Effect of uncertainty parameters on graphene sheets Young’s modulus prediction

Software based on molecular structural mechanics approach (MSMA) and using finite element method (FEM) has been developed to predict the Young’s modulus of graphene sheets. Obtained results have been compared to results available in the literature and good agreement has been shown when the same values of uncertainty parameters are used. A sensibility of the models to their uncertainty parameters has been investigated using a stochastic finite element method (SFEM). The different values of the used uncertainty parameters, such as molecular mechanics force field constants k _r and k _θ , thickness (t) of a graphene sheet and length (L _B ) of a carboncarbon bonds, have been collected from the literature. Strong sensibilities of 91% to the thickness and of 21% to the stretching force (k _r ) have been shown. The results justify the great difference between Young’s modulus predicted values of the graphene sheets and their large disagreement with experimental results.     

Investigating on performance parameters and flow field of centrifugal compressor based on the splitter blade leading edge’s location effect

Impeller design in turbomachines is one of the most challenging issues in these machines’ systems, which still plays a significant role in their efficiency and performance. This article considers different designs for splitter blades. Therefore, the CFD methods modify the position of the splitter blades leading edge at the hub and shroud. This modification shall lead to a different splitter blade profile from the main blades. Then, the effects of splitter blades are discussed, and the performance parameters have also been studied to improve this method’s implementation. The results revealed that the compressor’s efficiency was improved by approximately 1.5 % in one specific case. This finding proves that the previous design methods were not the optimum ones for compressors and how to increase the compressor’s efficiency by CFD methods and by changing the splitter blades’ location.

     

Effect of welding seam spacing and relative bar wall thickness of bus framework on joint’s local mechanical property

Now the researches concerning integral bus mainly focused on design and analysis of overall mechanical property of bus body,and paid little attention to characteristic of local structures,such as joint,plug welding hole,and bolt connection point,etc.So there is much blindness on the design of local connecting structure.Since integral bus body structure cancels large section longitudinal beam,and uses framework made by welding small section bars together as principal part to bear the whole load when the vehicle works,there are many joints receiving high load in the body structure,and local stress concentration can not be avoided.Under such circumstances,by adopting beam-shell mixed model based on super element technique,and selecting a joint commonly used by bus sidewall,the rule of the effect of bar joint’s welding seam spacing on joint’s local mechanical property is investigated in this paper,and the investigating results show that joints have minimum stress concentration with welding seam spacing of 8 mm.To learn whether the above rule is affected by relative bar wall thickness,many groups of bars with different relative bar wall thicknesses are studied experimentally,and the experimental results show that the joints local stress levels vary with different relative bar wall thicknesses,but the rule of the effect of bar joint’s welding seam spacing on joint’s local stress level remains the same.The research is significant for local structure design of bus joint in the future.