ratio may be either a nominal value determined from nominal dimensions or an actual value determined
from measured dimensions.
3.2.10 edge distance ratio, e/D [nd],n— in a bearing specimen, the ratio of the distance between the center of the hole and the
specimen end to the hole diameter.
3.2.10.1 Discussion—
The edge distance ratio may be either a nominal value determined from nominal dimensions or an actual value determined from
measured dimensions.
3.2.11 nominal value, n—a value, existing in name only, assigned to a measurable quantity for the purpose of convenient
designation. Tolerances may be applied to a nominal value to define an acceptable range for the quantity.
bro
3.2.12 offset bearing strength, F [ML-1T-2],n—the value of bearing stress, in the direction specified by the subscript, at the
x
point where a bearing chord stiffness line, offset along the bearing strain axis by a specified bearing strain value, intersects the
bearing stress/bearing strain curve.
3.2.12.1 Discussion—
Unless otherwise specified, an offset bearing strain of 2 % is to be used in this test method.
3.2.13 width to diameter ratio, w/D [nd],n— in a bearing specimen, the ratio of specimen width to hole diameter.
3.2.13.1 Discussion—
The width to diameter ratio may be either a nominal value determined from nominal dimensions or an actual value, determined
as the ratio of the actual specimen width to the actual hole diameter.
bru
3.2.14 ultimate bearing strength, F [ML-1T-2],n—the value of bearing stress, in the direction specified by the subscript, at
x
the maximum force capability of a bearing specimen.
gr_byp
3.2.15 ultimate gross bypass strength, F [ML-1T-2],n—the value of gross bypass stress, in the direction specified by the
x
subscript, at the maximum force capability of the specimen.
net_byp
3.2.16 ultimate net bypass strength, F [ML-1T-2],n—the value of net bypass stress, in the direction specified by the
x
subscript, at the maximum force capability of the specimen.
3.3 Symbols:
A = cross-sectional area of a specimen
CV = coefficient of variation statistic of a sample population for a given property (in percent)
d = fastener or pin diameter
D = specimen hole diameter
e = distance, parallel to applied force, from hole center to end of specimen; the edge distance
br
E = bearing chord stiffness in the test direction specified by the subscript
x
f = distance, parallel to applied force, from hole edge to end of specimen
br_byp
F = bearing stress at the ultimate bypass strength in the test direction specified by the subscript
x
gr_byp_c
F = ultimate compressive gross bypass strength in the test direction specified by the subscript
x
gr_byp_t
F = ultimate tensile gross bypass strength in the test direction specified by the subscript
x
net_byp_c
F = ultimate compressive net bypass strength in the test direction specified by the subscript
x
net_byp_t
F = ultimate tensile net bypass strength in the test direction specified by the subscript
x
g = distance, perpendicular to applied force, from hole edge to shortest edge of specimen
h = specimen thickness
k = calculation factor used in bearing equations to distinguish single-fastener tests from double-fastener tests
L = extensometer gage length
g
n = number of specimens per sample population
P = force carried by test specimen
f
P = force carried by test specimen at failure
max
P = maximum force carried by test specimen prior to failure
s = standard deviation statistic of a sample population for a given property
n-1
w = specimen width
x = test result for an individual specimen from the sample population for a given property
i
x¯ = mean or average (estimate of mean) of a sample population for a given property
D7248/D7248M − 12 (2017)
FIG. 1 Illustration of FHT, FHC, Bearing and Bearing/Bypass Bolted Joints Data and Bearing/Bypass Interaction Diagram (Refs 1-3)
δ = extensional displacement
ε = general symbol for strain, whether normal strain or shear strain
br
ε = bearing strain
br
σ = bearing stress
w = specimen width
d = countersink depth
csk
d = countersink flushness (depth or protrusion of the fastener in a countersunk hole)
fl
4. Summary of Test Method
4.1 Bearing/Bypass Procedures—Definition of the uniaxial bearing/bypass interaction response requires data for varying
amounts of bearing and bypass forces at a fastener hole. Fig. 1 shows a typical composite laminate bearing/bypass interaction
diagram (Refs 1-3), along with illustrative data from various test types. Data from Practice D6742/D6742M and Test Method
D5961/D5961M define the 100 % bypass and bearing ends of the interaction diagram. Rationale for the baseline bearing/bypass
specimen geometry and fastener torques are given in 6.7 and 6.8. Procedures A and B of this test method provide data in the
bypass/high bearing region, while Procedure C provides data in the bypass/low bearing region. More complicated test setups have
been used to develop data across the full range of bearing/bypass interaction.
...
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