Irreversible Plastic Deformation Research Articles

Quantifying sandstone crack extension and expansion via deep learning methods

This study investigates the damage evolution of sandstone under loading stresses, which can lead to irreversible plastic deformation and reduced project stability service life. To achieve this objective, we identify and quantify the emergence and expansion process of sandstone cracks using deep learning methods. Specifically, our approach employs a crack segmentation model enhanced by an attention mechanism, achieving a remarkable effective crack detection MIoU of 93.38. Through the application of connectivity domain analysis, skeleton extraction, and orthogonal projection techniques, we extract crucial crack parameters, which are subsequently formulated into equations to determine their actual dimensions. These evolving parameter variations serve as the foundation for predicting the sandstone's entire damage progression, encompassing both microscopic crack growth and eventual catastrophic failure preceding macroscopic manifestation of damage. Validation of our method through uniaxial compression tests on sandstone specimens confirm its efficacy and practical applicability. In conclusion, this study presents a novel framework for quantifying sandstone crack evolution, providing invaluable insights into the intricate mechanisms governing damage fracture progression in rocks.

Experimental study on the influence of particle morphology on compression characteristics of coral sand in South China Sea

Particle morphology is an important physical parameter that influences the engineering properties of coral sand, especially its compressibility. According to the quantitative analysis of particle morphology via the dynamic image analysis technology, a series of one-dimensional compression tests on coral sand and quartz sand with different particle morphology and densities were performed to reveal the effect of particle morphology on the compressibility of coral sand. The results demonstrated that the morphology of particles can be quantified using the shape-angularity group indicator (SAGI), whereas the SAGI of coral sand was greater than that of quartz sand. Coral sand exhibited a yield stress ranging from 1 to 2.5 MPa, and compressive deformations in both coral sand and quartz sand were dominated by irreversible plastic deformation. As the SAGI and densification increased, the number of particle coordination increased while the contact stress between grains decreased, which caused the yield stress of coral sand specimens to increase as well as the compression index and particle crushing rate to decrease. The SAGI of quartz sand particles remained relatively unchanged while that of coral sand particles gradually decreased after crushing, i.e., the coral sand particles developed a more regular shape after crushing.

Spatio-temporal physics-informed neural networks to solve boundary value problems for classical and gradient-enhanced continua

Recent advances have prominently highlighted physics informed neural networks (PINNs) as an efficient methodology for solving partial differential equations (PDEs). The present paper proposes a proof of concept exploring the use of PINNs as an alternative to finite element (FE) solvers in both classical and gradient-enhanced solid mechanics. To this end, spatio-temporal PINNs are designed to represent continuous solutions of boundary value problems within spatio-temporal space. These PINNs directly incorporate the equilibrium and constitutive equations in their differential and rate forms, bypassing the requirement for incremental implementation. This simplifies application of PINNs to solve complex mechanical problems, particularly those involved in the context of gradient-enhanced continua. Moreover, traditional meshing is no longer required as it is replaced by a point cloud, making it possible to overcome meshing drawbacks. The results of this investigation prove the effectiveness of the proposed methodology, especially with regards to non-monotonic loading conditions and irreversible plastic deformation. Compared to classical FE approaches, the proposed spatio-temporal PINNs are more readily applied to complex problems, which are tackled in their raw form. This is especially true for gradient-enhanced continuum problems, where there is no need to introduce additional degrees of freedom as in classical FE approaches. However, PINNs training generally requires more computation time, a challenge that can be mitigated by employing the concept of transfer learning as shown in this paper. This concept, which is very useful when performing parametric studies, involves applying knowledge grained from solving one problem to another different but related one. The use of PINNs as mechanical solvers is shown to be highly promising in the forthcoming era, where advancements in GPU technology can further enhance their performance in terms of computation time.

A metamaterial with enhanced effective stiffness and negative Poisson's ratio for frictional energy dissipation

Unlike traditional energy dissipation structures that dissipate energy through irreversible plastic deformation or collapse, metamaterials based on friction energy dissipation have attracted attention due to their reusability. This article proposed a novel energy dissipation metamaterial by integrating friction energy dissipation mechanism into negative Poisson's ratio (NPR) structures. The integration of friction energy dissipation mechanism can simultaneously enhance the effective stiffness and NPR effect. The mechanical properties of the proposed structure were investigated using theoretical analysis, experiments, and finite element (FE) simulations. The influence of variables such as internal concave angle, friction coefficient, and number of reinforcing ribs was discussed. The results indicate that both unit cell and honeycomb structure can repeatedly dissipate energy within the elastic range. Compared with the traditional concave hexagonal structure, the effective stiffness and NPR effect were enhanced. This work provides a novel idea for the design of NPR energy dissipation structures.

Mode-I failure and mechanical behavior of sandstone under cyclic loading: Laboratory testing and DEM simulation

To study the mode-I failure and mechanical behavior of rock under cyclic loading, the cracked chevron notched Brazilian disc (CCNBD) of sandstone was employed in this paper, and thus three different upper-limit loads cyclic tests were carried out, including 95 %SUL(static ultimate load) ∼ 35 %SUL, 85 %SUL ∼ 25 %SUL, 75 %SUL ∼ 15 %SUL. The 3D discrete element model of CCNBD specimen was built to study mechanical properties and cracking behavior at a meso-scale. Meanwhile, the effect of cyclic loading on microstructure characteristics and fracture process zone (FPZ) was discussed. The results show that cyclic loading has a weakening effect on fracture toughness, and a modified fracture toughness calculation method was proposed considering the effect of irreversible plastic deformation under cyclic loading. There are obvious stages of microcracking behavior under cyclic loading, specific for the condition of 85 %SUL ∼ 25 %SUL, and the microcrack density is positively correlated with the number of cycles. Meanwhile, the effect of cyclic load on sandstone microstructure contains weak-structure fracture effect and compaction effect, and they exist simultaneously and work together. In addition, cyclic loading has a great influence on the length of FPZ, and the length of FPZ under cyclic loading is greater than that under monotonic loading.

The Gradient Effect on Cyclic Behavior of 316L Stainless Steel in the Ultrasonic Bending Test.

Nanoindentation measurements were conducted to investigate the high-cycle response of 316L stainless steel in bending fatigue. Hardness variation owing to the gradient flexure stress amplitude for different curvatures was plotted along with the thickness and length, respectively. Scanning electron microscopy (SEM) was subsequently conducted to explore the deformation characteristics in multiple layers, which had cyclic gradient stress, on the cross-section of specimens. The nanoindentation results indicated that the cyclic hardening response of 316L stainless steel is correlated with the level of stress amplitude in the high-cycle fatigue (HCF) regime. Furthermore, an analytical model was proposed to clarify the relationship between nanohardness and stress amplitude. Finally, the evolution of damage accumulation due to irreversible plastic deformation is continuous during stress reduction up to the neighboring zone at the neutral surface of the flexure beam in some individual grains.

INVESTIGATION OF THE EFFECT OF TEMPERATURE FIELDS OF DELAYED COKING REACTOR BODIES ON THE STRESS-STRAIN STATE OF THE MATERIAL

The article continues to explore the topic of damage to DCR (delayed coking reactors) or coke drums during operation. Based on the temporary localization of damage formation during the cooling stage, the most critical stage of the technological process during the operation of the DCR is determined and a damage mechanism is proposed in the form of the influence of an uneven temperature distribution over the DCR body. The description of method for studying the temperature field on the outer surface of the body of the DCR using original mobile temperature measuring devices is given. The results of research with data on the distributions and actual values of temperature differences along the outer surface of the body of the DCR during operation are presented. The DCR with a material design made of stainless steel was selected as the object of research. The case of damage in the form of cracking of the welded joint of the body during the operation of the DCR with the occurrence of a leak is considered. To justify the occurrence of damage in the form of corrugations, calculations of the stress-strain state (SSS) of the material of the body elements are carried out. The applied finite element complex «ANSYS» is used for calculations. As the initial data for SSS calculations, the results of studies of the temperature distribution over the outer surface of the DCR are used. During the calculations, it was found that at the cooling stage, the greatest stresses in the body material correspond to the level of the yield strength of the material and lead to irreversible plastic deformation with the occurrence of the process of accumulation of deformations (ratcheting process). A comparison is being made with data from foreign studies of the operating conditions of the DCR. As measures to prevent operational damage to the DCR, it is proposed to change the technical requirements for steels for the manufacture of main parts in terms of increasing the level of mechanical properties (tensile strength and yield strength). Recommendations are formulated on the material execution of the DCR, the design and manufacture of the DCR.

Self-Unfolding Properties of Smart Grid-Reinforced Membrane Origami

Origami-based membrane structures have shown great potential to revolutionize the construction of deployable and lightweight space structures in the future. However, the efficient unfolding mechanism puts forward major challenges to the practical realization of space-deployable structures. Here, a smart grid-reinforced membrane origami (SGRMO) is presented. The unfolding action hinges upon the application of forces facilitated by shape memory polymer composites (SMPCs). Subsequent locking action ensues through the restoration of the initial rigidity, accomplished via cooling mechanisms. This novel structure achieves the required lightweight and functionality by employing the grid design concept and effectively reduces the decline in unfolding extent caused by irreversible plastic deformation at the crease. Its recovery properties, including unfolding angle, distance, and surface precision, are experimentally and analytically investigated under different conditions. The results indicate that the structure can be reliably unfolded into the predefined shapes. In the case of Miura-SGRMO, the optimal surface precision is attained when the angle-ψ registers at 30°. The results of this study are expected to serve as the design of ultra-large flexible solar arrays and deployable antenna structures.

Discrete element modeling of rock-filled gabions under successive boulder impacts

A discrete element model consisting of irregular crushable filling particles and a flexible wire mesh is established. The numerical model is validated against the static net punching test and the dynamic pendulum impact test to ensure that the large irreversible plastic deformations and the impact forces during successive impacts can be captured. The impact force reduces at small friction coefficients, which is associated with the significant particle rearrangement during the impact process. The important role of friction is further confirmed by the energy evolution, showing that friction is the dominant mechanism for energy dissipation, instead of the more intuitionistic collision or particle crushing. Besides, the increase of impact force with the number of impacts becomes more significant at a higher impact energy due to the faster rate of momentum exchange. A bounce-back behavior of the boulder is observed when the impact energy is low, which may attenuate the impact force like the reflection waves in real debris flow events where multiple boulders are present. Our results highlight the combined effects of contact properties and impact energy, which are valuable in the design of rigid barriers shielded by rock-filled gabions for hazard mitigation in engineering practice.

Experimental and numerical analysis for the dry patch and thermal stress of one heating surface

In this study, an experiment to explore the surface temperature rise of an artificial dry patch at different heating powers was done. Then under specific sizes of the dry patches, the influences of these factors on thermal stress were thoroughly investigated through sensitivity analyses of factors such as the thickness of the heated wall surface, the location of the dry patch, and the thermal conductivity of the heating surface. It is found that in the case of CHF occurrence, even though the local maximum temperature inside the dry patch is much lower than the melting point of the material, the thermal stress caused by the dry patch exceeds the yield strength of the material, which triggers irreversible plastic deformation. Therefore, the heated wall fracture caused by thermal stress will occur prior to wall melting. At the same time, this study also found that changing the thickness of the stainless steel base plate and the thermal conductivity of the material both affect the maximum temperature in the dry patch region. Reducing the thickness of the heating plate makes the temperature in the dry patch region increase, which leads to a dramatic increase in the thermal stresses inside the material. Increasing the thermal conductivity of the material can flatten the temperature field, and the equivalent stresses also decrease.

Development of High-Entropy Shape-Memory Alloys: Structure and Properties

Amongst functional materials, shape-memory alloys occupy a special place. Discovered in the beginning of 1960th in XX century, these alloys attracted quite an attention because of the possibility to restore significant deformation amounts at certain stress–temperature conditions due to the martensitic diffusionless phase transformation involved in a process. It was possible to exploit not only so-called ‘shape-memory’ effect, but also superelasticity and high damping capacity. Over the years, more than 10 000 patents on shape-memory alloys were filed, appreciating not only the possibility to exploit energy transformation to ensure the response (feedback) at the change in independent thermodynamic parameters (temperature, stress, pressure, electric or magnetic field, etc.), but the significant work output as well. Applications ranged from different gadgets to automotive, aerospace industries, machine building, civil construction, etc. Unfortunately, the structural and functional fatigue restricted successful business application to medical sector with nitinol shape-memory alloy (different implants, stents, cardiovascular valves, etc.). Emerging high-entropy shape-memory alloys can be considered as a chance to overcome fatigue problems of existing industrial shape-memory alloys due to their specific structure that ensures superior resistance to irreversible plastic deformation.

Tuning the mechanical properties of sol-gel monolithic metal-organic frameworks by ligand engineering

The sol-gel monolithic MOFs has come to prominent attention for industrial application owing to the higher powder packing density, enhanced processabilities and mechanical stabilities compared to the powder counterpart. The mechanical properties are particularly important during machine shaping processing because of porous framework structure. We used ligand engineering to design and synthesize monoUiO-66-type materials modified different chemical functional groups (–NH2, –2OH, –2COOH) by sol-gel method, with the aim to assess the impact of different functional groups on the mechanical properties of these monolithic materials based on nanoindentation technology. We observe larger mass and sterically bulky functional groups (–2COOH) can significantly decrease the BET areas and pore volume of monoUiO-66 through N2 adsorption isotherms at 77 K. Hence, the two –COOH groups modified monoUiO-66 tends to exhibit the higher H of 0.589 ± 0.018 GPa and E of 15.471 ± 0.250 GPa compared with monoUiO-66 modified with –NH2 (0.334 ± 0.009 GPa/11.959 ± 0.243 GPa) and –2OH (0.331 ± 0.008 GPa/10.251 ± 0.142 GPa) groups. The creep indentation tests and the jump indentation tests further demonstrate the modification by larger functional groups –COOH on monoUiO-66 could resist irreversible plastic deformation. Furthermore, the monoUiO-66-(COOH)2 has significantly smaller the activation volume of 0.34 ∼ 0.43 nm3, highlighting the introduction of –COOH groups reduced the pore volume and restrict the number of pores involved in one collapse event. Our results demonstrate the larger mass and sterically bulky functional groups have significant influence on the mechanical properties of the monoMOFs materials.

STUDY ON THE VISCOELASTOPLASTIC PROPERTIES OF POLYTETRAFLUOROETHYLENE AND NANOCOMPOSITES WITH INCREASED WEAR RESISTANCE BASED ON IT. PART 1. MATERIALS, TEST PROGRAMS AND BASIC PROPERTIES

This is the first (introductory) article in a series of articles devoted to a comprehensive experimental study and modeling of the viscoelastoplastic properties of polytetrafluoroethylene and a number of composites with increased wear resistance based on it, obtained in recent years in the laboratories “Technology of Polymer Nanocomposites” and “Polymer Composites for the North” of the Ammosov North-Eastern Federal University by introducing layered silicates (mechanically activated kaolin and serpentine, magnesium spinel) and short basalt or carbon fibers as fillers. Data from quasi-static tensile tests of these materials under different loading programs are presented: a family of stress-strain curves (until failure) at different strain rates, loading and unloading curves at different strain rates, creep and recovery curves for different stress levels, etc. The basic scalar characteristics of materials are determined (instantaneous modulus, yield strength, stress and strain at failure depending on the loading rate, etc.), the influence of the composition and proportion of fillers on them, and their strain rate sensitivity are analyzed. After mechanical tests, changes in the microstructure of PTFE and composites with different filler contents in the destruction zones of the samples were studied using a scanning electron microscope. An initial analysis of the volume of test data accumulated over 2 years revealed high deformability of materials, pronounced hereditary properties, the ability of materials to creep (flow) under constant load and accumulate irreversible (plastic) deformation, very high strain rate sensitivity, a strong influence of small amounts of fillers on the structure and mechanical properties. A more detailed presentation of the entire volume of test data and effects found, a systematic study of the viscoelastoplastic properties of these materials with different filler contents and their detailed comparative analysis as well as detection of connection with wear resistance are the topics of subsequent articles in the series in 2023-2025.

An energy dissipation metamaterial based on Coulomb friction and vibration

Compared with traditional energy dissipation structures, negative stiffness metamaterials can repeatedly dissipate energy without incurring irreversible plastic deformation. The existing negative stiffness structures are generally multistable, and their energy dissipation mechanism is either through internal component vibration or friction. In this paper, a self-recoverable negative stiffness structure was proposed which can dissipate energy through both vibration and Coulomb friction. The structure consists of an external I-shaped structure and a buckle-like structure composed of a plug and cantilever beams inside. The proposed structure achieves monostable characteristics by utilizing the concept of self-contact. To investigate the mechanical properties, quasi-static loading-unloading experiments were performed and verified using finite element simulation. The energy dissipated in the proposed structure by vibration and friction was quantified theoretically. The influence of geometric parameters on energy dissipation was studied using simulation and analytical methods. This type of metamaterial has the potential to be employed in the production of multi-functional metamaterial structures such as deformable robots or reusable bumpers.

Exact solutions for the symmetric elastoplastic response of functionally graded pressure vessels

With the development of functionally graded (FG) composite material technology, mechanical analyses of FG pressure vessels have attracted attention. Due to the non-uniform stress distributions inside such vessels, irreversible plastic deformation first occurs in some zones of the structure under the action of external loads. It is necessary to perform an elastoplastic analysis of FG structures to determine their load-bearing capacities. In this paper, exact solutions are obtained for the purely elastic, partially plastic, and fully plastic deformation of FG cylindrical and spherical shell pressure vessels under mechanical loads. The material properties (elastic modulus and yield strength) are assumed to vary nonlinearly in the radial direction of the vessel and the Poisson's ratio is assumed to be constant due to Poisson's ratio slight variations in the engineering materials. The novelty of the current work lies in the presentation of complete exact elastoplastic solutions for FG thick cylindrical and spherical shell pressure vessels, taking into account all deformation zones. Tresca's yield criterion is used to formulate four different deformation zones for an ideal plastic material. All of these states of deformation are studied in detail. It is shown that the elastoplastic response of the FG pressure vessels is notably affected by the radial variation of the material properties. With an increase in the FG parameter β, the first yielding position of the FG pressure vessels changes from the inner surface to the outer surface. The conclusions of this work should help with developing designs of FG pressure vessels to prevent yielding under excessive circumferential stresses.

Rheology of Gels and Yielding Liquids.

In this review, today's state of the art in the rheology of gels and transition through the yield stress of yielding liquids is discussed. Gels are understood as soft viscoelastic multicomponent solids that are in the incomplete phase separation state, which, under the action of external mechanical forces, do not transit into a fluid state but rupture like any solid material. Gels can "melt" (again, like any solids) due to a change in temperature or variation in the environment. In contrast to this type of rheology, yielding liquids (sometimes not rigorously referred to as "gels", especially in relation to colloids) can exist in a solid-like (gel-like) state and become fluid above some defined stress and time conditions (yield stress). At low stresses, their behavior is quite similar to that of permanent solid gels, including the frequency-independent storage modulus. The gel-to-sol transition considered in colloid chemistry is treated as a case of yielding. However, in many cases, the yield stress cannot be assumed to be a physical parameter since the solid-to-liquid transition happens in time and is associated with thixotropic effects. In this review, special attention is paid to various time effects. It is also stressed that plasticity is not equivalent to flow since (irreversible) plastic deformations are determined by stress but do not continue over time. We also discuss some typical errors, difficulties, and wrong interpretations of experimental data in studies of yielding liquids.

Experimental Investigation of Stress Sensitivity of Elastic Wave Velocities for Anisotropic Shale in Wufeng–Longmaxi Formation

The shale of the Wufeng–Longmaxi formation in the Sichuan Basin is the preferred layer for shale gas exploration in China, and its petrophysical characteristics are the key to geological and engineering sweet spot prediction. However, the characteristics and impact mechanisms of its acoustic wave velocity and elastic anisotropy are currently unclear. In this paper, the Wufeng–Longmaxi shale is taken as the research object, and the P-wave and S-wave velocities of the samples are tested under the loading and unloading processes of confining pressure. The stress sensitivity variations in parameters such as wave velocity, wave velocity ratio, and anisotropy are discussed. P-wave and S-wave anisotropy parameters are correlated under different pressure conditions. X-ray diffraction, casting thin sections, scanning electron microscopy, micron CT scanning, and other analytical techniques are used to explore the mechanisms of stress sensitivity of elastic parameters. The research results indicate that: (1) the acoustic velocities of samples from different angles are V90° > V45° > V0°, and there is a positive correlation between the wave velocity and the confining pressure. After unloading the confining pressure, irreversible plastic deformation occurs due to the closure of some microfractures in the rock core, causing the wave velocity to be higher than the initial value. (2) The stress sensitivity coefficient of the P-wave (The mean is 3.00 m·s−1·MPa−1) is higher than that of the S-wave (the mean is 1.23 m·s−1·MPa−1), and the stress sensitivity coefficient of the compacted stage (the mean is 3.02 m·s−1·MPa−1) is higher than that of the elastic stage (the mean is 1.21 m·s−1·MPa−1). (3) The anisotropy of the P-wave and S-wave is negatively correlated with the confining pressure. When the confining pressure is loaded to 65 MPa, the change rate of the P-wave anisotropy coefficient is 23%, and its stress sensitivity is higher than that of S-wave anisotropy coefficient (the change rate is 13.7%). After unloading the confining pressure, the degree of anisotropy is reduced due to the closure of some microfractures. The empirical formula of P-wave and S-wave anisotropy parameters under different pressures is established through linear regression, which can provide a reference for mutual predictions. (4) The variation in wave velocity anisotropy with stress can be divided into stress and material anisotropy, which are related to the directional arrangement of microfractures and clay minerals, respectively. The quantitative characterization of shale anisotropy can be realized by evaluating the development degree of reservoir fractures and mineral components, providing a reference for logging interpretations, sweet spot prediction, and fracturing construction of shale gas reservoirs.

Evolution of B19’ phase during annealing and its influence on the mechanical properties of Zr45Cu45Al10 metallic glass composites

Metallic glass composites containing shape memory crystals demonstrate strain hardening owing to the deformation-induced martensitic transformation, which encompasses the B2 ⇌ B19′/B33 (martensite) transformation in Zr-based metallic glasses. However, the impact of the B19’ martensitic phase on strain hardening remains ambiguous. In this study, we conduct a rapid annealing treatment of Zr45Cu45Al10 bulk metallic glass at 748 K to form the B19’ phase and employ small-angle neutron scattering to explore its evolution. The B19’ phase forms in the first 10 min of annealing treatment and begins to grow after 30 min. The presence of the B19’ phase significantly increases the strain rate sensitivity and irreversible plastic deformation. These findings not only deepen our understanding of the role of the B19’ phase in metallic glass composites but also offer a methodology to enhance their mechanical properties through modulation of the B19’ phase.

Fatigue behavior evaluation in Fe-20Mn-3Al-0.9C alloys by dynamic nanoindetation

The fatigue response by applying cyclic loads on individual grains using monotonic and cyclic nanoindetation to analyze the effect on load or displacement control in an austenitic Fe-20Mn-3Al-09C alloy were analyzed. The material response to the cycles considering the load control and the displacement control to properties such as hardness, elastic's modulus, and contact stiffness, was studied by analyzing the load-unload curves (P-h). The material softening Analysis showed that these properties decrease with increasing cycles due to the activation of deformation mechanisms. The elasticity's Modulus and hardness values for monotonic loads in load control presented values close to those reported in the literature. On the other hand, in displacement control, the values were lower. In load and displacement control mode, the first two cycles presented no overlap between unloading and loading between cycles, due to large irreversible plastic deformation and low elastic recovery after unloading. In the subsequent cycles, overlaps between the hysteresis curves were predominant, due to the activation of the deformation mechanisms.

Intrinsic-Strain Engineering by Dislocation Imprint in Bulk Ferroelectrics.

We report an intrinsic strain engineering, akin to thin filmlike approaches, via irreversible high-temperature plastic deformation of a tetragonal ferroelectric single-crystal BaTiO_{3}. Dislocations well-aligned along the [001] axis and associated strain fields in plane defined by the [110]/[1[over ¯]10] plane are introduced into the volume, thus nucleating only in-plane domain variants. By combining direct experimental observations and theoretical analyses, we reveal that domain instability and extrinsic degradation processes can both be mitigated during the aging and fatigue processes, and demonstrate that this requires careful strain tuning of the ratio of in-plane and out-of-plane domain variants. Our findings advance the understanding of structural defects that drive domain nucleation and instabilities in ferroic materials and are essential for mitigating device degradation.