Energy dissipation of ordinary concrete under discontinuous cyclic compression tests and numerical simulations for the residual stress

This paper presents an experimental investigation of ordinary concrete under discontinuous cyclic compression tests and numerical simulations for the residual stress. Stress cycles in discontinuous cyclic compression tests were interrupted by zero or very low loading intervals (ZLIs). Fatigue tests showed that the dissipated energy and the unloading deformation modulus of a cycle after the ZLI ( A cycle) were significantly larger than those of the cycle before the ZLI ( B cycle). The dissipated energy and the unloading deformation modulus both increased with the increase of the stress level. The mechanism of discontinuous fatigue results from the effect of the residual stress which is caused by the uncoordinated mechanical response. Simulations showed that stress concentration occurs on the interface between the aggregate and the main material. The greater the elasticity modulus difference between the aggregate and the main material, the larger the residual stress and plastic deformation.

Measurement and Simulation Analysis of Vertical Cross Longitudinal Settlement between Turning Shield and Foundation Pit

Using numerical simulation technology, the dynamic three-dimensional model of the turning shield and the foundation pit under the condition of vertical intersection is established. The disturbance law of the longitudinal settlement of the foundation pit under the condition of shield construction is studied, and the stress path in the soil is analyzed. The results show that with the gradual advance of the turning shield construction, the settlement mode of the foundation pit changes with the shield construction. During the construction of the turning shield, when the tunnel face is located in front of the foundation pit and under the foundation pit, the ground loss rate is inconsistent, which leads to the change of settlement mode. Under the influence of turning shield construction disturbance, the soil undergoes compression deformation caused by larger additional stress increase; after shield crossing, the soil undergoes unloading deformation caused by more obvious stress relaxation.

Physical modeling and numerical simulation of bar deformation under axial loading in the channel. Part 2

In two parts the article describes physical modeling and numerical simulation of bar deformation under axial compression in the channel. The regularities of nonlinear bending of the rod in the plane have been revealed. Bar shapes were determined by the load history and can differ at the same force value. The problem was to find the shape with the lowest potential energy. The second part of the article describes numerical modeling of gradual loading of the bar with rigid fixing at the ends and unloading the bar with hinges at the ends; physical modeling loading and unloading, as well as overall final comparison of the forms of numerical and physical models. When unloading, deformation occurs in a more variable way compared to loading. The forms remain stable under compressive forces being within the range of existence for loads. Forming symmetrical shape variants differing in the sign of deflections is possible. In the shape-critical state, the bearing pressure becomes minimal. The forms of the physical model under loading and unloading confirm the results of numerical simulation. The results obtained are applicable to the analysis of the state of such bar objects as drilling, casing, pumping and compressor columns and pipelines.

The Analysis of Bolted Flange Joints under Internal Pressure at High Temperature

Working temperature, internal pressure and the creep of bolted flange joints are the direct factors that influencing the gasket stress of bolted flange joints, the tightness of the whole system will be reduced because of these factors. thus the security level of bolted flange connection will be affected. In this paper, the deformation coordination equation of bolted flange connection system, the gasket compressive and resilient performance, as well as the gasket creep equation are combined to study the effect of internal pressure on bolted flange connections under a certain bolt preload and operating temperature, the equation about the relationship of the gasket force and internal pressure is simplified, and the main objective of the work is the calculation of the time-correlated gasket force, flange rotation and gasket unloading deformation under the different internal pressure. The results show that when the internal pressure is greater, the gasket force is smaller, on the contrary, the leakage rate are greater. Through the relevant conditions, in a period of the safe operation time, the maximum working internal pressure is got when reaching the condition of corresponding level of tightness.

COMBINED VIBRATION ISOLATOR OF DISC SPRINGS FOR CLOSED HIGH-SPEED PRECISION PRESS: DESIGN AND EXPERIMENTS

The structure, strength, and stiffness of disc springs are analyzed or investigated. Based on the previous studies, two finite element models of combined disc springs are established and their loading and unloading deformation patterns are analyzed to determine the optimal combination of disc springs for a desirable vibration isolator of high-speed press. The structural parameters and loading data of JF75G-200 high-speed press are used for simulation and other experiments. The dynamic working points of disc springs in different combinations are drawn, and complete test data are collected. Results show that combined vibration isolator, an isolator with nonlinearly combined disc springs functioning as a whole for vibration isolation, is the best choice. Results from both simulation and tests confirm the feasibility and validity of the proposed isolator. The isolator can efficiently minimize the vibration of the high-speed press.