Future Armoured Troop Carrying Vehicles

Present-day reliance on wheeled and tracked armour personnel carriers (APCs) and infantry fighting vehicles (IFVs), may be changed in the future. Shaped charge grenades and impovised explosive devices (IEDs)represent a considerable threat, even to well protected main battle tanks (MBTs). Paradoxically, the crew of wheeled and tracked troop-carrying vehicles is numerically three to four times larger than that of MBTs, however, their protection in all aspects is significantly lower. Therefore, heavier vehicles may get more attention in the future, where sharing the chassis and a number of components with MBTs could provide significant reductions in procurement costs and maintenance, as well as a simplified logistics in relation to the latest tracked. Obviously, the IFVs mobility of heavy vehicles would be lower than that of lighter vehicles. However, by applying various degrees of modular armour protection, a significant rise in strategic, operational, and tactical mobility could be achieved. Such heavy tracked vehicles, built on a common chassis as MBTs, may equip the future heavy brigades, which will be in contrast to the lighter wheeled vehicles included in rapid deployment brigades. As a result, tracked personnel carrying vehicles may extinct in the future.Defence Science Journal, 2010, 60(5), pp.483-490, DOI:http://dx.doi.org/10.14429/dsj.60.55

Perforated plate for ballistic protection - a review

In recent years, the interest of the scientific community in perforated plates for ballistic protection has increased. Perforated plates do not represent protection by themselves, rather, they are used in the armour systems of armoured vehicles, in conjunction with base armour, since they are intended to induce bend stresses, where a penetrating core fracture occurs. The fragments are subsequently stopped by base armoured vehicle armour. Although for the first time used several decades ago, perforated plates are found to be attractive even today. The main reason is the combination of very convenient properties. Besides high mass effectiveness, they possess a high multi-impact resistance, since their perforations arrest cracks. Therefore, a relatively wide array of materials is suitable for perforated plate fabrication, ranging from alloy steel to some types of cast iron. Being made of metallic materials, raw material costs are relatively low compared to ceramics or composite materials, making them very attractive for present and future armoured vehicles. Finally, armour system consisting of a perforated plate and base plate at some distance, reduce the effectiveness of both shaped charge jets and act as blast mitigators

Activated flux tig welding of stainless-steel pipes

In this work, the presence of TiO2 nanoparticle-based activated flux combined with orbital welding of seamless thick-walled pipes of stainless steel and low-cycle pulse current was done, representing a novel combination of welding processes parameters. Control specimens were welded without flux and consumable material, and without flux with the consumable material. Experimental welding with different welding parameters was done. Special attention was given to characterize the flux by zetasizer method, representing a new approach, versus the conventional approach where the nominal oxide particle size is reported. The obtained welds were visually tested, macroanalyzed, their microstructures examined, and their tensile and bending properties determined. The results show that the flux influences a significant increase in penetration depth, up to full penetration, which has a positive effect on the increase in the tensile and bending properties of the weld metal. Material beahvior model was developed, based on microstructural features of the near weld-line. Without the flux, grain enlargement occurred near the surface, while with flux, it occurred under the weld, which can be attributed to recrystallization and a reversed Marangoni convection

The influence of polymer addition on flexural strength, fracture mode and porosity of traditional ceramics

The usage of air-swept milling of raw materials is the most efficient method for preventing the negative lime-blowing process of ceramic roofing tiles. How-ever, after air-swept milling the clay minerals lose water which has to be re-turned back before the shaping procedure. Addition of surface active materials could increase hydrophilicity of the raw material and reduce needed time for re-wetting trough the control of meso-, micro- and nanoporosity of the clay ma¬terial. In view of that, the object of this research was to study the influence of polyethylene glycol (PEG600) on porosity, mechanical properties and fracture surface characteristics of traditional ceramic materials. It was founded that with the addition of polyethylene glycol (PEG600) to traditional clay materials it is possible to achieve desired porosity, from meso, through micro and up to na¬no, without degrading the mechanical properties of the final products

Polymethylmethacrylate (PMMA) welding technology

Polimetilmetakrilat (PMMA), zbog svojih karakteristika, pre svega transparentnosti i relativno male gustine, predstavlja danas vrlo atraktivan materijal u inženjerstvu. Zbog toga, istražuju se nove mogućnosti spajanja ovog materijala u cilju dobijanja kompleksnijih i većih radnih predmeta. U ovom radu su prikazane tehnike zavarivanja i spajanja, koje imaju potencijal za primenu u proizvodnji: ultrazvučno zavarivanje, toplotno spajanje, mikrotalasno zavarivanje i tačkasto zavarivanje trenjem. Takođe, prikazani su i uporedne vrednosti smicajne čvrstoće, jednog od dominantnih pokazatelja kvaliteta zavarenog spoja. Na osnovu prikazanih rezultata, najveću smicajnu čvrstoću ima tačkasto zavarivanje trenjem, sledi mikrotalasno zavarivanje, dok najmanju nosivost zavarenog spoja imaju toplotno spajanje i ultrazvučno zavarivanje. Pored toga, na osnovu specifičnosti pojedinih tehnika zavarivanja, može da se konstatuje da je tačkasto zavarivanje trenjem pogodnije za veće radne predmete, dok je veličina radnog predmeta kod mikrotalasnog zavarivanja ograničena veličinom mikrotalasne komore.Polymethylmethacrylate (PMMA) has attractive features, primarily its transparency and low density, which make it a very promising engineering material. Therefore, a novel bonding and welding techniques are being developed, to enable obtaining more complex and larger products. In this paper, perspective bonding and welding processes are presented: ultrasound welding, thermal bonding, microwave welding and friction spot welding. Furthermore, shear strengths of joints obtained by different techniques are shown. Shear strength of joints is commonly used to evaluate the quality of joints. The highest shear strength has friction spot welding, followed by microwave welding. The lowest shear strengths were obtained with thermal bonding and ultrasound welding. Specific characteristics of each joining technique determine their usefulness: friction spot welding is more suited to welding large pieces, while the work piece dimensions weldable by microwave welding is limited by microwave chamber size

Hydrophobic silica nanoparticles as reinforcing filler for poly (lactic acid) polymer matrix

Properties of poly (lactic acid) (PLA) and its nanocomposites, with silica nanoparticles (SiO2), as filler were investigated. Neat PLA films and PLA films with different percentage of hydrophobic fumed silica nanoparticles (0.2, 0.5, 1, 2, 3 and 5 wt. %) were prepared by solution casting method. Several tools were used to characterize the influence of different silica content on crystalline behavior, and thermal, mechanical and barrier properties of PLA/SiO2 nanocomposites. Results from scanning electron microscope (SEM) showed that the nanocomposite preparation and selection of specific hydrophobic spherical nano filler provide a good dispersion of the silica nanoparticles in the PLA matrix. Addition of silica nanoparticles improved mechanical properties, the most significant improvement being observed for lowest silica content (0.2wt.%). Barrier properties were improved for all measured gases at all loadings of silica nanoparticles. The degree of crystallinity for PLA slightly increased by adding 0.2 and 0.5 wt. % of nano filler

Suppressing the use of critical raw materials in joining of AISI 304 stainless steel using activated tungsten inert gas welding

The aim of this study was to study the influence of TiO2 coating for its efficacy during the activated-tungsten inert gas (TIG) welding and to suppress the use of consumables that are rich in critical raw materials. Post-welding penetration depth, particle size distribution, microstructure, and microhardness of welded samples were assessed. Based on these results, it was found that there is no direct correlation between the weld metal surface area and the coating. The particle size in the coating, although, seemed to have played an important role, e.g., nanoparticles resulted in an increased penetration depth and depth/width (D/W) ratio as opposed to the submicron-sized particles. The most optimal welding condition resulted when a mixture of submicron-sized and nanometric-sized particles were used. It was demonstrated by the Zeta analyser results that the micron particles rub the nanoparticles due to mechanical friction resulting in smaller oxide particle formation in the coating. Finally, the presence of Marangoni convection in TIG and reversed Marangoni convection in the activated TIG (A-TIG) process were proven by means of the microstructure analysis and measurement, which were found to be positively correlated

Vickers hardness indentation size effect in selective laser melted MS1 maraging steel

© IMechE 2019. In this paper, selective laser melting fabricated specimens in non-heat-treated and heat-treated conditions were subjected to Vickers microhardness testing, by using a full range of loadings: 10, 25, 50, 100, 200, 300, 500, and 1000 g. Microhardness of longitudinal sections and cross-sections were correlated and the obtained values were plotted against loadings and indentation size effect was studied, in order to find the optimal loading range, that gives the material true microhardness, or load-independent hardness. The load dependence of the measured Vickers hardness values was described quantitatively through the application of the Meyer’s law, proportional specimen resistance, and the modified proportional specimen resistance model. It was found that the microhardness rises as the loading is higher, causing a reversed indentation size effect, clearly indicating the range of true hardnesses of the tested material. Also, proportional specimen resistance and modified proportional specimen resistance models were found to have the highest correlation factors indicating their higher adequacy compared to Meyer’s prediction model.The authors wish to acknowledge the support of European Commission through the project “Advanced design rules for optimal dynamic properties of additive manufacturing products – A_MADAM”, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 734455

Knoop hardness optimal loading in measuring microhardness of maraging steel obtained by selective laser melting

© IMechE 2019. Knoop microhardness method possesses several advantages over Vickers testing: lower penetration depth, higher accuracy in indentation measurement, and a better suitability to measuring thin and elongated morphological features. This study explores the optimal loading and load independent hardness of selective laser melted specimens in non-heat-treated and heat-treated conditions, by using different Knoop test loads. The obtained results were used to plot load to indentation size charts, which, in turn, were used to obtain prediction curves in accordance to Meyer, proportional specimen resistance, and modified proportional specimen resistance models. The fitting of fitting curves to the measured values was used to calculate appropriate correlation factors. The results indicate that indentation size effect occurs in all measured specimens. This suggests that there is material true microhardness. Also, the most adequate model was modified proportional specimen resistance, with correlation factors just under one.The authors wish to acknowledge the support of European Commission through the project “Advanced design rules for optimal dynamic properties of additive manufacturing products – A_MADAM”, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 734455

Influence of rotational speed on the electrical and mechanical properties of the friction stir spot welded aluminium alloy sheets

An efficient and productive joining technique to weld aluminium has become a priority challenge for promoting the use of aluminium in the electrical industry. One of the challenges is to obtain welds with superior mechanical properties with the consistent quality of weld surface as well as low electrical resistance. In this paper, the influence of rotational speed during the friction stir spot welding of AA 5754-H111 was studied to analyse the mechanical and electrical properties of the welds. The results from two rotational speeds (1000 rpm and 4500 rpm) are presented and compared to the base material. It was observed that the samples welded at 1000 rpm showed a higher average shear failure load (~ 1.1 kN) compared to the samples welded at 4500 rpm (~ 0.94 kN). The microhardness of the samples welded at 1000 rpm was higher than that of the base material, while the microhardness of samples welded at 4500 rpm was lower. It was also found that the friction welded sheets, regardless of the rotational speed used, showed increased electrical resistance compared to the base material, albeit this increase for the samples welded at 1000 rpm was about 42%, compared to samples welded at 4500 rpm where this increase was just 14%