Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session C5: BIEP: Spall I |
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Chair: David Jones, LANL Room: Broadway I/II |
Monday, June 17, 2019 11:00AM - 11:15AM |
C5.00001: Scaling laws for the pressure and rate dependence of spall strength Justin Wilkerson Experimental studies have found that the spall strength of many face-centered cubic metals increases linearly with shock pressure. Additionally, an anomalous grain size dependence of spall strength has been measured in a few face-centered cubic metals. Here we derive the first quantitative theory capable of explaining these phenomena. The scaling laws agree well with experimental measurements and atomistic calculations of both single crystal and polycrystalline materials subject to a very wide range of conditions. Utilizing these scaling laws, we are able to map out three distinct regimes in which spall strength (i) increases with decreasing grain size in accordance with conventional wisdom, (ii) non-intuitively decreases with decreasing grain size, and (iii) is independent of grain size. With respect to shock pressure dependence, the scaling laws address both shock hardening and shock softening. Shock hardening is induced by a shock-induced increase in the total dislocation density. Shock softening can be induced by either thermal softening or shock-induced reductions in material viscosity. These phenomena are captured quite well by rather simple scaling relations. [Preview Abstract] |
Monday, June 17, 2019 11:15AM - 11:30AM |
C5.00002: Dynamic mechanical properties and fracture response of Dual Phase steels spanning a strain rate range of 10$^{\mathrm{2}}$/s to 10$^{\mathrm{6}}$/s. Sukanya M Sharma, Shrikant Bhat, Arun Gokhale, Naresh Thadhani The dynamic mechanical properties and spall fracture response of three commercial Dual Phase (DP) steels under strain rates of 10$^{\mathrm{2}}$/s-10$^{\mathrm{6}}$/s are described in this work. DP steels are used in automotive industry due to their combination of high strength and moderate ductility. Formability and crash resistance expose the steel to high strain rates and are driven by microstructure. DP steels in this work contain ferrite and \textasciitilde 65{\%} of a harder phase (mixture of martensite and bainite). Two steels have protective galvannealed coating and one of the coated steels contains decarburized surface layer {\&} gradient microstructure. Stereological techniques are used to quantify features in microstructures and reveal differences in phase distribution due to changes in processing conditions. Dynamic mechanical properties at strain rates in the range of 10$^{\mathrm{2}}$/s-10$^{\mathrm{6}}$/s, achieved using a hopkinson bar and plate on plate impact tests show that while the strength of these steels exhibit a positive strain rate sensitivity and increase with strain rate, the strain to fracture is more a function of the underlying microstructure. Quantitative fractography of the fracture surfaces at different strain rates reveal sensitivity of operative micromechanisms to strain rate, loading conditions and microstructure. [Preview Abstract] |
Monday, June 17, 2019 11:30AM - 12:00PM |
C5.00003: Metallurgical Effects on the Spall Response of Metals and Alloys. Invited Speaker: Jeremy Millett Dynamic tensile failure induced by shock loading -- spallation -- has long been used as a method to characterize the high strain-rate response of materials. However, as well as being controlled by materials properties such as unit cell, stacking fault energy or Peierls stress, and the microstructure, it should also be bourn in mind that spall measurements are not only amplitude dependent, but also geometry dependent as well; in essence they are time integrated. Therefore, the spall strength itself can be time dependent. In this presentation we compare the variation of spall response with impact conditions, and how it compares with other shock induced mechanical properties. [Preview Abstract] |
Monday, June 17, 2019 12:00PM - 12:15PM |
C5.00004: ABSTRACT WITHDRAWN |
Monday, June 17, 2019 12:15PM - 12:30PM |
C5.00005: Investigating the effects of plastic deformation on the dynamic tensile strength of Lean Duplex Stainless Steel Ali Ameri, J.P. Escobedo-Diaz, M. Gonzales, H. Wang, Z. Quadir, P. Hazell Lean Duplex Stainless Steel 2404 (LDX 2404) is a new dual phase alloy with equal volume fractions of the austenite (FCC) and ferrite (BCC) phases. This study explores the effects of plastic deformation, in the form of 20{\%} quasi-static compressive strain, on the subsequent mechanical behavior and damage evolution of this alloy when subjected to shock loading. Plate impact experiments were conducted in a single-stage light gas-gun at impact velocities in the 200-400 m/s range. The examination of the damage fields was done using Optical Microscopy (OM) and Electron Backscatter Diffraction (EBSD). Results indicate that the material experienced incipient spall damage at an impact velocity of \textasciitilde 200 m/s and full spall at an impact velocity of \textasciitilde 370 m/s. The pre-strained specimens show an increase in the spall strength compared with the as-received condition. Under all conditions, the spall damage occurs primarily within the ferrite phase while the austenite phase seems to suppress crack propagation, thereby creating barriers for crack propagation into the austenite phase. [Preview Abstract] |
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