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In this paper, test results for woven ceramic matrix composites (CMCs) based on an oxide matrix and oxide fiber are presented. Stress–strain curves under cyclic loading for different in‐plane fiber orientations as well as strength values for different fiber orientations under tension and compression and under pure shear are presented. Based on the experimental data, a nonlinear damage model is derived which allows to determine the progressive degradation of the elastic moduli and the nonelastic remanent strain in a satisfactory manner. It has been implemented into the finite element code ANSYS and shows excellent convergence behavior. To predict the failure of CMC components, the failure mode concept proposed by Cuntze is extended to include friction effects due to tension and compression on the in‐plane shear failure mode. The predicted failure onset matches the experimental data very well, whereas existing models like the max‐stress or the Tsai–Hill criteria show larger deviations. [ABSTRACT FROM AUTHOR]

During undrained cyclic loading, clayey soils experience substantial stiffness and strength degradation when subjected to shear amplitudes exceeding a critical threshold. This paper presents an enhanced bounding surface rate‐independent plasticity model, an evolution of the previous SANICLAY model, tailored to capture this specific behavior during cyclic loading. A distinguishing feature of the proposed model is the introduction of an activation mechanism. This mechanism triggers degradation modeling based on the applied cyclic shear amplitude. To measure this amplitude, the activation mechanism incorporates a novel state variable that serves as a proxy for the applied cyclic stress. The effectiveness of the proposed model is demonstrated by comparing it to experimental data from various materials subjected to cyclic shearing under undrained conditions. The study encompasses a broad range of constant strain or stress amplitudes. Compared to the reference model, the proposed model exhibits improved predictive accuracy for the stress‐strain response of clays at small amplitudes of cyclic loading and large number of cycles. Furthermore, it accounts for strength degradation due to cyclic loading. [ABSTRACT FROM AUTHOR]

Moment resisting frame (MRF) beams under cyclic loading are vulnerable to local flange and web buckling. The Seismic Provisions for Structural Steel Buildings (AISC341) prescribe width-to-thickness ratio limits, which are contingent on target rotations during predefined cyclic loadings. Some rolled I-sections available in the market cannot be employed in special MRFs since they fall short of satisfying the AISC341 flange slenderness limit. Moreover, local buckling leads to a decrease in both strength and stiffness in cyclically loaded MRF beams, ultimately increasing the risk of frame side-sway collapse. This paper introduces a stiffening method aimed at improving the behavior of I-section MRF beams. The proposed method involves placing a pair of stiffeners at the plastic hinge regions. A two-phase numerical study was conducted to assess the effectiveness of this approach. In the first phase, nine unstiffened beam cross-sections with varying flange and web slenderness were considered. The slenderness limits specified by AISC341 were evaluated based on cyclic analyses of these beams. In the second phase, a parametric study was conducted on the same cross-sections, with the flange width and the placement of the pair of stiffeners considered as variables. The results revealed a substantial improvement in behavior with the addition of a pair of stiffeners. Cross-sections that failed to meet the flange slenderness limit could be used in MRFs when stiffened. The optimal location for the stiffeners was found to be significantly influenced by the flange width. Design recommendations for the ideal stiffener placement are presented in this paper. • Local buckling in MRF beams was studied alongside a proposed stiffening method for improving the behavior. • The highly ductile flange and web limits recommended in AISC341 were found to be adequate. • The proposed stiffening method was found to be effective in reducing the deleterious effects of local buckling. • The ideal stiffener position was found to depend significantly on the flange width. • Practical design recommendations were developed for the ideal stiffener location [ABSTRACT FROM AUTHOR]

The paper presents the impact of exceeding the railway rails lifespan which usually causes a railway structural failure, thus an accident. The research highlights the rails's high degradation, especially on the running area, consisting in 60-70% weight loss by advanced wear of the rail, followed by fatigue fracture caused by alternating cyclic stresses that initiates the crack and also by tensile stresses resulting in the crack growth. The chemical composition, structural and mechanical properties were analyzed in order to establish the causes that led to the railway rails rupture. [ABSTRACT FROM AUTHOR]

Highlights • Bond behavior of deformed bar in ECC under cyclic loading were investigated. • Effects of various parameters on energy dissipation capacity were evaluated. • Degradation laws of bond strength under cyclic loading were discussed. • A calculating equation of bond strength was proposed. Abstract The bond behavior between deformed bar and ECC has a significant effect on the mechanical performance of reinforced ECC structures when subjected to dynamic loading. In this paper, 12 groups of ECC specimens and one group of concrete specimen as control were prepared to investigate the bond behavior of deformed bar under cyclic loading. Designed parameters included compressive strength, flexural toughness, cover thickness and anchorage length. Experimental results showed that, owing to the fiber bridging effect preventing the opening and propagation of internal cracks, failure modes of ECC specimens demonstrated an obvious ductility whereas the brittle splitting failure occurred for concrete specimen. The bond strength of steel bar in ECC had an extreme enhancement as the compressive strength of matrix increased. In comparison with the monotonic specimen, the cyclic specimen undergoes an obvious degradation in terms of bond strength as well as stiffness, and the degradation coefficient of bond strength ranged from 0.6 to 0.9. It was noticed that the increase in compressive strength and cover thickness can reduce the degradation degree of bond strength. Furthermore, the energy dissipation capacity of cyclic specimens rose first and then fell since the toughness of matrix increased. Finally, a calculating equation of bond strength under cyclic loading was proposed and the predicted results had a great agreement with the test results. [ABSTRACT FROM AUTHOR]

• Shutdowns of thermal power plant units affect the technical state of steel. • A new approach to evaluating the actual technical state of steel is developed. • Intergranular elements are considered as fractographic signs of steel's degradation. • A quantitative fractographic indicator of operational changes in steel is proposed. • Hardness for heat-resistant 15Kh1M1F steel in the critical state is substantiated. The paper discusses metallographic studies and the results of mechanical testing of 15Kh1M1F (DIN 15CrMoV5-10) steel in the initial state and after its long-term operation in the steam pipeline of TPP. The revealed adverse impact of shutdowns of TPP units on the structural and mechanical state of steel is associated with the occurrence of cyclic thermal stresses in the pipe walls. Structural changes in metal across the pipe wall are uneven and consistent with regularities of mechanical properties changes. Intergranular fragments detected on the background typical transgranular relief of specimen's fracture surfaces are considered fractographic signs of steel's degradation. The part of intergranular fracture in the unit area of the fracture surfaces is proposed as the quantitative indicator of the changes in the structural and mechanical state of 15Kh1M1F steel due to its degradation. The critical state of steel is substantiated based on the regularities of operational changes in its mechanical properties and the revealed fractographic features. [ABSTRACT FROM AUTHOR]

Soft clay forms a big proportion of the seabed ground. In a marine environment, waves, wind, and earthquakes, often known as cyclic loads, are a main contributor to the loading of the seabed. The safety of offshore structures relies on the response of soft marine clay to these cyclic loadings. Its very fine-grained composition, and hence low permeability, is the defining factor for soft marine clay showing a very different response to cyclic loading than sand. The responses of soft marine clay subjected to cyclic loading range from degradation in soil strength and stiffness to principal stress rotation, excess pore pressure generation, and deformation accumulation. These dynamic characteristics of soft marine clay are strongly influenced by several factors, including loading level (amplitude, frequency, and number of cycles), loading history, and path. The purpose of the present paper is to present an overview of the research results on the characteristics of soft marine clay under cyclic loading in the past decades. Some remarks on future research for improving the understanding of dynamic characteristics of soft marine clay are also provided based on the results of up-to-date research. [ABSTRACT FROM AUTHOR]

Embedded rings are widely used in onshore wind turbine foundations to resist uplift and compressive forces at the interface of steel towers and concrete foundations. These embedded rings are subjected to high-cycle fatigue loading due to the high ratio of the live load to dead load in such structures. The properties of concrete in the anchorage zone of the embedded ring change with time and its strength deteriorates under the effects of the cyclic loads. Therefore, research has been initiated to investigate the local deterioration of foundations and its effect on the whole structure. This paper presents a numerical study on the fatigue behaviour of the concrete foundation of onshore wind turbines. A constitutive model was developed for the onshore turbine foundation at the section level for fatigue loading. The model in the initial state was verified against strain data from nonlinear finite element simulations with regard to the strain distribution characteristics in the cross section. The fatigue theoretical model provided a realistic description of concrete foundation fatigue processes and their redistribution characteristics. A parametric study was performed to investigate the effects of different parameters that would influence the fatigue life of the foundation. The results of this study may help explain the fatigue behaviour of foundations under repeated loads and thus lead to a more accurate depiction of the actual long-term behaviour of foundations. [ABSTRACT FROM AUTHOR]

A 3-D electromagnetic-thermal-mechanical coupling finite element model of a gas-insulated bus plug-in connector is proposed in this paper with a subsequent analysis for the contact fatigue mechanism. Special attention has been paid to the contact degradation mechanism under normal cyclic operation conditions, which is important for the optimal designing and condition monitoring of the equipment. The current constriction effect and the contact resistance are considered through modeling the equivalent contact bridges between contact interfaces, and the current densities derived from the electromagnetic field are applied as load inputs in a electrical-thermal-mechanical analysis where varying of friction coefficient is considered. The validity of the calculation model has been demonstrated by temperature rise and relative motion experiments, and the influence of daily changing current and environmental temperature on the thermal and mechanical characteristics of plug-in connector has been analyzed. Analysis results show that the temperature rise among different contact fingers of plug-in connector is not the same with different contact forces, and the plastic deformation can be induced on contact spots. The insert depth of connector can be changed under the action of alternating thermal loading induced by daily change of current and environmental temperature, leading to contact degradation and overheating fault of plug-in connector. [ABSTRACT FROM AUTHOR]

Pile foundations subjected to cyclic load is an age-old problem dealt with for decades by geotechnical engineers. The ocean environment necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action. Substantial experimental and analytical investigations have already been conducted by the author and other researchers. The quasi-static load reversal induces deterioration in the strength and stiffness of the soil-pile system introducing progressive reduction in the bearing capacity as well as settlement of the pile foundation, the degree of such degradation has been observed to be a function of the cyclic load parameters and the type of soil. Based on these observations, a design recommendation has been attempted in this paper for piles subjected to cyclic load in cohesive soil. [ABSTRACT FROM AUTHOR]

This paper presents the results of the influence of frequency on the permanent deformation and degradation behavior of ballast during cyclic loading. The behavior of ballast under numerous cycles was investigated through a series of large-scale cyclic triaxial tests. The tests were conducted at frequencies ranging from 10–40 Hz, which is equivalent to a train traveling from 73 km/h to 291 km/h over standard gauge tracks in Australia. The results showed that permanent deformation and degradation of ballast increased with the frequency of loading and number of cycles. Much of breakage occurs during the initial cycle; however, there exists a frequency zone of 20 Hz<=f<=30 Hz where cyclic densification takes place without much additional breakage. An empirical relationship among axial strain, frequency and number of cycles has been proposed based on the experimental data. In addition, discrete-element method (DEM) simulations were carried out using PFC2D on an assembly of irregular shaped particles. A novel approach was used to model a two-dimensional (2D) projection of real ballast particles. Clusters of bonded circular particles were used to model a 2D projection of angular ballast particles. Degradation of the bonds within a cluster was considered to represent particle breakage. The results of DEM simulations captured the ballast behavior under cyclic loading in accordance with the experimental observations. Moreover, the evolution of micromechanical parameters such as a distribution of the contact force and bond force developed during cyclic loading was presented to explain the mechanism of particle breakage. It has been revealed that particle breakage is mainly due to the tensile stress developed during cyclic loading and is located mainly in the direction of the movement of ballast particles. [ABSTRACT FROM AUTHOR]

The objective of the contribution is to understand the fatigue bond behaviour of brass-coated high-strength micro steel fibres embedded in ultra-high performance concrete (UHPC). The study contains experimental pullout tests with variating parameters like load amplitude, fibre orientation, and fibre-embedded length. The test results show that fibres are generally pulled out of the concrete under monotonic loading and rupture partly under cyclic tensile loading. The maximum tensile stress per fibre is approximately 1176 N/mm2, which is approximately one third of the fibre tensile strength (3576 N/mm2). The load-displacement curves under monotonic loading were transformed into a bond stress-slip relationship, which includes the effect of fibre orientation. The highest bond stress occurs for an orientation of 30° by approximately 10 N/mm2. Under cyclic loading, no rupture occurs for fibres with an orientation of 90° within 100,000 load changes. Established S/N-curves of 30°- and 45°-inclined fibres do not show fatigue resistance of more than 1,000,000 load cycles for each tested load amplitude. For the simulation of fibre pullout tests with three-dimensional FEM, a model was developed that describes the local debonding between micro steel fibre and the UHPC-matrix and captures the elastic and inelastic stress-deformation behaviour of the interface using plasticity theory and a damage formulation. The model for the bond zone includes transverse pressure-independent composite mechanisms, such as adhesion and micro-interlocking and transverse pressure-induced static and sliding friction. This allows one to represent the interaction of the coupled structures with the bond zone. The progressive cracking in the contact zone and associated effects on the fibre load-bearing capacity are the decisive factors concerning the failure of the bond zone. With the developed model, it is possible to make detailed statements regarding the stress-deformation state along the fibre length. The fatigue process of the fibre-matrix bond with respect to cyclic loading is presented and analysed in the paper. [ABSTRACT FROM AUTHOR]

According to the objectives of the research group 1498, this paper deals with degradation effects in concrete structures that are caused by cyclic flexural loading. The goal is to determine their influence on the fluid transport processes within the material on the basis of experimental results and numerical simulations. The overall question was, to which extent the ingress of externally supplied alkalis and subsequently an alkali-silica reaction are affected by such modifications in the microstructure. Degradation in the concrete microstructure is characterized by ultrasonic wave measurements as well as by microscopic crack analysis. Furthermore, experiments on the penetration behavior of water into the investigated materials were performed. The penetration behavior into predamaged concrete microstructures was examined by the classical Karsten tube experiment, nuclear magnetic resonance method, and time domain reflectometry techniques. In order to create an appropriate model of the material's degradation on the water transport, the Darcy law was applied to describe the flow in partially saturated concrete. Material degradation is taken into account by an effective permeability that is dependent on the state of degradation. This effective permeability is obtained by the micromechanical homogenisation of the flow in an Representative Elementary Volume (REV) with distributed ellipsoidal microcracks embedded in a porous medium. The data gained in the microscopic crack analysis is used as input for the micromechanical model. Finite element simulations for unsaturated flow using the micromechanical model were compared with the experimental results showing good qualitative and quantitative agreement. [ABSTRACT FROM AUTHOR]