Experimental and numerical studies on the impact response of
damage-tolerant hybrid unidirectional/woven carbon-fibre reinforced
composite laminates
Liu, H., Falzon, B., & Tan, W. (2018). Experimental and numerical studies on the impact response of damage-
tolerant hybrid unidirectional/woven carbon-fibre reinforced composite laminates.
Composites Part B:
Engineering
,
136
(1), 101-118. https://doi.org/10.1016/j.compositesb.2017.10.016
Published in:
Composites Part B: Engineering
Document Version:
Peer reviewed version
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Download date:09. Aug. 2022
1
Experimental and numerical studies on the impact response of damage-tolerant
hybrid unidirectional/woven carbon-fibre reinforced composite laminates
Haibao Liu
a
, Brian G. Falzon
a
*, Wei Tan
b
a
School of Mechanical and Aerospace Engineering, Queen`s University Belfast, Ashby Building, Belfast BT9 5AH, UK
b
Engineering Department, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK
ABSTRACT
A woven Five-Harness Satin (5HS) weave with AS4 carbon fibres, and unidirectional high strength IMS60 carbon fibres
were used to manufacture hybrid laminates, using resin infusion, to assess their performance in low velocity impact tests.
Load/energy-time curves and load-displacement curves were extracted from the experimental data, and non-destructive C-
scanning was performed on all pre- and post- impacted specimens to quantify the extent of damage incurred. A finite
element-based computational damage model was developed to predict the material response of these hybrid
unidirectional/woven laminates. The intralaminar damage model formulation, by necessity, consists of two sub-models, a
unidirectional constitutive model and a woven constitutive model. The built-in surface-based cohesive behaviour in
Abaqus/Explicit was used to define the interlaminar damage model for capturing delamination. The reliability of this model
was validated using in-house experimental data obtained from standard drop-weight impact tests. The simulated reaction-
force and absorbed energy showed excellent agreement with experiment results. The post-impact delamination and
permanent indentation deformation were also accurately captured. The accuracy of the damage model facilitated a
quantitative comparison between the performance of a hybrid unidirectional/woven (U/W) laminates and a pure
unidirectional (PU) carbon-fibre reinforced composite laminates of equivalent lay-up. The hybrid laminates were shown to
yield better impact resistance.
Key words: A: Laminates; B. Impact behaviour; C. Finite element analysis; D. Non-destructive testing;
1. Introduction
Carbon Fibre Reinforced Polymers (CFRPs) have been widely adopted in modern high performance lightweight structures.
The main advantages of composite materials include high specific strength, stiffness and good fatigue resistance [1–3].
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These excellent mechanical properties have made composites the pre-eminent material in the primary structure of the latest
generation of passenger aircraft, such as the Boeing 787 and Airbus A350, where composites account for around 50% of
the aircraft`s weight. However, the superior properties of CFRP laminates tend to be in the fibre direction and actually exhibit
very low strength and fracture toughness through the thickness direction [4–6]. As a consequence, low velocity impact is a
critical load case for composite aerostructures. Delamination, matrix cracks and fibre breakage, resulting from an impact
event, may significantly reduce the residual strength of composite structures [7,8].
For this reason, studies associated with low velocity impact on composites attract a great deal of attention [9,10]. In order to
attain a comprehensive understanding of the failure mechanisms, a number of experimental investigations have been
conducted by researchers. Mehmet et al. [11] investigated the impact response of cross-ply and angle-ply glass/epoxy
laminates under different impact energy levels. Due to the optically transparent nature of glass-epoxy composites, the
damage modes and damage process were easily observed and discussed. They found that lower impact energies induced
more delamination and matrix cracking, while, the higher impact energies resulted in more fibre failure. In the study
presented by Celal and Mufit [12], different types of composites specimens; unidirectional E-Glass, woven E-Glass and
woven aramid composite specimens, were tested under low velocity impact. Based on experimental results, the damage
growth in woven composites was constrained within a smaller area compared with unidirectional composites, and shown to
have superior damage resistance than unidirectional composites.
In order to mitigate extensive physical testing, it is also essential and practical to improve the capability to predict damage in
composite laminates due impact. Some finite element-based composite damage models are available in commercial
packages. Examples include the Abaqus built-in progressive composite damage model based on the work by Matzenmiller
et al. [13]; and the LS-DYNA [14] material model type 262 which uses an approach based on the failure criteria presented by
Chang and Chang [15]. Despite the widespread application of these commercial packages, calibration of non-physical
parameters to control the damage propagation, is generally required.
Y. Shi et al. [16,17] used stress-based criteria and fracture mechanics techniques to capture composite laminate damage
initiation and evolution of damage during an impact event. The nonlinear shear properties of composites were defined by a
semi-empirical shear stress–strain relationship. X-ray radiography was used to validate the proposed numerical model.
Ansari and Chakrabarti [18] conducted a numerical investigation on the penetration and perforation behaviour of composite
laminates under impact loading. The effects of boundary conditions and thickness-to-span ratio were discussed. Donadon et
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al. [19,20], Faggiani et al. [21] and Falzon et al. [22,23] proposed a three-dimensional (3D) computational damage
mechanics (CDM) based material damage model to capture the intralaminar degradation of composite laminates with
nonlinear shear behaviour. This model was combined with cohesive elements to investigate impact damage. Bouvet et al.
[7,24] presented a model which captured the permanent indentation caused by low velocity/low energy impact, similar to
that reported by Faggiani [21]. Recently, a computational model was developed by Tan et al. [25–27] for predicting the
material response of composite laminates under compressive, impact or crush loading. The intralaminar damage model,
which accounts for physically-based failure mechanisms associated with the fibres and matrix, was implemented as a user
subroutine in Abaqus/Explicit. The in-built cohesive behaviour [28] in Abaqus/Explicit was employed to capture the
interlaminar failure.
In addition, damage models have been developed to specifically capture the material response of woven composite
laminates. Zhong et al. [29] proposed a continuum damage model for predicting the damage initiation and development in
3D woven composites. The fibre damage was considered at the level of the fibre yarn, and a series of variables were
defined to characterise the fibre and matrix failure modes. This damage model was implemented within the finite element
method, and validated the quasi-static tensile experiments of a type of 3D woven composite. A 3D micromechanical model
was developed by Donadon et al. [30] to predict the elastic behaviour of woven laminates. Composite laminates including a
hybrid plain-weave with different materials and undulations in the warp and weft directions were manufactured and tested
under tension and in-plane shear loading to validate the model.
In spite of extensive research in this area, there is still considerable work to be done to understand the intrinsic
characteristics of a composite`s response to low velocity impact. In this study, the impact response of carbon fibre/epoxy
laminates with different lay-up was investigated using a drop-weight impact testing machine. The American Society for
Testing Material (ASTM) D7136/D7136M standard was adopted in this study. Following the drop-weight impact tests,
preliminary visual observation was performed on the top (impacted) and bottom surfaces of all specimens. These specimens
were subsequently scanned using a C-scan system to obtain damage maps [7,8,24,31]. Specimen cross-sections along the
0°, 45° and 90° fibre directions were extracted from selected impacted specimens for optical microscopy [32–34]. The
microscopic analysis yielded further insight into composite damage arising from low velocity impact. A physically-based
composites damage model, which accounts for material shear nonlinearity and damage mode interaction, was validated to
predict the impact response of hybrid unidirectional/woven carbon fibre reinforced epoxy composite laminates. The in-plane
damage in the warp and weft directions of the woven composites was defined by a fibre-dominated failure mode. A matrix-
4
dominated failure mode was used to initiate the through-thickness damage of woven composites and the transverse
damage of unidirectional composites. This model is shown to be able to reproduce the laminate`s impact response and yield
accurate results without calibrating any of the input material parameters obtained from standard physical tests [26]. This
enabled the computational model to attain a truly and reliably predictive capability. The predictive results delivered by this
damage model are shown to be in excellent agreement with experimental results.
2. Material and specimen
The materials used in this study were IMS60 unidirectional carbon fibre, five harness satin (5HS) woven AS4 carbon fibre
fabric and an epoxy resin (propriety information). The panels, from which the specimens were produced, were manufactured
using Resin Infusion under Flexible Tooling (RIFT) [35–37]. A flow distribution medium was used on the upper and lower
surfaces of the preform to ensure complete wetting. All panels were subsequently inspected using C-scanning to ensure the
pristine specimens were free of any major defect [38]. The material properties of the manufactured laminates were obtained
using standard testing methods and are presented in Table 1.
Table 1
Mechanical properties of IMS60/Epoxy unidirectional (UD) lamina and AS4/Epoxy five harness satin (5HS) woven lamina
Materials
Modulus (GPa)
Poisson`s ratio
Strength (MPa)
Unidirectional
lamina
5HS woven
lamina
Specimens were cut from the RIFT-manufactured panels according to the ASTM D7136/D7136M testing standard. The
geometric parameters and lay-up of the specimens used for low velocity impact tests are shown in Table 2.
