Plastic Failure Research Articles

Numerical analyses of spherical indenter intrusion into sandstone: From laboratory tests to numerical simulations

To explore the mechanical mechanisms of rock fracturing under compression during ball milling. The study investigates the effects of intrusion depth and indenter diameter on the evolution of stresses and plastic strains, integrating laboratory tests and numerical predictions. The results reveal a reduction in both axial and radial stresses with increasing intrusion depth into the rock. Shear stress experiences an initial rise followed by a decline, while circumferential stress demonstrates an initial increase followed by a rapid decrease in the radial direction. As the intrusion deepens, the predominant influence on plastic strain of rock shifts from shear stress dominance to a combined dominance of shear and circumferential stresses. The influence of the indenter diameter on the stress field diminishes following an exponential decay pattern. In terms of the plastic strain field, smaller indenters are more likely to induce plastic failure due to shear and circumferential stresses, larger indenters are more prone to plastic failure induced solely by shear stresses. As the number of indenters increases, the integration of the stress and plastic strain fields is enhanced. This implies that introducing more spherical indenters amplifies the collaborative effect, leading to a more cohesive fracturing of the rock.

Coal‐wall spalling prevention mechanism using advance‐grooving pressure relief in the large‐mining‐height working face of a shallow coal seam

AbstractIn mining, the roof structure of a working face with a large mining height in a shallow‐buried coal seam is prone to cutting instability in front of the support, which causes support crushing and coal‐wall spalling. This study analyzes 2201 working faces with large mining heights in the Haiwan No. 3 Mine by investigating the mechanical response law of coal walls under the transient excitation of roof structure instability. A mechanical model of coal walls under dynamic and static load coupling is established, revealing the formation mechanism of coal wall spalling and its main influencing factors. Prevention and control technologies of advanced grooving and pressure relief are proposed, and grooving parameters are determined. The results show that: During the mining process of large mining height working face in shallow buried coal seam, the step change of static response of coal wall is induced by the transient instability of roof structure, and the high abutment pressure is formed on the coal wall. At the same time, the strain energy and gravitational potential energy of roof cutting instability are released to form a dynamic load. Under the action of dynamic and static load, the plastic failure dissipation power of the coal wall is greater than the critical power, and the coal wall spalling occurs. The main influencing factors are mining load, mining height, and internal friction angle of the coal wall. The method of advanced grooving pressure relief can change the roof structure and coal force mechanism, by cutting off the connection between the coal wall and immediate roof, reducing the height of the coal wall force, effectively controlling the position of the roof cut off break line, reducing the static load effect of the roof on the coal, and transferring the position of the dynamic load response to the depth of the coal wall. When the grooving height‐depth ratio k is 0.75, the peak value of the abutment pressure moves 5.57 m to the front of the working face, and the pressure relief effect is the best. The above research results provide an effective active protection method for controlling coal wall spalling in fully mechanised working face with large mining height.

Reliability Simulation of IGBT Module with Different Solders Based on the Finite Element Method

The interconnecting solder is a key control factor for the reliability of electronic power packaging because it highly affects the junction temperature of insulated-gate bipolar transistor (IGBT) modules and is prone to plasticity, creep, and other failure behaviors under temperature-change environments. In this paper, the interconnecting performance and fatigue life of five different kinds of solders such as SAC305, sintered silver, Au80Sn20, sintered copper, and pure In under direct current (DC), power cycle, and electro-thermal coupling complex environments were studied based on electro-thermal multi-physical field coupling finite element simulation method, respectively. Results show that the sintered silver owns the most outstanding thermal reliability and the DC operating junction temperature of the IGBT module after utilizing sintered silver solder is only 90.2 °C, which is nearly 15 °C lower than that of the IGBT module utilizing SAC305 solder. Furthermore, in the power cycle reliability test, the fatigue life of Au80Sn20 solder reaches a maximum of 3.26 × 107 cycles while the life of indium presents only 5.85 × 103 cycles, a difference of nearly four orders of magnitude. Finally, under the complex environment of electro-thermal coupling, the fatigue life of Au80Sn20 solder is also the largest at 1.9 × 106 cycles, while the smallest life of solder becomes SAC305 solder at 4.44 × 102 cycles. The results of this paper can provide a theoretical basis for solder selection and life prediction of the IGBT module, which is of great significance in improving the reliability of power electronic packaging.

Experimental study on bearing capacity performance of glued bamboo-wood bolted joints

The paper presented an experimental investigation of glued bamboo-timber bolted joints to study the influence of bolt grade, bolt diameter, and material type on the load-bearing capacity of bolted joints. The results showed that the failure mode of glued bamboo-timber bolted joints was characterized by compression deformation of the bolt holes, with a plastic hinge failure occurring at each shear plane. Additionally, the failure of the specimens involved the failure of both the primary material and the adjacent substrate at the edge of the joint. As the diameter of the bolts increased, the load-bearing capacity of the specimens also increased. The increase in maximum load from a bolt diameter of 10 mm to 12 mm was 13.78 %, while the increase in maximum load from a bolt diameter of 12 mm to 14 mm was 42.29 %. Enhancing the bolt grade increased the load-bearing capacity of the specimens. The increase could be 10.32 % under the circumstance of WBW (wood on the outer layer and bamboo on the inner layer) combination while 8.4 % when it was BWB (bamboo on the outer layer and wood on the inner layer) combination. Moreover, when the material type was changed into BWB, the increase in load-bearing capacity was 55.33 % and 32.84 % when the diameter varies. The load-bearing capacity of the BWB material was higher than that of the WBW material. After comparing the existing methods of calculating bolt load carrying capacity, optimizations were made to the calculation formulas in Eurocode 5. The modified formula provided more accurate predictions of the load-bearing capacity of glued bamboo-timber bolted joints.

Hydrogen susceptibility of Al 5083 under ultra-high strain rate ballistic loading

Abstract The effect of hydrogen on the ballistic performance of aluminum (Al) 5083H131 was examined both experimentally and numerically in this study. Ballistics tests were conducted at a 30° obliquity in accordance with the ballistic test standard MIL-DTL-46027 K. The strike velocities of projectiles were ranged from 240 m s−1 to 500 m s−1 level in the room temperature. Electrochemical hydrogen charging method was utilized to introduce hydrogen into material. Chemical composition of material was analyzed using energy dispersive X-ray (EDX) analysis. Instant camera pictures were captured using high-speed camera to compare H-uncharged and H-charged specimen ballistics tests. The volume loss in partially penetrated specimens were assessed using the 3D laser scanning method. Microstructural examinations were conducted utilizing scanning electron microscopy (SEM). It was observed that with the increased deformation rate, the dominance of the HEDE mechanism over HELP became evident. Furthermore, the experimental findings were corroborated through numerical methods employing finite element analysis (FEM) along with the Johnson–Cook plasticity model and failure criteria. Inverse optimization technique was employed to implement and fine-tune the Johnson–Cook parameters for H-charged conditions. Upon comparing the experimental and numerical outcomes, a high degree of consistency was observed, indicating the effective performance of the model.

Eco-Friendly 3D-Printed Concrete Using Steel Slag Aggregate: Buildability, Printability and Mechanical Properties

Utilizing steel slag aggregate (SA) as a substitute for river sand in 3D concrete printing (3DCP) has emerged as a new technique as natural resources become increasingly scarce. This study investigates the feasibility of using steel slag (SS) as fine aggregate for 3DCP. Ninety mixtures with varying steel slag aggregate-to-cement ratios (SA/C), water-to-cement ratios (W/C), and silica fume (SF) contents were designed to study the workability and compressive strength of the 3D-printed concrete. Additionally, the actual components were printed to evaluate the printability of these mixtures. The experimental results indicate that it is feasible to fully employ SA in concrete for 3D printing. Mixtures with slump values ranging from 40 to 80 mm and slump flow values varying from 190 to 210 mm are recommended for 3D printing. The optimal mix is determined to have SA/C and W/C ratios of 1.0 and 0.51, respectively, and an SF content of 10% by cement weight. A statistical approach was utilized to construct the prediction models for slump and slump flow. Moreover, to predict the plastic failure of the 3D-printed concrete structure, the modified prediction model with an SA roughness coefficient of 4 was found to fit well with the experimental data. This research provides new insights into using eco-friendly materials for 3D concrete printing.

Study on the structure and strata behavior regularity of repeated mining overburden of close-distance shallow buried coal seam group

This paper studies the collapse structure, plastic failure regularity, and overburden movement regularity in the mining process of the Shallowly Buried Coal Seam (SBCS) group in the Yulin area using physical similar material simulation, computer numerical simulation, and theoretical analysis. The objective of the present article is to explore the strata behavior regularity of the SBCS group, taking the engineering geological conditions of Hongliulin Coal Mine as the sample. According to the results, when the lower coal seam of the SBCS group is mined, the initial stress step increases, and the periodic stress step decreases compared to the upper first coal seam. During the mining of the lower coal seam, there is an extreme collapse span in the interlayer rock formation: the process induces the activation of the collapsed roof in the goaf of the upper coal seam, and the overall sinking phenomenon occurs. The dynamic stress is obvious. The roof stress is significant in passing through the upper coal seam's residual coal pillar (CP) into the lower coal seam. The CP is at a certain distance, and the residual CP is violently unstable and sinks the strata behavior regularity. The interlayer rock layer forms an inclined shear staggered fracture zone along the coal wall. The research results provide a theoretical method for controlling mine stress and green and safe mining in the SBCS group of coal production enterprises.

Off-axis mechanical behavior and dynamic characteristics of UHMWPE composite laminates

An understanding of the off-axis mechanical behavior and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) cross-ply laminates subjected to quasi-static and dynamic loadings is developed, with focus on the influence of off-axis angle and strain rate. For off-axis tension, UHMWPE laminates exhibit polymer shear response characteristics. An orientation-hardening phenomenon is captured, as fiber rotation leads to local increment of load capacity along the loading orientation. The failure strength presents an evidentially descending trend with off-axis angle from 0° to 45°. A non-monotonic variation of strength with strain rate is further observed: increasing with strain rate up to 500 s−1 but decreasing above, which is attributed to failure mode switching from plastic failure to brittle failure. The Tsai-Wu failure criterion, on homogenized cross-ply laminae, is experimentally modified with rate dependence. Further investigation on detailed information of the unidirectional properties should be conducted with the backing-out scheme to establish unidirectional failure criterion.

Evaluation of plasticity and determination of deformation index of 3D-printed composite cement-based materials

ABSTRACT Given the current situation that the evaluation system of the deformation and instability failure of 3DPC is immature, this study was devoted to shaping the performance of 3DPC to provide new ideas and ways for exploring the stable forming of 3DPC. The relationship between the deformation in different directions and the number of layers was analysed. The deformation regulation of 3DPC was revealed, and the controllable index was determined. Results show that the vertical and horizontal deformation in the plastic state is correlated to evaluate the overall deformation by considering only the lateral deformation. The horizontal and vertical deformation of each layer decreases as the number of layers increases, forming a trapezoidal shape. The relationship between the horizontal deformation and the number of layers varies with the shape of the printed component. This relationship follows a linear pattern in the vertical direction and remains independent of the printing shape. The deformation process of 3DPC can be divided into three stages: linear deformation, elastoplastic, and plastic failure. The elastoplastic stage is identified as the primary stage, and the horizontal deformation begins here. Comparatively, the horizontal strain is more suitable for evaluating the plasticity of 3DPC than the vertical strain.

Investigating the Influence Mechanism of Different Shielding Gas Types on Arc Characteristics and Weld Quality in TA2 Laser–Arc Hybrid Welding

The effective welding of a 6 mm thick TA2 pure titanium medium-thickness plate was achieved by laser–arc hybrid welding (LAHW) with helium–argon mixed shielding gas. Conducted research on the influence of helium–argon mixed shielding gas on plasma and arc characteristics during welding, and its further impact on the microstructure, internal porosity defects, tensile properties, and corrosion resistance of welded joints was explored. The study demonstrated that under the shielding gas with 75% helium, the arc width narrowed significantly from 6.96 mm to 2.61 mm, achieving a 63% reduction, which enhanced the concentration of arc heat flux density. Achieved a well-formed weld with no surface spatter and significantly reduced the internal porosity rate from 3.02% to 0.47%, which is an 84% decrease. Tensile fractures are located in the base material, all exhibiting plastic failure. The corrosion resistance of the welded joint initially increased and then decreased with the increase of helium content in the shielding gas, peaking at 75% helium content.

Clustering of negative topological charges precedes plastic failure in 3D glasses.

The deformation mechanism in amorphous solids subjected to external shear remains poorly understood because of the absence of well-defined topological defects mediating the plastic deformation. The notion of soft spots has emerged as a useful tool to characterize the onset of irreversible rearrangements and plastic flow, but these entities are not clearly defined in terms of geometry and topology. In this study, we unveil the phenomenology of recently discovered, precisely defined topological defects governing the microscopic mechanical and yielding behavior of a model 3D glass under shear deformation. We identify the existence of vortex-like and antivortex-like topological defects within the 3D nonaffine displacement field. The number density of these defects exhibits a significant anticorrelation with the plastic events, with defect proliferation-annihilation cycles matching the alternation of elastic-like segments and catastrophic plastic drops, respectively. Furthermore, we observe collective annihilation of these point-like defects via plastic events, with large local topological charge fluctuations in the vicinity of regions that feature strong nonaffine displacements. We reveal that plastic yielding is driven by several large sized clusters of net negative topological charge, the massive annihilation of which triggers the onset of plastic flow. These findings suggest a geometric and topological characterization of soft spots and pave the way for the mechanistic understanding of topological defects as mediators of plastic deformation in glassy materials.

Experimental investigation on the dynamic response of vent plate under methane-air mixtures explosion load

The dynamic response study of explosion venting components is of great significance for the assessment of explosion disasters and the determination of damage. Based on the self-developed rectangular explosion venting device, a series of experimental investigations on the dynamic response and failure mode of calcium silicate vent plates under the methane explosion loads induced by a detonator were conducted. The results show that the vent plate mainly exhibits brittleness and presents a plastic hinge failure mode under the blasting loads. When the gas concentration is closer to the stoichiometric concentration, P2 (the peak overpressure generated by the vent plate rupture) and its pressure rise rate dP2/dt are higher. Conversely, when the methane concentration is closer to the upper or lower limits of the explosion, the explosion load tends to be static, the yield line of the vent plate is shorter, and there are fewer fragments generated by the failure of the plate. The pressure-displacement curve and the correlation diagram of failure modes proposed provide a reference for predicting the failure mode of light and fragile explosion venting components.

Nonlinear behavior of existing pre-tensioned concrete beams: Experimental study and finite element modeling with the constitutive Serial-Parallel rule of mixtures

The performance of existing prestressed concrete (PC) beams and their time-dependent behavior have been concerns for bridge maintenance services. In this paper, laboratory tests of three PC void slab beams taken away from an obsolete bridge were conducted and an alternative more efficient finite element (FE) method was developed. In preparing the three beam specimens, two retained their original reinforced concrete (RC) overlay and one chiseled off its RC overlay. Through the four-point loading tests, the load response plots of the beams from elastic to plastic failure were carefully documented, including the strains along the mid-span section, the strains of longitudinal rebars and strands, and the mid-span deflection. The test results showed that no interface slip was observed between the RC overlay and the top of void slab during the whole loading process, and the yield load of the test beams with the overlay was approximately 45 % higher than that without the overlay. Regarding the proposed nonlinear numerical formulation, the modelling process avoided the treatment of complex reinforcement and prestressing tendon layouts. The prestressed concrete was simulated as a composite material whose behavior is depicted by a constitutive serial-parallel rule of mixtures (SP-RoM). The generalized Maxwell model and generalized Kelvin model were applied to calculate the time-dependent losses of prestress. All the developments have been implemented within the open-source FE code Kratos-Multiphysics environment and are fully available. Compared with the test outcomes, it shows that the numerical results are in good agreement with the solutions in terms of stiffness, load-deflection curves, and damage evolution. The differences between the experimental and numerical values of ultimate load for the specimens with and without RC overlay were all within 10 %. Furthermore, the proposed nonlinear models can also predict the time-dependent prestress losses of existing PC beams.

Deformation mode and energy absorption of self-assembly CFRP composites cellular structure by 3D printing

Compared with traditional cellular structures, self-assembly structures exhibit significantly higher assembly flexibility, allowing for more scientific and rational protection design in the realm of structural protection. Moreover, self-assembly structure had the potential to mitigate the rapid decrease of load bearing capacity often observed in integral molding due to plastic hinge failure between adjacent cells. Therefore, self-assembly CFRP composites cellular structure was proposed, Quasi-static compression test and finite element simulation were carried out to analyze the deformation modes and energy absorption characteristics. Hexagon (H) structure formed a shear failure band, and re-entrant (R) structure was fully densified with large deflection. The deformation of inclined struts of HR and RH structures were well compatible. The total absorption energy of R structure was max, and H structure was min. The specific energy absorption and mean compression force of two-layer structures were higher, but the increasing number of layers could reduce the peak compression force, RH and R structures showed excellent energy absorption ability.

Constraining Earth’s nonlinear mantle viscosity using plate-boundary resolving global inversions

Variable viscosity in Earth's mantle exerts a fundamental control on mantle convection and plate tectonics, yet rigorously constraining the underlying parameters has remained a challenge. Inverse methods have not been sufficiently robust to handle the severe viscosity gradients and nonlinearities (arising from dislocation creep and plastic failure) while simultaneously resolving the megathrust and bending slabs globally. Using global plate motions as constraints, we overcome these challenges by combining a scalable nonlinear Stokes solver that resolves the key tectonic features with an adjoint-based Bayesian approach. Assuming plate cooling, variations in the thickness of continental lithosphere, slabs, and broad scale lower mantle structure as well as a constant grain size through the bulk of the upper mantle, a good fit to global plate motions is found with a nonlinear upper mantle stress exponent of 2.43 [Formula: see text] 0.25 (mean [Formula: see text] SD). A relatively low yield stress of 151 [Formula: see text] 19 MPa is required for slabs to bend during subduction and transmit a slab pull that generates asymmetrical subduction. The recovered long-term strength of megathrusts (plate interfaces) varies between different subduction zones, with South America having a larger strength and Vanuatu and Central America having lower values with important implications for the stresses driving megathrust earthquakes.

Seismic Stability Study of Bedding Slope Based on a Pseudo-Dynamic Method and Its Numerical Validation

Earthquakes are one of the main causes of bedding slope instability, and scientifically and quantitively evaluating seismic stability is of great significance for preventing landslide disasters. This study aims to assess the bedding slope stability under seismic loading and the influences of various parameters on stability using a pseudo-dynamic method. Based on the limit equilibrium theory, a general solution for the dynamic safety factor of bedding slope is proposed. The effects of parameters such as slope height, slope angle, cohesion, internal friction angle, vibration time, shear wave velocity, seismic acceleration coefficient, and amplification factor on stability are discussed in detail. To evaluate the validity of the pseudo-dynamic solution, the safety factors are compared with those given by early cases, and the results show that the safety factors calculated by the present formulation coincide better with those of previous methods. Moreover, a two-dimensional numerical solution of bedding slope based on Mohr–Coulomb’s elastic–plastic failure criterion is also performed by using the finite element procedure, and the minimum safety factor is essentially consistent with the result of the pseudo-dynamic method. It is proved that the pseudo-dynamic method is effective for bedding slope stability analyses during earthquakes, and it can overcome the limitations of the pseudo-static method.

Investigation on elastic–plastic deformation and mechanical failure of varied-moisture expansive soil subjected to dry–wet cycles

Investigation on elastic–plastic deformation and mechanical failure of varied-moisture expansive soil subjected to dry–wet cycles

Comprehensive crashworthiness simulation analysis of a large aircraft fuselage barrel section in various crash scenarios

To utilize computational techniques in investigate and evaluate the crashworthiness of typical fuselage section of a large transport aircraft in various crash scenarios, the finite element model of fuselage section was modeled and validated based on the vertical drop test of fuselage section at 6.02 m/s. The crash simulation analysis in various crash scenarios (such as concrete ground, soft soil grounds and water) were further conducted based on the validated model of fuselage section, and the crash response characteristics (deformation and failure mode, acceleration response and occupant injury risk, energy-absorbing characteristics) were analyzed and compared. The results show that the finite element model can accurately simulate the unrolling failure mode (three plastic hinges failure mode) of fuselage section and the failure of the connections of cargo floor crossbeams and fuselage frames, and it is in good agreement with the test results in terms of impact velocity and acceleration response. In the case of various soft soil grounds impact scenarios, the partial impact energy is absorbed by the soft soil ground, resulting in slightly different failure modes of fuselage section and a reduction in the peak acceleration. The water-entry impact failure mode of fuselage section is consistent with the rigid ground impact failure mode, the overall deformation degree of fuselage section decreases, but the degree of bending and upturning of fuselage frames increases with the increasing of the water-entry impact velocities The safety of occupants can be effectively protected in the soft soil ground and water-entry impact scenarios. The unrolling failure mode of fuselage section can be changed to the flattening failure mode (multiple plastic hinges failure mode) through the reasonable design to avoid the rupture of cargo floor crossbeams, and the more crash energy can be absorbed due to the production of more plastic hinges for the flattening failure mode, and the crashworthiness of fuselage section can be significantly improved.

Suppression of eEF2 phosphorylation alleviates synaptic failure and cognitive deficits in mouse models of Down syndrome.

Cognitive impairment is a core feature of Down syndrome (DS), and the underlying neurobiological mechanisms remain unclear. Translation dysregulation is linked to multiple neurological disorders characterized by cognitive impairments. Phosphorylation of the translational factor eukaryotic elongation factor 2 (eEF2) by its kinase eEF2K results in inhibition of general protein synthesis. We used genetic and pharmacological methods to suppress eEF2K in two lines of DS mouse models. We further applied multiple approaches to evaluate the effects of eEF2K inhibition on DS pathophysiology. We found that eEF2K signaling was overactive in the brain of patients with DS and DS mouse models. Inhibition of eEF2 phosphorylation through suppression of eEF2K in DS model mice improved multiple aspects of DS-associated pathophysiology including de novo protein synthesis deficiency, synaptic morphological defects, long-term synaptic plasticity failure, and cognitive impairments. Our data suggested that eEF2K signaling dysregulation mediates DS-associated synaptic and cognitive impairments. Phosphorylation of the translational factor eukaryotic elongation factor 2 (eEF2) is increased in the Down syndrome (DS) brain. Suppression of the eEF2 kinase (eEF2K) alleviates cognitive deficits in DS models. Suppression of eEF2K improves synaptic dysregulation in DS models. Cognitive and synaptic impairments in DS models are rescued by eEF2K inhibitors.

Shear response and deformation mechanism of boron nitride nanosheets reinforced aluminum matrix composites

Atomistic simulations are performed to study the shear response and deformation mechanism of boron nitride nanosheet (BNNS) reinforced aluminum (Al) matrix composites. In this work, stacked BNNS/Al composites and dispersed BNNS/Al composites with various BNNS layers are constructed, respectively. Our computations show that the wrinkle deformation of BNNS under shear loading does not lead to the loss of load-bearing capacity. However, the yield of the Al matrix causes it to lose load-bearing capacity. The occurrence of wrinkles in BNNS aggravates the plastic failure of the Al matrix. High BNNS volume fraction increases the shear modulus and flow stress of stacked BNNS/Al composites but decreases the shear strength. Compared with stacked BNNS/Al composites, the mechanical properties of dispersed BNNS/Al composites are remarkably improved with the increase of BNNS interface in both elastic and plastic stages. In addition, the BNNS interface is able to obstruct the propagation of dislocations and stacking faults in the Al matrix. These findings may deepen our understanding of the mechanical properties and deformation mechanisms of BNNS/Al composites.