Investigation On Ultimate Loads Of Notched HDPE Pipes

High density polyethylene(HDPE)pipes are widely used in chemical and petrochemical,nuclear plant,urban construction and other industries.The damage research about HDPE pipes has been the focus of many industries.This work aims at studying the ultimate load and damage behavior of notched HDPE pipes by burst testing,tensile limit experiment and finite element analysis.The burst experiments are performed by a general burst testing system and a pair of sealing caps are designed for notched HDPE pipes that three types notches including U-type,V-type and L-type.The evolution of the pressure in function of the time and the burst pressures with different notches and depths can be got from the experimental data.Results indicate that the notch shape and depth have important influence on the burst pressures of HDPE pipes.Generally,the notch type impact extent from low to high in order is L-type,V-type and U-type,this indicates that the groove with the larger volume reduces the burst pressure of notched HDPE pipes more remarkably under the same depth condition.The burst pressure obviously decreases with the increment of the notch depth.When the notch depth is relatively shallow comparing with the wall thickness,the HDPE pipes have good fracture toughness.The tensile limit of HDPE rings under different notch shapes and depths are also researched in this work.The results show that the L-type notch has the least impact on the tensile ultimate load of HDPE ring,the tensile limit force of U-type and V-type HDPE rings are relatively close.The limit load decreases with the increase of the notch depth.Moreover,the creep and fatigue experiments of the HDPE rings show that the notch shape and depth have a deep influence on the life of the HDPE pipes.The burst pressure of HDPE pipes and the limit load of HDPE rings can be compared through dimensionless processing.The results show that the strength reduction factor of the two tests are relatively close,and a simple and safe notch tensile experiment can be used instead of the complex and dangerous test under some cases.A functional relationship between the intensity reduction factor and the depth ratio is derived by the experiment data,it can be used to predict extreme load of HDPE pipes.The stress-strain curve can be obtained from test and be used to simulate the ultimate pressure and load of notched HDPE pipes.The results of simulation are in good agreement with the experiment values,and the blasting and tensile failure of notched HDPE pipes occurs from the outside to inside.The ultimate load of L-type notched HDPE pipes were derived by combining tangential stress formula of U-type defect and the stress intensity factors of single edge crack.Based on the Linear Miner Damage(LMD)model,the unified theory and used the pressures instead of the stresses,a unified damage assessment model is proposed to predict the damage behavior of notched HDPE pipes,and it agrees well with the experimental data.The LMD model overestimates those damage factors of notched HDPE pipes.