Michele Scafidi

Bio: Michele Scafidi is an academic researcher from University of Palermo. The author has contributed to research in topics: Residual stress & Photoelasticity. The author has an hindex of 13, co-authored 28 publications receiving 476 citations.

RGB Photoelasticity: Review and Improvements

Abstract: This paper considers the main developments of RGB photoelasticity with reference to the maximum measurable retardation. In this paper, a new procedure based on the standard error function evaluated on a subset of the calibration array is also proposed and experimentally tested. The experiments show that the filament lamp makes it possible to find retardations until approximately 4 fringe orders while the fluorescent lamp makes it possible to determine higher fringe orders (12 fringe orders in this paper) owing to the discrete spectrum of the source. The paper shows that, by using the incandescent lamp, the primary limiting factor is the lack of modulation of the R, G and B signals whereas, by using the fluorescent lamp, the limitation of the maximum fringe order derives mainly from the gradient of the fringes and the procedure of search of the retardation.

Mechanism of Yellowing: Carbonyl Formation during Hygrothermal Aging in a Common Amine Epoxy.

Abstract: Epoxies are often exposed to water due to rain and humid air environments. Epoxy yellows during its service time under these conditions, even when protected from UV radiation. The material’s color is not regained upon redrying, indicating irreversible aging mechanisms. Understanding what causes a discoloration is of importance for applications where the visual aspect of the material is significant. In this work, irreversible aging mechanisms and the cause of yellowing were identified. Experiments were performed using a combination of FT-NIR, ATR-FT-IR, EDX, HR-ICP-MS, pH measurements, optical microscopy, SEM, and DMTA. Such extensive material characterization and structured logic of investigation, provided the necessary evidence to investigate the long-term changes. No chain scission (hydrolysis or oxidation-induced) was present in the studied common DGEBA/HDDGE/IPDA/POPA epoxy, whilst it was found that thermo-oxidation and leaching occurred. Thermo-oxidation involved evolution of carbonyl groups in the polymeric carbon–carbon backbone, via nucleophilic radical attack and minor crosslinking of the HDDGE segments. Four probable reactive sites were identified, and respective reactions were proposed. Compounds involved in leaching were identified to be epichlorohydrin and inorganic impurities but were found to be unrelated to yellowing. Carbonyl formation in the epoxy backbone due to thermo-oxidation was the cause for the yellowing of the material.

Powder-based additive manufacturing – a review of types of defects, generation mechanisms, detection, property evaluation and metrology

Abstract: Powder-based additive manufacturing (AM) technologies have been evaluated for use in different fields of application (aerospace, medical, etc.). Ideally, AM parts should be at least equivalent, or preferably better quality than conventionally produced parts. Manufacturing defects and their effects on the quality and performance of AM parts are a currently a major concern. It is essential to understand the defect types, their generation mechanisms, and the detection methodologies for mechanical properties evaluation and quality control. We consider the various types of microstructural features or defects, their generation mechanisms, their effect on bulk properties and the capability of existing characterisation methodologies for powder based AM parts in this work. Methods of in-situ non-destructive evaluation and the influence of defects on mechanical properties and design considerations are also reviewed. Together, these provide a framework to understand the relevant machine and material parameters, optimise the process and production, and select appropriate characterisation methods.