Static Stress Changes Research Articles

Evaluation of the effect of various types of tools on a weld joint during wave strain hardening

The article studies the problem of increasing the durability of weld joints using surface plastic deformation by the method of wave strain hardening (WSH). Earlier, WSH was not used for these purposes. The prospect of using WSH for increasing the durability of weld joints is associated with the possibility of increasing the microhardness and the formation of compressive residual stresses at a depth of more than 10 mm. To identify the most effective conditions for the use of various types of tools for WSH of weld joints and accelerate the search for rational modes and conditions of WSH, finite element modeling was used. As a result of the research, recommendations related to the use of various types of WSH tools, depending on the thickness of weld joints, changes in hardness and stress state of the near-weld zone after welding, were given.

The Influence of Cement Layer Thickness on the Stress State of Metal Inlay Restorations-Photoelastic Analysis.

The successful restoration of teeth requires a good connection between the inlay and natural tissue. A strong bond may improve retention and reinforce tooth structure. The purpose of this study was to evaluate the influence of cement layer thickness on contraction stress generated during photopolymerization, and to determine the changes in stress state of the cement occurring during aging in water (over 84 days). Two cements were used: resin composite cement (NX3) and self-adhesive resin cement (Maxcem Elite Chroma). A cylindrical sample made of CuZn alloy was used to imitate the inlay. The stress state was measured by photoelastic analysis. The contraction stress of the inlay restoration was calculated for cement layer thicknesses of 25 µm, 100 µm, 200 µm, and 400 µm. For both tested materials, the lowest contraction stress was observed for the thinnest layer (25 µm), and this increased with thickness. Following water immersion, a significant reduction in contraction stress was observed due to hygroscopic expansion. Applying a thin layer (approximately 25 µm) of composite and self-adhesive resin cements resulted in high levels of expansion stresses (over −6 MPa) after water aging.

The formation of intragranular stress concentration in plastic deformed Ni-base superalloy: Governing factors and process

Abstract For Ni-base superalloy, the creep property is still vital. Polycrystalline Ni-base superalloy samples with different creep strain are investigated by electron backscatter diffraction along with phase field simulation to analyze the formation of intragranular stress concentration (ISC) with respect to the governing factors and process. The results show that ISCs are more likely to form at vicinity of grain boundaries (GBs) because of the multiple-slips near GBs which are activated by the mediated stress at GBs. The frequency of ISCs near the GBs decreases first at low strain and then increases with increasing strain because of the formation and destroy of stress concentrations in grain interior. The ISCs are more likely to form at vicinity of the GBs with misorientation of 45°–55°, independent of the strain. In addition, the GBs parallel or perpendicular to the loading direction will not emit dislocations to activate multiple-slips near GBs when the strain is small because of their triaxial stress state. As the strain increases, these GBs begin to emit dislocations because of the change of stress state or the formation of ‘weak points’. The GBs perpendicular to the applied stress own the highest probability when the strain is 9.38%. Our results provide unique and critical data to support future optimization of alloy properties and the development of new alloys.

Plastic accommodation during tensile deformation of gradient structure

Gradient structure (GS) possesses a typical trans-scale grain hierarchy with varying internal plastic stability, and the mutual plastic accommodation plays a crucial role in its superior strength-ductility combination. Using the in-situ synchrotron X-ray diffraction (XRD) during tensile loading, we measured lattice strains sequentially from the nanostructured (NS) surface layer to the central coarsegrained (CG) layer to elucidate when and how plastic accommodation occurs and evolves within the GS, along with their roles in plastic deformation and strain hardening. Throughout the tensile deformation, two types of plastic incompatibility occur in the GS. One is an extended elastoplastic transition due to layer-by-layer yielding. The other is strain localization and softening in the NS layer, in contrast with the stable plastic deformation in the CG layer. Plastic accommodation thus occurs concurrently and manifests as both an inter-layer and intra-layer change of stress state throughout tensile deformation. This produces different micromechanical responses between layers. Specifically, the NS layer initially experiences strain hardening followed by an elastoplastic deformation. The hetero-deformation induced hardening, along with forest hardening, facilitates a sustainable tensile strain in the NS layer, comparable to that in the CG layer.

A Systematic Approach to Mapping Regimes of Earthquake‐Induced Static Stress Changes Acting on Magmatic Pathways

AbstractLarge earthquakes alter the crustal stress field across great distances (hundreds to thousands of kilometers) over geologically short timescales (seconds to years). These stress changes can affect magmatic systems, triggering (or suppressing) volcanic unrest and eruption, along with other deeper processes. We use simple kinematic source models in an isotropic elastic half‐space to assess earthquake‐induced static stress changes (>1 kPa) over the entire thickness of the lithosphere and consider the implications for magma ascent and storage. Modeling subduction zone earthquakes, we calculate static normal stress changes with depth on three mutually perpendicular end‐member magma pathways: vertical arc‐parallel, vertical arc‐perpendicular, and horizontal. From this, we define seven stress change regimes within the adjacent volcanic arc. Three of these regimes may strongly encourage magma ascent in dykes by inducing unclamping (decreased compressive normal stress) of vertical pathways which increases in magnitude toward the surface and clamping of horizontal pathways. Two of the regimes may encourage stalling and storage of magma in sills near the base of the crust by inducing unclamping of horizontal pathways at depth. The spatial distribution of the regimes is largely dependent on earthquake magnitude, but also varies with slip distribution and interface dip. We show how the responses of magmatic systems to earthquakes also depends on the stress change magnitude and the state of the magmatic system, with a greater impact expected for larger stress changes acting on weaker, more thermally mature systems.

О РЕЗУЛЬТАТАХ ТЕРМОУСТАЛОСТНЫХ ИСПЫТАНИЙ ЧУГУНА И ОЦЕНКЕ ЕГО ДОЛГОВЕЧНОСТИ

The article notes that at present, despite numerous studies of thermal fatigue, the thermal fatigue strength of cast irons due to stresses in parts made of this material requires additional study. Issues of thermal fatigue strength are especially relevant for such heat-stressed parts of internal combustion engines of autotractor diesel engines as the cylinder head. Of particular importance for these parts in their design and restoration is the ability to predict thermal fatigue strength, which is the main criterion that determines their durability. The article describes an approach to solving the problem of predicting the thermal fatigue strength of cast iron parts based on the data on their stress state and the results of thermal fatigue testing of samples on a specially designed and manufactured installation. The setup consists of two massive plates mounted on racks, between which a sample with a hole was rigidly installed. During the tests, the sample was heated by a special annular furnace to a temperature of 550°C for two minutes, and then cooled with running water through the central hole. A sample bounded on both sides during heating and thermal expansion accumulated residual tensile stresses as a result of relaxation processes and, upon reaching critical values and the appearance of fatigue defects in the form of cracks, ruptured. The proposed mode quite accurately repeats the operating conditions of the heat-receiving surface of the cylinder heads in the area of the intervalve jumpers when changing the operating mode at rated power and subsequent engine shutdown. As a result of the tests, the curves of the number of cycles to failure depending on the achieved stresses were obtained and their approximation was carried out. On the basis of approximating expressions and dependences of "limited durability" under low-cycle loading of parts, the thermal fatigue strength of a part made of cast iron can be predicted when its stress state changes as a result of design changes or after restoration.

Coseismic deformation and multi-fault slip model of the 2019 Mindanao earthquake sequence derived from Sentinel-1 and ALOS-2 data

From October to December 2019, a sequence of four earthquakes of Mw > 6.0 occurred in southern Mindanao, the Philippines, and revealed complex tectonics in this region. We used Advanced Land Observing Satellite (ALOS)-2 and Sentinel-1A/B Synthetic Aperture Radar (SAR) data to map the coseismic deformation and to constrain both the fault geometry and kinematics of coseismic slip distributions during the four earthquakes. Our observed coseismic deformation field shows that these four earthquakes ruptured two intersected conjugate faults with NE and NW strikes. Based on ascending and descending Interferometric SAR (InSAR) data, we constructed elastic half-space models to search for the optimal fault dip angle and inverted the slip distributions of the four earthquakes. The results show that these four earthquakes were all dominated by left- and right-lateral strike-slip motion. The two conjugate faults clearly had significant differences in terms of slip behaviour and fault kinematics. The static Coulomb stress change indicates that earlier earthquakes had a significant triggering effect on subsequent earthquakes. The static Coulomb stress change induced by the four earthquakes suggests a significant stress loading effect on NW-trending faults. The results of this study show that the potential for future earthquakes on NW-trending faults cannot be ignored; however the magnitudes of future earthquakes should be limited by complex fault geometry and segmentation.

Stress state of metal dome meridional ribs at different stages of overhang erection process

Research aim. The aim of the present research was an analysis of a metal ribbed ring-shaped dome metallic ribs stress state at different stages of a skeleton overhang erection process. The considered dome is hemispherical and is assembled bottom-up of individual elements. Due to a varying slope of meridional ribs elements at different relative elevations their stress state changes during mounting. The effect of the overhang erection process onto the stress state of the metal dome meridional ribs has been investigated. The relationship between the stress state of a meridional rib and mounting of each next dome skeleton tier has been established. Methods. A mathematical model of the metal ribbed ring-shaped dome assembled of steel H-shaped elements with rigid connections has been developed. Several extra models corresponding to different skeleton erection stages have been also generated to determine stresses in the meridional ribs at these stages. Response of each dome mathematical model under dead-weight load has been simulated. The obtained values of stresses in the meridional ribs within different models have been compared with corresponding design stresses values. Results. The dependence of the metal dome meridional rib stress state onto the stages of overhang erection process has been plotted. A degree of utilization of ribs steel strength at different erection stages has been represented by diagrams. An estimation of the dome skeleton stress state during overhang erection has been given. Imminence of assembly stresses during overhang erection and their influence onto dome structural reliability has been pointed out.

Unraveling long-term volcano flank instability at Pacaya Volcano, Guatemala, using satellite geodesy

Edifice collapse represents one of the most dangerous volcanic hazards threatening communities and infrastructure near volcanoes, having caused over 20,000 casualties in the past 400 years. Despite its prevalence across volcanic settings, flank instability has mostly been considered at ocean island volcanoes. In Guatemala, all but one volcano with elevation greater than 2000 m have undergone edifice failure. Pacaya is one of these Guatemalan volcanoes, which experienced at least one past episode of flank collapse and where recent transient flank motion has been identified. Using Interferometric Synthetic Aperture Radar (InSAR) time-series analysis, we reveal, for the first time, long-term displacement of the southwest flank of Pacaya between 2010 and 2014, including the interval 2011–2013 where the volcano remained relatively quiescent. Subsequent geodetic data inversions and static stress change analysis suggest that the observed flank motion could be accommodated by slip on a southwest-dipping detachment fault, with an observed increase in slip rate attributed to magma intrusion associated with a major eruption in 2014. This study highlights that long-term volcanic flank creep is likely more widespread than previously recognized and that magma-faulting interactions, as well as the existence of structural weaknesses within volcanic edifices, are vital considerations in the assessment of likelihood and nature of flank collapse at volcanoes worldwide.

Re-distribution of residual stress in polymer extrusion: An eccentric approach

The development of residual stresses in plastic pipes due to post-die cooling rate differences of the polymer melt was investigated using concentric and eccentric circular geometries in the shape of an annular tube. Heat transfer simulations were performed to understand the effect of non-uniform wall thickness on the temperature and residual stress profiles of melt solidified polymers. Residual stress measurements and thermal analysis of the end products and heat transfer simulation of the post die cooling process were evaluated to understand the change in stress state in the polymer products as a function of temperature. This was done through an example of extruded high-density polyethylene pipes using an industrial scale extrusion line. The outcome of this research helps better understanding of the melt solidification process and its effect on application related properties in a way that was never presented before.

Seismic Attenuation Monitoring of a Critically Stressed San Andreas Fault

AbstractWe show that seismic attenuation ( ) along the San Andreas fault (SAF) at Parkfield correlates with the occurrence of moderate‐to‐large earthquakes at local and regional distances. Earthquake‐related anomalies are likely caused by changes in permeability from dilatant static stress changes, damage by strong shaking from local sources, and pore unclogging/clogging from mobilization of colloids by dynamic strains. We find that, prior to the 2004 M6 Parkfield earthquake, prefailure conditions for some local events of moderate magnitude correspond to positive anomalies of on the Pacific side, with local and regional earthquakes producing sharp attenuation reversals. After the 2004 Parkfield earthquake, we see higher anomalies along the SAF, but low sensitivity to local and regional earthquakes, probably because the mainshock significantly altered the permeability state of the rocks adjacent to the SAF, and its sensitivity to earthquake‐induced stress perturbations.

Study on the improvement of the surface integrity and efficiency of electrical-discharge-machined TC4 titanium alloy via abrasive flow machining

To simultaneously optimize the surface quality and machining efficiency of the electrical discharge machining (EDM) processes used to produce titanium alloy quadrilateral group small hole parts, a combined “EDM + AFM” machining technology is proposed in this paper as an efficient and high-quality machining approach. In the proposed method, TC4 titanium alloy is first machined using the EDM process with graphite electrodes and the abrasive flow machining (AFM) process is then used to finish the machined surface. The effects of various electrical parameters on EDM-derived surface quality and improvements in EDM-derived quality under the application of AFM were assessed and, using the final surface roughness as a constraint condition, the effects of various combinations of EDM and “EDM + AFM” on efficiency were studied. The results revealed that the thickness and surface roughness of the superficial recast layer of the TC4 titanium alloy increase with both current and pulse width; in particular, increasing these parameters can increase the surface roughness by two to three grades. Following AFM, the alloy has a more uniform hardness distribution and the surface stress state changes from tensile to compressive stress, indicating that the combined “EDM + AFM” machining scheme can significantly enhance the surface quality of EDM-produced titanium alloy quadrilateral small group holes. The combined scheme achieves a balancing point beyond which increasing the roughness or the number of machining holes enhances either the machining efficiency or the machining surface quality. In the case of typical titanium alloy quadrilateral group small hole parts, the combined machining process can improve the finishing efficiency and total machining efficiency by 71.2% and 25.36%, respectively.

Potential of magnetic Barkhausen noise analysis for in-process monitoring of surface layer properties of steel components in grinding

Abstract Grinding processes are often the last step in the value-added chain of high-performance hardened steel components. However, thermo-mechanical loads which can take place during the process can have a detrimental effect on the surface integrity of ground parts, which are generally tested by post-process measurements. In the present study, two different approaches for an in-process inspection of the workpiece surface integrity were assessed using magnetic Barkhausen noise analysis during cylindrical grinding of hardened workpieces. The results showed that both measuring systems are able to detect changes in the surface state of workpieces in-process or directly after grinding in the grinding machine. After preparations to protect the sensors from influences during the grinding process, changes in the residual stress state and a decrease of hardness could be reliably detected. Due to constant contact conditions between sensor and workpiece a high reproducibility of the measurements was achieved.

Multi-Segment Rupture Model of the 2016 Kumamoto Earthquake Revealed by InSAR and GPS Data

The 2016 Kumamoto earthquake, including two large (Mw ≥ 6.0) foreshocks and an Mw 7.0 mainshock, occurred in the Hinagu and Futagawa fault zones in the middle of Kyushu island, Japan. Here, we obtain the complex coseismic deformation field associated with this earthquake from Advanced Land Observation Satellite-2 (ALOS-2) and Sentinel-1A Interferometric Synthetic Aperture Radar (InSAR) data. These InSAR data, in combination with available Global Positioning System (GPS) data, are then used to determine an optimal four-segment fault geometry with the jRi method, which considers both data misfit and the perturbation error from data noise. Our preferred slip distribution model indicates that the rupture is dominated by right-lateral strike-slip, with a significant normal slip component. The largest asperity is located on the northern segment of the Futagawa fault, with a maximum slip of 5.6 m at a 5–6 km depth. The estimated shallow slips along the Futagawa fault and northern Hinagu fault are consistent with the displacements of surface ruptures from the field investigation, suggesting a shallow slip deficit. The total geodetic moment release is estimated to be 4.89 × 1019 Nm (Mw 7.09), which is slightly larger than seismological estimates. The calculated static Coulomb stress changes induced by the preferred slip distribution model cannot completely explain the spatial distribution of aftershocks. Sensitivity analysis of Coulomb stress change implies that aftershocks in the stress shadow area may be driven by aseismic creep or triggered by dynamic stress transfer, requiring further investigation.

Influence of mineral dissolution on the mechanical behaviour of a granular assembly under complex stress states

Rock and soil are natural assemblies of mineral grains. Dissolution of mineral compositions in a granular assembly can dramatically disturb and change the microstructure. Once the soil fabric and inter-particle contacts change, large deformations can develop and the shear strength can decrease. Currently there is a lack of understanding and experimental evidence of geomaterial behaviour subjected to mineral dissolution under realistic complex stress conditions. In this experimental study, extensive laboratory tests were conducted to investigate changes in the stress-strain relation, shear strength and critical state of a granular assembly after experiencing a substantial loss of particles by salt dissolution. During the salt dissolution process, a larger shear stress or confining pressure leads to a smaller increase of void ratio, a smaller positive state parameter, and a weaker strain-hardening behaviour. After the salt dissolution, the material grading becomes narrower, the grading state index decreases and the specific void ratio increases, leading to an upward shift of the critical state line. However, the increase of void ratio is more than the upward shift of the critical state line, thus the stress state changes from the dense side to the loose side, accompanied by a change of shearing behaviour from strain-softening to strain-hardening. Nevertheless, as the critical friction angle is dominated by the inter-particle contacts among coarse particles, with almost no change in the coarse content of the post-dissolution materials, only a slight decrease of 2.3° in the critical friction angle is found.

Dependence of stress state on the histories of burial, erosion, mechanical properties, pore pressure and faulting

Most onshore basins have experienced one or more phases of burial and erosion. The geomechanical evolution of simplified and idealised fault-bounded mudrock basins on crystalline basement subject to burial and erosion cycles is examined numerically. The changes in strains and stress state and the displacements, including bedding slip, which occur with changes of the overlying load, are tracked. Changes of mechanical properties to represent diagenesis are included. Development of the widely reported ‘high’ horizontal normal stresses results from the changes of vertical load and does not rely directly on applied horizontal tectonic shortening strains. Lateral gradients of normal stress associated with faults are described. The final basin stress state is related to the magnitudes of the burial and erosion, diagenetic or otherwise changes of mechanical properties and pore pressure changes during burial and at depth. The magnitudes of the horizontal stress developed for the 1 km and 2 km burial and erosion cycles tested here exceed the magnitude of the vertical stress for a range of depths extending downwards from the surface unless the horizontal stress is reduced at shallow depths by failure during erosion. Bedding shear instability during erosion, around faults and otherwise, may influence the response to engineering disturbance.

What Governs the Spatial and Temporal Distribution of Aftershocks in Mining-Induced Seismicity: Insight into the Influence of Coseismic Static Stress Changes on Seismicity in Kiruna Mine, Sweden

ABSTRACTStrong mining-induced earthquakes are often followed by aftershocks, similar to natural earthquakes. Although the magnitudes of such in-mine aftershocks are not high, they may pose a threat to mining infrastructure, production, and primarily, people working underground. The existing post-earthquake mining procedures usually do not consider any aspects of the physics of the mainshock. This work aims to estimate the rate and distribution of aftershocks following mining-induced seismic events by applying the rate-and-state model of fault friction, which is commonly used in natural earthquake studies. It was found that both the pre-mainshock level of seismicity and the coseismic stress change following the mainshock rupture have strong effects on the aftershock sequence. For mining-induced seismicity, however, we need to additionally account for the constantly changing stress state caused by the ongoing exploitation. Here, we attempt to model the aftershock sequence, its rate, and distribution of two M≈2 events in iron ore Kiruna mine, Sweden. We could appropriately estimate the aftershock sequence for one of the events because both the modeled rate and distribution of aftershocks matched the observed activity; however, the model underestimated the rate of aftershocks for the other event. The results of modeling showed that aftershocks following mining events occur in the areas of pre-mainshock activity influenced by the positive coulomb stress changes, according to the model’s assumptions. However, we also noted that some additional process not incorporated in the rate-and-state model may influence the aftershock sequence. Nevertheless, this type of modeling is a good tool for evaluating the risk areas in mines following a strong seismic event.

The Influence of Multiaxial Stress Relaxation on Component Creep Damage Accumulation

Abstract Unless inelastic analysis is used, high temperature codes base creep relaxation on the start-of-dwell equivalent stress, which relaxes according to a uniaxial creep law. Elastic follow-up is also included. This approach only evaluates equivalent stress and creep strain rate and the multiaxial stress state is assumed to remain at its initial value as the stress relaxes. Codes suggest that the stress drop is limited to a fraction (typically 20%) of the initial equivalent stress to ensure this assumption does not introduce significant inaccuracies. This article provides a numerical examination of creep relaxation of a cruciform plate subjected to displacement-controlled biaxial loading, with the aim to provide clarification of any required constraint on stress drop. The initial biaxial stress ratio, the plate geometry and the power in a power–law creep model are varied, leading to variations in the elastic follow-up describing the creep relaxation. The biaxial stress ratio is generally found to change with relaxation and a multiaxial ductility approach is used to evaluate the associated creep damage accumulation. This is compared with the damage estimated assuming relaxation is controlled by the equivalent stress with no change in multiaxial stress state. For biaxial plane stress with one principal stress initially being compressive and one tensile, it is found that significant equivalent stress drops (about 40% of the initial stress) can be allowed without the simplified equivalent stress approach becoming inaccurate. More care is required for tensile–tensile stress biaxiality where multiaxial stress changes depend on the initial stress biaxiality and the degree of elastic follow-up. The results will be used to propose improved guidance for simplified inelastic calculations.

Multifault complex rupture and afterslip associated with the 2018 Mw 6.4 Hualien earthquake in northeastern Taiwan

SUMMARYWe investigate the coseismic and post-seismic deformation due to the 6 February 2018 Mw 6.4 Hualien earthquake to gain improved insights into the fault geometries and complex regional tectonics in this structural transition zone. We generate coseismic deformation fields using ascending and descending Sentinel-1A/B InSAR data and GPS data. Analysis of the aftershocks and InSAR measurements reveal complex multifault rupture during this event. We compare two fault model joint inversions of SAR, GPS and teleseismic body waves data to illuminate the involved seismogenic faults, coseismic slip distributions and rupture processes. Our preferred fault model suggests that both well-known active faults, the dominantly left-lateral Milun and Lingding faults, and previously unrecognized oblique-reverse west-dipping and north-dipping detachment faults, ruptured during this event. The maximum slip of ∼1.6 m occurred on the Milun fault at a depth of ∼2–5 km. We compute post-seismic displacement time series using the persistent scatterer method. The post-seismic range-change fields reveal large surface displacements mainly in the near-field of the Milun fault. Kinematic inversions constrained by cumulative InSAR displacements along two tracks indicate that the afterslip occurred on the Milun and Lingding faults and the west-dipping fault just to the east. The maximum cumulative afterslip of 0.4–0.6 m occurred along the Milun fault within ∼7 months of the main shock. The main shock-induced static Coulomb stress changes may have played an important role in driving the afterslip adjacent to coseismic high-slip zones on the Milun, Lingding and west-dipping faults.

Slip distribution of the 2020 Elazığ Earthquake (Mw 6.75) and its influence on earthquake hazard in the Eastern Anatolia

SUMMARYWe analysed coseismic surface displacements of the 2020 January 24 Elazığ (M 6.75) Earthquake using GPS (Global Positioning System) measurements to investigate the associated fault slip distribution and static stress change. Our geodetic analysis of 13 GPS sites surrounding the epicentre included data from four additional sites. We accurately located the nucleation point of the main shock at 38.310° N, 39.081° E (±1.4 km) and at a depth of 5.2 ± 1.2 km. Both seismograph and GPS-derived fault plane solutions confirmed that it has a nearly pure sinistral mechanism with a negligible obliquity. The main shock generated 29.2 cm average sinistral slip along an approximately 70 km long and 20 km wide section of the East Anatolian Fault. Based on its rupture size and average slip, its magnitude was found to be Mw 6.75. An average of 6.6 bars of stress drop occurred on the rupture plane. The rupture occurred bilaterally failing two separate segments both to the northeast and to the southwest of the nucleation point. Average sinistral slips were 14.6 and 47.4 cm along the southwestern and northeastern segments, respectively. Sinistral slip reached up to 53.1 cm along the southwestern segment and 110.5 cm along the northeastern segment. During the generation process of the 2020 earthquake, 78 per cent of the slip deficit had been released aseismically since 1875. Increasing Coulomb stress by an average of 2.5 bars, it substantially increased earthquake hazard on the 1874 (M 7.1) rupture zone, which might have already accumulated 1.51 m slip deficit on its fully locked patches. Furthermore, increasing Coulomb stress by an average of 0.5 bars, it raised earthquake hazard on the 1893 (M 7.1) rupture zone, which might have already stored 1.01 m slip deficit along the fully locked patches.