Aluminium
Carbon composite
Glass composite
Kevlar composite
From Aluminium
Alloys to Composites
THE STRENGTH OF
COMPOSITES
An Introduction to Composite
Materials: D. Hull and T.W. Clyde
THE STRENGTH OF
COMPOSITES
The matrix in polymer matrix
composites is almost only a way
of holding the reinforcement
architecture in place
DENSITY
YOUNGS MODULUS
Components carry the same strain
There is a redistribution of the load
= f/Ef =m/Em
Ef >> Em f >> f
YOUNGS MODULUS
If components carry the same stress
actually a stress distribution in the matrix
POISSONS RATIO
SHORT FIBRES
failure initiation
Aspect ratio=2, aligned in direction of tensilestress
INTERFACIAL STRENGTH
Van der Waals Forces
Interdiffusion
Chemical reaction
Mechanical keying
THE STRENGTH OF
CONTINUOUS FIBRE
COMPOSITES
THE LONGITUDINAL STRENGTH OF
CONTINUOUS FIBRE COMPOSITES
THE TRANSVERSE STRENGTH OF
CONTINUOUS FIBRE COMPOSITES
The transverse strength can be weaker!! than the matrix
strength
Square array of cylindrical holes
precise response to loading
through automated 3-d
textile engineering to obtain
precisely controlled fiber
spacing, directionality and
dimensionality
Bamboo: Ramachandra Rao and coworkers
FAILURE OF COMPOSITES
Covalent Ceramics
Ionic ceramics
Non-metals and non metals
Metal and a Non metal
high-performance ceramics
Glasses based on SiO2
silica is combined with metal oxides like MgO, CaO or Al2O3
hydrated alumino-silicate kaolin,
vitreous ceramics, or clay products
Al2(Si2O5)(OH)4.
ROCK
Igneous :granite and basalt
And concrete?
Sedimentary:Sandstone /Limestone:silica, bonded together
eitherby more silica or by calcium carbonate (CaCO3).
THE STRENGTH OF CERAMICS
flaw distribution and volume effects
E(Gpa) Tenslie Compressiv
Strength e
(Mpa) Strength(Mp
a)
Concrete 13.8
ZrO2 138 138
MgO 207 2
Si3N4 304 350-580
Al2O3 380 200-310 6.3
SiC 404
TiC 462 240-275
B4C 4
Diamond 1035 8.9
PLASTICITY CAN BE LOCALISED OR
UNIFORM
YIELD AND WORK HARDENING
Work hardening in a polycrystals
Nb
5 independent slip systems to maintain compatibility
Local stress results in activation of multiple slip
FRACTURE
Theoretical
estimates
th=E/10
FRACTURE IN
TENSION
(limits of bevaiour)
Fracture prior to yield: brittle fracture
Single crystal single slip system
Single crystal multiple slip systems
Polycrystalline: multiple slip sytems
FRACTURE IN
TENSION
Fracture stress
BRITTLE
FRACTURE
POLYCRYSTAL BRITTLE
5 independent slip systems for genera
shape change
Transgranul
stress concentration ar
from dislocation cleavage
pile up
plastic
yield
SINGLE CRYSTAL Grain size, Grain boundary
BRITTLE D decohesion
During WWII, there were nearly 1,500
instances of significant brittle
fractures. Twelve ships, including
three of the 2,710 Liberties built, broke
in half without warning,
Constance Tipper of Cambridge
University demonstrated that the
fractures were not initiated by welding,
but instead by the grade of steel used
which suffered from embrittlement.[7]
She discovered that the ships in the
North Atlantic were exposed to
temperatures that could fall below a
critical point when the mechanism of
failure changed from ductile to brittle,
and thus the hull could fracture rather
easily
FRACTURE IN
TENSION
SHEAR
FRACTURE IN
TENSION
DUCTILE
FRACTURE
FRACTURE IN
TENSION
DUCTILE
FRACTURE
Clean aluminium !
Clean steel !
Engineers know that the
properties of real materials
are controlled by defects
Scripta Materialia 157 (2018) 67–71
Intermetallics 168 (2024) 108228
