Cyclic Loading Conditions Research Articles

A carbon nanotube-based thermoelectric generator integrated into a smart composite for structural health monitoring

The next generation of advanced composite materials needs to simultaneously address issues such as energy harvesting and structural health monitoring (SHM). The objective of this study is to explore, for the first time, the possibility of utilizing a build-in thermoelectric generator (TEG) to fulfil self-sensing purposes. To this end, carbon nanotube-based (CNT) inks are employed to print TEGs onto a glass fiber substrate, which is then incorporated into a glass fiber reinforced polymer (GFRP) laminate. The output characteristics of the TEG-enabled specimens are measured, displaying an exceptional performance. The specimens are subjected to static, quasi static cyclic and dynamic loading. Adopting a novel idea, the conductive, fully integrated printed path is then exploited to serve as a strain/damage sensor. For this reason, its resistance is monitored online during mechanical loading. To corroborate the findings, acoustic emission (AE) is simultaneously applied. Results reveal that the self-sensing multifunctional composite can successfully monitor its structural integrity. In fact, it demonstrates high sensitivity with a gauge factor approximately equal to 3. Moreover, when the TEG operates as a piezoresistive sensor, it is characterized by reliability. We thus believe that the herein suggested approach unveils new prospects regarding the efficiency and the sustainability of composite structures.

Evolution of the Stored Energy Density in a X2CrNiMo17-12-2 Austenitic Steel Under Cyclic Loading Conditions

Evolution of the Stored Energy Density in a X2CrNiMo17-12-2 Austenitic Steel Under Cyclic Loading Conditions

Experimental Study on the Mechanical Properties of Rock–Concrete Composite Specimens under Cyclic Loading

The foundations of bridges and other tall buildings are often subjected to cyclic loads. Therefore, it is essential to investigate the mechanical properties of rock–concrete composite foundations under cyclic loads. In this paper, uniaxial cyclic loading and unloading tests were conducted on rock–concrete composite specimens using the TFD-2000 microcomputer servo-controlled rock triaxial testing machine. The stress–strain curves, elastic modulus variation, and energy dissipation were analyzed. The results showed that the stress–strain curves of composite specimens under uniaxial cyclic loading and unloading conditions formed hysteresis loops. The hysteresis loop exhibited a sparse–dense–sparse pattern under the upper stress of 27.44 MPa, which was 90% of the uniaxial strength. The elastic modulus, as well as the dissipated energy, decreased rapidly in the first few cycles and then gradually decreased at a constant rate, with the upper stress increasing to 27.44 MPa. Both the elastic modulus and the dissipated energy exhibited an accelerated stage before specimen failure. The primary failure mode of the composite specimen was split failure from concrete to sandstone. A damage variable was derived to better reflect the laws governing the damage evolution of the composite under cyclic loads.

Ductile rupture under cyclic loadings at high triaxiality: The influence of strain hardening and elasticity

Previous works (Devaux et al., 1997; Cheng et al., 2017) have emphasized the effects of strain hardening and elasticity upon ductile rupture of metals under cyclic loading conditions. This work pursues the study and modelling of these two effects by distinct theoretical methods, each coupled with micromechanical finite element simulations of the behaviour of some “representative cell”. For the effect of strain hardening, we employ Morin et al. (2017)’s approach, based on the theory of sequential limit-analysis (Yang, 1993; Leu, 2007; Leblond et al., 2018). This approach is applied to various types of hardening of the metallic matrix: isotropic, linear kinematic, nonlinear kinematic with one or two kinematic variables (Armstrong and Frederick, 2007) , and even a simplified version of Chaboche (1991)’s model accounting for complex cyclic effects. Numerical micromechanical simulations of a hollow sphere made of elastic–plastic materials obeying the various hardening laws considered, and subjected to cyclic loadings at high triaxiality, fully confirm the predictions of the model developed, provided elasticity is made negligible by using an artificially high value of Young’s modulus. When a realistic value is employed, however, the agreement between theoretical predictions and numerical results is degraded, thus emphasizing again the importance of the effect of elasticity in cyclic ductile rupture. To deal with this effect we derive, apparently for the first time, an evolution equation of the porosity accounting for (compressible) elasticity. However, numerical micromechanical simulations reveal that simply using this new evolution law, while keeping all other aspects of the model unchanged, remains insufficient to get a good match of theoretical and numerical results. Such a match is achieved by introducing the ad hoc hypothesis that the yield criterion and flow rule derived from sequential analysis still apply in the presence of elasticity, but with some “effective porosity” slightly differing from the true one through some heuristic, adjustable factor.

Comparative analysis of two intergranular strain-based hypoplastic models through elemental and centrifuge testing

While hypoplastic models have demonstrated accurate predictions of sand behavior under monotonic loading, their accuracy diminishes when applied to cyclic loading conditions. To address this limitation, the intergranular strain approach is used as an extension to the model. The current investigation focuses on the analysis of two variants: the original Intergranular Strain (IS) approach proposed by Niemunis and Herle (1997) and the Intergranular Strain Anisotropy (ISA) by Fuentes et al. (2019). Although both models have the same objective, they present distinct mathematical structures and therefore different repercussions on the simulations. In this study, sand Hypoplasticity is enhanced with IS and ISA, and employed to simulate a series of experimental tests conducted on Fontainebleau sand. These tests encompass isotropic compression, drained monotonic triaxial, and undrained cyclic triaxial tests, while considering different initial densities and test characteristics. Furthermore, the calibrated models were applied to simulate a series of centrifuge tests, involving a pile embedded in the same sand, which is subjected to various episodes of monotonic and cyclic lateral loading. A comparison and discussion of the similarities and differences in elemental and finite element predictions, arising from the two intergranular strain formulations is presented.

Experimental and Computational Analyses of Sustainable Approaches in Railways

Railway transportation is widely recognized as an environment-friendly and sustainable means for conveying freight and passengers over long distances. This article investigates the effectiveness of utilizing scrap tire rubber granules and geosynthetics to enhance track performance in response to the growing demands for railway transport and the consequent escalation of train-induced loading. A multi-faceted methodology, incorporating experimental, numerical, and analytical techniques, is employed to examine the efficacy of these sustainable approaches. Results from three-dimensional (3D) finite element (FE) analyses conducted on slab tracks for high-speed railways reveal that the addition of a resilient layer, comprising scrap tire rubber granules, reduces vertical stress within the track substructure. Laboratory investigations on an innovative composite material consisting of soil, scrap rubber granules, and polyurethane demonstrate its potential to enhance track performance. Findings from two-dimensional (2D) FE analyses conducted on pile-supported railway embankments highlight an enhanced transfer of load to the pile head following the installation of a geogrid layer at the embankment base. Finally, the results from the analytical approach indicate a reduction in track settlement and a decrease in the track geometry degradation rate on reinforcing the ballast layer with 3D cellular geoinclusion. The novelty of this study lies in the comprehensive assessment of the innovative composite material under drained and cyclic loading conditions, the investigation of the influence of train loading on geosynthetic tension and the load transfer mechanism in railway embankments, and the development of an innovative computational methodology capable of assessing the effectiveness of 3D cellular inclusions in improving the ballasted railway track performance. The findings from this article underscore the effectiveness of these sustainable approaches in mitigating the challenges posed by increased loads on railway tracks, providing valuable insights for the ongoing efforts to optimize railway transportation infrastructure.

Evaluation of strength and mechanical properties of Disang sandstone from Tertiary formation in Indian Himalaya under complete and incomplete uniaxial cyclic loading conditions

Evaluation of strength and mechanical properties of Disang sandstone from Tertiary formation in Indian Himalaya under complete and incomplete uniaxial cyclic loading conditions

Cyclic behaviour of circular CFT-SG columns under axial tension-compression: Novel FE modelling and design methods

The ultra-high concrete-filled steel tubular (CFT) power transmission tower is popularly applied in engineering practice, which may be under a typical cyclic axial tension-compression loading condition due to the dynamic wind load. Nonetheless, the CFT columns of the tower may be accompanied by significant gap defects due to the influence of structural feature, material property, and service environment. Hence, to figure out the performance of circular CFT columns with spherical-cap gaps (CFT-SG) subjected to cyclic axial tension-compression, this paper investigates a constitutive relationship for the gapped core concrete, which is verified by several existing experiments. A novel numerical modelling approach for simulating the irregular cross-section of the circular CFT-SG columns under cyclic axial load was following established based on the triangulation method and code programming. The influence of important parameters such as gap ratio, material strength, and diameter to thickness ratio on the hysteresis characteristics, load-bearing capacity, elastic stiffness, energy dissipation and ductility of circular CFT-SG columns under cyclic axial tension-compression force is studied. Moreover, the restoring force model of the circular CFT-SG columns under cyclic axial tension-compression is finally presented. Research results declare that the compressive bearing capacity, stiffness, ductility, and energy dissipation of circular CFT-SG columns under cyclic axial tension-compression are gradually weakened with the increment in the gap ratio. The numerical modelling approach and restoring force model proposed in this article can accurately evaluate the hysteresis performance of circular CFT-SG columns subjected to cyclic axial tension-compression.

Bond behaviour of steel rebar in polyethylene engineered cementitious composites under various load conditions

Engineered Cementitious Composites (ECC) are a special type of ultra-ductile fiber-reinforced concrete that uses microfibers. The bond strength of Polyethylene ECC with steel reinforcement was found to be not well investigated in the literature under both monotonic loading and cyclic loading conditions. This study aims to investigate the bond strength properties of Polyethylene ECC with steel reinforcement under monotonic and cyclic loading conditions and to evaluate the effect of embedment length, loading rate, and the cover on bond strength experimentally. The beam-end test was selected for this experiment since it is a relatively simple test, yet it produces a realistic stress field. The results indicated that ECC's main failure mode is splitting-pullout, with high slippages occurring. Furthermore, increasing the cover thickness from 3db to 4db enhanced the bond strength by 91%, while raising the anchorage length from 5db to 7db improved it by 105%. Increasing the load rate from 0.01 mm/s to 32 mm/s resulted in a significant 63% improvement in bond strength. Moreover, ECC performed exceptionally well under cyclic loading, displaying increased peak loads by an average of 76.8% compared to monotonic loading. The study findings are expected to guide the formulation of development length equations and finite element models incorporating ECC.

Combined anisotropic and cyclic constitutive model for laser powder bed fusion fabricated aluminum alloy

This study presents new methods to effectively model the anisotropic yielding and hardening behavior of laser powder bed fusion fabricated aluminum alloy under both monotonic and cyclic loading conditions. The proposed model combines the yield surface-interpolation method to accurately describe the anisotropic hardening rates in various directions, with the Chaboche kinematic hardening rule to precisely reflect the cyclic characteristics. For numerical implementation of the combined anisotropic and cyclic constitutive model, a fully implicit stress integration algorithm based on return mapping method is provided. Moreover, the multiple parameters associated with the model are categorized and identified in an uncoupled manner. The isotropic and cyclic hardening parameters are determined by an inverse method, and the stability of the optimization outcomes is validated by applying different starting points for the parameters. Particularly, the back-stress effect on the identification of anisotropic parameters associated with the stress invariant-based Hill48 yield function is considered for the first time. This consideration leads to an improved prediction accuracy compared to the identification of anisotropic parameters without considering back-stress effect. The combined anisotropic and cyclic constitutive model, along with the calibrated parameters, are proven capable of accurately reproducing the intricate deformation behavior of laser powder bed fusion fabricated AlSi10Mg.

A new criterion of rock burst proneness based on residual energy release rate index

The natural property of rock material, whether impact occurs, is the key influencing factor of the occurrence of rock burst disaster. To accurately assess rock burst proneness, this study focuses on typical sandstone as the research object. Uniaxial cyclic loading and unloading tests were conducted to measure the elastic strain energy accumulated in sandstone under different stress levels and a relationship between elastic strain energy and stress level was established. The results show that: (1) The peak stress under cyclic loading and unloading conditions is slightly lower than the uniaxial compressive strength. With an increase in the number of cycles, the internal damage of sandstone continues to accumulate, and the mechanical properties such as compressive strength continue to deteriorate; (2) With an increase in stress, the input strain energy, elastic strain energy, and dissipated strain energy also increase; (3) When the stress is low, the increase in elastic strain energy is large and shows a steady growth; with an increase in stress, the increase of elastic strain energy decreases; (4) The square of stress at any time has a good linear relationship with elastic strain energy. According to the relationship obtained from the test, the elastic strain energy at the peak stress time can be obtained; (5) A new criterion for assessing rock burst proneness is proposed: residual energy release rate index WT, which characterizes the energy release per unit time when the rock burst occurs. The intervals for evaluating the rock burst proneness of the residual energy release rate index WT are as follows: WT <0.025, indicating no rock burst proneness; 0.025≤ WT <0.15, indicating weak rock burst proneness; 0.15≤ WT <2, indicating medium rock burst proneness; WT >2, indicating strong rock burst proneness; and (6) The rationality of the proposed residual energy release rate index WT is verified by the multi-index method and the multi-sample method, and the proposed residual energy release rate index is used to determine the rock burst proneness of 10 kinds of rock samples. The evaluation accuracy is shown to be high, and it can reflect the actual rock burst proneness

EXPERIMENTAL STUDY ON THE STRUCTURAL BEHAVIOUR OF RECYCLED PLASTIC ONE STORY HOUSES

Recycling plastic materials may constitute a relief measure to the global plastic problem. Several companies are now producing recycled plastic for use as construction material in single-story houses. One commercially available layout involves assembling Recycled Plastic Lumber units in a running bond pattern, forming panels confined by horizontal and vertical tie elements joined through bolted steel plate connections. As production of houses is industrialized, the architectural layouts are standardized according to specific distribution and dimensions. This paper presents the findings of an experimental program aimed to characterize the seismic behavior and properties of a one-story house model. To facilitate practical application, the model is referred here as Architectural Standard Model (ASM). The objectives of the test campaign were to investigate the structural behavior of the constituting members and assemblies, and the response of structural walls to cyclic static lateral loads. Three natural scale wall specimens were tested in-plane and two out of plane. Results of natural scale cyclic loading tests demonstrated that structural system of the ASM can perform acceptably safely under high seismic loads if it is adequately fixed to the foundation. The results showed that out of plane loading was the critical pattern and behaved like a unidirectional plate that transmitted load to the columns. In plane observed behavior exhibited predominating rocking component, which suggests considering an evaluation of the system's response using dynamic methods.

Large-Scale Triaxial Testing of Geogrid-Stabilized Field-Sourced Fouled Ballast Under Simulated Progressive Rainfall Wetting and Cyclic Loading Conditions

Railroad track ballast composed of uniformly graded crushed aggregate is susceptible to fouling from substances like ballast fines degraded during track service, coal dust, clay, and sand. Fouling reduces the drainage capacity of ballast, often leading to water accumulation and subsequent performance degradation. Fouled ballast with high moisture content experiences excessive settlement and could benefit from stabilization for safe operations. While previous studies have highlighted the efficacy of geogrids in stabilizing fouled ballast and minimizing the overall track settlement, the effect of geogrid on the performance of fouled ballast under progressive rainfall wetting and continuous cyclic loading conditions remains unexplored. This study examines the performance of geogrid-stabilized field-sourced fouled ballast through large-scale triaxial tests. The findings reveal that the inclusion of a single-layer geogrid can effectively reduce settlement and deformation rates under equivalent water content conditions. A layer of geogrid could prevent sample failure under saturated conditions, retaining approximately 1,000 kPa post-cyclic shear strength. Furthermore, the results indicate that geogrid stabilization enhances the resilience of fouled ballast and maintains the track geometry under progressive rainfall conditions. These findings offer crucial insights for geogrid applications in railroad maintenance.

Experimental study of the static and hysteretic performance of grouted steel beam-column inter-connections for modular integrated construction

Modular Integrated Construction (MiC) has gained prominence as a construction method, and the integrity of its structural connections plays a critical role in ensuring the overall stability and safety of buildings. This paper presents an experimental investigation into the static and hysteretic performance of grouted steel beam-column inter-connections designed for MiC. The study examines eight full-scale specimens subjected to both monotonic and cyclic loading conditions, with a focus on failure characteristics, deformation behavior, loading-displacement curves, loading-strain curves, skeleton curves of hysteretic loops, stiffness degradation, and energy dissipation. Key findings of the study include the observation of weld cracking between beam flanges and columns in all specimens, highlighting the necessity of welding quality control to prevent such issues. Grouted connections exhibited superior integrity, with no gap opening or misalignment between upper and lower columns. Additionally, it was found that grouting could enhance the stiffness of certain connections. Removal of diagonal stiffeners significantly decreased peak bearing capacity, emphasizing their importance. The composite action brought about by bolts connecting ceiling and floor beams also proved influential. According to Eurocode 3, all grouted specimens fall under the classification of semi-rigid connections, with a distinction made for partial and full-strength connections. This research contributes valuable insights into the static behavior and hysteretic performance of grouted steel beam-column inter-connections for MiC, providing essential knowledge for the structural design and safety of buildings utilizing this innovative construction method.

Characteristics of Geogrid-Reinforced Rubber-Coated Ballast under Cyclic Loading Conditions

Rubber-coated ballast (RCB) is a newly invented ballast made up of natural aggregates coated with recycled crumb rubber with the help of polyurethane binder. The deformation, degradation, resilience, damping, and acceleration time response for unreinforced (UR) and geogrid-reinforced (GR) RCB-natural ballast mix were explored under cyclic loading conditions. The results from the cyclic loading tests indicated that the deformation of RCB samples was higher than that of natural ballast owing to the softening properties of crumb rubber. It was also seen that the deformation of the RCB-natural ballast mix increased with the increase in RCB content. Furthermore, the resilient modulus ( Mr) of the RCB-natural ballast mix reduced while the damping ratio ( Dr) increased with the increase in RCB content. Moreover, the GR RCB-natural ballast mix exhibited lesser deformations, whereas the Mr and Dr improved compared with the UR RCB-natural ballast mix. Additionally, RCB significantly reduced the sleeper acceleration and ground-borne vibration compared with natural ballast. These accelerations were further reduced, to some extent, when the RCB-natural ballast mix was reinforced with geogrid. The particle breakage of the GR RCB-natural ballast mix was reduced considerably compared with the UR natural ballast. To minimize the volumetric strain and particle breakage of the RCB-natural ballast mix and maximize the Mr and Dr, it is recommended that around 50% of RCB content is mixed with GR natural ballast.

Rate dependent cohesive zone model for fatigue crack growth

Experimental observations indicate that the frequency of cyclic loads can influence fatigue crack growth. To address this phenomenon in simulation modelling, this study introduces a rate-dependent cohesive zone model designed for analysing fatigue crack growth under arbitrary cyclic loading conditions. The model operates in the time domain, where both critical traction and fracture toughness are modelled as functions of the separation rate, thereby considering the rate dependency of material damage and cracking. Unlike conventional models, this approach does not rely directly on loading frequency, suggesting its capability to address fatigue crack growth under non-periodic loading or repeated impacts effectively. An algorithm for modelling fatigue crack evolution and growth was developed based on this model, employing a time-incremental strategy in conjunction with a linear cumulative damage method. This algorithm was implemented in ABAQUS using a user element subroutine (UEL). The effectiveness of the proposed model and algorithm is validated through examples of fatigue crack growth in a plate under cyclic loading with varying frequencies. The results demonstrate agreement with experimental and computational findings reported in the literature. Additionally, the model was applied to scenarios involving frequency-variable cyclic loadings, yielding reasonable outcomes. Analysis of these examples confirms the model's utility in predicting fatigue crack growth under diverse alternating load conditions.

Experimental investigation on mechanical behavior of silane‐modified polyurethane sealant under biaxial cyclic loading

AbstractThe biaxial tension–tension cyclic loading experiments were conducted on the cruciform specimens prepared using a silane‐modified polyurethane sealant to investigate their mechanical behavior. The finite element method was employed to validate the mechanical behavior of cruciform specimens under the biaxial cyclic loading conditions. It is shown that the highest stress concentration is in the central region of the cruciform specimens, indicating that the shape design of the specimen is suitable for the biaxial tension–tension cyclic tests. Additionally, the effects of loading path, mean stress, and stress amplitude on ratcheting strain and dissipated energy were analyzed through the experimental data. The experimental results demonstrated that the loading path had an influence on the mechanical behavior of the cruciform specimen. The additional ratcheting strain caused by the non‐proportional loading path was found to be loading path dependent of the adhesive. Moreover, the mean stress and stress amplitude greatly affected the strain response curves of the specimen under biaxial cyclic loading. The ratcheting strain and dissipated energy increased with increasing mean stress and stress amplitude; nevertheless, stress amplitude had more influence on the mechanical behavior than the mean stress.

Effects of pressurized water reactor environment and cyclic loading parameters on the low cycle fatigue behavior of 304L stainless steel

Austenitic stainless steels used in light water reactor coolant environments are susceptible to environmentally assisted fatigue due to non-monotonic loading conditions, primarily associated with load-follow, thermal transients, or intermittent plant shutdowns and start-ups. This study investigates the effects of a high-temperature pressurized water reactor (PWR) water environment and cyclic loading parameters on the low cycle fatigue behavior of austenitic 304L stainless steel. Prolonged exposure to a PWR environment and cyclic loading conditions such as a lower strain rate or a higher fraction of slow strain rate enhances the initiation and accelerates the crack growth rate of fatigue cracks, resulting in decreased fatigue life. The deformation-induced α'-martensite is observed in proximity to fatigue crack tips primarily in specimens tested in simulated PWR primary water, while cellular dislocation structures are more frequently observed near crack tips in specimens tested in high-temperature air. The deformation-induced martensitic transformation from γ-austenite to α'-martensite, occurring via the precursor ε-martensite phase, contributes to the accelerated fatigue crack growth rate in a PWR environment with hydrogen.

Installation and test procedure for frequency stability under cyclic loading of metals and alloys

Manufacture of parts operating under difficult conditions of cyclic loading, as well as products with stable dimensions necessitates the use of materials with minimal manifestations of inelastic properties. Study of these materials suggests conducting specialized narrowly focused tests using newly developed machines and installations with appropriate experimental techniques. We present the design, operation and control features of the original electromagnetic installation for testing fatigue and frequency stability and operating in a self- oscillating mode, which provides the equality of the frequency of cyclic loading and natural frequency of the sample. The system of the installation control contains two closed circuits: for excitation of self-oscillations and for stabilization of the oscillation amplitude. The sample is loaded by electromagnetic force, and unloading occurs due to the elastic forces of the material. The methodology and algorithms for calculating the stresses of samples of various geometric shapes for estimating changes in amplitude-frequency characteristics are presented. The calculated relationship between the force applied to the sample and its movement at the point of application of force is derived with subsequent determination of the stress by a known force. The results of calibration tests for the static mode of sample loading are presented and the forces acting on the sample (external, inertia, and elastic forces) are evaluated taking into account the maximum stress and maximum strain amplitude. Static and cyclic loading modes are compared. The frequency characteristics obtained during testing steel samples according to the proposed method are obtained. The experimental results of tests with interruptions in the process of cyclic loading and continuous testing are analyzed. It is shown that interruptions in cyclic tests lead to a jump-like increase in the frequency, whereas continuous tests revealed no jumps. At the same time, a comparative analysis with the results of continuous tests showed that the overall frequency deviation is approximately the same for the entire operating cycle in both cases. It is shown that an increase in the frequency after rest is random and does not depend on the number of operating cycles.

Tie system to upgrade out‐of‐plane performance of infill masonry walls

AbstractThe objectives of this study were to investigate the out‐of‐plane behavior of unreinforced masonry (URM) infill walls and to identify the effectiveness of tie systems that were proposed to enhance the infill stability under both in‐ and out‐of‐plane effects. This study examined three types of tie systems: a full‐length tie system (prototype), a staggered tie system and a half‐length tie system. For this purpose, four 1/4‐scale, single‐story, one‐bay masonry infilled reinforced concrete (RC) frame specimens with and without the proposed tie systems were sequentially tested under in‐plane static cyclic loading and out‐of‐plane dynamic excitation. In the experimental study, two series of shaking table tests were conducted to investigate the out‐of‐plane behavior of the infill walls. The first series compared the fundamental out‐of‐plane performance of three proposed tie systems, and the second series verified the effectiveness of the full‐length tie system to prevent infill out‐of‐plane failure under an excitation simulating the severe floor response in medium‐rise buildings. The test results indicated the following: (1) the presence of the tie systems caused minor differences in the in‐plane capacity and ductility of each specimen, (2) the effectiveness of the full‐length and staggered tie systems was superior to that of the half‐length tie system, and (3) the full‐length tie system not only prevented the infill out‐of‐plane failure but also significantly reduced the infill damage under realistic excitation conditions. The above research outcomes provide a useful contribution of the infill to upgrade the seismic resistance of buildings.