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As known, the wire and arc additive manufacture technique can achieve stable process control, which is represented with periodic surface waviness, when using empirical methods or feedback control system. But it is usually a tedious work to further reduce it using trial and error method. The purpose of this paper is to unveil the formation mechanism of surface waviness and develop a method to diminish it.

Two forming mechanisms, wetting and spreading and remelting, are unveiled by cross-section observation. A discriminant is established to differentiate which mechanism is valid to dominate the forming process under the given process parameters.

Finally, a theoretical method is developed to optimize surface waviness, even forming a smooth surface by establishing a matching relation between heat input (line energy) and materials input (the ratio of wire feed speed to travel speed).

Formation mechanisms are revealed by observing cross-section morphology. A discriminant is established to differentiate which mechanism is valid to dominate the forming process under the given process parameters. A mathematical model is developed to optimize surface waviness, even forming a smooth surface through establishing a matching relation between heat input (line energy) and materials input (the ratio of wire feed speed to travel speed).

To address challenges such as inadequate funding and inefficiency in public infrastructure construction, PPPs have gained significant global traction. This study aims to comprehensively assess the impacts and mechanisms of PPPs on the SDI and to provide rational policy recommendations based on the findings.

We collated a dataset from 30 Chinese provinces covering the years 2005–2020 as our research sample. The study’s hypotheses are tested using a double fixed-effects model, a chained mediated-effects model and a multidimensional heterogeneity analysis.

Our findings indicate that PPPs have a facilitating effect on SDI in general. This boost usually lags behind policy implementation and is cyclical in the time dimension. In the spatial dimension, PPPs contribute significantly to SDI in the eastern and western regions, but not in the central region. From the perspective of the dynamics of economic, social and industrial development, PPPs in economically backward areas are difficult to promote SDI, promote it the most in economically medium regions and are slightly less in economically developed regions than in medium regions. This promotion effect has an inverted U-shaped relationship with social development and diminishes with industrial structure upgrading. Finally, due to the negative relationship between PPPs and social development and between social development and SDI, PPPs are shown to contribute to SDI and are identified as critical paths. However, PPPs suppress SDI by inhibiting economic and industrial development.

This study makes three novel contributions to the existing body of knowledge: (1) we innovatively introduce the United Nations Sustainable Development Goals (SDGs) into the field of infrastructure research, offering fresh perspectives on SDI enhancement; (2) revealing the mechanisms by which PPPs affect SDI through the three dimensions of economic, social and industrial development enabling policymakers to better understand and optimize resource allocation and improve planning, design and management of PPP projects for sustainable infrastructure and (3) we assess the spatiotemporal variances of PPPs’ effects on SDI and the diversity across regions at different social, economic and industrial structures developmental stages, offering critical insights to global decision-makers to devise tailored policy measures.