A Fracture Criterion for Prediction of Fracture Initiation of Metal Materials at Various Stress States for Nuclear Waste Storage

A fracture criterion is newly proposed to evaluate fracture behavior and predict fracture initiation of metal materials in different complicated stress states for four different fracture mechanisms including quasicleavage fracture, normal fracture with void, shear fracture with void, and shear fracture without void. The dominant factors of these four different mechanisms are distinct, so it is impossible to capture all features of fracture initiation under different stress states with a single criterion, and different functions are necessary to predict fracture initiation of different mechanisms. In the new fracture criterion, different branches of the fracture criterion have been proposed corresponding to different fracture mechanisms. Quasicleavage fracture and normal fracture with void are described as a function of the principal stress, shear fracture with void is a function of the stress triaxiality and maximal shear stress, and shear fracture without void is only controlled by the maximal shear stress. The new fracture criterion is applied to predict the fracture initiation site and the fracture direction of nodular cast iron QT400-15 in combined tension-torsion tests. Predicted results are compared with experimental results to validate the performance of the new criterion in the intermediate stress triaxiality between 0 and 1/3. The new criterion is also applied to predict the crack initiation site and the direction of crack initiation of LY12 aluminium alloy and HY130 mild steel in mixed mode fracture tests to validate the performance of the new criterion in the high stress triaxiality. The new fracture criterion gives consistent results for these materials in a wide stress triaxiality range. It is shown that the new fracture criterion is a better supplement to the deficiency of fracture mechanics and also a better amendment to traditional strength theory in complicated stress states. Therefore, the new fracture criterion is recommended to be utilized to evaluate the fracture initiation of metal structures in nuclear waste storage and other engineering applications.

Criteria for predicting the initiation of rolling contact fatigue damage in the railway wheels and rails

The development of the methods for modeling the processes of accumulation of the rolling contact fatigue damage and wear of the wheels of the railway rolling stock and the rails is particularly relevant due to the increase in the number of damage in the recent times. The work is underway to improve the chemical composition and the technology of production of the wheel and rail steels in order to improve their mechanical properties and ability to resist the action of the cyclic loads. The methods of modeling allow predict the possibility of initiation of the fatigue cracks during operation with the sufficient accuracy in the short time. The selection of the contact fatigue criterion and the mathematical apparatus for calculating the stresses at points in the area adjacent to the contact patch to obtain the numerical values of the criterion components is the most important task in the development of modeling methods. The article focuses on the approaches based on the Dang Van criterion and the shakedown diagram for a material undergoing to the action of cyclic loads, which are widely used to assess the rolling contact fatigue of the wheels and rails. The assumptions that are used in the development of the algorithms concerning the models of the contacting bodies, the shape of the contact patch, the distribution of the contact pressures and the tangential forces are considered. The approach using the criterion — the amplitude value of the maximal shear stress is also considered. The example of modeling the process of accumulation of the rolling contact fatigue damage in the wheel of the freight car is given. The results of modeling are presented in the form of the isolines of the criterion values and the accumulated damage in the area adjacent to the contact patch. This work was supported by the Russian Foundation for Basic Research under Grant [17-01-00815A].

Multiaxial cycle counting method for non-proportional multiaxial variable loading signals based on modified maximal shear stress

One of the most challenging task in field of multiaxial fatigue is fatigue lifetime estimation of components loaded with multiaxial non-proportional variable amplitude loading. While this task consists of multiple smaller problems, one of the most crucial ones is loading cycles identification (and extraction) for future use with multiaxial damage criterions. By now, several cycle counting methods have been proposed for multiaxial loading conditions. The most wildly accepted methods are Bannantine-Socie’s method and Wang-Brown’s method (which has been later modified by Meggiolaro and Castro). The aim of this paper is the comparison of newly developed method with Bannantine-Socie’s method and Wang-Brown’s method. The new cycle counting method is based on cycle identification in relative maximum shear stress histories (calculated from multiaxial loading histories). The extracted data than composes part of each loading channel of multiaxial loading histories corresponding to identified loading cycle. The comparison of chosen methods has been done by using data sets created by authors as well as using real measured data from real operation.

Numerical modeling of the hydraulic impact of riparian vegetation

This paper presents results of numerical modelling of riverbed segment with riparian vegetation performed with use of CCHE2 software. Vegetation zones are places where dynamic of water flow increases. Therefore, there is a need of careful examination of hydraulic impact structure of such zones. Accurate research is necessary and should be performed with use of physical or numerical models, two or three dimensional. Paper presents distribution of velocity and area of water surface for two variants of vegetation deposition acquired in CCHE2D software and modelled for riverbed with distinctive riparian vegetation. Results point to significant (30–40%) increase of maximal velocities in riverbed with riparian vegetation, while directly near the vegetation there were zones with very low velocities. Local damming occurs before vegetal zone. Maximal shear stress in zones with increased velocity is significantly augmented compared to conditions with no vegetation, which can cause more intensive erosion in those zones

The Different Pavement Structure Combination Shear Stress Analyze

Based on the multi-layer elastic system theory, large general used finite element software is used to analysis in the paper. The pavement structure layer bottom three-direction maximal shear stress SXY, SYZ and SXZ are computed under the different axis load for four kind combinations. Through contrasting the three direction shear stress, the paper obtained some curves and laws about the pavement structure layer bottom three-direction shear stress along with the axis load change.

Maximum Shearing Stress Analysis of Asphalt Pavement Structure

Based on the multi-layer elastic system theory, large general used finite element software is used to analysis in the paper. The maximal shear stress SXY is analysed entirely by computing the structure layer bottom maximal shear stress SXY of the different combinations under the different axis load. The results show: the more the axis load, the more the shear stress SXY; the shear stress SXY decreases quickly along with the structure layer deep increasing; the relations between the basic layer rigidity and the shear stress are curve change laws.

Bearing Capacity Predicting Method on Mortar-Rock Interface of Compression Type Rock Anchor

To predict bearing capacity on mortar-rock interface of compression type rock anchor, the failure model of fixed anchor length is established. The maximal shear stresses on the interface in front of the bearing plate are determined based on tests. The relation of maximal shear stress and fixed anchor length is assumed. Double exponential function curves are adopted to simulate the ultimate state of the fixed anchor length. Two parameters are introduced to adjust the curve shape. According to the results of the field test, the values range of the parameters in soft rock is determined. After comparing ultimate bearing capacity measured in test with predicting value, it is shown that the empirical formula can calculate the bearing capacity of fixed anchor length reasonably. Compression type rock anchors have more capacity than ordinary tension type anchors and the capacity is convergent gradually with fixed anchor length increase.

Rupture propagation in strong earthquake sources and tectonic stress field

Problems of physical basis of earthquake source mechanics are discussed. Results of stress state reconstruction based on the cataclastic analysis of discontinuous dislocations in some seismotectonic active earth crust domains are presented. Common features of the stress state in areas of preparation of strong earthquake in this century are revealed. It is demonstrated that the distribution of the effective isotropic pressure and of the maximal shear stress in areas of earthquake source preparation is characterized by essential heterogeneity. The main part of the source is always associated to crust domain under low effective confining pressure. Specific role of crust domains characterized by high stress gradients is recognized. The nucleation point of the earthquake is usually associated to such domains. Based on some strong earthquake case studies it is demonstrated that usually the rupture propagates from the region of high gradients of stresses toward the crust domains characterized by low effective compression.

Unsteady Effects on the Flow Across Tilting Disk Valves

The present study simulates numerically the flow across two-dimensional tilting disk models of mechanical heart valves. The time-dependent Navier-Stokes equations are solved to assess the importance of unsteady effects in the fully open position of the valve. Flow cases with steady or physiological inflow conditions and with fixed or moving valves are solved. The simulations lead into mixed conclusions. It is obvious that steady inflow cases that account for vortex shedding only cannot model realistic physiological cases. In cases with imposed physiological inflow, the details of the flow field for fixed and moving valves might differ in the fully open position as well, although the gross features are quite similar. The fixed valve case consistently results in safe estimations of several critical quantities such as the axial force, the maximal shear stress on the valve, or the transvalvular pressure drop. Thus, fixed valve simulations can provide useful information for the design of prosthetic heart valves, as long as the properties in the fully open position only are sought.

Shear Deformation Of The Spherical Shell Acted On By An External Alternating Electric Field: Possible Applications To Cell Deformation Experiments

Shape deformation of the thin, area non-compressible spherical shell separating two different media, subjected to an external, alternating, homogeneous electric field is considered. The function relating shape deformation of the shell to the shear stress in its plane is presented. Shear stress develops as a result of Maxwell stress acting on both shell surfaces. All media are considered as lossy. The theoretical model predicts that the shear stress reaches its maximal value at the shell “equator” in relation to the field direction. The magnitude of the shear stress depends on the strength and frequency of the electric field, on the geometric parameters of the shell, and on the electric parameters of the system studied. The foregoing was applied to an analysis of cell deformation, e.g., an erythrocyte in an electric field. The analysis predicts that the maximal shear stress in the membrane develops at field frequencies close tof = 107 Hz. This is comparable to the electrocompression stress of the same membrane, maximal at the cell “pole”. At lower frequencies, compression predominates over shear stress