Effect Of Loading History Research Articles

Cyclic deformation of 316L stainless steel and constitutive modeling under non-proportional variable loading path

In order to investigate the effect of non-proportional loading history on cyclic deformation of 316L stainless steel, a series of multiaxial cyclic experiments with variable loading path are conducted at room temperature. It is found that the materials exhibit cyclic hardening at initial stage, followed by a long period of cyclic softening. Significant cyclic softening is observed when non-proportional loading path changes into proportional loading path and the rate of cyclic softening is related to non-proportional loading history. A visco-plasticity constitutive model based on Ohno-Wang kinematic hardening rule and Marquis isotropic hardening rule is used to characterize non-proportional cyclic behavior. Simulation results agree with experiments very well in terms of cyclic hardening effects. However, this model is found to be less effective in simulating cyclic softening effect, especially considering the influence of non-proportional loading history. A modified isotropic hardening model is thus proposed to simulate the cyclic softening behavior of 316L stainless steel by introducing a memory non-proportionality and qualifying a partial recoverable softening term of isotropic hardening rule. Simulation results of the proposed model agree much better with experimental values.

Liquefaction and post-liquefaction assessment of lightly cemented sands

Post-liquefaction response of lightly cemented sands during an earthquake may change and become similar to uncemented sands due to bonding breakage. In the current study, the effect of degree of cementation on liquefaction and post-liquefaction behaviour of lightly cemented sands was studied through a series of cyclic and monotonic triaxial tests. Portland cement with high early strength and Sydney sand were used to reconstitute the lightly cemented specimens with unconfined compression strength ranging from 25 to 220 kPa. A series of multi-stage soil element tests including stress-controlled cyclic loading events with different amplitudes and post-cyclic undrained monotonic shearing tests were carried out on both uncemented and cemented specimens. Furthermore, a series of undrained monotonic shearing tests without cyclic loading history on different types of specimens was conducted to investigate the effect of cyclic loading history on the post-cyclic response of the specimens. The results show that residual excess pore-water pressure is correlated to the cyclic degradation of lightly cemented sands during cyclic loading. In addition, optical microstructure images of the cemented specimens after liquefaction showed that a major proportion of cementation bonds remained unbroken, which resulted in a superior post-liquefaction response with respect to initial stiffness and shear modulus in comparison to the uncemented sand.

Rate and temperature dependent relations for CFSTs and CFFTs subject to post-impact fire conditions

Experimental research on the behaviour of conventional construction materials subject to extreme loading condition of post-impact-fire has indicated the effect of rate dependent loading history on the temperature performance of these materials. In order to analyse and design structures to withstand such combined loading, it is desirable to develop models that can reflect the mechanical properties of materials under initial impulsive loading and subsequent elevated temperature. In this study, a rate-pre-damage-temperature dependent empirical expression is proposed to predict the residual strength of partially damaged steel-concrete and fibre rein-forced polymer-concrete composite materials, in the form of concrete-filled steel tubes (CFST) and Concrete filled carbon-fibre reinforced polymer tubes (CFFT), at high temperatures up to 600 °C. The developed model is calibrated and validated on the basis of actual experimental data published by the authors. The proposed expression proves to be capable of successfully reproducing material strengths by considering the extent of high strain rate induced pre-damage together with temperature exposure.

Pressure loading histories and clay fraction effects on the static and dynamic elastic properties of sand-clay synthetic sediments

Investigations of the elastic mechanical characteristics of loosely compacted mixed sand-clay samples are essential for the characterization of shallow seafloor sedimentary reservoirs. Here, we used a series of sand-clay mixtures (0–100% clay by weight) to investigate the effects of pressure load histories (2–50 MPa) and clay fraction on porosity, P-wave velocity, S-wave velocity, and static modulus. The results indicated that, under pressure load cycles, the sand-clay mixture samples exhibited high permanent compaction, and porosity decreased rapidly with increasing clay content. However, porosity changed differently in response to pressure load as compared to pressure unload. Correspondingly, P-wave velocities differed significantly between pressure load and unload.The rock physical models implied that the sample frame evolved with the varying clay fraction. As the clay fraction increased, the sample frame gradually transitioned from primarily sand grains with dispersed pore-filling clay to primarily clay, ultimately transforming into a clay frame with dispersed sand grains. The measured data generally conformed to the theoretical model and falling within the Voigt and Reuss bounds. Moreover, for all sand-clay mixture samples, although the static bulk modulus was consistently lower than the dynamic bulk modulus, the ratio of the dynamic modulus to the static modulus was highly dependent on pressure loads and clay fraction.

Technical Note: Post-Fire Axial Load Resistance of Concrete-Filled, Double-Skin Tube (CFDST) Stub Columns

This technical note reports findings on a series of squash tests to investigate the effects of a significant fire loading history on the axial load strength of concrete-filled, double-skin tube (CFDST) stub columns. Axial loading tests were conducted on two stub columns that were previously subjected to the first 60 minutes of the standard ASTM E119 (ASTM, 2012) fire. Results were compared to the resistance of an identical virgin stub column. Comparisons indicated an average reduction of 28% in the axial load strength of stub columns when subjected to the mentioned fire loading history.

Fatigue crack growth of G20Mn5QT cast steel based on a two-parameter driving force model

This paper performs a research on fatigue crack growth in G20Mn5QT cast steel using the experimental method and a semi-empirical fatigue crack growth model. The model combines the two-parameter driving force and fatigue damage accumulation. It would take into account the effects of mean stress and load history, and the fatigue crack growth rate curve would only be influenced by the sort of material. Comparing to the experimental results, the proposed model has good simulation results. A unified fatigue crack growth rate equation for G20Mn5QT cast steel has been given out, which is more convenient for engineering applications.

Cyclic deformation behavior of friction-stir-welded dissimilar AA5083-to-AA2024 joints: Effect of microstructure and loading history

The microstructural evolution across the friction-stir-welded dissimilar AA5083-H112 to AA2024-T351 aluminum alloy joints was characterized via electron backscatter diffraction (EBSD), aiming to identify the effect of inhomogeneous microstructures on the tensile properties and cyclic deformation behavior along with the influence of loading history. Results show that the top region of the stir zone (SZ) mainly consisted of AA2024 which was initially positioned on the retreating side during welding. On the AA5083 side, the lowest density of the geometrically-necessary dislocations (GNDs) assessed from the local misorientations of 0°–2° appeared in the SZ, while it occurred in the heat-affected zone (HAZ) of the AA2024 side. The fractions of recrystallized grains in the AA5083 SZ and AA2024 SZ were ~73% and ~34%, respectively. Strain localization and the resultant failure occurred in the lowest hardness zone of the AA5083 side. The extent of cyclic hardening increased as the stress amplitude increased. Both plastic strain amplitude and plastic strain energy density decreased with increasing number of cycles at higher total strain amplitudes. In the stepwise cyclic deformation tests in the form of ascending-descending loading, the prior cyclic deformation process tended to generate more stabilized structure and performance.

Effect of Loading History and Restraining Parameters on Cyclic Response of Steel BRBs

This study presents a numerical modelling and prediction of cyclic response of all-steel buckling-restrained braces (BRBs) under different loading histories using a finite element software ABAQUS. The numerical models are validated by comparing the predicted hysteretic response, core fracture, energy dissipation and displacement ductility with the results of a past experimental study. Later, the validated numerical model is used in a parametric study to investigate the influence of coefficient of friction and clearance between the steel core and restrainers, the length of yielding core segment and the position of stoppers on core segments on the cyclic response of steel BRBs. The coefficient of friction is varied in the range of 0–0.5, whereas the gap value is varied in the range of 0–5 mm. The main parameters studied are the hysteretic response, axial resistance, instance of core fracture and energy dissipation response. Based on the analysis results, the optimum values of friction coefficient, gap, length of yielding core and stopper orientation have been recommended for steel BRBs.

Post-cyclic shear behavior of reconstituted marine silty clay with different degrees of reconsolidation

In this paper, a series of dynamic triaxial tests have been carried out to study the post-cyclic shear behavior of the reconstituted marine silty clay. Most previous studies on the post-cyclic shear characteristics of clay considered no reconsolidation after cyclic loading, and a few studies investigated the influence of full reconsolidation. The actual marine clay after cyclic loading tends to be in a state between no reconsolidation and full reconsolidation after cycling. Therefore, different reconsolidation processes including no reconsolidation, full reconsolidation and different degrees of reconsolidation were conducted to investigate their effects on the post-cyclic shear characteristics. Various factors including confining pressure, initial consolidated deviator stress ratio, cyclic stress ratio and degree of reconsolidation were taken into account. Results show that the post-cyclic shear strength will be enhanced and weakened with the full and no reconsolidation, respectively. And a specific degree of reconsolidation is existed for the specimens, with which the post-cyclic shear strength equals to the corresponding static shear strength. During the post-cyclic monotonic shear process, the silty clay always have a positive pore pressure and show dilative tendency. Moreover, no significant effects of cyclic loading and reconsolidation history on the change of critical stress ratio in p′-q plane was observed for the reconstituted silty clay. The critical stress line for specimens in e-log p′ plane tends to be affected by the previous cyclic loading amplitude, irrespective of the reconsolidation process. Besides, a post-cyclic shear strength model which can consider different degrees of reconsolidation was obtained based on the Yasuhara equivalent overconsolidation model. The predicted results demonstrate a good agreement with the measured one.

Влияние вида напряженного состояния и истории нагружения на холодную ползучесть титанового сплава

Влияние вида напряженного состояния и истории нагружения на холодную ползучесть титанового сплава

Phenomenological constitutive modeling of ferromagnetic shape memory alloys considering the effects of loading history on reorientation start conditions

Ferromagnetic shape memory alloys (FSMAs) are a branch of smart materials which can undergo inelastic deformation when exposed to magnetic fields. In this work, experiments are carried out on an FSMA consisting of elastic interruptions during reorientation to study the effects of loading history on reorientation start conditions. Correspondingly, a phenomenological approach is introduced to propose appropriate kinetic laws capable of modeling cases in which loading history plays an important role. Conventional phase diagrams in 2D field–stress space are generalized to 3D reorientation surfaces to directly enter the effects of loading history on reorientation start conditions. Algebraic approaches are utilized to find conditions guaranteeing the continuation of variant reorientation. Further experiments are also carried out to verify the proposed model under various incomplete loading–unloading cycles and minor loops. Comparison between numerical and experimental results indicates the validity of the proposed model. Appropriate continuation conditions for the biaxial loading case are proposed, and biaxial results are used to verify the proposed model.

Numerical and experimental simulation of dowel action across reinforced concrete (RC) cracks under two-directional loading

The local and global behavior of reinforced concrete (RC) members and structures may be affected by cracks and the capabilities of stress transfer mechanisms. Dowel action is one of the shear transfer mechanisms across RC cracks and particularly is the only mechanism in pre-formed joints that are common in precast concrete connections. Herein, the path-dependent behavior of dowel action mechanism is examined experimentally and analytically. Firstly, the effect of loading history and direction on the shear transfer capabilities of crossing bars are investigated experimentally. Then, according to the experimental results and observations, a model is extended to simulate and capture the directional path-dependent behavior of dowel action by introducing consistent formulas for subgrade springs based on the beam on the elastic foundation analogy. Verification is carried out by comparing with the corresponding experimental results and shows the fair accuracy of the proposed model and assumptions.

Characterization of fatigue delamination growth under mode I and II: Effects of load ratio and load history

The study of fatigue delamination growth in composite materials aims to develop a slow-growth approach for composite materials that would provide conservative and reliable results. The present work focuses on the study of the load ratio effect on fatigue crack growth at constant amplitude and on the effect of variable amplitude loading on crack propagation. With this in mind, a Crack Driving Force (CDF) is chosen to attempt to overlap delamination growth curves obtained from different load ratio values for mode I and mode II. It is shown that the CDF collects the effect of the load ratio on the crack growth curves and allows to build a crack growth master curve for mode I and II. Variable amplitude loads are then considered for delamination propagation in mode I. However, variable amplitude loads bring to light a load history effect during fatigue crack growth that the CDF does not take into account.

Loading History Effect on Creep Deformation of Rock

The creep characteristics of rocks are very important for assessing the long-term stability of rock engineering structures. Two loading methods are commonly used in creep tests: single-step loading and multi-step loading. The multi-step loading method avoids the discrete influence of rock specimens on creep deformation and is relatively time-efficient. It has been widely accepted by researchers in the area of creep testing. However, in the process of multi-step loading, later deformation is affected by earlier loading. This is a key problem in considering the effects of loading history. Therefore, we intend to analyze the deformation laws of rock under multi-step loading and propose a method to correct the disturbance of the preceding load. Based on multi-step loading creep tests, the memory effect of creep deformation caused by loading history is discussed in this paper. A time-affected correction method for the creep strains under multi-step loading is proposed. From this correction method, the creep deformation under single-step loading can be estimated by the super-position of creeps obtained by the dissolution of a multistep creep. We compare the time-affected correction method to the coordinate translation method without considering loading history. The results show that the former results are more consistent with the experimental results. The coordinate translation method produces a large error which should be avoided.

Effect of load history on shear strength of reinforced concrete I-Beams

A series of 32 reinforced concrete I-beams was tested to investigate the effect of existing inclined cracks on shear strength. Testing of beams consisted of two stages. At the preliminary stage, load large enough to cause a formation of a developed crack pattern in the web was applied with the primary shear span-depth ratio. After that, the load with breaking shear span-depth ratio was applied until failure of the specimen. The load applied during the preliminary loading stage was maintained with a full or partial value by a lever, or removed. The test variables include shear span, shear reinforcement ratio and angle of stirrups inclination. Pre-cracking was found to decrease the ultimate shear strength of beams by a maximum of 16 percent depending on the angle of stirrups. A corresponding reduction factor is suggested to the formula of the Russian code for the design of bridges. The finite element simulation of beams was fulfilled by using the program OpenSees. The webs of beams were simulated with a 2D element built on the Cyclic Softened Membrane Model to take into account the deterioration of concrete due to the previous loading. The accuracy of the proposed FE model was verified with the aforementioned tests and the results of several other studies.

Crack path and life prediction under mixed mode cyclic variable amplitude loading through XFEM

In the present paper, a mesh independent computational algorithm is developed and incorporated into a commercial finite element software (Abaqus) for automated fatigue crack growth analysis under mixed mode variable amplitude loading conditions. The algorithm calculates the stress intensity factor (SIF) at predetermined small crack growth increments in the finite element software by using Extended Finite Element Method (XFEM) and predict the fatigue crack growth (FCG) path through local symmetry (KII=0) criterion. The aforementioned algorithm also computes the FCG life by means of cycle-by-cycle integration method through Nasgro equation based on the equivalent SIF range. Load history effects are also taken into account by using appropriate retardation models according to nature of the loading. For verification purpose, experimental crack path trajectories and fatigue life data available in the open literature are compared with computational results. Quite good agreements are obtained between the computed and the experimental results.

Effect of single tensile peak overload on the performance of bonded composite repair of cracked Al 2024-T3 and Al 7075-T6 plates

Under real working conditions, structures are subjected to variable and peak loads. It is well known that cracks growth rate is load history dependent. Overloads generate crack growth retardation while underloads produce acceleration in crack growth. The effect of load history on patch repair is not covered so far. In this work, we investigated experimentally, how a single overload peak affects the performance of a bonded composite patch repair in cracked Al 2024-T3 and 7075-T6 samples fatigued under a cyclic loading. We studied the effect of three overload peaks; 9, 12 and 14 kN, applied just before and soon after the bonded composite repair. The fatigue lives and retardation cycle numbers exhibited that subjecting the test sample to overload before the repair will cause more retardation of the crack growth, while the reverse will result in less retardation, yet still better than that subjected to an overload alone. We carried out SEM observations to analyse the fractographs of failed specimens subjected to overloads and observed mixed mode fracture type.

Resistant force model of viscous damping wall considering influence of loading frequency

Due to the heterogeneity and velocity-dependency of viscous fluid, it’s quite difficult to simulate the dynamic behavior of viscous damping wall (VDW). The existing formulae for resistant forces need different parameter values for different loading frequencies. This may lead to large errors in resistant forces of VDWs subjected to an earthquake with large frequency change. A small-scale shaking table test and a large-scale dynamic actuator test were performed to investigate the influence of loading frequency, showing that direct data fitting with a single set of parameter values for different frequencies will lead to erroneous hysteretic cycles. Based on experimental results, five assumptions were proposed and thereafter a unified model was developed considering the influence of loading frequency by means of introducing the effect of loading history. The proposed model was validated with satisfactory accuracy in predicting the test results.

High‐Resolution Mapping of Yield Curve Shape and Evolution for Porous Rock: The Effect of Inelastic Compaction on Porous Bassanite

AbstractPorous rock deformation has important implications for fluid flow in a range of crustal settings as compaction can increase fluid pressure and alter permeability. The onset of inelastic strain for porous materials is typically defined by a yield curve plotted in differential stress (Q) versus effective mean stress (P) space. Empirical studies have shown that these curves are broadly elliptical in shape. Here conventional triaxial experiments are first performed to document (a) the yield curve of porous bassanite (porosity ≈ 27–28%), a material formed from the dehydration of gypsum, and (b) the postyield behavior, assuming that P and Q track along the yield surface as inelastic deformation accumulates. The data reveal that after initial yield, the yield surface cannot be perfectly elliptical and must evolve significantly as inelastic strain is accumulated. To investigate this further, a novel stress‐probing methodology is developed to map precisely the yield curve shape and subsequent evolution for a single sample. These measurements confirm that the high‐pressure side of the curve is partly composed of a near‐vertical limb. Yield curve evolution is shown to be dependent on the nature of the loading path. Bassanite compacted under differential stress develops a heterogeneous microstructure and has a yield curve with a peak that is almost double that of an equal porosity sample that has been compacted hydrostatically. The dramatic effect of different loading histories on the strength of porous bassanite highlights the importance of understanding the associated microstructural controls on the nature of inelastic deformation in porous rock.

Influence of prior cyclic plasticity on creep deformation using crystal plasticity modelling

This paper proposes a simple, yet effective, modified crystal plasticity framework which is capable of modelling plasticity and creep deformation. In particular, the proposed model is sufficiently versatile to capture the effects of complex load histories on polycrystals, representative of those experienced by real materials in industrial plant. Specifically, the methodology was motivated by the need in the power generation industry to determine whether cyclic pre-straining influences the subsequent creep behaviour of type 316H austenitic stainless steel as compared to non-cyclically pre-strained material. Cyclic pre-straining occurs widely in plant and it is of paramount importance to accurately account for its impact on the subsequent deformation and integrity of relevant components.The framework proposed in this paper considers the effects of dislocation glide and climb in a relatively simple manner. It is calibrated using experimental tests on 316H stainless steel subjected solely to monotonic plasticity and forward creep. Predictions are then obtained for the creep response of the same material after it had been subjected to cycles of pre-strain. The predictions are compared to experimental results and good agreement was observed. The results show slower creep strain accumulation following prior cyclic loading attributed to hardening structures developed in the material during the cyclic pre-strain. The model also highlights the importance of accounting for directionality of hardening under reverse loading. This is hypothesized to affect the development of an internal stress state at an intragranular level which is likely to affect subsequent creep accumulation.