Mechanical and thermal properties of composite material system reinforced with micro glass balloons

Transcription

1 IOP Conference Series: Materials Science and Engineering Mechanical and thermal properties of composite material system reinforced with micro glass balloons To cite this article: Y Ozawa et al 2010 IOP Conf. Ser.: Mater. Sci. Eng Related content - Stochastic multiscale stress analysis via identification of microscopic randomness S Sakata and F Ashida - Multi-scale modeling of the progressive damage in cross-ply laminates under thermal and mechanical loading D Yang, Y Sheng, J Ye et al. - Experimental investigation of CNT effect on curved beam strength and interlaminar fracture toughness of CFRP laminates M A Arca and D Coker View the article online for updates and enhancements. This content was downloaded from IP address on 01/05/2018 at 10:07

2 Mechanical and Thermal Properties of Composite Material System Reinforced with Micro Glass Balloons Y OZAWA 1, M WATANABE 2, T KIKUCHI 3, and H ISHIWATARI 4 1 Fukushima University, 1, Kanayagawa, Fukushima, , JAPAN 2 Koriyama Technical Academy, 5, Kaminoyama, Koriyama, , JAPAN 3 Fukushima Technology Centre, Machiikedai, Koriyama, , JAPAN 4 Graduate School, Fukushima University, 1, Kanayagawa, Fukushima, , JAPAN Yoshihito Ozawa <p145@ipc.fukushima-u.ac.jp> Abstract. The mechanical and thermal properties of polymer composites reinforced with micro glass balloons are investigated in temperature conditions. The matrix resin of the composite is epoxy resin and its dispersion is micro glassy spherical shells of Sirasu Balloon. The composite system developed is a kind of micro porous materials with lightweight. From the experimental data of bending and tension tests, mechanical behaviours of the composites were clarified, and the effects of material properties and configurations on the mechanical properties of composites were discussed from the viewpoint of micromechanical study. A homogenization theory with multi-scale analytical method has been applied in order to evaluate the composite material system in temperature conditions. Numerical calculations were performed by using a model of micro porous materials and setting properties of each material at the temperature. Analytical results for the mechanical behaviour made a good agreement with experimental result of the composites in temperature conditions. 1. Introduction In developing the high speed robotics hand system, a newly designed structure component must be needed with excellent features, i.e., ultra lightweight (its density less than 0.5g/cm 3 ), high stiffness and high strength. In order to satisfy both of lightweight and high stiffness/ strength, a lightweight composite material system, which will consist of core material with lightweight and outer fibrous material of woven type or knitted type, is one of the candidates for application. In this study, mechanical behavior of newly developed core composite material with lightweight is investigated in temperature conditions. From the experimental results, the mechanical properties of the composite will be discussed from the viewpoint of micro-mechanical study. By using an analytical model of micro porous materials, a homogenization theory with multi-scale analytical method will be described in order to evaluate the mechanical and thermal properties of the composite material system in temperature conditions. c 2010 Published under licence by Ltd 1

3 2. Specimens and experimental procedure We have developed a micro porous composite material for the core material of composite material system. The matrix resin of the composite was epoxy resin, and its dispersion for reinforcement was micro glassy spherical shells of Sirasu Balloon Maarlite 713D of Marunaka-Hakudo Co. That is, the composite material system is micro glass balloon reinforced epoxy resin (Sirasu Balloon/Epoxy) composites [1]. Bending tests and tension tests were performed by using the solid and hollow cylindrical specimens (length 190mm and diameter 25mm for solid type; same geometry with thickness 2.5mm for hollow type) of the composite, under the conditions of 50%RH at 298K. The density of specimen is 0.6 for solid type, and the apparent density is 0.3 for hollow one. From the experimental data of bending tests and tension tests, the mechanical behavior of the composites was discussed from the viewpoint of micro-mechanical study, and the method of molding was also evaluated. In the case of tension test shown in Fig. 1(a), the load P displacement curves for porous composite specimen both of solid type and hollow type indicate linear behaviors from earlier stage of displacement to the maximum. In the case of bending test (Fig. 1(b)), P - curve of hollow specimen indicates non-linear behavior from displacement 2mm to maximum. On the other hand, P - curve of solid specimen indicates linear behavior from earlier stage of loading to the maximum. Any load drop could not be observed. We observed a fracture surface of micro porous composite specimen by using a scanning electron microscope (SEM) in order to discuss the influence of the dispersion of Sirasu Balloons on the characteristics of the composite. From Fig. 2, a large number of Sirasu Balloons and many air cavities with different size were observed. We performed image processing analysis for SEM photograph. Sirasu Balloons and air cavities were recognized as circles and the diameter of each circle was measured automatically. The result of stochastic analysis was also shown in same figure to examine diameter size distribution of balloon particles and air cavities in micro porous composite specimens. We found some characteristic peaks on the axis of diameter for balloon particles and air cavities. There obviously exists the highest peak of Sirasu Balloon at m of diameter in the diagram. In addition, the peak at about 2 m indicates the existence of micro cavities of air which might be produced from inside of Sirasu Balloon, and the peak at 200 m shows relatively large air bubbles which could be caught in molding process. The strength of the composites would be affected by the existence of large size of air bubbles. Better fabrication method should be desired for the composites with lightweight, sufficient strength and rigidity. Load (N) rigid cylindrical rod 4510N Displacement (mm) (a) tension test 1780N hollow cylindrical rod Load (N) rigid cylindrical rod Displacement (mm) (b) bending test 780N hollow cylindrical rod 660N Figure 1. Load P -Displacement curve of composites. (CHS=1.0mm/min) 2

4 500 m Diameter of Void ( m) Figure 2. SEM photograph of porous composites and Diameter histogram for voids Improvement of fabrication method of lightweight composites The Sirasu Balloon Maarlite 723C of Marunaka-Hakudo Co. was used for new reinforcements. Sirasu Balloon has micro glassy spherical shell body which was manufactured from volcanic glassy pumice tuff by heating rapidly at about 1300K. Therefore, it has superior heat resistance, strong impact resistance, and high thermal insulation, for this reason, it could be applied to exterior wall and so on. From the reference of Maarlite 723C, the bulk density is 0.15±0.025g/cm 2, the average diameter is m, float ratio wt%, and Ph [2]. The epoxy resin used was Ciba-Geigy GY-250. The resin is unplasticized diglycidyl ether of bisphenol A (DGEBA) with mean molecular weight of 380 and an epoxide equivalent of g/eq. From technical data for mechanical properties of the matrix resin, bending strength b is 55MPa, tensile strength t is 62MPa, glass transition temperature tan dry ; 428K, fracture toughness GIC; 0.15kJ/m 2 and water absorption ratio is 0.16%. The hexahydrophthalic anhydride hardener HN of Hitachi Chemical Co., Ltd. and the accelerator #2E4MZ of Shikoku Chemical Co. were also used for mixture. The Sirasu Balloon/Epoxy composites was fabricated in batches by mixing 100g of GY250 with 85g of HN-5500 and 1g of #2E4MZ, and then adding the 200ml of Maarlite 723C. Degas processes for the resin system were sometimes taken by holding it in a vacuum chamber before and during cure in order to prevent the entrapment of air bubbles. Heating procedure for the specimens is shown in Fig Temperature ( ) Time (minute) Figure 3. Heating procedure of composites specimens. 3

5 2.2. Experiments In order to examine the mechanical behaviors and properties of composites, three point bending tests were performed by using the specimens of coupon type under the conditions of 50%RH at 298K. For the experiments, the Sirasu Balloon/Epoxy composites was carefully machined into the precise geometry of specimens; length 80mm, width 10mm and thickness 4.0mm. Three groups of specimens are chosen with three different depth position along the thickness direction; upper position, middle and lower. The cross head speed (CHS) of bending tests was kept at 1.0mm/min. The load and the strain at 11mm offset point from the loading were recorded by personal computer during the tests. After the test, we observed the damage propagation in the micro porous composites specimen by using an optical microscope and a scanning electron microscope (SEM). 3. Experimental results and consideration 3.1. Experimental results of the composites From experimental results for porous composite specimens of coupon type cut from the different point along the depth direction, Fig. 4 shows the load P - Displacement curves of three point bending tests. In the case of the specimens from the lower position, P - curve indicates slightly non-linear behavior at loading stage from displacement 1.2mm to maximum, and the maximum load is 55N. Additionally, the slope of P - curve, which means bending rigidity of the composites, takes larger value than that of the specimens cut from middle or upper position. On the other hand, P - curve of a specimen from upper position indicates non-linear behavior from earlier stage of loading to the maximum, and the maximum load takes low values of 32N. We could not observe any load drop in all the case of specimens from three different positions. From the experimental result of bending tests, mechanical behavior and properties of micro porous composite were examined. For specimens from lower position at 298K and 50%RH, bending modulus 4.46GPa and bending strength is 44.2MPa. For specimens from middle, bending modulus 3.14GPa and bending strength is 28.3MPa while bending modulus 2.97GPa and bending strength is 22.6MPa for specimens from upper. The density of specimens was measured by using small samples cut from the specimens. The mechanical properties of porous composites are summarized in Table 1. Lower Middle Upper Figure 4. Load P - Displacement curve of bending test for composites. (CHS=1.0mm/min) 4

6 WCCM/APCOM 2010 Table 1. Mechanical property of SB Composites and Epoxy Resin. Density (103kg/m3) Bending modulus (GPa) Bending strength (MPa) Specific bending modulus (GPa) Specific bending strength (MPa) SB composites improved Upper Middle Lower Old data Epoxy resin SEM observation for specimens We observed a fracture surface of micro porous composite specimen by using a SEM in order to discuss the influence of the dispersion of Sirasu Balloon on the characteristics of the composites. Viewing the Fig. 5, a lot of Sirasu Balloons were observed with some variation of balloon size. However, there are few air cavities and large air bubbles of different size were not observed in the figure. Therefore, dispersion of Sirasu Balloons is good and the improved method is effective for fabrication of Sirasu Balloon/Epoxy composites materials. From the observations of the surface of cross section by using a SEM, the analysis of digital image processing was performed. Fig. 6 shows the result of stochastic analysis for mean diameter size distribution of balloon particles against the depth along thickness direction in micro porous composite specimens. We observed a characteristic curve for balloon diameter due to the buoyancy of balloons in matrix resin. In the upper position near the surface of fabricated materials, relatively large size of balloons were observed and mean diameter takes larger value of 51 m. Therefore, the density of composites could be small and bending modulus and bending strength take lower values than that of specimens from middle or lower position. In addition, in the case of lower position, the mean value of diameter of Sirasu Balloon decreased with sharp slope of the curve, and it is easily found that bending modulus would change with increasing the depth along the thickness direction of molding process. The strength of the composites might be affected by the existence of balloons with different sizes. (a) micro porous composites (upper) (b) inside of Sirasu Balloon Figure 5. SEM photograph of micro porous composites. 5

7 Mean diameter of SB ( m) Upper Middle Lower Depth along thickness direction (mm) Figure 6. Mean diameter of Sirasu Balloon against depth along thickness direction. 4. Theoretical analysis of the Composites 4.1. A Model for FEM Analysis From the experimental results, the effects of material properties and configurations on the mechanical properties of the composite were discussed from the viewpoint of micromechanical study. Making dispersion models of micro porous materials microscopically, we apply a homogenization theory with multi-scale analytical method [3] for evaluation of the macroscopic mechanical behavior of the composite material system in temperature conditions. From Fig. 5, the developed porous composite materials have a structure which contains a lot of spherical shells of Sirasu Balloon with some deviation of diameter in the matrix resin. It is easily found that the balloons were dispersed well over the observed area and few air bubbles were observed in the figure. Therefore, the microscopic structure of the composites could assume to be periodical for the analysis. From the viewpoint of micro-mechanical study, a homogenization theory with multiscale analytical method will be described for evaluation of the macroscopic mechanical behavior of the composites at various temperatures. We design a simple two- and three-dimensional dispersion model on the basis of the balloon density as shown Fig. 7(a) for 2D model and 7(b) for 3D model. In the experiment, any surface treatment such as a silane coupling agents were NOT applied, however it is easily seen that the bonding between the balloons and the matrix was good. Then, we assume that micro balloons are perfectly bonded to the matrix, and the air of 1013 hpa (1 atm) is filled inside the balloon. Temperature is uniform in the composites. And the diameter of balloon are set as 40 m from the mean value of Sirus Balloons and the distance between the two balloons were determined by the volume fraction of the composites used in the experiments. Fig. 8 shows a unit cell model for FEM analysis for 2D model, which consists of two quartered Sirasu Balloon aligned diagonally and the epoxy resin of remaining part. The white part of quarter circle shows the air in the Sirasu Balloon. The unit cell model is divided into quadrangle elements for FEM analysis. The total number of node is 586 and the total number of quadrangle element is 523. FEM analysis was performed for tensile test at the temperature condition of 123K (-150 C), 298K (25 C) and 403K (130 C). The elastic properties used in the analysis are shown in Table Results of FEM Analysis Some numerical calculations were performed by using a model of micro porous materials and setting thermal properties of each material at the temperature. The Sirasu Balloon was assumed to take constant elastic property independent of temperature. Stress distribution as obtained from the numerical model shows that the stresses in the membrane of balloon is higher than that in the matrix as shown in Fig. 9. Though the thickness and diameter of 6

8 WCCM/APCOM 2010 balloons are small, the micro balloons could play an important role as reinforcements of the composites. Fig. 10 shows the analytical results of stress-strain curves for tension test in various temperature conditions. The experimental results of tension test at temperature of 298K are also shown in the same figure. The analytical results at 298K made a good agreement with experimental ones of the composite. It can be said that a unit cell model of micro porous materials is valid for evaluation of the mechanical behaviour of the composite material system in temperature conditions. The other mechanical characteristics can be also evaluated by using this model for homogenization theory with multi-scale analytical method. The feasibility of using a periodic model for this material should be examined for different types of unit cells e.g. square, face-centered, body-centered, hexagonal, diamond to evaluate the influence on stress results and to explain the rule for filler alignment in the composites by considering the energy balance. It would be further work for us. Table 2. Elastic property used in FEM analysis [4, 5]. Temperature K E(resin) GPa E(sb) Gpa ν(resin) ν(sb) [5] [6] Sirasu Balloon Epoxy resin Unit cell mm (a) 2D model of dispersion (b) 3D model Figure 7. Finite element model for micro porous composite material. Figure 8. Unit cell model for FEM analysis. Figure 9. Stress Distribution in Composites with 3D model. 7

9 10 8 Stress (MPa) K experiment 298K analysis 403K analysis 123K analysis Strain (%) Figure 10. Stress - strain curves of FEM analysis for tension tests in temperature environments. 5. Conclusion We developed the micro porous composites with lightweight for advanced mechanical system, especially robotics hand system. The mechanical properties of developed composites were investigated, and elastic moduli of composites at various temperature conditions were analyzed by using a model of micro porous materials. Acknowledgments The authors also gratefully acknowledge support from the Ministry of Education, Culture, Sports, Science and Technology through Grant for City Area Program [Development Stage] in Koriyama Area during References [1] Ozawa, Y., Kikuchi, T., Watanabe, M., and Yabuki, K., Mechanical Behavior of Composite Material System with Ultra Light Weight, Proceedings of the JSASS/JSME/JAXA Structures Conference, pp , 2006.(in Japanese) [2] Marunaka-Hakudo Co., Catalogue of Maarlite723D [3] Shibuya, Y., Thermo-Mechanical Behavior of Quasi-Random Fiber Composite and Its Modeling, THERMAL STRESSES 03, MA-10-4, [4] Ashby, M. F. and Jones, D. R. H., Engineering Materials - An Introduction to their Properties and Applications, Part B, Pergamon Press, Oxford, UK. [5] Fiori, C. and Devine, R. A. B., Evidence for a wide continuum of polymorphs in a-sio2, Phys. Rev. B, 33, pp ,