Effect Of Loading History Research Articles

Load history dependency of stiffness properties of PTFE-coated glass fibre membranes

The aim of this contribution is to investigate whether the order of load ratios applied to a textile structure impacts the biaxial stiffness behaviour of the structural textile itself. These investigations are performed based on biaxial tests on an architectural woven glass fibre fabric, a representative of such membranes. The first part of the paper investigates the existence and extent of load history dependency in the material response. Biaxial test results show that effects of a previous load history on the weave geometry cannot be eliminated by further load cycling in all biaxial stress ratios. Moderate to strong effects are recognized in two stress ratios, although not in both weave directions.The second part of the paper examines how these effects influence material stiffness parameters and structural calculations. Two boundary value problems are investigated: a pressure chamber test and a roof structure. Parameters obtained by fitting biaxial tests with or without history are considered. By incorporating an adaptive load-ratio dependent scheme, highly predictive numerical results are obtained, showing that while the effect of load history may appear small in the biaxial tests and pressure chamber test, it can be significant in complex structural problems like roof structures.

The Importance of Preconditioning for the Sonographic Assessment of Plantar Fascia Thickness and Shear Wave Velocity.

Plantar fasciopathy is a very common musculoskeletal complaint that leads to reduced physical activity and undermines the quality of life of patients. It is associated with changes in plantar fascia structure and biomechanics which are most often observed between the tissue's middle portion and the calcaneal insertion. Sonographic measurements of thickness and shear wave (SW) elastography are useful tools for detecting such changes and guide clinical decision making. However, their accuracy can be compromised by variability in the tissue's loading history. This study investigates the effect of loading history on plantar fascia measurements to conclude whether mitigation measures are needed for more accurate diagnosis. The plantar fasciae of 29 healthy participants were imaged at baseline and after different clinically relevant loading scenarios. The average (±standard deviation) SW velocity was 6.5 m/s (±1.5 m/s) and it significantly increased with loading. Indicatively, five minutes walking increased SW velocity by 14% (95% CI: -1.192, -0.298, t(27), p = 0.005). Thickness between the calcaneal insertion and the middle of the plantar fascia did not change with the tissues' loading history. These findings suggest that preconditioning protocols are crucial for accurate SW elastography assessments of plantar fasciae and have wider implications for the diagnosis and management of plantar fasciopathy.

Time-dependent soil–structure interaction analysis using a macro-element foundation model

The delayed settlement of foundations due to soil consolidation, creep or particle breakage can alter the internal load distribution and differential settlements in a superstructure through soil–structure interaction (SSI). The study introduces a novel methodology to simulate time-dependent SSI that overcomes the complexity of incorporating the time-dependent behaviour of foundations into routine SSI analysis. The proposed approach represents the superstructure as a condensed stiffness matrix, and replaces the foundations and underlying soils with macro-element foundation models that encapsulate the foundation–soil interaction into load–displacement relationships derived from constitutive models. To examine the performance of the proposed method, a macro-element model for time-dependent analysis of shallow foundations on sand was integrated with structural analysis to simulate two tests performed in a geotechnical centrifuge on a 3D-printed aluminium framed structure supported by footings on sand. The simulated responses of the superstructure and foundations were found to agree well with those observed in the centrifuge tests. Parametric analyses were conducted to investigate the effect of loading history, load level on the superstructure, and creep tendency of soil on post-construction load redistribution and differential settlements. The findings suggest that creep of foundations on sand facilitates load redistribution in the structure from heavily loaded sections to lightly loaded sections. Moreover, post-construction load redistribution depends on the differential creep between footings and should be considered for structures that are quickly constructed or at high levels of strength mobilisation (low factor of safety). Overall, the study highlights the potential of the proposed methodology in analysing the time-dependent SSI and its applicability in practical SSI analysis.

Uniaxial ratcheting and ductile damage in structural steel with a stochastic spreading of experimental data

AbstractThis paper provides new experimental data regarding inelastic strain accumulation in structural steel samples. The samples are subjected to stress‐controlled cyclic loading with positive mean stress within each cycle; the loading blocks are combined in a complex pattern to study the effect of load history. A large‐strain ratcheting model is constructed based on a material law with a nonlinear kinematic and isotropic hardening. A new rule of ductile damage accumulation is suggested and a class of models with hardening stagnation is introduced. We show that models which include the hardening stagnation describe the experimental data more accurately. Unfortunately, due to a large spread of mechanical properties from sample to sample, it is impossible to describe the entire set of experiments using a single set of parameters. To address this challenge, we have developed novel mathematical tools for parameter identification in the context of stochastic variations in mechanical properties. These tools include the concept of a collar of model responses and the notion of protrusion. We propose an extended parameter identification problem that rethinks the standard error functional. We demonstrate that the extended identification problem effectively accounts for the large spread observed in experimental data when applied to the developed ratcheting model.

Buckling and fracture behavior of cold formed carbon/stainless steel tubular braces under far field and near fault loadings

To date, many studies have been conducted on the experimental behaviors of circular and square hollow section braces. In those studies, the effect of material properties, cross-sectional shape and loading history on the performance of braces were investigated independently of each other. In this study, the effects of the combined actions of these variables on the performance of steel braces were examined. For this purpose, approximately 1/3 scaled 12 specimens (6 circular and 6 square), which were cold formed from carbon/stainless steel sheets, were experimentally and numerically investigated under 3 different cyclic load effects representing far field and near fault loadings. The buckling strength, energy dissipation capacity and displacement ductility of the specimens were evaluated. In addition, parametric studies, using 198 FE analyses verified with current study, were conducted. Experimental results indicate that the buckling strength limits provided in AISC 360–22 and EN 1993-1-1 for carbon steel braces are significantly influenced by the cross-section, loading protocol and material properties. On the other hand, it has been determined that the buckling strength limits given in AISC 370–21 and EN 1993-1-4 for stainless steel braces are safe for far field loadings, but insufficient for near fault loadings along the full slenderness range. It has been seen that the most disadvantageous results for the buckling strength, energy dissipation capacity and displacement ductility of the braces can only be obtained by applying different loading protocols. Moreover, It has been determined that the effect of material properties on the performance of braces varies considerably depending on the cross-section geometry.

Effects of cyclic loading history on liquefaction resistance for saturated sand

Effects of cyclic loading history on liquefaction resistance for saturated sand

Study on low-cycle hysteresis properties of seawater corroded steel considering loading history effects

To investigate the combined effects of wave loading history and time-dependent corrosion damage on the hysteresis mechanical properties of long-term serviced marine engineering materials, this study conducted hysteresis mechanical experiments and a generalized mechanical model research on corroded steel, considering the influence of high-cycle loading history. Steel corrosion was pre-generated by accelerated electrochemical corrosion method. Developing the early-stage high-cycle fatigue loading system and later-stage low-cycle hysteresis loading system based on the dynamic characteristics of wave loads, seismic actions, and typhoon-level pulsating wind loads. Analyze the influence of the independent and combined effects of early-stage load stress levels, cycle times, and corrosion damage on the steel capacity to withstand low-cycle high-stress hysteresis loading. Based on test results and mechanical properties, an improved generalized hysteresis mechanical model was established that encompassed monotonic tension curves, skeleton curves, and well-defined loading and unloading rules. The validity and universality of the model were verified through various loading systems and hysteretic tests of corroded steel. The results indicated that the early-stage high-cycle fatigue history led to a reduction in the material's elastic range, causing the material to transition into plasticity earlier. The combined effects of early-stage loading history and corrosion damage resulted in a significant degradation of the material's hysteresis mechanical properties.

Effect of Stress Ratio, Constraint, and Load History on the Intrinsic and Extrinsic Components of Threshold Stress Intensity

Abstract Threshold intensity range, ΔKth, was experimentally investigated as the sum of two components, both of which are sensitive to applied loading conditions. The intrinsic component, ΔKth,i, is characterized as a sole function of a near-tip stress parameter, σ*, in much the same way as fatigue limit depends on mean stress or stress ratio. The extrinsic component, ΔKcl, is the attenuated fraction of crack tip response because of crack wake contact, whose exact value is not readily measured at threshold. The ΔKth,i versus σ* relationship is established using a specially designed load shedding process under constant baseline maximum load, with σ* modulated through periodic overload-underload combinations whose periodicity is regulated to avoid undue crack extension at threshold. This relationship is then used to extract the ΔKcl component from ΔKth readouts obtained on the same batch of material using conventional load shedding procedure. The effect of constraint on ΔKth and its two components was studied using specimens with sharp side grooves to maximize constraint across the crack front. The study was performed on a medium strength low-alloy steel.

Experimental investigation on axially-loaded threaded rods inserted perpendicular to grain into cross laminated timber

This paper presents an experimental work on axially-loaded threaded rods inserted perpendicular to grain into the narrow face of cross laminated timber (CLT). Penetration length, loading type (tension, compression, fully reversed), and loading configuration (pull-pull and pull–push) were varied. The use of self-tapping screws as reinforcement was also explored. Stiffness under cyclic and monotonic loading, damping ratio, withdrawal capacity, failure mode, reinforcement effect, and influence of loading history were investigated. The experimental results highlight the high withdrawal stiffness and capacity of threaded rods embedded into CLT elements, and hence their effectiveness as fasteners for stiff timber connections.

Probabilistic evaluation of the Step-Stress fatigue testing method considering cumulative damage

A general testing and analysis framework for the Step-Stress fatigue testing method is identified, utilizing interval-censored data and maximum likelihood estimation in an effort to improve estimation of fatigue strength distribution parameters has been performed. The Step-Stress method’s limitations are characterized, using a simple material model that considers cumulative damage to evaluate load history effects. In this way, the performance including cumulative damage was evaluated and quantified using a probabilistic approach with Monte-Carlo simulations, benchmarked against the Staircase method throughout the work. It was found that the Step-Stress method, even when cumulative damage occurs to a wide extent, outperforms the Staircase method, especially for small sample sizes. Furthermore, positive results reaches further than the increase performance in estimating fatigue strength distribution parameters, where improvements in secondary information, i.e. S-N data gained from failure specimens, are shown to be distributed more closely to the fatigue life region of interest.

Ductile fracture of LYP225 steel: Effects of stress states and loading histories

This paper presents the experimental and modeling studies of the ductile fracture initiation of LYP225 steel, considering the stress state and loading history dependency. The monotonic material tests, including the notched round bars (NRBs), flat grooved plates (FGPs), and the shear plates (SPs), confirm the prominent stress state dependency of the ductile fracture. The increased stress triaxiality will significantly reduce the fracture strain, and the shear effect quantified by the Lode angle parameter will degrade the deformability under similar triaxiality. The Hosford-Coulomb fracture criterion can well characterize the relationship between fracture strain and stress state variables. Regarding the cyclic loading, a generalized expression of the cut-off region is proposed to consider the temporarily frozen damage accumulation under compression applied. In addition, the premature cyclic fracture initiation predicted by the monotonic fracture criterion highlights the necessity of considering the loading history effect. Based on the plastic strain memory surface, a reduced factor is introduced for the lower damage accumulation rate under cyclic loading. By comparing the testing and predicted plastic deformation corresponding to fracture initiation, the proposed fracture model is validated under different stress states and loading protocols, as indicated by the low average percentage errors of 4.02% for monotonic loading and 16.7% for cyclic loading.

Experimental investigation on service safety and reliability of full-scale HMPE fiber slings for offshore lifting operations

In recent years, high modulus polyethylene (HMPE) fiber slings have been increasingly used in marine transportation and installation projects due to their numerous advantages including lighter than steel ropes, easily handling operation, and no fish hooks et al. Due to the complex behavior of fiber ropes, an effective bedding-in method is necessary to proposed to stabilize the sling length and ensure the safety and reliability of offshore lifting operations. This study proposes a detailed procedures and techniques for evaluating the creep behaviors and load elongation properties of full-scale slings with a normal breaking strength of 10,000 kN. The experimental results reveal that the HMPE exhibits the viscoelastic-viscoplastic behavior and load history effect. Based on the experimental results, the crucial mechanical parameters such as Young's modulus and static stiffness of the HMPE sling are established. A bedding-in procedure of HMPE slings is proposed to remove the structural elongation and to ensure the stability of the length of the sling. The present results have been applied and verified on the evaluation of the slings in Sewol Salvage Engineering. The results can serve as a reference for the application of HMPE slings in offshore lifting operations.

Analysis of rail–bridge interaction of a high-speed railway suspension bridge under near-fault pulse-type earthquakes

Abstract Due to the limitations of railway route selection, some high-speed railways are inevitably built near or across fault zones. To study the distribution of rail–bridge interaction under different load history states of suspension bridges under three types of near-fault pulse-type earthquakes, this paper takes China's longest high-speed railway suspension bridge—Wufengshan Yangtze River Bridge—as the background and establishes a spatial model of the rail–bridge interaction of a suspension bridge. The results show that: under the constant load state, the distribution of additional force under three types of pulse-type earthquakes is generally consistent, and pulse-type earthquakes produce more significant responses than non-pulse-type earthquakes; with fling-step pulse being the largest, it is advised to specifically consider the influence of the fling-step pulse in the calculation. Under the initial condition of the main beam temperature loading history, all rail-bridge additional forces increase significantly, particularly affecting the steel rail system. The value of the rail–bridge interaction additional force under the near-fault earthquake in the initial state of the suspension bridge when the train deflection load is loaded from the tower to the mid-span is more significant and particularly unfavourable. The initial effect of the braking load will weaken the effect of the deflection load loading history. The results of the study indicate that the effect of the initial state of suspension bridges is an important factor influencing the rail–bridge interaction under near-fault pulse-type earthquakes, which needs to be considered in future seismic design.

Enhancing understanding of fracture mechanisms in brittle rocks under static and cyclic loads: Experimental insights and theoretical model

The present study investigates the fatigue behavior of granite and red sandstone under coupled static and cyclic loading. Experimental results reveals a three-stage evolution trend for the deformation modulus, Young's modulus, peak strain, residual strain, dissipated energy as a function of the absolute cycle. Acoustic emission (AE) rate also exhibits a three-phase stage, including the initial phase, uniform velocity phase, and accelerated phase. To explain the mechanical responses and fracture mechanisms related to rock fatigue, this study built a micromechanics-based damage model that adopts a modified Paris law and considers both the effect of static stress and stress amplitude. The theoretical model successfully reflects the effect of static loading history and reproduces the three-stage evolution of residual strain during rock fatigue. The SIF deduced by the theoretical model exhibits a distinct behavior: it initially decreases during the first few cycles, stabilizes at a lower value, and subsequently undergoes a significant increase as it approaches the final cycles. The internal cause behind the three-stage evolution of crack growth rate, AE rate, and mechanical properties is attributed to subcritical crack growth during cyclic loading. Finally, the theoretical model successfully characterizes the effect of static stress and stress amplitude of cyclic loads on fatigue damage evolution.

Influence of cyclic hardening characteristic on seismic performance of welded austenitic stainless steel H-section beam-column

Previous studies have revealed that the cyclic hardening feature of austenitic stainless steel depended on the applied strain amplitude and exhibited unsaturation prior to failure, which greatly affected the seismic response of austenitic stainless steel structures. In view of the limited research on the seismic performance and design of structural stainless steel members, this study investigates the influence of cyclic hardening characteristic on the performance of welded austenitic stainless steel H-section beam-column under combined uniaxial cyclic bending and constant compression. The finite element (FE) models of unsaturated cyclic hardening austenitic stainless steel grade S30408 beam-columns with H-section were initially created and validated with the available test data. The effects of loading history in conjunction with the axial compressive load level and the cross-section slenderness on the seismic performance of specimens were then studied through extensive parameter analysis. Results show that the capacities of load-carrying and deformation for the austenitic stainless steel member are discrete under different loading histories. Apparently, the unsaturated cyclic hardening property of stainless steel S30408 influences the performance of the member under seismic loading. Moreover, current codified design methods and the Continuous Strength Method (CSM) underestimated the ultimate strengths of stainless steel beam-columns under seismic loading. The over-strength factor and seismic deformation capacity design formulae of welded austenitic stainless steel H-section beam-columns were finally proposed.

Loading history effect on ratcheting behavior: Modelling and simulation

In this paper, an elastoplastic constitutive model is developed to describe the effect of loading history on the ratcheting. The loading history variable is introduced to record stress history variation during cyclic loading, such as equivalent peak stress and equivalent stress amplitude. Based on Ohno-Wang model, an improved kinematic hardening rule is proposed to simulate the ratcheting effect by establishing the nonlinear evolution equation of ratcheting parameter. A new memory evanescence term is introduced to the plastic strain range memory surface. The evanescence term is activated to describe the difference of yield stress evolution during ratcheting and strain-controlled cyclic loading as the plastic strain range radius exceeds a certain threshold. Compared with the experiments and existing models, the results show that the proposed model can better capture the ratcheting effect with loading history.

Experimental investigation and seismic analysis of a novel self-centering piston-based bracing archetype with polyurethane cores

This paper introduces a novel self-centering Piston-based Bracing with Polyurethane Cores (PBPC) as a passive seismic control device. Frames fitted with such bracing elements will be able to mitigate the loss of life, post-earthquake repair costs, and downtime recovery after a major seismic event. The proposed earthquake-resistant archetype integrates a steel shaft, steel tubes, and hollow and solid polyurethane (PU) cylindrical cores. The PU cylinders are activated using a bracing shaft and dissipate seismic energy with a self-centering response. A set of unidirectional cyclic tests were conducted on a scaled PBPC specimen to quantify the effects of pre-compression force level, loading rate, and past loading history. The pre-compressed force curtailed the undesirable viscoelastic deformation and the energy dissipation capacity of PU cores. The non– and pre-compressed PBPC elements exhibited large deformability and adequate energy dissipation; nonetheless, they recovered their initial conditions with stable flag-shaped hysteresis loops following successive compression cycles. Additionally, a new material model was developed in OpenSees software for PBPC and a comparative seismic analysis was conducted. The simulation outcomes supported by experimental data proved the efficiency of the frame fitted with PBPCs in mitigating damage compared with a buckling-restrained braced frame.

A crack growth rate model with load history effects for mode I fatigue-driven delamination under multi-level block loading

Load interaction effects in fatigue-driven delamination in fiber-reinforced polymer composites are neglected in state-of-the-art models although this assumption highly underestimates the delamination growth under variable amplitude (VA) loading. A new phenomenon called “transient delamination growth” has recently been observed in VA fatigue experiments by the authors. In the current work a new crack growth rate model with transient delamination growth capabilities is presented. The new model evaluates the crack growth rate by addition of a steady-state non-interaction term and a transient interaction term. The former term neglects load interaction effects and is characterized from constant amplitude loading tests, while the latter term includes load interaction effects and is characterized from two-level block loading tests. Fatigue tests are conducted on glass/epoxy DCB specimens by means of a new test fixture. The new crack growth rate model is able to accurately represent the crack growth rate at high-to-low load amplitude changes during multi-level block loading tests and reduces the error in delamination growth prediction by nearly 50% compared to non-interaction models.

Towards neural network‐based numerical friction models

AbstractFriction contacts can be found in almost all mechanical systems and are often of great technical importance. However, they are usually difficult to describe, and their behavior and influence on the whole system are hard to predict accurately. Modern product design and system operation strongly benefit from numerical simulation approaches today, but reliable friction models still represent a major challenge in this context.To tackle this problem, we employ neural network regression to capture the characteristics of frictional contacts and make them accessible for numerical methods in a minimal intrusive fashion. In particular, we test our approach using a Finite Element model of a 2D cantilever beam subject to stick‐slip vibrations induced by a moving conveyor belt at its free end. As a reference solution, we perform a transient analysis based on a simple analytical friction model, where the kinetic friction force only depends on the normal load and the relative sliding velocity. We take the same friction model, add some artificial noise to mimic uncertainties coming with experimental measurements, and pick a limited set of data points to train a regression neural network. The machine learning friction model is then deployed in the Finite Element code to predict the kinetic friction force acting on the beam tip during the slip phases.The deflection curves obtained by the transient numerical analysis using the new neural network friction model agree well with the reference solution based on the underlying analytical model. The results indicate that data‐driven approaches may also be capable of capturing more complex frictional contacts, including effects of temperature, humidity, and load history. The trained neural network friction models can then be employed in numerical simulations in a minimally intrusive manner. This approach opens up new possibilities to predict individual mechanical system behavior as accurately as possible.

Predicting fatigue crack growth through the small and long crack regimes for a military transport aircraft loading spectrum using FASTRAN

Predicting fatigue crack growth across the small and long crack regimes in airframe components is a challenging task. Current fracture mechanics methods require, amongst other things, high fidelity small crack growth rate data and a thorough understanding of the different behaviours of small and long cracks. This paper presents a case study where a fatigue crack growth prediction of Aluminium Alloy 7075-T7351 coupons tested to a military transport aircraft loading spectrum, from nucleation to failure, is attempted using the most recent version of the linear-elastic fracture mechanics-based analysis tool FASTRAN v5.76. The military transport aircraft loading spectrum was applied to different coupon configurations to show the effectiveness of FASTRAN for a range of crack growth scenarios. Crack growth rate data for the prediction in the near-threshold region was experimentally obtained from small cracks using quantitative fractography and this data is shown to be a determining factor in the accuracy of the prediction. This paper highlights the challenges faced by engineers in predicting fatigue crack growth under variable amplitude loading from nucleation to failure and demonstrates the ability of FASTRAN to accurately predict load history effects. Areas for continued improvement are identified with the aim of accurate and reliable fatigue crack growth prediction in a range of structures, conditions, and scenarios.