A review on measurement science needs for real-time control of additive manufacturing metal powder bed fusion processes

Additive manufacturing technologies are increasingly used in the development of new products. However, variations in part quality in terms of material properties, dimensional tolerances, surface roughness and defects limit its broader acceptance. Process control today based on heuristics and experimental data yields limited improvement in part quality. In an effort to identify the needed measurement science for real-time closed-loop control of additive manufacturing (AM) processes, this paper presents a literature review on the current AM control schemes, process measurements and modelling and simulation methods as it applies to the powder bed fusion process, though results from other processes are reviewed where applicable. We present our research findings to identify the correlations between process parameters, process signatures and product quality. We also present research recommendations on the key control issues to serve as a technical basis for standards development in this area. Complimentary details to this paper with summary tables, range of values, preliminary correlations and correlation figures can be accessed from a National Institute of Standards and Technology Report (http://nvlpubs.nist.gov/nistpubs/ir/2015/NIST.IR.8036.pdf). This paper is developed based on the report.     

Analysis of the Finite Element Method for the Laplace–Beltrami Equation on Surfaces with Regions of High Curvature Using Graded Meshes

We derive error estimates for the piecewise linear finite element approximation of the Laplace–Beltrami operator on a bounded, orientable, \(C^3\), surface without boundary on general shape regular meshes. As an application, we consider a problem where the domain is split into two regions: one which has relatively high curvature and one that has low curvature. Using a graded mesh we prove error estimates that do not depend on the curvature on the high curvature region. Numerical experiments are provided.     

Three-Dimensional Magnesia-Based Nanocrystal Assemblies Via Low-Temperature Magnesiothermic Reaction of Diatom Microshells

A low-temperature (≤700°C) magnesiothermic reaction has been used for the first time to convert three-dimensional (3-D) silica-based diatom microshells into nanocrystalline magnesia-based replicas. Exposure of diatom microshells to Mg( g ) at only 650°–700°C resulted in the initial (direct) formation of MgO and Si nanocrystals (≤5 nm), that is, no intermediate magnesium silicate compounds were detected. Further reaction of Si with Mg( g ) led to the formation of Mg₂Si, and then a Mg–Si liquid that sweated away to yield free-standing, nanocrystalline MgO-based replicas. Such direct low-temperature magnesiothermic conversion of diatom microshells enables the synthesis of large numbers of 3-D nanocrystal assemblies with well-controlled morphologies for catalytic/chemical, biological, optical, and other applications.     

Modification of maillard browning in a microwaved glucose/glycine model system by water-soluble natural antioxidants and foods containing them

Inhibition of pyrazine formation by natural antioxidants and the foods containing them was measured in a microwaved glucose/glycine model system. Inhibition of lipid oxidation by the same materials was assayed in both bulk and emulsion systems. Pyrazines were determined by solid-phase micro extraction followed by GC. Lipid oxidation volatiles were assayed by polyamide fluorescence produced by either a bulk oil display or a hematin- or 2,2′-azobis-(2-amidino=propane) dihydrochloride-accelerated lecithin or fish oil emulsion. It was shown that (i) the inhibition of pyrazine formation depends on high concentrations of water-soluble antioxidants; (ii) such antioxidants occur naturally in some foods and are usually polyphenols; (iii) during pyrazine inhibition, oxidized polyphenols show enhanced nonfluorescing browning similar to enzymic browning products; (iv) monophenols, which structurally cannot form quinone polymers on oxidation, inhibit pyrazines with less browning; (v) during the final pyrazine-forming phase of the Maillard reaction, polyphenolics and reducing agents such as glutathione and ascorbic acid are partially consumed with some nutritional loss; (vi) fruit powders of grape seed, grape skin, and red wine are highly pyrazine-inhibitory, steeped blueberry strongly so, but plum purees are moderately pro-pyrazine, and freeze-dried vegetables strongly pro-pyrazine; and (vii) black and green tea infusions are highly inhibitory, whereas spices have mixed effects.     

Toughening of polylactide by melt blending with linear low‐density polyethylene

Melt blending of polylactide and linear low‐density polyethylene (LLDPE) was performed in an effort to toughen polylactide. In addition, two model polylactide‐polyethylene (PLLA‐PE) block copolymers were investigated as compatibilizers. The LLDPE particle size and the impact resistance of binary and ternary blends were measured to determine the extent of compatibilization. For the amorphous polylactide (PLA), toughening was achieved only when a PLLA‐PE block copolymer was used as a compatibilizer. For the semicrystalline polylactide (PLLA), toughening was achieved in the absence of block copolymer. To decrease the variability in the impact resistance of the PLLA/LLDPE binary blend, as little as 0.5 wt % of a PLLA–;PE block copolymer was effective. The differences that were seen between the PLA and PLLA binary blends were investigated with adhesion testing. The semicrystalline PLLA did show significantly better adhesion to the LLDPE. We propose that tacticty effects on the entanglement molecular weight or miscibility of polylactide allow for the improved adhesion between the PLLA and LLDPE. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3757–3768, 2003     

Cultural, sociofamilial, and psychological resources that inhibit psychological distress in African Americans exposed to stressful life events and race-related stress.

This study tested a sociocultural model of stress and coping in a sample of 215 African Americans. Psychological resources (optimism, ego resilience) were modeled as a "nested self" (S. E. Hobfoll, 2001), supported by social resources (family adaptability and cohesion) and cultural resources (racial pride, religiosity). Race-related stress was a significantly more powerful risk factor than stressful life events for psychological distress. Structural equation modeling results confirmed the hypotheses that psychological resources had a significant direct effect in minimizing psychological distress, and social resources had a significant stress-suppressing effect on race-related stress. Theoretical and practical implications for counseling psychologists are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Concern about weight gain associated with quitting smoking: Prevalence and association with outcome in a sample of young female smokers.

This study investigated the relationship between weight gain concern and outcomes of a large-scale smoking cessation study among 506 young female smokers attending Planned Parenthood clinics. Results of this prospective study did not support the clinical importance of weight gain concerns. Using an index of weight concern that was predictive in previous research, baseline weight concern was unrelated to smoking cessation efforts, whether participants made a quit attempt, reduced the number of cigarettes they smoked, or reported a change in self-efficacy for stopping smoking. Both the overall level of concern expressed in this sample of predominantly White young women and the lack of relationship between weight gain concern and smoking cessation outcomes suggest that weight gain concern may not be a critical factor for cessation programs targeting similar female smokers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of alcohol on vagal regulation of cardiovascular function: Contributions of the polyvagal theory to the psychophysiology of alcohol.

Research was conducted to evaluate the influence of acute alcohol consumption on vagal regulation of heart rate. Nine men with histories of polydrug use participated in this residential study. On 5 separate days, they drank liquids consisting of cold water (on 2 days), a moderate dose of alcohol (0.64 g/kg), a high dose of alcohol (1.12 g/kg), and a placebo. Continuous recordings of heart period were quantified to produce 3 measures of heart rate variability, reflecting the amplitude of 3 neurophysiologically mediated rhythms. Heart period, respiratory rhythm (i.e., respiratory sinus arrhythmia [RSA]), and the 0.06–0.10-Hz vasomotor rhythm were significantly lower during the high alcohol dose condition, relative to the placebo and water conditions. Because the neural regulation of the heart by the vagus contributes to these variables, these findings suggest that alcohol reduces cardiac vagal tone. In support of this explanation, alcohol also decreased the coupling between changes in heart period and changes in RSA. This study demonstrated that alcohol produces a dysregulated state in which heart rate is relatively uncoupled from vagal activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rigid‐Rod Polymers: Synthesis,Processing, Simulation,Structure, and Properties

Synthesis, structure, and properties of rigid‐rod polymers with special emphasis on poly(p‐phenylene benzobisoxazole) (PBO) and poly(p‐phenylene benzobisthiazole) (PBZT) have been reviewed. Recent studies on chemical modifications and molecular simulations have also been given. After nearly 20 years of research and development, PBO fiber was commercialized in the late 1990s. However, due to processing difficulties, the concept of the so called molecular composites has not been successful. Development of the high compressive strength M5 and dihydroxy‐PBI fibers clearly suggest that there is potential for further developing properties of this class of materials. Opto‐electronic properties have also been reviewed.

Synthesis of PBZT.