Improving mechanical properties of flowable dental composite resin by adding silica nanoparticles

Background/Aim. The main drawback of flowable dental composite resin is low strength compared to conventional composite resin, due to a low amount of filler, neccessary for achieving low viscosity and ease of handling. The aim of this study was to improve mechanical properties of flowable dental composite resin by adding small amount of nanoparticles, which would not compromise handling properties. Methods. A commercially available flowable dental composite resin material was mixed with 7 nm aftertreated hydrophobic fumed silica and cured by an UV lamp. Four sets of samples were made: control sample (unmodified), the sample containing 0.05%, 0.2% and 1% nanosilica. Flexural modulus, flexural strength and microhardness were tested. One-way ANOVA followed by Tukey’s test with the significance value of p < 0.05 was performed to statistically analyze the obtained results. Furthermore, differential scanning calorimetry (DSC) and SEM analysis were performed. To asses handling properties, slumping resistance was determined. Results. It was found that 0.05% is the most effective nanosilica content. All the tested mechanical properties were improved by a significant margin. On the other hand, when 0.2% and 1% nanosilica content was tested, different results were obtained, some of the mechanical properties even dropped, while some were insignificantly improved. The difference between slumping resistance of unmodified and modified samples was found to be statistically insignificant. Conclusions. Low nanosilica addition proved more effective in improving mechanical properties compared to higher additions. Furthermore, handling properties are unaffected by nanosilica addition

Ballistic Behaviour of Austempered Compacted Graphite Iron Perforated Plates

In this study, the performance of austempered compacted graphite iron was evaluated to find its suitability as perforated plates used in add-on armour. Perforated compacted graphite plates were subjected to austenitisation at 900 degrees C for 2 h followed by austempering at 275 and 400 degrees C for 1 h. The basic plate was fixed at 400 mm away from the perforated plate and armour and then piercing incendiary projectile was shot from a distance of 100 m. It was observed that both 7 mm and 9 mm perforated plates austempered at lower temperature of 275 degrees C producing higher hardness and lower ductility were effective in fracturing the penetrating core, thereby significantly decreasing the chances of penetrating the basic plate

Ballistic Behaviour of Austempered Compacted Graphite Iron Perforated Plates

In this study, the performance of austempered compacted graphite iron was evaluated to find its suitability as perforated plates used in add-on armour. Perforated compacted graphite plates were subjected to austenitisation at 900 °C for 2 h followed by austempering at 275 and 400 °C for 1 h. The basic plate was fixed at 400 mm away from the perforated plate and armour and then piercing incendiary projectile was shot from a distance of 100 m. It was observed that both 7 mm and 9 mm perforated plates austempered at lower temperature of 275 °C producing higher hardness and lower ductility were effective in fracturing the penetrating core, thereby significantly decreasing the chances of penetrating the basic plate

Cold Radial Extrusion of a Gear-Like Element with Flow Relief Opening

When divided material flow is enabled during extrusion process, the required forming load is lower compared to a conventional process. The reduction of forming load leads to higher quality of extruded part and longer tool life. One way to achieve divided material flow is the application of a relief opening, either in the billet or in the tool. In this paper, theoretical solution based upon the Upper bound theorem was used to determine the forming load for radial extrusion of a gear-like element with straight parallel flank profile. Two possible positions of relief openings were analysed - in the centre of the billet and in the centre of the punch. Theoretical solution was compared to experimental results. Material of billets was Al 99,5. Comparison between theoretical and experimental values of the forming load showed fairly good agreement. Further development of the proposed theoretical solution should lead to better process description and more accurate value of the forming load

Utjecaj kinematičkih faktora zavarivanja trenjem miješanjem na karakteristike zavarenog spoja kovanih ploča od legure aluminija EN AW 7049 A

U radu se analiziraju utjecaji broja okretaja i brzine zavarivanja na udarnu žilavost, metalografska obilježja i raspodjelu mikrotvrdoće po površini poprečnog presjeka FSW zavarenog spoja kovanih ploča od visokočvrste legure aluminija faznog sastava Al-Zn-Mg-Cu. Broj okretaja je mijenjan u rasponu od 750 min−1 do 850 min−1, a brzina zavarivanja od 60 mm/min do 80 mm/min. Razdvajanjem energije inicijacije pukotine od energije potrebne za njezinu propagaciju, uočava se da je čak i do tri puta veća vrijednost energije koja je potrebna za njezinu propagaciju. Odnos energije inicijacije i energije propagacije je dobiven ispitivanjem Charpy epruvete sa zarezom u središtu, lijevo i desno od središta metala šava 4 mm u smjeru suprotnom od smjera zavarivanja. Distribucija mikrotvrdoće metala šava ne pokazuje veliko rasipanje vrijednosti bez obzira da li je mjerno mjesto u gornjoj ili donjoj razini površine zavarivanih komada. Na mikrograficima jasno se uočavaju zone strukturnih sadržaja zavarenog spoja na osnovi veličine zrna i linija tečenja materijala.In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min−1 to 850 min−1 and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow

Consistency analysis of mechanical properties of elements produced by FDM additive manufacturing technology

Additive manufacturing (AM) technology refers to the process of producing 3D objects by adding material insuccessive layers. Fused deposition modeling (FDM) is one of the AM technologies where objects are builtby adding layers of melted thermoplastic filament onto the printing surface. Mechanical properties of FDMprinted part depend on many influencing factors such as material composition, extruding temperature,printing parameters and environment temperature.The aim of this study was to investigate consistency of mechanical properties of elements produced by FDMadditive manufacturing technology. To do so, mechanical tensile and compression tests were conducted onten samples using polylactic acid (PLA) and ten samples using acrylonitrile butadiene styrene (ABS)thermoplastic material. Tensile tests were conducted using Shimadzu Compact Tabletop Testing MachineEZ-LX and the compression tests were done using VEB ZDM 5/91 testing machine. The ultimate tensilestrength, strain, Young modulus and compression yield strength values were analyzed. The ABSthermoplastic material showed greater consistency in mechanical properties during tensile tests. Tensilestrength values for PLA material varied between samples thus showing greater inconsistency in repeatabilityof mechanical properties. Compression tests, on the other hand, showed that PLA samples had greaterconsistency in mechanical properties compared to ABS samples.Keywords: additive manufacturing, FDM, mechanical properties

Characterization of films based on cellulose acetate/poly(caprolactone diol) intended for active packaging prepared by green chemistry principles

Biodegradable active packaging films based on a cellulose acetate and poly(caprolactone diol) blend with incorporated lemongrass oil were developed. Films were prepared using a novel bio-based plasticizer, glycerol tritartarate, synthesized using the principles of green chemistry. The influence of the plasticizer, as well as the essential oil amount, on the structural, surface, mechanical, and thermal properties of the blend was investigated. The plasticizer was shown to work as a compatibilizer for two polymers, according to the results of scanning electron microscopy and surface energy analysis. Blends with a greater amount of plasticizer possessed better mechanical properties but showed worse resistance to water. The antimicrobial property of the blend with lemongrass oil was found to be superior to that of the blend without essential oil. The incorporation of lemongrass oil into the polymer blend resulted in one more step longer thermal degradation process. The optimal film properties, biodegradability, cost-effective preparation method, and additional functions made these films suitable for the production of packaging for grapefruit.This peer-reviewed accepted version of the article will be available in open access on 15 July 2023. The published article available at the publisher [https://pubs.acs.org/doi/10.1021/acssuschemeng.2c02009

Austempering Kinetics of Cu-Ni Alloyed Austempered Ductile Iron

The aim of the paper was to investigate the effect of austempering parameters (time and temperature) on the microstructure and mechanical properties of ADI alloyed with 1.5% Cu and 1.6% Ni (in wt.%) in order to establish the optimal processing window. It was shown that the strength, elongation and impact energy strongly depend on the amounts of ausferritic ferrite and retained austenite. A processing window was established according to the results of the kinetics of the isothermal transformation. The results show that the processing window for ADI alloyed with Cu and Ni at 350 degrees C was relatively wide, while the processing window for the isothermal transformation at 400 degrees C becomes narrower and shifted to the left. The processing window of ADI austempered at 300 degrees C is also narrower, but shifted to the right towards the longer times compared to the processing window of ADI austempered at 350 degrees C

Tensile properties of ADI material in water and gaseous environments

Austempered ductile iron (ADI) is an advanced type of heat treated ductile iron, having comparable mechanical properties as forged steels. However, it was found that in contact with water the mechanical properties of austempered ductile irons decrease, especially their ductility. Despite considerable scientific attention, the cause of this phenomenon remains unclear. Some authors suggested that hydrogen or small atom chemisorption causes the weakening of the surface atomic bonds. To get additional reliable data of that phenomenon, in this paper, two different types of austempered ductile irons were tensile tested in various environments, such as: argon, helium, hydrogen gas and water. It was found that only the hydrogen gas and water gave a statistically significant decrease in mechanical properties, i.e. cause embrittlement. Furthermore, the fracture surface analysis revealed that the morphology of the embrittled zone near the specimen surface shares similarities to the fatigue micro-containing striation-like lines, which indicates that the morphology of the brittle zone may be caused by cyclic local-chemisorption, micro-embrittlement and local-fracture