Advanced Characterization Techniques for Quantifying and Modeling Deformation Mechanisms: Session VII
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Shaping and Forming Committee
Program Organizers: Rodney McCabe, Los Alamos National Laboratory; John Carpenter, Los Alamos National Laboratory; Thomas Beiler, Michigan State University; Khalid Hattar, Sandia National Laboratory; Wolfgang Pantleon, DTU; Irene Beyerlein, Los Alamos National Laboratory

Thursday 8:30 AM
March 2, 2017
Room: 33C
Location: San Diego Convention Ctr

Session Chair: Asher Leff, Drexel University; Veronica Livescu, Los Alamos National Laboratory

8:30 AM  
Representation of Materials Microstructure for Modeling: Veronica Livescu1; Curt Bronkhorst1; George Gray1; Carl Trujillo1; Daniel Martinez1; James Valdez1; Bineh Ndefru1; Olivia Dippo1; Roberta Beal1; 1Los Alamos National Laboratory
    The materials-by-design idea is built upon the premise that critical aspects of materials function can be captured in computational environments that includes making, measuring, and modeling materials. Past research efforts have focused on developing constitutive laws and numerical solvers but less attention has been paid to the representation of material microstructure. Results of quasi-static and high strain-rate mechanical testing indicate that mechanisms of deformation and damage nucleation are strongly dependent on material processing and resulting microstructure and are as yet a significant challenge to predict accurately. This work focuses on techniques for collection and quantification of material statistical distributions, virtual generation of materials models, and modeling requirements for simulating material response. Morphological and textural differences of forged and additively manufactured steels are discussed in the context of material response to deformation and damage, while microstructural statistics of these polycrystalline structures are discussed in the context of predictive capability development.

8:50 AM  
Determination for Dynamic Fracture Toughness of Linear Elastic Materials Using the Large Dimensional Hopkinson Tube: Chunhuan Guo1; Ding Yuan1; Peijun Zhou1; Kennth. S. Vecchio2; Fengchun Jiang1; 1Harbin Engineering University; 2University of California, San Diego La Jolla
    Owing to limitation of a conventional Hopkinson loading bar dimensions, the geometrical sizes of dynamic fracture specimen are hard to satisfy the plane strain condition. Therefore, the incident and transmission tubes are developed instead of solid bars. In this presentation, the specimens with 10mm×20mm×100mm made of 40Cr was loaded by a novel Hopkinson tube experimental apparatus, the strain gauge method was used to obtain the initial crack onset time of specimen and then the dynamic fracture toughness of 40Cr was calculated by Spring-Mass model and Timoshenko beam theory using the incident, reflected and transmitted pulses. The results indicated that the dynamic force equilibrium is achieved and the dynamic fracture toughness of 40Cr obtained by different calculated methods are very close, which means that there is no significant difference between the dynamic fracture toughness determined by different methods when the force state of fracture specimen is in the dynamic force equilibrium.

9:10 AM  
Determination of Geometrically Necessary Dislocations in Large Shear Strain Localization in Metals: Chaoyi Zhu1; Veronica Livescu2; Tyler Harrington1; Olivia Dippo2; George T. Gray III2; Kenneth Vecchio1; 1UC San Diego; 2Los Alamos National Laboratory
    Shear localization and shear banding propensity has been extensively studied for more than half a century. However, the study of shear localization still has significant limitations in terms of quantitative assessments of shear localized microstructure evolution. With the recent introduction of the compact forced simple shear (CFSS) sample, detailed quantitative examination of the influence of microstructural anisotropy and crystallographic anisotropy on the evolution of shear localization and shear banding phenomena is now possible. Combined with EBSD-based geometrically-necessary dislocation density calculations from lattice rotations, we are able to show how GND evolution near shear bands can provide quantitative information about how damage in 7039-aluminum alloy is determined by the anisotropy in grain morphology in the shear direction, and how initial crystallographic anisotropy in texture relative to the shear orientation in high-purity titanium affects work-hardening, ductility and energy absorption ability of the material.

9:30 AM  
High Temperature Dynamic Mechanical Behavior Characterization of Ti-6Al-4V Using a NEW Compression Kolsky Bar Technique: Sindhura Gangireddy1; Steven Mates1; 1NIST
     We investigate dynamic mechanical response of titanium alloys at high temperatures through a new variation of compression Kolsky bar technique. Here resistive heating is utilized and we have the ability to closely simulate extreme thermo-mechanical processes like high speed machining and blast impact – rapid heating + rapid loading. Results will be crucial in understanding component failure as well as in theimprovement of manufacturing processes. The constitutive response of Ti-6Al-4V alloy and CP-Ti will be presented from a wide range of testing conditions: room temperature - 1200C, 0.1-0.3 plastic strains and 0.000001-3000 strain rate. Effect of time dependent microstructural evolution (annealing, grain growth, phase transformation) and grain morphology (globular, lamellar, widmanstatten, martensitic) was also studied. All results are very recent from last year study conducted at NIST.

9:50 AM Break

10:10 AM  
Dissecting Dislocation Dynamics Simulations : The Search for the Origins of Dislocation Microstructure Evolution: Ahmed Hussein1; Brahim Akdim2; Edwin Antillon2; Christopher Woodward1; Satish Rao3; Triplicane Parthasarathy2; 1Air Force Research Laboratory; 2UES Inc.; 3EPFL
    Large-scale Discrete Dislocation Dynamics simulations were performed on single-crystal Ni micro-pillars ranging in size from 5-50 microns. Using a range of initial dislocation densities and microstructures, the dislocation ensembles were evolved under tensile loading along (111), (110), and (100) directions. Plastic strain bursts resulting from the motion of individual dislocations were tracked and analyzed. Several microstructure metrics are suggested and compared based on how well they capture the experimentally observed dislocation microstructures (i.e. dislocation cells and walls). Detailed history of the evolution controlling mechanisms (e.g. junction formation and cross-slip) was studied and a model that captures their effects is suggested. A special focus is given to the evolution of the dislocation mean free path as an intrinsic length scale that controls several of these mechanisms. Progress towards a mechanistic description of strain hardening based on correlating the flow strength evolution with the evolving microstructure and dislocation controlling mechanisms is presented.

10:30 AM  
Toward a Description of Disinclination Densities Using Orientation Imaging Data: Asher Leff1; Christopher Weinberger1; Mitra Taheri1; 1Drexel University
    Disclinations, defects that accommodate rotational incompatibilities in a crystal lattice, have been described in detail in the literature, but rarely observed in solid materials. They are a convenient explanation for how the incompatibility inherent to five-fold twin structures is accommodated and are often discussed in reference to liquid crystals, in which they are common. Recently, a method has been described in the literature by which it is proposed that disclination densities can be estimated using spatially resolved orientation data generated from electron backscatter diffraction or precession electron diffraction. A rigorous evaluation of this approach, however, yields contradictions in methodology that make its estimations either absolutely zero or always within the error bounds of the numerical method. In this work, we use a series of constructed and real data sets to evaluate this methodology for estimating disclination densities and demonstrate the inherent error associated with this and similar techniques.

10:50 AM  
Effects of Crystal Orientation on Shock Induced Dislocation Dynamics of Single Crystalline Copper: Anupam Neogi1; Nilanjan Mitra1; 1IIT Kharagpur
    An attempt has been made to investigate the effects of crystallographic orientation (e.g. <100>, <110> and <111>) over the dislocation dynamics, originated due to shock compression with various intensities, through large scale non-equilibrium molecular dynamics (NEMD) simulation. Due to the geometrically favorable orientations of the operative slip planes in <100>, simple glide based plasticity, including stacking faults (SF), dislocations and twining has been observed to be predominated. For other directions, <110> and <111>, formation of jogs and multiple slips are observed, along with significant delocalization of shear strain in the deformed microstructure. During the reactions of Shockley partials, Hirth-type locking is significant in case of <100>, whereas, Stair-rod and Frank type sessile locks predominates in other above mentioned directions due to complex geometrical orientations of highly dense planes. Temporal evolution of details statistics of the dislocation density and analysis of associated deformation microstructures will be discussed during the presentation.

11:10 AM  
Dislocation Interaction and Fatigue Damage Evolution at Grain Boundaries Studied by In-situ Cyclic Loading of Bi-crystalline Micro Samples: Christian Motz1; Jorge Rafael Velayarce1; 1Saarland University
    The size of typical fatigue dislocation structures is in the order of micrometers. Hence, reducing the sample-size down into this regime raises questions about developing microstructures and damage. Thus, the development of fatigue microstructures and the damage evolution will be studied by in-situ fatigue tests in the SEM on single and bi- crystalline micro-samples depending on specimen size, dislocation density and crystal orientation. Not only the microstructure and damage evolution is measured, but also local stresses and strains. This allows the correlation between microstructure and damage and the local loading of the sample. In the case of grain boundaries incompatibilities in local stresses and strains are of interest as these are correlated with the damage evolution at the grain boundary. The main advantage of using micron-sized specimen is the knowledge of the local stresses and strains, which allows to associate changes in the stress vs. strain response with microstructural events.

11:30 AM  
On the Optimization of a Biaxial Tensile Test Specimen Design: Dilip Banerjee1; Mark Iadicola1; Adam Creuziger1; 1NIST
    Biaxial testing is quite common in the metal forming industry for evaluating mechanical properties of sheet material. This is because traditional uniaxial test data are not easily applicable in the multi-directional forming process as sheet metal possesses highly anisotropic properties. One major challenge in biaxial testing is the determination of an optimum specimen design. Using an initial specimen design, a verified finite element analysis (FEA) model of an AISI 1008 alloy specimen was developed by carefully comparing predicted strain and displacement fields with measured data. Thereafter, an optimum shape of the specimen was developed by coupling this verified FEA model with an optimization software along with an appropriate selection of design variables and objective function. Biaxial tensile tests are conducted on the optimum specimen design and measured strain and displacement data in the gauge section are compared with FEA predicted results to validate the technical approach used.

11:50 AM  
Microstructure Characterisation of Drilled Chips of 316L Stainless Steel: Guocai Chai1; Raveendra Siriki1; Fritz Yah2; 1Sandvik Materials Technology; 2Sandvik Coromant
    The present study was aimed at understanding the deformation and damage behaviors of drilled chips of 316L stainless steel. The analyzed chips were noticed to be curled/spiraled containing several rotations. Further, the electron microscopy analysis showed that the cross-section of all the rotations contains segments and these are separated by adiabatic shear bands (ASBs)/primary shear bands (PSBs). The heights of peaks and valleys of the segments were observed to increase significantly from inner to outer rotations. This might be due to increase in tool wear. Furthermore, the SEM analysis revealed presence of significant numbers of cracks. The cracks were observed at the regions where ASBs were originated and also along the ASBs. The microstructures in these regions seem to significantly refined/deformed. The severe deformation might have decreased the ductility and further lead to cracking.