Residual Deformation Research Articles

Nanoindentation of nano-SiC/Si hybrid crystals and AlN, AlGaN, GaN, Ga<sup>2</sup>O<sup>3</sup> thin films on nano-SiC/Si

The review presents systematization and analysis of experimental data on nanoindentation (NI) of a whole class of new materials – wide-gap AlN, GaN, AlGaN and β-Ga2O3 heterostructures formed on a hybrid substrate of a new SiC/Si type, which were synthesized by the method of coordinated atom substitution. The deformational and mechanical properties of the investigated materials are described in detail. The methodology of the NI is described, and both advantages and disadvantages of the NI method were analyzed. The description of the apparatus to conduct the experiments on NI was given. The basic provisions of a new model for describing the deformation properties of a nanoscale rigid two-layer structure on a porous elastic base were proposed. The original method of visualization of residual (after mechanical interaction) deformation in transparent and translucent materials was described. Experimentally determined values of elastic moduli and hardness of SiC nanoscale layers on Si formed by the method of coordinated substitution on three main crystal planes of Si, namely (100), (110) and (111), and elastic moduli and characteristics (elastic modulus, hardness, strength) of surface layers of semiconductor heterostructures AlN/SiC/Si, AlGaN/SiC/Si, AlGaN/AlN/SiC/Si, GaN/SiC/Si and GaN/AlN/SiC/Si grown on SiC/Si hybrid substrates. The unique mechanical properties of a new material β-Ga2O3 formed on SiC layers grown on Si surfaces of orientations (100), (110) and (111) were described.

Deformation-fractional change in resistance model of SMA fiber reinforced mortar beams

Superelastic shape memory alloys (SMA) are metallic alloys that can enable components with self-recovery of cracks and deformation when combined with cement-based materials. Meanwhile, the monitoring method based on fractional change in resistance (FCR) can achieve self-monitoring of components throughout the entire loading process. In this study, the relationship between crack recovery characteristics and FCR of SMA fiber reinforced mortar beams subjected to flexural cyclic loading was analyzed. The beams with SMA fiber volume fractions of 0.1 %, 0.3 %, 0.5 %, and 1.0 % were tested under three-point bending loads. During the loading process, the FCR of the specimens were monitored by the four-electrode method. Finally, the deformation-FCR model for the whole process of the specimens was established to realize the real-time monitoring of the loading state of mortar beams. The results show that SMA fibers can enhance the flexural strength of mortar beams by a maximum of about 64 %, reduce residual deformation, and improve deformation self-recovery ability. The mid-span deflection recovery rate and crack size recovery rate generally increase with higher fiber volume fraction, which can maintain a better deformation recovery effect at the early stage of cracking and gradually decrease with the expansion of cracks. There is a close relationship between the FCR and the degree of crack development that the FCR increases with crack expansion and the magnitude of FCR decreases with increasing fiber content. The established first-order logarithmic fitting model can well describe the relationship between the FCR and cracking, which can provide reference for crack monitoring.

Experimental Investigations of Seismic Performance of Girder–Integral Abutment–Reinforced-Concrete Pile–Soil Systems

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment–reinforced-concrete (RC) pile (IAP)–soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder–integral abutment–RC pile (GIAP)–soil system was conducted for an IAB in China. The experiment’s results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of −8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP–soil system was better than that of the IAP–soil system. Therefore, to accurately reflect the seismic performance of GIAP–soil systems in IABs, it is suggested to consider the influence of the girder.

Evaluation of Steel Slag as a Sustainable Alternative Aggregate for Railway Ballast: A Shakedown Theory-Based Approach

Recent advancements in railway construction have emphasized environmental sustainability, integrating considerations of environmental impact into the planning and execution of infrastructure projects to reduce costs and mitigate adverse effects. This study investigates the use of steel slag as a sustainable alternative for railway ballast, grounded in shakedown theory. The characterization of the aggregates was performed in accordance with NBR 5564 and AREMA standards, confirming that the material meets most requirements. The mechanical behavior of the ballast was analyzed under cyclic loading conditions, assessing permanent deformation and the material’s ability to achieve stability (shakedown). Triaxial tests with repeated loading simulated real railway conditions, applying vertical stresses up to 600 kPa and confining pressures ranging from 35 to 200 kPa. The results indicate that steel slag aggregates exhibited promising performance, with seven specimens achieving stable deformation levels, characterized by residual deformations of less than 2.5 mm. Notably, these specimens approached deformations on the order of 10−7, indicating stability under cyclic loading. Furthermore, a comparative analysis of shakedown criteria proposed by various authors revealed variations in limits for granular materials, enhancing the understanding of steel slag aggregate behavior. The experimental results were validated through numerical simulations conducted with Systrain software 2.0, which simulated a loading condition of 32.5 tons per axle, confirming the observations with maximum principal stresses ranging from 166 to 184 kPa in the ballast. The analysis showed that steel slag aggregates can withstand stress levels higher than those of granodiorite, reinforcing their viability as a sustainable alternative for railway ballast.

Investigation of support structure configurations for selective laser melting of In718

The Selective Laser Melting (SLM), as a widely used metallic Additive manufacturing (AM) process, relies heavily on support structures. This study investigated the impact of different support structure configurations on the quality of In718 samples fabricated through SLM. On the basis of a comprehensive review of existing support structures configurations from the literature, three typical configurations: block, cone, and lattice, were designed to support cantilever parts for performance comparison. A coupled thermo-structural finite element simulation using ANSYS was performed to evaluate the temperature, deformation, and thermal stress evolution during the printing process of the three supported cantilever structures. The residual stress and deformation of the printed In718 cantilevers with different support structures were measured for validation. The results showed that block support exhibits the best strength and heat dissipation capability, making it the most effective support configuration for the SLM of In718 material. This research provides a fundamental procedure for evaluating the supporting performances among various support structures for the SLM process.

Experimental study on seismic damage of SRC-RC vertical hybrid structure

In order to analyze the seismic performance of the SRC-RC vertical hybrid structure, three substructure models were designed, and the key data of structural performance, such as hysteresis curve, skeleton curve, bearing capacity, energy dissipation of structure, residual deformation and damage degree were obtained by carrying out low cyclic loading tests. According to the tests, the plastic development at the column base was delayed because of the reinforcement of section steel, and the plastic development at beam end was much more sufficient, which benefited the beam hinge mechanism in the transition area, so that the transition area has better energy dissipation capacity and deformation capacity. Based on the more sufficient lateral displacement of beam hinge, the beams suffered bending deformation obviously, and interaction between the beams and the infilled wall was significant, which led to a more complex interface force transmission, so the bending cracks and the shearing cracks were densely distributed along the full length of the beam. Meanwhile, the reinforcement of section steel not only improved the deformation capacity of the models but also resulted in more significant damage difference in positive and negative loading. To quantitatively evaluate the damage level, a seismic damage index system was proposed, including displacement damage degree, bearing capacity damage degree and residual deformation index, which reflect the increment of deformation caused by structural damage, the deterioration of bearing capacity and the residual deformation, respectively. It is suggested that the structural failure should be defined respectively under different modes: For the strength degradation behavior mode and ductility behavior mode, structural failure should be confirmed if the load reduces to 0.90 and 0.85 times of the peak load, respectively; and for the brittle behavior mode, the frame is considered to fail when the load reaches the peak without considering the structural performance after the peak load.

Self-centering rocking steel frame with column mid-height uplift: Experimental and numerical investigation

This paper proposes a self-centering rocking steel frame with column mid-height uplift (SCRSF-CMU) that exhibits high post-yield stiffness and energy dissipation capacity. The hysteretic performance of the SCRSF-CMU was investigated through cyclic loading tests. A numerical model of the SCRSF-CMU was established and validated against experimental results. Subsequently, the seismic performance of the SCRSF-CMU was compared with that of the self-centering rocking steel frame with column base uplift (SCRSF-CBU) using nonlinear time history analysis. Finally, the seismic responses of the SCRSF-CMU and SCRSF-CBU under varying earthquake intensities were analyzed using the endurance time analysis. The results indicate that the designed SCRSF-CMU demonstrates excellent lateral force resistance, energy dissipation, and self-centering capabilities. The rocking effect and the restoring force of the post-tensioned steel strands effectively controlled the residual lateral displacement of the specimens. The multi-scale numerical model of the SCRSF-CMU accurately captured its hysteretic behavior and deformation patterns. Compared to the SCRSF-CBU, the SCRSF-CMU exhibited superior rocking deformation capacity, post-yield stiffness, and hysteretic energy dissipation. Under MCE excitation, both SCRSF-CMU and SCRSF-CBU showed uniform inter-story drift distribution with minimal residual deformation, creating a satisfactory condition for the post-earthquake repair work if necessary. The high post-yield stiffness of the SCRSF-CMU was more effective in reducing both maximum and residual displacements. Endurance time analysis revealed that SCRSF-CMU and SCRSF-CBU exhibited relatively uniform inter-story drift distribution under SLE, DBE, and MCE earthquakes. Under FE excitation, the inter-story drift ratio of both structures were nearly identical; however, under DBE and MCE excitations, the maximum roof drift ratio and inter-story drift ratio of the SCRSF-CBU were larger, indicating that the SCRSF-CBU had higher deformation demands than the SCRSF-CMU.

Enhancing strength-ductility synergy of Cu alloys with heterogeneous microstructure via rotary swaging and annealing

The trade-off of strength and ductility in the Cu alloys seriously restricts its wide application. In this study, the paradox of strength and ductility of the Cu alloy is ameliorated by rotary swaging (RS) and subsequent annealing, and reveals its microstructural evolution. It was found that the grain size was obviously refined after the RS, resulting in yield strength as high as 760 MPa but with a ductility of only 1.5 %. After annealing, the RS-350-20 sample (RS sample annealed at 350°C for 20 min) exhibited partial recrystallization at the edge and middle positions, while full recrystallization occurred at the center position, which formed a gradient grain size distribution. Tensile results showed that RS-350-20 sample exhibited an excellent combination of the yield strength of 495 MPa and ductility of 27%. High strength stemmed from residual deformation grains, recrystallized ultrafine/fine grains and heterogeneous deformation-induced (HDI) strengthening. The good ductility originated from recrystallized coarse grain, pronounced HDI hardening and activated deformation twins. In addition, microstructural characterization further revealed that dislocations were accumulated near the recrystallized grains to maintain strain continuity at the interface of deformed grains and recrystallized grains during tensile strain. With increasing strain, deformation twins were activated near the recrystallized grains, which facilitates high strain hardening capability meanwhile maintaining high strength. These findings provide insight for optimizing the strength and ductility of Cu alloys by a feasible processing.

Study on the Mechanical and Permeability Evolution of a Composite Rock Mass in an Aquifuge Under Hydraulic Coupling

The lithology and composition type of an aquifuge in overburden play a crucial role in influencing the crack evolution and permeability changes of the aquifuge. This study utilized the high-temperature and high-pressure rock triaxial seepage test system to conduct triaxial compression tests on mudstone, sandstone, and their combined rock samples. The mechanical characteristics and permeability evolution of each lithology law during the failure were investigated. Furthermore, computed tomography (CT) scanning technology was utilized for the three-dimensional (3D) reconstruction and theoretical permeability calculation of single and combined rock samples. The results indicated that the stress–strain curves for single and combined rock samples exhibited similar patterns, which were divided into four stages: pore compaction, linear elasticity, yield deformation, and post-peak residual deformation. The peak strength of rock samples positively correlated with confining pressure. Permeability trends for mudstone and sandstone exhibited an “N”-type pattern characterized by “slow decrease–gradual stabilization–sudden increase–rebound decrease”, while the permeability of mudstone–sandstone combined rock followed a “U”-type pattern of “initial decrease–stabilization–subsequent increase”. Notably, the permeability of the combined rock samples was significantly lower compared to the single rock samples. The failure mode indicated that fractures in a single rock sample transversed the entire sample, whereas failures in the combined rock samples were confined to the mudstone component. This observation accounted for the differences in the permeability changes between the rock sample types. Additionally, the theoretical permeability results from the 3D reconstruction correlated with the experimental results.

Study on the performance of cast-in-situ concrete wet joints in PCSBs under cyclic loading

The closure section of precast concrete segmental bridges (PCSBs) usually adopts the wet joint, the regular longitudinal reinforcement is discontinuous, which makes the section the vulnerable part. To study the performance of the wet joint in the closure section under cyclic loading, six specimens considering loading mode, interface treatment method, setting of regular reinforcement and prestressing are tested. Results show that the damage of the wet joint accumulates and the plasticity develops under cyclic loading, the specimens undergo residual deformation, strength attenuation and stiffness degradation. Increase in prestressing level can delay the cracking, the cracking load of specimens with a prestressing level of 8MPa and 10MPa is 21.9% and 32.8% respectively higher than that of the specimen with a stress level of 6MPa, and the results also confirm that excessive prestressing level cannot significantly improve the shear strength of the specimens. When the controlled displacement is small, the residual deformation of the specimen is small and the strength attenuates slowly; with the increase in controlled displacement, the residual deformation of the specimen increases and speeds up, the strength decreases continuously, and the development of the crack tends to be stable, leading to the leveling off of degradation of the stiffness.

Investigation on the failure mechanism of friction-based self-centering timber beam-column joint considering bolt bearing effect: Experimental study and theoretical analyses

For friction-based self-centering timber structures, the bearing between friction bolts and the edge of holes is inevitable, due to machining inaccuracies and significant deformations at the beam-column joints. However, this issue has yet to be addressed in existing research. A limit state investigation was conducted on these friction-based self-centering timber beam-column joints under extensive deformation to analyze the failure mechanism and the loss of pretension force throughout the loading process. The influence of bolt bearing behavior on the residual deformation, loading capacity, energy dissipation capacity, and stiffness of the joint was studied. Finally, a theoretical prediction model considering single bolt and multi bolts bearing was proposed incorporating theoretical analysis and experimental results. The results indicate that the damage of the joint is concentrated on the compression deformation at the edge of bolt holes in friction pads and timber beams. The joint ultimately fails due to the end face of the column being crushed by the anchor used to fix post-tensioned (PT) strands. The joint exhibits good hysteresis characteristics within a 4 % drift and still demonstrates good recoverability within a 6 % drift. The loss rate of pretension force is below 15 % when the drift is lower than 4 %, but it increases significantly after the drift exceeds 5 %. When the drift is less than 4 %, the joints primarily exhibit single bolt bearing mode, resulting in only a slight increase in stiffness for the joints. When the drift exceeds 8 %, the joints primarily exhibit a multi bolt bearing mode, resulting in a maximum increase of approximately 64.5 % in joint stiffness. The theoretical bolt bearing model derived can better predict the position of bolts bearing the edge of holes and the damage state of friction-based self-centering timber beam-column joints.

Residual stress and deformation of welded T-joint between low carbon steel and stainless steel

The welded structures between carbon steel and stainless steel are widely used in many sectors such as pedestrian bridges, food industry, chemical industry, petroleum, and thermal power plants, … These composite structures take advantages of each material for different parts of structure. In the welded structures between carbon steel and stainless steel, the structure is made by T-joint that is the most common. The calculation of residual stress and welding strain of the T-joint between low-carbon and stainless steel materials is the basis to evaluate the working ability of this structure. In this study, the residual stress and welding deformation of the T-joint are determined by the imaginary force method. The double-sided weld of T-joint between low carbon steel and stainless steel is welded simultaneously by MIG welding process. The obtained results of residual stress and welding deformation in this case are compared with the case of single-sided weld so that we can find the difference between residual stress and welding deformation in two cases.

Characterization and simulation of AlSi10Mg reinforcement structures by direct energy deposition by means of laser beam and powder

Among metal additive manufacturing technologies, direct energy deposition (DED) processes have the advantage to be easily integrable in a manufacturing chain with other conventional technologies. This characteristic can be exploited by designing reinforcement structures to be added by DED onto pre-existing subcomponents to tailor the part’s mechanical properties while keeping the part lightweight. This study focuses on DED by means of laser beam and powder process optimization to improve material quality and geometrical accuracy of AlSi10Mg reinforcement structures while preventing excessive thermal deformations and material dilution into the substrate. These results are compared with finite elements numerical simulations of the deposition process, comprising thermo-elastic deformation and material deposition, to predict the bending and reinforcement of the processed substrate. In particular, the model includes the deterministic prediction of the deposition profile as a function of the process parameters and a few condition-specific coefficients: once calibrated, the model was used to compare the numerical and experimental residual deformation of the reinforced sample, obtaining promising agreement. The reinforcement provided to a 1.5 mm thick substrate by a single wall of deposited materials, with cross-sectional dimensions of 2 mm in width and 2.5 mm in height, was evaluated by three points bending. With the reinforcement on the tensile side of the stresses, the energy absorbed by the material plastic deformation increased by 2.4% as compared to the substrate alone, while with the reinforcement on the compression side of the stresses the energy absorption increased by 75.8% on average.

Seismic Performance of Precast Drift-Hardening Concrete Walls Connected by Grout-Sheath Duct.

In order to find a suitable size of sheath duct and a reliable construction method for precast walls, a cast-in-place and five 1/2 scale precast drift-hardening concrete walls reinforced with weakly bonded ultra-high strength SBPDN rebars were fabricated and tested under reserved lateral load and constant compression. The experimental variables were the diameter of sheath ducts (45 mm, 100 mm, and 120 mm), embedded length (20d and 35d; d is the nominal diameter of SBPDN rebars), axial load ratio (0.075 and 0.15), and the construction method. The experimental observations, hysteresis behaviors, envelope curves, residual deformation, crack propagation, and energy dissipation were compared in the study. Moreover, a formula was applied to calculate the bond strength of the sheath duct. The experimental and calculated results revealed that increasing the axial load ratio and embedment length could not enhance the bond strength of the sheath ducts, and increasing the diameter decreased the bond strength significantly. Anchored the SBPDN rebars in smaller sheath ducts separately was a more stable connection method for precast concrete shear walls and provided sufficient drift-hardening capability, even at a large drift level (over 3%).

Generalized SmartScan: An Intelligent LPBF Scan Sequence Optimization Approach for Reduced Residual Stress and Distortion in 3D Part Geometries

Abstract Laser powder bed fusion (LPBF) is an additive manufacturing technique that is gaining popularity for producing metallic parts in various industries. However, parts produced by LPBF are prone to residual stress, deformation, cracks and other quality defects due to uneven temperature distribution during the LPBF process. To address this issue, in prior work, the authors have proposed SmartScan, a method for determining laser scan sequence in LPBF using an intelligent (i.e., model-based and optimization-driven) approach, rather than using heuristics, and applied it to simple 2D geometries. This paper presents a generalized SmartScan methodology that is applicable to arbitrary 3D geometries. This is achieved by: (1) expanding the thermal model and optimization approach used in SmartScan to multiple layers; (2) enabling SmartScan to process shapes with arbitrary contours and infill patterns within each layer; (3) providing the optimization in SmartScan with a balance of exploration and exploitation to make it less myopic; and (4) improving SmartScan’s computational efficiency via model order reduction using singular value decomposition. Sample 3D test artifacts are simulated and printed using SmartScan in comparison with common heuristic scan sequences. Reductions of up to 92% in temperature inhomogeneity, 86% in residual stress, 24% in maximum deformation and 50% in geometric inaccuracy were observed using SmartScan. An approach for using SmartScan for printing complex 3D parts in practice, by integrating it as a plug-in to a commercial slicing software, was also demonstrated experimentally, along with its benefits in significantly improving printed part quality.

Seismic behavior of resilient concrete column-base connection with SMA bolts and RSPs

This paper presented a novel resilient concrete column-base connection with shaped memory alloy (SMA) bolts and rectangular slotted plates (RSPs) to achieve the demountable and recoverable capabilities in precast concrete columns. Quasi-static tests were conducted on one monolithic and three resilient concrete connections to investigate the effects of RSP number and yield strength on seismic behavior. Results showed that the resilient connection with both flange and web RSPs had superior lateral capacity, ultimate drift ratio, and energy dissipation compared to the monolithic connection. The resilient connection also exhibited minimal concrete damage and smaller residual deformation. However, low-yield-strength flange RSPs significantly reduced lateral capacity, initial stiffness, and energy dissipation, which should be considered in engineering design. Additionally, adjustment coefficients for rocking interface rotations were determined from digital image correlation (DIC) data using a fitting method. A formula was proposed to predict the flexural capacity of resilient specimens, assuming a plane section in the compression zone. The predictions closely matched the test data, with differences within 10 %, demonstrating the formula's effectiveness. The length, diameter, and material yield strength of the anti-shear steel bar (ASB) had a significant impact on the shear capacity of the interface.

Seismic response study of multi-span continuous beam bridges near faults considering permanent displacement attenuation effects

The fling-step effect caused by near-fault ground motion induces a step-like permanent displacement of the ground surface, which decays sharply with increasing fault distance, leading to varying degrees of ground motion at each supporting point of the bridge structure. In this context, multi-span long-span bridges exhibit echelon displacement of the main beam and a more complex internal force response compared to ordinary bridges. To investigate the seismic response characteristics of multi-span long-span continuous girder bridges under near-fault ground motion, this study is based on the permanent displacement attenuation model. The main bridge of the Hongyazi Yellow River Bridge in Shizuishan City, consisting of 16 spans, is taken as the research object. Using OpenSees software, a finite element model for the dynamic analysis of the multi-span long-span continuous girder bridge was established, and its structural dynamic characteristics were compared with the natural vibration test of the actual bridge. Based on simulated ground motions that consider the permanent displacement attenuation effect and spatial variability, the seismic response of the key components of the near-fault multi-span long-span continuous beam bridge is examined. The results indicate that under near-fault ground motion considering the attenuation effect of permanent displacement, the main girder of multi-span long-span bridges frequently deviates from the axis in different directions, ultimately resulting in residual deformation of the main girder post-earthquake. The permanent displacement attenuation effect increases the maximum bending moment response at the pier bottom and causes uneven internal force distribution in the bridge. Ignoring this effect can lead to overestimation of bearing deformation.

Linking Metastatic Potential and Viscoelastic Properties of Breast Cancer Spheroids via Dynamic Compression and Relaxation in Microfluidics.

The growth and invasion of solid tumors are associated with changes in their viscoelastic properties, influenced by both internal cellular factors and physical forces in the tumor microenvironment. Due to the lack of a comprehensive investigation of tumor tissue viscoelasticity, the relationship between such physical properties and cancer malignancy remains poorly understood. Here, the viscoelastic properties of breast cancer spheroids, 3D (in vitro) tumor models, are studied in relation to their metastatic potentials by imposing controlled, dynamic compression within a microfluidic constriction, and subsequently monitoring the relaxation of the imposed deformation. By adopting a modified Maxwell model to extract viscoelastic properties from the compression data, the benign (MCF-10A) spheroids are found to have higher bulk elastic modulus and viscosity compared to malignant spheroids (MCF-7 and MDA-MB-231). The relaxation is characterized by two timescales, captured by a double exponential fitting function, which reveals a similar fast rebound for MCF-7 and MCF-10A. Both the malignant spheroids exhibit similar long-term relaxation and display residual deformation. However, they differ significantly in morphology, particularly in intercellular movements. These differences between malignant spheroids are demonstrated to be linked to their cytoskeletal organization, by microscopic imaging of F-actin within the spheroids, together with cell-cell adhesion strength.

Nonlinear mechanical response of UHSS rectangular plate under thermo-mechanical-metallurgical coupling

The mechanical properties of ultrahigh-strength steel (UHSS) produced through the gradient thermoforming process (GTP) are significantly influenced by residual stress and deformation. However, the precise distribution of these factors during GTP remains unclear. To address this issue, a detailed thermal model is developed, incorporating key heat transfer mechanisms, including coupled heat conduction and radiation, using the method of separation of variables. Furthermore, the displacement and stress fields of UHSS rectangular plates are derived using the differential quadrature method (DQM), accounting for phase transitions and external load. The combination of the separation of variables and DQM methods significantly improves computational efficiency. Furthermore, this study presents the first analysis of the combined effects of thermal load, phase transitions, and external forces on UHSS rectangular plates. Finally, through a combination of theoretical analysis, experimental validation, and case studies, the influence of material properties, geometric parameters, and external load on the temperature, stress, and displacement fields is examined. The findings reveal that heating rate, phase transitions, and external load play a critical role in the stress and displacement distribution in UHSS plates during GTP. This research provides a theoretical foundation for optimizing GTP process parameters and material design, ultimately enhancing the quality and performance of UHSS components.

Prediction and Analysis of Surface Residual Deformation Considering the Impact of Groundwater in Mines

With economic development and coal resource exploitation, the area of mined-out zones is expanding continuously. The traditional waste disposal methods no longer meet the current demands, making it urgent to evaluate and reuse the surface stability of these mined-out zones. Surface residual deformation is a process where voids and fissures within the mined-out zones are gradually filled and compacted, affecting the overlying rock structure. Additionally, groundwater significantly impacts the strength of the overlying rock, leading to increased subsidence. Therefore, predicting surface residual deformation while considering the effects of groundwater is crucial for forecasting surface deformation and assessing stability in mined-out zones. This study, taking into account the characteristics of subsidence zones and the impact of groundwater on the compaction of fractured rock masses, uses equivalent mining height and probability integral methods to develop a predictive model for surface residual deformation incorporating groundwater effects. Predictions for the study area show that groundwater exacerbates surface residual deformation, with various deformation values ranging from 33.8% to 51.9%. The surface stability categories are divided into stable and essentially stable regions based on the residual deformation’s impact on the working face. This model fully considers the influence of groundwater on residual deformation in mined-out zones, refining existing mining subsidence theories, addressing deformation issues caused by adverse groundwater factors, and providing a theoretical basis for predicting residual deformation and evaluating stability in mined-out zones, promoting the sustainable development of land and environmental resources in mining areas.