polymer fibre composites
TRANSCRIPT
Polymer fibre
reinforced composites
Prepared by
Dr. K. PadmanabhanProfessor Asst Director, CENC,Manufacturing Division School of MBSVIT-UniversityVellore 632014August, 2010
Contents
• High strength and modulus polymer fibres• Flexibility and mechanical behaviour• Structure property correlation• Moisture attack• Thermal characteristics• Case studies from publications• Applications
High-modulus high-strength organic fibers
• Theoretical estimates for covalently bonded organics show strength of 20-50 GPa (or more) and modulus of 200 – 300 GPa
• Serious processing problems• New fibers developed since the early 1970s: high axial
molecular orientation, highly planar, highly aromatic molecules
• Major fibers: Kevlar (polyaramid); Spectra (PE); polybenzoxazole (PBO) and polybenzothiazole (PBT).
• The latest entry being Zylon made by Toyobo Company of Japan.
N H CH2 6 NH C
O
CH2 4 C
O
C
O
N H
N H
C
O C
O
H N
N H
N H
C
O
C
O
N H
N H
C
O
Nylon 6,6
Poly(m-phenylene isophthalamide) (Nomex)
Poly(p-phenylene terephtalamide)PPT (Kevlar)
Aramid Fibers
• Aramid (aromatic polyamide) fibers = poly(paraphenylene terephthalamide)
• Kevlar behaves as a nematic liquid crystal in the melt which can be spun
• Prepared by solution polycondensation of p-phenylene diamine and terephthaloyl chloride at low temperatures. The fiber is spun by extrusion of a solution of the polymer in a suitable solvent (for example, sulphuric acid) followed by stretching and thermal annealing treatment
Liquid crystal Conventional (PET)
Solution
Extrusion
Solidstate
Nematic structureLow entropy Random coil
High entropy
Extended chain structureHigh chain continuityHigh mechanical properties
Folded chain structureLow chain continuityLow mechanical properties
Schematic representation of structure formationduring spinning, contrasting PPT and PET behavior
Producing Kevlar fibers
Stephanie Kwolek--Synthesized Kevlar
Phase diagram of the anisotropic solution of PPT in 100% H2SO4
•Various grades of Kevlar fibers: Kevlar-29, 49, 149 (Kevlar-49 is the more commonly used in composite structures) and Kevlar 981.
•X-ray diffraction: the structure of Kevlar-49 consists of rigid linear molecular chains that are highly oriented in the fiber axis direction, with the chains held together in the transverse direction by hydrogen bonds. Thus, the polymer molecules form rigid planar sheets.
•Strong covalent bonds in the fiber axis direction - high longitudinal strength•Weak hydrogen bonds in the transverse direction - low transverse strength. ( Van Der Vaal’s bond)
•Aramid fibers exhibit skin and core structures – Core = layers stacked perpendicular to the fiber axis, composed of rod-shaped crystallites with an average diameter of 50 nm. These crystallites are closely packed and held together with hydrogen bonds nearly in the radial direction of the fiber.
0.51 nm
Schematic diagram of Kevlar® 49 fibershowing the radially arranged
pleated sheets
Microstructure of aramid fiber
Kevlar fibers
Kevlar-49 Structure
Kevlar - High flexibility but poor compressive
performance
Also low shear performance, moisture-sensitive, UV-sensitive
Twaron(Akzo)
Twaron
HM
Kevlar
29
Kevlar
49
Kevlar
149
HM-50(Teijin
) Density, g/cm3 1.44 1.45 1.44 1.44 1.47 1.39Tensile strength, GPa 2.8 2.8 2.8 2.8 2.8 3.0Tensile modulus, GPa 80 125 62 124 186 74Tensile strain, % 3.3 2.0 3.5 2.5 1.9 4.2Coefficient of thermal
expansion,10-6oC
Longitudinal:0 to 100 oC … … -2.0 … -- …
Radial: 0 to 100 oC … … 59 … -- …
The Aramid fiber family
Kevlar/epoxy בא
Note the fibrillar structure of the fiber
•Little creep only•Excellent temperature resistance (does not melt,
decomposes at ~500°C)•Linear stress-strain curve until failure in Tension•Low density : 1.44•Negative CTE along the axis•Fiber diameter = 11.9 micron•Fiber strength variability
Kevlar fiber
Zylon Fibrewww.toyobo.co.jp
ZYLON consists of rigid-rod chain molecules of poly(p-phenylene-2,6-benzobisoxazole)(PBO).
Tensile Strength : 5.8 GPa
Tensile Modulus : 270 GPa
Ref: K. Padmanabhan , Toyobo Confidentiality Report, 2002.
Polyethylene fibers
The theoretical elastic modulus of the covalent C-Cbond in the fully extended PE molecule is 220 Gpa.
Experimental value in PE fibres - 170 Gpa.
Stretching
Entanglement network Fibrillar crystal
Dyneema or SpectraOrientation > 95%Crystallinity up to 85%
Normal PEOrientation lowCrystallinity < 60%
Extended chain polyethylene
minimum chain folding
UHMWPE fibre structure: (a) macrofibril consists of array of microfibrils;(b) microfibril; (c) orthorhombic unit cell; (d) view along chain axis
•UHMWPE (Spectra or Dyneema) are highly anisotropic fibers•Even higher specific properties than Kevlar because of lower density (0.98 g/cc)•Limited to use below 120°C•Creep problems; weak interfaces•Applications – ballistic impact-resistant structures
UHMWPE
UHMWPE (Spectra) – high flexibility and toughness, poor
interfacial bonding
Poly(p-phenylene benzobisthiazole)
PBT or PBZT
Kevlar
Spectra
Flexibility, compressibility, and limit performance of fibers
FLEXIBILITYIntense bending strains and stresses applied to fibers during manufacturing operations (weaving, knitting, filament winding, etc)
Definition of flexibility:Bending of an elastic beam: M = (EI)/R = (EI) Units: [N/m2][m4]/[m] = [N*m]M = bending momentI = second moment of area of cross-section R = radius of curvature to the neutral surface of cross-section
dAyI 2
E = Young’s modulusEI = flexural rigidity (≈ resistance of beam to bending)= curvature = 1/R
Intuitively: the flexibility of a fiber is the highest when:o The radius of curvature is as small as possible (or the
curvature is as large as possible)o The bending moment necessary to reach a given curvature is as small as possible
o The appropriate parameter to focus on is = /M, which must be maximized for highest flexibility.
b
hM M
12
3bhI
64
4dI MM d
Moment of inertia
Flexibility is thus defined as (for a circular fiber)
where E and d are the fiber bending modulus and diameter, respectively
As seen, the effect of size (diameter) on flexibility is by far the strongest, and thus nanoscale reinforcement promotes high flexibility. Low modulus also promotes high flexibility.
Units of flexibility are [1/Nm2]
464 dE
ASSUMING A CONSTANT DIAMETER:
material d (m) E (Pa) [N-1m-2]
E-glass 1.00E-05 72.0 E+9 28 E+9max
HM carbon 1.00E-05 750 E+9 2.7 E+9 min
HS carbon 1.00E-05 250 E+9 8.2 E+9
Kevlar 49 1.00E-05 130 E+9 16 E+9
Nicalon 1.00E-05 190 E+9 11 E+9
(Steel) 1.00E-05 210 E+9 9.7 E+9
Performing a ‘gedanken’ experiment:
Using real diameters and moduli:
USING REAL DIAMETERS AND MODULI:material d (m) E (GPa) [N-1m-2]
E-glass 1.10E-0572.0 E+9 19 E+9
HM carbon 8.00E-06 750 E+9 6.6 E+9HS carbon 8.00E-06 250 E+9 20 E+9 maxKevlar 49 1.20E-05 130 E+9 7.6 E+9Nicalon 1.50E-05 190 E+9 2.1 E+9 min
SWNT 1.10E-091200 E+9
1.16E+25 !
Glass fibers and HS carbon fibers are more tolerant to bending
Compressibility
• The compressive strength of single fibers is very difficult to measure and is usually inferred from the behavior of composites including the fibers.
• Euler buckling is one possible mode of compressive failure: it occurs when a fiber under compression becomes unstable against lateral movement of its central region.
EILkPcr 2
2
EULER’s WORK ON BUCKLING
0 10 20 30 40 500.01
0.1
1
10
E S
GLASS
K29
SiC
K49 K149
LM CF
BORON
PBTPBO
HM CF
STEEL
SPECTRA 1000
THEORETICALLIMIT FOR GRAPHITE
SPEC
IFIC S
TREN
GTH,
106 m
SPECIFIC MODULUS, 106 m
21
1260
E
Hydrolytic Stability of Kevlar
Moisture Regain of Kevlar
TGA of Kevlar
Multiple Fibre Pull out Test
Kevlar Fibre Surface after Treatment with Acetic Anhydride
Kevlar Fibre Surface
ILSS of Kevlar/Epoxy Composites
Mechanical Testing
Ref: K. Padmanabhan and Kishore , ` Failure behaviour of carbon/epoxy composites in pin ended buckling and bending tests’, Composites, Vol:26,No: 3, 1995, p201.
Asymmetric Hybridization
Kevlar Fibre Fibrillation
Composites in Defense
A Bulletproof Vest A missile material case
Uses• Performance Apparel• Adhesives and Sealants• Belts and Hoses• Composites
Fiber-Optic and ElectroMechanical Cables
• Friction Products and GasketsProtective ApparelTires
Uses• Ropes and Cables
Uses• Ballistics& • Defense
Winners don’t do different things but they do things differently - Shiv Khera