Papers by Keyword: Cyclic Behavior

Abstract: There has been considerable attention drawn to the application of textile reinforced mortar (TRM) composites for strengthening existing masonry and concrete structures. These composites are made from textile fibers embedded in an inorganic matrix and act as externally bonded reinforcement (EBR). Therefore, a careful observation must be made of the bond of the mortar to the substrate and the bond of the mortar to the textile. Despite numerous studies of the bond behavior of TRM composites conducted in recent years, no constitutive bond behavior law under cyclic loading has been determined. In most available studies, the most common method of testing TRM-to-substrate bonds is the single-lap shear test. Contrary to that, the bond performance of fibers to mortar has received little attention and has been the subject of this study. This paper describes a laboratory study investigating the textile's interfacial bond behavior to the mortar fiber under cyclic loading. It was shown that cycling can cause a loss in strength, which varies with the number of cycles.

Abstract: Shape memory alloys with their phase transformation properties; have been broadly implemented in smart structures. In this study, a functional design is presented where two wires actuate antagonistically to achieve motion in bending. Effect of heat treatment parameters on the actuator materials is investigated. For this purpose, a novel experimental test bench appropriate for characterizing a smart joint is presented, and joint performance including actuation force and cyclic behavior are demonstrated. Accordingly, a smart joint configuration capable of 60 degrees bending with a repeatability of 50 cycles is developed.

Abstract: In this work, we will study the cyclic behavior (tension-compression under strain control) and the fatigue of 304L austenitic SS after application of a boriding thermochemical treatment. 304L specimens was borided in a solid medium at 900 °C for 4 hours. The phase analysis of boride layers formed at the surface was performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The obtained results show that the layers formed on 304L steel contained the following boride phases FeB, Fe₂B, CrB, Cr₂B, NiB and Ni₂B. The fatigue tests show that the boriding treatment improves the life a factor which may be greater than four. The borided specimens show a negative average stress during cycling which may explain the increase of fatigue life. Analysis of the fracture surface by SEM show that crack initiation takes place in the substrate rather than in the boron-treated area.

Abstract: Light-weight design is one of the main drivers for material development in the automotive industry. For optimum weight reduction new materials and their fatigue behavior under real cyclic service loads have to be taken into account (Gassner test). Currently the casted components made from Austempered Ductile Iron (ADI) show better service fatigue life for variable load cases than some traditional forging steels because of it’s inherent retained austenite. The traditional forging steels are the precipitation hardening ferritic-pearlitic steels (PHFP steel) and the martensitic quenched and tempered (Q&T) steels. The next steel generation for forged components in the drive train might be bainitic steels with an optimized microstructure with respect to cyclic behavior. Depending on the chemical composition and the heat treatment it includes a ferritic primary phase and a secondary phase, which consists of either carbides, martensite, retained austenite or M/A constituents. By alloying of more than 1% Si the formation of cementite will be suppressed and a carbide free bainite (CFB) will be formed. The secondary phase of this CFB contains retained austenite, which has the possibility to close crack tips by local compression stresses due to the transformation to martensite. As a result of this CFB exhibits better cyclic properties than the commonly used forging steels. The materials and process design as well as results of the fatigue behavior will be presented.

Abstract: Based on the obtained experimental results, the features of stress-strain behavior of the metallic foam were discussed firstly in this paper. Then, in the framework of 2M1C visco-plasticity constitutive model, a cyclic constitutive model was proposed to simulate the stress-strain responses under monotonic and cyclic compression. In proposed model, plastic strain is divided into two parts, i.e., plastic strain of matrix metal and plastic strain of voids structure, which are associated with relative density. Additionally, a kinematic hardening rule of yield surface center is used to describe ratchetting effect during cyclic loading. The simulated stress-strain responses of aluminum foam are in a good agreement with the experimental ones.

Abstract: The stress-strain behaviors were investigated by monotonic and cyclic stressing tests for high density aluminum foam at room temperature. The cyclic accumulations of deformation for the material were measured in varied loading levels. The effects of mean stress and stress ratio on the ratcheting strain were discussed. The experimental results show that tension response is different from the compressive response. There is obvious cyclic accumulations of deformation (i.e., ratcheting effect) under compression-compression cyclic loading even if the holistic stress-strain response is linear. And the ratcheting of aluminum foam greatly depends on mean stress and stress ratio in asymmetric stress cycling. The experimental rules and data are significant for constitutive description and numerical simulation of aluminum foam.

Abstract: This work is devoted to a survey of the ratcheting phenomenon and follows the study presented in [1]. Two current austenitic stainless steels 304L and 316L are considered and tested under cyclic stress and strain control at 350°C. Under stress control ratcheting seems very small under proportional as well as non-proportional stress control. The elastic shakedown steady state exhibited by both materials may be explained by their capabilities to develop very significant cyclic hardening (especially isotropic) at 350°C.

Abstract: The aim of this study is to investigate the cyclic behavior and the fatigue life of an industrial α/β brass through mechanical tests and microstructural observations. The main obtained results are about the cyclic behavior of the alloy and the characterisation of fatigue life in connection with the evolution of the microstructure. Cyclic tensile test shows a great and rapid evolution of the isotropic hardenig during cycling.

Abstract: A self-centring bridge pier is a combination of elastic recovery devices and internal or external energy dissipaters. During the cyclic loading test, it is proved that the self-centring system can minimize the residual drift of the pier whereas holding sufficient energy dissipate capacity as well as bearing capacity. It is worth noting that a simplified analytical model is proposed based on the experimental response regarding flexural deformation, unbounded length of mild steels and strain penetration. Comparison between the analytical model and test results has indicated that a reasonable envelope of the cyclic behavior of the system can be achieved by the model presented.

Abstract: Carbon nanofiber (CNF) has good electrical conductivity. Addition of a few percentages of carbon nanofiber to polymer yields electrical conductivity but hardly affects the mechanical properties of polymer. This conductive polymer may be useful for sensing applications such as strain sensors and chem-resist sensors. Many researchers have reported on the electrical conductivity, but the electrical resistance change under strain of the carbon nanofiller composites is not fully investigated. In this study, the electrical resistance change under strain of CNF/flexible-epoxy composites was investigated experimentally. More than 100% of quasi-static strain can be measured by using CNF/flexible-epoxy composite with Young’s modulus of less than 1MPa. Cyclic and unloading behaviors were also measured and discussed. It was found that the cyclic behavior was strongly affected by viscoelasticity and damage.