The Bauschinger effect or Bauschinger effect is a phenomenon occurring in metals and alloys that undergo deformation and then after annealing effects also develop an opposite force from the original load. It was first observed by Johann Bauschinger in 1865. The Bauschinger effect is important for materials which are subjected to cyclic loading.
The Bauschinger effect is due to the internal stresses existing in the material on account of its plastic deformations, and can also appear in the form of a change in the metals electrical or magnetic properties. In the case of a metal under cyclic loading, a certain amount of deformation accumulate and need to be relieved. On releasing the pre-stressing force, the ability of the metal to deform further decreases, leading to an increase in the modulus of resilience. This phenomenon is due to the formation of a hardening phase such as martensite, for instance, in steels.
The Bauschinger effect also causes an increase in the resistance to plastic deformation of alloyed steels. This is because the plastic deformations produce a harder material as compared to the virgin material. The Bauschinger effect indicates that in tension the yield strength of the same material decreases after being subjected to repeated stressing cycles in compression. As the yield strength decreases so its ductility increases.
The Bauschinger effect is caused by a combination of two factors: intergranular shear-induced slip, and athermal reversal (the lack of material heat up during plastic deformation). The combination of these factors creates internal stresses that reduce the local elastic modulus, which causes a decrease in the materials yield strength and an increase in its ductility. Further, the same factors cause intergranular shear to occur in order to relieve the internal stress in the material.
In order to understand the effect of Bauschinger on reinforcing steel bars, it is important to consider the characteristics of the steel, such as its composition and the environment in which it is used. The Bauschinger effect is the change in the mechanical properties of steel strain, due to cyclic loading. It is caused by the rapid, reversible plastic deformation of the material under cyclic load, which is followed by strain hardening.
This strain hardening effect is caused by the rapid, reversible plastic deformation, which creates a wide range of stresses/strains in the material, that result in a decrease in the material’s ductility and an increase in its yield strength. As a result, it has been found that the strength of a steel bar subjected to cyclic loading can increase significantly and thus can lead to the failure of the steel bar due to the forming of cracks.
The effects of Bauschinger are considered to be an important aspect when manufacturing or using reinforcing steels due to its potential for structural failures. It is particularly important for reinforced steel bars in compression, such as in precast concrete where the bars may be subjected to repeated load cycles. In these cases, the load is applied periodically, and the deformation induced by the load is frequently reversed, leading to an increase in the yield strength of the steel and a decrease in its ductility.
In order to reduce the effects of Bauschinger on steel bars, several methods can be employed. One is to use low-carbon steel bars of greater ductility to minimize internal stress, which helps to prevent cracking and thus reduce the effects of Bauschinger. Additionally, the use of stress-relief treatments between each stress cycle can prove beneficial. This ensures that the internal stresses are relieved to a certain extent and the ductility of the steel is restored.
The manufacturing process and working environment can, of course, also influence the effects of Bauschinger on steel bars. For instance, the use of pinning joint, or welding can reduce the amount of stress exerted on steel bars, as this is necessary for achieving a mechanically secure and rigid joint. Additionally, an appropriate temperature must be maintained during the manufacturing and loading process, as higher temperatures can cause the formation of hydrogen embrittlement in steel bars, which reduces the steel’s ductility.
In conclusion, the Bauschinger effect is an important phenomenon for reinforced steel bars, as it can have a significant effect on its mechanical properties. The effects can be reduced by ensuring the steel bars are of high quality and that the temperature is appropriately controlled during manufacturing, loading and cycling of the bars. Additionally, stress-relief treatments, pinning joints, or welding should be used to reduce the amount of stress exerted on steel bars while they are being used.
