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.

TYPES OF DEFECTS

TYPES OF DEFECTS Cont…

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 Brinellnumber, 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 TEST Cont… 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

BRINELL HARDNESS TEST Cont…where

BHN = the Brinell hardness numberF = the imposed load in kgD = the diameter of the spherical indenter in mmDi = 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.

TENSILE TESTING INSTRUMENT

COMPRESSIVE STRENGTHCOMPRESSIVE 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…

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.

CHARPY IMPACT TEST Cont…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.

CHARPY IMPACT TEST Cont…

CHARPY IMPACT TEST Cont… 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.

PICTURE OF FAILED COMPOSITES

CHARPY IMPACT TEST Cont… 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 TESTINGVISUAL 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.

VISUAL INSPECTION SAMPLES

LIQUID PENETRANT TESTING

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.

ULTRASONIC TESTING Cont… 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.

ULTRASONIC TESTING Cont… 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.

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