Secondary Deformation Research Articles

La forme de la cavité glénoïdale de la scapula humaine: variabilité et hypothèse fonctionnelle

The glenoid cavity of the scapula can be sorted according to its shape in lateral view: pear-shaped cavities are more frequent than egg-shaped ones, elliptic shapes being the rarest. The morphology of the glenoid cavities is usually the same on both sides of a given individual, but when asymmetrical, pear-shaped cavities are more often present on the right, the other shapes being more frequent on the left. Elliptic and egg-shaped cavities are more common in men than in women. Elliptic glenoid cavities and the associated humeral heads are usually of big size, suggesting that they could be well adapted to sustain significant loads. No other functional particularity stood out from the analysis of the shape of the glenoid fossa. By contrast, egg-shaped and mainly elliptic types much more frequently show a remodelled border. This suggests that those shapes could be the result of a secondary deformation of the pear-shaped type under the action of loads applied on the scapulohumeral joint. Either their intensity or their direction would determine the shape acquired by the glenoid cavity at the time of death.

Influence of Evolution in Anisotropy During Strain Path Change on Failure Limits of Sheet Metals

Effects of evolution in anisotropy during plastic deformation under strain path changes on the formability and failure were investigated in the present study. The evolution in anisotropic property of the extra deep drawing steel was considered by implementing the non-quadratic anisotropic yield function Yld2000-2d as a function of effective plastic strain, and the corresponding forming behaviour in two-step forming processes was analysed. For the strain path effect, pre-strain was applied under biaxial mode using Marciniak in-plane stretch forming set-up, followed by the secondary deformation using the out-of-plane stretch forming tool. For failure prediction of the proposed two-step forming, different failure limit approaches were investigated. First, a strain based forming limit diagram (FLD), proposed as the Marciniak–Kuczynski model was modified to include the evolution in anisotropic yield function. The dynamic shift in FLD was also determined by taking strain path change into consideration. In addition, the influence of evolution of yield function on the strain path independent failure limit criteria was also assessed in terms of stress based forming limit diagram. Finally, the prediction accuracy of the failure limit criteria was compared among different models in terms of failure location and limiting dome height (LDH). It was observed that the incorporation of evolution in anisotropic yield surface improved the prediction of formability in terms of the LDH and strain distribution for the investigated material.

The effect of Y and Nd additions on the microstructure and creep behavior of AZ80

The effect of yttrium (0.2Y wt.%) and yttrium + neodyminum (0.1Y+0.1Nd wt.%) additions on the long-term (>1200 h) tensile creep and microstructural evolution of AZ80 was investigated at temperatures ranging between 100 °C and 150 °C and stresses ranging between 50 MPa and 100 MPa. The alloying resulted in both the formation of Y- and/or Nd containing particles, and lower tensile strengths and elongation-to-failure. The minimum creep rate (ε˙min) increased with increasing applied creep temperature and stress. Y addition resulted in greater creep-resistance compared with that for (Y + Nd) additions. The ε˙min of AZ80 + 0.2Y was approximately half that of AZ80 at 50 MPa at 150 °C. The apparent creep activation energy for each alloy ranged between 73 and 93 kJ/mol, and pipe-diffusion-assisted dislocation creep was suggested to be the dominant secondary stage creep deformation mechanism. Discontinuous precipitation (DP) occurred during the creep exposure but was impeded by precipitate-containing twins. The DP was less concentrated in the Y and (Y + Nd) containing alloys, which exhibited lower Vickers hardness values than AZ80. Grain boundary and twin boundary cavitation/cracking were prevalent during creep. Minor Y or (Y + Nd) addition, resulted in less oxidation and extended the intermediate-temperature creep life.

PVD AlTiN coating effects on tool-chip heat partition coefficient and cutting temperature rise in orthogonal cutting Inconel 718

Significant cutting temperature rise is induced in dry machining Inconel 718 with high cutting speed due to its low thermal conductivity and high hot hardness. PVD AlTiN coating can avoid direct contact between tool substrate and moving chip, which will affect tool-chip interface heat partition and temperature rise. However, few studies were relevant with the effect of AlTiN coating on tool-chip interface heat partition and temperature rise in dry cutting Inconel 718. In this study, the tool-chip interface temperature rises due to heat generations in primary and secondary deformation zones (PDZ and SDZ) are predicted with various heat partition coefficients, respectively. The cutting temperatures measured by two-color thermometer are utilized to determine the heat partition coefficient, and to verify the proposed interface temperature predictive model for dry orthogonal cutting Inconel 718 at cutting speed 40, 80 and 120 m/min with uncoated and PVD AlTiN coated tools. It is found that AlTiN coating decreases crater wear, and tool-chip contact length compared with that using uncoated tool. AlTiN coating decreases the maximum tool-chip interface temperature 39.00 °C and 5.47% compared with that using uncoated tool at 120 m/min. Heat partition model RG-W and RR was suitable for temperature prediction with least summary relative errors in cutting Inconel 718 with uncoated and AlTiN coated tools. The results illustrate that the PVD AlTiN coated tool could be beneficial in high-speed dry cutting Inconel 718 due to its less tool-chip interface temperature rises and tool crater wear.

Determination of Constitutive Material Model Constants for Ti6Al4V Alloy at Near Orthogonal Machining Conditions

Abstract The accuracy of numerical modeling of a machining process largely depends on material model constants. The Johnson-Cook (J-C) material model constants, i.e., A, B, C, n, and m, describe deformation behavior of material under thermomechanical loading. This paper considers an equivalent strain hardening exponent neq in place of ‘n’ in the J-C constitutive law for accurate prediction of material model constants at near orthogonal machining conditions. The effect of strain on the secondary deformation zone, i.e., the tool-chip interface, is also considered for accurate prediction of material parameters. In the present work, a machining approach based on response surface methodology and particle swarm optimization technique are used to identify J-C material model constants for the Ti6Al4V alloy. The cutting force, feed force, and chip thickness obtained from orthogonal experiments are used to evaluate the physical quantities of Oxley’s extension theory at different rake angles. It is noted that J-C constants determined from the present approach at a 7° rake angle are more accurate in predicting flow stress than J-C constants determined from other methods. J-C constants identified from a machining approach show less deviation from the measured equivalent flow stresses obtained at similar machining conditions.

Microstructure-based three-dimensional characterization of chip formation and surface generation in the machining of particulate-reinforced metal matrix composites

Particulate-reinforced metal matrix composites (PRMMCs) are difficult to machine due to the inclusion of hard, brittle reinforcing particles. Existing experimental investigations rarely reveal the complex material removal mechanisms (MRMs) involved in the machining of PRMMCs. This paper develops a three-dimensional (3D) microstructure-based model for investigating the MRM and surface integrity of machined PRMMCs. To accurately mimic the actual microstructure of a PRMMC, polyhedrons were randomly distributed inside the matrix to represent irregular SiC particles. Particle fracture and matrix deformation and failure were taken into account. For the model’s capability comparison, a two-dimensional (2D) analysis was also conducted. Relevant cutting experiments showed that the established 3D model accurately predicted the material removal, chip morphology, machined surface finish, and cutting forces. It was found that the matrix-particle-tool interactions led to particle fractures, mainly in the primary shear and secondary deformation zones along the cutting path and beneath the machined surface. Particle fracture and dilodegment greatly influences the quality of a machined surface. It was also found that although a 2D model can reflect certain material removal features, its ability to predict microstructural variation is limited.

Influence of Structure and Liquid Limit on the Secondary Compressibility of Soft Soils

The macroscopic mechanical properties of natural sedimentary soft soils, which are usually linked to their microstructure, are different from those of remolded soils. The interaction between soil structure and mechanical behavior is a manifestation of structural mechanics effects. It is essential to understand the effects of secondary compressibility to predict long-term foundation deformations. The effects of soil composition on secondary compression deformation are little studied, and the soil structure is rarely involved in the compression process. The sedimentary environment creates the initial composition and structure of soft soil, and it also basically determines its grain size and mineral composition, while different depths give soft soil different overburden pressures, and the soil composition and depth directly affect its yield stress during compression. So, natural sedimentary soft soils sampled at different depths and from different sedimentary environments (such as marine-neritic facies, sea shore facies and limnetic facies) were selected to study the influence of structure on the secondary compression coefficient Cα during pressure change and the relationship between soil composition and Cα. One-dimensional compression and consolidation creep tests were carried out on undisturbed and remolded samples. The undisturbed samples were obtained by the thin-wall samplers in rotary wash borings, and the quality of the samples met the test standard. Based on the concept of the void index Iv and the intrinsic compression line (ICL) proposed by Burland, the role of structure in the compression process was studied, and the influence of soil composition and structure on secondary compression characteristics was summarized. The Cα/Cc values are 0.031, 0.034, 0.030, and 0.036 for Shanghai, Tianjin, Suzhou, and Ningbo soft soils, respectively, within the range of inorganic clays and silts (0.04 ± 0.01) given by Mesri. According to the compression index Cc obtained by compression test, Cα/Cc can be used to estimate Cα. The yield stress of normal consolidated soil is near pre-consolidation pressure, while that of structural soft soil is greater than its pre-consolidation pressure. Natural sedimentary soft soils show over-consolidation characteristics due to the action of the structure; the soil structure resists the external load and hinders secondary compression. When the soil structure is almost destroyed, the pressure reaches the structure full yield stress P′. The tests of structural soft soils show that Cα changes with pressure before the structure completely yields, first increasing and reaching peak Cαmax near P′; the value of P′ is approximately 1.6–3.0 σ’k, where σ’k refers to the structure yield stress of soil obtained by the Casagrande method. After the structure disappeared, Cα gradually decreased and then stabilized, which is considered to be independent of the load. The Cαmax is positively correlated with the liquid limit, indicating that the peak value that can be reached by the Cα is related to the maximum content of bound water in soft soil, thus the soil composition has a significant influence on secondary compressibility, which contributes to the prediction of long-term foundation deformation.

Microstructure evolution of ultra-high-strength twinning-induced plasticity (TWIP) steel under dynamic loading

To prepare ultra-high-yield strength twinning-induced plasticity (TWIP) steel and reveal its work hardening mechanism at different strain rates from the microcosmic range, the microstructure evolution mechanism of Fe–20Mn–0.6C TWIP steel was investigated at strain rates of 10−4–103 s−1 using a high-speed tensile testing machine and a transmission electron microscope. The results show that the strain rate and deformation had a significant effect on the twin morphology of TWIP steels. At a strain rate of 102 s−1, secondary deformation twins were developed, which intersected with the initial deformation twins and increased the resistance of dislocation movement, as well as the plasticity. TWIP steel at a strain rate of 102 s−1 had a higher twin formation speed than that at 100 s−1. At the same amount of deformation, the twin boundary fraction was higher and increased linearly at a strain rate of 102 s−1, while the rule of twin growth at 100 s−1 was conformed to S-curve change of DoseResp model.

ON IMPROVING TREATMENT OF SUPRACONDYLAR AND CONDYLAR HUMERAL FRACTURES IN CHILDREN

The article presents the analyses of the treatment outcomes of 155 children with supracondylar (45 cases, 29%) and condylar (110 cases, 71%) humeral fractures. The age of patients ranged from 1 to 15 years; boys 107 (69%) got traumas twice as much as girls 48 (31%); the traumas of left upper extremities were more commonly registered and made up 100 cases (64,5%). All patients were examined clinically and radiologically. Domestic injuries resulted in supracondylar and condylar femoral fractures were the most commonly registered in 8-10 year old children. Most patients (63.2%) demonstrated good treatment outcomes, 42 (27.1%) patients demonstrated satisfactory outcomes, and in 15 cases (9.7%) the outcomes were unsatisfactory. Analysis of the treatment outcomes showed that stable fixation ensured good functional results and did not cause secondary joint deformation. Long-term results were studied in 136 operated patients, 94 cases (60.6 ± 3.92%) were defined as excellent, 31 cases (20.0 ± 3.21%) were found as satisfactory, 11 (7.1 ± 2, 06%) cases were unsatisfactory due to the damage to the growth zone. Following the conservative treatment of 19 patients, the articulation in the joint was restored in 7.1%; in 4 (2.6 ± 1.27%) patients the results were defined as good, in 11 (7.1 ± 2.06%) as satisfactory, and in 4 (2.6 ± 2.7%) as unsatisfactory. The decreased oedema and muscle retraction during the development of secondary displacement of fragments, closed one-step reposition and osteosynthesis with Kirchner needles was performed in 2.6% of patients. Thus, the proposed working scheme for the treatment of supracondylar and condylar femoral fractures enables to determine differentiated treatment tactics in the children depending on their age and the type of the fracture. Stable fixation ensures achieving of good functional treatment outcomes and prevents the development of the secondary joint deformation.

Three-dimensional temperature prediction in cylindrical turning with large-chamfer insert based on a modified slip-line field approach

Chamfered inserts have found broader applications in metal cutting process especially in high-performance machining of hard-to-cut materials for their excellent edge resistance and cutting toughness. However, excessive heat generation and resulting high cutting temperature eventually cause severe tool wear and poor surface integrity, which simultaneously limits the optimal selection of machining parameters. In the present study, an analytical thermal–mechanical model is proposed for the prediction of the three-dimensional (3-D) temperature field in cylindrical turning with chamfered round insert based on a modified slip-line field approach. First, an innovative discretization method is introduced in a general 3-D coordinate system to provide a comprehensive demonstration of the irregular cutting geometry and heat generation zones. Then, a plasticity-theory-based slip-line field model is developed and employed to determine the intensities and geometries of every elementary heat sources in Primary Deformation Zones (PDZ), Secondary Deformation Zones (SDZ) and Dead Metal Zones (DMZ). At last, a 3-D analytical model is suggested to calculate the temperature increases caused by the entire heat sources and associated images. The maximum cutting temperature region predicted is found existing upon the chip-tool contact area rather than the tool edge. Moreover, the rationalities of cutting parameters employed are analyzed along with theoretical material removal rates and ensuing maximum cutting temperatures. The results indicate that the cutting conditions with large depth of cut and high cutting speed are more desirable than those with high feed rates. The proposed models are respectively verified through a series of 3-D Finite Element (FE) simulations and dry cutting experiments of Inconel 718 with chamfered round insert. Satisfactory agreement has been reached between the predictions and simulations as well as the measurements, which confirms the correctness and effectiveness of the presented analytical model.

Finite beam element with exact shape functions for torsional analysis in thin-walled single- or multi-cell box girders

In this paper, a new formulation of beam-type finite element for the non-uniform torsion of simple or continuous thin-walled single- or multi-cell box girder with open and closed cross-sections is developed, considering both torsional warping and shear deformation effects (primary shear deformation due to Saint-Venant torsion and secondary shear deformation due to restrained torsion). The warping displacement of the cross-section is defined as the product of warping function representing the warping moment along the girder axis and a series of segmental shape functions describing the warping shape of each wall of the cross-section. Two different warping functions haven been defined and incorporated in Model A and Model B. The girder is subjected to arbitrary distributed or concentrated twisting moment and restrained by the general torsional-bending boundary conditions. The governing differential equations pertaining to torsion and torsional warping are obtained through the principle of minimum potential energy and the proposed finite beam element is refined by selecting closed-form homogeneous solutions of the differential equations as interpolation functions. Numerical examples are presented regarding rectangular hollow section (RHS) girders and single- or multi-cell box girders with open and closed cross-sections and the results obtained are compared with those provided by pioneering work or examined by using commercial finite-element models to validate the proposed beam-type element and to demonstrate the wide range of applicability and the convenience of using it.

Test study on secondary consolidation behavior of soft soil under different loading paths

Based on a series of one-dimensional consolidation tests for undisturbed samples in Guangzhou Nansha, the relationship between secondary consolidation properties and the stress history, load ratios and overload pre-pressure had been researched. The results show that the division of primary and secondary consolidation of soft soil is not only associated with the consolidation pressure, but also with loading ration, soil compression process and soil permeability decreased, etc factors. The main factors to affect the secondary consolidation coefficient are the loading ratio, pre-consolidation pressure, load duration, pre-consolidation pressure pc etc. Cα presents different regularities. For example, the larger the ratio is, the greater the influence of the coefficient of secondary consolidation is; secondary consolidation coefficient has a peak value when consolidation pressure equal to the pre-consolidation pressure;the longer duration of the front load, the smaller secondary consolidation coefficient of the later load. After preloading, the secondary consolidation ratio Cα and compression index Cc is a constant: Cα/Cc≈0.03. The test results indicate that preloading processing is a good way to reduce post-construction settlement: the secondary consolidation coefficient is small when the soil is over-consolidated state, and it can greatly reduce the amount of secondary consolidation deformation.

Enhanced wear performance of laser machined tools in dry turning of hardened steels

Polycrystalline boron nitride cutting tools are currently used for precision machining of automotive components made of hardened steel due to their high wear resistance and long durability, however adhesion of workpiece to the cutting tool can reduce cutting tool lifetime. Laser surface engineering of polycrystalline boron nitride single point cutting tools using a nanosecond fibre laser is proposed to improve their wear properties and extend tool life in turning of continuous hardened steel components. The effect of different designs on the wear properties was investigated in turning tests under dry conditions and compared to benchmark cutting tools made of the same material. Condition monitoring of machining forces revealed a 20% reduction of cutting force and 30% reduction of feed force for tools with crosshatch design and grooves perpendicular to chip flow direction, when benchmarked to commercial cutting tools. The number of grooves in contact with the forming chip contributed to the creation of three distinguished interfacial secondary deformation areas. Texturing the chamfer proved to alter the dynamic of chip formation in the secondary deformation zone, while engineering the formation of laser-induced solid lubricant h-BN improved the heat dissipation rate in the secondary and tertiary deformation areas.To the best of authors’ knowledge, this paper reports for the first time the possibility of simultaneously engineer geometry and chemistry of PcBN cutting tools so to enhance their service life by up to 20%.

Deformation and Fault Propagation at the Lateral Termination of a Subduction Zone: The Alfeo Fault System in the Calabrian Arc, Southern Italy

The Calabrian Arc subduction, southern Italy, is a critical structural element in the geodynamic evolution of the central Mediterranean basin. It is a narrow, northwest-dipping slab bordered to the southwest by the Alfeo Fault System (AFS) and to the northeast by a gradual transition to a collision. We used a dense set of two-dimensional high-penetration (up to 12 s) multichannel seismic reflection profiles to build a three-dimensional model that spans the AFS for over 180 km of its length. We find that the AFS is made up of four deep-seated major blind segments that cut through the lower plate, offset the subduction interface, and only partially propagate upward across the accretionary wedge in the upper plate. These faults evolve with a scissor-like mechanism (mode III of rupture propagation). The shallow part of the accretionary wedge is affected by secondary deformation features well aligned with the AFS at depth but also mechanically decoupled from it. Despite the decoupling, the syn-tectonic Pliocene-Holocene deposits that fill in the accommodation space generated by the AFS activity at depth, constrain the age of inception of the AFS and allows us to estimate its throw and propagation rates. The maximum throw value is 6,000 m in the NW sector and decreases to the SE. Considering the age of faulting, the fault throw rate decreases accordingly from 2.31 mm/yr to 1 mm/yr. The propagation rate decreases from 62 mm/yr to 15 mm/yr during the Pliocene-Pleistocene, suggesting that also the Calabrian subduction process should have slowed down accordingly. The detailed spatial and temporal reconstruction of this type of faults can reveal necessary information about the evolution of subduction systems.

Shear behaviors and failure mechanisms of 2D C/SiC pins prepared by chemical vapor infiltration

Connecting and fastening large-scale all-C/SiC airfoils to the fuselage of hypersonic vehicle requires C/SiC fasteners of high-performances under the re-entry environment. In this paper, 2D C/SiC pins prepared by chemical vapor infiltration (CVI) were sheared off to demonstrate their strength sensitivity to the nonuniform microstructures, such as porosity and ply orientation. Results showed that their average shear strengths increase linearly from 85.8 to 134.8 MPa as their average total porosity decreases from 23.2% to 14.5%. The shear strengths of 2D C/SiC pins are almost the same as the in-plane shear strengths of 2D C/SiC composites, under the condition that both have identical total porosity. In contrast, the variances of the pin shear strength are much higher than the in-plane shear strength, which is mainly ascribe to the effects of the loading angle between the shear plane and the ply orientation. The porosity of the 2D C/SiC pin is the main microstructural factor influencing the pin shear strength. Matrix shear cracking, debonding between matrix and fibers, crack deflection along fibers and interlayer sliding are the main shear failure mechanisms. Due to the secondary bending deformation, the interlayer sliding and the corresponding fiber pull-out mechanisms dominate the final ductile fracture behavior.

Effect of Warm Rolling and Annealing on Microstructure, Texture, and Mechanical Properties of a 2205 Duplex Stainless Steel

The effect of warm rolling and annealing processes on the microstructure, microtexture, and mechanical properties of a 2205 duplex stainless steel is investigated in this work. To evaluate the microstructure, scanning (SEM) and transmission electron microscopy (TEM) and electron backscatter diffraction are used as the main techniques. The mechanical properties are assessed through tensile tests. A transition from a bamboo type into a pearl structure is observed as the thickness reduction increases. Furthermore, the ferrite phase presents a weakening of the α‐fiber (<011>//rolling direction, RD) and a development of γ‐fiber (<111>//normal direction, ND), whereas the austenite has a reduction in the intensity of the {110}<112> brass component and a strengthening of the {110}<001> Goss and {112}<111> copper components. Multistage work hardening behavior is observed by Jaoul–Crussard analysis, which indicates the presence of secondary deformation mechanisms during the plastic deformation of the steel. Post‐deformation SEM and TEM results reveal the formation of α′ and ε‐martensite at deformed regions. The orientation relationship that develops between γ‐ and ε‐martensite is Shoji–Nishiyama (S–N) <110>γ//<2110>ε.

Optimization of a Fuze MEMS Setback Arming Device Based on the EDM Process

This paper introduces the working principle of a MEMS safety and arming (S&A) device and measures and tests a setback arming device. To solve the problem of large fabrication errors in the UV-LIGA process, a MEMS S&A fuze device fabricated by low-speed wire electrical discharge machining (EDM) is proposed. Microsprings are susceptible to flexural deformation and secondary deformation in the EDM process, which is solved by setting the auxiliary support beam, using multiple cuts and destress annealing. The linewidth, thickness and elastic coefficient of the microspring fabricated using the EDM process are closer to the designed values than those fabricated using the UV-LIGA process under the same conditions. When comparing the MEMS S&A devices fabricated by the two processes, it is found that the EDM process has a the higher machining accuracy. In view of the plastic deformation of the upper end of the microspring, the structure of the microspring is optimized to incorporate a gradient linewidth, and the optimized setback arming device is tested. The results show that the device can ensure service process safety and launch reliability. The maximum overload that can be withstood in service processing is 17000 g, and the minimum overload for insurance release during launch is 1500 g.

Surface and New Building Deformation Analysis of Deep Well Strip Mining

Aiming at the problem of surface movement and long‐term stability of a work plane of deep well strip mining in Shandong Province, an observation station is set up on the surface of strip mining, and the surface deformation value during strip mining is measured with advanced measuring instruments; on the stable surface of the old mining area, the surface deformation monitoring work is also carried out for new buildings. In addition, the FLAC3D simulation method is used to determine the subsidence factor of different mining depth, mining width, mining length, and mining thickness, and the mathematical model between the subsidence factor and mining depth, mining width, mining length, and mining thickness is established. After the surface of the old goaf is basically stable after strip mining, the high‐rise buildings are built. By changing the size of the new buildings and the amount of the load imposed on the surface, the surface deformation is simulated and calculated, and the relationship between the different load positions, load sizes, loading building sizes, and the surface activated deformation is obtained. The measured value of the surface deformation confirms that the load of the new buildings can induce the activation of the old goaf and make the surface generate secondary deformation, but the activated deformation makes the new building within the range of 1, so the new building is safe.

Mechanism of Secondary Deformation of Extruded AZ31 Magnesium Alloy by Viscoplastic Self‐Consistent Model

The viscoplastic self‐consistent (VPSC) model is used to establish a combination of different deformation mechanisms. By using this model, axial tension and compression tests of extruded AZ31 magnesium alloy at room temperature are simulated. The influence of secondary deformation mechanism (prismatic <a> slip, pyramidal <c + a> slip, and compression twin) on mechanical response and texture evolution is expounded. Increased activity of the prismatic <a> slip is conducive for the improvement of flow stress in mechanical response during axial tension and for the splitting of pole densities in the {0002} pole figure during axial compression. However, increased activity of the pyramidal <c + a> slip causes the basal texture to transfer to the extrusion direction in the {0002} pole figure during axial compression. The compression twinning has a negligible influence on the plastic deformation and mechanical response of AZ31 magnesium alloy during axial tension and compression. However, the compression twinning should be included in VPSC modeling to predict the texture evolution accurately.

Rupture and Migration Law of Disturbed Overburden during Slicing Mining of Steeply Dipping Thick Coal Seam

Steeply inclined and thick coal seams in Huainan Panbei Coal Mine in Anhui Province, China, were analyzed by physical analog modeling, acoustic emission (AE), and distributed fiber sensing (DBS). The secondary deformation breakage law, sound, and light response characteristics in the rock mass deformation process induced by lower slice mining of steeply inclined coal seams were determined. The results show that the mutation of the hinged rock beam structure in the lower region and the cantilever beam structure in the upper region of the lower slice disturbed overburden is the main cause of the rupture of the workface roof. Based on the AE energy and distributed fiber strain response characteristics, the six stages of disturbed overburden instability in the lower slice and cyclic patterns of steeply inclined coal seams were revealed. The key prevention and control areas of the workface were found to be related to the disturbed high‐level immediate roof rupture during the lower slice mining process, rupture of the disturbed main roof, and sliding of disturbed overburden. The three‐stage AE positioning morphological characteristics and DBS response stepped jump patterns were analyzed in detail. The research results are considered instrumental in the combined AE and DBS monitoring of deformation and damage of rock and soil structures.