•Presents a survey of manufacturing oriented topology optimization methods.•Investigates the length scale control and geometric feature based design for machining oriented topology ...optimization.•Investigates the part ejection and rib thickness control for injection molding/casting oriented topology optimization.•Proposes the future research direction for additive manufacturing oriented topology optimization.
Topology optimization is developing rapidly in all kinds of directions; and increasingly more extensions are oriented towards manufacturability of the optimized designs. Therefore, this survey of manufacturing oriented topology optimization methods is intended to provide useful insight classification and expert comments for the community.
First, the traditional manufacturing methods of machining and injection molding/casting are reviewed, because the majority of engineering parts are manufactured through these methods and complex design requirements are associated. Next, the challenges and opportunities related to the emerging additive manufacturing (AM) are highlighted. SIMP (Solid Isotropic Material with Penalization) and level set are the concerned topology optimization methods because the majority of manufacturing oriented extensions have been made based on these two methods.
This paper presents a novel level set-based topology optimization implementation, which addresses two main problems of design-for-additive manufacturing (AM): the material anisotropy and the ...self-support manufacturability constraint. AM material anisotropy is widely recognized and taking it into account while performing structural topology optimization could more realistically evaluate the structural performance. Therefore, both build direction and in-plane raster directions are considered by the topology optimization algorithm, especially for the latter, which is calculated through deposition path planning. The self-support manufacturability constraint is addressed through a novel multi-level set modeling. The related optimization problem formulation and solution process are demonstrated in detail. It is proved by several numerical examples that the manufacturability constraints are always strictly satisfied. Marginally, the recently popular structural skeleton-based deposition paths are also employed to assist the structural topology optimization, and its characteristics are discussed.
•This paper presents a deposition path planning-integrated structural topology optimization method for 3D additive manufacturing.•Local material anisotropy is addressed by considering the build direction and the in-plane raster directions.•The support-free manufacturability constraint is addressed through a novel multi-level set modeling.•Both the contour-offset and structural skeleton-based deposition path patterns have been considered.
A quaternary carbon center containing an oxindole motif is constructed via NHC-catalyzed transition-metal and aldehyde-free intermolecular Heck-type alkyl radical addition initiated annulation. This ...redox-neutral protocol also features a simple procedure, broad substrate scope, good functional group tolerance and could be smoothly amplified to a gram scale. The mechanism study shows that the reaction possibly undergoes two folds of SET processes with an NHC radical cation intermediate involved.
Purpose
Structural performance of additively manufactured parts is deposition path-dependent because of the induced material anisotropy. Hence, this paper aims to contribute a novel idea of ...concurrently performing the deposition path planning and the structural topology optimization for additively manufactured parts.
Design/methodology/approach
The concurrent process is performed under a unified level set framework that: the deposition paths are calculated by extracting the iso-value level set contours, and the induced anisotropic material properties are accounted for by the level set topology optimization algorithm. In addition, the fixed-geometry deposition path optimization problem is studied. It is challenging because updating the zero-value level set contour cannot effectively achieve the global orientation control. To fix this problem, a level set-based multi-step method is proposed, and it is proved to be effective.
Findings
The proposed concurrent design method has been successfully applied to designing additively manufactured parts. The majority of the planned deposition paths well match the principle stress direction, which, to the largest extent, enhances the structural performance. For the fixed geometry problems, fast and smooth convergences have been observed.
Originality/value
The concurrent deposition path planning and structural topology optimization method is, for the first time, developed and effectively implemented. The fixed-geometry deposition path optimization problem is solved through a novel level set-based multi-step method.
Novel CdS quantum dot (QD)-coupled graphitic carbon nitride (g-C3N4) photocatalysts were synthesized via a chemical impregnation method and characterized by X-ray diffraction, transmission electron ...microscopy, ultraviolet–visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The effect of CdS content on the rate of visible light photocatalytic hydrogen evolution was investigated for different CdS loadings using platinum as a cocatalyst in methanol aqueous solutions. The synergistic effect of g-C3N4 and CdS QDs leads to efficient separation of the photogenerated charge carriers and, consequently, enhances the visible light photocatalytic H2 production activity of the materials. The optimal CdS QD content is determined to be 30 wt %, and the corresponding H2 evolution rate was 17.27 μmol·h–1 under visible light irradiation, ∼9 times that of pure g-C3N4. A possible photocatalytic mechanism of the CdS/g-C3N4 composite is proposed and corroborated by photoluminescence spectroscopy and photoelectrochemical curves.
Manufacturing-oriented topology optimization has been extensively studied the past two decades, in particular for the conventional manufacturing methods, for example, machining and injection molding ...or casting. Both design and manufacturing engineers have benefited from these efforts because of the close-to-optimal and friendly-to-manufacture design solutions. Recently, additive manufacturing (AM) has received significant attention from both academia and industry. AM is characterized by producing geometrically complex components layer-by-layer, and greatly reduces the geometric complexity restrictions imposed on topology optimization by conventional manufacturing. In other words, AM can make near-full use of the freeform structural evolution of topology optimization. Even so, new rules and restrictions emerge due to the diverse and intricate AM processes, which should be carefully addressed when developing the AM-specific topology optimization algorithms. Therefore, the motivation of this perspective paper is to summarize the state-of-art topology optimization methods for a variety of AM topics. At the same time, this paper also expresses the authors’ perspectives on the challenges and opportunities in these topics. The hope is to inspire both researchers and engineers to meet these challenges with innovative solutions.
pH-responsive polymer poly(4-vinyl pyridine) is coated on mesoporous silica through the facile “grafting to” method. The grafted polymer nanoshell can work as a pH-sensitive barrier to control the ...release of trapped molecules from mesoporous silica.
Thermal residual stress and distortion inherent in metal melting and solidification process is the main cause of build failure in metal additive manufacturing (AM) techniques such as laser powder bed ...fusion and directed energy deposition. To ensure build quality against residual stress/distortion, it is desirable to tailor the scanning path for a given geometry that needs to be built. Since the local deformation introduced by the moving heat source is anisotropic due to non-uniform heat transfer and mechanical constraints, the scanning path can affect residual stress within a part significantly. Aiming at thermal residual stress/distortion mitigation, this paper presents a novel level set-based scanning path optimization method. The method is developed to enable layer-wise continuous scanning path optimization for geometrically well-defined parts. To make the optimization efficient, a fast process simulation method called the inherent strain method is employed to simulate the thermal residual strain. Full sensitivity analysis for the formulated compliance- and stress-minimization problems is provided, where a novel strategy called the adaptive level set adjustment (ALSA) is proposed to remedy the deficiency of ignoring the non-implementable sensitivity terms. The effectiveness of the proposed continuous scanning path optimization method and ALSA strategy has been proved by a few numerical examples. Finally, the concurrent design scenario for simultaneous scanning path and structural optimization is investigated to demonstrate the further residual stress reduction.
Tungsten trioxide (WO
3
) has been conceived as a promising photoanode material for photoelectrochemical (PEC) water oxidation. Therefore, many efforts have been made to improve its PEC performances. ...Herein, a novel heterojunction is fabricated through combining rocksalt CoO (R-CoO) or blende CoO (B-CoO) nanosheets with WO
3
nanoplates using a spin-coating method. The typical type II heterojunctions, e.g., WO
3
/R-CoO and WO
3
/B-CoO, both have exhibited higher photocurrent densities than pristine WO
3
photoanode. The photocurrent densities of WO
3
/R-CoO, WO
3
/B-CoO and WO
3
are 0.53 mA cm
−2
, 0.45 mA cm
−2
and 0.31 mA cm
−2
at 1.23 V vs. reversible hydrogen electrode, respectively. For the WO
3
/R-CoO photoanode, the surface charge separation efficiency is 50.95% and the photoconversion efficiency is 0.062%, which are both higher than the WO
3
and WO
3
/B-CoO photoanodes. The enhanced PEC performances are due to the type II heterojunction between WO
3
and R-CoO (or B-CoO), which facilitates the absorption of visible light and charge transport. The better performance of WO
3
/R-CoO than that of WO
3
/B-CoO may be due to the deeper valence band position of R-CoO. Our work demonstrates that R-CoO (or B-CoO) can couple with WO
3
to form a type II heterojunction to improve the PEC water oxidation performance.
Porous infill, rather than the solids, can provide high stiffness-to-weight ratio, energy absorption, thermal insulation, and many other outstanding properties. However, porous structure design to ...date have been majorly performed with topology optimization under small deformation assumption. The effect of porosity control under large deformation is not explored yet. Hence, this paper exploits the topological design method of porous infill structures under large deformational configuration. Specifically, the neo-Hookean hyperelasticity model is adopted to simulate the large structural deformation, and the adjoint sensitivity analysis is performed accordingly with the governing equation and constraint. The maximum local volume fractions before and after deformation are concurrently constrained and especially for the latter, the representative volume points (RVPs) are modeled and tracked for evaluating the local volume fractions subject to the distorted mesh configuration. The local volume constraints are then aggregated with the P-norm method for a global expression. Iterative corrections are made to the P-norm function to rigorously restrict the upper bound of the maximum local volume. Finally, several benchmark cases are investigated, which validate the effectiveness of the proposed method.
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