Papers by Keyword: Elastic Strain

Abstract: Fatigue crack generation and propagation processes in oxygen-free copper for power equipment were investigated in a time series to search for new parameters that indicate the fatigue damage degree. The damage behavior of crystal grains was observed by optical microscopy, electron backscattered diffraction (EBSD) analysis and elastic strain analysis. The obtained results suggest that the change in grain orientation spread (GOS) and grain average misorientation (GAM) values is possible to detect the fatigue crack generation. Moreover, it was found that the change in the plastic strain range is also possible to detect it.

Abstract: One of the main aims of our work is to obtain general equations for the diffusion fluxes under strain that give the possibility for using these equations at low temperatures, as in this case the strain influence on the diffusion fluxes is manifested in maximal degree. Our approach takes into consideration that the strains can alter the surrounding atom configuration near the jumping atom and consequently the local magnitude of the activation barrier and a rate of atom jumps. The approach is derived under assumptions that the total energy depends on the pair distances only and the attempt frequencies are the same for all jumps. The rates of atom jumps in different directions define the flux density of the defects. Now we take into account that the strain tensor is different at the saddle point and at the rest atom position, that differentiates our approach from previous ones. As a result, general equations for the vacancy fluxes and impurity fluxes are obtained for fcc and bcc metals. These equations differ significantly from those obtained earlier.

Abstract: We examine the effect of elastic stresses induced by growing voids on the diffusion vacancy fluxes using newly derived equations. One of the main goals of our work is to obtain a kinetic equation for the growth rate of voids in cubic metals. The diffusion equation for vacancies, in which the influence of elastic stress near the void on the flux is taken into account, is linearized and solved. Then after mathematical transformations that are similar to Lifshitz - Slyozov theory, kinetic equations for the growth rate of the voids in fcc and bcc metals are obtained. The kinetic equations contain additional terms due to developed strain. This feature distinguishes the present equation from known ones and changes the kinetic of void growth. The functional dependence on strain is determined by coefficients, which characterize the strain influence on diffusion (SID coefficients). These coefficients are very sensitive to the atomic structure in the nearest vicinity of the saddle-point configuration. We have built an advanced model to evaluate them. SID coefficient simulation is the next step of this work. Using the kinetic equations and the SID coefficients, we calculate the void growth rate in cubic metals under different conditions.

Abstract: With responsibility as its central element, sustainable development is a concept that calls for permanently increasing information usage while minimising material and energy consumption. Waste – particularly of energy – cannot last, and is evidently not a long-term solution. In the field of machine-tools structures deemed sustainable fulfil their functions for a sufficiently long period of time, while consuming as small as possible amounts of energy and including a small as possible volume of material. In a machine-tool, as in numerous other industrial products, energy consumption in deployment significantly exceeds that of their manufacturing. A conclusive example is that of mechanical presses, machine-tools with long service lives and considerable deployment energy consumption. With increasing stiffness of presses, deployment energy consumption is smaller. Detailed research conducted by the authors has yielded a series of innovative constructive solutions for mechanical press cast C-frames – frames with ribbed lateral walls, frames with pre-stressed front columns and shortened frames – with increased stiffness and minimum additional metal consumption as their main relevant characteristics. The finite element based study of these novel constructive solutions has revealed stiffness increases of 1 to 12 %, significantly depending on the type of constructive solution. The novel solutions can be combined in view of cumulating the obtained positive effects. The paper presents relevant examples of such combined constructive solutions and the results related to stiffness increase obtained by means of the conducted FEA study.

Abstract: Here, we developed single crystalline Cu@C nanowires with fivefold twinned structure via a facile hydrothermal method. In situ uniaxial tension tests of these NWs performed in transmission electron microscopy chamber reveal the ultrahigh strength (as much as 6.2 GPa) accompanied by favorable ductility (elongation>15%). The excellent performances benefit from nanoscale dimensions, unique penta-twinned geometry and good crystalline quality with protection of carbon shells. The study also provides direct experimental evidence for the theoretical modeling on the deformation mechanisms of metallic nanowires that have appeared in recent years. We expect that these findings can open a new window for applications in micro-or nanoelectromechanical devices where superior mechanical performances are desirable.

Abstract: To model the stress-strain relation of frozen soil under different temperatures, an elasto-plastic constitutive model coupling with temperature variable was proposed. Under axisymmetric condition, elastic strain was calculated by the K-G model coupling with temperature. The plastic strain was calculated by using the DP yield criterion, associated flow rule and isotropic hardening law. All of the elastic and plastic parameters are related to the temperature variable. The simulated results show that the proposed model can predict the deformation behavior of frozen soil under different temperatures.

Abstract: Reducing exploitation energy consumption for any technical system is an effective way, which is in complete accordance with the concept of sustainable development [1]. The presses, particularly the mechanical ones, are machine tools with a long-term exploitation [2]. At these ones, the operating energy consumption, significant in value, decreases only if the rigidity of the structure of resistance increases, including that of the frame. Several analytical models, developed and studied by the authors, confirmed the hypothesis that a solution to increase the rigidity of a mechanical press with open frame is obtained by shortening it. Moreover, it occurs also a slight decrease in material consumption integrated into the frame, which is a favourable effect. There have been developed more new constructive solutions [3, 4], characterized by minimal changes to the reference design solution, that of the press frame PAI 25. The new suggested constructive solutions are obtained as 3D models, accomplished in Pro Engineer Wildfire 4, and the finite element analysis was made in Catia V5 R16. The present paper shows results on increasing stiffness and reducing stress state for a few constructive solutions of shortened C-frame, having reduced distance between the working surface of the table and the spindle bore axis.

Abstract: Xiaolangdi sediment tunnel is the first waterway engineering used un-bonded circumferential pre-stressed lining in China. Based on data obtained by concrete strain meters over tensioning and operation periods, strain of concrete creep of sediment tunnel lining was analyzed. The results show that concrete creep developed over tensioning period is 26.4% of total strain and 35.8% of elastic strain respectively; Creep strain had a good linear relation with pre-stress and loading time and can be calculated by εc=ασiti , which are agree with the measured results; Over operation period, concrete creep strain can be analyzed by rejecting the effect of temperature and water level from the total strain.

Abstract: The microstructure evolution and precipitation behaviors of ordered γ (Ni₃Al) phase in Ni-Al alloys were studied using the phase field dynamic model. Under the interactions of internal elastic strain, the γ phase morphology changes from the separated cuboidal to connected rectangle shape with the decrease of the aging temperature or the increase of the Al concentration. It also shows that the ordering of precipitates is finished instantly when they precipitate from the matrix phase. The γ phase volume fraction and the phase transformation velocity are affected by the aging temperature and composition of the Ni-Al alloys.

Abstract: Ion implantation into 4H-SiC induces a local gradient of strain which increases with the nuclear energy losses. With the increase of temperature the strain tends to become uniform in the whole implanted area requiring the migration of particles. In case of helium implantation, defects are more stabilized and their evolutions observed post thermal annealing are concomitant with the surface swelling. The local modifications imputed to the ion process lead to the formation and the pile-up of stacking faults in the highly damaged region.