Maximum Plastic Research Articles

Plastic zone characteristics and rapid stability evaluation indexes of circular tunnels subjected to non-hydrostatic stress: A novel complex variable solution incorporating 3D rock mass strength

The morphological characteristics and distribution range of the plastic zone around tunnels, influenced by the true three-dimensional high geostress environment in deep engineering, constitute fundamental reference data for both tunnel design and the control of surrounding rock stability. Based on the GZZ three-dimensional rock mass strength criteria and the complex variable method, a novel semi-analytical method for solving the plastic zone of a circular tunnel subjected to non-hydrostatic stress is presented. The conformal mapping is employed to intricately transform the complex boundaries of plastic zones characterized by diverse shapes onto the unit circle boundary within the image plane. This framework proves invaluable for the precise analytical process of the complex plastic zone morphology and the plastic influence range within the surrounding rock under complex stress conditions. In contrast to traditional analytical methods, the efficacy and versatility of our proposed approach are substantiated. Notably, it demonstrates unique advantages, particularly in the context of non-hydrostatic stress fields and varied rock mass parameters, with respect to predicting both surrounding rock stability and plastic zone morphology. Through the analysis of numerous cases, the study reveals the systematic patterns of influence that in-situ stress and surrounding rock characteristic parameters have on the shape and maximum depth of the plastic zone. The results indicate that (1) there are notable disparities in the morphology and extent of the plastic zone between the GZZ and GHB criteria; (2) the transition of the plastic zone in surrounding rock from U-shaped to V-shaped is significantly influenced by the geostress-to-strength ratio Kσ; (3) there is a notable linear correlation observed between the maximum plastic zone thickness rmax and both Kσ and the stress concentration factor KSCF, importantly, this correlation is independent of far-field stress and the brittleness characteristics of the surrounding rock. These findings provide a novel discriminative method for the rapid analysis of surrounding rock stability in deep circular tunnels.

Effect of thermomechanical processing on mechanical properties and microstructural evolution of Al-Mg-Zn alloy

This study investigates the impact of thermomechanical processing route on the microstructural evolution, and mechanical properties (tensile strength, hardness and elastic plastic (J1c) fracture toughness) of the 7075-aluminum alloy. As received 7075 Al Alloy underwent for the solution heat treatment (SHT) followed by artificial aging and cold rolling (CR) process, respectively. Generally, it was observed that cold rolling of 7075 Al alloy is very challenging, but in this work 90 % cold rolling successfully achieved by optimizing the thermo-mechanical process. The novel heat treatment process for achieving the 90 % cold rolling reduction as follow: firstly, SHT was performed at 470°C for 8 hours(h), there after aging at 140°C for 21 h was performed. Characterization techniques like X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) was employed to assess the microstructure and phase constituents. Elastic plastic (J1c) fracture toughness was studied well on SHT, peak aged and rolled sample. Additionally, Vickers hardness and tensile test were performed. Aging and Cold rolling treatment effectively enhanced tensile strength and hardness ascribed to formation of fine rod shape precipitates of η"(Mg2Zn3) and formation of sub grains with localized strain accumulation, respectively. Split diffraction spots with satellite pattern in long range ordering has also observed in selected area electron diffraction (SAED) pattern of η" attributable to stacking faults and periodic arrangement of precipitates, respectively, as a consequence of this 90 % cold rolling of 7075 Al alloy was accomplished. The maximum Vickers hardness, Tensile strength and Elastic plastic (J1c) fracture toughness values were achieved after SHT (470°C for 2 h), peak aged (PA) (140°C for 21 h) and 90 % cold rolling are 226 HV, 526 MPa and 344.54 kJ/m2, respectively.

Cavern spacing of CAES cavern group in hard rock based on plastic zone and deformation analysis

Existing research on layout parameters of compressed air energy storage (CAES) cavern groups in hard rock has indicated that the key influential factors for group stability include buried depth, diameter, and cavern spacing. Among these, in contrasting to other factors, the research on cavern spacing is limited. This paper focuses on the issue of safe spacing and proposes a numerical method to determine it. By establishing a series of finite element models, the stress state of surrounding rock, changes in shape, equivalent plastic strain of plastic zone, and cavern wall deformation under different spacing have been studied. When a group of air storage caverns in rows is subjected to high internal pressure, for a small spacing, the plastic zone of the surrounding rock between two caverns is connected. Here, the size of the plastic zone, equivalent plastic strain value, and deformation of the cavern wall are relatively large, making the surrounding rock highly susceptible to damage. As the spacing increases, the horizontal width of the plastic zone, the maximum equivalent plastic strain value, the displacement changes of the cavern wall remain stable. This spacing is virtually the same as that when the plastic zone of the surrounding rock is no longer connected and can be selected as a safe spacing. This study explores the design of cavern safe spacing of underground CAES cavern groups and discusses several influencing factors, which can provide references for follow-up energy storage engineering and research.

Simplifying finite elements analysis of four-point bending tests for flip chip microcomponents

PurposeThe purpose of this study is to propose a simplifying approach for modelling a reliability test. Modelling the reliability tests of printed circuit board (PCB)/microelectronic component assemblies requires the adoption of several simplifying assumptions. This study introduces and validates simplified assumptions for modeling a four-point bend test on a PCB/wafer-level chip scale packaging assembly.Design/methodology/approachIn this study, simplifying assumptions were used. These involved substituting dynamic imposed displacement loading with an equivalent static loading, replacing the spherical shape of the interconnections with simplified shapes (cylindrical and cubic) and transitioning from a three-dimensional modelling approach to an equivalent two-dimensional model. The validity of these simplifications was confirmed through both quantitative and qualitative comparisons of the numerical results obtained. The maximum principal plastic strain in the solder balls and copper pads served as the criteria for comparison.FindingsThe simplified hypotheses were validated through quantitative and qualitative comparisons of the results from various models. Consequently, it was determined that the replacement of dynamic loading with equivalent static loading had no significant impact on the results. Similarly, substituting the spherical shape of interconnections with an equivalent shape and transitioning from a three-dimensional approach to a two-dimensional one did not substantially affect the precision of the obtained results.Originality/valueThis study serves as a valuable resource for researchers seeking to model accelerated reliability tests, particularly in the context of four-point bending tests. The results obtained in this study will assist other researchers in streamlining their numerical models, thereby reducing calculation costs through the utilization of the simplified hypotheses introduced and validated herein.

Numerical model of aneurysm formation in vascular grafts

Background. Using numerical modeling to study biomechanics of implantable devices for cardiovascular healthcare can help specialists understand underlying mechanisms of clinical complications caused by these devices.Aim: To describe the results of numerical modeling of aneurysm formation in vascular grafts based on the simulation of degradation of their mechanical properties.Material and Methods. The simulation was carried out using a three-dimensional computer model obtained by high-resolution computed tomography of the vascular graft “KemAngioProtez” (CJSC “NeoKor”, Russia). Using the 3D model obtained with a specialized script in the Abaqus/CAE environment (Dassault systems, USA), we have simulated the decrease in the elastic modulus (from 100 to 10%) with post-threshold stresses in the material and the accumulation of plastic strain.Results. Undergoing 150 loading cycles, the vascular wall in the model swelled up to 0.7 mm in the radial direction, and its mechanical properties degraded significantly (by 90% compared to baseline) due to prolonged pressure exposure. The value of maximum plastic deformation was 0.55%.Conclusion. Numerical modeling of graft mechanical properties degradation can assist in qualitative and quantitative assessment of the areas of aneurysm formation. The method makes it possible to visualize the swelling areas and can be used as a valuable tool to complement the existing approaches to studying vascular grafts, and biografts in particular.

Comparison of Crack Initiation Sites and Main Factors Causing Hydrogen Embrittlement of Tempered Martensitic Steels with Different Carbide Precipitation States

The dependence of crack initiation sites and main factors causing hydrogen embrittlement fracture on carbide precipitation states has been investigated for tempered martensitic steels with the same tensile strength of 1450 MPa. Notched specimens charged with hydrogen were stressed until just before fracture and subsequently unloaded. The crack initiation site exhibited intergranular (IG) fracture at 21 μm ahead of the notch tip as observed by scanning electron microscopy (SEM) for 0.28% Si specimens with plate-like carbide precipitates on prior austenite (γ) grain boundaries. This crack initiation site corresponded to the vicinity of the maximum principal stress position as analyzed by a finite element method (FEM). The initiation site corresponded to the triple junction of prior γ grain boundaries as analyzed by electron backscattered diffraction (EBSD). In contrast, the crack initiation site exhibited quasi-cleavage (QC) fracture at the notch tip for 1.88% Si specimens with fine and thin carbide particles in the grains. This crack initiation site corresponded to the maximum equivalent plastic strain site obtained by FEM. Additionally, the crack initiated on the inside of prior γ grain boundaries and propagated along the {011} slip plane with higher kernel average misorientation (KAM) values as analyzed by EBSD. These findings indicate that differences in carbide precipitation states changed the crack initiation sites and fracture morphologies involved in hydrogen embrittlement depending on mechanical factors such as stress and strain and microstructural factors.

The evolution law of deviatoric stress and asymmetric control technology in roadways during panel mining through overlying residual coal pillars

Close-distance coal seams (CDCS) are widely distributed, and the layout of the upper and lower panels can be divided into “=” type and “+” type. The “+” superposition of upper and lower coal pillars in CDCS caused strong mine pressure, but there are few studies on the panel crossing residual coal pillars (RCP) when the upper and lower coal seams are “+” type layout. In view of the special spatial position (“+” type layout), this paper takes the typical panel 4-301 of a particular mine as the project indagation background and studies mining and crossing the overlying coal pillars by dint of field measurement, numerical simulation, indoor test, and engineering application. Compared with vertical stress or horizontal stress alone, the indexes of deviatoric stress and plastic zone can reflect the failure evolution of surrounding rock more comprehensively. Hence, this paper analyzes the expansion form of the plastic zone and the variation law of deviatoric stress before and after mining influence in the underlying mining roadway. The research results show that: (1) There is a sub-peak zone of deviatoric stress under the RCP. The deviatoric stress is bimodal in the range of 9 m below. After the peak value decays to 7.4 MPa, it changes to a single peak located in the area directly below the middle of the RCP. (2) The maximum plastic zones of the roof and two ribs of the roadway below the RCP are 3.4 m and 5 m, respectively. The crest value of deviatoric stress reaches 10 MPa. As the distance between the panel and the RCP decreases, the shape of the high deviatoric stress area presents the evolution law from the “ellipse” of the roof → the “crescent” of two ribs → the “cochlea” of the tips of the ribs. (3) When the mining of the underlying panel is 10 m, 0 m, or − 10 m away from the RCP (without passing through the RCP). The crest value of deviatoric stress within 5–10 m in advance of the roadway increases in turn. However, the peak value is significantly reduced when it is − 20 m away from the RCP (through the RCP). The crest value of deviatoric stress of two ribs decreases in turn along the panel rib → section coal pillar rib → solid coal rib. Based on this, the underlying 45 m of the RCP is divided into area I (10 m), area II (overlapping area 20 m), and area III (15 m) based on the degree of disturbance. And propose the technical scheme of asymmetric combined control in different zones by using asymmetric channel steel truss anchor cable for the top-ribs of areas I and III, and top-ribs asymmetric channel steel truss anchor cable + door-type support in area II. On-site project practice shows that the partitioned control technology successfully resisted the roadway instability and failure caused by the dynamic-static superimposed stress disturbance under the RCP and realized the primary support of the sectional coal roadway. The conclusion provides technical support and scheme design for the partitioning support of roadways under similar “+” type cross‐panels.

Stress and strain analysis and parameter optimization of pipe truss tower connection of super-large tower crane based on FEM

Clamping bushing structure is an internode connection mechanism designed for the standard section of tubular truss tower. In this paper, the clamping bushing structure of the connecting mechanism of super-large tower crane is taken as the research object, a three-dimensional model of clamping bushing structure is established and imported into ABAQUS, and its multi-body contact model is further constructed to study the contact and bearing relationship of the structure under multiple working conditions, and the accuracy of the calculation results of the model is verified by the experimental stress test under tensile working conditions. In addition, this study is based on the control variable method, and through the design of orthogonal test table, the influence degree of five variable parameters of clamping bushing on the bearing capacity of the structure is investigated. Finally, through the range analysis, the optimal horizontal combination of variables and parameters of clamping bushing structure is obtained, and the optimal matching relationship between the shape of the tower connecting mechanism and the bearing capacity is obtained. The results show that, compared with the original model, the stress concentration at the most dangerous section of the optimized joint and the bushing is obviously alleviated, in which the stress peaks of the upper and lower joints are kept below 500 MPa, and the stress peaks of the bushing groove are also reduced to between 573 and 722 MPa. Moreover, the designed and optimized lower joint can reduce the maximum equivalent plastic strain of the joint root circumference by 56.05% under the original maximum tensile condition, and the overall distribution trend of equivalent plastic strain is more uniform, and a more reliable structural design is obtained, which plays an important guiding role in the design, optimization and analysis of the connecting mechanism of the tower body of large tower crane.

Research on Wellbore Stability in Deepwater Hydrate-Bearing Formations during Drilling

Marine gas hydrate formations are characterized by considerable water depth, shallow subsea burial, loose strata, and low formation temperatures. Drilling in such formations is highly susceptible to hydrate dissociation, leading to gas invasion, wellbore instability, reservoir subsidence, and sand production, posing significant safety challenges. While previous studies have extensively explored multiphase flow dynamics between the formation and the wellbore during conventional oil and gas drilling, a clear understanding of wellbore stability under the unique conditions of gas hydrate formation drilling remains elusive. Considering the effect of gas hydrate decomposition on formation and reservoir frame deformation, a multi-field coupled mathematical model of seepage, heat transfer, phase transformation, and deformation of near-wellbore gas hydrate formation during drilling is established in this paper. Based on the well logging data of gas hydrate formation at SH2 station in the Shenhu Sea area, the finite element method is used to simulate the drilling conditions of 0.1 MPa differential pressure underbalance drilling with a borehole opening for 36 h. The study results demonstrate a significant tendency for wellbore instability during the drilling process in natural gas hydrate formations, largely due to the decomposition of hydrates. Failure along the minimum principal stress direction in the wellbore wall begins to manifest at around 24.55 h. This is accompanied by an increased displacement velocity of the wellbore wall towards the well axis in the maximum principal stress direction. By 28.07 h, plastic failure is observed around the entire circumference of the well, leading to wellbore collapse at 34.57 h. Throughout this process, the hydrate decomposition extends approximately 0.55 m, predominantly driven by temperature propagation. When hydrate decomposition is taken into account, the maximum equivalent plastic strain in the wellbore wall is found to increase by a factor of 2.1 compared to scenarios where it is not considered. These findings provide crucial insights for enhancing the safety of drilling operations in hydrate-bearing formations.

Seismic behavior of reduced beam section joints considering concrete floor effect

SummaryThis study investigates the seismic impact of concrete floors on reduced beam section beam‐to‐column joints through four quasi‐static cyclic tests. We examine mechanical properties, failure modes, and processes against specific criteria. Additionally, we analyze hysteretic response, energy dissipation, stiffness, capacity, and stress–strain mechanisms. Moreover, the ABAQUS platform was used to reproduce the specimen nonlinear finite element model to compare and analyze the test results. The results showed that the specimens exhibit excellent energy dissipation capacity and ductility (with a coefficient of 5.00); the column‐bar connection characteristics affect the maximum capacity and plastic hinge behavior in the reduced beam area. The reduced section of beam's upper flange could not improve the overall seismic performance of the joint. The observed failure sequence is as follows: concrete floor cracking, beam flange yielding, reinforcement fracture, lower flange yielding in the reduced beam area, and overall joint failure. This sequence confirms that the joint fulfills the design criteria of a “strong column‐weak beam” by achieving the target of plastic hinge outward movement.

Microstructure, mechanical, electrical and wear properties of friction stir back extruded copper-6 vol.%Ti2SnC composite material

ABSTRACT This study investigates the impact of extrusion speed on the microstructure, mechanical and electrical properties, and wear resistance of friction stir back extruded Cu-6 vol.% Ti2SnC composite. The findings reveal that severe plastic deformation and heat generated during friction stir back extrusion (FSBE) of Copper-6 vol.% Ti2SnC composite prevented the formation of inter metallics at the particle-matrix interface and resulted in improved bonding. Increasing the speed from 45 to 85 mm/min reduced the maximum plastic strain from 65 to 48 and increased the strain gradient from the surface to the centre of the wire sample. The average grain size decreased from 7.6 ± 0.3 to 3.6 ± 0.2 µm and the average hardness increased from 121.59 ± 8.87 to 130.06 ± 9.95 HV. The yield strength, ultimate tensile strength and elongation decreased by 5.6%, 24% and 12.7% respectively. Wires obtained at the reduced speed of 45 mm/min exhibited an increase of 13% and 26% in electrical conductivity and wear resistance respectively relative to those of the copper matrix material. Analysis of results in the light of a few models indicate that they are in conformity with the results of some of them.

Low-damage performance of blast resilient steel rocking column base with friction connection

This paper presents an experimental and numerical study on the dynamic response and blast resilience of a low-damage rocking column base under blast loading. A conventional rigid column base was used as a reference for comparison. A novel test setup was designed to reflect the actual force state of the column base in an explosive environment. During the test, the column was subjected to a constant axial force with a compression ratio of 0.17. Under the blast loading with a scaled distance of 0.43 m·kg−1/3, the rocking column base exhibited remarkable low-damage and self-centering characteristics, with a maximum equivalent plastic strain of 0.01 and a residual deformation of 0.07%. In contrast, the rigid one suffered irreparable local buckling, resulting in a residual deformation of 3.74%. The results demonstrate that the rocking column base effectively mitigates internal forces through controlled rocking motion and dissipates input energy mainly through frictional sliding. This approach proves to be highly effective in enhancing blast resilience. Finally, a refined finite element analysis (FEA) model was developed to quantitatively evaluate the deformation mode and damage of the joints, based on which the low-damage characteristic of the rocking column base was verified.

Influence of a mesial cantilever on stress, strain, and axial force in fixed partial dentures with a distally tilted implant in the atrophic posterior maxilla.

This study aimed to investigate whether the presence of a mesial cantilever influences the biomechanical behavior and screw loosening in fixed partial dentures (FPDs) with a distally tilted implant in the atrophic posterior maxilla and where to best place the distal implant. Two configurations of implant-supported four-unit FPDs were modelled using finite element analysis. Five interabutment distances were considered. The stress and strain distributions in the implants, abutments, and prosthetic screws were verified under occlusal loading. The development of the axial force on the abutments and screws was also examined. Two-sample t-tests were used to identify differences (P < 0.05). The von Mises stress distributions of the components in the two configurations were similar, as were the maximum plastic strains of the distal prosthetic screws, distal implants, and 30° abutments. The difference in the maximum plastic strains of the straight abutments was statistically significant. The preload of the 30° abutment screws was significantly reduced after the initial loading. In the absence of a mesial cantilever, the axial force on the straight abutments increased. However, when a mesial cantilever was used, the preload of the straight abutments was maintained, and the axial force on the prosthetic screws fluctuated less. The axial force fluctuation of the abutments gradually decreased as the interabutment distance increased. Mesial cantilever usage had minimal effect on stress or strain distribution in FPD implants, abutments, or prostheses. However, it helped resist screw loosening. The distal screw access hole was preferably positioned close to the prosthetic end.

Reasonable top coal thickness for large cross-section open-off cut in lower-layer mining

The thickness of top coal is the main factor affecting the stability of the large cross section open-off cut under the goaf. The 1-2 lower 203 cross section open-off cut of the Huojitu Coal Mine was used as the background to investigate the top coal rational thickness of the large cross section open-off cut under the goaf in slicing mining. The top coal above the cut was simplified into a beam model to calculate its plastic zone range with the elastoplastic theory under the influence of the upper slicing mining and the lower slicing cut excavating. The deformation law of the top coal of the large cross section open-off cut under different top coal thicknesses was studied with both a simulation experiment and numerical simulation. The displacement, stress, and top coal structure of the surrounding rock of the cut were observed in situ using several observation methods. The results show that the plastic zone of the floor in the upper slicing face and the influence of the cut excavation are 2.02 m and 1.43 m, and the maximum plastic zone of the top coal is 3.45 m. A top coal thickness of more than 3.45 m is conducive to maintaining the stability of the large cross section open-off cut. The top coal of the cut can be divided into the roof-fall hazard zone and roof-fall warning zone according to the results monitored by distributed optical fiber. When the top coal thickness is 3.0 m, 3.5 m, and 4.0 m, the deformation law changes from an exponential deformation to a linear and then to a logarithmic relationship in the roof-fall hazard zone and from a linear to a logarithmic relationship in the roof-fall warning zone. When the thickness of top coal is 3.5 m and 4.0 m, the subsidence trend of the top coal visibly decreases, and the subsidence is only 56% and 39% of the subsidence of that of a thickness of 3 m. The deformation law of top coal measured using the DIC (Digital Image Correlation, DIC) is consistent with that of distributed optical fiber. The average thickness of the top coal reserved in the 1-2 lower 203 large cross section open-off cut is 4.0 m. The maximum surface subsidence of the top coal cut hole is 12 mm in the field monitoring. The maximum internal subsidence is 6 mm, and the maximum shed beam strain is –416 με. The deformation of the top coal is slight, indicating that the top coal thickness of 3.5–4.0 m is reasonable.

Evolution of microstructure and mechanical properties of cold spray additive manufactured aluminum deposit on copper substrate

The microstructure and mechanical properties of cold sprayed aluminum coatings on copper substrates were studied in this paper. The impact and deposition mechanisms of single and multiple particles during cold spraying were investigated using finite element modeling. The results of single particle model show that the maximum equivalent plastic strain is located at the contact surface between particle and substrate, decreasing from the jet site to the center of particles, and the equivalent plastic strain at the top of particles is almost zero. The results of multi-particle model show that the regions with large equivalent plastic strain include the contact surface between particle and substrate and the region between particles. The experimental results show that particle deposition has a significant impact on compaction during the spraying process. When the spraying distance is set to a fixed value of 30 mm, and the gas pressure is 2.2 MPa, 2.6 MPa, 3.0 MPa and 3.4 MPa, the coating porosity is always stable at about 1 %. The bonding strength of coating increases with the increase of gas pressure. When the gas pressure increases from 2.2 MPa to 3.4 MPa, the coating bonding strength has increased by 142.0 %, and the maximum value of bonding strength between the coating and the substrate is 16.9 MPa. When the gas pressure is 3.4 MPa with the gas preheating temperature of 300 °C, and the spraying distance is 20 mm, 30 mm and 40 mm, the coating porosity is 1.74 %, 0.95 % and 1.21 %, respectively. The maximum value of bonding strength between the coating and the substrate is 21.3 MPa under the spraying distance of 30 mm.

Cyclic behavior of dual-steel beam-to-column welded flange-bolted web connections

Cyclic loading tests on dual-steel beam-to-column welded flange-bolted web connections were conducted to quantify their moment resistance, plastic deformation and energy dissipation capacities. The test program consisted of five one-sided connection specimens, where Q355 grade beams and Q690 grade columns were used, to study the effects of beam-to-column welded flange connection details and panel zone shear strength on the connection seismic performance. Two types of welded connection details were considered; one was the traditional complete-joint-penetration (CJP) welded connections by use of backing bars, and the other type was those with the bottom backing bar further reinforced by a fillet weld. Three column web thicknesses were designed to arrive at strong, intermediate and weak panel zones, respectively. It was found that the CJP weld with the backing bar reinforced only under the bottom beam flange produced satisfactory performance and accommodated plastic rotations larger than 0.03 rad, while a maximum plastic rotation of 0.04 rad could be developed in the high-strength steel panel zone before fracture occurred. These results evidenced that those dual-steel connections could still sustain high seismic deformation demands.

Influences of the bond-slip on the flexural performance of CFRP plate-strengthened damaged steel beams with intermediate debonding: A numerical study

The interfacial intermediate debonding between the steel beam and CFRP (carbon-fiber-reinforced polymer) is a considerable issue for a CFRP plate-strengthened damaged steel beam. The interfacial bond-slip property determines the interfacial debonding and thus affects the strengthening efficiency. To comprehend the influence laws of the bond-slip behavior, this study conducted a finite element (FE) modelling to assess the strengthening efficiency of the damaged steel beam using CFRP plates. The triangular and trapezoidal cohesive zone models were considered in parametric investigations. The comparisons of FE and experimental results verify the developed FE models. The FE modelling shows that the interfacial fracture energy is the most important bond-slip parameter affecting the flexural strengthening efficiency, relative to the maximum bond stress, elastic and plastic slips. The flexural capacity, ultimate deflection, and debonding load of the damaged steel beam are significantly increased with an increase in the interfacial fracture energy. However, changing the maximum bond stress, elastic slip or plastic slip only produce a minor influence under the same interfacial fracture energy. The selection of the adhesive type is critical for strengthening the damaged steel beam using CFRP plates. In this study, the debonding load, flexural capacity, and ultimate deflection are increased by 75.0%, 51.0%, and 131.1%, respectively, when Araldite-2015 adhesive with the trapezoidal bond-slip model is used instead of Sikadur-30 adhesive with the triangular bond-slip model. Moreover, the debonding load and flexural capacity are hardly increased but the ductility can be considerably improved with an increasing CFRP plate length.

Optimization Method of Multi-parameter Coupling for a Hydraulic Rolling Reshaper Based on Factorial Design

A hydraulic rolling reshaper is an advanced shaping technology with superior protection for casings, and the structural parameters of the reshaper affect its shaping effect on deformed casing directly. To improve the shaping capacity of the reshaper, a multi-parameter coupling optimization method of hydraulic rolling reshaper is proposed to optimize the design of the factors with significant influence under the premise of screening multi-structural parameters. In this paper, according to the working principle of the reshaper, considering the contact nonlinearity between the hydraulic rolling reshaper and deformed casing, as well as the material nonlinearity of the casing, a parametric finite element model of the hydraulic rolling reshaper repairing the shrinkage deformation of casings was developed. The remarkable factors were screened by factorial design, the sample points were generated by optimal Latin hyper-cube design (OLHD), and the response surface models were established by stepwise regression. Therefore, with the maximum plastic deformation of casings as the objective function, the maximum equivalent stress, residual stress, and the plastic deformation of casings as the constrained conditions, an optimized mathematical model for a reshaper was constructed, and the genetic algorithm (GA) is performed to obtain the optimal combination of parameters. The results showed that the optimal reshaper made the shaping process safe and effective, the plastic deformation of casings after single shaping was increased by 11.38 %, and the shaping effect was better (96.48 %), which can effectively improve the safety performance and shaping ability of the reshaper.

Experimental and numerical assessment of thermomechanical and morphological characteristics of pin and pinless micro friction stir welds

In the realm of micro-Friction Stir Welding (FSW), distinct challenges arise compared to conventional FSW, encompassing faster heat dissipation through the backing surface, and higher impact of hooks on joint performance due to the reduced effective sheet thickness. Given the limited variability in tool design in micro-FSW, this study delves into the influence of pinless tool in comparison to pin tool on hook formation, temperature evolution, and bonding mechanisms. By conducting a combination of experiments and numerical investigations on 0.5 mm lap FSW joints, the study unveils that pin tool, with an 11% higher peak temperature and 46% greater effective sheet thickness, achieved 4% increase in joint strength with 26% lesser axial force during traversing. Pin tool exhibited a 10–11% higher proportion of recrystallized grains, with 11.1% and 57.6% grain refinement in the weld centre and hook regions, respectively, primarily due to pin-assisted material stirring. In contrast, pinless tool exhibited a flat nugget with directional grain growth toward the weld bottom. The pin weld demonstrated nearly three times the maximum equivalent plastic strain compared to the pinless weld, confirming the intense movement of plasticized material in the vicinity of the pin and effective intermixing across the sheet-interface.

Stability analysis and support requirements for haulage drift in the vicinity of mined stopes

In this study, combined empirical, numerical, and in-situ monitoring methods were combined to carry out stability analyses and support design for a haulage drift subjected to mining activity. The rock mass quality of the haulage drift was characterized by the RMR, Q, and GSI, and the rock mass properties were calculated. The support requirements for haulage drift during mining were determined by rock mass classification systems. RS2 was used to analyze the plastic zone and displacement of the haulage drift during mining. After the stope was mined, the surrounding rock exhibited a butterfly plastic zone with an asymmetric distribution, and the roof damage was most severe near the stope side. Overall, the haulage drift tended to move in the stope direction, which is consistent with engineering expectations. The support systems determined using the empirical method were analyzed using RS2 and UNWEDGE software. The maximum plastic zone depth of the roof decreased from 4.2 to 2.01 m, and the safety factor of the unstable wedge block increased from 0 to 10.2 after support. In-situ drilling detection shows that the failure depth of the haulage drift roof is 2.37 m. Therefore, a combination of empirical, numerical, and in-situ monitoring methods can be effective for quantitative stability assessments and support design optimization of haulage drifts in the vicinity of mined stopes.