International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
Impact and Strength Analysis of All-Steel
Sandwich Structures for Different Core Shapes
Satya Kiran O. N. V #1, Dr. A. Gopichand *2, Mahesh Krishna B #3, P S N Raju*4
Student2, Professor1, Assistant Professor3, Assistant Professor4
Department of Mechanical Engineering, Swarnandhra College of Engineering & Technology (Autonomous), JNTUKakinada, Andhra Pradesh, INDIA.
Abstract: The aim of this work is to evaluate
hence the bending stiffness) of the material cross section
the effect of core shape in All Steel sandwich panels.
with only a small increase in weight. The construction is
Three different core shapes, namely C-Core, Rectangu-
often used in light weight applications such as aircraft,
lar Core and HAT Core sandwich panels are taken into
marine applications, wind turbine blades, industrial plat-
study and their mechanical behavior is compared. For
forms and floors. The face sheets of sandwich panels
evaluating mechanical behavior, both numerical simula-
provide structural stiffness and protect the core against
tions based on FE techniques as well as Experimental
damage and weathering. During loading, the face sheets
testing were employed. As a part of the evaluation, static
take compressive and tensile loads and core is subjected
analyses to find the response of the sandwich panels to a
to shear loads between the faces, thus providing high
UDL of 10kN were executed. Compressive testing is
bending stiffness. Sandwich structures are used in appli-
then carried out on fabricated models on UTM. During
cations requiring high stiffness to weight ratios, since
fabrication, adhesive bonding is made use of when
for a given weight, the sandwich structure has a much
bonding core to face sheets. The panels are then tested
higher moment of inertia compared to solid or I- beam
for their crushing strength during compression. The
structures.
testing reviled that the failure of the panels began with
A. Classification of sandwich structures
the failure of the bonding and then the core. Modal
analysis is then simulated to find the natural frequencies
and impact analyses are simulated to study the behavior
of the panels under impact. The results and inferences
based on the results are presented in this paper.
A wide range of materials can be used for
sandwich facings and cores. Common facing materials
include metals (Ex. Steel or aluminum) and composites.
Common core materials or structures include metallic
stiffeners, foams (polymer or metallic), honeycombs and
Key Words: Impact Analysis, FEA, Rectangular Core,
balsa wood. The core-to-facing joint is normally
HAT Core, C-Core, Sandwich Panels
achieved through adhesive bonding or welding.
I.
INTRODUCTION
B. All-metal-sandwich structures
A sandwich structure is a fabricated material
All-metal, hybrid metal, and composite sand-
that consists of two thin, stiff facing sheets joined to
wich structures are most commonly used for industrial
either side of a low density core material or structure.
applications. This section details All – metals sandwich
The separation of the facing by a light weight core acts
structures. An all-metals sandwich structure is defined
to significantly increase the second moment of area (and
as one in which both the facings and the core are formed
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
from metallic materials. In the marine industry, this
carried out, corrugated and prismatic cores perform the
normally means steel or aluminium. Aside from the con-
best when optimized for a particular loading direction.
stituent materials, All-metals sandwich structures can be
Gopichand, et al [12] studied numerically (using FE
further classified by the geometry of the core.
techniques) the behavior of corrugated sandwich panels
with SS face sheets and MS core when subjected to
C. Steel sandwich panels
compressive load. The results are verified experimentalMetallic sandwich panels with top and bottom
ly.
plates as well as the core made up of steel are called
steel sandwich panels. The core structures are of differ-
B. IMPACT ANALYSIS
ent types according to core structures the steel sandwich
Sharma, et al [2] investigated the effect of local
structures are divided some of them are I-Core, O-Core,
resonators in reducing the amplitudes during impact
with rectangular beams, Vf/V-Cores with hat or corru-
loading. Both experimental and numerical simulations
gated sheets as a core, web core ,round O Core C-Core
were carried out as a part of this investigation. Based on
and X-Core with two hats ass a core. The figure 1 shows
the investigations, it was found that properly placed re-
the different core shapes that are used in this paper.
sonators is an effective method of improving flexural
bending behavior during impact loads. Foam cored
sandwich panel has been used during the study. Nusrathulla, et al [5] focused to development of statistical
equations using multiple regression analysis, correlating
Figure 1: Different types of core shapes.
II.
LITERATURE REVIEW
various process parameters to responses such impact
load, energy and deflection of the impacts. Wadley, in
two of his works with other authors, [6] investigated the
A. STATIC STRUCTURAL:
effect of unit cell size and shape of a extruded sandwich
Blanken [9] proposed the use of hat-stiffened
structures, when they are stiffened using Alumina, dur-
panel as an alternative for a conventional sandwich
ing impact loading. The impact projectile speeds consi-
structure (which is used as a skin) in modern wind tur-
dered are of 1050m/s to 1400m/s. A combination of X-
bine blades. The sandwich panel has been analyzed on
Ray tomography and high speed imaging has been used
failure modes due to longitudinal compression. An op-
to study the impact performance of sandwich panels.
timization methodology for designing mass efficient
Naresh, et al [3] studied the impact behavior of honey-
blade has been proposed. Verification of the methodolo-
comb sandwich panels with different cell shapes using
gy has been done experimentally by fabricating a scaled
FE Simulations. Thomas [7] gave a review of the expe-
model. Casey [10] proposed the use of web core sand-
rimental testing and related analytical methods of sand-
wich panels for roof construction. The author also inves-
wich panels in their report. The experimental procedure
tigated the shear buckling behavior of the same both
followed and instrumentation used by them when testing
numerically and experimentally. Valdevit, et al [1] com-
a Nomex honeycomb sandwich panel are described. The
pared the behavior of corrugated and prismatic diamond
same tests are studied using FE analysis. Based on the
cores with truss and honeycomb cores. FE simulations
results of FEA, Multicontinuum Failure Theory (MCT)
are carriedout for this purpose. As per the investigations
for progressive failure analysis (PFA) in composite la-
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
minates has been proposed. The theoretical results
agreed well with experimental results.
III.
IMPACT AND STRENGTH ANALYSIS
A. Specifications Of Sandwich Panel
Face sheets material -Stainless steel
Figure 2: Sandwich panel with different cores under a
Core material – Mild steel
UDL of 10kN applied on the face
Thickness of the face sheets and core – 18 gauge
Core shapes – HAT-core, C-core, Rectangular- core
Core height – 25 mm
Panel shape – Square – 250 x 250 mm.
B. Static Analysis
Static analysis is performed to evaluate the behavior of sandwich panels for two cases (i) uniformly
distributed load i.e. force of 10kN on face of each sandwich panel, (ii) force on the face plate equal to crushing
load. Figures 2 & 3 show various boundary conditions
and loading applied on the panels for static analysis.
Figure 3: Sandwich Panels of different cores under
Crushing load obtained on UTM
C. Compression Test:
Based on the results of static analysis on panels
when subjected to UDL, it can be observed that rectangular core will have greater resistance when subjected to
compression also. The same is observed during com-
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
pression testing. Compression testing is done on fabricated models of the same sandwich panels using UTM.
Figures 6 (a), (b) and (c) show the fabricated sandwich
panels. During testing on UTM, it is observed that the
failure was primarily due to bonding failure. After bond
failure, the failure of core further resulted in the crushing of sandwich panel. Figures 7 (a), (b) and (c) show
the sandwich panels loaded in UTM after crushing and
the crushing loads are shown in the table 2
(a) C-Core Sandwich Panel
(b) Rectangular Core Sandwich Panel
Figure 8: Sandwich Panels different core shapes and
boundary conditions for Modal Analysis
E. Impact Analysis
To study the performance of the sandwich pa-
(c) HAT Core Sandwich Panel
Figure 6: Fabricated Sandwich Panels
D. Modal Analysis
nels under impact, explicit analyses are performed. During the study, an impact due to a rectangular block of
50mm X 50mm X 20mm at the center of the panel is
simulated. For this the block is modeled and placed at
Modal analysis is also performed to study the
the center and given an initial velocity of 4.42 m/s. Dur-
natural frequencies of the sandwich panels. When per-
ing simulation, all the faces on the four edges are fixed.
forming modal analysis, fixed boundary condition is
As shown in figure 10 for all the three sandwich panels.
applied to all the faces on the four boundaries of each
sandwich panel. Figure show the boundary conditions
applied for each model as a part of this analysis.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
Figure 5: comparative graph of stresses when subjected
to UDL of 10kN
B. Static Analysis when subjected to crushing
Figure 10: Configuration used for Impact Analysis (the
load:
square block at the center of the panel is the loading
member and is given an initial velocity of 4.4m/s).
Table 1 summarizes the result of deformation
and stress distribution of sandwich panels when sub-
RESULTS
jected to crushing loads.
A. Static Analysis when subjected to UDL of
Core type
10kN
The results showing displacement and stress
distribution for different panels are given in figures 4 &
Deformation (mm)
Stress (Mpa)
C-Core
0.020346
67.514
Rectangular Core
0.013708
54.615
HAT Core
0.017559
91.606
5.
Table 1: Result summary of Static Analysis When
Sandwich Panels are Subjected to Crushing Load
C. Compression Test On Utm:
Figure 4: comparative graph of deformations when subjected to UDL of 10kN
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(a) C-Core Sandwich Panel
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
Graph 1 : Plot showing the variation in natural frequencies of considered sandwich panels.
E. Impact Analyses:
Graph 2 shows the Variation of Equivalent stress wrt
(b) Rectangular core Sandwich
Panel
time during impact analysis.
(c) HAT Core Sandwich Panel
Figure 7: Sandwich Panel failure
during UTM testing
Core Shape
Crushing Load (N)
C-Core
42000
Rectangular Core
67000
HAT Core
60000
Graph 2: Variation of Equivalent stress wrt time during
impact analysis
Table 2: Crushing load obtained during Compression
Testing for various core shapes
D. Modal Analyses:
Graph 1 shows the variation of frequencies in the considered sandwich panels under applied boundary conditions.
CONCLUSION
A. Static analyses:
Based on the results of the analyses, it is
observed that though the deformations are comparable,
the deformation of rectangular core sandwich panel has
lower deformation. The stress distribution plots of these
analyses also indicate the same. This is in agreement
with the fact that deformation and stresses should be
minimum for designed Rectangular core sandwich panel
as it has higher section Modulus.
Compressive tests are then executed using
UTM on these panels. The tests also indicate that rectangular panels have higher compressive strength.
B. Modal analyses:
Based on the results, it is observed that modal frequencies are high for rectangular core sandwich panels.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 32 Number 2- February 2016
C. Impact Analyses:
The response plots obtained as a result of simulations showed that peak stress is seen in the core indicating that the core is taking the load. Also it is observed
that least load is observed HAT core sandwich panel.
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