Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session E4: Inelastic Deformations, Fracture and Spall IV |
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Chair: Leslie Lamberson, Drexel University Room: Regency Ballroom A |
Monday, July 10, 2017 3:30PM - 3:45PM |
E4.00001: Strain rate effects on fracture behavior of Austempered Ductile Irons Andrew Ruggiero, Nicola Bonora, Domenico Gentile, Gianluca Iannitti, Gabriel Testa, Magnus H\"{o}rnqvist Colliander, Stefano Masaggia, Federico Vettore Austempered Ductile Irons (ADIs), combining high strength, good ductility and low density, are candidates to be a suitable alternative to high-strength steels. Nevertheless, the concern about a low ductility under dynamic loads often leads designers to exclude cast irons for structural applications. However, results from dynamic tensile tests contradict this perception showing larger failure strain with respect to quasistatic data. The fracture behaviour of ADIs depends on damage mechanisms occurring in the spheroids of graphite, in the matrix and at their interface, with the matrix (ausferrite) consisting of acicular ferrite in carbon-enriched austenite. Here, a detailed microstructural analysis was performed on the ADI 1050-6 deformed under different conditions of strain rates, temperatures, and states of stress. Beside the smooth specimens used for uniaxial tensile tests, round notched bars to evaluate the ductility reduction with increasing stress triaxiality and tophat geometries to evaluate the propensity to shear localization and the associated microstructural alterations were tested. The aim of the work is to link the mechanical and fracture behavior of ADIs to the load condition through the microstructural modifications that occur for the corresponding deformation path. [Preview Abstract] |
Monday, July 10, 2017 3:45PM - 4:00PM |
E4.00002: One-Dimensional Simulations for Spall in Metals with Intra- and Inter-grain failure models Brian Ferri, Sunil Dwivedi, David McDowell The objective of the present work is to model spall failure in metals with coupled effect of intra-grain and inter-grain failure mechanisms. The two mechanisms are modeled by a void nucleation, growth, and coalescence (VNGC) model and contact-cohesive model respectively. Both models were implemented in a 1-D code to simulate spall in 6061-T6 aluminum at two impact velocities. The parameters of the VNGC model without inter-grain failure and parameters of the cohesive model without intra-grain failure were first determined to obtain pull-back velocity profiles in agreement with experimental data. With the same impact velocities, the same sets of parameters did not predict the velocity profiles when both mechanisms were simultaneously activated. A sensitivity study was performed to predict spall under combined mechanisms by varying critical stress in the VNGC model and maximum traction in the cohesive model. The study provided possible sets of the two parameters leading to spall. Results will be presented comparing the predicted velocity profile with experimental data using one such set of parameters for the combined intra-grain and inter-grain failures during spall. [Preview Abstract] |
Monday, July 10, 2017 4:00PM - 4:15PM |
E4.00003: Modeling gradual and rate dependent closing and opening of pores in porous materials Yehuda Partom Most dynamic porous materials models assume that under shock loading pore closure is immediate. Such an approach is known as the snowplough model. But pore closing, as well as pore opening, is a relatively slow mechanical process that involves fracture, plastic flow and material motion. As a result, a shock loaded porous material may become overstressed relative to its quasistatic pore closing/opening curves. Being overstressed, the material state point tends to fall back onto the appropriate quasistatic curve at a rate that is an increasing function of the amount of overstress. In this way the pores opening/closing processes become rate dependent. Here we develop and outline such a rate dependent pore closing/opening model. The model includes: 1) an equation of state for porous materials based on Herrmann's assumptions [1]; 2) the quasistatic closing/opening curves; and 3) rate functions for the overstress decrease. We implemented our model in a hydrocode, and to demonstrate how the model works we show examples of some planar impact runs. W. Herrmann, J. Appl. Phys. 40, 2490-2499 (1969). [Preview Abstract] |
Monday, July 10, 2017 4:15PM - 4:30PM |
E4.00004: Dynamic Tensile Strength of Silicone Oils Justin Huneault, Jihane Kamil, Andrew Higgins, David Plant The spall strength of various liquids has been studied using the planar impact of thin flyers to generate large transient negative pressures near the free surface of target samples. The liquids were contained within sealed capsules in which a 4 $\mu m$ thick aluminized Mylar diaphragm formed a free surface at the back of the sample. The liquid targets were impacted by aluminum and PMMA flyers at velocities ranging from 100 to 700 m/s using a 25-mm-bore gas-gun, thus allowing for large variations in the strain rate and incident shock pressure. The peak tension in the liquid was determined by monitoring the free surface velocity using a photonic Doppler velocimetry (PDV) system. The experimental technique was validated against previously published results for water samples. The paper focuses on the study of a system of silicone oils having vastly different viscosities (5 cP to 30 000 cP), but otherwise similar liquid properties. The results are compared to existing data and models for the dynamic cavitation of liquids. [Preview Abstract] |
Monday, July 10, 2017 4:30PM - 4:45PM |
E4.00005: Strain Rate and Stress Triaxiality Effects on Ductile Damage of Additive Manufactured TI-6AL-4V Gianluca Iannitti, Nicola Bonora, Domenico Gentile, Andrew Ruggiero, Gabriel Testa, Simone Gubbioni In this work, the effects of strain rate and stress triaxiality on ductile damage of additive manufactured Ti-6Al-4V, also considering the build direction, were investigated. Raw material was manufactured by means of EOSSINT M2 80 machine, based on Direct Metal Laser Sintering technology, and machined to obtain round notched bar and Rod-on-Rod (RoR) specimens. Tensile tests on round notched bar specimens were performed in a wide range of strain rates. The failure strains at different stress triaxiality were used to calibrate the Bonora Damage Model. In order to design the RoR tests, numerical simulations were performed for assessing velocities at which incipient and fully developed damage occur. Tests at selected velocities were carried out and soft-recovered specimens were sectioning and polishing to observe the developed damage. Nucleated voids maps were compared with numerical simulations results. [Preview Abstract] |
Monday, July 10, 2017 4:45PM - 5:00PM |
E4.00006: The ductility of $\alpha +\beta $ titanium alloys over a wide range of strain rates and stress triaxiality Vladimir V. Skripnyak, Evgeniya G. Skripnyak, Irina K. Vaganova, Natalia V. Skripnyak, Vladimir A.. Skripnyak This paper presents the results of experimental research and numerical simulation of mechanical behavior of alpha $+$ beta titanium alloys VT--6 (this is an analog of alloy Ti--6Al--4V) and BT--5 (this is an analog of Ti--5Al) in a wide range of strain rates (from 0.001 to 1000 1/s) and stress triaxiality (0.025--0.6). Samples of different shapes were used in experiments to study the deformation and fracture under uniaxial tension, shear. The model of inelastic deformation and fracture is proposed to describe the ductility of the titanium alloy in a wide range of strain rates and stress states. The model was calibrated using experimental data for alpha $+$ beta titanium alloys at room temperature. The model describes the ductility of the alpha $+$ beta titanium alloys at temperatures below\textasciitilde 873 K when the volume concentration of beta-phase varies slightly. [Preview Abstract] |
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