The performance of triangular elements satisfying either compatibility or incompatibility conditions in the plate bending analyses is of great importance. To achieve highly accurate responses, four elements are formulated for the structural analysis in this study. All of these elements have thirteen nodes with different degree-of-freedom arrangements. Two of them are displacement-based compatible triangular elements, which are named Karimi Pour Compatible Triangular (KCT) and Noroozinejad Compatible Triangular (NCT) elements. Besides, the other two stress-based incompatible triangular elements are also suggested with the names of Karimi Pour Incompatible Triangular (KIT) and Noroozinejad Incompatible Triangular (NIT) elements. In this study, several benchmark problems are solved by using four proposed elements. These structures were previously analyzed by analytical or numerical schemes. Findings clearly indicated the improvement of answers, when various behaviors of the plate bending structures were studied. Additionally, it is concluded that the solution time is considerably declined if the recommended stress-based elements are utilized.

The paper presents the results of a simulation on a 3D model of undeformed chips and cutting forces during three-pass gear cutting using the power skiving method. At the level of individual blades and teeth in successive angular cutting positions, the main component of the cutting force and the tangential force on the cutter axis are shown. The analysis of the forces acting on a single gear tooth and the continuous cutting forces allowed the development of a methodology for the selection of rational cutting modes – the value of the axial feed, the number of passes with different cutting depths in order to ensure the minimum time consumption and to achieve the required accuracy of the gears in terms of the parameter of the permissible angular deviation of the profile of the cut gear. It is shown that, provided the required machining accuracy is ensured, higher productivity is achieved by increasing the axial feed at a lower depth of cut and increasing the number of passes, rather than by reducing the feed and increasing the depth of cut.

Electrical contacts are used in general electrical applications such as circuit breakers, switches, relays, connectors, etc. Repeated separations of the parts (anode and cathode) of these contacts under input power can damage their contact materials. The objective of this work is to study the influence of the input electric power (100 W and 256 W) and the contact sizes (hemispherical contacts with diameters D=5 mm and D=8 mm) on the variation of the arc energy and the damage of the contact surfaces by oxidization or by erosion. These parameters are decisive for selecting the best arc-resistant contact sample. Experimental results, SEM, and EDX analysis show that high input power leads to more degradation of contact surfaces. Also, the smaller and the larger contact diameters generate similar arcing energies with similar erosion sizes and oxidation rates, but the contact with a small diameter has a higher lifetime (1215 operations) and oxidizes less quickly than the one with a large diameter that has a lower lifetime (374 operations). Experimental and numerical analyses demonstrate that arc mobility is one of several factors influencing the change in contact lifetime.

This study was conducted under the 4R-UAV project. The project is funded by the Latvian Council of Science with the goal of creating an innovative, aerodynamically improved, environmentally friendly, zero waste, and zero emission UAV. For the Circular Aviation 4R (Reduce, Recycle, Reuse, Redesign) concept, this paper covers two Rs (Reduce and Redesign) aspects of the 4R-UAV project. Topology optimization of structures has gained enormous potential with the advances in additive manufacturing techniques. However, it is still challenging when it comes to conventional manufacturing. Aircraft/UAV wings are conventionally hollow structures and leave almost little or no space for further material removal. It becomes even more complicated when conventional manufacturing limitations are further imposed. Nevertheless, topology optimization is indeed an excellent way of reducing the mass of the structures by keeping the mechanical strength intact. This computational study attempts to implement topology optimization on a small-scale aircraft aluminum alloy wing as well as on a carbon composite UAV wing. In order to ensure the feasibility of not only additive manufacturing but also conventional manufacturing, controlled/limited topology optimization was applied only to the ribs of the wings. It was found that topology optimized wing ribs (aluminum and carbon composite) demonstrated a 20% mass reduction while up to 10% overall mass reduction of the wings was achieved. Moreover, after the topology optimization, the wings demonstrated improved mechanical characteristics and factor of safety. The knowledge learned from this study will be implemented for the topology optimization of the future small-scale 4R-UAV wings which will be mainly manufactured using additive manufacturing.

Development of synthetic bone graft via bone tissue engineering involves seeding of patient’s stem cells onto a porous scaffold in presence of growth factors. Porosity, strength and dimensional accuracy of the porous scaffold play a vital role in this process. This work aims at ascertaining influence of build orientation on porosity, mechanical strength and dimensional accuracy of the selectively laser sintered polyamide porous scaffolds. Initially, CAD models of test specimens with pre-designed porosity were created in Solidworks® software. All the specimens were fabricated on EOSINT P395, a selective laser sintering machine, along various primary (Flat, Edge, Upright and Flat_diag) and secondary (0^o, 30^o, 45^o, 60^o and 90^o) orientations. Results show that measured porosity of most of the specimens was (range: 42.89-35.26%) less than the designed porosity (41.71%). Maximum average tensile strength (16.84 MPa) was recorded for specimens printed along Flat_0^o orientation. Specimens printed along Upright_90^o orientation showed highest average compressive strength (8.26 MPa). Specimens printed along Flat orientation showed relatively better average impact strength. Best dimensional accuracy was obtained for specimens printed along Flat orientation.