Statement 1: To test a brittle material, maximum principle stress theory is suitable.
The maximum principle stress theory is a failure criterion used to predict the failure of brittle materials, such as ceramics or glass. According to this theory, failure occurs when the maximum principal stress in a material exceeds its tensile or compressive strength.

Brittle materials have very low ductility and fail suddenly without any significant deformation. They have high compressive strength but low tensile strength. The maximum principle stress theory is suitable for these materials because it considers the maximum stress in the material, which is likely to be the controlling factor for failure.

When a brittle material is subjected to an external load, it develops tensile and compressive stresses within it. The maximum principle stress theory states that failure will occur if the maximum of these stresses exceeds the material's strength. Since brittle materials have low tensile strength, failure is likely to occur when the maximum principal stress reaches a critical value.

Statement 2: Maximum Principle stress theory is not good for mild steel body.
Mild steel is a ductile material that exhibits both plastic deformation and significant elongation before failure. It has high tensile strength and can withstand large amounts of deformation before failure. The maximum principle stress theory is not suitable for mild steel because it does not consider the material's ability to undergo plastic deformation.

In mild steel, failure occurs due to excessive plastic deformation rather than the maximum stress reaching a critical value. The material can undergo significant elongation and strain hardening before failure, and the maximum principle stress theory does not account for this behavior.

The suitable failure criterion for mild steel is the maximum shear stress theory or the von Mises yield criterion. These criteria consider the shear stress and the material's ability to undergo plastic deformation.

Conclusion:
In conclusion, the maximum principle stress theory is suitable for testing brittle materials that fail suddenly without significant deformation. However, it is not suitable for mild steel, which is a ductile material capable of undergoing plastic deformation before failure.