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PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping and M. Papadrakakis
Simulation of a Foreign Object Damage Test on a Silicon Nitride Specimen
R. Dotoli, D. Lisi, D. Bardaro and O. Manni
Department of Materials and Structures Engineering, CETMA Consortium - Engineering, Design and Materials Technologies Centre, Brindisi, Italy
R. Dotoli, D. Lisi, D. Bardaro, O. Manni, "Simulation of a Foreign Object Damage Test on a Silicon Nitride Specimen", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 208, 2008. doi:10.4203/ccp.88.208
Keywords: foreign object damage, Johnson-Holmquist constitutive model, impact, ball projectile, silicon nitride.
The analysis of ceramics subject to impact is of significant interest because of their extensive use in protection applications. Ceramics are interesting materials because of their low density and high hardness, which are critical parameters in the performance of protective systems. These materials used in protective shield applications may be subject to high energy impacts; in these loading conditions ceramics may fail structurally, even by small particles, if the kinetic energy of impacting objects exceeds certain limits.
Although experimental testing is always necessary, there is a considerable motivation for simulation and the in-depth study of numerical models. The response of ballistic impacts on ceramics is related with: the projectile characteristics (size, velocity, material), the material supporting the specimen and, of course, the ceramic mechanical properties . The understanding of these dependencies through experimental testing can be very costly and time-consuming, because of the considerable degree of scatter in this type of data.
The aim of this paper is to evaluate the Johnson-Holmquist (JH-2) constitutive model and analyze the material model, damage and strength constants proposed . Within this model, the crack initiation and propagation through the material is tracked with a representative damage variable. The constitutive model expresses the material strength as a function of pressure and damage, while incorporating material bulking due to damage.
Simulation of a steel sphere impacting a silicon nitride specimen is carried out to evaluate the application of this constitutive model to a foreign object damage (FOD) test. The specimen has a rectangular cross-section: 3 mm in thickness, 4 mm in width and 45 mm in length. Each target specimen is impacted in the middle of the wide side with a normal incidence angle.
Numerical simulation results are compared with experimental tests to observe damage evolution, fracture propagation, and damage resulting from compression waves reflected at a free surface. Finally it can be appreciated that the JH-2 material model (mat 110 in LS-Dyna) is suitable to simulate the ballistic impact of foreign object damage in order to support the understanding of the physical phenomenon.
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