Jelena M. Djoković

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.

Characteristic Parameters of Dynamic Crack Growth along the Interface between the Two Orthotropic Materials

In this paper is analyzed the behavior of parameters that characterize the process of a dynamic crack growth along the interface between the two orthotropic materials. The emphasis is placed on the application of the fracture mechanics concept for the interfacial crack that propagates dynamically, at high speed. In this work is considered the behavior of the oscillation index, the traction resolution factor and the energy factor depending on the crack tip speed and the stifnesses ratio. The oscillatory index increases with the crack tip speed and tends to infinity when the crack speed approaches the Rayleigh wave speed of the less stiff of the two materials. The traction resolution factor depends strongly on the crack speed but weakly on the stiffness ratio. The behavior of the energy factor is completely different from the behavior of the traction resolution factor. Results provided in this paper can be used as a guide for micromechanical modeling of materials.

Screening Efficiency Analysis of Vibrosieves with the Circular Vibrations

Abstract The analysis of influence of factors that depend on construction characteristics of the vibrosieves with circular vibrations on screening efficiency is presented in this paper. The dependence of the screening efficiency on the aperture size, length and inclination of the screen, as well as on vibration amplitude, is considered. Based on obtained results, one can see that the screening efficiency increases with vibration amplitude and the screen length increase. Further, increases of the screen inclination and aperture size are causing an initial increase of the screening efficiency, which is later decreasing.

Criteria for Prediction the Interfacial Crack Growth in Concrete

To understand the mechanical behavior of the concrete structures, one must analyze deformation and fracture of the interfaces between the constituents of the material that the structure is made of. Criteria for predicting the crack growth along an interface, based on the linear elastic fracture mechanics concept, applied for the cement substrate/aggregate interface, are presented in this paper. The two possible directions of the interfacial crack growth – the crack propagation along the interface and the crack kinking away from the interface are considered, with the corresponding energy release rates. For the case of the crack approaching the interface from one of the materials – cement, the competition between the crack deflecting into the interface and the crack penetrating the interface is considered with the corresponding energy release rates.

Optimization of the Sandwich Column with the Truss Core Which is Subjected to the Compressive Loading

Abstract The sandwich structures have multifold advantages with respect to other types of structures. Besides the architectural possibilities due to their appearance, those structures can carry the same or even higher loads than some other similar structures. Optimization of the sandwich columns with the truss core, subjected to the compressive axial load, is presented in this paper. The two types of optimization were performed: the three-parameter and the four-parameter optimization - the so called full optimization. The optimization of the column geometry (face thickness, core member height and core member diameter and core height) was performed, from the aspect of the minimal weight of the structure in terms of the load index. It was performed for four types of restrictions imposed by the corresponding column failure modes: column buckling, truss macro-buckling, local buckling of the face and face wrinkling. The tree-parameter optimization resulted in somewhat larger weight of the column than the full, four-parameter optimization.

Impact of the Weld Geometry on the Stress Intensity Factor of the Welded T-Joint Exposed to the Tensile Force and the Bending Moment

Abstract In this paper it is analyzed the welded T-joint exposed to the axial tensile force and the bending moment, for determining the impact of the weld geometry on the fracture mechanics parameters. The stress intensity factor was calculated analytically, based on the concept of the linear elastic fracture mechanics (LEFM), by application of the Mathematica® programming routine. The presence of the weld was taken into account through the corresponding correction factors. The results show that increase of the size of the triangular welds leads to decrease of the stress intensity factor, while the SIF increases with increase of the welds’ width. The ratio of the two welded plates’ thicknesses shows that plate thicknesses do not exhibit significant influence on the stress intensity factor behavior.