【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20190714

The difference between relaxation and creep is that in creep, the stress remains constant while the strain is a variable that changes over time； In relaxation, strain is constant, while stress is a variable that changes over time.

The difference between relaxation and creep is that in creep, the stress remains constant while the strain is a variable that changes over time； In relaxation, strain is constant, while stress is a variable that changes over time.

The difference between relaxation and creep is that, in creep, the stress remains constant； And in relaxation, the strain is constant.

The difference between relaxation and creep is that in creep, the stress remains constant while the strain is a variable that changes over time； In relaxation, strain is constant, while stress is a variable that changes over time.

Creep: The strain increases over time under constant stress. Stress relaxation: Under constant stress, the strain decreases over time. Creep: The phenomenon in which the strain of a solid material increases over time while the stress remains constant. It is different from plastic deformation, which usually occurs only after the stress exceeds the elastic limit, whereas creep can occur even when the stress is below the force required to reach the elastic limit, as long as the stress is applied for a sufficient length of time. Many materials (such as metals, plastics, rocks, and ice) exhibit creep properties under certain conditions. Due to creep, the stress state of a material at a given instant is generally related not only to the deformation at that instant but also to the deformation processes that have taken place prior to that instant. Many engineering problems involve creep. In materials that maintain a constant deformation, the stress decreases over time; this phenomenon is known as stress relaxation, and it can be regarded as a form of creep. 　　Stress relaxation: In materials subjected to a constant deformation, the stress decreases over time; this phenomenon is known as stress relaxation, and it can be considered a form of creep. 　　Measuring the stress relaxation curve is the experimental basis for determining the relaxation modulus. In fastening components under high temperatures, the elastic pre-tensioning stress within them diminishes over time, which can lead to sealing leaks or loosening. The relaxation process also causes the internal forces in statically indeterminate structures (see structural mechanics) to redistribute over time. Eliminating residual stresses using vibration methods involves accelerating the relaxation process in order to remove the internal stresses caused by inconsistencies in the deformation of the material’s microstructure. The process in which the velocity gradient of a flowing viscoelastic fluid is reduced or suddenly brought to zero, causing the stress in the fluid to gradually decrease or disappear, is also known as stress relaxation. 　　Stress relaxation phenomenon: The packing tape loosens, and the rubber band loosens

High-temperature creep refers to the phenomenon in which, under the combined action of high temperature and stress with constant stress, the amount of inelastic deformation of a metal increases slowly over time. High temperature, stress, and time are the three essential factors for creep to occur. The greater the stress and the higher the temperature, and the longer the exposure time at high temperatures, the more severe the creep becomes. Stress relaxation refers to the phenomenon in which metal components operating at high temperatures, under the condition of constant total deformation, see their elastic deformation gradually transform into inelastic deformation over time, thereby causing the stress in the metal to decrease gradually and approach a stable value. Similarities and differences: Creep and stress relaxation are essentially the same; both represent a process of cumulative inelastic deformation in materials over time at high temperatures. The difference is that stress relaxation involves the conversion of some of the elastic deformation into inelastic deformation under the specific condition that the total amount of deformation remains constant ； Creep, on the other hand, results in inelastic deformation under the long-term action of a constant stress.

Creep: The strain increases over time under constant stress. 　　Stress relaxation: Under constant stress, the strain decreases over time.

The difference between relaxation and creep is that in creep, the stress remains constant while the strain is a variable that changes over time； In relaxation, strain is constant, while stress is a variable that changes over time.

In creep, the stress is constant; stress is a variable that changes over time, whereas in stress relaxation, the strain is constant

Creep: The phenomenon of slow plastic deformation that occurs in steel when it is subjected to a constant temperature and constant stress over an extended period of time (even if the stress is less than the yield strength). General rule: Creep consists of three typical stages: the unstable creep stage, the stable creep stage, and the failure stage ； The higher the temperature and the greater the stress, the more pronounced the creep becomes. Stress relaxation: The phenomenon in which, when steel is under stress at high temperatures, the stress within the material gradually decreases while maintaining a constant total deformation. Essentially, it is a transformation of some elastic deformation into plastic deformation, whereas creep is the cumulative effect of slow plastic deformation over time.