part 4 mechanical properties - yazd composite materials m. s. ahmadi 192 part 4 mechanical...
TRANSCRIPT
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Part 4
MECHANICALPROPERTIES
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TENSILE PROPERTIES
Tensile properties, such as tensile strength, tensile modulus, and Poisson’s ratio of flat composite laminates, are determined by static tension tests in accordance with ASTM D3039.
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As end tab materials, balanced [0=90] cross-ply tabs of nonwoven E-glass–epoxy have shown satisfactory results. Any high-elongation (tough) adhesive system can be used for mounting the end tabs to the test specimen.
Recommended cross-head speed: 2 mm/min
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COMPRESSIVE PROPERTIES
Compressive properties of thin composite laminates are difficult to measure owing to sidewise buckling of specimens. A number of test methods and specimen designs have been developed to overcome the buckling problem
ASTM D3410
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FLEXURAL PROPERTIES
Flexural properties, such as flexural strength and modulus, are determined by ASTM test method D790. In this test, a composite beam specimen of rectangular cross section is loaded in either a three-point bending mode or a four-point bending mode.
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Using a homogeneous beam theory, the flexural strength in a three-point flexural test is given by
Flexural modulus is calculated from the initial slope of the load–deflectioncurve:
where m is the initial slope of the load–deflect ion curve.
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IMPACT PROPERTIES
A variety of standard impact test methods are available for metals (ASTME23) and unreinforced polymers (ASTM D256). Some of these tests have alsobeen adopted for fiber-reinforced composite materials.
CHARPY, IZOD, AND DROP-WEIGHT IMPACT TEST
Charpy and Izod impact tests are performed on commercially availablemachines in which a pendulum hammer is released from a standard height to contact a beam specimen (either notched or unnotched) with a specified kinetic energy. A horizontal simply supported beam specimen is used in the Charpy test, whereas a vertical cantilever beam specimen is used in the Izodtest.
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Charpy impact tests Izod impact tests
The dimensions of a standard specimen for ASTM D256 are 63.5 × 12.7× 3.2 mm (2.5 × 0.5 × 0.125 in). The most common specimen thickness is 3.2 mm (0.125 in), but the width can vary between 3.0 and 12.7 mm(0.118 in and 0.500 in).
ASTM D6110For 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
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ASTM D 5628
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The drop -weight impact test uses the free fall of a known weight to supplythe energy to break a beam or a plate specimen. The specimen can be either simply sup ported or fixed . The kinetic energy of the falling weight is adjusted by varying its drop height . The impact load on the specimen ismeasured by instrumenting either the striking head or the specimen supports.Energy absorbed by the specimen is calculated as
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Composite Material Stiffness Predictions
–Rule of Mixtures (ROM) –ROM with Efficiency Factor –Hart Smith 10% rule –Classical Laminate Analysis
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Lamina Axis Notation
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Example Material for Analysis
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Rule of Mixtures: Efficiency Factor
• The Efficiency Factor or Krenchel factorcan be used to predict the effect of fibreorientation on stiffness• This is a term that is used to factor theRule of Mixtures formula according to thefibre angle
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