Dragoslav Šumarac

Analysis based on the energy release rate criterion of a dynamically growing crack approaching an interface

A problem of a dynamically growing crack, which is approaching an interface between the two elastic isotropic materials at an arbitrary angle, is considered in this paper. That crack could behave in three ways: (i) it can arrest at contact with the interface, (ii) it can deflect into the interface and continue to propagate along it or (iii) the crack can penetrate the interface and continue to propagate in the material across it. The competition between the latter two cases can be estimated by considering the ratio of the energy release rates necessary for the crack penetrating the interface and for the crack deflecting into the interface. A concept that the criterion for the dynamic crack growth in homogeneous solids could be based on the static stress field, with addition of the stress intensity factor dependent on time, is used here to explain the behavior of the crack approaching the interface in dynamic loading conditions. Obtained results enable comparison of the interface dynamic fracture toughness to the fracture toughness of the base material (without the interface), to determine whether the incoming crack would deflect into or would penetrate the interface. If the ratio between the dynamic fracture toughness of the interface and the dynamic fracture toughness of the material into which the crack continues to propagate was less than the ratio of the dynamic release rates for the deflecting and penetrating crack, the incoming crack would deflect into the interface. If the case was reversed, the crack would cross the interface and continue to propagate in the material across it. Comparison of results for the load phase angle dependence on the crack tip propagation speed and on the approaching angle, obtained by this criterion and by the maximum stress direction criterion, proves the validity of the energy release rate concept adopted in this analysis.

Elastoplastic and Damage Analysis of Trusses Subjected to Cyclic Loading

In the present paper, the Preisach model of hysteresis is extended to structural analysis of trusses damaged under cyclic loading in plastic range. Parameters for the Preisach model of cyclic plasticity are obtained from uniaxial loading experiment. Damage, as a consequence of micro cracks appearance due to alternating loading in plastic domain, is modeled using brittle elements according to Preisach procedure. Results of this research are compared with the already existing in the literature. In the paper examples of trusses under various cyclic loadings are presented.

Cyclic Plasticity with an Application to Extremly Low Cycle Fatigue of Structural Steel

In the present paper the Preisach model of hysteresis is applied to model cyclic behavior of elasto-plastic material. The problem of axial loading of rectangular cross section will be studied in details. Hysteretic stress-strain loop for prescribed history of stress change is plotted for material modeled by series connection of three unite element. All obtained results clearly show advantages of the Preisach model for describing cyclic behavior of so called stable plastic material. Other effects such are racheting and creep will be studied elsewhere. In this paper extremely low cycle fatigue will also be examined. Extremly low cycle fatigue stands for number of cycles to failure in between 10 and 20. The stress level is larger than the yield stress and the plastic strain is of the same magnitude as the elastic strain. In this paper it is shown that this case is of importance to dampers applied for reconstruction of earthquake damaged structures.

Damage Control and Repair for Security of Buildings

Civil engineering objects, especially buildings, suffer the damage and failure under earthquake. Invented DC Damper System can increase the resistance and strengthen the construction, enabling tougher behaviour under seismic load. Experimental research and experience in repairing 350 damaged objects on four continents is the base for system development.