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IMPACT DAMAGE IN COMPOSITES STRUCTURES
G. P. Rodríguez Donoso, M.A. Caminero Torija, V. Muñoz Rucián,
A. Romero Gutiérrez, J.L. Martínez Vicente, M.C. Serna Moreno & J.J. López Cela
Universidad de Castilla-La Mancha.
e-mail: [email protected], [email protected]
The objective of this work is the characterization and the assessment of the damage in CFRP laminates subjected to low-velocity impact
loading. An experimental test series was carried out to determine energy absorption and failure mechanisms of composite laminates
made from M21E/IMA, an unidirectional prepreg used in A350 XWB primary structures (wing spars and wing covers, fuselage sections,
keel beam and central wing box). Specimens were cut from the CFRP plates and Charpy impact tests were conducted to study energy
absorption properties under impact loadings, taking the standard UNE-EN ISO 179 as a reference. Different stacking sequences were
examined to gain an insight into the assessment of different type of damage in the previous laminates. It has been established the
failure mechanisms for each laminate and how the crack spreads through the material. Finally, SEM and optical micrographs of fracture
surfaces were used to explain the changes in failure mechanisms, and therefore impact properties of the different stacking sequences.
EXPERIMENTAL PROCEDURE
MATERIAL: Hexply ® M21E/34%/UD268/IMA-12k/300/ATL
PROPERTIES ON A CURED PREPEG PLY:
LAMINATE SEQUENCES:
Theoretical fibre volume
59.2%
Theoretical ply thickness
0.184 mm
Laminate density
1.58 g/cm³
Tensile strength
3050 MPa
CROSS PLY
[(0/90)3]S
Modulus of elasticity
178 GPa
ANGLE PLY
[(±45)3]S
Shear modulus
5.2 GPa
QUASI ISOTROPIC
[0/90/(±45)2]S
CURING PROCESS:
Hot Plate Press and
Vacuum system
[0]12
UNIDIRECTIONALS
[90]12
[45]12
Unidirectional 0
Quasi isotropic
CHARPY (UNE-EN ISO 179 / ASTM D6110)
Low velocity impact damage by a 300 J Charpy
Pendulum:
• Impact velocity = 5.42 m/s
• Hammer mass = 20 kg
• Arm length = 800 mm
• Supports distance = 40 mm
Impact resistance dependant on laminate
Multidirectional laminates
Unidirectional laminates
Unidirectional 0
[0]12
E = 18.91 J/cm2
Specimen measurements (mm)
Total delamination
35
Absrobed energy (J/cm2)
Fibre breakage
Angle Ply
[(±45)3]s
E = 30.63 J/cm2
Delaminations placed at
the impacted area
30
25
90
45
20
0
0/90
15
0/90/±45
±45
Brittle matrix breakage
10
Unidirectional 90
[90]12
5
E = 4.64 J/cm2
Quasi isotropic
[0/90/(±45)2]s
0
E = 26.52 J/cm2
Matrix breakage at ±45º
SEM micrographs at the fracture zone
(Unidirectional 0 laminates)
Fibre pull-out
Fibre debonding
Delamination
Unidirectional 45
[45]12
E = 5.31 J/cm2
Cross Ply
[(0/90)3]s
E = 23.22 J/cm2
Matrix cracking
Fibre breakage
Brittle matrix breakage
Penetration failure
Fibre debonding
Brittle matrix breakage
Delamination at 0-90 interface
Delaminations
Fibre breakage
CONCLUSIONS
 Unidirectional 0º laminate sequence behaved opposite to unidirectional 90º. The first one exhibited higher impact energies due to the tough intervention of the fibre, although it presented
a remarkable anisotropy. Unidirectional 90º laminate decreased significantly this property due to brittle matrix fracture.
 Unidirectional 45º sequence showed a behaviour similar to 90º as the fracture is by matrix and the crack spreads througout the fibre direction.
 Multidirectional laminates exhibited better impact energy absortion. Cross ply [(0/90)3]s laminate showed a broad spread of data due to polar behaviour of adjacent plies. Angle ply
laminate [(±45)3]s had the best energy absortion value because of a macroscopic pseudo ductility in its failure mechanism.
 Quasi isotropic laminate exhibited high impact energy as it benefited from resistance of 0º plies and from ductility properties of angle ply laminate, reinforcing impact properties in most
loading directions.