**2. Low-cycle symmetric three-point bending of a beam with edge notch**

In the performed tests, the effect of various loading conditions, change in the geometry of a specimen, and preliminary plastic strain of material from which the specimens were made on the process of damage accumulation were studied. The attempt was made to determine parameters, which may be extended from the particular cases considered in the tests, to more general loading conditions. A possibility for description of regularities of damage accumulations with the aid of simple analytical functions involving constants just as determined from experiments, so specific for every material is considered.

The specimens were made from aluminum alloy D16T in the original state, so from preliminary stretched materials with the various degrees of plastic strain. The composition of the D16Т alloy is as follows: Al was as a base metal, the alloying elements were Fe (0.3%), Si (0,19%), Mn (0.76%), Cu (4.0%), Mg (1.29%).

The experiments were conducted on electromechanical testing machine (the rated capacity load was 100 kN). The loading was repeated three-point bending with unloading and it was given by travelling of a moveable cross-head with a constant velocity. Loading diagrams were recorded at each loading cycle.

The minimum force of a cycle was min *P* ≈ 0 for all the conducted tests. The maximum force of a cycle *P*max was considered in three forms: *i*) *P const* max = (stationary low-cycle loading), *ii*) *P PN* max max ≡ ( ) was increasing step-function of *N* for which the number of cycles at one step was constant (non-stationary low-cycle loading with increasing load), and *iii*) *P PN* max max ≡ ( ) was analogous decreasing step-function. The *P*max value in all tests was chosen to provide plastic material deformation ahead of the notch tip. Tests under stationary cyclic loadings were conducted for different *P*max values in the range from the limit of elasticity to the strength limit of a specimen. Besides, tests with different notch depth to beam height ratios were conducted.

Increment of the residual deflection δ δ *w wN* = ( ) depends on the cycle number. The increment of the δ *w* deflection arises mainly due to mechanical properties of material in a pre-fracture zone near the notch tip, and therefore, as it was said before, it is considered as a measure of damage increment in this zone. The increment is considered to achieve the limit \* *<sup>w</sup>*value if subsequent deflection of the beam proceeds without increase in *<sup>P</sup>* .
