Failure analysis of pin loaded glass epoxy polystyrene composite plates

International Journal of Advanced Research in OF ADVANCED RESEARCH IN
INTERNATIONAL JOURNAL Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME
ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online) IJARET
Volume 3, Issue 2, July-December (2012), pp. 137-144
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Journal Impact Factor (2012): 2.7078 (Calculated by GISI)
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FAILURE ANALYSIS OF PIN LOADED GLASS EPOXY/POLYSTYRENE
COMPOSITE PLATES

D.Lingaraju1, *, K.Srinivas2, B.A.Ranganath2

1. Aditya Institute of Technology and Management, India (*Corresponding Author)
2. Maharaj Vijayaram Gajapati Raj College of Engineering, India

ABSTRACT

Composites are becoming an essential part of today’s materials because they offer
advantages such as low weight, corrosion resistance, high fatigue strength, faster assembly
etc. Composites are used as materials in making aircraft structures to golf clubs, electronic
packaging to medical equipment and space vehicles due to their good mechanical properties.
In the practical use of the composite materials in structures, some geometrical discontinuities
like cut outs and holes are necessary for some functions such as riveted and bolted joints.
Therefore it is necessary to study the failure behaviour at these joints.
In this study, behaviour of pin loaded laminated composite plates with different
dimensions are observed experimentally. The aim is to investigate the stress and failure load
and failure mode in laminated glass epoxy/polystyrene composite plates with one circular
hole. The hole of the plate is subjected to a traction force by rigid pin.
The analysis is then extended to find the effect of varying K/D and W/D. It is observed
that the strength of the specimen increases with the increase in K/D and W/D to an extent and
then becomes constant. W/D has a greater effect on the mode of failure.

Keywords: Pin Load, Failure analysis, FRP, Epoxy, Polystyrene.

INTRODUCTION

Composite civil and mechanical structures are appearing more frequently in load-bearing
applications because of their low cost, lightweight and environmental resistance. Low cost
glass-fiber/plastic composites are used in the process industry when the environment is highly
hostile and metal corrosion is a serious problem. In the practical use of the composite
materials in structures, some geometrical discontinuities like cut outs and holes are necessary
for some functions such as riveted and bolted joints. Therefore it is necessary to study the
failure behaviour at these joints. For this reason and because civil structures are designed for

137

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976

longevity, it is becoming increasingly important that engineers have tools to design
composite structures for both life and strength.
Typical failure mechanisms for the pin loaded-joint configuration are shown in
Figure-1. The joint fails in one of these three modes or a combination of these. The strength
of the joint is the least of normal, shearing and bearing strengths. The mode of failure
depends on the type of strength which is the least. In general, failure of a joint means either
the failure of the plate or the failure of the pin / joint. The normal mode of failure occurs for
plate while shearing and bearing modes of failure occur either for plate or pin depending on
which is weaker. In the present work, the pin is considered to be rigid and therefore the
failure is considered only in the plate.

(a) (b) (c)
Figure-1: Modes of failure (a) Normal (b) Shear (c) Bearing

FU-KUO Chang et.al. [1] Studied the progressive damage model for notched laminated
composites subjected to tensile loading. The model is capable of assessing damage in
laminates with arbitrary ply-orientations and of predicting the ultimate tensile strength of the
notched laminates.
The failure strength and failure mode of bolted connections of glass woven fabric
composites was investigated by H.J.LIN et.al. [2]. the failure criteria and the material
degradation model were successfully used to model the behaviour of laminates subjected to
in-plane loads. They considered five types of failures: matrix failure in tension, matrix failure
in compression, fiber failure in tension, fiber failure in compression and fiber- matrix de-
bonding failure. Experimental results showed that laminates with moulded-in holes are
stronger when the edge distance is small. When the edge distance is large, specimens with
moulded-in holes have about the same strength as those with drilled holes.
Camanho et.al. [3] developed a three-dimensional finite element model to predict
damage progression and strength of mechanically fastened joints in carbon fiber-reinforced
plastics that fail in the bearing, tension and shear-out modes. Aktas et.al. [4] investigated
failure strength and failure mode of a mechanically fastened carbon-epoxy composite plate of
arbitrary orientation. Bearing strength and failure modes were taken as functions of three
variables: orientation angle of fibers, E/ D, and W/ D. By changing the value of one of the
variables while keeping the values of the others constant, experimental and numerical
analyses were performed.
Dano et.al. [5] carried out analysis on single mechanically fastened joint in fiber-
reinforced plastics. A finite-element model was developed to predict the response of pin-
loaded composite plates. The model takes into account contact at the pin-hole interface,
progressive damage, large deformation theory, and a non-linear shear stress-strain
relationship.

138


Bulent Murat Icten et.al. [6] investigated the possibility of predicting the properties of
the joint from the properties of the material measured with standard tests. A composite
rectangular plate of length L+E and width W with a hole of diameter D, with a hole at a
distance E, from the free edge of the plate was taken as the specimen. A rigid pin was located
at the center of the hole and a uniform tensile load P was applied to the plate. A compression
testing was applied to the specimen to fan-out failure in net tension, shear out mode, and
bearing mode. A progressive damage model was applied which consisted of three: stress
analysis, failure criteria, and property degradation rules. The two dimensional finite element
method was used to determine the failure load and failure mode using Hoffman and Hashin
criteria. The mechanical properties of the composite material were obtained from standard
tests. Load displacement curves for various W/D, the effect of W/D ratio, and orientation on
bearing strength were plotted and results were in close agreement with the experimental
results.
Okutan et.al. [7] performed an investigation to study the response of pin-loaded and
laminated composites. Tensile tests were performed on E/glass epoxy composites for two
different ply orientations such as [0/±45] s and [90/±45] s. For each ply orientation, 20
different geometries were chosen. The major focus of the study was to characterize the failure
mechanisms and to evaluate the effect of geometric dimensions on the bearing, shear-out and
net tension strengths of pinned joints. For this purpose, the specimens were tested to find first
failure and final failure load. Tayfun Gulem et.al. [8] carried out a study to deal with the
bearing strength, failure mode and failure load in a woven laminated glass vinyl ester
composite plate with circular hole subjected to a traction force by a rigid pin. They
investigated for two variables; the distance from the free edge of the plate to- the diameter of
the hole (E/D) ratio and the width of rectangular plate-to-the diameter of the hole (W/D) ratio
numerically and experimentally.
The effects of preload moment, moisture and interference-fit on bearing strength and
failure mode in pin-jointed and bolted carbon–epoxy plates which were subjected to a
traction force studied by Servet Kapti et al. Two different geometrical parameters, end
distance to pin diameter ratio (E/D) and width to pin diameter ratio (W/D), were considered
experimentally. E/D and W/D ratios were selected ranging from 1 to 4 and from 2 to 4,
respectively. The test results showed that the ultimate failure loads were directly affected by
the geometrical parameters, preload moments and interference-fit. Tsai-Wu criterion was
used to determine bearing strength corresponding to first failure load [9].
Alaattin Aktas et al. [10] studied the Failure load and failure mode of glass-epoxy
composite plates with single and double parallel pinned-joints have analysed experimentally
and numerically. Two variables were investigated during analyses; the distance from the free
edge of plate to the diameter of the first hole (E/D) ratio (2, 3, 4, 5), and the width of the
specimen to the diameter of the holes (W/D) ratios (2, 3, 4, 5).
The effect of the clearance and interference-fit on the failure mode, failure load and
bearing strength of the pin-loaded joints subjected to traction forces are examined by Binnur
et al. [11]. A failure investigation was performed to determine the failure mode and bearing
strength of mechanically fastened bolted-joints in glass fiber reinforced epoxy laminated
composite plates, experimentally. Two different geometrical parameters, the edge distance-
to-hole diameter ratio (E/D) and plate width-to-hole diameter ratio (W/D) were considered.
For this purpose, E/D ratio was selected from 1 to 5, whereas W/D ratio was chosen from 2 to
5. since an important target of this study was observed by Faruk Sen et al. [12] and reported
the changing of failure mechanism under various preloads.

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July December

With the above study it has observed that a progressive damage analysis consists of
three important steps: stress analysis, application of failure criteria and degradation of
material properties according to failure mode.

EXPERIMENTAL STUDY
In this study, composite materials rectangular plates (length L, Width W, Thickness t)
,
made on fiber-reinforced woven rove mat with a circular hole filled with rigid pin is used.
The diameter (D) of the hole is fixed at a constant value of 5mm. The hole is located along
he
the central line of the plate at a distance K from end of the plate. A uniform tensile load P is
applied to the plate. Load is parallel to the plate and is symmetric with respect to the central
respect
line. Thus, the load cannot create bending moments about X, Y, Z axis. The set up is shown
,
in figure-2.

Figure-2: Geometry of a laminated composite plate with circular hole
Geometry parameters: specimen width (W) or ratio of width to hole diameter (W/D),
edge distance(K)or ratio of the edge distance to hole diameter(K/D), Specimen thickness
)or /D),
(t),hole ratio(D)and pitch for multiple joints and the Length of the plate is L.
h

TESTING PROCEDURE

To find the failure load and the failure mode, a series of experiments were performed.
performed
The specimens were trimmed as depicted in figure The effects of the pin location were
e figure-3.
studied by varying the width to diameter (W/D) ratio from 3 to 5, edge distance to diameter
,
(K/D) ratio from 1, 2 and between two holes distance to diameter (K/D) ratio from 1 and 2.
The experiments were carried out in tension mode on the Universal Testing Machine.
The lower edge of the specimen clamped and loaded from the steel pin by stretching the
specimens at a ratio 0.5 mm/min is shown in Figure-3. The load pin displacement diagrams
.
for all composite configurations were plotted.

Figure-3: Experimental setup for pin joint testing and test specimens (epoxy/ polystyrene
polystyrene)

140


TESTING
Take the specimen holder and place the specimen in the holder using the pins and
place that one in the UTM machine to get the shear and tension properties of that specimen
and the load that withstand the plate and the deflection are as tabulated.
The specimens with varying K/D and W/D the specimen failure, the load at which it
can withstand is observed and the graphs and the results are discussed. In the analyses the
diameter of the hole and the thickness of the plate were taken as constant. To understand the
failure behavior of specimens with K/D and W/D, a parametric study was done and presented
in this Paper.

Effect of variation in K/D
The diameter of the pinhole is kept constant and the W/D, K/D are varied to find the
failure load. The effect of W/D, K/D are studied by taking the diameter of hole as D = 5 mm
and for each value of this diameter K/D is varied as 1 2, 3 whereas W/D is varied as 3, 4, 5.
Here W/D is varied when K/D=2. This brings up 9 different specimen models obtained from
combinations of W/D and K/D. Load is applied on each specimen model till failure takes
place. The failure load and failure mode are noted.

250
W/D epoxy
BEARING STRENGTH

200 =3
150

100

50

0
1 K/D
2 3

Figure-4: Bearing strength Vs K/D at W/D=3 for epoxy and polystyrene

Fig-4 to 6 shows the graphs plotted between the Bearing strength and K/D. The observations
from this graph are as follows:
Bearing strength of different specimens with same W/D, K/D is found to increase with
increasing W/D. This is because of the change in the width of the specimen.
As W/D increases, the failure mode will be normal and shear. Firstly, it will be normal
and by increasing the W/D value, the normal becomes shear. The bearing strength will
slightly increase and become constant.
Bearing strength for a specific diameter value initially increases as K/D increases, and
then almost becomes constant with further increase in K/D. keeping D as constant, when
K/D increases, the distance of the hole from one edge of the plate increases i.e. the hole
simply shifts its position away from the edge of the plate towards the centre of the plate.
This increases the shear strength of the specimen.

141


300

BEARING STRENGTH
W/D
=4
200
EPOXY

100

0
1 K/D 2 3

Figure-5: Bearing strength Vs K/D at W/D=4 for epoxy and polystyrene.

300
W/D=5
BEARING STRENGTH

200
epoxy
100

0
1 2 3

K/D

Figure-6: Bearing strength Vs K/D at W/D=5 for epoxy and polystyrene

Effect of variation in W/D
The effect of W/D is studied keeping the diameter of hole as D = 5mm and for each
value of this diameter W/D is varied as 3, 4 and 5. Initially K/D is kept constant at 1and W/D
at 3. This brings up 9 different specimen models obtained from combinations W/D ratio.
Load is applied on each specimen model till failure takes place. Bearing strength and failure
modes are noted.
Graphs are plotted between the failure load and W/D for different values of K/D.
From these figures the following observations are made while in case of epoxy as the
material of the plate the following conditions are observed
As K/D=1 is kept constant and then increasing W/D value results in increasing of
Bearing strength, as that increases slightly and then kept constant this will because that
the varying in width of the specimen and D as constant. the failure mode of the specimen
are normal and shear takes place
As K/D=2 is kept constant and varying the distance between hole and edge then
increasing W/D value, then Bearing strength will increase as that increases and becomes
decrease slightly and then it fails. This is because of the varying in width of the
specimen and the distance between edge and hole and D as constant. Bearing is the
failure type of mode.
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While in case of polystyrene as the material of the plate, the following conditions are
observed
As K/D=1 is kept constant, then increasing W/D value, then Bearing strength will
increase as that increases slightly and then kept constant. This is because of the varying
in width of the specimen and D as constant. The failure mode of the specimen are normal
and shear takes place
As K/D=2 is kept constant, then increasing W/D value, the Bearing strength will increase
as that increases and becomes decrease slightly and kept constant This is because of the
varying in width of the specimen and D as constant. The failure mode of the specimen is
bearing.
Table-1: W/D along bearing strength and failure mode
Epoxy Bearing Failure Polystyrene Bearing Failure
Strength Mode Strength Mode
K=1 150.85 S W/D=3 K=1 27.65 S
W/D=3 K=2 192.46 S K=2 53.73 B
K=3 194.24 B K=3 67.11 B
W/D=4 K=1 132.72 B W/D=4 K=1 28.46 B
K=2 240.94 B K=2 33.82 B
K=3 246.78 B K=3 48.83 B
W/D=5 K=1 145.36 B W/D=5 K=1 30.26 B
K=2 260.42 B K=2 33.33 B
K=3 267.46 B+S K=3 40.22 B+S

As compared to both the materials the strength is more to epoxy material and it can with
stand high Bearing strength as compared to the polystyrene material composite plate

CONCLUSIONS
In the present work failure analysis on double pin loaded glass epoxy/polystyrene
composite plates is performed for different values of E/D, K/D, and W/D. The following
conclusions are drawn from this analysis.
• The analysis to find the effect of varying K/D and W/D. It is observed that the
strength of the specimen increases with increase in K/D and W/D to an extent and
then becomes constant. W/D has a greater effect on the mode of failure.
• The failure load of the specimen increases with increase in K/D as a result of
increase in edge distance of the specimen and becomes constant for higher values.
• The failure load of the specimen increases with increase in K/D as a result of
increase in edge distance of the specimen and becomes constant for higher values.
• As W/D increases the failure load initially increases then decreases or becomes
constant as a result of increasing stress concentration factor.
• As the thickness of the specimen increases the failure load increases as a result of
increase in cross sectional area of the specimen.

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REFERENCE
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Composite Containing Stress Concentrations”. Journal of Composite Materials, 21, 834-855.
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Fastened Joints in Composite Laminates”, Journal of Composite Materials, 33(24) 2248-
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pin-loaded composites”, Materials and Design 31, 85–93.
12. Faruk Sen, Murat Pakdil, Onur Sayman, Semih Benli, (2008) “Experimental failure
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preload”, Materials and Design 29, 1159–1169.

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Failure analysis of pin loaded glass epoxy polystyrene composite plates

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