International Journal of Application or Innovation in Engineering & Management... Web Site: www.ijaiem.org Email: Volume 3, Issue 3, March 2014

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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: [email protected]
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Impact Behavior of Sandwich Panels Made of
Composite Material
Dipak D.Bari1, Prashant S. Bajaj2
1
2
PG Student. S.S.G.B.C.O.E. & T; Bhusawal, Maharashtra, India.
Faculty of S.S.G.B.C.O.E. & T; Department of Mechanical Engineering, Bhusawal, Maharashtra, India.
Abstract
Thin sandwich panel made of high strength, high stiffness face sheets and light weight core material was envisaged here to
replace the sheet metals. That may be frequently subjected to low intensity foreign body impacts. In this paper sandwich panels
made of GF face sheets are tested under 6J, 12J and 18J impact energy. Study of the impact behavior and collection of data on
impact resistance of the candidate material was considered. The damage area was observed on the front and rear side of the face
sheets. Also the space contours plot of sandwich panel was constructed using AUTOCAD software. Result shows that Sandwich
panels with GF face sheets can sustain higher impact loads up to18J and No fiber breakage, only de-bonding between face sheet
and core over damage area is observed. There was negligible permanent depression in case of sandwich panels as the panel
restores its original shape when the load is released.
Keywords: Glass fabric [GF], Polyester Coremat XM foam, Sandwich, Impact.
1. INTRODUCTION
The impact behavior of a structural material is an important requirement. The structural members are frequently
subjected to mild or high intensity impacts such as bird hitting the aircraft, hail, dropping of tools during fabrication or
maintenance, etc. In sandwich panels, impact analysis is more critical because the face sheets are likely to separate from
the core easily. They can behave in a ductile manner in case of static loading, but may behave in a brittle manner and fail
catastrophically when subjected to impact loads. Therefore it is a basic need to predict the impact behavior and to collect
data on impact resistance of the candidate material.
Generally, when a sandwich panel is subjected to an impact, a part of the energy associated with impact is used for the
elastic deformation of the material and returned back by the system. The energy in excess is dissipated through several
mechanisms such as fiber breakage, fiber matrix de-bonding and delamination of the face sheets, crushing and sheardeformation of the core, etc. Both the face sheet configuration and the core structure control the impact behavior. The
core in the conventional sandwich panels is generally formed by simple foam whose aim is to increase moment of inertia
and flexural stiffness without increasing the weight [1, 4, 7]. Therefore the foam used in the core does not always have
high mechanical properties.
In the impact, the main performance of the foam core is limited to cushion the inertial loads, while the composite face
sheet performs the energy absorption. In order to determine the impact behavior of the thin sandwich panels, impact tests
are conducted using the drop weight test set-up. The impact tests are conducted at different energies 6J, 12J and18J with
low velocity in the range of 3.3-5.7 m/s. The impact induced damage areas are reported for the thin sandwich composites
developed in the current study.
2. SPECIMEN GEOMETRY AND FABRICATION
The plates of dimensions 168 mm x 168 mm are used for impact test. The impact loading have been performed on the
specimen plate clamped at all edges by the fixture. The unsupported area of the plate is 150 mm x 150 mm. Thickness of
the sandwich panel is nearly 3 mm[13].
Fig.1 Thin Sandwich Plate Geometry
Sandwich panels were fabricated by using symmetric hand lay-up process. Glass fibre Reinforced polymer skin will be
used as its modulus and strength are high. However, Polyester Coremat XM foam was sandwiched in between two face
sheets. Core increases moment of inertia and flexural stiffness without increasing weight.
Volume 3, Issue 3, March 2014
Page 303
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: [email protected]
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
3. EXPERIMENTAL SET-UP
The impact drop test set up has been developed so as to perform the test under controlled conditions. Schematic diagram
of cylindrical punch is shown in Fig.2.
Fig.2 Schematic Diagram of Cylindrical Punch
A short cylindrical punch with hemispherical head, made of mild steel weighing 1.084kg was dropped through the
seamless tube to impact the specimen of size 168 mm x 168 mm clamped at all four edges by the fixture. The cylindrical
punch is used for the transverse central loading on small patch of 10 mm diameter rather than point load. The length and
diameter of the cylindrical piece used were 200 mm and 30 mm respectively as shown in Fig.2.
The clamping fixture is made of two square shaped clamps. Each clamp is made of square rods of size 25mm x 25 mm,
welded together as shown in Fig.3. The specimen is rigidly held between two clamps by 20 numbers of bolts [3].
Fig.3 Clamped Thin Sandwich Plate Specimen.
4. RESULTS AND DISCUSSION
Thin sandwich panels, envisaged to replace the sheet metals, may be frequently subjected to such low intensity foreign
body impacts. Therefore, it is of fundamental importance to study the impact behavior and to collect data on impact
resistance of the candidate material. Sandwich structures must be designed to allow maximum energy absorption in
impact besides the ability to withstand static and dynamic loads.
For the current study, sandwich panels made of GF face sheets are tested under 6J, 12Jand 18J impact energy. Three
samples of each kind of sandwich panel are tested at different impact energy. The impacted specimens have a clearly
visible damage area on the front as well as on rear sides. The permanent deflection over damage area, indentation depth
and failure mechanism are observed at different impact energy and results are compared with the conventionally used 0.8
mm thick MS sheet.
4.1. Damage Area
The damage area of the specimen is clearly marked on front and rear side. The damage area is measured by digital
Planimeter. Here sandwich panel made of high strength glass fabric face sheets and light weight core material (CorematXM) was considered. The damage area on rear side of sandwich panels made of GF face sheets under impact loading at
6J, 12J and 18J energies are shown in Fig.4. There is delamination between core and face sheet, but no fibers breakage
are observed at the damage area due to impact loading up to 12J energy. There is no fiber breakage is observed in case of
GF/XM/GF panel at 18J impact energy. The damage area on front side of sandwich panels made of GF face sheets under
impact loading at 6J, 12J and 18J energies are shown in Fig.5.
Volume 3, Issue 3, March 2014
Page 304
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: [email protected]
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Fig.4 Damage area on rear face of sandwich panels made of GF face sheets
Fig.5 Damage area on front face of sandwich panels made of GF face sheets
Table 1 GF/XM/GF Thin Sandwich Panel
Expt.
1
2
3
4
Damage Area (mm2) at Incident
Impact Energy
6J
12J
18J
683.6
715.8
866.3
570.8
782
1067.4
649
770
971.5
698.3
951.2
1004.5
4.2. Deflection Contour Plot over Damage Area
The deflection of sandwich panels at different impact energies is measured over damage area. The number of points is
marked over damage area. The normal depth is measured at all the points. The deflection contour plot is constructed by
spline command using AUTOCAD software. Fig.6-8 represent the deflection over damage area at different impact
energies for sandwich panels and 0.8 mm thick MS Sheet. If an impact load acts on the MS sheet, it would plastically
deform the MS sheet on a fairly large area, resulting into an extensive depression.
However, sandwich panel bends and regains its shape; there was not permanent depression as in the case of MS sheet.
MS sheets were deformed with a dent at the point of impact due to plastic deformation of the metal as shown in Fig.9the
dent spoils the aesthetics of the automobile body. This can often be observed in car bodies that undergo minor impacts or
collisions where in a small dent spoils the aesthetic surface finish.
Fig.6 Deflection Contour Plot At 6 J Impact Energy
Fig.7 Deflection Contour Plot At 12 J Impact Energy
Volume 3, Issue 3, March 2014
Page 305
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: [email protected]
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Fig.8 Deflection Contour Plot At 18J Impact Energy
Fig.9 0.8 mm thick MS Sheet under Impact Loading
5. COMPARISON OF DAMAGE AREA
Damage area of sandwich panels with GF face sheets is very less compared with conventional material, 0.8 mm thick MS
Sheet. No fiber breakage, only debonding between face sheet and core over damage area is observed in case of sandwich
panels with GF face sheets. Also, the sandwich panels with GF face sheets are strong enough to sustain 12J impact
energy; hence it was further studied at 18J impact. Sandwich (GF/XM/GF) panel is having maximum impact strength,
where no fibers breakage is observed. Damage area of sandwich panels is very less compared with conventional material,
0.8 mm thick MS Sheet shown in Fig. 10.
Fig. 10 Comparison Of Damage Area
6. CONCLUSION
Sandwich structures are found to be most in case of high specific bending stiffness and strength. From this paper it is
observe that there is delamination between core and face sheet, some fibre breakage over the damage area under impact
loading. Sandwich panels with GF facesheets (GF/XM/GF) that studied here can sustain higher impact loads up to
18J.There were negligible permanent depression in case of sandwich panels as the panel restores its original shape when
the load is released. That means sandwich panels regain its shape after the impact but there is permanent deformation in
MS sheet. Damage area and contour plots of sandwich panel are very less compared to 0.8mm thick MS sheet.
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Volume 3, Issue 3, March 2014
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: [email protected]
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
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