Papers by Keyword: Cyclic Loading

Abstract: We perform finite element homogenization (FEH) analysis to investigate the effect of strain hardening on the monotonic and cyclic loading behavior of plate-fin structures with two pore pressures. As a typical base metal of plate-fin structures, 316 stainless steel is considered and assumed to be the viscoplastic material that obeys the Ohno-Wang kinematic hardening rule. The plate-fin structures are assumed to be periodic and subjected to uniaxial monotonic and cyclic loadings in the stacking direction. A periodic unit cell is used for FEH analysis. Results are compared with those based on three special cases derived from Hill’s macrohomogeneity equation. It is found that the mean pore pressure entirely affect the homogenized viscoplastic behavior. It is further found that the differential pore pressure causes the remarkable accumulation of ratcheting strain in the periodic unit cell, although this internal ratcheting gives no effect on macroscopic relations, resulting in providing a closed hysteresis loop for the plate-fin structures.

Abstract: Fatigue and fatigue damage leads to a change in material properties that can lead to the element failures. Generally, it is necessary to verify the influence of the fatigue effects on the concrete members according to European standard EC2, [1]. FRP materials have been possibly used for the fatigue damage structure rehabilitation. There we can apply the condition of the limit boundaries stress on concrete and limit force in FRP material theoretical approach. Fatigue assessment will be analyzed for T-beam cross section with reinforcement and strengthened FPR material in this paper.

Abstract: Aeolian sand is one commonly used subgrade filling in Xinjiang Oasis-desert region, engineering practices also proved its applicability as subgrade filling. In order to find the law of Aeolian sand subgrade static strength after cyclic loading, the paper studied the static strength of Aeolian sand before and after cyclic loading through the dynamic and static triaxial tests. It is concluded that the greater cyclic loading is, the more Aeolian sand static strength peak decreases. When cyclic loading is small, the bigger confining pressure and consolidation ratio are, the static strength peak increases more after cyclic loading. The bigger initial static deviator stress is, the more Aeolian sand static strength peak reduces. The frequency of cyclic loading has little effect on static strength. In order to keep the stability of low embankment, we should restrict overload , ensure subgrade and foundation consolidation adequately, at the same time using gravel or geosynthetic materials to package edge of roadbed, so as to increase confining pressure. The research results can provide reference for the design and construction of Aeolian sand low subgrade in Xinjiang Oasis-desert region.

Abstract: The aim of this study is to discuss the plastic shakedown and true stress of the cyclically loaded pressure vessel. A thin-walled cylinder pressure vessel is made according to actual working state and a water pressure test system is built. The vessel is loaded to different strain levels of plastic deformation first. Then it is loaded cyclically to shakedown state. The relationship between plastic strain and shakedown range is given based on numerous experiments. The constitutive model of the true stress-true strain of the vessel is obtained. The experimental results show that the ratcheting obviously occurred when the vessel is cyclically loaded to plastic deformation. The true stress-strain constitutive model which is presented in this paper can show appropriately the constitutive relation of the vessel when it is under multi-axial stress state. The application of uniaxial shakedown constitutive model has been demonstrated in this study.

Abstract: Distribution of microstructure and hardness by RBT (Rotary Bending and Tensile) loading at ambient temperature is presented. Grain size is one of the important parameters of microstructures of alloys, and affects mechanical characteristics depending on deformation conditions. At higher temperatures, coarsening of grain size improves creep strength, while the finer improve tensile strength at ambient temperature. Grain size shows opposite effect on strength of alloys depending on temperatures and not always possible to improve strength both at ambient and high temperatures. Authors have attempted microstructural control by formation of distribution of plastic strain prior to heat treatment of aluminum alloys to obtain well-balanced strength both at high and ambient temperatures. In this report, distribution of grain size and hardness in 2017 aluminum by RBT loading are presented, and compared with results in 1070 reported previously. RBT loading equipment is designed for combined loading by rotary bending and static tensile loading to distribute plastic strain. In 2017 alloy, obtained microstructure after suitable heat treatment show distribution of hardness, while grain size show homogeneous distribution. The distributions, however, are different from that in 1070 alloy.

Abstract: Ductility is an important aspect of cyclically loaded reinforced concrete (RC) structures. One of the method that can be used to measure the ductility of an RC structure is the moment-curvature approach. However, due to it being a strain-based approach it cannot be used to directly simulate behaviour associated with interface displacement that occur when an RC member is cracked. This leads to dependency on empirical values, which imposes limitations on how the moment-curvature approach can be used. In recent years a new displacement based method for measuring ductility has been developed, and can simulate the interface displacement behaviours through the use of partial-interaction theory and shear friction theory. This paper aims to extend the general tension stiffening analysis of the displacement-based approach to allow for cyclic loading. The tension-stiffening analysis was then validated against experimental results and the results were found to agree fairly.

Abstract: Densification and settlement are two important behavior parameters of railway ballast under cyclic loading. This paper presents numerical simulation using discrete element method which studies the evolution of densification of railway ballast in specified region under cyclic loading. The simulation results show that with the increase of cyclic loading time, the densification of railway ballast under sleeper is also increasing, and the rate of increase becomes smaller and smaller. This paper presents a new full-scale complete railway track loading experimental facility which studies the evolution of settlement of ballasted railway track under cyclic loading. The experimental results show that with the increase of number of load cycles, the settlement of ballasted railway track is also increasing, and the rate of increase becomes smaller and smaller.

Abstract: Because of the progress in cementitious composites material engineering, modern concrete structures are designed as more slender in comparison to previous years. For structures subjected to cyclic loadings it means higher stress ranges and thus higher probability of fatigue failure. These types of structures are often located in places of severe environment (bridges, crane tracks in chemical plants etc.). The paper presents an experimental research focused on the effect of coupled deterioration by aggressive environment and cyclic loading on the concrete specimens. The evaluation of the deteriorative effect of aggressive environment is based on kinetics of chemical reaction between concrete and aggressive solution of hydrochloric acid.

Abstract: Structural Health Monitoring (SHM) systems are developed to decrease the maintenance cost and increase the life of engineering structures by fundamentally changing the way structural inspections are performed. However, this important objective can only be achieved through the consistent and predictable performance of a SHM system under different service conditions. The capability of a Piezoelectric lead Zirconate Titanate (PZT)-based SHM system in detecting structural flaws strongly depends on the sensor signals as well as actuator performance. But service conditions can change the behaviour of transducers, raising questions about long term SHM system capability. Although having a clear understanding of the reliable sensor life is important for surface mounted systems, however, this is particularly critical for embedded sensors. This is due to the fact that opportunity for replacement of sensors exists for surface bonded transducers while for the embedded systems, sensor replacement is not straightforward. Therefore, knowledge of the long term behaviour of embedded-SHM systems is critical for their implementation. This paper reports a study on the degradation of embedded PZT transducers under cyclic loadings. Carbon/epoxy laminates with an embedded PZT were subjected to fatigue loading and their performance was monitored using Scanning Laser Vibrometery (SLV). The functionality of PZT transducers under sensing and actuating modes were studied. High and low cycle fatigue tests were performed to establish strain-voltage relationships which can be used to identify critical cyclic loading parameters (number of cycles and R value) under sensing and actuating modes.

Abstract: To evaluate the influence factors of accumulative plastic strain of frozen silt clay, the dynamic cyclic triaxial tests with stress-controlled are conducted to investigate the behaviors of frozen soil induced by cyclic loading. The relationships between accumulative plastic strain and vibration numbers for frozen silt at different dynamic stress amplitudes under different temperature, vibration frequency and initial water content are obtained. The test results show that the accumulative plastic strains increase with rising tempeature, increasing the vibration numbers and dynamic stress amplitude. The accumulative plastic strain rate increases with increasing the vibration frequency. With increasing the initial water content, the accumulative plastic strain of frozen silt clay increases.