Abstract: In this paper, the displacement and strain fields around double edge cracks are measured for different hardening materials (the strain hardening exponents n = 3.350→ 9.180) using optical methods (in-plane moire and projected moire methods). The experimental singularity fields are analyzed and compared with HRR theoretical solution. The experimental HRR singularity fields around crack-tip are obtained and their distribution with different loading and hardening exponents are discussed.