Flexural tests of the composite materials reinforced with both glass woven fabric and oak wood flour.

Cerbu, Camelia

1. INTRODUCTION

Nowadays, it is known the great interest for recycling of the large amount of wood waste (Kandem et al., 2004) obtained during the different stages in the wood processing and wood applications such as furniture industry and building constructions. On the other hand, there were preoccupations concerning the recycling of the fibre materials (Bartl et al, 2005) such as the textiles, carpets, composite materials reinforced with fibres etc.

Some previous studies (Kandem et al., 2004) had already shown that the wood wastes in the form of wood flour, is suitable as filler for polyolefin matrix composites or for recycled plastics.

Some researchers (Adhikary et al., 2008) shown that the composites made of high-density polyethylene and pinus wood flour as filler could be desirable as building materials due to their improved stability and strength properties.

Although the use of wood filler in plastic composites has several advantages over inorganic fillers, it may be safely said that the hydrophilic nature of the wood has a negative effect on performances of the wood-plastic composites. This assumption is based on some previous researches (Cerbu, 2007).

Worldwide, there is a lot species of wood depending of the location on globe due to the nature of the climate. This means that practically, there are more kinds of wood flour or wood fibre that may be used as filler for a composite material.

Taking into account the actual trend of composite manufacturing by recycling the wood wastes, the paper analyses the mechanical properties of a hybrid composite material made of a polyester resin reinforced with glass woven fabric and filled with oak wood flour. Certainly, the technology and the structural composition directly affect the mechanical properties of the composite material resulted (Cerbu et al., 2008). To mechanically characterize the composite material the flexural test (three point method) was used.

2. MATERIALS AND METHODS

The first of all, the composite plate having the dimensions 350 x 250 mm2 and 8 mm in thickness, is manufactured. The composite plate was made by using a polyester resin reinforced with both oak wood flour and glass woven fabric EWR145 (six layers).

The mechanical characteristics of the polyester resin used without reinforcing are shown in the table 1.

Then, the specimens where cut from each plate for the flexural test (three-point method). The dimensions of the specimens (100x15) were established according to the actual european standards (***SR EN ISO 178, 2001).

Before flexural test, the specimens were kept at room temperature and dried environment for three weeks.

The testing equipment used for flexural test consists of a hydraulic power supply. The speed of loading was 3 mm/min. The span between the supports was 80 mm.

Before each flexural test of a specimen, the dimensions of the cross-section were accurately measured and then, they were considered as input data in the software program of the machine. The testing equipment allowed us to record pairs of values (force F and deflection v at midpoint of the specimens, stress [sigma] and strain [epsilon]) in form of files having 100-150 recordings. The testing machine also gave us the results of a statistical calculus for the set of the specimens tested.

3. RESULTS AND DISCUSSIONS

Experimental results recorded during bending tests in case of all specimens tested, may be graphically drawn by using F v coordinates (fig. 1).

[FIGURE 1 OMITTED]

Even if the maximum value of the loading force didn't exceed 185 N, analysing the F--v curves it may rapidly observe the very greate values of the deflection v (at midpoint of the specimen) recorded during the flexural test. This remark shows the low stiffness of the involved composite material filled with oak wood flour and reinforced with glass woven fabric.

The experimental results concerning some mechanical characteristics (flexural modulus E, flexural stress [[sigma].sub.max] at maximum load) for the all specimens tested, are shown in the figures 2 and 3, respectively.

It may be noted that Young's modulus was computed on the linear portion of the [sigma]--[epsilon] curve. It may remark that generally speaking, the both Young's modulus E for bending and maximum normal stress [[sigma].sub.max] have lower values in case of the composite material tested.

The mean values of the mechanical characteristics graphically plotted (fig. 2, 3) and other experimental results may be found in the table 2.

But, the most important remark remains that concerning the values of the maximum deflection [v.sub.max] of the midpoint of the specimens during and after the flexural test (tab. 3). Analysing the experimental results shown in the table 3, it may easily observe that the maximum residual deflection [v.sub.max] after flexural test is much smaller than the maximum deflection recorded at maximum load and also, than the one recorded at the final test. The reason of this mechanical behaviour could be assigned to the oak wood flour used to manufacture the composite specimen because no suchlike observation was recorded in the previous researches (Cerbu, 2007; Cerbu et al., 2008) when E-glass / polyester composite materials were tested.

4. CONCLUSIONS

Analysing of the actual experimental results shows that the manufacture of the composite materials with polyester resin reinforced with both glass woven fabric and oak wood flour could be one of the good solutions recommended for the recycling of the wood wastes resulted from the wood industry.

Taking into account the low mechanical characteristics obtained by using the flexural test, these kind of composite materials filled oak wood flour and reinforced with glass woven fabric, should be used only to manufacture products that are not strength members. However, taking into account the recycling necessity of the large quantity of wood wastes, the very good flexibility of the new hybrid composite material, it may recommend it for the boards in construction, furnish ornaments, carcasses, electrical switches etc.

With the idea of the good flexibility of the new hybrid composite material in my mind, the future researches would be focused on the determining of the dynamical characteristics to find the others advantages of the using of this new material.

5. ACKNOWLEDGEMENT

The research described within the present paper was possible owing to a national scientific project exploratory research, Project ID_733 / 2009 (CNCSIs), supported by Ministry of Education and Research of Romania.

6. REFERENCES

Adhikary, K. B.; Pang, S. & Staiger, M. P. (2008). Dimensional stability and mechanical behaviour of wood-plastic composites based on recycled and virgin high-density polyethylene (HDPE). Composites J. : Part B, 39 (2008), pp. 807-815, ISSN 1359-8368

Bartl, A.; Hackl, A.; Mihalyi, B.; Wistuba, M. & Marini, I. (2005). Recycling of fibre materials. Process Safety and Environmental Protection J., 83 (B4), (2005), pp. 351-358, ISSN 0957-5820

Cerbu, C. (2007). Aspects concerning the degradation of the elastic and strength characteristics of the glass / polymer composite material due to the moisture absorption, Plastic Materials J., 44, nr. 2, (june 2007), p.97-102, ISSN 0025 5289

Cerbu, C.; Ciofoaia V. & Curtu I. (2008). The effects of the manufacturing on the mechanical characteristics of the E-glass / epoxy composites, Proceedings of The 12th International Research / Expert Conference "Trends in the development of machinery and associated technology"-, pp. 229-232, ISBN 978-9958-617-41-6, Istanbul, Turkey, august, 2008, Faculty of Mec. Eng. in Zenica

Kamdem, D. P.; Jiang H.; Cui, W.; Freed, J. & Matuana L. M. (2004). Properties of wood plastic composites made of recycled HDPE and wood flour from CCA-treated wood removed from service. Composites J.: Part A, 35, (2004), pp. 347-355, ISSN 1359-835X

*** (2001) SR EN ISO 178. Plastics. Determination of flexural properties, European Committee for Standardization, Brussels

Tab. 1. Mechanical characteristics of the polyester resin used
without reinforcing

 Characteristic Unit of measure Value

Tensile stress in tension MPa 50-60
Flexural stress MPa 80-90
Modulus of elasticity E MPa 3600-3900
Impact strength kJ/[m.sup.2] 12-Aug
Elongation in tensile test % 1,5-2
Toughness Barcol -- 35-45

Tab. 2. Mean values of some mechanical characteristics
obtained by flexural test

 Type of the composite Unit of measure Mean value
 material

Young's modulus E MPa 215.01
Flexural stress
 [[sigma].sub.max] MPa 20.98
Mechanical work done until
 maximum load N-mm 3060.21
Flexural rigidity [EI.sub.z] N-[mm.sup.2] 119264.02
Maximum load [F.sub.max] N 153.59

Tab. 3. Maximum values of deflection [v.sub.max]

Specimen No. 1 2 3

[v.sub.max] at max. load 22.143 29.513 19.984
[v.sub.max] at final
 of the flexural test 58.674 54.592 59.396
[v.sub.max] after
 [approximately
 equal to] 30
 minutes after test 7.1 5.2 5.8

Specimen No. 4 5

[v.sub.max] at max. load 39.387 31.504
[v.sub.max] at final
 of the flexural test 59.400 59.396
[v.sub.max] after
 [approximately
 equal to] 30
 minutes after test 4.1 5.7

Fig. 2. Experimental results concerning Young's modulus

Number of the Young's Modulus
specimen tested specimen E (MPa)

1 287.23
2 208.22
3 200.30
4 160.74
5 218.57

Note: Table made from bar graph.

Fig. 3. Experimental results concerning the
flexural stress [[sigma].sub.max]

Number of the Flexural stress
specimen tested [sigma] (MPa)

1 21.56
2 21.41
3 20.7
4 19.18
5 22.07

Note: Table made from bar graph.