In this work, homogeneous thermochemical co-precipitation method was used to fabricate W-25wt%Cu nanocomposite. Synthesized nanocomposite powder was calcined and reduced. A hydrogen atmosphere sintering at 1200oC for 105 consolidated the product up to a density close to 98% theoretical density. Wear experiment were carried out using a pin-ondisc set up at three normal loads of 5, 10 and 15 N and the dissipated energy was calculated in each case as a funsction of wear distance. Evalustion of the slope of the “dissipated enargy-wear distance” plot demonstrated the constancy of this slope at each certain normal load. However, the steepness of this slope, was in direct relation with the magnitude of the normal load (a J/m for 5N, b J/m for 10N and c J/m for 15N), demonstrating the higher potency of larger normal loads for injecting energy and thus, wear damage to the material. According to this constant slope of this plot at each normal load, constancy of the wear mode under each loading condition can be ruled out. Simultaneous consideration of mechanical and microstructural parameters of wear revealed that the dominant wear mode in all loading conditions was fatigue wear and the corresponding active wear process was delamination. Formation of sub-surface cracks and gradual degradation of the worn surface by flaking off, were of importance in the evolution of this type of wear damage. تفاصيل المقالة

High speed wind tunnels are widely used in the study of fluid flow behavior around various objects. The air flow in the starting step of supersonic wind tunnels is transient including strong shock waves caused by the interaction of the tunnel main stream and the boundary layer at walls. To arrive in running step, the tunnel must be designed so as these waves leave immediately the test section. Otherwise, they will hinder the air flow through the tunnel. Accordingly, as a clear practical fact, the tunnels unable to pass the starting step are considered as unusable.In this paper, a 3-D computational fluid dynamic analysis of the starting stage of a supersonic wind tunnel with a target Mach number of 3 is performed. The results obtained in this work are in agreement with the expected physical behavior of the flow field and can be applied as the design criterion of the high speed wind tunnels. تفاصيل المقالة

Wear is a complicated phenomenon caused by the relative movement of two contacting surfaces compressed together by a normal force. Prediction of the wear, in most cases, requires various experiments and microstructural characterization of the contacting surfaces. Mathematical models based on physical concepts could provide considerable help in understanding the physical behavior and hence the prediction of this phenomenon. Considering the importance of the generated heat in wear, it seems that thermodynamic parameters are suitable measures for wear modeling proposals. One of these thermodynamic parameters is entropy, the rate of generation of which is mathematically modeled for the sliding wear in this work. For this purpose, experimental wear data from two different materials, namely, Steel 4140 and 70-30 Brass were also considered. The results showed a direct relation between the wear depth of 70-30 Brass and the generated entropy. Moreover, a linear relationship was observed between a number of parameter pairs such as 70-30 Brass temperature – rate of entropy generation, wear depth – transferred heat to 70-30 Brass, wear depth – dissipated energy, and rate of entropy generation – dissipated energy. The wear rate also showed a linear relationship with the 70-30 Brass temperature and the rate of entropy generation. The linearity of the “wear depth – rate of entropy generation” suggests the rate of entropy generation as a decent criterion for the prediction and design of the tribo-systems. تفاصيل المقالة