Contexto externo

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

This thesis utilizes Synchrotron Microtomography (SMT) in order to better understand the compaction behavior of aluminum powders. Two configurations of compaction dies were used in the experiments scanned at APS. IDL algorithms were developed to render the scan images and to perform quantitative analysis. In general, SMT can be successfully applied to examine density variation and to track microscopic deformations of aluminum powders under compaction. SMT provides efficient, quantitative access to internal density distributions during compaction. Comparison of density maps at different strains levels may be used to investigate spatial variation, thus providing critical measurements that may be used to calibrate constitutive models to predict the behavior of compacted powder.

The main factors that influence the density distribution of compacted powder are a) the friction interaction between powder and die wall; and b) the geometry of die and punches. The following conclusions are drawn:

• The density distribution within the compaction die was controlled by several factors. The sample preparation and initial randomness of filling show a profound influence on the uniformity. The initial punching of ram can result in a different distribution of density within the die, which can be observed from the density maps. • Springback is another important factor which influences density distribution, especially during the scanning procedure. Since the release of stress results in the release

of elastic energy stored in the powders, the deformation of particles changes. This result has an influence on the density distribution.

• The aluminum compacts show a considerable side-to-side asymmetry. Although the average density in each column and row is relatively uniform, the maximum and minimum column density reveals clearly a greater side-to-side asymmetry in the aluminum compacts. When a high axial strain level is reached, the density distribution begins to exhibit great side-to-side symmetry.

• The generation of a void gap between layers indicates an inefficiency regarding the transmission of stress during the compaction. The occurrence of this layer is probably due to the clearance between the ram and die wall at the top. Stress may be inefficiently transferred to these particles, because of their ability to move into the protected area between the wall and the advancing punch.

5.2 Recommendations

Future research recommendations are as follows:

• Investigate the effect of sample filling procedures to determine a method to reduce the influence on the density distribution and springback effect.

• The different scales of compaction die could be tested, especially when length to diameter ratios are large. The L/D effect should be examined and analyzed.

• A higher compaction strain level should be achieved in order to test particle behavior at high strain condition under compaction.

REFERENCES

Alramahi, B. A. (2004) “Assessment of Shearing Phenomenon and Porosity of Porous Media Using Microfocus Computed Tomography”. MS Thesis, Louisiana State University, Baton Rouge, LA. 83 pages.

Ariffin, A.K., Ihsan, M., (1995). Powder Compaction, Finite Element Modeling and

Experimental Validation, Ph.D. Thesis. University of Wales Swansea, United Kingdom. ASTM (2003). E1935 Standard Test Method for Calibrating and Measuring CT Density.

American Society for Testing and Materials.

Bhattad, P., Willson, C.S., and Thompson, K.E. (2010) Segmentation of low-contrast three-phase X-Ray computed tomography images of porous media: Proceedings of the GeoX 2010. 3rd International Workshop on X-ray CT for Geomaterials in New Orleans, LA, March 1-3, edited by K. Alshibli and A.H. Reed. 254-

261. http://www.cee.lsu.edu/geox2010/workshop/Program.html

Burch, S.F., (2001). “Measurement of density variations in compacted parts using X-ray

computed tomography”. In Proceedings of EuroPM 2001, Nice, France, October 22–24, 52(2): 398–404.

Chtourou, H., Guillot, M., Gakwaya, A., Guillot, M. (2002) “Modeling of the metal powder compaction process using the cap model. Part I: Experimental material characterization and validation.” International Journal of Solids and Structures. 39(4): 1059–75.

Deis, T.A. and Lannutti, J.J. (1998). “X-ray Computed Tomography for Evaluation of Density Gradient Formation During the Compaction of Spray-dried Granules,” J. Am. Ceramic Soc., 81(5): 1237-1247.

Garino T., M. Mahoney, M. Readey, K. Ewsuk, J. Gieske, G. Stoker, and S. Min, (1995) ‘‘Characterization Techniques to Validate Models of Density Variations in Pressed Powder Compacts’’, 610–621 in Proceedings of the 27th International SAMPE Technical Conference, Diversity into the Next Century. Edited by R. J. Martinez, H. Arris, J. A. Emerson, and G. Pike. SAMPE International, Covina, CA.

Hasan, A. (2009) “ Micro characterization of deformations in granular materials during shear”. Ph. D. Dissertation, Louisiana State University, Baton Rouge, LA.146 pages.

Hubbell, J. and Seltzer, S. (1997). “Tables of x-ray mass attenuation coefficients and mass energy-absorption coefficients.” http://physics.nist.gov/PhysRefData/XrayMassC oef/cover.html.

Nam, J., Wenxia L. and John J.J. (2003) Density gradients and springback: environmental influences.” Powder Technology. 133(3): 23-32.

Kamm, R., Steinberg, M. A. and Wulff, J. (1949) “Lead-Grid Study of Metal Powder Compaction,” Trans. Am. Inst. Mining Met. Eng., 694–706.

Kong, C.M., Lannutti, J.J., (2000). “Localised densification during the compaction of alumina granules: the stage I–II transition.” J. Am. Ceram. Soc. 83(4): 685–690.

Kuczynki, G. C. and Zaplatynskyj, I. (1956) “Density Distribution in Metal Powder Compacts,” J. Met., 215.

Li, W., Nam, J., Lannutti, J.J. (2002). “Density gradients formed during compaction of bronze powders: the origins of part-to-part variations.” Metall. Mater. Trans. 33(1): 165–170. Lin, C.L., Miller, J.D., (2000). “Pore structure and network analysis of filter cake.” Chem. Eng. J.

80(1-3): 221–231.

Lowell, S., Shields Joan. E. (1984) “Powder Surface Area and Porosity”. London: Chapman & Hall. 2nd ed. HC. Exlibrary. VG. ISBN: 0412252406.

Macleod, H. M., Marshall, K., (1977). “The determination of density distributions in ceramic compacts using autoradiography.” Powder Technol. 16(1): 107–122.

Mori, Y., Sato, M., Shiomi and Osakada, K., (1999) “Prediction of fracture generated by elastic recoveries of tools, in multi-level powder compaction using finite element simulation.” Int. J. Machine Tools Manuf. 39(7): 1031–1045.

Oh, W. and Lindquist, W. (1999). “Image thresholding by indicator kriging.” Transactions on Pattern Analysis and Machine Intelligence, IEEE, 21(7): 590-602.

Phillips, D.H., Lannutti, J.J., (1997). “Measuring physical density with X-ray computed tomography”. NDT&E Int. 30(6): 339–350.

Rajab, M. and Coleman, D. S., (1985). “Density Distribution in Complex Shaped Parts Made from Iron Powders,” Powder Metall., 28 (4): 207–16.

Razavi, M., Muhunthan, B., Hattamleh, O. (2007) “Representative Elementary Volume Analysis of Sands Using X-Ray Computed Tomography.” Geotechnical Testing Journal, 30(3): 212–219.

Reed, J. S. (1988) “Introduction to the Principles of Ceramic Processing, 1st ed” Wiley, New York, 486.

Matsumoto, R.L.K. (1990) “Analysis of powder compaction using compaction rate diagram.” J. Am. Ceramic. Soc. 73(2): 465–468.

Sinka, I.C., Cunningham, J.C., Zavaliangos, A., (2003). “The effect of wall friction in the compaction of pharmaceutical tablets with curved faces: a validation study of the Drucker–Prager Cap model.” Powder Technol. 133(1-3): 33–43.

Thompson, K. E., Willson, C. S., and Zhang, W. (2006). “Quantitative computer reconstruction of particulate materials from microtomography images.” Powder Technology,163(3): 169-182.

Train, D., (1957). “Transmission of forces through a powder mass during the process of pelleting.” Trans. Inst. Chem. Eng. 35: 258–266.

VITA

Yi Yang was born in September, 1986, in ShaoXing. Then, he moved to HuBei Province with his family and began his study there from elementary school to college. He finished his high school in 2005 and went to one of the top ten universities-Wuhan University in China. He spent four years there and earned his bachelor degree both in civil engineering and economics. After graduation from college, he received full graduate research assistantship to begin his study in geotechnical engineering program in the Civil and Environmental Engineering Department at Louisiana State University, Baton Rouge, United States, in August 2009. He conducted research under the supervision of Dr. Khalid Alshibli and received his master degree in May 2011.