Mechanical Properties of All MoS_(2) Monolayer Heterostructures:Crack Propagation and Existing Notch Study

The outstanding thermal,optical,electrical and mechanical properties of molybdenum disolphide(MoS_(2))heterostructures make them exceptional candidates for an extensive area of applications.Nevertheless,despite considerable technological and academic interest,there is presently a fewinformation regarding the mechanical properties of these novel two-dimensional(2D)materials in the presence of the defects.In thismanuscript,we performed extensive molecular dynamics simulations on pre-cracked and pre-notched all-molybdenum disolphide(MoS_(2))heterostructure systems using ReaxFF force field.Therefore,we study the influence of several central-crack lengths and notch diameters on the mechanical response of 2H phase,1T phase and composite 2H/1T MoS_(2) monolayers with different concentrations of 1T phase in 2H phase,under uniaxial tensile loading at room temperature.Our ReaxFF models reveal that larger cracks and notches decrease the strength of all 2D MoS_(2) single-layer heterostructures.Additionally,for all studied crack and notch sizes,2H phase of MoS_(2) films exhibits the largest strength.Maximum tensile stress of composite 2H/1T MoS_(2) nanosheet with different concentrations are higher than those for the equivalent 1T phase,which implies that the pre-cracked composite structure is remarkably stronger than the equivalent 1T phase.The comparison of the results for cracked and notched all-MoS_(2) nanosheet heterostructures reveal that the load bearing capacity of the notched samples of monolayerMoS_(2) are higher than the cracked ones.

Investigating peak stresses in fitting and repair patches of buried polyethylene gas pipes

Nowadays,polyethylene composes a large number of natural gas distribution pipelines installed under the ground.The focus of the present contribution is two fold.One of the objectives is to investigate the applicability of polyethylene fittings in joining polyethylene gas pipes which are electrofused onto the pipe ends and buried under the ground,by estimating stress distribution using finite element method.The second objective is to study the effectiveness of polyethylene repair patches which are used to mend the defected pipelines by performing a finite element analysis to calculate peak stress values.Buried polyethylene pipelines in the natural gas industry,can be imposed by sever loadings including the soil-structure interaction,traffic load,soil’s column weight,internal pressure,and thermal loads resulting from daily and/or seasonal temperature changes.Additionally,due to the application of pipe joints,and repair patches local stresses superimposed on the aforementioned loading effects.The pipe is assumed to be made of PE80 resin and its jointing socket,and the repair patch is PE100 material.The computational analysis of stresses and the computer simulations are performed using ANSYS commercial software.According to the results,the peak stress values take place in the middle of the fitting and at its internal surface.The maximum stress values in fitting and pipe are below the allowable stresses which shows the proper use of introduced fitting is applicable even in hot climate areas of Ahvaz,Iran.Although the buried pipe is imposed to the maximum values of stresses,the PE100 socket is more sensitive to a temperature drop.Furthermore,all four studied patch arrangements show significant reinforcing effects on the defected section of the buried PE gas pipe to transfer applied loads.Meanwhile,the defected buried medium density polyethylene gas pipe and its saddle fused patch can resist the imposed mechanical and thermal loads of 22℃ temperature increase.Moreover,increasing the saddle fusion patch length to 12 inches reduces the maximum stress values in the pipe,significantly.