Introduction: Low resistance of composite resins to abrasion is a primary concern in the application of these materials for posterior restorations which are prone to high occlusal loads.This study compared the Wear resistance of three types of composites.Methods: In this laboratory experiment, five specimens of each of the three types of composites (z250, Heliomolar, Opallis) were prepared separately in brass molds. Composites were placed in 1-mm layers and were cured for 40 seconds. Using an abrasive device, Pedeb 1, with a chromecobalt abrasor, the specimens were abraded under a 20-MPa force, after 5000, 20000, 40000, 80000, 120000 abrasive rotations. Before and after all abrasion cycles, the specimens were weighed with an electronic balance with a precision of 10-4 g. The collected data were analyzed using paired samples statistics t-test and ANOVA analysis.Results: All the specimens showed a reduction pattern from the initial weights to weights after 120000 abrasive rotations. With more abrasive rotations, greater weight reduction occurs and this is of statistical significance. ANOVA analysis showed no significant difference between the three types of composites; yet, the z250 and Heliomolar groups were associated with the least and the greatest amount of Wear, respectively.Conclusions: In all specimens, significant weight reduction occurred after abrasion but there were no significant differences between the 3 types of composites.

Wear damage is a common failure in engine bearing shells. Wear failure induces changes in the bearing geometry and affects the oil film pressure and the durability of bearing shells. In this paper, Wear failure in journalpin (main) bearings of a reciprocating engine is studied. Using a dynamic model, forces and torques in the journalpin bearings have been calculated and used in the analysis. To calculate the lubricating characteristics of the bearing, such as minimum oil film thickness and maximum oil film pressure, the Elasto-HydroDynamic (EHD) model that incorporate mass conservation algorithms is utilized. Wear failure in journalpin bearings of a reciprocating engine is assessed and the results are presented. Archard’s model is used as a Wear model of journalpin-bearing material. The asperity interaction of two rough surfaces is considered by the boundary lubrication model. The results show that the Wear rate at the initial stage of engine running is high. The results indicate that the main reason for Wear in the journalpin bearings is the applied torque on the bearing, leading to edge Wear. In a V-12 or 6Inline engine, journalpin bearing number 4 has the highest amount of torque applied and therefore has the highest amount of Wear.

An investigation of the friction and sliding Wear of gray cast iron against chromium plated cast irons was carried out on a newly constructed reciprocating friction and Wear tester. The tests were the first to be done on the test rig under dry conditions and at the speed of 170 cm/mm and variable loads of 20-260 N for duration of 15 min to 3 hours. The gray cast iron surfaces worn by a process of plastic deformation at the subsurface, crack nucleation, and crack growth leading to formation of plate like debris and therefore the delamination theory applies. No evidence of adhesion was observed. This could be due to formation of oxides on the Wear surface which prevent adhesion. Channel type chromium plating picked up cast iron from the counter body surfaces by mechanically trapping cast iron debris on and within the cracks. The removal of the plated chromium left a pitted surface on the cast iron.