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A Study on the Stress Distribution Around Filler of Polymer Composite Materials

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A Study on the Stress Distribution Around Filler of Polymer Composite Materials

journal or

publication title

福井大学工学部研究報告

volume 24

number 2

page range 355‑360

year 1976‑09

URL http://hdl.handle.net/10098/4584

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MEMOIRS OF THE FACULTY OF ENGINEERING FllKUl UNIVERSITY VOL. 24 NO.2 1976

A Study on the Stress Distribution Around Filler of Polymer Composite Materials

Hiroshi KIMURA *, Takuzi Y AMAGUCHI*, Masakazu TSUBOKAWA*, Tsuneo SENSHU*

(Received March 31, 1976)

In this paper, process of bonding and bonding rupture of matrix and spheroid oxidizing iron grains contained in polyethylene film are photographically observed by means of optical microscope, stress distribution around filler is sought for by finite element method, and the process of rupture of bonding by stress concentration is studied.

1. INTRODUCTION

Many attempts have been made in recent years to make high molecular compound materials composite by adding various fillers and to turn out new materials suitable for practical applications by improving physical properties. In bonding of matrix and filler, there are mechanical bonding type relying upon uneven surface of the filler, electro-static bonding type between molecular compound material and filler, and chemical bonding type at the boundary surface. Above three types act as an effective bonding, individually or working together and interacting each other. 1) In

filler

( Mechanical Anchor Effect ) ( Chem/cal Bonding Effect)

Fig, 1 A model of Composite material. Fig. 2 A model of composite material,

*Dep. of Textile Engineering

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( Electro - Static Effect)

Fig. 3 A model of composite material.

( Before forming )

- I

P . . - -

-

- 1/ / / )--1'---... Q

/.

- . : : : : :

-

p

0 . - - -_ _ 60 - - _

( After forming 1

Fig, 4 Specimens for observation by optical microscope,

this article, process of bonding and bonding rupture of matrix and spheroid oxidizing iron grains contained in polyethylene film are photographically observed by means of optical microscope, stress distribution around filler is sought for by finite element meth- od,2l and the process of rupture of bonding by stress concentration is studied.

2. EXPERIMENTAL PROCEDURES Specimen for observation by optical micr- oscope is as shown in Fig. 4. This specimen, prepared by hot press, consists of four layers of 0.05mm. thick polyethylene of high and low density, with spheroid oxidizing iron having grain diameter of about 100,um.

arranged at center. This specimen was subjected to tension by manual drawing machine, area around filler was photographed with the aid of an optical microscope, and magnitude of strain was looked into in comparison with conditions of bonding rup- ture. Data of calculation3l,4) used in finite element method are as follows. Shape of specimen is as shown in Fig. 6, from which it is known that a disc of oxidizing iron having the same thickness as that of polyethylene sheet is arranged at the center of the polyethylene sheet of unit thickness. Stress distribution around the oxidizing iron when uniform distribution load P was applied at both ends of the specimen was analyzed. Namely, as with Fig. 7, upper right half of Fig. 6 was divided into 67 triangular elements, and stress arising in each triangular element under load P applied on the right side was sought for.

3. EXPERIMENTAL RESULTS AND CONSIDERATION

Fig.5 are optical microscopic photographs of the polyethylene film containing spheroid oxidizing iron grains. High density polyethylene as matrix is pictured on the right side, and low density one on the left side. Fig. 5 (a) is the photograph of a specimen not drawn yet, no load applied, and strain ratio 0%. Diameter of oxidizing iron grains in both cases is approximately 100 ,am. (b) is the photograph

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Matrix

Strain (%)

L.D.P.E

HD.P.E

(a) left: strain 0%

right: ~ 0%

(b) left: strain 3.2%

right: ~ 2.3%

(c) left: strain 11.4%

right: ~ 3.6%

(d) left: strain 20.3%

right: ~ 6.2%

(e) left: strain 43.0%

right: ~ 10.3%

Fig. 5 Optical microphotograph during tension.

under strain of 3.2% and 2.3% applied to low and high density polyethylene films respectively, from which it is observed that bonding of both films have already ruptured, creating a void on the boundary surface between polyethylene and oxidizing iron grains. Strain under which rupture took place was as small as less than -about 1% in both cases, and it was found that the bonding force between polyethylene and oxidizing iron grain was weak. Once rupture occurs, stress concentrates there. Photograph (c) was taken under strain of 11.4% and 3.6%

applied to low and high density polyethylene films respectively, and both of these

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x

Fig. 6 Shape of examination sample for finite element analysis.

p • 0.67 kg Imm '

Fig. 8 Result of stress analysis by finite element method, matrix:

x

L. D. P. E, uniformal distribution load: p=O.67kg/mm2.

p= 1.0 kg/mm'

Fig. 10 Result of stress analysis by finite element method, matrix:

L. D. P. E, uniformal distribution load: p= 1.0kg/mm2

Fig. 7 Node number and element number of examination sample divided by triangular plane element.

P=0.67 kg/mm2

Fig. 9 Result of stress analysis by finite element method, matrix:

y,

I

~-x

L. D. P. E, uniformal distribution load: p=O.67kg/mm2.

100----' P=10 kg/mm2

Fig. 11 Result of stress analysis by finite element method, matrix:

H. D. P. E, uniformal distribution load: p= 1.0kg/mm2.

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Fig. 12 Result of stress analysis by finite element method, matrix:

H. D. P. E, uniformal distribution load: p=1.6kg/mm2.

l-!

p= 2.2 kg/ mm'

Fig. 13 Result of stress analysis by finite element method, matrix:

H. D. P. E, uniformal distribution load: p=2.2kg/mm2.

strains are more or less in the vicinity of limit of elasticity in their respective S-S curve. Photographs Cd) and (e) were taken under more strain, from which it is observed clearly that the ruptures propagate in different directions. Namely, rupture in low density polyethylene film propagates in the same direction of strain, while that in high density polyethylene film in the normal direction to the direction of strain causing many tiny cracks to occur. Results of analysis by finite element method are shown in Figs. 8-13. Figs. 8-10 are the results when low density polyet- hylene is used as matrix. Result under the load just before causing bonding rupture on the boundary surface of polyethylene and filler is given in Fig. 8, from which it is known that the stress of about 1.4 times as much of uniform distribution load P=0.6kg/mm2 acted upon element numbered

®

in Fig.7 where the rupture of bonding occurred. Fig. 9 is the result of analysis of the case when the element numbered

®

is ruptured and a void is created there; further, in Fig. 10 where this void is become greater. When P=1.0kg/mm2, maximum stress concentration reaches 3.85 times as much. Results when high density polyethylene is used as matrix are given next. Fig. 11 shows the result under the load just before bonding rupture took place, and P in this instance was 1.0kg/mm2 Fig. 12 is when a void was created in element numbered @, and P was 1.6kg/mm2 in this case. P was then increased to 2.2kg/mm2, the void became greater, and the result is given in Fig. 13.

4. CONCLUSION

As is clearly observed in optical microscopic photographs, direction of rupture propagation in low density polyethylene matrix is in the same direction of strain.

On the contrary, when matrix is of high ~density polyethylene, rupture propagates creating small cracks in the direction normal to the direction of strain. Reviewing the results of analysis by finite element method, it is found that the stress concen- tration just before the bonding rupture was about 1.40 and about 1.41 times of

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uniform distribution load when the matrix was low and high density polyethylene respectively. When a void was created, low density polyethylene was found to be subjected to stress concentration of 2.16 times as much of uniform distribution load; high density polyethylene also received stress concentration of 2.16 times.

When the void grew bigger, stress concentration which low and high density polyethylene were subjected to were 3.85 and 3.98 times respectively of uniform distribution load. If still greater load is to be applied, it will be necessary to have elastic-plastic analysis.

ACKNOWLEDGMENTS

The authors would like to express sincere thanks to Mr. Hayabara of Daiichi Nenryo Industry Co. Ltd. and to Mr. Hashimoto of Showa Denko Co. Ltd. to experimental materials.

REFERENCES

1) Hiroshi KIMURA: Industrial Materials, Vol. 23, No.5 (1975)

2) Mikimoto, Yoshimura: Structure Analysis by Finite Element Method, Baifukan 3) Toshikazu MORIGUCHI : JIS Fortran Guide, Tokyo University Shuttupan Kai.

4) Shoji URA : Fortran Guide, Baifukan.

Fig,  1  A  model  of  Composite  material.  Fig.  2  A  model  of  composite  material,
Fig.  3  A  model  of  composite  material.  (  Before  forming  )  - I  P  . . - - -- 1/  / /   )--1'-----------.....
Fig.  5  Optical  microphotograph  during  tension.
Fig.  8  Result  of  stress  analysis  by  finite  element  method,  matrix:
+2

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