Textile composite testing

Presented by:
S.Rajesh kumar
PSG TECH

INTRODUCTION
 Composite materials are being used in an ever-
increasing variety of products and applications, as
more and more industries realize the benefits that
these materials offer.
 As the demands for light-weight composite structures
for aerospace, ground transportation, and
environmentally sustainable energy systems develop,
so do the mechanical testing requirements for
composite materials, components and structures.

TYPES OF TESTING
 This Mechanical & Non-Destructive
Testing program explores Both mechanical and non-
destructive tests used to gage the quality of materials
and parts throughout the manufacturing process.
 Mechanical tests are used to gather specific
performance or property values of materials for part
design purposes and quality control.
 Non-destructive tests examine an object or material in
a manner that does not impair it's future usefulness.

MECHANICAL TESTING
 The brinell hardness test,
 Rockwell hardness test,
 Tensile tests,
 Compression tests,
 The charpy impact test,
 The izod impact test,
 Fracture-toughness tests,
 Fatigue tests, and
 Creep tests.

NON DESTRUCTIVE TESTING
 Visual inspection,
 Liquid penetrant testing,
 Magnetic particle inspection,
 Eddy-current testing,
 Ultrasonic testing and
 Radiographic testing.

MECHANICAL TESTING
 BRINELL HARDNESS TESTING

BRINELL HARDNESS TEST Cont…
 Brinell hardness is determined by forcing a hard steel
or carbide sphere of a specified diameter under a
specified load into the surface of a material and
measuring the diameter of the indentation left after
the test.
 The Brinell hardness number, or simply the Brinell
number, is obtained by dividing the load used, in
kilograms, by the actual surface area of the
indentation, in square millimeters.
 The result is a pressure measurement.

 Brinell Hardness Testing Machine is used.
 The specimen size used here is a circular rod of length
of 65mm and the diameter of 35mm.
 The specifications of the machine are ball intender of
diameter 20mm and the maximum load of 4000N.
 The load is usually applied for 10 to 15 seconds
 The formula used to determine the BHN of the
specimen is given below,
 BHN = P/A

where
BHN = the Brinell hardness number
F = the imposed load in kg
D = the diameter of the spherical indenter in mm
Di = diameter of the resulting indenter impression
in mm
 BHN is usually quoted as a range of values (e.g. 210 to
245, or 210-245)

TENSILE TESTING
 ASTM D3039 tensile testing is used to measure the
force required to break a polymer composite specimen
and the extent to which the specimen stretches or
elongates to that breaking point.
 Tensile tests produce a stress-strain diagram, which is
used to determine tensile modulus.
SPECIMEN SIZE
 The most common specimen for ASTM D3039 is a
constant rectangular cross section, 25 mm (1 in) wide
and 250 mm (10 mm) long.

TENSILE TESTING Cont…
TESTING PROCEDURE:
 Specimens are placed in the grips of a Universal Test
Machine at a specified grip separation and pulled until
failure.
 For ASTM D3039 the test speed can be determined by
the material specification or time to failure (1 to 10
minutes).
 A typical test speed for standard test specimens is 2
mm/min (0.05 in/min).
 An extensometer or strain gauge is used to determine
elongation and tensile modulus.

COMPRESSIVE STRENGTH
COMPRESSIVE PROPERTIES ASTM D6641
 This test method determines compressive properties
of polymer composite materials by applying combined
end-loading and shear-loading using a combined
loading compression (CLC) fixture.
 ASTM D6641 is designed for polymer matrix
composite laminates which contain at least one 0˚ ply,
but other materials can also be tested.
 The test fixture is designed to provide a combined
loading to the unsupported center 12 mm (0.5 inch)
gauge length of the specimen.

COMPRESSIVE STRENGTH Cont….
TESTING PROCEDURE
 The test specimen is inserted into the two halves of the
test fixture so that the ends of the specimen are flush
with the top and bottom of the test fixture, and the
bolts in the fixture are tightened to a specified torque
to capture the test specimen.
 The fixture is placed between the platens of a
Universal Testing Machine, and if a strain measuring
device is being used, it is attached to the specimen.
 The specimen is compressed to failure.

COMPRESSION TESTING
INSTRUMENT

CHARPY IMPACT TEST
 For a typical fiber reinforced polymer Charpy
specimen, L = 126 ± 1 mm, D = 12.7 ± 0.15 mm, and 3.00
mm < w < 12.7 mm.
 The specimen is then placed in a vacuum to remove
excess resin, and allowed to cure (with or without
external pressure and heat).
 The resultant plate can then be cut into small
rectangles which will be used as Charpy impact
specimens.
 The final step is to cut the notch into the specimen.

CHARPY IMPACT TEST Cont…
 The specimen that fits into the Charpy impact tester is
rectangular with a notch cut in one side.
 The notch allows for a predetermined crack initiation
location.

TESTING PROCEDURE
 The Charpy impact test method works by placing a
notched specimen (with the notch facing away from
the point of contact) into a large machine with a
pendulum of a known weight.
 The pendulum is raised to a known height and allowed
to fall.
 As the pendulum swings, it impacts and breaks the
specimen, rising to a measured height.

 The difference in the initial and final heights is directly
proportional to the amount of energy lost due to fracturing
the specimen.
 The total energy of fracture is determined by
 where
 total is the total energy,
 m is the mass,
 g is gravitational acceleration,
 ho is the original height, and
 hf is the final height.

 Specimens were tested with lay-up angles of 0, 10, 22.5,
30, 45, 67.5, and 90 degrees.
 It is possible to see that specimen 1 failed from fiber
breakage and pull-out.
 Specimen 2 failed from a combination of fiber pull-out
and fiber-matrix separation.
 Specimens 3-7 failed at the fiber-matrix interface.
 Composites therefore may need to be tested in different
fiber directions due to the anisotropy of the material.
 The failure type is important when characterizing
composites.

FRACTURE TOUGHNESS TEST
 Fracture toughness by using a mixed-mode bending test.
 Understand susceptibility to delamination by determining the
interlaminar fracture toughness of a polymer composite with an
initiated delamination.
SCOPE
 ASTM D6671 measures mixed-mode (Mode I and Mode II)
fracture toughness - the strain energy release rate for
delamination in mixed mode.
 The test applies load to split laminate specimens at various ratios
of Mode I and Mode II loading. Fracture Mode I is crack opening
mode.
 Fracture Mode II is sliding mode with delamination occurring as
faces slide over each other.

FRACTURE TOUGHNESS TESTING
INSTRUMENT

FRACTURE TOUGHNESS TEST
Cont…
SPECIMENS
 Panels prepared per test standard including piano hinge
loading tabs.
 Typical specimen size is 137 mm (5.5 in) long x 50 mm to 25
mm (0.8 in to 1.0 in) width x 3 mm to 5 mm (0.12 in to 0.2
in) thick. 5 specimens are tested.
PROCEDURE
 Insert the specimen in the Mixed Mode Bending Fixture
and set desired mode mixture.
 A Universal Testing machine is used to apply a force to the
specimen at a rate of 0.5 mm/min (0.02 in/min).
 Record force and displacement.

FATIQUE TEST
 Composite materials exhibit very complex failure
mechanisms under static and fatigue loading because of
anisotropic characteristics in their strength and stiffness.
 Fatigue causes extensive damage throughout the specimen
volume, leading to failure from general degradation of the
material instead of a predominant single crack.
 There are four basic failure mechanisms in composite
materials as a result of fatigue:
 Matrix cracking,
 Delamination,
 Fiber breakage and
 Interfacial debonding.

FATIQUE TEST Cont…
 Fatigue failure can be defined either
as a loss of adequate stiffness, as a
loss of adequate strength.
 There are two approaches to
determine fatigue life;
Constant stress cycling until loss of
strength, and
Constant amplitude cycling until
loss of stiffness.

COMPARISON BETWEEN METAL AND
COMPOSITE STIFFNESS REDUCTION

NON DESTRUCTIVE TESTING
VISUAL INSPECTION
 A basic and useful part of inspection on composite
structures is a visual inspection.
 The inspector looks for visible signs of damage to the
structure like
burns,
disbonds, and
delaminations.

LIQUID PENETRANT TESTING
 LPI is a simple, cheap and easily portable inspection
method that requires no equipment apart from spray cans.
 It can detect surface breaking imperfections only and relies
on a coloured or fluorescent dye, sprayed on the surface
and penetrating the imperfection.
 About 15 minutes is generally specified to enable the dye to
penetrate any very fine imperfections.
 After cleaning the excess the dye is drawn to the surface by
spraying on a developer in the case of the colour contrast
dye or exposing the surface to ultra-violet light in the case
of a fluorescent dye.

EDDY CURRENT TESTING
 Eddy Current systems visualize fiber structure of hidden
layers within a multi-axial composite or fabric.
 The EC-scan (eddy current image) provides insights on
quality parameters such as fiber orientation or distribution
of the carbon fiber textile.
MEASURABLE PARAMETERS:
 STRUCTURAL PARAMETERS
 Fiber orientation of individual & hidden layers
 Fiber spacing and distribution
TESTING
Eddy current testing utilizes the electrical conductivity
of the fiber to characterize the amount of fibers within a
locally defined area approximated 50 mm².

COMPARISON OF EC-SCAN AND
SAMPLES

EDDY CURRENT TESTING Cont…
DEFECTS AND ERRORS
 Gaps
 Misalignment
 Wrinkles & Overlaps
 Undulation & Distortion
 Impact Damage & Delamination
 Voids or Inclusion

ULTRASONIC TESTING
 Ultrasound pulses are reflected by interfaces between
materials of different properties.
 In the case of delaminations and disbonds, this can
cause a discrete reflection from a particular depth in
the material.
 Such a reflection also results in a loss of transmission
through the material.
 Porosity does not produce a discrete reflection but
scatters the ultrasound in a range of directions,
resulting in a transmission loss.

ULTRASONIC TESTING Cont…
 These transmission losses can be detected by mapping
the transmitted signal over the whole structure, known
as a through-transmission C-scan.
 Variations in the transmitted signal can be caused by
delaminations,
disbonds and
porosity.

 Ultrasound is sound whose frequency of the upper
limit of human audibility, of~ 20 kHz, although for
ultrasonic materials evaluation the frequency range 0.5
to 50 MHz is most often employed.
 Ultrasound, unlike electromagetic waves, requires a
medium to propagate and travels through it in the
form of stress waves.

 There are three basic types of scanning system to
produce the results
A-Scan,
C-Scan, and
ANDSCAN.

RADIOGRAPHIC TESTING
 Radiography is used to detect the features of a component
or assembly that exhibit a difference in thickness or
physical density as compared to the surrounding material.
 Radiographic testing usually requires exposing film to x-
rays or gamma rays that have penetrated a specimen,
processing the exposed film, and interpreting radiograph.
 Radiography can be used as gamma, neutron, and x-ray.
 The most common to the inspection of aircraft composite
components is x-ray.

RADIOGRAPHIC TESTING Cont…
 Radiographic inspection of the bonded part will detect an
unbond if there is a lack of adhesive condition (adhesive
missing) because this would cause a density change.
 Radiographic inspection can also detect foreign material,
and core crush if the damage to the core is extensive.
 Radiographic inspection is commonly used in conjunction
with ultrasonic inspection for bonded components.
 Radiography of composite materials is generally done at
lower energy levels to obtain the required contrast and
definition.
 Lower KV and smaller portable systems such as 160 KV
units are very practical for performing radiographic tests on
aircraft.

Textile composite testing

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