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Experimental and Theoretical Analysis of Plastic Deformation of Metals under Impact Loading Using Taylor Impact Test

Khayyer Dastjerdi Toroghi, Ahmad | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39092 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza
  7. Abstract:
  8. In most of the engineering applications, the mechanical behavior of materials in high strain rate deformations differs from their behavior in quasi-static deformations. In some engineering problems like impact loading on structures, metal forming and explosive forming, the range of strain rate is about . Taylor impact test is one of the experiments used for characterizing the dynamic behavior of materials in high strain rate deformations. In the Taylor impact test a rigid cylindrical projectile is impacted normally onto a hard and massive surface (anvil), the projectile deforms by mushrooming at the impact end. With plastic wave propagation analysis, the plastic deformation of projectile is related to dynamic flow stress. Momentum equation has been used for the study of plastic wave propagation in the Taylor specimen for many years, and also final length, final undeformed length and mushroom diameter of specimen are used for determining dynamic behavior of materials. In this thesis, plastic deformation of metals under impact loading in Taylor impact test has been studied experimentally and analytically. For this purpose, energy equation of the specimen during plastic deformation was derived and used for calculating final dimensions of the specimen. In addition to the mushroom diameter, specimen dimension in two other sections of plastic region were applied in the equations. Moreover, some specimens of copper in four length-to-diameter ratios, 1.5, 2, 3 and 4, were constructed and tested under impact loading. Then, coefficients of Johnson-Cook model were extracted with optimization of a least square function of final dimensions using Genetic Algorithm with using once the energy equation and second time the momentum one. Finally, these two sets of coefficients were used for simulating the Taylor specimens in LS-DYNA software. Comparison of final dimensions of specimens shows that the results of the energy equation are closer to the experimental ones than those of the momentum equation. The average error of the energy equation results with respect to the experimental results for copper specimens was 5% and 9% for moment equation. This error for iron specimens using energy equation was 6% and momentum equation was 7.7%
  9. Keywords:
  10. High Strain Rate ; Impact Loading ; Taylor Impact Test ; Dynamic Flow Stress ; Johnson-Cook Model

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