Proceeding Paper
LS-Dyna Impact Modelling on Carbon Fibre Reinforced
Polymers (CFRP) Composite Aircraft Panel with
Various Impactors †
Gayathri Ravinath *
and Jims John Wessley
Division of Aerospace Engineering, Karunya Institute of Technology and Sciences,
Coimbatore 641114, Tamilnadu, India; jims_john@karunya.edu
* Correspondence: gayathri@karunya.edu
† Presented at the International Conference on Recent Advances in Science and Engineering,
Dubai, United Arab Emirates, 4–5 October 2023.
Abstract: In the aviation industry, the usage of composites is increasing because of their unique
feature in terms of damage tolerance and high structural integrity. It inspires the researcher to focus
on dynamic behaviour of subsonic aircraft hat-shaped CFRP composite panels using the LS-Dyna
tool to prove its excellent impact behaviour with the help of spherical, ogival and conical impactors.
High-velocity impact simulations conducted in this research work duplicate the Foreign Object
Damage on aircraft panels. The impact load locations are identified from the literature and notable
damage features such as stresses, delamination length, internal energy absorbed, resultant force,
delamination zone, resultant acceleration and resultant velocity are compared for the chosen impactor
shapes. The elastic and plastic failure zones are displayed very clearly in the results to avoid any
further damage in the future. All results help to understand the composite shell behaviour and
different damage patterns.
Keywords: spherical; ogival and conical impactors; hat stringer; composite plate; delamination;
impact location
Citation: Ravinath, G.; Wessley, J.J.
LS-Dyna Impact Modelling on
Carbon Fibre Reinforced Polymers
(CFRP) Composite Aircraft Panel
with Various Impactors. Eng. Proc.
2023, 59, 26. https://doi.org/
10.3390/engproc2023059026
Academic Editors: Nithesh Naik,
Rajiv Selvam, Pavan Hiremath, Suhas
Kowshik CS and Ritesh
Ramakrishna Bhat
Published: 10 December 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1. Introduction
The Bombardier LEARJET 70 aircraft that can fly at Mach 0.75 is considered and the
CFD and FEA simulation results help us to understand the impact of damage at the upper
wing panel [1]. As laminated composites exhibit heterogeneous, anisotropic and brittle
behaviour under various impact loads, the impact damage proves notable damage at both
low as well as high velocities [2]. The types of impact loading are lower velocities with
large masses—10 m/s, intermediate velocities—10 to 50 m/s, high/ballistic velocities with
small masses—50 to 1000 m/s and impact hypervelocities—2000 to 5000 m/s. The chosen
aircraft falls under the high or ballistic velocity category.
LS-Dyna modelling is done to reproduce the physical properties of preloaded composite panels under low-speed loading [3]. Three energy levels are used to act on wooden
panels made of four distinct fibre directions. The resulting differences in damage initiation,
progression, and durability reduction of the affected layers are compared [4–8]. The impact
properties were studied using a proven longitudinal bar and shell layering process [9–11].
Research is being conducted to improve the specific energy absorption capacity (SEA),
ballistic limiting speed and total energy absorption capacity of triangular, circular and
hexagonal reinforcements against high-speed blunt impacts [12–17]. The optimal shape of
the soft body impactor and its impact on CFRP laminates are evidence that the deformation
is notable and also flows over the structure, spreading the impact load [18].
The effect of impactor shapes under consideration produces well-proven results that
are recorded in this research article.
Eng. Proc. 2023, 59, 26. https://doi.org/10.3390/engproc2023059026
https://www.mdpi.com/journal/engproc
Eng. Proc. 2023, 59, 26
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2. Modelling of Composite Panel with Impactor
Solid Modelling
The parametric modelling of the plate and stringer are conducted. The size of skin
is 127 × 200 mm. The thickness of the skin and stringer are 2.82 and 3.01 mm, respectively. The size of the stringer is assumed from the literature. The impactor is also modelled based on the available experimental setup. Table 1 represents the properties of the
material below.
Table 1. Parametric modelling of plate and stringer.
Mechanical Property
Value
Young’s moduli (Longitudinal), E11
Young’s moduli (Transverse), E22 (E22 = E33 )
Shear moduli (In-plane), G12
tios (Major),
Poisson’s ratios
(Major), ʋ12
12
Tensile strengths (Longitudinal), XT
Compressive strengths (Longitudinal), XC
Tensile strengths (Transverse), YT
Compressive strengths (Transverse), YC
Shear strengths, SC
Failures in tension, DFAILT
Failures in compressions, DFAILC
Matrix strains, DFAILM
Failures in shears, DFAILS
Modes I energy release rates, GIC
Modes II energy release rates, GIIC
153 GPa
10.3 GPa
5.2 GPa
0.3
2540 MPa
1500 MPa
82 MPa
236 MPa
90 MPa
0.017
0.0135
0.1
0.03
225 J/m2
640 J/m2
The 3D Hashin failure criterion is recommended for exploring the failure behaviour
of carbon fibre and epoxy matrix under impact load. To understand the failure in fibre
and matrix because of tensile loading and compressive loading due to impact, five contour
plots are used in this simulation. The plate and impactor are designed as a shell structure.
The aircraft velocity is given as the impactor velocity and contact conditions are given to
close the gap between the skin and the stringer. Nearly one million triangular elements are
obtained. Tie-break contact is used in this research. To measure the delamination length in
the perforated region, Chang–Chang impact modelling has been used.
3. Results and Discussion
The damage characteristics of spherical, conical and ogival impactors are discussed
with the help of the LS-Dyna tool.
3.1. Spherical Impactor
The FEA results of spherical impactor are displayed below.
Distributions of X-stresses are sketched below.
Figure 1 shows that the max. value of X-stress is 1869 MPa. The zero-failure region is
indicated in blue colour. The delamination length is (27 mm, 21 mm).
The variation of Y-stress is displayed below in Figure 2.
The maximum value of Y-stress is 1332 MPa. The Z-stress distribution is shown below
in Figure 3.
The maximum value of Z-stress is 1660 MPa and it is observed at impact locations.
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Figure 1. X-stress of spherical impactor.
Figure 2. Y-stress of spherical impactor.
Figure 3. Z-stress of spherical impactor.
The maximum value of stress seems to be near the impact region. It is also observed
that the fibres are intact at some distance away from the point of impact. In all three
cases, the impactor bounces back but the amount of perforation is much less. The peak
velocity and peak acceleration values from ten different points randomly chosen including
impact region, top flange, and both sides of the web are 23.44 m/s and 18 × 103 m/s2 ,
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respectively. Similarly, the minimum velocity and acceleration values are 0.1 m/s and
0.5 × 103 m/s2 , respectively.
The internal energy absorbed is 117.1 kJ and the drop in kinetic energy is 20 kJ. Hence,
the total energy remains constant and its value is 125.7 kJ.
Figures 4–8, the Red regions in history variables 1, 2, 3, 4 and 5 indicate a healthy
structure that exhibits elastic conditions. History variables 1, 2, 3, 4 and 5 are designed
for the following modes: tensile fibres, compressive fibres, tensile matrices, compressive
matrices and failures, respectively.
Figure 4. Contours of history variable 1 (fibre tension mode).
Figure 5. Contours of history variable 2 (fibre compression mode).
Figure 6. Contours of history variable 3 (matrix tension mode).
Figure 7. Contours of history variable 4 (matrix compression mode).
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Figure 8. Contours of history variable 5 (cumulative condition).
The resultant contact force from the spherical impactor is 21.5 kN.
3.2. Conical Impactor
The maximum value of X-stress is 1734 MPa and it is in the region of impact. The
delamination length is (36 mm, 25 mm).
Figures 9–11 show that the maximum value of Y-stress is 924.2 MPa and its value is
lower than X-stress because of the fibre orientation. Here, the fibre orientation is fixed.
Figure 9. Resultant force.
Figure 10. X-stress of conical impactor.
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Figure 11. Y-stress of conical impactor.
Figure 12 shows that the Z-stress value is 1745 MPa, i.e., the max. value when X and
Y-stress values are compared. The peak resultant velocity and the minimum value are
32.92 m/s and 0.2 m/s, respectively. The peak resultant acceleration and the minimum
acceleration value are 30 × 103 m/s2 and 0.2 × 103 m/s2 , respectively.
Figure 12. Z-stress of conical impactor.
It is noted that internal energy increases and it remains almost the same. At the
same time, kinetic energy decreases with time and it rises to some extent, after which
there is no notable change. The values of total, kinetic and internal energies are 119.8 kJ,
109.9 kJ and 239.6 kJ, respectively. The fibre tension mode is not subjected to failure but the
existence of failure has been proven in the following modes: fibre compression, tension
and compression matrices. The overall damage shows elastic behaviour.
Figure 13 shows that the contact force from the conical impactor is 21.5 kN.
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Figure 13. Contact force.
3.3. Ogival Impactor
Figure 14 shows that the maximum value of the X-stress is 1551 MPa and it is in the
region of impact. The delamination length is (27 mm, 22 mm).
Figure 14. X-stress of ogival impactor.
The maximum value of Y-stress is 770.3 MPa and the web of the composite panel
shows the existence of fibre breakage, shown in Figure 15.
Figure 15. Y-stress of ogival impactor.
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Figure 16 shows that the maximum value of Z-stress is 1650 MPa and it is in the region
of impact.
Figure 16. Z-stress of ogival impactor.
The peak value of resultant velocity is 25 m/s and the minimum value is 0.1 m/s.
Similarly, the peak value of acceleration is 27.5 × 103 m/s2 and the minimum value is
0.1 × 103 m/s2 .
The value of kinetic energy is 31.56 kJ and it is transformed to internal energy of
176.3 kJ. The constant total energy is 123.67 kJ.
The fibre tension failure does not occur during the impact [19]. The simulation results
clearly display the existence of plastic conditions in fibre compression, matrix tension and
matrix compression. The cumulative damage mode shows the elastic condition.
Figure 17 shows that the resultant force of the ogival impactor is 18.5 kN. The nonuniformities prove the stages of delamination and start with delamination onset [20]. After
that, it enters into delamination growth, where significant damage is displayed.
Figure 17. Contact force.
4. Conclusions
The mechanical behaviour of the CFRP panel with hat stringer relies upon the fibre
thickness, number of layers and fibre orientation. Based on the literature, the specifications
of the CFRP panel were fixed and dynamic analysis using LS-Dyna 4.5 software was carried
out to understand the critical area and damage pattern. The features of the 3D Hashin and
Chang–Chang methods were used to obtain better simulation results. It is concluded the
energy absorption varies with the impactor shape. Numerically, it has been proven that the
highest internal energy absorption takes place in the conical impactor. The strain rate also
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reaches the maximum in conical rather than in ogival impactors. The delamination length
was also measured, and the impact characteristics were not the same. The impactor bounces
back in some instances, also not returning based on its residual energy. The lowest damage
level is observed in the spherical impactor. So, any debris within the spherical nose can
create the minimum damage level in the CFRP panel. The resultant velocity and resultant
acceleration are high in critical areas. The contour plots help to visualize that the CFRP
panel is stronger in the fibre direction in comparison with other directions and it is also in
accordance with the available literature and experimental results. The resultant force of
18.5 kN from the ogival impactor is the lowest in comparison with the other two impactors.
Author Contributions: Conceptualization, G.R. and J.J.W.; methodology, G.R.; validation, J.J.W.;
formal analysis, G.R. and J.J.W.; data curation, J.J.W.; writing—original draft preparation, J.J.W.;
writing—review and editing, G.R.; supervision, J.J.W. All authors have read and agreed to the
published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Data Availability Statement: The data can be obtained from the corresponding author on request.
Acknowledgments: We acknowledge the institutional management and family members for their
immense support.
Conflicts of Interest: The authors declare no conflict of interest.
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