The need to use components with improved surface characteristics in relation to severe operating conditions, together with the aim of cost reduction associated with the replacement of damaged components, has led to an increasing use of coatings and repairing processes. The most common deposition processes are generally characterized by high equipment costs and, sometimes, by long deposition time. Furthermore, some repair technologies, especially those characterized by high heat input, are not suitable for alloys used in aerospace applications due to the degradation of their mechanical characteristics. In the last decades, a novel eco-friendly method capable of overcoming the limits set out above emerged: the electrospark deposition (ESD) technology. Thanks to its efficiency, simplicity, cost-effectiveness, and low heat input, this technology has proved to be suitable both for improving surface properties, such as thermo and wear resistance, higher hardness and corrosion resistance, and for the repair of high-value components. The aim of this review is to describe in detail some aspects of the ESD technique to understand the ESD processing preparation of alloys normally considered difficult to weld by traditional processes and to give some important clues to the readers to contribute to the defect-free repair of damaged areas and coatings deposition.

The widespread adoption of clear aligners in orthodontic treatments in recent years has necessitated a more precise examination of the mechanical properties of the devices currently available in orthodontics. Recent studies indicate that aligners, when exposed to the forces exerted during swallowing, undergo fatigue-like phenomena, leading to chip formation and cracks. The cumulative damage results in a compromised fit between the tooth and aligner, which is crucial for the effective execution of orthodontic treatment. Additionally, the formation of chips poses a potential risk to patients, as there is a possibility of inadvertently ingesting microplastics that become detached from the aligner over time. This study attempts to assess the release of microplastics from the aligners subjected to cyclic compressive loading. Three different aligners (Essix Ace, Ghost Aligner and Invisalign) are tested to simulate swallowing conditions over the aligner usage period. The mechanical performance is studied in terms of the energy absorbed by the aligner, which shows that the Essix Ace has a stable energy absorption behaviour, while the energy absorbed by the Invisalign is significantly higher than their counterparts. Ghost Aligner did not perform well in the cyclic compression tests. The microplastics (MPs) released by the aligners are examined under an optical microscope. A dimensional analysis based on k-means image segmentation and edge detection algorithm is developed to analyse the MPs. The dimensional analysis of the MPs revealed that the ingestion of the MPs released by all the three aligners does not pose a health risk.

Hole drilling is the most widespread method for measuring residual stress. It is based on the principle that drilling a hole in the material causes a local stress relaxation; the initial residual stress can be calculated by measuring strain in correspondence with each drill depth. Recently optical techniques were introduced to measure strain; in this case, the accuracy of the final results depends, among other factors, on the proper choice of the area of analysis. Deformations are in fact analyzed within an annulus determined by two parameters: the internal and the external radius. In this paper, the influence of the choice of the area of analysis was analysed. A known stress field was introduced on a Ti grade 5 sample and then the stress was measured in correspondence with different values of the internal and the external radius of analysis; results were finally compared with the expected theoretical value.

The diffusion of composite materials in aeronautical and aerospace applications is attributable to the high specific mechanical properties they offer. In particular, the recent use of Carbon Fiber Reinforced Polymer (CFRP) materials is highly increased. The main disadvantage in using this kind of material is related to the possibility of including damages or defects not visible on the surface that compromise their behavior and make their use extremely unsafe if not properly supervised. The most conventional nondestructive techniques allow the detection of damages when they already compromise the life of these materials. The use of the same techniques makes it harder to monitor in-situ of the progress of damages, especially if they occur inside the materials. The implementation of the innovative strain analysis method, like those based on full-field measurements, could provide additional information about the damage mechanisms by supplying the complete strain distribution of the surface of the sample. The present paper examines the mechanical behavior of two different CFRP specimens, with and without damage, subjected to compressive load in an anti-buckling fixture by using the Digital Image Correlation (DIC). The purpose is to measure the out-of-plane displacements, characteristics of the compression tests, in all the points of the ROI (Region of Interest), using a full-field and noncontact technique. The innovative aspect of this work is therefore to solve this problem through an experimental approach with DIC 3D technique.