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This paper aims to study the residual stress of deposited components which is a main issue to impede the widespread application of wire and arc additive manufacturing (WAAM). The interlayer dwell time is believed to have an effect on residual stress distributions in WAAM due to variance in heat dissipation condition. A coupled thermomechanical finite element model was established to evaluate the role of dwell time in between layers on the mechanical behavior of thin-walled components in WAAM, mainly involving thermal stress evolutions and residual stress distributions of the component and substrate.

Four interlayer dwell times including 0, 120 and 300 s and cooling to ambient temperature were selected in finite element modeling, and corresponding experiments were conducted to verify the reliability of the model.

The results show that with the interlayer dwell time, the stress cycling curves become more uniform and the interlayer stress-releasing effect is weakened. The residual stress levels on the substrate decrease with the increasing interlayer dwell time. In the outside surface of the component, the distributions of axial and longitudinal residual stress along the deposition path are the smoothest when the interlayer dwell time is cooling to ambient temperature. In the inside surface, a longer interlayer dwell time leads to an obvious decrease in the longitudinal and axial residual stress along the deposition path.

The comprehensive study of how the interlayer dwell time influences stress field of components is helpful to improve the deposition defects generated by WAAM.

This paper aims to fabricate inclined thin-walled components using positional wire and arc additive manufacturing (WAAM) and investigate the heat transfer characteristics of inclined thin-walled parts via finite element analysis method.

An inclined thin-walled part is fabricated in gas metal arc (GMA)-based additive manufacturing using a positional deposition approach in which the torch is set to be inclined with respect to the substrate surface. A three-dimensional finite element model is established to simulate the thermal process of the inclined component based on a general Goldak double ellipsoidal heat source and a combined heat dissipation model. Verification tests are performed based on thermal cycles of locations on the substrate and the molten pool size.

The simulated results are in agreement with experimental tests. It is shown that the dwell time between two adjacent layers greatly influences the number of the re-melting layers. The temperature distribution on both sides of the substrate is asymmetric, and the temperature peaks and temperature gradients of points in the same distance from the first deposition layer are different. Along the deposition path, the temperature distribution of the previous layer has a significant influence on the heat dissipation condition of the next layer.

The established finite element model is helpful to simulate and understand the heat transfer process of geometrical thin-walled components in WAAM.

This paper aims to introduce a novel concept of a double-wire feed (DWF) to alleviate heat accumulation and improve the cooling rate of the molten pool in gas tungsten arc (GTA)-based additive manufacturing (AM), in which the former wire is fed into the arc and the latter wire is melt by the molten pool.

The microstructure, phase composition and mechanical properties of 308 L stainless steel components built by single-wire feed (SWF) AM and DWF-AM are compared, and the differences are analyzed in detail.

The microstructures for both wire feeding modes include δ and γ phases. Compared with the SWF-AM, the sample fabricated in the DWF-AM exhibits finer microstructure, and the microstructure in the middle region is transformed from columnar grains to cellular grains. Microhardness of the sample produced in the DWF-AM is higher than the SWF-AM. In comparison to the SWF-AM, the tensile strength of the specimen fabricated using the DWF-AM reaches 571 MPa and increases by 16.14%.

This study proposes a novel concept of the DWF-AM to reduce heat accumulation as well as enhance the cooling rate of the molten pool, and improved mechanical properties of the 308 L stainless steel component are obtained.

The purpose of this study is to present how the thermal energy transmission of circular parts produced in robotized gas metal arc (GMA)-based additive manufacturing was affected by the substrate shape through finite element analysis, including distributions of thermal energy and temperature gradient in the molten pool and deposited layers.

Three geometric shapes, namely, square, rectangle and round were chosen in simulation, and validation tests were carried out by corresponding experiments.

The thermal energy conduction ability of the deposited layers is the best on the round substrate and the worst on the rectangular substrate. The axial maximum temperature gradients in the molten pool along the deposition path with the round substrate are the largest during the deposition process. At the deposition ending moment, the circumferential temperature gradients of all layers with the round substrate are the largest. A large temperature gradient usually stands for a good heat conduction condition. Altogether, the round substrate is more suitable for the fabrication of circular thin-walled parts.

The predicted thermal distributions of the circular thin-walled part with various substrate shapes are helpful to understand the influence of substrate shape on the thermal energy transmission behavior in GMA-based additive manufacturing.

An accurate prediction of process-induced residual stress is necessary to prevent large distortion and cracks in gas metal arc (GMA)-based additive manufactured parts, especially thin-walled parts. The purpose of this study is to present an investigation into predicting the residual stress distributions of a thin-walled component with geometrical features.

A coupled thermo-mechanical finite element model considering a general Goldak double ellipsoidal heat source is built for a thin-walled component with geometrical features. To confirm the accuracy of the model, corresponding experiments are performed using a positional deposition method in which the torch is tilted from the normal direction of the substrate. During the experiment, the thermal cycle curves of locations on the substrate are obtained by thermocouples. The residual stresses on the substrate and part are measured using X-ray diffraction. The validated model is used to investigate the thermal stress evolution and residual stress distributions of the substrate and part.

Decent agreements are achieved after comparing the experimental and simulated results. It is shown that the geometrical feature of the part gives rise to an asymmetrical transversal residual stress distribution on the substrate surface, while it has a minimal influence on the longitudinal residual stress distribution. The residual stress distributions of the part are spatially uneven. The longitudinal tensile residual stress is the prominent residual stress in the central area of the component. Large wall-growth tensile residual stresses, which may cause delamination, appear at both ends of the component and the substrate–component interfaces.

The predicted residual stress distributions of the thin-walled part with geometrical features are helpful to understand the influence of geometry on the thermo-mechanical behavior in GMA-based additive manufacturing.

Taking advantage of the 2008 Sichuan Great Earthquake as a natural experiment, the purpose of this paper is to examine the motives and effects of corporate donations by focusing on how firm ownership identity as the first-order governance mechanism affects the motives and effects of disaster relief donations.

The authors conduct regressions and market event studies, and use matching to address the confounding effects of differences in firm characteristics.

The authors hypothesize that private firms that are better governed than state-owned enterprises (SOEs) are more likely to donate for value maximization. Consistent with this, the authors find that private firms are more likely to donate to the 2008 Sichuan earthquake and donate more than SOEs. The effects of secondary governance variables in the donation determinant models (e.g. board independence and managerial ownership) are more consistent with the value maximization argument. While short-term market reaction to donation announcement is not significant for private firms, it is lower when SOEs make a large donation. Consistent with the hypothesis, the authors find that over the 24–36 months following the donation, private donors realize a higher abnormal stock return.

The study contributes to the debate over the merits/costs of corporate donations and helps better understand how SOEs and private firms (particularly family-owned firms) differ in their governance and financial decision-making.

Both managers from private firms and SOEs can use the findings of this study to better guide their donation and other philanthropic decisions.

This study is the first to examine both the motives and effects of corporate donations by both private and SOEs taking advantage of the 2008 Sichuan, thereby significantly extending prior related studies.

The purpose of this paper is to focus on alleviating the problems of both hidden and exposed terminal, which remain unsolved in many directional MAC protocols.

GPS is used to calibrate synchronization among the nodes, and directional antennas are used. In the protocol, different antenna mode and transmit power are used. The assertion signal and omni‐directional RTS are transmitted in omni‐directional mode, while directional CTS, directional RTS, DATA and ACK are transmitted in directional mode. With properly designed RTS‐CTS handshake, the protocol can make full use of spatial reuse of directional communication and enhance parallelism in data transmission.

The preliminary simulation results indicate that the protocol works well and achieves considerably high performance in both sparse and dense ad hoc networks.

The line of sight environment is the main limitation that the MAC protocol will be applied.

The protocol is a very useful solution for employing directional antennas for ad hoc networks.

The MAC protocol can effectively alleviate the directional hidden and exposed terminal problems as well as node deafness. It can greatly improve throughput and achieve low‐medium access delay, making it suitable for ad hoc networks.

The purpose of this paper is to aggregate different preference information in group decision‐making process such as interval preference order, interval utility value, interval number reciprocal comparison matrix, and interval number complementary comparison matrix.

First, the consistency definitions of four kinds of uncertain preference information are defined. Then, the upper‐ and low errors are introduced to solve the inconsistent decision‐making case. Following that, the weight model for each uncertain preference is proposed, respectively.

The aggregation approach based on minimal group deviation errors is suggested in order to obtain the utmost consistent opinion. In addition, the consistency judgment level and consistency extent are defined owing to the aggregation result.

The calculation scale is large, if many decision makers will attend group decision‐making process.

A very useful approach for aggregation of the different preference in group decision‐making case.

Because of differences in knowledge structure, judgment level, and individual preference, decision makers express their judgment preferences via differently structured decision‐making processes. Owing to the complexity and uncertainty of decision‐making problems and the fuzziness of human thought, it is unrealistic to depict complex problems in the certain preference style. For decision‐making preference structures, group decision‐making aggregation approaches include the aggregation on the same kind of preference structure and the different kinds of preference structures. The study on the aggregation of the same kind of preference structure has received a deal of attention, but study into the aggregation of the different kinds of uncertainty preference structures is still a new field.

The purpose of this paper is to develop a build strategy for inclined thin-walled parts by exploiting the inherent overhanging capability of the cold metal transfer (CMT) process, which release wire-arc additive manufacturing from tedious programming work and restriction of producible size of parts.

Inclined thin-walled parts were fabricated with vertically placed welding torch free from any auxiliary equipment. The inclined features were defined and analyzed based on the geometrical model of inclined parts. A statistical prediction model was developed to describe the dependence of inclined geometrical features on process variables. Based on these models, a build strategy was proposed to plan tool path and output process parameters. After that, the flow work was illustrated by fabricating a vase part.

The formation mechanism and regulation of inclined geometrical features were revealed by conducting experimental trials. The inclined angle can be significantly increased along with the travel speed and offset distance, whereas the wall width is mainly dependent on the ratio of wire feed speed to travel speed. In contrast to other welding process, CMT has a stronger overhanging capability, which provides the possibility to fabricate parts with large overhanging features directly with high forming accuracy.

This paper describes a novel build strategy for inclined thin-walled parts free from any auxiliary equipment. With the proposed strategy, a complex structural component can be deposited directly in the rectangular coordinates additive manufacturing system, indicating infinite possibilities on the producible size of the parts. Moreover, equipment requirements and tedious program work can also be significantly reduced.

Modeling and control of bead geometry in wire and arc additive manufacturing is significant as it affects the whole manufacturing process. The purpose of this paper is to establish an efficient model to control the bead geometry with fewer experiments in wire and arc additive manufacturing (WAAM).

A multi-sensor system is established to monitor the process parameters and measure the bead geometry information. A dynamic parameters experimental method is proposed for rapid modeling without dozens of experiments. A deep learning method is used for bead modeling and control. To adaptively control the bead geometry in real-time, a closed-loop control system was developed based on the bead model and in situ monitoring.

A series of experiments were conducted to train, test and verify the feasibility of the method and system, and the results showed that the proposed method can build the bead model rapidly with high precision, and the closed-loop system can control the forming geometry adaptively.

The proposed modeling method is novel as the experiment number is reduced. The dynamic parameters experimental method is effective with high precision. The closed-loop control system can control the bead geometry in real-time. The forming accuracy is elevated.