The whole process can be divided into three stages: the stage of no cracking, the stage of crack and the stage of failure.

First stage - uncracked stage

At the moment is small, concrete strain across the beam section along the beam height measured as a linear relationship, and the strain value is small, in line with the plane section assumption beam; the strain of tensile reinforcement and CFRP strain is smaller and measured, reinforcement beam and RC beams is similar to that of compression zone and concrete tensile stress distribution graph of triangle.

With the increase of bending moment, because the tensile strength of concrete is far less than the compressive strength, the stress of concrete in the tensile area increases faster, and the concrete enters the plastic stage. The stress figure in the tensile area is shown as a curve shape. When the moment at the cracking moment, concrete tensile strain reaches ultimate tensile strain, cross section is in a state of compression zone of concrete cracking, the compressive stress is much less than its compressive strength, compressive concrete basically in elastic phase, compressive stress figure close to the triangle distribution.

The second stage - the crack stage

When the tensile strain of the tensile area exceeds the ultimate tensile strain, cracks appear in the weak section of the concrete in the tensile area. The tensile stress of the concrete at the crack is transferred to the reinforcing bar and the carbon fiber cloth. At that time, the stress of the reinforcing steel and the stress of the carbon fiber cloth suddenly increase. With the increase of bending moment, cracks continue to expand, and the position of neutral axis moves upward. The tensile stress in tensile area is mainly subjected to reinforcement and carbon fiber cloth. The concrete in compression zone develops to plastic deformation, and the stress figure in compression area is curvilinear.

The third stage - the stage of destruction

As the bending moment continues to increase, when the tensile stress reaches the yield strength, the increment of tensile stress at the crack section is mainly borne by CFRP. The bending moment continues to increase, the crack continues to expand, the neutral axis position continues to move upward, the compression area height further decreases, the compressive stress concrete increases, the concrete plasticity characteristic is more obvious, the compression area stress graph's curve distribution is quite full. When the concrete strain of the compression zone reaches the limit strain, the crushed concrete is crushed, which marks the failure of the reinforced beam.