Papers by Keyword: Temperature Influence

Abstract: On the basis of previously accumulated irreversible deformations, and, consequently, residual stresses, the process of removing residual stresses in metal workpieces under the action of low and high temperatures is simulated. Boundary value problems are solved and here are described regularities that are responsible for removing residual stresses for processing modes: high-temperature heating - cooling, high-temperature heating - holding - cooling, low-temperature heating - holding - cooling. The holding stage is modeled, taking into account the creep properties of materials under Norton creep conditions. According to the dependences of the obtained exact solutions, it is shown that it is the holding process that leads to the relaxation of residual stresses.

Abstract: The authors on the basis of numerical studies have analyzed the effect of progressive destruction and temperature influence on the operation and stress-strain state of the bearing elements of the frame of hinged facade systems.

Abstract: The article describes the results of an experiment that was done to develop a technique of reinforcement strength characteristics determination by using method of “thread cut”, after various temperature effects on it.

Abstract: The results of experimental and theoretical studies of the process of destruction of concrete by the methods of fracture mechanics are considered. Results of studies of long-term strength, durability and deformability of concrete subjected to a preliminary short-term temperature action up to 300° C and 400° C under load and without load are presented. It is shown that after short-term heating up to 300о С the long-term strength of concrete decreases insignificantly. It is established that heating up to 400° C can be considered the boundary of the structural integrity of concrete. The conditions for using the results of these studies in determining the values of a function that characterizes the change in the long-term strength of a material in the mechanics of heterogeneous structures are formulated. The function of the material destruction measure is introduced to describe the nature of the structural changes in the material at a given constant continuous load, and its change for different levels of a continuous load is considered.

Abstract: In the article the results of the eccentrically compressed reinforced concrete element calculation operating under the dynamic loading in fire conditions are shown. The calculation of the compressed reinforced concrete element was carried out, taking into account the conducted experimental studies. The calculation showed that, depending on the temperature effects, the curvature of the reinforced concrete element in stages I and II decreases while the class concrete, which varies from 28.9% to 55%, is increasing. When the temperature reaches 250⁰, the cracking moment and the moment of internal forces at the end of the stage II are reduced to 22% with respect to these forces at normal conditions. With increasing temperature, the dynamic stiffness of the element in the stage I is reduced by 29.3%.

Abstract: Within the linear theory of elastic-plastic body we carried out the modeling of technological process of annealing: slow heating stage, the holding stage under constant temperature and slow cooling step. Holding stage is simulated with consideration of creeping properties of materials. Boundary value problems are examined and patterns responsible for the removal of residual stresses at temperature influence are described. An analytical solution is found. It is proved that the holding stage is essential for describing the process of residual stress relief.

Abstract: The contribution describes an original optical measuring technique serving for the investigation of temperature influence on the shift of investigated objects natural frequencies. The mentioned method uses a modified high-speed digital image correlation system with original program Modan 3D created in Matlab, by which it is possible to non-contactly determine the natural frequencies using complex mode indicator function (CMIF) or normal mode indicator function (NMIF), the mode shapes as well as the damping ratio. Influence of the temperature on the shift of natural frequencies was analyzed at the planar steel specimen of circular shape with three holes. To the excitation a modal hammer was used. The specimen heating was realized by a hot-air gun, whereby the influence of the elevated temperature on the shift of natural frequencies was investigated by three temperatures distinguishing the room temperature 50° C, 75° C and 100° C.

Abstract: Key structure of multi-planetary gear transmission such as gear box body, planetary carrier should be monitored by non-destructive testing technology under work to ensure reliable operation. However, temperature of such components under operation is not normal, which will affect the detection result. Temperature influence upon ultrasonic on-line detection was researched. Such factors as ultrasonic propagation velocity, ultrasonic attenuation, ultrasonic probe emissive power and refraction angle of angle probe were analyzed. Multi-planetary gear transmission ultrasonic monitoring case has been completed.

Abstract: Temperature influence on the residual Mode-I fracture behaviors of concrete was investigated in present paper. The test specimens were exposed to temperatures varying from 65oC to 600oC with their weight losses monitored. The wedge splitting method was employed to obtain the load-crack mouth opening displacement (P-CMOD) curves of post-fire specimens from which the fracture energy G_F was calculated. It is demonstrated that G_F sustains a hold-increase-decrease tendency with T_m. The fracture energy is closely related to the ultimate weight loss w_u of the concrete and their relationship is also established.

Abstract: This paper concerns the possibility of use of the Jiles-Atherton-Sablik extended model to describe the magnetic characteristics for construction steel ST3. Result of the modelling utilizing extended Jiles-Atherton-Sablik model are in good agreement with results of experimental measurements for magnetic hysteresis loops B(H). However experimental results indicated, that the influence of temperature on B(H) characteristics is relatively small and can be neglected from the point of view of modelling for technical applications, such as stress estimation for non-destructive testing.