Dear Sir,

I suppose you mean cracks in 3D Solid65 element. There are 3 directions of principal stresses. If the value of the maximum principal stress reaches the value of the material strength , the "first" crack forms; if the value of the average principal stress reaches the value of the material strength , the "second" crack forms and If the value of the minimum principal stress reaches the value of the material strength , the "third" crack forms. I think that this colors were chosen in order to show the difference between directions.

thank you so much for your kind response sir

The crack numbers represent the direction of the cracks along the x, y and z axes, respectively.

dear sedat komurcu sir, i want to know how can i relates all these 3 principal stress with my ANSYS results, what these stresses are incating in analysis part, does it relates to any maximum tensile or compressive stress of concrete or simply relates to any cracking efficiency of concrete model. i need the clear explanation about these 3 principal stress contours with respect to ANSYS contour results.

please clarify this query...

thank you,

Dear Sir,

You can find this stresses in results viewer.

The stress state in every point of the structure can be described by the stress tensor, which consist of 9 components - 3 normal and 6 shear stresses. These stresses depend on the chosen plan. However, you cand find plane, where all 6 shear stresses = 0. The normal stresses on this plane are called principal. For brittle and quasibrittle materials like a concrete, the failure of material starts, when the maximum principal stress reaches the value of the material ( tensile or compressive ) strength. And, it causes the crack formation process, as it was mentioned above.

https://en.wikipedia.org/wiki/Cauchy_stress_tensor#Stress_deviator_tensor

You can find more information about this in the continuum mechanics course.