We present CasADi, an open-source software framework for numerical optimization. CasADi is a general-purpose tool that can be used to model and solve optimization problems with a large degree of ...flexibility, larger than what is associated with popular algebraic modeling languages such as AMPL, GAMS, JuMP or Pyomo. Of special interest are problems constrained by differential equations, i.e. optimal control problems. CasADi is written in self-contained C++, but is most conveniently used via full-featured interfaces to Python, MATLAB or Octave. Since its inception in late 2009, it has been used successfully for academic teaching as well as in applications from multiple fields, including process control, robotics and aerospace. This article gives an up-to-date and accessible introduction to the CasADi framework, which has undergone numerous design improvements over the last 7 years.
Directed energy deposition (DED) stands as an advancement in material utilization, facilitating the production of highly precise near-net shape components using wire and powders ...
•We present a non-conservative robust NMPC scheme for economic NMPC.•The proposed approach has better performance than other typical NMPC approaches.•We present an algorithm to reduce the variability ...of the system under uncertainty.•The results are illustrated for an industrial example provided by BASF SE.•The efficient implementation achieves real-time computation times.
In the last years, the use of an economic cost function for model predictive control (MPC) has been widely discussed in the literature. The main motivation for this choice is that often the real goal of control is to maximize the profit or the efficiency of a certain system, rather than tracking a predefined set-point as done in the typical MPC approaches, which can be even counter-productive. Since the economic optimal operation of a system resulting from the application of an economic model predictive control approach drives the system to the constraints, the explicit consideration of the uncertainties becomes crucial in order to avoid constraint violations. Although robust MPC has been studied during the past years, little attention has yet been devoted to this topic in the context of economic nonlinear model predictive control, especially when analyzing the performance of the different MPC approaches. In this work, we present the use of multi-stage scenario-based nonlinear model predictive control as a promising strategy to deal with uncertainties in the context of economic NMPC. We make a comparison based on simulations of the advantages of the proposed approach with an open-loop NMPC controller in which no feedback is introduced in the prediction and with an NMPC controller which optimizes over affine control policies. The approach is efficiently implemented using CasADi, which makes it possible to achieve real-time computations for an industrial batch polymerization reactor model provided by BASF SE. Finally, a novel algorithm inspired by tube-based MPC is proposed in order to achieve a trade-off between the variability of the controlled system and the economic performance under uncertainty. Simulations results show that a closed-loop approach for robust NMPC increases the performance and that enforcing low variability under uncertainty of the controlled system might result in a big performance loss.
•The recent advances in the additive manufacturing of maraging steels are reviewed.•Various defects are formed with the use of inappropriate processing parameters.•Different techniques contribute to ...forming different molten pool profiles.•Distinct precipitation behaviors are observed during different techniques.•Mechanical properties of the additive manufactured and wrought parts are compared.
This paper reviews the latest research progress in the additive manufacturing (AM) process of 18% nickel maraging steels, which involves laser-based powder bed fusion (L-PBF), laser-based directed energy deposition (L-DED), and wire arc additive manufacturing (WAAM). The emphasis is on the defects, structure, and mechanical properties of the additive manufactured 18% nickel maraging steels. At first, this article outlines the influences of the processing parameters of AM techniques on the defects formed in the fabricated parts, in terms of the L-PBF and WAAM. The macrostructure and microstructure characteristics of as-built and heat-treated 18% nickel maraging steel are then described in detail. Later, the mechanical properties of as-built and heat-treated 18% nickel maraging steel are assessed, such as their tensile, hardness, impact toughness, and fatigue performances. Finally, future directions for work on the AM of 18% nickel maraging steel are provided.
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Understanding the microstructural behaviour of materials during thermomechanical processing is a vital step towards optimizing the mechanical properties. One important aspect during forming ...processes, such as forging, is dynamic recrystallization (DRX), which sets the starting microstructure for the subsequent manufacturing steps. Here we investigated the DRX behaviour of Ni-base superalloy Haynes 282 during hot compression with a strain rate of 0.05 s−1 at 1080 °C, with care taken to minimize the effects of meta-dynamic recrystallization (mDRX) and adiabatic heating. Small DRX grains could be observed already at ε = 0.1, i.e. before the peak strain εp = 0.15. The DRX process accelerated significantly above ε = 0.2, and the material was fully recrystallized at ε = 1.5. Up to ε = 0.8 DRX occurred through continuous nucleation of new grains, whereas above ε = 0.8 the number density of DRX grains decreased and the increase in recrystallized fraction was due to growth of existing grains. Contrary to common assumptions of DRX nuclei being essentially dislocation free, many of the DRX grains contained pronounced dislocation substructures, even at small strains where they are not expected to have undergone deformation.
•Dynamic recrystallization in a Ni-base superalloy was investigated.•Recrystallized grains existed at strains below the maximum stress.•The microstructure is fully recrystallized at a strain of 1.5.•Kinetics derived from microstructure and stress response agree well.
An approximately 90 km long Palaeoproterozoic supracrustal
belt in the northwestern Norrbotten ore province (northernmost Sweden) was
investigated to characterize its structural components, assess ...hydrothermal
alteration–structural geology correlations, and constrain a paired
deformation–fluid flow evolution for the belt. New geological mapping of
five key areas (Eustiljåkk, Ekströmsberg, Tjårrojåkka,
Kaitum West, and Fjällåsen–Allavaara) indicates two major
compressional events (D1 and D2) have affected the belt, with each
associated with hydrothermal alteration types typical for iron oxide–apatite
and iron oxide Cu–Au systems in the region. Early D1 generated a
regionally distributed, penetrative S1 foliation and oblique reverse
shear zones that show a southwest-block-up sense of shear that formed in
response to NE–SW crustal shortening. Peak regional metamorphism at
epidote–amphibolite facies broadly overlaps with this D1 event. Based
on overprinting relationships, D1 is associated with regional scapolite ± albite, magnetite + amphibole, and late calcite alteration of
mafic rock types. These hydrothermal mineral associations linked to D1
structures may form part of a regionally pervasive evolving fluid flow event
but are separated in this study by crosscutting relationships. During D2 deformation, folding of S0–S1 structures
generated F2 folds with steeply plunging fold axes in low-strain areas.
NNW-trending D1 shear zones experienced reverse dip-slip reactivation
and strike-slip-dominated movements along steep, E–W-trending D2 shear
zones, producing brittle-plastic structures. Hydrothermal alteration linked
to D2 structures is a predominantly potassic–ferroan association
comprising K-feldspar ± epidote ± quartz ± biotite ± magnetite ± sericite ± sulfides. Locally, syn- or post-tectonic
calcite is the main alteration mineral in D2 shear zones that intersect
mafic rocks. Our results highlight the importance of combining structural
geology with the study of hydrothermal alterations at regional to
belt scales to understand the temporal–spatial relationship between
mineralized systems. Based on the mapping results and microstructural
investigations as well as a review of earlier tectonic models presented for
adjacent areas, we suggest a new structural model for this part of the
northern Fennoscandian Shield. The new model emphasizes the importance of
reactivation of early structures, and the model harmonizes with tectonic
models presented by earlier workers based mainly on petrology of the
northern Norrbotten area.
Stationary shoulder friction stir processing (SSFSP) in thick AZ31B magnesium alloy was performed to refine the microstructure followed by evaluating corrosion behavior. The use of stationary ...shoulder exhibited low heat input and small temperature gradient across the thickness of stir zone (SZ). Moreover, smooth surface morphology with little flash was obtained. The probe-dominated SZ developed fine equiaxed uniform grain structure across the thickness of SZ, which in turn increased the corrosion resistance of SSFSPed alloy as compared to BM. SSFSPed alloy surface confirm uniform corrosion behavior with mud cracking and intergranual corrosion patterns instead of pitting corrosion in BM. This improvement in corrosion was attributed to homogenization of magnesium alloy microstructure by using low-heat-input stationary shoulder tool.
Hot cracking in cast alloy 718 Singh, Sukhdeep; Andersson, Joel
Science and technology of welding and joining,
10/2018, Letnik:
23, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Hot cracking susceptibility of the Fe-Ni-based precipitation hardening cast superalloy Alloy 718 was studied by Varestraint weldability testing. The effect of two hot isostatic pressing (HIP) ...treatments commonly employed in the aerospace industry was investigated in reference to the as cast condition. It was found that the heat affected zone (HAZ) liquation cracking susceptibility increased for samples with pre-weld HIP treatments. The as cast condition disclosed the best response for liquation cracking followed by HIP-1120 (1120°C/4h (HIP) + 1050°C/1h and furnace cooling to 650°C/1h in vacuum + 950°C/1h) and HIP-1190 (1190°C/4h (HIP) + 870°C/10h and furnace cooling to 650°C/1h in vacuum + 950°C/1h). The amount of the secondary precipitates and base metal grain size was found to be important parameters influencing the cracking susceptibility. Regarding solidification cracking susceptibility, the three conditions appear to behave similarly.