Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session T6: Inelastic Deformations, Fracture and Spall IX: Brittle Ceramics |
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Chair: James Hogan, Johns Hopkins University, Min Zhou, Georgia Institute of Technology Room: 8/9/10 |
Thursday, June 18, 2015 11:15AM - 11:45AM |
T6.00001: High Speed Dynamics in Brittle Materials Invited Speaker: Stefan Hiermaier Brittle Materials under High Speed and Shock loading provide a continuous challenge in experimental physics, analysis and numerical modelling, and consequently for engineering design. The dependence of damage and fracture processes on material-inherent length and time scales, the influence of defects, rate-dependent material properties and inertia effects on different scales make their understanding a true multi-scale problem. In addition, it is not uncommon that materials show a transition from ductile to brittle behavior when the loading rate is increased. A particular case is spallation, a brittle tensile failure induced by the interaction of stress waves leading to a sudden change from compressive to tensile loading states that can be invoked in various materials. This contribution highlights typical phenomena occurring when brittle materials are exposed to high loading rates in applications such as blast and impact on protective structures, or meteorite impact on geological materials. A short review on experimental methods that are used for dynamic characterization of brittle materials will be given. A close interaction of experimental analysis and numerical simulation has turned out to be very helpful in analyzing experimental results. For this purpose, adequate numerical methods are required. Cohesive zone models are one possible method for the analysis of brittle failure as long as some degree of tension is present. Their recent successful application for meso-mechanical simulations of concrete in Hopkinson-type spallation tests provides new insight into the dynamic failure process. Failure under compressive loading is a particular challenge for numerical simulations as it involves crushing of material which in turn influences stress states in other parts of a structure. On a continuum scale, it can be modeled using more or less complex plasticity models combined with failure surfaces, as will be demonstrated for ceramics. Models which take microstructural cracking directly into account may provide a more physics-based approach for compressive failure in the future. [Preview Abstract] |
Thursday, June 18, 2015 11:45AM - 12:00PM |
T6.00002: Multi-scale peridynamic modeling of dynamic fracture in concrete Christopher Lammi, Min Zhou Peridynamics simulations of the dynamic deformation and failure of high-performance concrete are performed at the meso-scale. A pressure-dependent, peridynamic plasticity model and failure criteria are used to capture pressure-sensitive granular flow and fracture. The meso-scale framework explicitly resolves reinforcing phases, pores, and intrinsic flaws. A novel scaling approach is formulated to inform the engineering-scale plasticity model parameters with meso-scale simulation results. The effects of composition, porosity, and fracture energy at the meso-scale on the engineering-scale impact resistance are assessed. The fracture process zone at the meso-scale is found to propagate along adjacent pores and reinforcing phases under tensile and shear loading conditions. The simulations show that tensile strength decreases and dissipation increases as the porosity in the concrete increases. The framework and modeling approach allow the delineation of trends that can be used to design more impact-resistant materials. [Preview Abstract] |
Thursday, June 18, 2015 12:00PM - 12:15PM |
T6.00003: Mechanical Model for Dynamic Behavior of Concrete Under Impact Loading Yuanxiang Sun Concrete is used substantively in the civil building and military safeguard. One coupled model of damage and plasticity to describe the complex behavior of concrete subjected to impact loading is proposed in this research. The concrete is assumed as homogeneous continuum with pre-existing micro-cracks and micro-voids. Damage to concrete is caused due to micro-crack nucleation, growth and coalescence, and defined as the probability of fracture at a given crack density. It induces a decrease of strength and stiffness of concrete. Compaction of concrete is physically a collapse of the material voids. It produces the plastic strain in the concrete and, at the same time, an increase of the bulk modulus. In terms of crack growth model, micro-cracks are activated, and begin to propagate gradually. When crack density reaches a critical value, concrete takes place the smashing destroy. The model parameters for mortar are determined using plate impact experiment with uni-axial strain state. Comparison with the test results shows that the proposed model can give consistent prediction of the impact behavior of concrete. The proposed model may be used to design and analysis of concrete structures under impact loading. [Preview Abstract] |
Thursday, June 18, 2015 12:15PM - 12:30PM |
T6.00004: Fracture Mechanisms of Zirconium Diboride Ultra-High Temperature Ceramics under Pulse Loading Vladimir V. Skripnyak, Anatolii M. Bragov, Vladimir A. Skripnyak, Andrei K. Lomunov, Evgeniya G. Skripnyak, Irina K. Vaganova Mechanisms of failure in ultra-high temperature ceramics (UHTC) based on zirconium diboride under pulse loading were studied experimentally by the method of SHPB and theoretically using the multiscale simulation method. The obtained experimental and numerical data are evidence of the quasi-brittle fracture character of nanostructured zirconium diboride ceramics under compression and tension at high strain rates and the room temperatures. Damage of nanostructured porous zirconium diboride -based UHTC can be formed under stress pulse amplitude below the Hugoniot elastic limit. Fracture of nanostructured ultra-high temperature ceramics under pulse and shock-wave loadings is provided by fast processes of intercrystalline brittle fracture and relatively slow processes of quasi-brittle failure via growth and coalescence of microcracks. A decrease of the shear strength can be caused by nano-voids clusters in vicinity of triple junctions between ceramic matrix grains and ultrafine-grained ceramics. [Preview Abstract] |
Thursday, June 18, 2015 12:30PM - 12:45PM |
T6.00005: Dynamic Fragmentation of an Advanced Ceramic during High-Speed Impact James Hogan, Lukasz Farbaniec, Debjoy Mallick, James W. McCauley, K.T. Ramesh The development of the next generation of light-weight protection materials requires an improved understanding of impact-induced fragmentation of advanced ceramics. We investigate the impact behavior of a hot-pressed boron carbide for impact velocities between 200 and 1000 m/s, and study the response in the context of the material properties, microstructure, and boundary conditions (e.g., confinement). We use measurements of fragment size and shapes to inform us about the mechanisms that are activated during dynamic failure. The fragment measurements are linked with physical evidence of failure processes obtained using scanning electron microscopy and Raman spectroscopy. [Preview Abstract] |
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