Ratcheting Strain Rate Research Articles

Local ratcheting and stress relaxation at notch root of CP-Ti specimen under cyclic loading: Experiment and simulation

Damage and crack always origin from notch, and it is necessary to understand the local ratcheting and stress relaxation at notch root for commercially pure titanium (CP-Ti). Symmetric strain-controlled cyclic test for smooth CP-Ti specimen is conducted to determine the cyclic constitutive relationship based on the combined hardening model. Asymmetric force-controlled cyclic test combined with Digital Image Correlation (DIC) technology is conducted to reveal local ratcheting strain distribution at notch root of CP-Ti specimen, while the distributions of stress, local stress ratio, and local hysteresis curve at notch root are obtained by finite element (FE) simulation. It is found that plastic zone, local ratcheting and stress relaxation at notch root area change significantly with cyclic load levels. In the low stress amplitude region with the mean nominal stress lower than 87 MPa, the small-scale yield occurs, and the notch root is in a state of plastic shakedown. With the mean nominal stress increasing to 96 MPa in the transition region, the notch root is in a state that exceeds the plastic shakedown limit but the continuous ratcheting progress is not found. In the high stress amplitude region with the mean nominal stress higher than 104 MPa, the plastic zone significantly expends, and the notch root is in a continuous ratcheting progress state, accompanied by stress relaxation. For a specific structural configuration, the local ratcheting at notch root is affected by both the load level and the cyclic deformation characteristics of the material. In the high stress amplitude region, the reverse yield occurs at the notch root during unloading, which promotes continuous ratcheting progress and stress redistribution, resulting in stress relaxation. The higher the load level, the larger the ratcheting strain rate, and the lower the stress relaxation rate.

Ratcheting Effect of 304 Stainless Steel Manufactured by Laser Metal Deposition Under Uniaxial Cyclic Stress

Laser metal deposition (LMD) is an advanced manufacturing technology which has become increasingly popular in recent years. The cyclic tests of 304 austenitic stainless steel (SS304) manufactured by LMD are conducted under symmetrical and asymmetrical cyclic stress. In the results, it is shown that SS304 manufactured by LMD exhibits cyclic softening/hardening and ratcheting effect under symmetrical cyclic stress. The ratcheting strain and ratcheting strain rate of the smooth specimen both increase as the cyclic stress amplitude under the asymmetric cyclic stress. The ratcheting strain and ratcheting strain rate of the smooth specimen change non‐monotonously as the mean stress increases. As the stress amplitude increases, the area of fatigue fracture becomes smaller until no fatigue crack initiation zone can be observed. In this case, only the characteristic of plastic fracture is significant. Park et al.'s model has the worst predicted accuracy. Modified Goodman equation and Smith–Watson–Topper model have the similar predicted accuracy.

Uniaxial ratcheting behavior and microstructure evolution of 316H stainless steel under the random cyclic loads

In this study, the Computational Fluid Dynamics (CFD)-Finite Element Method (CFD-FEM) were used to simulate the transient stress response of the structure surface under thermal striping environment, and a uniaxial random cyclic loading (RCL) method was used to reveal the mechanical properties and initial microstructure evolution of 316H austenitic stainless steel (SS) under random stress induced by thermal striping. The experimental results showed that 316H exhibited a lower saturation ratcheting strain rate at 334.44 MPa, along with stronger cyclic hardening effects and resistance to plastic accumulation at loading rate of 100 Hz. Random loading tests with different cycles were performed at σpeak=334.44MPa and fRCL=100Hz, and ratcheted specimens were characterized to investigate the effect of the micro-mechanism on cyclic softening/hardening. The geometrically necessary dislocation (GND) density increases and then decreases with cyclic loading, which is mainly attributed to the deformation twin (DT) and multi-dislocation slip mechanisms. The deformation mechanism during the ratcheting cycle from 1000 to 3000 cycles is mainly dominated by the twinning reduction, where the dislocation migration accelerated the transformation from dislocation walls to subgrain boundaries; the twinning increase dominates from 3000 to 9000 cycles, where the subgrain boundary grew into boundaries with high angle misorientations.

Experimental study of fatigue behaviour of Q690qENH bridge weathering high-strength steel welded joints

The Q690qENH weathering high-strength steel has a considerable potential for bridge engineering due to its superior mechanical strength, toughness, and corrosion resistance. To evaluate its performance under fatigue loads, the high-cycle fatigue behaviour of Q690qENH base metal and its welded joints is studied. A total of 68 specimens are tested to obtain their stress–fatigue life (S−N) curves. Results show that the fatigue strengths of the base metal, butt-welded joint, and cross-welded joint are greater than those specified in the ANSI/AISC 360-16, Eurocode 3-2005, and BS 7608-2014 design standards. The most suitable S−N curve for evaluating the fatigue properties of the Q690qENH base metal, butt-welded joint, and cross-welded joint was deemed to be that given by ANSI/AISC 360-16. New S−N curves were proposed for the base metal and butt-welded joint, whereas the S−N curve for the cross-welded joint remained unchanged as per the existing codes. Additionally, the cumulative fatigue damage behaviour of the butt-welded and cross-welded joints was analysed, and a safety threshold based on the ratcheting strain rate was established to provide early warning at 85%–95% of fatigue life. Through digital image correlation and fatigue fracture analysis, the cause of fatigue fracture in the welded joints was determined to be caused by stress concentration at the weld toe.

Rate-dependent ratcheting characteristics of high density polyethylene subjected to cyclic pulsating compression

Monotonic and pulsating cyclic compression tests were performed systematically based on high density polyethylene (HDPE). The compressive creep behaviors were further implemented to compare with the ratcheting deformation under the same peak stress level. Monotonic compression experiments reveal that HDPE shows obvious four-stage characteristics which are sensitive to temperature, but independent of the stress rate when the temperature is greater than 80 °C. Interestingly, the strain range during the stage III always starts at 7.4% and ends at 62.6% under various temperatures and stress rates. Moreover, the compressive ratcheting behavior of HDPE significantly depends on temperature T, peak stress σp, stress rate σ˙, stress amplitude Δσ and stress ratio R, especially when T ≥ 80 °C, σp ≥15 MPa, σ˙ ≤0.1 MPa/s and R ≥ 0.8. Additionally, decreasing the stress rate or increasing the temperature will decrease the compressive modulus of HDPE. An approximate linear relationship between the creep strain rate and the ratcheting strain rate under different temperatures and stress ratios was observed. The compressive deformation characteristics of HDPE were compared with that of some other gasket materials, a universal phenomenon is found that the compressive ratcheting evolution with time can be characterized by creep approximately under the same loading peak stress, stress rate and temperature for various gasket materials when the stress ratio is greater than zero, which indicates that the ratcheting deformation for gaskets under cyclic loads may be estimated by the corresponding static creep strain in practical engineering.

Influence of Microalloying on the Microstructures and Properties of Spalling-Resistant Wheel Steel

Microalloyed steels have emerged to replace conventional plain-carbon steels to achieve longer wheel life on Chinese railroads. In this work, with the aim of preventing spalling, a mechanism that consists of ratcheting and shakedown theory correlated with steel properties is systematically investigated. Mechanical and ratcheting tests were carried out for microalloyed wheel steel to which vanadium was added in the range of 0-0.15 wt.% and the results were compared with that obtained for conventional plain-carbon wheel steel. The microstructure and precipitation were characterized via microscopy. As a result, the grain size was not obviously refined, and the pearlite lamellar spacing decreased from 148 nm to 131 nm in microalloyed wheel steel. Moreover, an increase in the number of vanadium carbide precipitates was observed, which were mainly dispersed and uneven, and precipitated in the pro-eutectoid ferrite region, in contrast to the observation of lower precipitation in the pearlite. It has been found that vanadium addition can lead to an increase in yield strength by precipitation strengthening, with no reduction or increase in tensile strength, elongation or hardness. The ratcheting strain rate for microalloyed wheel steel was determined to be lower than that for plain-carbon wheel steel via asymmetrical cyclic stressing tests. An increase in the pro-eutectoid ferrite content leads to beneficial wear, which can diminish spalling and surface-initiated RCF.

A ratcheting mechanism-based numerical model to predict damage initiation in twin-disc tests of premium rail steels

This work presents a ratcheting mechanism-based numerical model to study the initiation location and initiation life of rolling contact fatigue (RCF) or wear damage and the initial wear rate of premium rail steels under the laboratory twin-disc test conditions. Twin-disc tests are widely used in the studies of rail steels due to their ability to reproduce critical aspects of full-scale wheel-on-rail contact under controlled conditions and a relatively short test period compared to field tests. This study introduces a computational model to simulate the cyclic rolling contact for three premium rail steels (HE1, HE2, and LAHT) against wheel steel AAR Class-C under twin-disc test conditions. The cyclic rolling contact is achieved by repeatedly moving a non-Hertzian distribution of contact pressure and the calculated longitudinal surface traction upon a segment of the circumferential surface of the lower disc until a stabilized maximum ratcheting strain rate is reached. The RCF or wear damage initiation location is determined by the location showing the stabilized maximum ratcheting strain rate, and the damage initiation life is estimated by applying the ratcheting failure mechanism. Wear and RCF damages are distinguished by the depth of the damage initiation location. Wear damage is dominant when the location is near the surface. Otherwise, the damage will be RCF-dominated. The initial wear rate due to wear-dominated damage is estimated by identifying a critical profile and affected volume of worn material within the ratcheting strain rate field. The predicted initial wear rate is compared with the experimental result of the examined contact pair. This research can assist in a more profound understanding of the experiment results of a twin-disc test and provide a numerical basis for an experimental twin-disc test design. Furthermore, it may provide significant references for choosing rail steels.

Dynamic strain aging-mediated temperature dependence of ratcheting behavior in a 316LN austenitic stainless steel

Tensile tests and ratcheting tests were performed on a 316LN austenitic stainless steel at 300 °C, 400 °C, 500 °C, and 600 °C, respectively, to study the influence of dynamic strain aging (DSA) on deformation behavior and microstructural evolution. The DSA temperature range in present work was determined to be ≥ 400 °C in both uniaxial tests and ratcheting tests. Especially in the ratcheting tests, a sudden drop in ratcheting strain accumulation as well as in steady ratcheting strain rate was evident when the temperature raising from 300 ° to 400 °C. While within the DSA temperature region, the ratcheting behavior was insensitive to the temperature. Microstructural examinations revealed dislocation cells and tangles in the sample ratcheted at 300 °C (free of DSA), while complex dislocation structure in the samples ratcheted at ≥ 400 °C (with DSA) that was consisted mainly by high-density dislocation walls, planar slip bands, and Lomer-Cottrell locks. This clearly indicates a change in predominant ratcheting deformation mechanism from cross-slip at DSA-free temperature region to planar-slip at DSA region. It was further demonstrated that, within the temperature range from 400 °C to 600 °C, the DSA-induced hardening effect balanced with the thermally-activated softening effect and this balance led to temperature-insensitive ratcheting behavior as experimentally observed. Finally, the DSA-affected dislocation structure was quantitatively evaluated in the ratcheted samples, with an aim in correlating to the ratcheting behavior.

Numerical study on ratcheting performance of heavy haul rail flash-butt welds in curved tracks

Ratcheting at the rail heads due to cyclic rolling contact stresses is often observed in heavy haul railways, especially when there are large steering forces developed in low-radius curves. Additionally, ratcheting behaviour can be exacerbated when associated with material strength loss in the heat affected zones of rail welds. However, the numerical evaluation of this failure mode requires a sophisticated representation of elastic–plastic contact pressures and traction distributions, which, to the best of the authors’ knowledge, cannot be directly measured by any existing tools. In this paper, in order to accurately evaluate the ratcheting performance at rail welds in curved tracks, attempts were conducted to modify the FaStrip algorithm to analytically estimate the traction distributions based on contact pressures and creepages obtained from static finite element analysis and multi-body dynamic simulations, respectively. Cyclic rolling contact was then simulated by repeatedly applying contact pressure and traction on the rail surface consisting of both the rail weld and the parent rail regions. The weld region was divided into 23 sub-zones in the rolling direction to represent the material inhomogeneity within the heat affected zones. Cases on a 2000 m radius curved track and a tangent track were studied for comparison. It was found that the ratcheting strain rate in curved tracks can be significantly elevated due to the higher magnitude of traction, and the location of the elements with the highest ratcheting strain rate was dependent on the traction distribution patterns. The proposed method provides a general tool for predicting rolling contact fatigue initiation life and location, which will benefit the maintenance efficiency of heavy haul rail welds in curved track.

Uniaxial ratcheting behavior and molecular dynamics simulation evaluation of 316LN stainless steel

In this study, a series of uniaxial ratcheting experiments under different mean stresses with a constant stress amplitude were performed on a 316LN stainless steel at room temperature. Meanwhile, molecular dynamics (MD) simulation was carried out to reveal the microstructure evolution mechanism at the initial stage of ratcheting deformation at atomic scale. The results showed that the initial stage of ratcheting deformation could be divided into three stages: the stage of beginning (ratcheting strain growth rate (RSGR, dεr/dN) >0.01%), the stage of decreasing ratcheting rate (RSGR at 0.00001–0.01) and the stage of elastic/plastic shakedown (RSGR <0.00001) based on the changes of ratcheting strain rate. The shakedown ratcheting strain was linearly increased with increase of the mean stress in both MD simulation and experiment. And the ratchet deformation at different stages strongly depended on dislocation evolution. At the stage of beginning, the dislocation originated from coincident site lattice (CSL) boundaries and formed pile-up structures at random angle grain boundaries (RAGBs); while at the stage of decreasing ratcheting rate, the dislocation tangled at CSL grain boundaries or inside the grain, the dislocation density gradually increased and tended to be stable. When the given stress was insufficient to produce more plastic strain, the dislocation density balanced dynamically and the ratchet deformation entered the stage of elastic/plastic shakedown.

Development of a new ratcheting fatigue life prediction model of a nickel-based superalloy based on ratcheting strain rate

The stress-controlled low cycle fatigue and ratcheting fatigue behaviors of a nickel-based superalloy were proposed under a series of symmetric and asymmetric cyclic loadings at 650 °C to explore the effects of stress amplitude and mean stress on fatigue life. The results show that ratcheting strain increases with cycle numbers increasing. Ratcheting strain rate curves exhibit three different stages including deceleration, steady state and acceleration growth stage. A fatigue life prediction model based on the ratcheting strain rate considering stress amplitude and mean stress was conducted to predict the fatigue life. The predicted fatigue life agrees with the measured fatigue life very well, and all the data points are located in 1.25X scatter band based on the model.

In situ neutron diffraction study of fatigue behavior of CrFeCoNiMo0.2 high entropy alloy

In situ neutron diffraction measurement was applied to study the low-cycle fatigue behavior of CrFeCoNiMo0.2 high entropy alloy. A two-step stress-controlled fatigue test with a stress range of 100–460 and 20–500 MPa was employed. The as-cast sample was cycled 129,000 and 61,000 times, respectively, before fracture. The evolution of the lattice strain and peak intensity demonstrates that the main deformation mechanism is dislocation slip, while no evidence of stacking fault was found. A three-stage ratcheting was clearly observed. Under the stress-controlled mode, the experimentally determined dislocation density increases linearly with the ratcheting strain. The increase of the dislocation density results in a decay of the ratcheting strain rate, which stabilizes the structure and is beneficial for fatigue resistance.

Ratcheting Behavior of Sintered Copper Joints for Electronic Packaging

This study experimentally investigated the whole-life ratcheting behavior of sintered copper joints with consideration of the effects of stress rate, stress amplitude, mean stress, maximum stress, and stress ratio. Deformation of joints under cyclic load was measured by a noncontact displacement detecting system. In these joints, ratcheting strain and ratcheting strain rate were found to be sensitive to loading factors. For example, strain decreased as mean stress and stress amplitude decreased, and also as stress ratio and stress rate increased. Meanwhile, larger stress amplitude or mean stress reduced ratcheting fatigue life, while increasing stress ratio and stress rate increased fatigue life. The results indicate the modified Goodman model accounting for the effects of mean stress can usefully predict the ratcheting fatigue life of sintered copper joints at room temperature.

Compressive fatigue properties of additive-manufactured Ti-6Al-4V cellular material with different porosities

Selective laser melting (SLM) is a novel additive manufacturing (AM) technique for producing cellular metallic materials with designed pore structures. SLM Ti-6Al-4V cellular alloys have been extensively studied for biomedical and other applications. The objective of this study was to investigate the effects of porosity (33 vol%, 50 vol%, and 84 vol%) on the compressive fatigue performance and fracture mechanism of an SLM Ti-6Al-4V cellular material with a new cuboctahedron COH-Z unit cell. Furthermore, the influences of hot isostatic pressing (HIP) at 1000 °C/150 MPa on the fatigue properties and fracture were also examined in this study.The results showed that the fatigue strain slowly accumulated when the stress cycle was below the 70% fatigue life. After the 70% fatigue life, the ratcheting strain rate (dε/dN) gradually increased. A shear band along a direction inclined at ~45° to the stress axis could be definitely identified at about 95% fatigue life, as demonstrated by the digital image correlation technique. With further increases in the stress cycle, the shear band was intensified and finally led to rapid fatigue failure. The HIP process did not alter the fracture behaviors of the SLM cellular alloy, although the fatigue life was much improved by several times. On the other hand, the fatigue endurance ratio of the SLM cellular alloy with 33 vol% was 0.5. Raising the porosity from 33 vol% to 84 vol% reduced the endurance ratio from 0.5 to 0.15 due mainly to the high notch sensitivity of α′-martensite in the SLM cellular alloy. The HIP treatment changed the microstructure from α′-martensite to lamellar α+β phases and thus significantly improved the fatigue endurance performance. With the combination of the COH-Z unit cell and HIP treatment, the endurance ratios at 106 cycles of the Ti-6Al-4V cellular alloy with porosities of 33 vol% to 84 vol% were as high as 0.5. This superior endurance ratio is advantageous to the long-term application of SLM Ti-6Al-4V cellular alloy.

Cyclic plasticity of an interstitial high-entropy alloy: experiments, crystal plasticity modeling, and simulations

The development of high-entropy alloys (HEAs) comprising multiple principal components is an innovative design strategy for metallic materials from the perspective of thermodynamic entropy. However, despite their potential candidacy for engineering applications, the lack of research on the cyclic loading responses as well as constitutive modeling of the HEAs is a major constraint. Therefore, the present work focuses on the cyclic plasticity of a typical carbon-doped interstitial HEA (iHEA) with nominal composition Fe49.5Mn30Co10Cr10C0.5 (at.%). The results of stress-controlled cyclic tests with nonzero mean stress showed that the iHEA exhibits significant cyclic hardening and stress level–dependent ratcheting. Owing to its improved cyclic hardening, the saturated ratcheting strain rate of the iHEA is lower than that of conventional steels such as the 316L stainless steel. Furthermore, microscopic characterizations revealed that the cyclic deformations caused massive martensitic phase transformation and hierarchical structures in the iHEA. The experimental results were used to develop a physical mechanism-based crystal plasticity constitutive model that is capable of describing the cyclic plasticity of the iHEA, which was implemented into a finite element framework. The simulation results showed that the loading stress significantly affected the microstructural evolutions, leading to a stress level–dependent cyclic plasticity. Thus, this investigation provides a fundamental basis for fatigue tests and service life prediction/optimization of the iHEA in the future, which can promote its engineering applications.

Uniaxial Ratcheting Behavior of a Weather-Resistant Rail Steel: Effect of Mean Stress and Stress Amplitude

Uniaxial ratcheting behavior of a weather-resistant rail steel belonging to 60 kg/m 90-UTS variety was studied in true stress control mode with varying mean stress (σm) and stress amplitude (σa) at constant σa and σm, respectively. In all the loading conditions, the ratcheting strain (er) increased almost monotonically and accumulation of ratcheting strain was found to increase at higher magnitude of σm or σa, perhaps due to the increase in remnant dislocation density in the substructure of the investigated steel. After the initial sharp fall in ratcheting strain rate with elapsed cycles in all the cases, a constant ratcheting rate was attained very soon; thereafter, the ratcheting strain kept on accumulating in the specimen at this constant rate till the failure of the specimen occurred. It was quite interesting to see that on increasing the mean stress level at a fixed stress amplitude, after the initial decrease, fatigue life of the steel improved marginally owing to the effect of mean stress-induced hardening. In absolute contrast, under the influence of stress amplitude at a fixed mean stress, fatigue life of the rail steel deteriorated gradually but to a significant extent. Finally, stress amplitude was found to have more severe effect than that offered by the mean stress in terms of` ratcheting strain accumulation and fatigue life of the investigated rail steel.

Uniaxial and biaxial ratcheting behavior of pressurized AISI 316L pipe under cyclic loading: Experiment and simulation

Ratcheting defined as the progressive accumulation of plastic strain occurring during cyclic loading in the presence of the mean stress is one of the most prevalent failure modes in engineering structures. Experimental studies were conducted to characterize the uniaxial and biaxial ratcheting responses of an AISI 316L pipe. Experimental results show that an obvious cyclic hardening occurs in the AISI 316L pipe under uniaxial strain loading. Uniaxial ratcheting rate obtained from the axial cyclic experiment reaches a quasi-steady rate after a certain number of loading cycles. Moreover, using a designed four-point bending experimental setup, different axial stress amplitudes in the presence of the constant hoop stress were considered to characterize the biaxial ratcheting response of the material. The ratcheting strain and ratcheting strain rate in the hoop direction increase with increasing axial stress amplitudes under the constant hoop stress. To simulate the uniaxial and biaxial ratcheting behavior of the AISI 316L pipe, the Chaboche nonlinear kinematic hardening model was used. Using the Particle Swarm Optimization (PSO) technique, parameters of the Chaboche model were identified efficiently from the monotonic response of a cold-worked sample. The elastic limit of the material was measured using a very careful quasi-static cyclic compression experiment. The procedure to calibrate the material parameters for the Chaboche model and finite element simulation results were validated well with experimental data for the AISI 316L pipe. It is shown that the Chaboche model with the suitably-calibrated parameters from the experimental study can be applied to rigorously predict the ratcheting behavior of the AISI 316L pipe under cyclic uniaxial and biaxial loading conditions.

Investigation on the uniaxial ratchetting and fatigue failure behaviors of silicone seal adhesive bonded butt-joints under tensile and torsional cyclic loading

In order to investigate the uniaxial ratchetting behaviors and fatigue failure of silicone seal adhesive bonded hollow cylinder butt-joints under uniaxial tensile and torsional cyclic loading, the effects of stress amplitude, mean stress, cycle time and loading history on the ratchetting strain, ratchetting strain rate and fatigue life were discussed respectively. The experimental results show that ratchetting strain appeared in both tensile and torsional cyclic loading. The ratchetting strain of tensile cycle evolved in three stages, while that of torsion cycle evolved in two stages. Furthermore, the effect of uniaxial tensile cycle on ratchetting strain is greater than that of uniaxial torsion cycle, and the fatigue life of torsion cycle is higher than that of tensile cycle. The stress amplitude, mean stress and cycle time have influence on the ratchetting strain, ratchetting strain rate and fatigue life of the adhesively bonded butt-joints. The ratchetting strain and ratchetting strain rate increase, and the fatigue life decreases with the increase of stress amplitude and mean stress, or the decrease of cycle time. In addition, it is also found that silicone seal adhesive bonded butt-joint has a strong memory of loading history for the stress amplitude. Prior stress cycle with higher stress amplitude restrains the ratchetting strain in subsequent cycle with lower stress amplitude.

Experimental study on rate-dependent uniaxial whole-life ratchetting and fatigue behavior of polyamide 6

Rate-dependent whole-life ratchetting and fatigue failure of polyamide 6 were explored by conducting a series of stress-controlled uniaxial fatigue tests at room temperature. Meanwhile, the temperature rises on the surface of specimens were recorded to reflect the self-heating occurred during the fatigue tests. The experimental results demonstrate that ratchetting strain rate is sensitive to the variation of prescribed stress rate, and the whole-life ratchetting of PA6 presents a tri-staged evolution feature at high stress rate but a four-staged one at low stress rate. Two failure modes (i.e., the necking controlled by unstable self-heating and resultant large ratchetting strain; and the fracture controlled by the low-cycle fatigue damage) are experimentally observed in the tests at different stress rates. By considering the relationship between ratchetting evolution and temperature rise, it is found that whether increasing the stress rate retards or promotes the ratchetting is dependent on the magnitude of self-heating produced at each fatigue stage, and whether it will be beneficial or detrimental to the total fatigue life is determined by the competition of resultant strain hardening and self-heating softening.

Ratcheting Behavior of Intervertebral Discs Under Cyclic Compression: Experiment and Prediction.

ObjectiveTo evaluate the ratcheting behavior of intervertebral discs (IVD) by experiments and theoretical study.MethodThe lumbar spines of sheep were obtained at a local slaughterhouse, and the IVD was processed with upper and lower vertebral bodies (about 5 mm) to ensure the mechanical state of the IVD in situ. The ratcheting tests of uniaxial cyclic compression loading for disc samples is carried out using the Electronic Universal Fatigue Testing System at room temperature. The effects of different stress variations, stress rates, as well as different segments on ratcheting behavior of discs were investigated.ResultsThe ratcheting strain evolution of lumbar IVD include stages of sharp increase and asymptotic stability. Both the ratcheting strain and ratcheting strain rate increase with an increase of stress variation (R = 0.962, P = 0.004) but decrease with an increase of the stress rate (R = −0.876, P = 0.019 ). Compression stiffness increases with an increase of the stress rate (R = 0.964, P = 0.004 ) or stress variation (R = 0.838, P = 0.037). Compared with L5 – 6, the L6 – 7 disc showed less ratcheting strain (P = 0.04 ), indicating that the disc at this segment was more resistant to the impact of the ratcheting cycle. In addition, ratcheting strain evolution was predicted using a ratcheting evolution constitutive equation, and the predicted results were in good agreement with experimental data.ConclusionsThe ratcheting behavior occurs in IVD, and this cumulative deformation is consistent with the general ratcheting behavior. The constitutive equation can predict the ratcheting strain evolution of IVD very well. These results are of great significance for the analysis of defects and the development of repair in IVD.