Paper has both elastic and plastic materials. When it receives an external force, its deformation has the following characteristics:
The elongation of the paper increases with the load, but the stress and strain are not proportional. When the load increases to a certain extent, the increase of the elongation will be faster than the increase of the load. This shows that the paper is initially an elastic object that begins to have plastic deformation after a certain deformation.
The paper can continuously stretch or creep under a certain load. When the load increases until the paper has undergone plastic deformation, if the load is kept constant, the paper will continue to undergo plastic deformation until it breaks. This delayed plastic deformation is called creep.
When the rate of increase in load is increased, the load value at break increases and the elongation decreases. When the load is increased slowly, the compound value at break decreases and the elongation increases.