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The purpose of this paper is to present an optimisation of four-point star-shaped structures produced through additive manufacturing (AM) polylactic acid (PLA). The study also aims to investigate the compression failure mechanism of the structure.

A Taguchi L₉ orthogonal array design of the experiment is adopted in which the input parameters are resolution (0.06, 0.15 and 0.30 mm), print speed (60, 70 and 80 mm/s) and bed temperature (55°C, 60°C, 65°C). The response parameters considered were printing time, material usage, compression yield strength, compression modulus and dimensional stability. Empirical observations during compression tests were used to evaluate the load–response mechanism of the structures.

The printing resolution is the most significant input parameter. Material length is not influenced by the printing speed and bed temperature. The compression stress–strain curve exhibits elastic, plateau and densification regions. All the samples exhibit negative Poisson’s ratio values within the elastic and plateau regions. At the beginning of densification, the Poisson’s ratios change to positive values. The metamaterial printed at a resolution of 0.3 mm, 80 mm/s and 60°C exhibits the best mechanical properties (yield strength and modulus of 2.02 and 58.87 MPa, respectively). The failure of the structure occurs through bending and torsion of the unit cells.

The optimisation study is significant for decision-making during the 3D printing and the empirical failure model shall complement the existing techniques for the mechanical analysis of the metamaterials.

To the best of the authors’ knowledge, for the first time, a new empirical model, based on the uniaxial load response and “static truss concept”, for failure mechanisms of the unit cell is presented.

This study aims to address the critical subject of building capacity for the circular economy in the global south. It complements the literature by providing information on the role of higher education institutions in developing skills for the circular plastic economy.

This study used a mixed method approach drawing on reflective analysis on qualitative data from 5 focus groups and 12 semi-structured interviews, and structural equation modelling of quantitative data from 151 students across 4 Nigerian Universities.

The results indicate that Nigerian university students are more likely to participate in the circular plastic economy through a high prominence of soft power features such as increased awareness, inspiration, idea generation, encouragement and capacity building.

The main limitation of this study is with the sample. A larger data set, including other tertiary institutions such as private universities, polytechnics and schools of vocational studies, would strengthen the results.

The study underlines the importance of targeted policy interventions and pedagogic innovations to drive awareness and knowledge building among Nigeria’s youth population.

This study makes a novel contribution by using empirical evidence to determine the predictors of student participation in the circular plastic economy. This understanding is important for the development and implementation of appropriate policies that promote participation in the circular plastic economy. Furthermore, given the typical youthful age bracket of university students, any plans to achieve a systemic shift in the plastic value chain must involve the young generation.

The purpose of this paper is to optimize the welding parameters: rotating speed and plunging depth of carbon steel and pure copper joints using friction stir spot welding (FSSW) with the aid of the design of experiments (DOE) method.

Carbon steel and pure copper sheets were welded using the FSSW technique with a cylindrical tool and without a probe. The welding parameters were: rotating speed: 1,120, 1,400 and 1,800 RPM and plunging depth: 0.2 and 0.4 mm. The welding process was carried out both with and without pre-heating. The welded specimens were analyzed using a shear tensile test. A microstructural investigation at the optimum conditions was carried out. The results were analyzed and optimized using the statistical software Minitab and following the DOE method.

Pre-heating the sample and increasing the rotating speed and plunging depth increased the tensile shear force of the joint. The plunging depth has the biggest effect on the joint efficiency compared with the rotating speed. The optimum shear force (4,560 N) was found at 1,800 RPM, 0.4 mm plunge depth and with pre-heating. The welding parameters were modified so that the samples were welded at 1,800 RPM and at plunging depths of 0.45–1 mm in 0.05 mm steps. The optimized shear force was 5,400 N. The fractured samples exhibited two types of failure mode: interfacial and nugget pull-out.

For the first time, pure copper and carbon steel sheets were welded using FSSW and a tool without a probe with ideal joint efficiency (95 percent).

The challenges confronting the Nigerian construction industry which led to the adoption of supply chain management (SCM) practice were evaluated in this chapter. It was discovered that the Nigerian construction industry is confronted with fragmentation and poor information management. The stakeholders within the Nigerian construction industry proposed the adoption of SCM to overcome the fragmentation and other shenanigans facing the industry. This chapter revealed that construction supply chain (CSC) practices within the Nigerian construction industry focus on waste elimination by adopting the lean concept. The focus on the lean concept could be attributed to the numerous research related to lean or the enormous waste emanating from the Nigerian construction industry. Regardless of the emphasis on lean, the Nigerian CSC is still confronted with fragmentation and heavy waste generation. Thus, this chapter proposed the adoption of principles and technologies driven by the fourth industrial revolution (4IR) is a paradigm shift for the management of CSC in the country. It was discovered in this chapter that Nigerian construction supply stakeholders had not embraced the technologies and principles of the 4IR. The failure to adopt the technologies driven by the 4IR is attributed to the absence of a CSC model that depicts the management of CSC in alignment with the 4IR. This chapter called for developing a SCM model for the Nigerian construction industry in tandem with the principles and technologies of the 4IR.