Plastic Deformation Characteristics Research Articles

Fracture mechanism and constitutive model considering post-peak plastic deformation of marble under thermal–mechanical action

Temperature plays an important impact on rock mechanical properties. In this paper, the mechanical properties, fracture mechanism and constitutive model of marble under 20–120 °C and 15 MPa are studied. The results show marble deformation can be divided into four stages: compaction, linear elasticity, crack propagation and post-peak failure. Stress–strain curve is not obviously affected by temperature. Macroscopic fracture characteristics change from shear failure to tensile mixed failure with temperature increasing. With the increase of temperature, the strength of marble tends to decrease, indicating that temperature increase has a weakening effect on marble, and there are temperature-sensitive areas of 20–60 °C and temperature sub-sensitive areas of 60–120 °C. The elastic modulus of marble decreases and Poisson’s ratio increases with increasing temperature. The energy evolution law of marble under different temperature is basically the same, which shows that before crack initiation, the energy dissipation is less, and after the damage and yielding occurs, the energy dissipation increases quickly. The energy dissipation in the failure process is mainly used for crack initiation-connection-penetration, as well as plastic deformation caused by friction and slip of cracks, and the plastic deformation and energy dissipation have good linear characteristics. The statistical damage constitutive model based on three-parameter Weibull distribution function can effectively reflect the characteristics of post-peak plastic deformation and strain softening. The weakening effect of marble at 20–120 °C is related to its internal moisture excitation. With the increase of temperature, water is stimulated to absorb and attach to the original relatively dry interface, which plays a role in lubrication. The relative motion friction resistance between solid particles or crack surfaces decreases, which leads to crack initiation and friction energy consumption reduction, changes the specific surface energy of rocks and weakens the strength of marble. The results provide a theoretical basis for predicting and evaluating the long-term stability and safety of surrounding rock of underground deep engineering in complex environment with high ground temperature and high geo-stress.

Effect of Alloying on Microstructure and Mechanical Properties of AlCoCrFeNi2.1 Eutectic High-Entropy Alloy.

In order to explore the effect of alloying on the microstructures and mechanical properties of AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs), 0.1, 0.2, and 0.3 at.% V, Mo, and B were added to the AlCoCrFeNi2.1 alloy in this work. The effects of the elements and contents on the phase composition, microstructures, mechanical properties, and fracture mechanism were investigated. The results showed that the crystal structures of the AlCoCrFeNi2.1 EHEAs remained unchanged, and the alloys were still composed of FCC and BCC structures, whose content varied with the addition of alloying elements. After alloying, the aggregation of Co, Cr, Al, and Ni elements remained unchanged, and the V and Mo were distributed in both dendritic and interdendritic phases. The tensile strengths of the alloys all exceeded 1000 MPa when the V and Mo elements were added, and the Mo0.2 alloy had the highest tensile strength, of 1346.3 MPa, and fracture elongation, of 24.6%. The alloys with the addition of V and Mo elements showed a mixed ductile and brittle fracture, while the B-containing alloy presented a cleavage fracture. The fracture mechanism of Mo0.2 alloy is mainly crack propagation in the BCC lamellae, and the FCC dendritic lamellae exhibit the characteristics of plastic deformation.

Mechanical behaviour and macro-micro failure mechanisms of frozen weakly cemented sandstone under different stress paths

Significant unloading failure zones in artificial freezing shaft sinking projects in western China are primarily caused by stress release. To investigate the deformation and failure mechanisms of frozen weakly cemented sandstone (FWCS), three groups of triaxial unloading tests were conducted under different initial principal stresses (σ₃ = 3, 6, and 10 MPa) with an unloading rate of 0.05 MPa/s. Scanning electron microscopy (SEM) was employed to examine the micro-fracture characteristics of the failure surfaces. The results revealed that, compared to traditional triaxial and room-temperature triaxial compression tests, the strength and plastic deformation characteristics of FWCS are significantly weakened under unloading conditions. However, lateral deformation, particularly volumetric strain, increased markedly, exhibiting pronounced dilatancy characteristics, especially along stress path III (i.e., post-peak axial stress loading with confining pressure unloading). Unloading leads to a reduction in cohesion and an increase in the internal friction angle of FWCS, with the most significant changes observed along stress path IV (i.e., pre-peak constant axial displacement loading with confining pressure unloading). Macroscopic and microscopic analyses indicate that the failure mechanism of FWCS under complex unloading stress paths is driven by the rapid accumulation of energy caused by unloading, which results in the development and propagation of axial and circumferential cracks, widespread particle breakage, and the formation of inter-granular and trans-granular fractures, as well as shear scratches at the micro level, ultimately manifesting macroscopically as shear-tensile composite failure.

Axial Crushing and Energy Absorption Integrated Design of Modular Filled Double-Hat Beam Composite Structures.

In order to study the influence of modular filled and composite material forms on the axial crushing and energy absorption properties of structures, modular filled composite structures were constructed, and innovatively applied to the inner side of double-hat beam (DHB) structures in automobiles. The modular filled structures comprise hexagonal, quadrilateral, and triangular sections. By analyzing the collision performance of modular filled DHB structures, significant enhancements were observed in both the sectional characteristics and the specific Mean Crushing Force of modular filled DHBs compared to the conventional double-hat beam structure. These advancements notably improved the plastic deformation characteristics of the structures. Additionally, dynamic weightlessness experiments were conducted to validate the accuracy of the simulation model. Among the proposed schemes, namely QU-5, HE-5, and TR-5, notable improvements in crashworthiness were identified. Specifically, crashworthiness indicators increased by 32.54%, 78.9%, and 116.53%. Compared with other thin-walled structures, modular filled composite DHBs have advantages in axial crushing and energy absorption. By optimizing layout characteristics, the modular filled structures will achieve significant lightweight and energy absorption performance improvements. This work has clear reference value for automotive engineers and scholars to further explore the axial crash safety, platform modularization, and lightweight design of vehicles.

Evolution Characteristics of Aluminum Thermal Weld Irregularity and Damage in Heavy-Haul Railway under Different Service Conditions

Aluminum thermal welding joints are widely used in the maintenance welding of heavy-haul railways due to their easy handling and high efficiency. However, due to their inherent welding characteristics, welding results in certain differences in the material’s physical properties at the welding zone compared to adjacent base materials, leading to the occurrence of short-wave irregularity under long-term wheel–rail interactive forces. In order to explore the evolution characteristics of weld irregularity, dynamic characteristics, and plastic deformation under long-term wheel–rail impact, a detailed tracking test was conducted on a normal aluminum weld, and the process from being put on the track to being damaged and replaced was evaluated. At the same time, a rigid–flexible coupling model was established for subsequent analysis, and plastic damage was analyzed using the finite element model. The results show that the service life of the weld can be divided into three different stages: the initial stage, the intermediate stage, and the damage stage. In the damage stage, a temporary separation occurred between the wheel and rail, leading to a sudden change in the wheel–rail interaction. The weight of 250 MT at the weld reached the repairment control limit. The concentration effect of equivalent plastic deformation was most serious at 2~5 mm below the rail head.

Compressive behavior and deformation mechanisms of gradient microstructures in a dissimilar welded joint

In this study TC4/TC17 titanium alloy dissimilar joints were obtained via vacuum electron beam welding. The compressive behavior of base metals and joint at different strain levels was studied, along with microstructural and fracture surface observations. The true stress–strain curves of base metals and joint at different strains demonstrated smooth and continuous plastic deformation characteristics. The compressive yield strength of the joint (1065 MPa) was basically equivalent to that of TC17 alloy (1196 MPa), which was significantly higher than that of TC4 alloy (920 MPa) for the failed samples. However, the compressive fracture strain of the joint was lower than that of base metals. Comparison of the microstructures of base metals and joint deformed at different strains, it revealed that the equiaxed α phase in TC4 alloy mainly underwent the deformation, while the TC17 alloy mainly relied on the rotation of lamellar grains to resist the deformation. In the dissimilar joint with a large microstructural gradient, the compressive deformation of several zones, including the weld zone, far heat-affected zone and the base metal, was also related to the rotation of finer grains.

Microstructure and mechanical properties of low cost co-free high strength steel fabricated by plasma arc-based directed energy deposition

Arc-based directed energy deposition (DED) is characterized by high efficiency and excellent manufacturing flexibility, making it a promising choice for fabricating large structural components. High power density plasma arc-based directed energy deposition (PA-DED) was employed to fabricate high strength steel (HSS) component with a new Co-free welding wire. The microstructure and mechanical properties of the component were investigated in detail. The results showed that the matrix microstructure consisted mainly of martensite and ferrite. Austenite was observed in the bottom and middle samples, and the bottom sample exhibited the highest austenite content. All the samples in different regions exhibited a pronounced {100} 〈001〉 cube texture. The vertical samples had worse tensile properties than horizontal samples, which would be contributed to the interlayer bands and preferred orientation. The horizontal-middle samples demonstrated the highest tensile strength (UTS: 1207.8 ± 14 MPa, EL: 15.91 ± 1.03%). All deposited samples showed strong plastic deformation characteristics, illustrating that the new Co-free HSS components manufactured by PA-DED might replace conventional high-alloy HSS components for industrial applications.

A rational multiscale nonlinear constitutive model for freeze–thaw rocks under triaxial compression

The stability and durability of rocks in cold regions are significantly impacted by the degradation of mechanical properties caused by freeze–thaw (F–T) environment. In this work, we shall propose a rational multiscale nonlinear constitutive model based on thermodynamics, micromechanics, and fractional calculus theory to describe the complete deformation and failure process of F–T rocks under triaxial compression. The F–T rocks at the mesoscale are regarded as consisting of porous matrix and cracks, while porous matrix is composed of the micropores and elastic solid grains at the microscale. According to experimental observations, we assume the F–T action mainly causes micropores growth and cracks opening, and mechanical damage is resulted from the initiation and propagation of cracks. In this context, the effects of F–T and mechanical damage on effective elastic properties of rocks can be quantitatively analyzed by using the two-step Mori–Tanaka (M-T) homogenization method. After subtly deriving the total free energy function of F–T rocks under compression, we systematically develop specific criteria for describing open cracks closure deformation, mechanical damage evolution and frictional sliding induced plastic distortion. Note that to correctly capture the plastic deformation characteristics, the non-orthogonal flow rule based on fractional differential calculations is employed. Following that, analytical analyses and numerical implementation of the proposed model are conducted. The performance of the model is evaluated by the simulations with experimental data on two kinds of F–T rocks, and discussions on parameters sensitivity and effects of fractional order are followed.

A Study on Yield Criteria Influence on Anisotropic Behavior and Fracture Prediction in Deep Drawing SECC Steel Cylindrical Cups.

The deep drawing process, a pivotal technique in sheet metal forming, frequently encounters challenges such as anisotropy-induced defects. This study comprehensively investigates the influence of various yield criteria on the anisotropic behavior and fracture prediction in SECC steel cylindrical cups. It integrates Hill'48R, Hill'48S, and von Mises yield criteria in conjunction with Swift's hardening law to evaluate material behavior under complex stress states. Experimental and numerical simulations assess the anisotropy effects across multiple orientations (0°, 45°, and 90°), revealing intricate relationships between stress criteria and material response. The findings indicate significant discrepancies between isotropic and anisotropic models in predicting fracture heights, emphasizing the importance of selecting appropriate yield criteria. Notably, the von Mises criterion results in lower fracture heights, suggesting higher susceptibility to fractures, while the Hill'48R model aligns closely with experimental data, validated through variations in punch corner radius and blank holder force parameters, with a maximum deviation of 3.23%. Hill'48S displays moderate plastic deformation characteristics.

Analysis of the Influence of Contact Stress on the Fatigue of AD180 High-Carbon Semi-Steel Roll

In this study, to investigate the problem of contact fatigue and the damage mechanism of an AD180 high-carbon semi-steel roll, rolling contact fatigue tests were conducted using specimens cut from the periphery of a roll ring. These specimens were characterized under different contact stresses using SEM, a profile system, an optical microscope, and a Vickers hardness tester. The results indicates that the main forms of fatigue damage of an AD180 high-carbon semi-steel roll are peeling, pitting corrosion, and plowing. Moreover, the surface of the roll exhibits delamination and plastic deformation characteristics under high contact stress. Meanwhile, the size and depth of peeling, as well as the amount of pitting corrosion, increase with the contact stress. Peeling is mainly caused by a crack that originates at the edge of the specimen surface and propagates along the pearlite structure and the interface between pearlite and cementite. High contact stress can lead to an increase in the crack propagation depth and angle, resulting in the formation of larger peeling. Under cyclic loading, the near-surface microstructure of the specimen hardens due to grain refinement and dislocation strengthening, and the depth of the hardened layer increases with the increase in contact stress. When the contact stress reaches 1400 MPa, the near surface structure of the specimen changes from pearlite to troostite.

Repeated impact response of honeycomb sandwich panels based on the failure parameters of adhesive layer and material

Honeycomb sandwich structure has been widely used in lightweight and impact protection of rail vehicle structures due to its excellent mechanical properties. In this paper, the plastic deformation, failure response and energy absorption characteristics of honeycomb sandwich panels for rail vehicles under repeated impact loads were studied. The three-point bending tests and low-speed impact tests of honeycomb sandwich panels were carried out, and a three-dimensional numerical model considering the detailed structure of the honeycomb core and the failure of the adhesive layer was established. The model can reasonably simulate honeycomb sandwich panels’ stiffness, strength, and structural failure. The effects of impact times and impact angle on the performance indexes of the honeycomb sandwich panel were studied. The results show that when the impact energy is the same, the impact times will affect the energy absorption distribution of honeycomb sandwich panels. With the increase in impact times, the panel’s absorption energy decreases, the core’s absorption energy increases, and the total absorption energy decreases. For multiple impact conditions, with the increase of impact times, the single energy absorption of the upper panel and core decreases, and the single energy absorption of the lower panel increases. When the impact energy is the same, the rise in impact angle will increase the damage to the honeycomb sandwich panel, and the energy absorption of each part will increase. In addition, the influence of impact times on the energy absorption efficiency of honeycomb sandwich panels is related to the impact angle.

TiAl Alloy Fabricated Using Election Beam Selective Melting: Process, Microstructure, and Tensile Performance

TiAl alloy is one of the most attractive candidates for a new generation of high-temperature structural materials and has broad application prospects in the aerospace field. As a typical intermetallic material, TiAl is inevitably difficult to process using conventional methods. Election beam selective melting (EBSM) is an effective method of addictive manufacturing to prepare TiAl alloy with a complex structure. However, the microstructure of TiAl alloy formed using EBSM often contains defects such as pores, which seriously reduces the mechanical properties of the material. In this work, the effects of EBSM and post-processing procedures on the microstructure and mechanical properties of Ti-48Al-2Cr-2Nb alloy were studied. The results show that the microstructure of Ti-48Al-2Cr-2Nb alloy formed using the EBSM process was dense and composed of equiaxed γ-phase and double-phase regions. A large number of dislocations that formed due to thermal stress were clearly observed inside the Ti-48Al-2Cr-2Nb alloy. When the EBSM process parameters were 13.5 mA, 4.0 m/s, and 40.50 J/mm3, as the current intensity increased, the Al content decreased, the content of α2 phase increased, and the microstructure of the material was coarse. The results of the tensile test fracture morphology indicate that the Ti-48Al-2Cr-2Nb alloy exhibited brittle fracture during tensile deformation, lacking the typical yield deformation of metal materials. As the energy density of the EBSM process increased, the mechanical properties of the Ti-48Al-2Cr-2Nb alloy first increased and then decreased. The samples prepared with an energy density of 34.50~40.50 J/mm3 had excellent mechanical properties, of which the maximum tensile strength and maximum elongation reached 643 MPa and 2.09%, respectively. The phase composition of the Ti-48Al-2Cr-2Nb alloy after hot isostatic pressing (HIP) treatment remained unchanged from the EBSM samples, but there was a slight difference in content. There was an increase in the amount of γ phase and a decrease in B2 phase, accompanied by the generation of a massive γ phase after HIP treatment. Moreover, the number of dislocations inside the material increased. The Ti-48Al-2Cr-2Nb alloy after HIP treatment exhibited obvious plastic deformation characteristics, with a tensile strength of 679 MPa and elongation of 2.5%. A heat treatment of 900 °C/5 h was performed on the Ti-48Al-2Cr-2Nb alloy after HIP. The dislocation density of the Ti-48Al-2Cr-2Nb alloy decreased, and the B2 phase transformed from massive to lamellar.

Experimental and theoretical investigation of failure mechanism in Al2O3/SiC composite under plane shock waves

The investigation of fracture and fragmentation is essential for evaluating the protection performance and structural design of ceramic armour. This paper focused on the dynamic failure and fracture mechanisms of the fine-grained Al2O3/SiC composite subjected to plane shock waves. The macroscopic shock response characteristic was determined through a series of plane impact tests, which included the Hugoniot curves of the composite. The results indicated that the fracture mechanism is significantly influenced by specific stress characteristics. The transgranular fracture in large grains and intergranular fracture in small grains exhibit obvious local plastic deformation characteristics. Moreover, the presence of second-phase SiC particles markedly influences both crack propagation and the microfracture mode of the composite. Lastly, a statistical analysis of the ceramic fragments was conducted after the soft recovery of specimens in impact experiments, and analytical models were developed and modified to predict the distribution of fragments under plane shock loading.

Lateral compressive behavior of multi-layer lattice-web reinforced composite cylinders

Several novel multi-layer lattice-web reinforced composite cylinders, consisting of glass fiber reinforced polymer (GFRP) face sheets and lattice webs, polyurethane (PU) foam core and clay ceramsite filler, were proposed and manufactured using a vacuum assisted resin infusion process (VARIP) method. A series of quasi-static lateral compressive experiments were carried out to investigate the feasibility of the proposed cylinders. For both the hollow composite cylinders and ceramsite filling composite cylinders, the bearing capacity and energy absorption performance can be significantly improved with the use of multi-layer lattice-web layouts. Among the proposed three types of lattice-web layouts, the double-layer dislocated lattice-web layout made the composite cylinder exhibit the greatest specific energy absorption (SEA) performance and can be chosen as an optimal configuration. Furthermore, numerical models were established using LS-‍DYNA software to simulate the large deformation of the composite cylinders with double-layer dislocated lattice-web layout. Based on the numerical models, parametric analysis was carried out to discuss the effects of various parameters on the crushing response of the composite cylinders. Generally, using thicker GFRP material or higher radial lattice web can make the composite cylinders present an increased likelihood of brittle failure. However, filling ceramsite can not only make them exhibit plastic deformation characteristics but also facilitate the full utilization of various components.

Slurry and liquid impingement erosion behavior of low-temperature plasma carburized AISI 420 martensitic stainless steel

The impact of plasma carburizing treatment on the erosion wear resistance of AISI 420 martensitic stainless steel (MSS) was studied. Experiments were carried out varying a broad spectrum of erosion parameters, including impact velocity, impact angle, and exposure duration. Both slurry and liquid impingement erosion were employed in the experiments, with testing conducted using both distilled water and saline solutions to assess the combined effects of corrosion and erosion wear. Compared to untreated samples, a significant improvement in the erosion wear resistance of AISI 420 MSS due to low-temperature plasma carburizing treatment was observed for all tested conditions. The observed performance enhancement can be attributed to the formation of the carburized layer, constituted of the α'C and Fe3C phases. Results also highlighted that the severity of the tribosystem was significantly influenced by the test solution characteristics. A marginal increase in severity was observed upon introducing the saline solution, while a more substantial severity increase occurred with the addition of solid particles in the test fluid. The specimens' mass loss was increased by increasing impact velocity, following a simple potential relationship, and with impact angle, following a first-degree linear equation. In the case of the exposure time, the mass loss curves depended on the test environment. For solutions containing quartz particles, an additional final stabilization stage was observed in addition to the acceleration stage observed in the absence of abrasive component. This phenomenon was attributed to surface work hardening induced by the impact of solid particles. Regarding wear mechanisms, samples tested only with distilled water displayed erosion flow marks. Those containing distilled water and NaCl exhibited not only flow marks but also pits. Lastly, solutions containing solid particles additionally presented features of plastic deformation, lip formation, craters, indentations, and extruded material.

Research on seismic performance of corrugated web rigid structures

Abstract: Corrugated web H-beam refers to a steel beam with a wavy shape along its length, which is extensively utilized in various parts of building structures such as beams, columns, and walls. It serves the purpose of connection and support, while the corrugated or folded design enhances the shear resistance and out-of-plane stiffness of the web to some extent. However, despite their advantages including high strength, stiffness, and lightweight construction, relevant regulations stipulate that these members can only be used in lower-intensity applications or higher-intensity scenarios if specific conditions are met. One crucial condition is that the ratio between the design value of axial force subjected to seismic action and the product of the member's flange section area and steel's tensile strength should not exceed 0.4. In this study, we aim to further investigate the seismic characteristics and applicable intensity of corrugated steel structures under earthquakes through large-scale finite element ABAQUS simulations. We will observe dynamic characteristics and failure modes of corrugated rigid frame structures using elastic-plastic time-history analysis methods as well as examine plastic deformation features of steel beam members under low cyclic loads via hysteretic analysis methods. The findings demonstrate that when properly designed with reasonable beam spans, corrugated web rigid frame structures can still be employed in high-intensity areas above 7 degrees even when subjected to an axial compression ratio up to 0.5.

Damage characterization and microscopic mechanism of steel slag-cemented paste backfill under uniaxial compression

The utilization of steel slag-cemented iron tailings for preparing mine backfill materials can effectively consume industrial solid waste generated from steel production and significantly reduce backfilling costs. The study analyzed the influence and mechanisms of steel slag (SS) content on the mechanical damage characterization of steel slag-cemented paste backfill (SS-CPB) through uniaxial compressive strength (UCS) tests and microscopic testing methods such as X-ray diffraction (XRD) and a scanning electron microscope (SEM). The engineering applicability and economic feasibility of the material were evaluated. The main conclusions were as follows: (1) With the increase of SS content, the strength of SS-CPB first increases and then decreases, with the highest strength observed at a 10% SS content. (2) The inclusion of SS in SS-CPB leads to higher peak strain and post-peak strength, demonstrating significant plastic deformation characteristics. (3) When the SS content increases from 30% to 60%, the Ca(OH)2 content in SS-CPB hydration products decreases by 20.2%, and internal micropores increase. (4) When the SS content reaches 30%, the damage mode of SS-CPB changes from purely splitting failure to a plastic combination of splitting and shear failure. These research findings provide a new application model for the collaborative utilization of steel slag, tailings, and other solid wastes.

Correlational fractal characteristics and damage progression of granite with different grain sizes based on acoustic emission monitoring

Mineral grain size caused by the geological diagenetic process is one of the fundamental reasons leading to the differences in rock mechanical behaviors, which brings challenges to the stability of underground engineering, especially in rock masses with continuous grain size changes. This study conducted uniaxial compression tests on granite samples obtained from the same invaded anticline with different grain sizes. During the tests, the acoustic emission (AE) signals were acquired synchronously. The correlation between damage evolution and AE data was then studied by frequency-spectrum analysis, fractal theory methods, and G-P algorithms. The mechanism of grain size effect on granite failure evolution was discussed. The results reveal that as the grain size increases, the strength and the elastic modulus decrease while the plastic deformation characteristic is enhanced. Grain size also affects the frequency distribution of AE signals and its time-varying characteristics. With the increase in grain size, the proportion of high-frequency signals declines during loading. The fractal dimension value of dominant frequency during loading fluctuates within the range from 0.5 to 2.25 and generally shows an overall ‘rise-fall-rise-fall’ mode. In addition, as the grain size increases from fine-grained to medium-grained, the fractal dimension changes from an increasing to a decreasing trend earlier in the compaction and elastic stages. Especially in coarse-grained samples, after a brief increase, the fractal dimension decreases continuously until approaching the overall failure. The frequency domain characteristics and correlation fractal variation of granites reflect the damage and crack evolution inside the rock sample. More scattered and unordered micro-cracks generated in samples with finer grains facilitate the dispersion of applied stress and the reduction of local stress concentration, resulting in higher strength and stiffness of the sample.

Distinguishing evaluation of plastic deformation and fatigue damage using pulsed eddy current testing

The vessels and pipes of nuclear power structures are subjected to complex forces. The structures suffer sudden loads that lead to plastic deformation and cyclic loads that result in fatigue damage. In practice, two types of microscopic damage may occur simultaneously. The effect of plastic deformation on material fatigue properties remains unclear, and there is a lack of effective methods to distinguish plastic deformation and fatigue damage. To address these issues, the fatigue life curve of 304 stainless steel is experimentally measured, and the influence of fatigue life due to the presence of plastic deformation under a certain load is investigated. It's identified that preset plastic deformation below 15% will increase the fatigue life of the structure. Additionally, a pulsed eddy current signal processing and reconstruction method based on the empirical modal decomposition (EBD) method is proposed. Finally, the pulsed eddy current signal characteristics of plastic deformation and fatigue damage are analyzed, and a distinguishing evaluation method of fatigue damage with preset plastic deformation is established.

Plastic Deformation Characteristics and Calculation Models of Unbound Granular Materials under Repeated Load and Water Infiltration

Unbound granular materials (UGMs) have advantages in their water storage and drainage capabilities in permeable pavement, which is a benefit for urban sustainable development. The plastic strain of UGM is a crucial mechanical property that affects its design and construction. During its service life, repeated load only, repeated load after infiltration, and simultaneous action with load and infiltration are the three inevitable working conditions that will impact plastic strain, especially dynamic water infiltration. How these working conditions influence plastic strain needs to be focused on and solved. This study conducted laboratory tests to investigate plastic strain considering factors such as loading strength and repetitions, as well as infiltration number and duration. The results showed that the plastic strain and plastic strain rate exhibited similar variations during the repeated load only test and repeated load after infiltration test. The plastic strain changed significantly with different infiltration numbers but had relatively small variations in terms of the plastic strain rate. Longer infiltration duration led to greater plastic strain. With the simultaneous action, the plastic strain presented different variation to the other two conditions. The first and second infiltrations had a more obvious influence on the plastic strain when infiltration was applied. Calculation models were established to predict the effects of loading strength and repetitions as well as infiltration number and duration on plastic strains. For the repeated load only test, an error of 4.6% was observed. In terms of the infiltration number and duration, the errors were found to be 18.5% and 8.5%, respectively. The power function and Sigmoidal Logistic model were used to establish calculation models under the simultaneous action test with a maximum error of 11.5% ranging from 100 to 60,000 repetitions. The proposed calculation models can characterize plastic strain under the three working conditions very well, which can help in the design and construction of fully permeable pavement.