Irreversible Plastic Strain Research Articles

Ratcheting damage evaluation based on critically refracted longitudinal wave combined with recurrence quantification analysis

Excessive accumulation of irreversible plastic strain in ratcheting poses a highly urgent need in early-stage damage evaluation. A strategy integrating critically refracted longitudinal (LCR) wave with recurrence quantification analysis (RQA) is proposed for iron. The signals at different damage stages are reconstructed in multidimensional phase space, and three features, recurrence rate RR, determinism DET, and entropy ENTR, are extracted. With increasing ratcheting cycle, the normalized ENTR difference, ENTRdif, exhibits an obvious increase within ∼1 % life followed by a stabilization trend, while the normalized RR difference, RRdif, fluctuates after an initial rapid rise. Both features show higher sensitivity to the amplitude-based indexes in the LCR wave and pulse-echo methods. The ultrasonic response mechanism is discussed with the rearrangement and mobility of dislocations confirmed by microstructural observation.

Safety Analysis and Emergency Response of Suspended Oil and Gas Pipelines Triggered by Natural Disasters

Pipelines play a dominant role in the transportation of oil and gas and the safety of pipelines is essential for the supply of energy. However, natural disasters such as floods and land subsidence may lead to suspended pipelines, resulting in pipeline failure accidents, causing casualties and environmental pollution. To deal with the emergency caused by suspended pipelines, it is needed to identify the failure mechanisms of suspended pipelines caused by natural disasters. Therefore, this study conducts a safety analysis of suspended pipelines using a nonlinear finite element method (FEM), considering the nonlinear pipe–soil contact and plastic deformation. A case study is conducted to investigate the influencing parameters (e.g., the suspended length, the operating pressure, and the fluid mass). This work demonstrates that irreversible plastic strains occur when the suspended length exceeds 50 m, and it will reach 2% when the suspended length is 340 m. Finally, an emergency response plan based on plastic strain and suspended length is proposed to determine the emergency level of the suspended pipelines caused by natural disasters. This study can provide technical support for the emergency response of pipelines in areas with frequent natural disasters, promoting the sustainable development of oil and natural gas pipelines.

Effects of martensitic phase transformation on fatigue indicator parameters determined by a crystal plasticity model

Fatigue indicator parameters are a powerful tool for materials design. These parameters represent the potency of various microstructures to incubate fatigue cracks in metal alloys and are useful in ranking deleterious microstructural features on which to focus process improvements. These fatigue indicator parameters are generally a function of irreversible plastic strain; however, for alloys with solid-state phase transformations (such as Nitinol), reversible transformation strains occur along with plastic strain. This article addresses the question of whether modeling a reversible transformation will affect the predicted value of a fatigue indicator parameter. For Nitinol, the effects of a reversible phase transformation on the fatigue indicator parameter and fatigue life are studied for a polygranular microstructure with and without an inclusion. The crystal mechanics of both plasticity and phase transformations are modeled using the finite element method. It is shown that the usage of a crystal-mechanics-based phase transformation model affects the values of fatigue indicator parameters, the shape of predicted strain–life curves, the distribution of fatigue indicator parameter values in the microstructure, and also the rank ordering of deleterious microstructural features.

Effect of Carbide Precipitation on “Precipitation Plasticity” and Residual Stress during Tempering

Materials with residual stress can experience irreversible plastic strains as carbides precipitate during the tempering process, thereby relaxing the residual stress. In previous studies, this plastic behavior is named “precipitation plasticity.” Although precipitation plasticity plays a key role in the relaxation of the residual stress, the micromechanism involved is not yet elucidated. Here in this study, experiments are performed on low‐carbon steel to study precipitation plasticity and the residual stress during tempering. The results show that precipitation plasticity is mainly produced by the generation of interfacial vacancies at the carbide–matrix interface and the diffusion and evolution of these vacancies under temperature and stress fields. Two precipitation plasticity regimes are observed, namely, Precipitation Plasticity I, which is associated with vacancy diffusion, and Precipitation Plasticity II, which is associated with dislocation proliferation. Precipitation Plasticity I is found to be controlled by the volume mismatch and carbide size and is the main cause of residual stress relaxation. The finer and more dispersed the carbide precipitates are, the more significant the precipitation plasticity is. Precipitation Plasticity II causes a slight increase in the residual stress, which, however, is considerably smaller than the stress relaxation corresponding to Precipitation Plasticity I.

Influence of chemical composition of NiTi alloy on the martensite stabilization effect

The influence of the chemical composition of a NiTi alloy on the martensite stabilization effect was studied. The Ni- 50.0 at. %Ti, Ni – 49.5 at. % Ti and Ni – 49.0 at. %Ti alloys were quenched from 900 °C (10 min) into water and after this heat treatment, the alloys underwent the B2 ↔ B19′ transformation on cooling and heating without the R phase formation. The martensite stabilization effect was observed in NiTi alloys regardless of the chemical composition and value of the preliminary strain. The value of the martensite stabilization effect was measured as the difference between the temperatures that were measured during the first and the second heating. When the residual strain was less than 2.5%, the martensite stabilization effect values were close to each other in all studied alloys. Otherwise, if the residual strain exceeded 2.5%, the martensite stabilization effect values in the Ni- 50.0 at. %Ti and Ni – 49.5 at. % Ti alloys were larger than in the Ni – 49.0 at. %Ti alloy. It was shown that there was no correspondence between the values of the martensite stabilization effect and the irreversible plastic strain that appeared in the samples during the preliminary deformation. The martensite stabilization effect was found in the Ni – 49.0 at. %Ti alloy after preliminary deformation up to 10% or less that was not accompanied by a plastic strain. Thus, it was shown that the plastic strain was not the main reason for the martensite stabilization effect. A new hypothesis was assumed that a loss in the coherency of the interface that was caused by the martensite reorientation and detwinning during the preliminary deformation might be responsible for an increase in the temperatures of the reverse transformation that occurred on the first heating.

Mechanical behavior of intermittent jointed rocks under random cyclic compression with different loading parameters

Rock engineering structures are likely to be subjected to random cyclic loading resulting from earthquakes during their service lives. Characterizing the mechanical behavior of rocks under random cyclic compression is thus essential, especially for the intermittent jointed rocks widely existing in various engineering structures. This study experimentally investigates the fatigue mechanical response of synthetic intermittent jointed rocks subject to different random cyclic compression, regarding four loading amplitudes and four loading durations. Our results report the influence of the two loading parameters on the mechanical behavior of synthetic jointed rocks, involving the strength and deformation characteristics, the fatigue damage evolution and the progressive failure behavior. Both the fatigue strength and the deformation modulus of jointed samples decrease with increasing loading duration, while they exhibit opposite variation with increasing loading amplitude. The hysteresis loops can be observed in the stress-strain curves of jointed samples under various random cyclic loading, and the irreversible plastic strain exists in each hysteresis loop; this irreversible strain develops in a two-stage manner with increasing cycle number. Under higher loading amplitude or duration, the synthetic jointed rock is characterized by higher cumulative fatigue damage. The fatigue failure modes of jointed samples are independent of random cyclic loading, and the tensile splitting failure is dominate in all the recovered jointed samples. Five crack coalescence patterns are observed in the present study based on the interaction between two adjacent joints, and the progressive failure process of tested jointed sample is captured via a high resolution industrial camera. The surface cracks always initiate from the joint tips, and then propagate at a certain angle with the intermittent joints towards to the maximum compression direction.

On the accumulation of irreversible plastic strain during compression loading of open-pore metallic foams

The accumulation of plastic strain as an essential element of the compression behavior of metal foams is investigated by analyzing effective stress-strain curves which were recorded during testing. By applying loading/unloading cycles within the low-strain region until reaching the stress plateau, it is studied how reversible elastic deformation is gradually transformed into irreversible plastic deformation and it is shown that both, elastic and plastic strains, contribute to the total strain ε. This behavior is found to be independent on the investigated mesostructural foam morphologies. Furthermore, a method is derived which can be used to determine a proof stress σϕPl=0.5 at which yielding dominates the deformation of a metal foam.

A damage constitutive model for intermittent jointed rocks under cyclic uniaxial compression

A damage constitutive model is proposed to describe the deformation and strength characteristics of intermittent jointed rocks under cyclic uniaxial compression. First, a coupled damage tensor for intermittent jointed rocks is derived based on the Lemaitre strain equivalence hypothesis, which combines the Weibull statistical damage model for micro-flaws and the fracture mechanics model for macro-joints. Second, a fatigue constitutive model with an internal variable (i.e., irreversible plastic strain) is proposed to reproduce the degradation behaviors in fatigue deformation and strength of rocks under cyclic loading. Finally, a damage constitutive model with a definite physical significance is constructed for the intermittent jointed rocks under cyclic uniaxial compression. Our new model comprehensively reflects the coupled damage induced by micro-flaws and macro-joints, in which the geometric parameters and the mechanical properties of intermittent joints are considered simultaneously. Moreover, this model is able to reproduce the hysteretic stress-strain curves and the cumulative fatigue plastic deformation of rock materials under cyclic loading. In addition, a compaction coefficient, which is defined as the ratio of the secant modulus to the Young's modulus, is proposed to reflect the compaction stage of rock materials during the first loading process. To validate this new model, nine cyclic uniaxial compression tests are conducted on both intact and jointed rock samples prepared with synthetic rock-like materials. A reasonable consistency is observed between the theoretical and experimental results for the cyclic stress-strain curves and the fatigue deformation modulus.

A cyclic slip irreversibility based model for fatigue crack initiation of nickel base alloys

The opportunity to define a microscopic law of fatigue crack initiation using Manson-Coffin law formulated in terms of cyclic slip irreversibility deduced from AFM measurements is discussed for a polycrystalline superalloy with different grain sizes and precipitate sizes. The results show that the modified Manson-Coffin law, relating cyclic slip irreversibility parameter to fatigue crack initiation life, is sustained through a two-parameter power law: ε′f and c. The analysis suggests that the exponent c-value can be related to the degree of plastic strain incompatibility between grains, and the cumulative irreversible cyclic plastic strain to crack initiation is a relevant damage indicator for crack initiation. Consequently, our approach allows giving a physical base of engineering law.

Stretching temperature dependence of the critical strain in the tensile deformation of polyethylene copolymer

The deformation behavior and structural evolution of the quenched ethylene-butene copolymer under uniaxial loading and unloading were investigated as a function of stretching temperature using step-cycle tests, in situ small angle X-ray scattering (SAXS), and wide angle X-ray diffraction (WAXD) measurements. The true stress-strain curves together with detailed analysis of SAXS results indicated that the irreversible plastic strain set in quite early at small strains as the drawing temperature was increased. The critical strain, at which the recoverable elastic strain reached the plateau region and the long period started to keep essentially constant upon stretching, was found to increase distinctly from about 0.65 at room temperature to 1.00 at 100 °C. This dependence of critical strain on the stretching temperature was directly related to the effective entanglement density of the amorphous network as derived from the Gaussian model of Haward-Thackray. Despite the considerable changes of the long period and the crystallite dimensions at identical strains upon stretching and unloading, there existed a one-to-one correspondence between the strain and the orientational order parameter of polymeric chains in the crystalline phase, irrespective of mechanical stress state. This work yielded new insight into the relationship between mechanical stability and operation temperature in industrial application of crystalline polymers.

A cyclic slip irreversibility based model for fatigue crack initiation of nickel base alloys

The opportunity to define a microscopic law of fatigue crack initiation using Manson-Coffin law formulated in terms of cyclic slip irreversibility deduced from AFM measurements is discussed for a polycrystalline superalloy with different grain sizes and precipitate sizes. The results show that the modified Manson-Coffin law, relating cyclic slip irreversibility parameter to fatigue crack initiation life, is sustained through a two-parameter power law: εf′ and c. The analysis suggests that the exponent c-value can be related to the degree of plastic strain incompatibility between grains, and the cumulative irreversible cyclic plastic strain to crack initiation is a relevant damage indicator for crack initiation. Consequently, our approach allows giving a physical base of engineering law.

Critical stress statistics and a fold catastrophe in intermittent crystal plasticity.

The statistics and origin of the first discrete plastic event in a one-dimensional dislocation dynamics simulation are studied. This is done via a linear stability analysis of the evolving dislocation configuration up to the onset of irreversible plasticity. It is found that, via a fold catastrophe, the dislocation configuration prior to loading directly determines the stress at which the plastic event occurs and that between one and two trigger dislocations are involved. The resulting irreversible plastic strain arising from the instability is found to be highly correlated with these triggering dislocations.

Inverse Thermal Analysis of Melting Pool in Selective Laser Melting Process

The Selective Laser Melting (SLM) process of metallic powder is an additive technology. It allows the production of complex-shaped parts which are difficult to obtain by conventional methods. The principle is similar to Selective Laser Sintering (SLS) process: it consists, from an initial CAD model, to create the desired part layer by layer. The laser scans a powder bed of 40 μm thick. The irradiated powder is instantly melted and becomes a solid material when the laser moves away. A new layer of powder is left and the laser starts a new cycle of scanning. The sudden and intense phase changing involves high thermal gradients which induce contraction and expansion cycles in the part. These cycles results in irreversible plastic strains. The presence of residual stresses in the manufactured part can damage the mechanical properties, such as the fatigue life. This study focuses on the thermal and mechanical modelling of the SLM process. One of the key points of the mechanical modelling is the determination of the heat source generated by the laser in order to predict residual stresses. This work is divided in three parts. In a first part, an experimental protocol is established in order to measure the temperature variation during the process. In the second part, a thermal model of the process is proposed. Finally, an inverse method to determine the power and the shape of the heat source is developed. Experimental and computational results are fitted. The influence of several geometries of the heat source is investigated.

On the unified view of the contribution of plastic strain to cyclic crack initiation: Impact of the progressive transformation of shear bands to persistent slip bands

To examine the local conditions necessary to create cracks around cyclic slip bands, we studied the evolution of surface topography by atomic force microscopy and deformation localization by transmission electron microscopy for a wide structural variety (grain and precipitate sizes) in nickel-base alloys. We observed that the variance σ2 associated with height emergence of deformation bands correlated directly with the type of bands, i.e. shear bands (SBs) or persistent slip bands (PSBs). An increase in the diameter of shearing precipitates induced a progressive transformation of SBs to PSBs with a decrease in the variance σ2. Surface analyses showed that a critical value of the local irreversible plastic strain accumulated in the band (γirr,pl,loc) was necessary to for crack initiation. The value of γirr,pl,loc increased with a progressive transformation of SBs to PSBs and the increase in band thickness. This last parameter is an internal length scale that plays an important role in diffusion of vacancies in accordance with Repetto’s model of crack initiation.

Process Induced Residual Stress Effect on Fatigue Lifetime of Automotive Steel Components

Metal Active Gas (MAG) welding process of steel sheets generates, in the vicinity of the welding joint, the well-known Heat Affected Zone (HAZ) in which the material presents more microstructural defects compared to the original metal. Since high cycle fatigue is largely dependent on the material microstructure features, the HAZ is considered as the weakest zone under high cycle fatigue loading. In addition, the welding causes, in the Heat Affected Zone, irreversible plastic strains that induce important residual stress fields in this critical zone of the structure. Therefore, in order to properly predict the high cycle fatigue life time of the welded automotive components, it is of primordial importance to first identify and then consider, if necessary, the welding induced residual stress field in the structure modeling. In this work, it is found that residual stresses have non-negligible impact on high cycle fatigue lifetime, while its effect is minor in the low cycle fatigue domain.

Propagation Behavior of Naturally Initiated Small Crack in Austenitic Heat Resistant Steel under Thermo-Mechanical Fatigue Loading

In this paper, the crack propagation behavior of naturally initiated small crack in in low-carbon/medium-nitrogen 316 stainless steel under thermo-mechanical fatigue loading was investigated. The experimental results indicated that the importance of the investigation of small crack propagation behavior because the information on the basis of physically long crack growth rate provides a dangerous evaluation on reliability to actual components. The small crack exhibits high growth rate under the In-phase TMF loading because of irreversible creep and plastic strains. However, the growth rates of small crack under the Out-of-phase TMF loading were lower because the effect of creep deformation became negligible in such condition.

Intracuticular wax fixes and restricts strain in leaf and fruit cuticles

This paper investigates the effects of cuticular wax on the release of strain and on the tensile properties of enzymatically isolated cuticular membranes (CMs) taken from leaves of agave (Agave americana), bush lily (Clivia miniata), holly (Ilex aquifolium), and ivy (Hedera helix) and from fruit of apple (Malus × domestica), pear (Pyrus communis), and tomato (Lycopersicon esculentum). Biaxial strain release was quantified as the decrease in CM disc area following wax extraction. Stiffness, maximum strain and maximum force were determined in uniaxial tensile tests using strips of CM and dewaxed CMs (DCMs). Biaxial strain release, stiffness, and maximum strain, but not maximum force, were linearly related to the amount of wax extracted. Apple CM has the most wax and here the effect of wax extraction was substantially accounted for by the embedded cuticular wax. Heating apple CM to 80°C melted some wax constituents and produced an effect similar to, but smaller than, that resulting from wax extraction. Our results indicate that wax 'fixes' strain, effectively converting reversible elastic into irreversible plastic strain. A consequence of 'fixation' is increased cuticular stiffness.

Influence of plastic strain on the hydrogen evolution reaction on nickel (100) single crystal surfaces to improve hydrogen embrittlement

Hydrogen-induced embrittlement can be accountable for premature failure of structure in relation with physical and/or chemical processes occurring on material's surface or in the bulk of the material. Hydrogen Evolution Reaction (HER) corresponding to the early step of hydrogen ingress in the material is explored in present study in relation with plastic strain. HER on nickel (100) single crystal in sulphuric acid medium can be related by a Volmer–Heyrovsky mechanism. The corresponding elementary kinetic parameters as symmetry coefficients, activation enthalpies, and number of active sites have been identified via a thermokinetic model using experimental data. These parameters can be affected by defects associated with plastic strain. Irreversible plastic strain modifies the density and the distribution of storage dislocations affecting the surface roughness at atomic scale and generating additional active adsorption sites. Furthermore, surface emergence of mobile dislocations induces the formation of slip bands, which modify the surface roughness and the electronic state of the surface and increases the (111) surface density. The consequence of plastic strain on HER is explored and discussed in relation with both processes.

The effect of grain size on the localization of plastic deformation in shear bands

The strain localization of plastic deformation in slip bands may induce damage on the specimen surface, characterized by critical values of extrusion height and local irreversible plastic strain accumulated in the band. The functional dependency of the grain size on critical values of these parameters is investigated for nickel-based superalloys. It is confirmed that cracking occurs when certain conditions are fulfilled at the microscopic scale and that the critical value of local irreversible plastic strain accumulated in slip bands is independent of grain size.

Fusicoccin affects cortical microtubule orientation in the isolated epidermis of sunflower hypocotyls

Epidermal peels isolated from sunflower hypocotyls provide a convenient model to study the relationship between cortical microtubule orientation and strain rate. Extension of peels can be modulated using chemical treatment and mechanical stress, i.e., by adding a chemical to the incubation medium and applying a load exceeding the yield threshold for irreversible (plastic) strain. In this study, peels were pre-incubated for ca. 12 h (long-term pre-incubation) or for 1 h (short-term pre-incubation). In the long-term pre-incubated peels, fusicoccin applied to the medium neither enhanced the rate of longitudinal plastic strain of loaded peels, nor affected microtubule orientation. However, fusicoccin increased the strain rate of short-term, pre-incubated peels and affected microtubule orientation in both extending (loaded) and non-extending (unloaded) peels. Without fusicoccin, microtubule orientation was generally longitudinal or steep, whereas in fusicoccin-treated unloaded peels it was transverse and oblique microtubules in peel portions corresponding to the apical part of the hypocotyl. Although the frequency of transverse orientation was increased through loading, there was no strong correlation between the rate of fusicoccin-induced strain and microtubule orientation. It is hypothesized that the insensitivity of long-term pre-incubated peels to fusicoccin with respect to strain rate is due to a lack of active plasma membrane H(+) -ATPases. Thus, the sensitivity of short-term, pre-incubated, unloaded (non-extending) peels to fusicoccin, with respect to microtubule orientation, indicates that orientation might be affected by electric currents resulting from fusicoccin stimulation of H(+) -ATPases.