Integrated Multi-Media with Experiment for Mechanics of Composite materials

Transcription

1 Integrated Multi-Media with Experiment for Mechanics of Composite materials Author: Gwo-Chung Tsai, Department of Mechanical Engineering, National I-LAN Institute of Technology, I-LAN, Taiwan Abstract _ The Multi-Media is a power tool to turn over the traditional teaching method. In this paper the basic mechanics of composite materials combined with the experimental equipments are to be integrated to a unit. The test specimen included the geometry shape and dimensions, combined with the test machine and test procedures are cooperated to become a section of the course of composite materials. The tensile test, three point bending test, and manufacturing procedures for the composite materials are described through the multi-media. The course designed by the multi-media becomes more active and attractive through color picture made by Digital Camera. The new material made by the multi-media can give the student the full concept of the mechanics of composite materials. The materials in the course can be read through the website of the school. The student can look into the materials at any location and any time through the network. The learning results are wonderful for the student. Also teacher is not necessary to go to the classroom and has more time to do research and courses development. Index Terms _ composite laminate, tensile test, flexure test, multi-media. INTRODUCTION The science of material is continuously developed, and lots of special materials were created such as the porcelain can be subjected to the higher temperature, the matrix based material has higher ratio of strength/weight and stiffness/weight and can resist the environmental corrosion under different loading conditions. Composite materials, in general, have consisted of two or two more materials and can mix together through different manufacture procedures. Composite material may have superior material properties came from each comprised material characteristics. The composite materials have three different types due to the different matrix: Epoxy matrix composite materials :a) the thermosetting composite material and have chemical reaction during the manufacture and cannot be recycled, (b) the thermoplastic composite material only have physical reaction during the manufacture processing and can be recycled. Metal matrix composite material. Ceramic matrix composite material. The advance material characteristic of composite material is the ratio of stiffness to weight and modulus to weight is larger than that of traditional metal. The material properties can also be designed [1] by arranging the fiber direction that cannot be done in the metal. Therefore, the composite is vastly used in different fields included the aerospace industry, automobile industry, boat and ship industry and sport goods. Before the composite materials are applied in the structure, the material properties must be known for structural design and reliability analysis. Therefore, how to design the specimens to perform the tests and get the material properties will be the required knowledge for the students. Because the composite material is an anisotropic and non-homogeneous material, the material properties would depend on the orientation of the fibers. For improving the composite material education, the integrated multi-media combined with the experimental equipments, experimental procedures, and material mechanics of composite laminate are developed. In this report, the following works are completed: (1) the manufacturing proceeding of the composite specimens; (2) the experimental tests and calculation of the longitudinal modulus of the composite materials; (3) the experimental tests and calculations of the transverse modulus of the composite materials; (4) the experimental tests of the three-point bending and calculations of the flexure modulus of the composite materials. SPECIMEN PREPARATION AND EXPERIMENTAL PROCEDURES In this paper, the specimens were made and tests were conducted to calculate the basic material properties. Min- An Company that their headquarters are in Taiwan supply the graphite/epoxy composites prepreg. The procedure to make the composite laminate is the following: 1. First get the prepreg shown in Figure 1 from the freezer and put on the table around 8 to 12 hours for defrosting. 2. Cut the prepreg to be the desired size and number.

2 3. All of the plies must be arranged depend on which kind of test will be performed. 4. Using the roller to pressure the air out from the pre-curing laminate. 5. On the top and bottom, peel ply, T1000, bleeder, absorbing cotton will be layered as shown in Figure 2, then put the material into the thermo-set machine shown in Figure 3. The thermo-set procedures have two steps: the first step is only increasing the thermo-set plate up to 80_ and keep it around 30 minute. The second step is to increase the temperature up to 120_ and the pressure up to 300 Psi. The maintain time for the second step is around 20 minutes, then slow down the temperature to the room temperature and keep the pressure around 20 minute to avoid the residual stress in the composite laminate. The curing processing curve is shown in Figure 4. The composite laminate plate will be cut by using the diamond coating knife to get the test specimen that depends on what kinds of experiments want to do. MATERIAL PROPERTIES TESTS After the laminate plate were cured, the specimen size for E11, based on ASTM D3039M-93, is shown in Figure 5. After the specimen was got, the end protection tape [2-5] must be stuck on both ends to protect the specimen during o the tension test. The [ ± 45 ] glass/epoxy laminate were cut to be a small tape that the size is also shown in Figure 5. In here, the 45 degree slope must be made to avoid the specimen failed at the clamped fixture that will effect the correction of the test. Before performing the tensile test, the double orientation of strain gauge must be stuck on the center of the specimen to get the strain in longitudinal direction and transverse direction for calculating the Poisson s ratio. The tensile test machine is shown in Figure 6. After the specimen was fixed at the clamp fixture, the speed of the moving head of the tensile machine is set to be 0.5 mm/min. The formula for tensile module (E11) and the Poisson s ratio are the following: E 11 = ( P wh ) 1 ν 12 2 = (1) 1 Where P _applied load w_the width of the specimen H_the thickness of the specimen ε 1 _the strain in the longitudinal direction ε 2 _ the strain in the transverse direction The result for the tensile test was depicted in Figure 7. E22 TEST PROCEDURE o Based on ASTM D , [ 90 ] fiber stacking angle must be available. The geometric size is plotted in Figure 8 8. The end protection tape should be made as the above method. The strain gauge is also put on the center of the specimen to measure the strain in loading direction. The speed of the moving head of the machine is set to be 0.1 mm/min. The formula for calculation of E22 will be: ( P wh ) E 22 = (2) 1 Where P _applied load w_the width of the specimen H_the thickness of the specimen _the strain in the longitudinal direction ε 1 G12 TEST PROCEDURE Generally, G12 can be calculated from the E11, E22, and _12 which are obtained from the above tests. The formula for G12 is the following: E11* E22 G12 = E11+ E22 + 2υ12 * E11 (3) 2

3 DENSITY TEST The density of composite material is necessary when the dynamic analysis would be performed. In our laboratory, PRECISA density equipment is available to measure the density of the composite material. To cut a small piece of composite material, and put it into the glass cup which the water was filled up. The material weight was measured in the water and air, then the specific weight can be obtained. The material properties of graphite/epoxy composite laminate supplied from Min-An Company can be obtained: E11= Mpa E22= Mpa G12= Mpa _12= 0.28 density=1.518 g/cm*cm THREE POINT FLEXURE TEST The flexure test can be performed with three point bending test. The composite material has different material properties in different direction. The geometric dimensions for 0 degree fiber direction composite specimen are plotted in the figure 9. Also the specimen for 90 degree fiber direction composite laminate was plotted in Figure10. For 0 degree fiber direction specimen shown in figure 9 that the length is mm, the width is 25.4 mm, and the ratio of span to thickness must be 40 or 32 which depend on the stiffness of material. In our laboratory, the graphite/epoxy composite laminate is experienced, the ratio of span to thickness must be 40 and that of glass/epoxy composite laminate would be 32. The loading speed has to keep at 2.54mm/min. For 90 degree fiber orientation specimen, the length and width are the same dimension as the specimen of 0 degree fiber orientation, but the ratio of span to thickness is 25. The loading speed is also maintained at 2.54 mm/min. The flexure modulus can be found from the following formula: E 3 L f 4wt l = 3 (4) Where: f l = the slope of the loading curve, L = Span, w = the width of the specimen, t = the thickness of the specimen, The flexure modulus of composite material used in the E11 and E22 test are listed in the following: E11 (0 degree)= Mpa E 22(90 degree) = Mpa CONCLUSION In this paper, the method for calculating and testing of composite material mechanical properties is described in detail. The operation proceeding for the test machine is recorded step by step by using the digital camera and also will post in the Website of school network. The student can go through the test procedures before doing the tests. In this way, teacher are not necessary to repeat the operation procedures in the class and can save lots of time to develop the other topics. Student can shorten the learning timeand the multimedia teaching methods is a valuable method. REFERENCES [1] Swanson, Stephen R., Introduction to Design and Analysis with Advanced Composite Materials, Prentice-Hall International, Inc., [2] Sih, G. C., and Skudra, A. M., Failure Mechanics of Composites, North-Hollansd, 1985, pp [3] Whitney, J. M., and Nuismer, R. J., Stress Fracture Criteria for Laminated Composites Containing Stress Concentration, Journal of Composite Materials, 1974, pp [4] Nuismer, R. J., and Whitney, J. M., Uniaxial Failure of Composite Laminates Containing Stress Concentrations, in Fracture Mechanics of Composites, ASTM STP 593, American Society for Testing and Materials, Philadelphia, PA, 1975, pp

4 [5] Sandhu, R. S., A Survey of Failure Theories of Isotropic and Anisotropic Materials, Technical Report, AFFDL-TR FIGURES AND TABLES FIGURE 1 PREPREG OF GRAPHITE/EPOXY. FIGURE 2 THE LAY-UP ORDER OF THE SUPPLIER MATERIALS FIGURE 3 THERMOSET MACHINE 4

5 FIGURE 4 THE FORMING CURVE OF COMPOSITE MATERIAL FIGURE 5 THE COMPOSITE LAMINATE SPECIMEN FOR E11 TEST THE HYDRAULIC TEST MACHINE FIGURE 6 5

6 FIGURE 7 TEST RESULT FOR TENSILE TEST FIGURE 8 THE GEOMETRIC DIMENSIONS OF E22 SPECIMEN FIGURE 9 0 DEGREE FIBER DIRECTION SPECIMEN 6

7 FIGURE DEGREE FIBER DIRECTION SPECIMEN 7