Unintended Consequences: How Qualification Constrains Innovation

The development and implementation of new materials and manufacturing processes for aerospace application is often hindered by the high cost and long time span associated with current qualification procedures. The data requirements necessary for material and process qualification are extensive and often require millions of dollars and multiple years to complete. Furthermore, these qualification data can become obsolete for even minor changes to the processing route. This burden is a serious impediment to the pursuit of revolutionary new materials and more affordable processing methods for air vehicle structures. The application of integrated computational materials engineering methods to this problem can help to reduce the barriers to rapid insertion of new materials and processes. By establishing predictive capability for the development of microstructural features in relation to processing and relating this to critical property characteristics, a streamlined approach to qualification is possible. This paper critically examines the advantages and challenges to a modeling-assisted qualification approach for aerospace structural materials. An example of how this approach might apply towards the emerging field of additive manufacturing is discussed in detail

Bi-Metallic Composite Structures With Designed Internal Residual Stress Field

Shape memory alloys (SMA) have a unique ability to recover small amounts of plastic strain through a temperature induced phase change. For these materials, mechanical displacement can be accomplished by heating the structure to induce a phase change, through which some of the plastic strain previously introduced to the structure can be reversed. This paper introduces a concept whereby an SMA phase is incorporated into a conventional alloy matrix in a co-continuous reticulated arrangement forming a bi-metallic composite structure. Through memory activation of the mechanically constrained SMA phase, a controlled residual stress field is developed in the interior of the structure. The presented experimental data show that the memory activation of the SMA composite component significantly changes the residual stress distribution in the overall structure. Designing the structural arrangement of the two phases to produce a controlled residual stress field could be used to create structures that have much improved durability and damage tolerance properties

Functionally Graded Metal-Metal Composite Structures

Methods and devices are disclosed for creating a multiple alloy composite structure by forming a three-dimensional arrangement of a first alloy composition in which the three-dimensional arrangement has a substantially open and continuous porosity. The three-dimensional arrangement of the first alloy composition is infused with at least a second alloy composition, where the second alloy composition comprises a shape memory alloy. The three-dimensional arrangement is consolidated into a fully dense solid structure, and the original shape of the second alloy composition is set for reversible transformation. Strain is applied to the fully dense solid structure, which is treated with heat so that the shape memory alloy composition becomes memory activated to recover the original shape. An interwoven composite of the first alloy composition and the memory-activated second alloy composition is thereby formed in the multiple alloy composite structure

Glare, a GIS tool to reconstruct the 3D surface of palaeoglaciers

Acknowledgements This research has been supported by the Leverhulme Trust International Network Grant IN-2012-140. Processing and collecting of ground penetrating data in Forgefonna was part of Elend Førre's master's project that was completed in 2009 at the Department of Geography, University of Bergen. We also acknowledge Dr Andreas Bauder for providing the subglacial topography data for Griessgletscher and Simone Tarquini for granting access to the high resolution TIN of Italy, a cut of which is provided to the reader to practice the tools (see Appendix). Referees Dr. Iestyn Barr, Dr. Jeremy Ely and Dr. Marc Oliva are thanked for their constructive comments and tool testing, which significantly improved the final output.Peer reviewedPostprin

Neutron Characterization for Additive Manufacturing

Oak Ridge National Laboratory (ORNL) is leveraging decades of experience in neutron characterization of advanced materials together with resources such as the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR) shown in Fig. 1 to solve challenging problems in additive manufacturing (AM). Additive manufacturing, or three-dimensional (3-D) printing, is a rapidly maturing technology wherein components are built by selectively adding feedstock material at locations specified by a computer model. The majority of these technologies use thermally driven phase change mechanisms to convert the feedstock into functioning material. As the molten material cools and solidifies, the component is subjected to significant thermal gradients, generating significant internal stresses throughout the part (Fig. 2). As layers are added, inherent residual stresses cause warping and distortions that lead to geometrical differences between the final part and the original computer generated design. This effect also limits geometries that can be fabricated using AM, such as thin-walled, high-aspect- ratio, and overhanging structures. Distortion may be minimized by intelligent toolpath planning or strategic placement of support structures, but these approaches are not well understood and often "Edisonian" in nature. Residual stresses can also impact component performance during operation. For example, in a thermally cycled environment such as a high-pressure turbine engine, residual stresses can cause components to distort unpredictably. Different thermal treatments on as-fabricated AM components have been used to minimize residual stress, but components still retain a nonhomogeneous stress state and/or demonstrate a relaxation-derived geometric distortion. Industry, federal laboratory, and university collaboration is needed to address these challenges and enable the U.S. to compete in the global market. Work is currently being conducted on AM technologies at the ORNL Manufacturing Demonstration Facility (MDF) sponsored by the DOE's Advanced Manufacturing Office. The MDF is focusing on R&D of both metal and polymer AM pertaining to in-situ process monitoring and closed-loop controls; implementation of advanced materials in AM technologies; and demonstration, characterization, and optimization of next-generation technologies. ORNL is working directly with industry partners to leverage world-leading facilities in fields such as high performance computing, advanced materials characterization, and neutron sciences to solve fundamental challenges in advanced manufacturing. Specifically, MDF is leveraging two of the world's most advanced neutron facilities, the HFIR and SNS, to characterize additive manufactured components

Electron Beam Freeform Fabrication of Titanium Alloy Gradient Structures

Historically, the structural optimization of aerospace components has been done through geometric methods. A monolithic material is chosen based on the best compromise between the competing design limiting criteria. Then the structure is geometrically optimized to give the best overall performance using the single material chosen. Functionally graded materials offer the potential to further improve structural efficiency by allowing the material composition and/or microstructural features to spatially vary within a single structure. Thus, local properties could be tailored to the local design limiting criteria. Additive manufacturing techniques enable the fabrication of such graded materials and structures. This paper presents the results of a graded material study using two titanium alloys processed using electron beam freeform fabrication, an additive manufacturing process. The results show that the two alloys uniformly mix at various ratios and the resultant static tensile properties of the mixed alloys behave according to rule-of-mixtures. Additionally, the crack growth behavior across an abrupt change from one alloy to the other shows no discontinuity and the crack smoothly transitions from one crack growth regime into another

Subcellular Epithelial HMGB1 Expression Is Associated with Colorectal Neoplastic Progression, Male Sex, Mismatch Repair Protein Expression, Lymph Node Positivity, and an 'Immune Cold' Phenotype Associated with Poor Survival.

New treatment targets are needed for colorectal cancer (CRC). We define expression of High Mobility Group Box 1 (HMGB1) protein throughout colorectal neoplastic progression and examine the biological consequences of aberrant expression. HMGB1 is a ubiquitously expressed nuclear protein that shuttles to the cytoplasm under cellular stress. HMGB1 impacts cellular responses, acting as a cytokine when secreted. A total of 846 human tissue samples were retrieved; 6242 immunohistochemically stained sections were reviewed. Subcellular epithelial HMGB1 expression was assessed in a CRC Tissue Microarray (n = 650), normal colonic epithelium (n = 75), adenomatous polyps (n = 52), and CRC polyps (CaP, n = 69). Stromal lymphocyte phenotype was assessed in the CRC microarray and a subgroup of CaP. Normal colonic epithelium has strong nuclear and absent cytoplasmic HMGB1. With progression to CRC, there is an emergence of strong cytoplasmic HMGB1 (p < 0.001), pronounced at the leading cancer edge within CaP (p < 0.001), and reduction in nuclear HMGB1 (p < 0.001). In CRC, absent nuclear HMGB1 is associated with mismatch repair proteins (p = 0.001). Stronger cytoplasmic HMGB1 is associated with lymph node positivity (p < 0.001) and male sex (p = 0.009). Stronger nuclear (p = 0.011) and cytoplasmic (p = 0.002) HMGB1 is associated with greater CD4+ T-cell density, stronger nuclear HMGB1 is associated with greater FOXP3+ (p < 0.001) and ICOS+ (p = 0.018) lymphocyte density, and stronger nuclear HMGB1 is associated with reduced CD8+ T-cell density (p = 0.022). HMGB1 does not directly impact survival but is associated with an 'immune cold' tumour microenvironment which is associated with poor survival (p < 0.001). HMGB1 may represent a new treatment target for CRC

Characterization of Titanium Alloys Produced by Electron Beam Directed Energy Deposition

Functionally graded materials offer the potential to improve structural efficiency by allowing the material composition and/or microstructural features to spatially vary within a component. Additive manufacturing techniques enable the fabrication of such graded materials and structures. While examining several titanium alloys, this paper focuses on Ti-8Al-1Er as it has a unique microstructure that is only feasible when produced by rapid solidification methods like electron beam directed energy deposition, an additive manufacturing process. The results show that, when mixed, Ti-8Al-1Er and commercially-pure titanium uniformly mix at various ratios and the resultant static tensile properties of the mixed alloys behave according to rule-of-mixtures. At discontinuous interfaces between Ti-8Al-1Er and commercially-pure titanium, the crack growth behavior progresses smoothly across the discontinuity as the crack transitions from one crack growth regime into another. Studies on monolithic samples shows the mechanisms of damage in the Ti-8Al-1Er; specifically, that strain localization occurs near grain boundaries of high mis-orientation on the microscale and that twinning and dislocation density is concentrated near erbia-strengthening particles (Er2O3) on the nanoscale