Strength calculation of pressure vessel materials

When the specimen is still under load, the plastic deformation (the non proportional extension rate) of the specimen is up to 0.2%. The material of Rr0.2, tensile test, load bearing reached a certain point when unloading, the specimen has elastic deformation of the specimen and disappear, residual plastic deformation (residual elongation) just equal to the gauge length of the sample is 0.2%. at the point of stress is Rr0.2.
One of the basic rules for the strength calculation of the pressure vessel is that the whole (shell, etc.) of the container should be controlled and the plastic deformation can not be produced, so the strength index of Rp0.2 as the material is appropriate. As for the factors of container unloading containers after whole residual plastic deformation is not the pressure vessel must be controlled, with Rr0.2 as the control index of material strength is obviously better than using Rp0.2 as the control index of material strength is more appropriate.
Rp0.2 is very easy to accurately measure the value of. From the origin of coordinates of the tensile curve, the length of the gauge length of 0.2% get a little on the deformation axis, parallel elastic line segments intersect with the tensile curve from this point, the intersection marked stress value is Rp0.2. and Rr0.2 is not accurate determination of the value of. The tensile specimen is loaded to a certain point, and the residual plastic deformation is equal to 0.2% of the length of the specimen. It is almost impossible to accurately determine the load point. GB/T228) 2002 in the specific provisions of the method for the determination of Rp and Rt, but there is no regulation method for determination of Rr, and provides only the verification method of Rr: / sample applied corresponding to the specified residual elongation strength (Rr) of the force, force 1012s, removable force after validation does not exceed the residual elongation the percentage of 0 to determine Rr0.2 can refer to Appendix 5 of the standard method for the determination of unloading force specified residual extension strength Rr0.2 for example 6, the process is more complex, but can only get the approximate value.
Our factory production of titanium in Rr0.2 inspection is qualified, generally measured Rp0.2. due to the same material Rr0.2 higher than Rp0.2, if the Rp0.2 value exceeds the prescribed limit of Rr0.2 index, the Rr0.2 can be considered qualified. This can only verify that the Rr0.2 is qualified, can not give the actual value of Rr0.2.
The United States materials with Rp0.2 and Rt0.5. in addition to China's titanium standard using Rr0.2, the pressure vessel has not seen other countries and other materials used in the case of Rr0.2. Standard Test Method for tensile America are ASTME8 and ASTMA370, the standard only used two kinds of conditional yield strength project, a name for the Yieldstrength, 0.2offse T; the other is Yieldstrength, only the name, the strength of the project in American Standard 0.5%extensionunderload. of different symbols, the two projects, with the symbol Rp0.2 and Rr0.5 in China, ISO is EN. The United States tensile test method standard does not correspond to the strength of the Rr0.2 project. It is believed that the standard of Chinese titanium material is not based on the Rr0.2 of American Standard.