ISO 18352:2009

INTERNATIONAL ISO
STANDARD 18352
First edition
2009-08-15


Carbon-fibre-reinforced plastics —
Determination of compression-after-
impact properties at a specified
impact-energy level
Plastiques renforcés de fibres de carbone — Détermination des
propriétés de compression après impact à un niveau d'énergie spécifié




Reference number
ISO 18352:2009(E)
©
ISO 2009

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ISO 18352:2009(E)
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ISO 18352:2009(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Principle. 3
5 Conditioning of specimens and test environment . 4
5.1 Standard conditioning procedure for specimens . 4
5.2 Environmental test chamber for impact and compression tests . 4
6 Test apparatus . 4
6.1 General. 4
6.2 Impact facility. 4
6.3 Support fixture for specimen. 4
6.4 Non-destructive testing instrument. 6
6.5 Compression-testing machine . 6
6.6 Compression-loading fixture. 6
6.7 Measuring apparatus. 7
6.8 Strain gauges . 8
7 Specimens . 8
7.1 Dimensions. 8
7.2 Specimen preparation . 9
7.3 Number of specimens . 10
8 Procedure . 10
8.1 Specimen conditioning . 10
8.2 Measurement of specimen dimensions. 10
8.3 Impact test . 10
8.4 Non-destructive testing (NDT). 11
8.5 Inspection of specimens. 11
8.6 Compression test. 11
9 Validation. 13
10 Calculation of results . 14
10.1 CAI strength . 14
10.2 CAI modulus. 15
10.3 Maximum CAI strain . 15
10.4 Rounding the results. 15
10.5 Standard deviation and coefficient of variation . 15
11 Test report . 16
Annex A (normative) Detailed drawings of the components of the compression-loading fixture . 17
Bibliography . 20

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ISO 18352:2009(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 18352 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 13, Composites
and reinforcement fibres.

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INTERNATIONAL STANDARD ISO 18352:2009(E)

Carbon-fibre-reinforced plastics — Determination of
compression-after-impact properties at a specified
impact-energy level
1 Scope
This International Standard specifies a method for determining the residual compression strength of
multidirectional polymer matrix composite laminate plates that have been damaged by impact prior to the
application of in-plane compressive loading.
The test method is suitable for continuous-fibre-reinforced polymer matrix composites. Application of the
method is limited to fibre-reinforced plastic laminates with multidirectional reinforcements manufactured from
unidirectional prepreg tapes/fabrics or woven fabrics.
The test method is referred to as the compression-after-impact (CAI) test when used to determine the residual
compression strength of an impacted plate. It can be used to obtain data for material specification, material
evaluation, research and development, or construction of a composite database.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 291, Plastics — Standard atmospheres for conditioning and testing
ISO 1268-4:2005, Fibre-reinforced plastics — Methods of producing test plates — Part 4: Moulding of
prepregs
ISO 5893, Rubber and plastics test equipment — Tensile, flexural and compression types (constant rate of
traverse) — Specification
ISO 14127, Carbon-fibre-reinforced composites — Determination of the resin, fibre and void contents
1)
ISO 80000-1:— , Quantities and units — Part 1: General

1) To be published. (Revision of ISO 31-0:1992)
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ISO 18352:2009(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
compression-after-impact test
CAI test
in-plane compression test undertaken on a composite laminate loaded in the plane of the laminate, after
applying an out-of-plane concentrated impact load under defined conditions
3.2
specified impact energy
potential energy of the drop-weight, specified by the mass and drop height of the indenter, to which composite
laminate specimens will be subjected, expressed in joules
3.3
barely visible impact damage
BVID
impact damage corresponding to a dent depth of 0,3 mm
3.4
energy to cause BVID
E
BVID
impact energy required to cause BVID, expressed in joules
3.5
compression-after-impact strength
σ
CAI
maximum compressive load sustained by the impacted specimen divided by the initial cross-sectional area of
2
the specimen, expressed in MN/m
3.6
compression-after-impact modulus
E
CAI
2
compression modulus of the specimen calculated between 0,05 % and 0,25 % strain, expressed in GN/m
3.7
maximum compressive strain
ε
cmax
maximum value of the compressive strain sustained by the specimen at the maximum compressive load
3.8
dent depth
residual depth of the depression formed by the indenter after the impact event, expressed as the maximum
distance, in millimetres, in a direction normal to the face of the specimen from the lowest point in the dent to
the plane of the undisturbed impact surface
3.9
damage parameters
quantities used to characterize the extent of impact damage, including the maximum diameter of the
delamination and the projected area of the delamination
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ISO 18352:2009(E)
4 Principle
The CAI test detailed in this International Standard consists of three phases as depicted in Figure 1.
The first phase is to generate barely visible impact damage (BVID), avoiding penetration of the test plate. The
preferred method of introducing BVID is based on a specified level of impact energy applied to one face of a
specimen made of a balanced and symmetrical composite laminate.
NOTE An alternative method allows the operator to vary the level of impact energy in order to determine the energy
level required to cause BVID. An additional ISO method will be proposed and drafted to cover this method of setting the
impact energy.
The second phase consists of assessing the level of impact damage by non-destructive testing (NDT) [also
referred to as non-destructive inspection (NDI)] and by measurement of the dent depth on the impacted face.
The area and geometry of the damage created by the impact shall be measured by means of an appropriate
non-destructive testing technique, and the dent depth measured by a suitable device.
Measurement of residual in-plane compression properties is undertaken in the third stage. A compressive load
is applied to the impacted specimen until failure occurs. The CAI strength, modulus and strain are calculated
from the load strain data collected, as detailed in Clause 10.

a)  Impact test configuration b)  Non-destructive testing and c)  Compression test
dent depth measurement
Key
1 specimen
2 delamination
3 compressive load, F
Figure 1 — Principle of the compression-after-impact test
A flat, rectangular composite plate is subjected to a transverse, concentrated impact using a drop-weight
device with a hemispherical indenter. The energy of the impact, determined by the mass and drop height of
the indenter, is specified. Equipment and procedures are prescribed for measurement of the contact force and
the indenter velocity during the impact event. Damage resistance is quantified in terms of the extent and type
of damage present in the specimen after impact.
After impact, an in-plane compressive load is applied to the specimen until failure, and the compression-after-
impact strength, modulus and strain are calculated from the recorded load-strain response.
The properties measured by this test method are highly dependent upon several factors, including specimen
geometry, laminate lay-up, indenter geometry, indenter mass, impact energy, impact force, damage size and
location and support conditions. Thus, the results are generally not comparable to other CAI test
configurations but are particular to the specific combination of geometric and physical test parameters used.
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ISO 18352:2009(E)
The test does not provide information to satisfy structural-integrity and safety requirements. It is the
responsibility of the user to consider and establish appropriate structural-integrity limits and safety factors.
5 Conditioning of specimens and test environment
5.1 Standard conditioning procedure for specimens
Specimens shall be conditioned at (23 ± 2) °C and (50 ± 10) % RH unless different conditions are agreed
upon by the interested parties.
5.2 Environmental test chamber for impact and compression tests
An environmental test chamber is required for test environments other than ambient. The chamber shall be
capable of maintaining the test specimen at the required temperature and humidity throughout the test. Tests
shall be conducted in the same environment as the specimens were conditioned in. When the interested
parties agree, it is permitted to undertake impact and compression tests under ambient conditions after hot-
wet conditioning procedures.
NOTE The impact and compression properties of fibre-reinforced plastics are affected by moisture absorption.
6 Test apparatus
6.1 General
The test apparatus consists of an impact facility, a specimen support fixture, suitable non-destructive testing
equipment, a compression-testing machine, a compression fixture, tools for measurement of the specimen
dimensions and a strain measurement system. Details of each of these items are provided in the following
subclauses.
6.2 Impact facility
The impact facility shall be fitted with a steel drop-weight indenter with a hemispherical head (16 ± 0,1) mm in
diameter. The impact facility shall be mounted on a rigid base and have a suitable guide mechanism for the
drop-weight indenter, as shown in Figure 2. The indenter shall impact the centre of the top surface of the
specimen by dropping under gravity with minimal friction effects from the guide rails. A second-strike
prohibition mechanism shall be employed to ensure that specimens are only impacted once, i.e. to prevent
bouncing of the indenter and therefore multiple strikes. The recommended mass of the indenter is 5 kg to 6 kg
and the hardness of the indenter tip shall be between 60 HRC and 62 HRC (Rockwell, diamond cone, 150 kg).
The minimum drop height is determined by the mass of the indenter, the specimen thickness and the specified
impact energy, as given in 8.3.
NOTE The use of an instrumented impact facility capable of measuring indenter velocity and indentation forces and
having a data acquisition system is preferred. ISO 6603-1 and ISO 6603-2 are suggested as references.
6.3 Support fixture for specimen during impact test
The specimen support fixture shall hold the specimen flat against the support frame during impact, holding it
down with sufficient, but not excessive, force at its four corners using rubber-tipped toggle clamps. The fixture
shall consist of a base 18 mm thick made of steel with a surface which is flat to within 0,1 mm in the region of
contact with the specimen. The base-plate shall contain a window (125 ± 1) mm in length and (75 ± 1) mm in
width. An example of a suitable support is shown in Figure 3.
The support fixture shall be supported rigidly on a solid base such as the impact facility or the room floor.
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ISO 18352:2009(E)
Key
1 indenter
2 crosshead
3 latch mechanism
4 guide rail
5 velocity sensor
6 stop block
7 base-plate

Figure 2 — Instrumented drop-weight impact device with double guide rails
Dimensions in millimetres
Key
1 specimen
2 guide pin
3 rubber bush
4 (75 ± 1) mm × (125 ± 1) mm window
5 base-plate
a
1 mm × 45° chamfer.

Figure 3 — Example of a specimen support fixture
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ISO 18352:2009(E)
6.4 Non-destructive testing instrument
Non-destructive testing shall be undertaken using a technique capable of detecting delamination damage
created by impact between laminae in the specimen. Although the recommended technique is ultrasonic
C-scan (using traceable procedures as detailed in Reference [1]), other proven techniques including X-ray
radiography with penetrant and pulse thermography may be used for determining delamination extent as well,
whereas X-ray radiography with penetrant is usually used for detecting fibre breakage and matrix cracks in
laminae. From the image, the edge of the delamination can be identified. Commercially available pulse
thermography systems can be used for delamination detection with almost the same reliability as ultrasonic
C-scan.
6.5 Compression-testing machine
6.5.1 General
The test machine shall comply with ISO 5893 and meet the specifications given in 6.5.2 and 6.5.3.
6.5.2 Test speed and configuration
The test machine shall be capable of maintaining the required test speed (see 8.6.3). A short loading train and
flat end-loading platens shall be used. The test machine shall be mounted with well-aligned, fixed (as opposed
to spherical-seat) platens. The platen surfaces shall be parallel to within 0,03 mm across the test fixture top-
plate length of 100 mm. If the platens are not sufficiently hardened, or simply to protect the platen surfaces, a
hardened plate (with parallel surfaces) can be inserted between each end of the fixture and the corresponding
platen. The lower platen should preferably be marked to help centre the test fixture between the platens.
6.5.3 Indication of load
The error in the indicated load shall not exceed ± 1 %.
6.6 Compression-loading fixture
The compression-loading fixture (see Figure 4) shall be designed to provide support to the specimen and to
introduce an in-plane compressive load perpendicularly to its upper and lower edges. The support conditions
at the four edges of the specimen shall be as follows: the specimen shall be supported in a way which
approximates to simple support using knife edges along the longitudinal sides (translational motion of the
specimen in the out-of-plane direction prevented, but rotation allowed) and the upper and lower edges shall be
clamped in a way which prevents, as far as possible, both translational motion in the out-of-plane direction
and rotational motion of the edges of the specimen. The fixture shall be adjustable to accommodate small
variations in specimen length, width and thickness. The sliding edges shall be sufficiently short to ensure that
a gap is maintained between each lateral angle bracket and the upper platen during the test. An example of a
suitable compression-loading fixture is shown in Figure 4. Detailed drawings of each component, including
dimensional tolerances, are provided in Annex A. The test fixture may be made of low-carbon steel for
ambient-temperature testing. For non-ambient environmental conditions, the recommended fixture material is
non-heat-treated ferritic or precipitation-hardened stainless steel (heat treatment for improved durability is
acceptable but not required).
Prior to the test, the fixtures shall be checked for conformity with the dimensions specified in Annex A. The
position of the lateral angle brackets shall be adjusted such that 0,8 mm to 1,5 mm clearance will be present
between each bracket and the longitudinal edge of the test specimen. The fixture shall be placed between the
platens and loaded in compression at each end.
NOTE This test is sensitive to the parallelism of the specimen ends as well as to the precise perpendicularity of the
various components of the compression-loading fixture. Experience has shown that fixtures may be damaged in use, thus
periodic verification of the fixture dimensions and tolerances is important.
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ISO 18352:2009(E)
Dimensions in millimetres

Key
1 specimen 5 upper platen
2 lower clamp plate 6 lateral angle bracket
3 clamp 7 base-plate
4 sliding edge
Figure 4 — Example of a compression-loading fixture
6.7 Measuring apparatus
6.7.1 Micrometer
A micrometer, or equivalent, capable of reading to 0,01 mm or better, shall be used to determine the thickness
and width of the specimen. The micrometer head shall have faces appropriate to the surface being measured
(i.e. flat faces for flat, polished surfaces and hemispherical faces for irregular surfaces).
A micrometer with a suitable attachment may also be used for the measurement of the depth of the dent
caused by the indenter on impact, as described in 8.5 (see Figure 5). For such measurements, the micrometer
head shall be hemispherical with a diameter of 1,5 mm to 5,0 mm. The length of the attachment shall not be
less than 40 mm.
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ISO 18352:2009(E)
Dimensions in millimetres

Key
1 depth micrometer
2 specimen
3 depth measured twice (in two directions at right angles to each other)
Figure 5 — Schematic diagram of micrometer with attachment for depth measurement
and placement of the attachment on the specimen
6.7.2 Vernier callipers
Vernier callipers, or the equivalent, capable of reading to 0,05 mm or better, shall be used to measure the
specimen length and the distances of the strain gauges (6.8) from the edges of the specimen.
6.8 Strain gauges
Longitudinal strain shall be measured during the compression phase by means of strain gauges at two
locations (see Figure 6) on each face of the specimen. The sensing element of the strain gauge shall not be
more than 3 mm in length. The error in the strain indicated shall not exceed ± 1 %. The gauges, the surface
preparation and the bonding agents used shall be chosen to give adequate performance with the material
being tested, and suitable strain-recording equipment shall be employed. Strain measurements shall be made
for all specimens tested.
7 Specimens
7.1 Dimensions
Each test specimen shall be a flat, rectangular plate (150 ± 0,2) mm in length and (100 ± 0,2) mm in width. A
specimen thickness of (5 ± 1) mm is recommended for laminates fabricated from unidirectional and fabric
prepreg material. A degree of variation in specimen thickness is permitted, depending on the density per unit
surface area of the prepreg fibre and the number of plies in the laminate. The specimen geometry and
dimensions are shown in Figure 6, together with the locations of the strain gauges used for monitoring the
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ISO 18352:2009(E)
strain and degree of bending during compression testing. Note that the direction of edge “A” shall coincide
with the 0° fibre direction (see ISO 1268-4:2005, Annex A). The parallelism between edges “B” and “C” shall
be better than 0,02 mm and that between the two longitudinal edges “A” better than 0,2 mm. The
perpendicularity between edges “A” and each of edges “B” and “C” shall be better than 0,2 mm.
Dimensions in millimetres

Key
1 impact point
2 locations of strain gauges (mounted in pairs back to back)
Figure 6 — Specimen geometry and dimensions and strain gauge locations
7.2 Specimen preparation
7.2.1 Specimens shall be machined from a laminated panel fabricated, using an autoclave or hot press, as
specified in ISO 1268-4 or as agreed between the interested parties. The size of the panel shall be such that,
after removal of a 25 mm strip round the edges, the desired number of specimens can be cut from it. Measure
the fibre content, by volume, of each panel in accordance with ISO 14127 or as agreed between the interested
parties.
If unidirectional prepreg tape is used as a constituent, a quasi-isotropic [45/0/−45/90] laminate shall be the
basic component (see ISO 1268-4:2005, Annex A, for details of the laminate stacking designation system
used in this subclause), and shall be repeated n times and symmetrically laminated with respect to the central
plane. The panel shall also be balanced in in-plane properties. A stacking sequence slightly different from
quasi-isotropic, [45 /−45 /0 /90 ] , where i, j and k are determined such that the total ply thickness in each of
i i j k ms
the four major directions exceeds 10 % of the plate thickness, may be used for the specimens.
2
NOTE If the density per unit surface area of the fibres in the prepreg is 190 g/m , n = 3 results in the recommended
thickness range. Hence the appropriate laminate is [45/0/−45/90] with 24 plies. If the density per unit surface area of the
3s
2
fibres in the prepreg is 145 g/m , the laminate is [45/0/−45/90] with 32 plies. If the density per unit surface area of the
4s
2
fibres in the prepreg is 95 g/m , the laminate is [45/0/−45/90] with 48 plies.
6s
If fabric prepreg is used as the constituent material, the basic component shall be [(± 45),(0/90)] and it shall be
repeatedly and symmetrically laminated. As with the tape case above, a stacking sequence of
[(± 45) ,(0/90) ] may be used under the same conditions.
i j ms
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ISO 18352:2009(E)
7.2.2 Specimens shall be machined from the panel, paying attention not to cause damage at the specimen
edges. Cut a margin of 25 mm or more from the panel as fabricated. The machined surfaces shall be smooth
and free of notches, scratches, burrs and any other flaws. In order to apply an exact in-plane load without any
offset, the upper and lower surfaces “B” and “C” of the specimen shall be machined with sufficient accuracy in
terms of roughness and parallelism (see 7.1). Check the rectangularity of the specimen by measuring the
lengths of the diagonals.
7.2.3 Because the state of the surface of the specimen can affect the result of the impact, either the top or
the bottom surface with respect to the curing shall be identified during the machining procedure to enable the
tool surface to be distinguished from the mould surface.
7.3 Number of specimens
The numbe
...