Research On The Winding Layer Stress Damage Mechanism Of CNG-2 Type Cylinder

CNG-2 cylinder are consisted of steel inner and outer winding layer composite material.The cylinder in the auto-frettage process the resin will be have some degree of racking,and will arise some circumferential cracks in the process of charging and discharging gas.Thus the wounding layer material is more susceptible to be corrode in an acidic environment.The cylinder is maintain a certain internal pressure while daily using,the high pressure let the winding layer has certain internal stress.The stress corrosion cracking is caused by both the effect of stress and corrosion.The cylinder wound layer composite is a unidirectional fiber composite,traditional method of research on cylinder mechanics is regard the mechanical properties of the cylinder winding layer as a homogenisation-based material,study by the macroscopic mechanical to research.But under the cylinder working pressure,the yield strength and breaking strength of the winding layer are far greater than the stress exist,the mechanism of resin cracking and stress corrosion cracking of winding layer can not be studied by macroscopic mechanics.To solve this problem,in this paper,firstly,the winding layer of new production cylinder and the cylinder which scrapped due to the stress corrosion cracking of the winding layer are sampled respectively,then the morphology of the failure was observed under scanning electron microscopy(SEM).Based on the observe damage morphology of the wound layer,a multi-scale modeling for gas cylinder is established.Using the multi-scale model,study the influence of the gel content and the fiber diameter which are the two important design parameters on the cracking degree of the composite resin,discussed by micro-mechanics;then the influence of circumferential crack on stress corrosion crack growth is studied;then the damage mechanism of stress corrosion cracking was studied on the basis of the multi-scale model.In this paper,the damage mechanism of the winding layer of gas cylinder is studied by the way of micro-mechanics method of composite materials,experiments show that the multi-scale model of gas cylinder is practicable in gas cylinder simulation.At the same time,the influence factors of resin cracking and the failure mechanism of stress corrosion cracking is well be revealed,all of this are provide a good theoretical reference to design the winding of CNG-2 type gas cylinder and control the force of winding.