Thread Content
Under internal pressure, a thick-walled cylinder experiences uneven stress distribution within its wall, with the inner wall experiencing higher stress than the outer wall. To improve this uneven stress distribution within the cylinder, it is possible to subject the thick-walled cylinder to overpressure treatment prior to its use. Under strictly controlled overload pressures, the inner layer of the cylinder undergoes plastic deformation, forming a plastic zone, while the outer layer of material remains in an elastic state. After maintaining this pressure for a period of time and then releasing it, the portion of the inner layer of the cylinder that has undergone plastic deformation cannot return to its initial position due to residual deformation. The outer layer of material, which is still in the elastic stage, tends to return to its original state, but it is prevented from doing so completely by the inner layer material that cannot revert to its original condition. Thus, a prestressed state is formed within the cylinder wall, with the inner layer under compression and the outer layer under tension. When the cylinder is put into operation and subjected to operating pressure, the tensile stress resulting from this pressure – which is higher on the inside and lower on the outside – combines with the prestress created during preprocessing, which results in internal pressure and external tension. This leads to a reduction in the stress levels on the inner wall, which originally had higher stress levels, while the stress levels on the outer wall, which originally had lower stress levels, increase slightly. The stress distribution along the wall thickness becomes more uniform, thereby enhancing the cylinder’s yield strength. This treatment method, which involves controlled overpressure to cause only the inner layer to yield while the outer layer remains elastic, and utilizes the elastic contraction of that outer layer to generate prestress thereby improving the load-bearing capacity of the cylinder, is known as self-reinforcement of thick-walled cylinders.