JEC COMPOSITES MAGAZINE - Issue #81 - May/June 2013 - 47

Tensile test
Tensile test were performed by using
an Instron universal testing machine
under a speed of 1 mm/min. For the
specimen with a hole, the notched
strength was calculated. Additionally, strain gage (KYOWA KFg10-120-C1-11) was used to measure
the strain during testing process. To
express the notched strength ratio of
materials to open hole, the parameter
h was introduced. The value can be
calculated by equation (1).

s
h= n
s
where σn is notched strength of
specimen with holes, σ is strength of
smooth specimens. From the formula,
it can be learned the notched strength
ratio can express notch sensitivity to
the materials.
Characteristic distance
To calculate the stress distribution,
MSC-Marc software was employed to
carry out finite element simulation. In
simulation process, the material was
considered to be isotropy and used
linear elasticity method. 2d triangle
plane element was considered suitable
in here. The max load value at fracture
for the drill-hole specimens during the
experimental tensile test together with
the material constant i.e. the modulus
are used for the analysis the distribution of stress around the drill hole.
After simulation the stress distribution
can export from the software and the
characteristic distance were calculated
from the results which is helpful for
further understanding of the fracture
behavior of glass mat composite with a
drill-hole.

Experimental results and discussion
Tensile feature
The damage process of notched was
showed in figure 1, the 30mm-width
specimens was chose to explain.
The typical stages during tensile test
were illustrated in the 4 pictures. The

distribution after second stage. The fan
shape distribution of cracks was defined as fan shape area. In the fan shape
area, lamination can be found. This is
the typical fracture characteristic of
notched specimen in gMC.

Fig. 1 : Damage process of notched specimens.

1st picture was the specimen state at
beginning. The 2nd picture was the
specimens subjected the maximum
load. Then the crack extended to the
outside slowly. The 3rd picture was the
specimen just before totally broken.
The last one was the specimen after
totally destroyed. The character was
that after 3rd picture, the specimens
would be destroyed suddenly and very
fast (within 30 ms).
Fracture behavior
different fracture areas were formed by
the 2 stage of tensile process, including
parallel area and fan shape area, like
figure 2 illustrated.

Fig.2 : Fracture of notched specimen.

during tensile test, the cracks occurred
on the edge of hole and extended to
the outside slowly at first stage. The
width of damage area was relatively
stable. This damage area was defined
as parallel area. After parallel area,
the width of damage area was became
bigger and bigger until ultimate failure
within very short time in the second
stage. The cracks showed fan shape

Simulation and tension results
Notched strength and unnotched
strength obtained from tensile test
were used to calculate notched
strength ratio of materials. On the
other hand, by using MSC-Marc
finite elements analysis software, the
characteristic distance (d0) of each
specimen on different plies were calculated under linear elastic condition.
The calculation simulated the tensile
test process using displacement control
to apply boundary condition. All the
results were summarized in figure 3 to
find the relation between characteristic
distance and sensitivity to notch. It was
indicated that the notched strength
ratio was increased with characteristic
distance from figure 3. However, the
trend was not clear and the degree
of dispersion was relative high when
different width specimens were compared together according to correlation
coefficient value.

Fig. 3 : Relation between characteristic distance
and notched strength ratio.

In figure 4, relative characteristic distance was introduced. The
parameter of d max was the nearest
distance from hole edge to outline of
specimens. In figure 4, the results of
different specimens according to w/d
ratio were separated in figure 4(a),
4(b) and 4(c). Each figure included
3, 5 and 7 plies specimens. All the

No81 May - June 2013 /

jec composites magazine 47

JEC COMPOSITES MAGAZINE - Issue #81 - May/June 2013

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