Joel V. Bernier

Experimental measurement of lattice strain pole figures using synchrotron x rays

This article describes a system for mechanically loading test specimens in situ for the determination of lattice strain pole figures and their evolution in multiphase alloys via powder diffraction. The data from these experiments provide insight into the three-dimensional mechanical response of a polycrystalline aggregate and represent an extremely powerful material model validation tool. Relatively thin (0.5mm) iron/copper specimens were axially strained using a mechanical loading frame beyond the macroscopic yield strength of the material. The loading was halted at multiple points during the deformation to conduct a diffraction experiment using a 0.5×0.5mm2 monochromatic (50keV) x ray beam. Entire Debye rings of data were collected for multiple lattice planes ({hkl}’s) in both copper and iron using an online image plate detector. Strain pole figures were constructed by rotating the loading frame about the specimen transverse direction. Ideal powder patterns were superimposed on each image for the purpos...

A rotational and axial motion system load frame insert for in situ high energy x-ray studies

High energy x-ray characterization methods hold great potential for gaining insight into the behavior of materials and providing comparison datasets for the validation and development of mesoscale modeling tools. A suite of techniques have been developed by the x-ray community for characterizing the 3D structure and micromechanical state of polycrystalline materials; however, combining these techniques with in situ mechanical testing under well characterized and controlled boundary conditions has been challenging due to experimental design requirements, which demand new high-precision hardware as well as access to high-energy x-ray beamlines. We describe the design and performance of a load frame insert with a rotational and axial motion system that has been developed to meet these requirements. An example dataset from a deforming titanium alloy demonstrates the new capability.

Quantitative Stress Analysis of Recrystallized OFHC Cu Subject to Deformation In Situ

Quantitative strain analysis (QSA) provides a means for assessing the orientation-dependent micromechanical stress states in bulk polycrystalline materials. When combined with quantitative texture analysis, it facilitates tracking the evolution of micromechanical states associated with selected texture components for specimens deformed in situ. To demonstrate this ability, a sheet specimen of rolled and recrystallized oxygen-free high conductivity Cu was subject to tensile deformation at APS 1-ID-C. Strain pole figures (SPFs) were measured at a series of applied loads, both below and above the onset of macroscopic yielding. From these data, a lattice strain distribution function (LSDF) was calculated for each applied load. Due to the tensorial nature of the LSDF, the full orientation-dependent stress tensor fields can be calculated unambiguously from the single-crystal elastic moduli. The orientation distribution function (ODF) is used to calculate volume-weighted average stress states over tubular volumes centered on the ∥[100], ∥[100], and ∥[100] fibers-accounting for ≈50% of the total volume-are shown as functions of the applied load along [100]. Corresponding weighted standard deviations are calculated as well. Different multiaxial stress states are observed to develop in the crystal subpopulations despite the uniaxial nature of the applied stress. The evolution of the orientation-dependent elastic strain energy density is also examined. The effects of applying stress bound constraints on the SPF inversion are discussed, as are extensions of QSA to examine defect nucleation and propagation.

Changing the Paradigm for Engineering Design by Merging High Energy X-ray Data with Materials Modeling

The nature of the application of structural materials demands that their performance be relLDEOH��,W∂ s well known that the behavior of such materials is a product of the microstructure, and that failure initiation sites can often be linked to local microstructural features. Yet modern design and sustainment methodologies for structural materials remain reliant upon continuum-level models and large-scale conventional mechanical testing efforts. This is extremely costly, both in the sense that conventional mechanical test databases are expensive to produce, and also that continuum-level design inherently requires unnecessary conservatism in component lifing schemes as local microstructural effects are ignored. Moving forward, the development and validation of a microstructure-sensitive modeling framework that can accurately predict materials behavior (including variability and uncertainty) would allow the maximization of component capability and life, while reducing cost/time to certify and improve safety. Such a model would also open new possibilities for design of components with graded microstructures, where the microstructure at a specific point in a component is tailored to provide optimized properties for that location. Toward this goal, we have endeavored to combine in-situ mechanical testing with advanced characterization methods, including microstructural characterization of the 3D test volume, in order to provide data which can be input and compared to deformation simulations which explicitly represent the 3D microstructure [1,2]. Such information is critical for the validation and further development of microstructure-sensitive modeling tools. In the present work, we describe in-situ tensile tests on polycrystalline metals during integration of three high energy synchrotron x-ray techniques. These techniques include near field orientation microscopy to map the 3D microstructure [3], absorption micro computed tomography to map the presence of voids and/or cracks [4], and far field lattice strain measurements to monitor the internal stress state of individual grains [5]. These experiments have been conducted at Sector 1 of the Advanced Photon Source at Argonne National Lab. An image of the experimental setup is shown in Figure 1.

A Methodology for the Accelerated Evaluation of Design Properties

A system for rapidly determining the strength and stiffness of polyphase alloys is presented that is based on a digital representation of the material structure. Working in concert with the representation are a number of digital tools and probes that are analogues of testing equipment and instrumentation of traditional laboratory methods. The strategy to achieve a more rapid determination of mechanical properties utilizes a system that integrates laboratory testing and computer modeling. Several ideas are embedded in the design of this system. First, it is presumed that neither testing nor modeling by itself will be sufficient to fully accomplish the task. Rather, both will be used, with the determination made task-by-task on the basis of which is the more effective tool for a particular task. Second, the system is designed so that the simulation tools will mimic in many ways the conventional testing methods. To this end, a number of numerical analogues will exist that correspond to components of a physical testing system. Finally, experiments that actively probe the mechanical response of the material on multiple size scales will be prescribed to validate the simulation tools.Copyright