Fractal dimensional evolution in the crazing PMMA under creep

The modified fractal dimension was imposed by the area transformation under the condition of finite deformation. It proved that the area deformation has little influence on the fractal dimension if the strain is less than 20%. The fractal dimensions of crazing images with different tensile stresses and acting time obtained by creep testing of PMMA were calculated by box-counting method. In the test the critical stress of crazing initiation decreases in exponential form with the creep time and tends to be constant at last. The fractal dimensions of creep crazes increases linearly with the tensile stress and in exponential form with the creep time. As the tensile stress is greater than the critical, a mass of crazes are formed instantaneously, which makes a step change in the fractal dimension of crazes. On the base of the testing results, the relation among the fractal dimension, tensile stress and creep time is obtained.