Instability Processes Research Articles

Shear Instability and Localization in High-Speed Cold Spray Processes: Impact on Particle Fragmentation and Bonding Mechanisms

This study investigates the deformation behavior and interfacial phenomena occurring during the high-velocity impact of a copper particle into a copper substrate under various conditions using FEM. It also offers an enhanced physics-based model based on discrete dislocation dynamics simulations to depict newly observed features such as interfacial instabilities and shear localization leading to bonding and particle fragmentation. To investigate bonding mechanisms at the particle–substrate interface, additional simulations using a one-element-thickness model are conducted. These simulations focus on the deformation behavior at the interface, revealing wavy shape formation in the substrate due to disparities in strain-rate levels. Material instabilities, localized at the intersection of plane and release waves, progress hand-in-hand during the early stages of impact, suggesting shear behavior as a precursor to instabilities. The effect of shear viscosity on particle deformation and interfacial behavior is also examined, showing that increased viscosity leads to thermal material softening and enhanced deformation. Material jetting and interfacial instability are observed, particularly at higher viscosity thresholds. Additionally, the impact of drag coefficient variations on particle deformation is explored, indicating a critical role in interfacial stability and particle flattening. Finally, the occurrence of adiabatic shear instability and localization is investigated, revealing shear localization regions at the particle–substrate interface and within the particle itself responsible for particle fragmentation. To this aim, damage initiation and evolution laws are applied to identify regions of shear localization, crucial for particle–substrate bonding and mechanical interlocking. The impact velocity is shown to influence shear localization, with higher velocities resulting in increased deformation and larger localization regions.

Study on the Instability Characteristics and Precursor Signals of Rockburst in Ancient Fluvial Sedimentary Microfacies Coal Seam

The complex geological structure of coal seam is one of the important causes of rockburst. This paper investigates the instability process and precursor characteristics of ancient fluvial sedimentary microfacies coal seam. The results show that: (1) When the inclination angle is small，the sample experiences fracture and instability with relatively high peak stress. When the inclination angle is large, the sample experiences slip and instability, and high energy release under low stress condition. (2) Before the instability of the combined samples, the fracture development clearly results in a low total fault area ( A(t) ) value, relatively high and obviously low microseismic activity (S) values alternately appear, and the acoustic emission (AE) count and lack of shock (b) value will fluctuate significantly. (3) The peak strength of the combined samples decreases with increasing the inclination angle. The thickness of the coal is large, the strength of the combined samples is small, and the development and expansion of cracks and energy release are relatively weak. When the loading rate is relatively small, the peak AE count and energy release are relatively large. This research not only enriches the theory of deformation failure and dynamic disaster of complex coal seams, but also provides a reference for early warning of rockburst.

Instability mechanism of composite structure involved coal pillar and key strata induced by multi-face mining

The complex instability mechanism of large-space stope structure formed by multi-face mining poses significant risk of mining-induced seismicity. Aiming at the composite structure of a mine in Shanxi, China, a mechanical model is established and the instability mechanism are investigated. The instability condition was explored, and the instability process was simulated. The theoretical results were verified with the field monitoring, and the main influencing factors of this instability were analyzed. The results indicate that in large-space stope, the coal pillar, which serves as the primary load-bearing structure, interacts with the key strata. Individual instability could induce interactive instability, resulting in the instability of composite structure. The stiffness of coal, the width of coal pillar and the strength of key strata rock mass have significant effects on the stability of composite structure. Taking measures against these factors can prevent the instability of composite structure from the perspective of preventing the instability of coal pillar and reducing the energy release of key strata instability. The results could contribute to the further exploration of the stability of large-space stope.

Dissipation Alters Modes of Information Encoding in Small Quantum Reservoirs near Criticality.

Quantum reservoir computing (QRC) has emerged as a promising paradigm for harnessing near-term quantum devices to tackle temporal machine learning tasks. Yet, identifying the mechanisms that underlie enhanced performance remains challenging, particularly in many-body open systems where nonlinear interactions and dissipation intertwine in complex ways. Here, we investigate a minimal model of a driven-dissipative quantum reservoir described by two coupled Kerr-nonlinear oscillators, an experimentally realizable platform that features controllable coupling, intrinsic nonlinearity, and tunable photon loss. Using Partial Information Decomposition (PID), we examine how different dynamical regimes encode input drive signals in terms of redundancy (information shared by each oscillator) and synergy (information accessible only through their joint observation). Our key results show that, near a critical point marking a dynamical bifurcation, the system transitions from predominantly redundant to synergistic encoding. We further demonstrate that synergy amplifies short-term responsiveness, thereby enhancing immediate memory retention, whereas strong dissipation leads to more redundant encoding that supports long-term memory retention. These findings elucidate how the interplay of instability and dissipation shapes information processing in small quantum systems, providing a fine-grained, information-theoretic perspective for analyzing and designing QRC platforms.

Star Cluster Population of High Mass Black Hole Mergers in Gravitational Wave Data

Stellar evolution theories predict a gap in the black hole birth mass spectrum as the result of pair instability processes in the cores of massive stars. This gap, however, is not seen in the binary black hole masses inferred from gravitational wave data. One explanation is that black holes form dynamically in dense star clusters where smaller black holes merge to form more massive black holes, populating the mass gap. We show that this model predicts a distribution of the effective and precessing spin parameters, χeff and χp, within the mass gap that is insensitive to assumptions about black hole natal spins and other astrophysical parameters. We analyze the distribution of χeff as a function of primary mass for the black hole binaries in the third gravitational wave transient catalog. We infer the presence of a high mass and isotropically spinning population of black holes that is consistent with hierarchical formation in dense star clusters and a pair-instability mass gap with a lower edge at 44−4+6M⊙. We compute a Bayes factor B>104 relative to models that do not allow for a high mass population with a distinct χeff distribution. Upcoming data will enable us to tightly constrain the hierarchical formation hypothesis and refine our understanding of binary black hole formation. Published by the American Physical Society 2025

Experimental study on face stability of shield tunnel in water-rich inclined composite strata considering different inclination angles

Shield method has developed rapidly in the construction of underground or subsea tunnels. The stability of the tunnel excavation face is essential for the safe construction of tunnels, particularly in water-rich and inclined strata. The present study conducted shield model tests in water-rich inclined strata to analyze the surface settlement, ground earth pressure, areas of instability, and failure mechanism during the process of instability. The results indicate a decrease in settlement of the longitudinal monitoring points as the backward distance from the tunnel boundary line increases. Additionally, the settlement analysis of transverse monitoring sections reveals that the most significant settlement occurs directly above the tunnel. When equidistant from the tunnel excavation face, the surface settlement exhibits a significantly greater magnitude in front of it compared to behind it. The extent of influence is maximized when the inclination angle is negative, regardless of whether it pertains to the collapse in width or height on the surface. The application of DIC image analysis reveals that distinct failure mechanisms are observed for varying stratum inclination angles. The shear strain concentration becomes more pronounced with an increase in the backward distance, resulting in predominant distribution of shear bands in front of and above the tunnel. Compared to water-rich horizontal stratification or homogeneous soil layers, there are distinct variations in surface collapse magnitude, stratum disturbance range, and the instability mechanism of stratum instability in water-rich inclined strata. Therefore, when confronted with engineering projects involving inclined strata, it is imperative to consider the influence of geological factors.

Linear theory of visco-resistive tearing instability

A new linear theory of a tearing instability is shown, where the modified LSC (Loureiro, Schekochihin, and Cowley) theory [T. Shimizu, arXiv:2209.00149 (2022)] is extended to visco-resistive MHD. In contrast to the original LSC theories [Loureiro et al., Phys. Plasmas 14, 100703 (2007)], in the modified LSC theory, the upstream open boundary condition is implemented at a finite point ξc. At this point, the original LSC theories are solved for ξc=+∞. This paper first studies when the resistivity and viscosity are uniform in space. In addition, some variations in the non-uniformity are studied. It is shown that the non-uniformity can enhance the linear growth rate, and the tearing instability can occur even in an unlimitedly thin current sheet. Unexpectedly, it suggests that the forward cascade process of the plasmoid instability (PI) does not stop, i.e., the finite differential MHD simulations fail. To stop the forward cascade, viscosity is required not only in the inner region of the current sheet but also in the outer region. When the uniform viscosity is assumed, the critical condition is predicted to be 2Pm/(Sξc)=0.06, beyond which the tearing instability, i.e., the forward cascade, stops. Here, S is the Lundquist number, and Pm is the magnetic Prandtl number. According to the critical condition, the resistivity and viscosity employed in most high-S MHD simulations of PI are too small to stop the forward cascade. This critical condition may be also applicable for the trigger problem of the current sheet destabilization.

Screen Printing Catalyst Inks With Enhanced Process Stability for PEM Fuel Cell Production

ABSTRACTCurrent state‐of‐the‐art coating techniques for PEM fuel cell electrode manufacturing such as slot‐die coating use closed ink reservoirs, allowing low boiling point solvents as the dispersion matrix for solid components of the catalyst ink. Applying such low boiling point inks to printing methods that expose catalyst inks to air, like flatbed screen printing, results in an instable and nonscalable production process due to the successive evaporation of these solvents. Within this study, a total of 12 different solvents are examined for process stability and electrochemical performance when applied with flatbed screen printing. Ink characteristics, such as contact angle, rheology, and sedimentation experiments, are quantified to reveal the most suitable set of solvents, enabling the use of open‐reservoir printing methods like flatbed screen printing. Additionally, electrochemical in situ characterization of catalyst‐coated membranes showed that 1,2‐propanediol and 1‐heptanol are solvents that combine process stability with high fuel cell performance.

Early identification on failure mode of loess landslide: insight from case study and physical model experiment

IntroductionThe Loess Plateau has long been plagued by cascading loess landslides. The rapid identification of these landslides, along with the accurate determination of their failure modes, is essential for conducting precise disaster assessments in the region. Such assessments are critical for minimizing both human casualties and economic losses. However, the lack of reliable reference data for the early identification of landslide failure modes has resulted in limited detection accuracy, complicating the differentiation between various failure modes. Therefore, investigating the deformation and failure characteristics of loess landslides under different failure modes is crucial for providing a scientific foundation for early hazard detection and the accurate assessment of risk profiles.MethodsThis work examines the pre-slip deformation and post-slip damage characteristics of the rotational-sliding Huzhu Landslide and the translational-sliding Zhongzhai Landslide through a combination of field investigations, unmanned aerial vehicle surveys, and remote sensing interpretation. Physical model tests were conducted to simulate the instability and failure processes of both rotational and translational loess landslides. Meanwhile, three-dimensional models and orthophoto graphic images at various stages of the landslides were generated using Contexcapture.ResultsThe initial stages of rotational sliding landslides are marked by the formation of distinct tensile cracks at the trailing edge of the slope and minor uplift at the front. As the uplift at the front progresses and numerous extension fissures develop, the stability of the landslide reduces progressively. Upon reaching instability, the sliding velocity of the sliding mass initially accelerates before decelerating, with majority of the mass remaining on the sliding surface and retaining relatively well structural integrity. At the trailing edge of the landslide, characteristic features such as falling scarps, fractured walls, and sunken grooves can be observed, while the front displays significant bulging phenomena. In contrast, translational sliding landslides are initially characterized by minor tensile cracks at the trailing edge and pronounced deformation at the front. As these tensile cracks propagate, the landslide are prone to sudden instability under external triggering factors. Following the onset of instability, the sliding mass undergoes rapid movement, with only a small part of the mass remaining on the sliding surface.DiscussionLandslides triggered by different factors and occurring under varying water content conditions may exhibit significant differences in their pre-failure behavior and post-failure characteristics. Thus, it is imperative to conduct further research in this field to better understand these complex dynamics.

Quasi-linear Analysis of Proton-cyclotron Instability

The proton-cyclotron (PC) instability operates in various space plasma environments. In the literature, the so-called velocity moment-based quasi-linear theory is employed to investigate the physical process of PC instability that takes place after the onset of early linear exponential growth. In this method, the proton velocity distribution function (VDF) is assumed to maintain a bi-Maxwellian form for all time, which substantially simplifies the analysis, but its validity has not been rigorously examined by comparing against the actual solution of the kinetic equation. The present paper relaxes the assumption of the velocity moment-based quasi-linear theory by actually solving for the velocity space diffusion equation under the assumption of separable perpendicular and parallel VDFs, and upon comparison with the simplified velocity moment theory, it demonstrates that the simplified method is largely valid, despite the fact that the method slightly overemphasizes the relaxation of temperature anisotropy when the system is close to the marginally stable state. The overall validation is further confirmed with the results of particle-in-cell and hybrid-code simulations. The present paper thus provides a justification for making use of the velocity moment-based quasi-linear theory as an efficient first-cut theoretical tool for the PC instability.

Model test study on instability mechanism during shield under-crossing existing pipeline

This paper aims at investigating the instability mechanism that occurs during the under-crossing of an existing pipeline using model tests and numerical simulations. The strain in the pipeline, earth pressure, surface settlement, and mechanisms of stratum instability during the process of instability have been obtained. The research findings reveal three distinct growth stages in the longitudinal deformation of the existing pipeline, with the strain growth rate during the rapid growth phase being 2–3 times higher than that observed during the slow growth phase. The pipeline displays a deformation pattern with tensile stress in the upper section and compressive stress in the lower section, due to the uneven force distribution along its length. In the absence of pipelines, the distribution of surface collapse exhibits a distinct “V” shaped. As the clear distance between the existing pipeline and the tunnel (CDPT) increases, there is a transition from a “partial W” to a “positive W” type distribution. The presence of the pipeline exerts the most significant inhibiting effect on the soil directly above it. In cases where there is no pipeline or the CDPT is small, soil leakage primarily occurs in front of the excavation. As the CDPT increases, soil leakage occurs around the pipeline and the instability range of the stratum significantly expands. The stable strata above the pipeline gradually widen, and the area with a significant influence range shifts from the right side to the left side of the existing pipeline.

The Significance of Internal Variability for Numerical Experimentation and Analysis

When regional (limited-area) models of the hydrodynamics of the atmosphere and ocean are run over an extended time, variability unrelated to external “drivers” emerges: this variability is colloquially named “hydrodynamical noise” or just “noise”. This article summarises what we have learned in the past few years about the properties of such noise and its implications for numerical experimentation and analysis. The presence of this noise can be identified easily in ensembles of numerical simulations, and it turns out that the intensity of the noise is closely linked to scale-dependent “memory”. The “memory” in the atmosphere and ocean describes the persistence of atmospheric and oceanic conditions, usually quantified by an autocorrelation function. At the system level, this “memory” term, as given by Hasselmann’s stochastic climate model, plays a key role. In the case of marginal seas, the process of baroclinic instability modulated by tides and the formation of seasonal thermoclines are significant aspects. Some more general aspects are discussed, such as the applicability of the stochastic climate model to systems outside of atmospheric and oceanic dynamics, for example, biogeochemical systems, the irreversibility of tipping points, the challenges of detecting changes beyond a noise level, and the attribution of causes of change.

Adiabatic Shear Localization in Metallic Materials: Review.

In advanced engineering applications, there has been an increasing demand for the service performance of materials under high-strain-rate conditions where a key phenomenon of adiabatic shear instability is inevitably involved. The presence of adiabatic shear instability is typically associated with large shear strains, high strain rates, and elevated temperatures. Significant plastic deformation that concentrates within a adiabatic shear band (ASB) often results in catastrophic failure, and it is necessary to avoid the occurrence of such a phenomenon in most areas. However, in certain areas, such as high-speed machining and self-sharpening projectile penetration, this phenomenon can be exploited. The thermal softening effect and microstructural softening effect are widely recognized as the foundational theories for the formation of ASB. Thus, elucidating various complex deformation mechanisms under thermomechanical coupling along with changes in temperatures in the shear instability process has become a focal point of research. This review highlights these two important aspects and examines the development of relevant theories and experimental results, identifying key challenges faced in this field of study. Furthermore, advancements in modern experimental characterization and computational technologies, which lead to a deeper understanding of the adiabatic shear instability phenomenon, have also been summarized.

Deposition and etching of (101)Zn facet exposed zinc electrode induced by trace COS achieving ultra-long cycle stability in zinc batteries

Rechargeable aqueous zinc-based batteries (RZBs) often suffer from poor cycling stability due to the instability of zinc deposition and etching processes. This work achieves dendrite-free zinc deposition with a smaller nucleation radius and rapid completion of the nucleation stage by a “triple regulation strategy” with trace chitosan oligosaccharide (COS) in ZnSO4 electrolyte (2 g L−1 COS). Theoretical and experimental results indicate that COS, with hydroxyl and amino functional groups, exhibits a high affinity for the (002)Zn and (100)Zn facets. Under the influence of a small amount of COS, the selective exposure of the (101)Zn facet is facilitated. The extensively exposed (101)Zn facet is protected by COS, which inhibits the occurrence of side reactions. Moreover, the presence of trace COS-02 changes the etching mode from three-dimensional (3D) to two-dimensional (2D), ensuring a uniform distribution of Zn2+ in the electric field during the deposition process. The unique 3D deposition and 2D etching mechanism induced by the COS additive result in exceptional cycling stability, exceeding 3800 h (1 mA cm−2) and 430 h (5 mA cm−2) in zinc symmetrical cells. Additionally, COS acts as a “molecular pillar” to stabilize VS2, enabling the Zn||VS2 full cell to achieve 1000 stable cycles with 89.6% capacity retention and an average coulombic efficiency of 99.95%. This work reveals a novel multiple regulation mechanism by using trace COS in RZBs, and provides a new approach for the development of long-term stable RZBs with preferential exposure facets.

Experimental Investigation on Rock Failure Characteristics of Large-Span Goafs Using Digital Image Correlation Analysis and Acoustic Emission Monitoring

Rockmass in deep mining is highly susceptible to large-scale collapses under high stress and blast-induced disturbances, leading to casualties and economic losses. To investigate the evolution characteristics of goaf instability and the types of seismic sources that induce instability, an experiment on goaf instability was designed under uniaxial compression conditions based on actual mining operations. The entire experimental process was monitored using digital image correlation analysis and acoustic emission monitoring. By calculating the digital speckle field on the surface of the rock specimen during the experiment, the evolution characteristics of the deformation and strain fields from the beginning of loading to complete failure were analyzed. The study explored the dynamic behavior of cracks from initiation to propagation and eventually inducing large-scale collapse. The results show that the instability process of the goaf begins with the formation of tensile cracks. As stress increases, shear cracks occur in the specimen, leading to macroscopic failure. Furthermore, based on the differences in overall microfracture types measured by RA-AF characteristic parameters during specimen failure, large amplitude acoustic emission events corresponding to the formation of dominant macroscopic cracks were selected, and the focal mechanisms of these events were inverted. The results indicate that shear failure sources are significantly more prevalent than tensile failure sources in acoustic emission events leading to goaf instability. These findings can provide useful guidance for the support design and the prevention and control of rockmass instability disasters.

Study on the characteristics of acoustic-thermal precursors of destabilization damage in coal-rock combination bodies with different proportions

The instability and failure processes of coal-rock combinations are accompanied by the release of acoustic emission (AE) and infrared radiation (IR) signals. To investigate the characteristics of AE and IR signals during the failure process in coal-rock combinations with different ratios, and to analyze the effectiveness and applicability of the monitoring methods for these two signals in various specimen ratios. In this paper, the uniaxial compression tests were conducted on seven coal-rock combinations with different ratios by using the rock mechanics loading system and the cooperative monitoring platform of infrared and acoustic emission. The results show that (1) the AE counts for failure precursors in coal-rock combinations are positively correlated with the coal-rock ratio, whereas the AE peak counts are negatively correlated. Moreover, as the coal-rock ratio decreases, the slope of the cumulative AE count curve during the peak failure stage approaches 1. (2) During the elastic and yield stages, the maximum infrared radiation temperature (MIRT) curve fluctuates, and just before peak failure, the curve displays a distinctive “V” shape. This “V” shape becomes more pronounced as the coal-rock ratio decreases. (3) In the monitoring of damage precursors of coal-rock combinations, when the ratio of coal to rock is 1:3 or less, IR monitoring is better than AE monitoring. Conversely, when the ratio of coal to rock is greater than 1:3, AE monitoring is more suitable. Consequently, the combined monitoring of AE and IR signals can increase the reliability and precision of early warning signals for coal-rock assemblage damage precursors.

Model test study on the dynamic failure process of tunnel surrounding rocks in jointed rock mass under explosive load

The presence of joints can significantly reduce the integrity and stability of an engineering rock mass. Under dynamic loads, such as from blasting excavation, the key blocks divided by joints may be destabilized and prone to sliding, potentially leading to engineering geological disasters like rockbursts. To study the dynamic instability process, similar materials for the rock mass and joints were developed based on the similarity theory, and a tunnel model in the jointed rock mass was constructed. Subsequently, a detonating fuse was used to generate a dynamic load, and the dynamic instability process of the tunnel surrounding rock in the jointed rock mass under explosive load was studied using the geotechnical multifunctional testing device. The deformation characteristics and dynamic instability process of the tunnel surrounding rock were analyzed using acceleration sensors, resistance strain gages, linear variable displacement transducers and motion camera. The study shows that the acceleration at the tunnel vault is significantly greater than at the straight wall and floor under blast loads, with differences reaching an order of magnitude. Acceleration waveforms were classified into three categories based on peak characteristics, explained through the propagation of explosive stress waves. Additionally, strain and displacement at the tunnel arch were also significantly greater than in other areas, indicating more severe stress concentration and dynamic damage at the arch, necessitating reinforced support in tunnel excavation. The entire dynamic instability process of the tunnel surrounding rock was successfully recorded using a motion camera. The dynamic failure process was divided into several phases, the appearance of cracks on the joint surface, particle ejection accompanied by the dropping of jointed blocks, a significant drop of the jointed blocks, and return to calm. The dynamic failure modes include the dropping and rotation of jointed blocks, local particle ejection, and shear cracks on jointed block.

Chatter stability analysis for non-circular high-speed grinding process with dynamic force modelling

To avoid instability and resulting chatter during the non-circular grinding process, it is necessary to elucidate the potential occurrence of periodic chatter behavior when high-speed grinding loses stability and to define the stability boundary of the grinding system. Building upon an analysis of the geometric kinematic characteristics of non-circular profiled components, a dynamic grinding force model for non-circular high-speed grinding was derived by considering both the delay effect and the elastic yielding mechanism between the grinding wheel and workpiece. Then, A multi-factor coupled dynamic model of non-circular grinding was established. By employing a multi-scale approach, bifurcation analysis and classification of the instability process in the grinding system were conducted, using a typical non-circular profiled shaft component, such as a camshaft, for theoretical analysis and experimental validation. The research determined the stability boundary of the high-speed grinding process for non-circular profile components, validated the possibility of the existence of a conditionally stable chatter region in the non-circular high-speed grinding process, and identified differences in grinding chatter characteristics among different segments of the cam profile, with a greater propensity for chatter at the juncture of the cam fall and base circle.

LES investigation of a H2-fueled supersonic combustor: A two-strut injection approach

Efficient combustion schemes are increasingly vital as scramjet expansion into higher Mach numbers emerges as a leading trend. Thus, in the current work, an LES investigation on mixing improvement caused by a two-strut injector has been carried out for a Mach 2.5 model H2 fueled scramjet combustor. The research focuses on understanding the flow field, flame lift-off characteristics and combustion stabilization in the two-strut combustor. The simulation results indicate that the two-strut configuration exhibits a broader pattern of temperature fluctuation, implying a more efficient spread of combustion downstream compared to the single-strut configuration. Analysis of Fast Fourier Transform (FFT) pressure data reveals inherent instability in the combustion processes for two-strut under supersonic air inflow conditions. The findings also demonstrate the significant improvement in mixing performance achieved by the two-strut design compared to conventional struts. The primary mechanism is a two-strut's ability to create significant streamwise vorticity, which can improve the mixing of H2 fuel with supersonic air. According to the mixing and total pressure loss plots, a two-strut produces a rapid complete mixing at 0.182 m at the expense of a minute rise in total pressure loss. Finally, the entropy change plot reveals that the two-strut configuration exhibits a reduced entropy change compared to the single-strut configuration. This is mainly due to enhanced air-fuel mixing, efficient shock wave management, and enhanced flame stabilization in the two-strut setup. These factors collectively contribute to reduced irreversibilities and disorder in the flow, leading to lower entropy within the system.

Management of bone loss in anterior shoulder instability.

Bone defects are frequently observed in anterior shoulder instability. Over the last decade, knowledge of the association of bone loss with increased failure rates of soft-tissue repair has shifted the surgical management of chronic shoulder instability. On the glenoid side, there is no controversy about the critical glenoid bone loss being 20%. However, poor outcomes have been described even with a subcritical glenoid bone defect as low as 13.5%. On the humeral side, the Hill-Sachs lesion should be evaluated concomitantly with the glenoid defect as the two sides of the same bipolar lesion which interact in the instability process, as described by the glenoid track concept. We advocate adding remplissage to every Bankart repair in patients with a Hill-Sachs lesion, regardless of the glenoid bone loss. When critical or subcritical glenoid bone loss occurs in active patients (> 15%) or bipolar off-track lesions, we should consider anterior glenoid bone reconstructions. The techniques have evolved significantly over the last two decades, moving from open procedures to arthroscopic, and from screw fixation to metal-free fixation. The new arthroscopic techniques of glenoid bone reconstruction procedures allow precise positioning of the graft, identification, and treatment of concomitant injuries with low morbidity and faster recovery. Given the problems associated with bone resorption and metal hardware protrusion, the new metal-free techniques for Latarjet or free bone block procedures seem a good solution to avoid these complications, although no long-term data are yet available.