Spatially Programmable Architected Materials Inspired by the Metallurgical Phase Engineering

Programmable architected materials with the capabilities of precisely storing predefined mechanical behaviors and adaptive deformation responses upon external stimulations are desirable to help increase the performance and the organic integration of materials with surrounding environments. Here, a new approach inspired by the physical metallurgical principles is proposed to allow the materials designers to not only enhance the global strength but also precisely tune mechanical properties (such as strength, modulus, and plastic deformation) locally in architected materials to create a new class of intelligent mechanical metamaterials. Such programmable materials not only have high strength and plastic deformation stability but also the ability to regulate the local deformation states and spatially control the internal propagation of deformation. This innovative approach also provides new and effective ways to enhance the adaptivity of the materials thanks to responsive strengths that not only make the materials increasingly stronger but also allow threshold-based adaptive responses to external loading.

The role of side-branching in microstructure development in laser powder-bed fusion

In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67° rotation between layers.

Forming limit prediction using a self-consistent crystal plasticity framework: a case study for body-centered cubic materials

A rate-dependent self-consistent crystal plasticity model was incorporated with the Marciniak-Kuczyński model in order to study the effects of anisotropy on the forming limits of BCC materials. The computational speed of the model was improved by a factor of 24 when running the simulations for several strain paths in parallel. This speed-up enabled a comprehensive investigation of the forming limits of various BCC textures, such as γ, σ, α, η and ϵ fibers and a uniform (random) texture. These simulations demonstrate that the crystallographic texture has significant (both positive and negative) effects on the resulting forming limit diagrams. For example, the γ fiber texture, which is often sought through thermo-mechanical processing due to a high r-value, had the highest forming limit in the balanced biaxial strain path but the lowest forming limit under the plane strain path among the textures under consideration. A systematic investigation based on the results produced by the current model, referred to as 'VPSC-FLD', suggests that the r-value does not serve as a good measure of forming limit strain. However, model predictions show a degree of correlation between the r-value and the forming limit stress.

Thermally-activated constitutive model including dislocation interactions, aging and recovery for strain path dependence of solid solution strengthened alloys: Application to AA5754-O

A thermally-activated constitutive model is developed based on dislocation interactions, crystallographic orientations and microstructural evolution to describe the elasto-plastic stress-strain behavior during multi-axial loading. The aim is to contribute to the quantification of complex strain path response in solid solution strengthened alloys. In detail, dislocation/dislocation interactions are incorporated in the model to quantify latent and kinematic hardening phenomena during loading path changes. Dislocation density-based constitutive relations are included to account for dislocation features such as dislocation forests, walls and channels. Moreover specifically, dislocation/solute atom interactions are also considered in order to account for both dynamic and static strain aging as well as static recovery. The model is validated against multiple multi-axial data sets for AA5754-O with changes of loading path and various degrees of pre-strain and time intervals between tests.

Pattern recognition of the pulmonary manifestations of AIDS on CT scans

More than 50% of patients with acquired immunodeficiency syndrome (AIDS) develop pulmonary disease during the course of their illness. The authors reviewed 96 computed tomographic (CT) scans of patients with AIDS in an attempt to describe disease entities by the patterns seen on the scans. Such patterns included isolated ground-glass and interstitial infiltrates, which are suggestive of Pneumocystis carinii pneumonia (PCP). If pleural effusions or parenchymal nodules are also present, AIDS-related lymphoma (ARL) or Kaposi sarcoma (KS) is more likely. Although diffuse alveolar infiltrates are most commonly present in PCP, a segmental alveolar infiltrate is suggestive of a bacterial pneumonia, especially when associated with cavitation or ipsilateral pleural effusion. Well-defined nodules are typical for ARL, whereas ill-defined nodules are more commonly suggestive of KS. Accompanying adenopathy or effusion with nodules further suggests ARL. Different combinations of parenchymal, nodular, and pleural abnormalities may be suggestive for additional diagnoses, including Mycobacterium tuberculosis, M avium-intracellulare, and Cryptococcus neoformans infections and human immunodeficiency virus adenopathy. The authors believe that a specific pattern of involvement can help suggest a likely diagnosis in many instances.