Reverse Loading Research Articles

Analysis of ductile damage evolution and failure mechanisms due to reverse loading conditions for the aluminum alloy EN‐AW 6082‐T6

AbstractThis paper deals with experiments and numerical simulations for reverse uniaxial tension‐compression and shear tests to investigate the ductile damage and fracture behavior of the aluminum alloy EN‐AW 6082‐T6. For this purpose, experiments with different loading sequences and number of loading cycles with uniaxial tensile and new shear specimens have been performed. Furthermore, the digital image correlation (DIC) technique captures the deformations and strain fields during the experimental processes. A modified anisotropic stress‐state‐dependent elastic‐plastic‐damage continuum model is proposed and is validated by experimental strain fields measured by DIC. Moreover, numerically predicted distributions of the principal damage strains are compared with fracture images taken by scanning electron microscopy (SEM).

Hysteretic model for bending-type frictional steel truss coupling beams

As a novel coupling beam for coupled shear wall structures, the bending-type frictional steel truss coupling beam (BFTCB) concentrates the deformation and energy dissipation in friction dampers at the bottom chord, allowing the main body to remain elastic during earthquakes. As the preparatory work for resilient structure design based on the BFTCB, this work concentrates on developing the hysteretic model for BFTCB. Firstly, the BFTCB stiffness-strength decoupling mechanism was introduced, i.e., the shear strength is provided by friction dampers while webs control its initial stiffness. Secondly, a hysteretic model that reflects the BFTCB two-stage sliding characteristic was proposed. The model consists of a trilinear backbone curve and the unloading and reverse loading rules. The model has eight control parameters, of which two core parameters (initial stiffness and limiting shear strength) are derived from the BFTCB stiffness-strength decoupling mechanism, whereas the remaining parameters are obtained by theoretical analysis and empirical calibration. The hysteretic model was then compared with the test curves and demonstrated good accuracy. Finally, a series of FE prototypes of BFTCB with different design stiffnesses and strengths was adopted to verify the hysteretic model. The results showed that the proposed model fitted well with the FE prototypes, indicating its applicability to BFTCB with varying core design parameters. Therefore, the hysteretic model can be adopted for BFTCB to support the resilient shear wall structure design.

Dynamic Features of Non-Return Mechanism in Hatch Door of Amphibious Aircraft

The non-return mechanism is the key device that plays the role of braking in the opening-and-closing electric actuator of an amphibious aircraft hatch door. The ball-and-socket contact pair, providing the pressing force, and the multi-disc friction pair, supplying the braking torque, are two core components in the non-return mechanism. In this paper, the dynamic model of the non-return mechanism is established considering the freedom of rotation-translation. Based on MATLAB/Simulink, the solution framework of the overall dynamic model is built. The dynamic response characteristics of the non-return mechanism in the process of reverse load braking, forward load braking, and continuous closing are analyzed. The braking time and the angular displacement of the output shaft in the braking phase have been presented. Compared with forward load braking, reverse load braking has a longer braking time and smaller angular displacement of the output shaft. In addition, the compaction function of the ball-and-socket contact pair is verified by experiment, and the influence of the cone angle, distribution radius of the ball socket, and the steel ball diameter on the pressing force has been discussed. This study provides a theoretical basis and parametric design platform for the design and optimization of non-return mechanisms, which can shorten the product development time.

Plastic deformation behavior of a Mg-1.5Zn-0.1Ca (mass%) alloy sheet under different strain paths

Mg–Zn–Ca alloy sheets with weak basal texture are expected to improve the room-temperature press formability of Mg-alloy sheets. The plastic deformation behavior of Mg–Zn–Ca alloy sheets should differ significantly from that of typical Mg-alloy sheets with strong basal texture. However, this has not yet been substantially studied. In this study, the plastic deformation behavior of a rolled Mg-1.5Zn-0.1Ca (mass%) alloy sheet with a thickness of 1 mm is studied experimentally. Tests of uniaxial tension, compression, reverse loadings from tension to compression, and from compression to tension are conducted in the rolling and transverse directions, and the work-hardening behavior and evolution of the Lankford value are investigated. Electron backscattered diffraction measurements are also conducted to examine the texture evolution. Under tension, the stress was less in the transverse direction than that in the rolling direction, and an apparent plateau region appeared only in the transverse direction. Under compression, the stress-strain curves exhibited plateau regions at the initial stage and were similar in the rolling and transverse directions. The Lankford values were less under compression than under tension in both directions. Under reverse loading from compression to tension, sigmoidal curves appeared, irrespective of the loading direction; however, they were more pronounced in the rolling direction than in the transverse direction. Under reverse loading from tension to compression, sigmoidal trends did not occur, irrespective of the loading direction, and the in-plane anisotropy in the work-hardening behavior was small. The mechanisms yielding these macroscopic deformation behaviors are discussed in terms of twinning and slip activities.

Numerical Model Calibration and a Parametric Study Based on the Out-Of-Plane Drift Capacity of Stone Masonry Walls

Failure under seismic action generally occurs in the form of out-of-plane collapses of walls before reaching their in-plane strength in historical stone masonry buildings. Consistent finite element (FE) macro modeling has emerged as a need for use in seismic assessments of these walls. This paper presents the numerical model calibration of U-shaped multi-leaf stone masonry wall specimens tested under ambient vibrations and out-of-plane (OOP) load reversals. The uncertain elastic parameters were obtained by manual calibration of the numerical models based on ambient vibration test (AVT) data of the specimens. To obtain nonlinear calibration parameters, static pushover analyses were performed on FE models simulating quasi-static tests. The calibrated numerical models matched well with the experimental results in terms of load–drift response and damage distribution. As a result, the modulus of elasticity and tensile and compressive degrading strength parameters of masonry walls were proposed. A parametric study was conducted to examine the effects of different materials and geometric properties (tensile strength, aspect ratio, slenderness ratio, and geometric scale) on the OOP behavior of stone masonry walls. A quite different strain distribution was obtained in the case of a large aspect ratio, while it was determined that the geometric scale had no effect on the strain distribution. Tensile strength was the dominant parameter affecting the load–drift response of the models. Within the presented work, a practical tool for out-of-plane seismic assessment has been proposed for the structures covered in this paper.

A Homogeneous Anisotropic Hardening Model in Plane Stress State for Sheet Metal under Nonlinear Loading Paths.

In sheet metal forming, the material is usually subjected to a complex nonlinear loading process, and the anisotropic hardening behavior of the material must be considered in order to accurately predict the deformation of the sheet. In recent years, the homogeneous anisotropic hardening (HAH) model has been applied in the simulation of sheet metal forming. However, the existing HAH model is established in the second-order stress deviator space, which makes the calculation complicated and costly, especially for a plane stress problem such as sheet metal forming. In an attempt to reduce the computational cost, an HAH model in plane stress state is proposed, and called the HAH-2d model in this paper. In the HAH-2d model, both the stress vector and microstructure vector contain only three in-plane components, so the calculation is significantly simplified. The characteristics of the model under typical nonlinear loading paths are analyzed. Additionally, the feasibility of the model is verified by the stress-strain responses of DP780 and EDDQ steel sheets under different two-step uniaxial tension tests. The results show that the HAH-2d model can reasonably reflect the Bauschinger effect and the permanent softening effect in reverse loading, and the latent hardening effect in cross loading, while the predictive accuracy for cross-loading softening remains to be improved. In the future, the HAH-2d model can be further modified to describe more anisotropic hardening behaviors and applied to numerical simulations.

Influence of Slag-Based Geopolymer Concrete on the Seismic Behavior of Exterior Beam Column Joints

In reinforced concrete (RC) constructions, the beam-column junctions are very sensitive to lateral and vertical loads. In the event of unforeseen earthquake and wind loads, this insufficient joint performance can lead to the failure of the entire structure. Cement industries emit a large amount of greenhouse gases during production, thus contributing to global warming. The nature of cement concrete is fragile. Cement output must be reduced in order to ensure environmental sustainability. Geopolymer concrete (GC), which is a green and low-carbon material, can be used in beam-column joints. M30 grade BBGC was developed and employed in the current study. Alkaline liquids are produced when sodium silicate and sodium hydroxide are mixed at room temperature. The alkaline liquid to fly ash ratio was fixed at 0.5, and the concentration of NaOH was fixed at 8 M. The mechanical properties of the Binary Blended Geopolymer concrete (BBGC), containing fly ash and GGBS, at proportions ranging from 0% to 100%, were investigated. This study was further expanded to examine the behavior of two groups of binary blended geopolymer concrete (BBGC) exterior beam-column joints, with cross sections of 230 mm × 120 mm and 170 mm × 120 mm. The column heights and lengths were both 600 mm under reverse cyclic loads in order to simulate earthquake conditions. The failure mechanism, ductility, energy absorption capacity, initial crack load, ultimate load carrying capacity, and structural performance was evaluated. The test findings showed that BBGC with 20% fly ash and 80% GGBS had the highest compressive strength and split tensile strength. When compared with other beam column joints, those containing 20% fly ash and 80% GGBS performed better under cyclic loading. The test findings imply that GGBS essentially enhances the joint performance of BBGC. The microstructural SEM and EDS studies revealed the reasons behind the improvement in strength of the GGBS fly ash-based Geopolymer concrete.

Mixed-mode dynamic fracture parameters for soda-lime glass

Dynamic mixed-mode fracture of soda-lime glass (SLG) was experimentally investigated using a full-field optical method - Digital Gradient Sensing (DGS) - in conjunction with ultrahigh-speed photography. Single edge-notched specimens were subjected to reverse impact loading using a modified Hopkinson pressure bar. The specimens were eccentrically loaded at different offset distances relative to the initial notch to achieve a wide range of mode-mixities, from mode-I to nearly mode-II condition, at initiation. Two time-resolved orthogonal angular deflection fields of light rays proportional to the respective full-field stress gradients were optically measured during experiments on different geometries. Mode-I and -II stress intensity factor histories spanning pre- and post-initiation behaviors were evaluated via over-deterministic least-squares error minimization of optically measured full-field data. By considering the critical stress intensity factors at different crack initiation modes, a fracture envelope for SLG encompassing various mode-mixities was developed for the first time for SLG and compared with predictions from prevailing approaches. An empirical fit of data seems to capture the overall trend whereas the prevailing methods do not. Measured crack kink angles are compared with the popular MTS and SED fracture criteria; both predict the kink angles reasonably well. Unlike brittle polymers, the critical effective stress intensity factors for SLG are independent of mode-mixity over a large range of values but show a decreasing trend as mode-II conditions become dominant and an extrapolated critical mode-II stress intensity factor of 0.37 MPa√m, approx. one-half of its mode-I counterpart, is seen.

Cyclic bending of steel tubes with Lüders bands

Preceding experiments and analyses revealed that bending of tubes whose material exhibits Lüders banding leads to the progressive nucleation of inclined bands of higher strain organized into periodic diamond clusters. The diamonds cover both the tensioned and compressed sides of the tube with the affected length developing a higher curvature than the unaffected section. Between the diamond patterns are elastic zones required for each periodic domain to conform to the curvature of the tube (Hallai and Kyriakides, 2011a,b). The present work examines how this inhomogeneously deformed structure behaves on unloading, reverse bending, and curvature symmetric cycling. The inelastic behavior of the material is modeled through a combined isotropic/kinematic hardening constitutive model. The model incorporates partial softening over the extent of the Lüders strain and uses nonlinear kinematic hardening for reverse loading. A tube of virgin material is bent until the whole length is Lüders deformed and is in uniform curvature. The curvature remains uniform during unloading with the strain in the diamonds gradually being erased, but simultaneously a secondary set of local higher strain patterns emerge in the hitherto elastic zones between the original diamonds. During reverse bending to the symmetric negative curvature, the secondary patterns continue to grow in intensity. The tube is unloaded again and bent back to positive curvature completing the cycle. In the course of the second half cycle, localized strain patterns evolve in the reverse order to that of the first half cycle. The secondary patterns are gradually erased, and the diamond patterns reappear now concurrently reaching the same intensity as that acquired progressively during the bending of the virgin material. The same appearance, erasure, and reappearance of localized deformation take place in subsequent cycles. Once past the initial bending, the structure bends uniformly.

Investigating the effectiveness of a CRM system: full scale reverse cyclic tests on a two-storey rubblestone masonry building

The research work aims at investigating the effectiveness of a minimally invasive strengthening technique used to repair a full scale two-storey building, consisting of 350 mm thick two-leaf rubblestone masonry walls, a timber floor, and a timber roof with clay tiles. The strengthening technique consists in applying on the external façade of the building a single layer of a Composite Reinforced Mortar (CRM) System, which consists in a mortar coating containing a Glass Fiber Reinforced Polymer (GFRP) mesh; artificial diatons connecting both wythes of the walls were also applied. The reverse cyclic load was applied to each of the two longitudinal walls of the building by means of a servo-controlled hydraulic jack pinned to a vertical steel beam. This beam allowed splitting the total lateral force into two forces, acting at first story and roof levels; these forces were calculated proportional to the product of the floor mass with the floor level.The first cyclic test was carried out on the Unreinforced Masonry (URM) building up to attaining a damage level quite close to that corresponding to the ultimate limit state of the structure. Then, the building was repaired (RM) with the proposed technique and tested again, up to reaching a near-collapse condition. The experiments proved the effectiveness of the proposed strengthening method showing a resistance increment of 240%, a larger displacement capacity (150%) and a significant increase of the total dissipated energy. The importance of the artificial diatons to prevent the separation of the masonry leaves in strengthened walls was also clearly highlighted.

Research on Bucket Loading Resistance Based on Discrete Element Method

Shovel loading resistance is the reaction force of the material on the bucket during the shovel loading process, which contains two parts: the resistance of the bucket insertion stage and the resistance of the lifting stage. The resistance of shovel loading has a great influence on the loading efficiency, so it is important to carry out resistance research. Based on the discrete element theory, this paper applies EDEM software to establish a simulation model of the loading process and realise the simulation of the forward and reverse shovel loading process. Through the simulation, the mechanical characteristics of the shovelling operation are visually analysed, and the obstructing effect of the material on the bucket is clarified; the shovelling resistance of the key parts of the bucket at different stages of the shovelling process is specifically analysed, and the parts where the peak shovelling resistance is located and the stages where it is located are identified. The influence of the shovel angle on the resistance is also analysed.

Reversal of right ventricular pressure loading improves function independent of fibrosis.

Reversal of right ventricular pressure loading improves function independent of fibrosis.

НАУЧНО-ПРАКТИЧЕСКИЙ МЕХАНИЗМ ЭКОНОМИЧЕСКОЙ ОЦЕНКИ ПРИМЕНЕНИЯ ТЕХНОЛОГИЧЕСКИХ СХЕМ В ЛОГИСТИЧЕСКИХ МУЛЬТИМОДАЛЬНЫХ СИСТЕМАХ

The industrial sector of Russia is the most important segment of the country's economy. The modern chemical industry has well-established technologies for the production of high-quality caustic soda. Caustic soda is widely used in various production segments, including: chemistry and petrochemistry, metallurgy, gas, food, textile, pulp and paper industry. The unstable economic situation in the world has stopped the action of freight traffic flows in the logistics systems and led to an increase in prices for raw materials. Many countries have started searching for import substitution of raw materials and goods against the background of a sharp break in import supplies. The "leading chemical enterprise" in the Volgograd region is engaged in the production of chemical products. The main volumes of the company's foreign supplies accounted for Europe and Asia. The paper studies the unevenness of foreign supplies in recent years (2020-2021). The characteristic of the links of the logistics system for the transportation of chemical products along the routes "Volgograd – Bishkek" and "Volgograd – Netherlands" is obtained. The time economic costs in the links of multimodal logistics systems are calculated. International routes for the transportation of chemical products to Kyrgyzstan and the Netherlands have been compiled. The effective modes of operation of drivers of automobile transport are determined. Technological schemes for the transportation of caustic soda from Volgograd to Bishkek, using reverse loading of motor transport, have been developed, ensuring a reduction in transport costs.

Cyclic Evaluation of Exterior Beam-to-Column Connections for Intelligent Accelerated Construction of Industrial Facilities

The rapid development towards automated construction has been witnessed in recent years mainly due to the growing shortage of skilled labor. Against that backdrop, an accelerated method, with the aid of robotic cranes, is emerging in China to speed up the construction of industrial facilities such as warehouse structures. This method requires that the steel bars in the precast beams do not extend beyond the beam ends to facilitate the temporary fixation of the robotic crane at the top of cast-in-place columns. This, nonetheless, brings a series of new problems, one of which is how to choose a suitable anchoring type for the beam bottom bars. To address this issue, three large-scale exterior beam-to-column connections were fabricated and tested under lateral load reversals. Two anchorage forms, namely, mechanical splices and grouted sleeves, were adopted and compared with the monolithically cast specimen. The test results showed that the specimen using the grouted sleeves had similar seismic performance to that of the cast-in-place specimen, whereas the specimen using the mechanical splices presented significant post-peak deterioration under positive beam bending moments. This happened because the congestion of steel bars within the joint core made it difficult to fully tighten the beam bottom bars into the threaded couplers; consequently, a “slop” was formed which could substantially impair the cyclic behavior of the specimen. As such, it is suggested that grouted sleeves should be more applicable and reliable for the new construction method. This counter-intuitive finding also indicates that, for intelligent construction, no detail should be taken for granted, but rather needs due consideration.

Moment Rotation behavior of Top and Seat Angle Connection with Angle Stiffeners

The design specifications for seven commonly used semi-rigid steel connections have been embodied in Indian Standard Code of Practice for General Construction in Steel (IS800:2007). Bolted connections are proved to be efficient by several researchers for its energy dissipating capability under reversal of loading; among them top and seat angle (TSA) connection has higher capacity. An attempt has been made to investigate the behaviour of stiffened TSA connection by finite element analysis in this research. Previously published experimental specimens of TSA connection (RAMAN 2005) semi-rigid TSA bolted connection and their results have been considered to develop 3D Non-linear Finite Element (FE) model and analyses have been executed using the general purpose FE software. The M-?r behavior of numerical analyses are compared with that of the experimental results and thus, the FE model is validated. Further studies are carried out on TSA with all angles stiffened and TSA with angles subjected to tension alone are stiffened. The FE analysis results showed that TSA connection with only tension angles stiffened behave similar to that of TSA connection with all angles stiffened i.e., the stiffeners provided in compression angles does not contribute to the stiffness and connection capacity. The plastic flexural resistance of stiffened TSA connection has enhanced by 30% to that of TSA connection and the ratio of initial stiffness of stiffened TSA to the unstiffened TSA is found to be 1.25. So, the stiffened TSA connection is proved to be efficient in terms of both capacity and failure. The further studies have been carried out to investigate the influence of stiffener properties on the M-?r mechanism of the connection and the results showed that thickness of stiffener equal to the beam web thickness is more efficient.

Influence of Tie Configuration on Seismic Behaviour of Ultra High Performance Concrete Columns

Ultra-High-Performance Concrete (UHPC) is one of the latest advances in concrete technology as it overcomes the shortcomings of conventional concrete such as low strength to weight ratio, high permeability, low tensile strength, low ductility, and volume instability. Confinement is capable of increasing capacity of the concrete structure to sustain large deformation without a substantial strength loss. The present study discusses the influence of tie configuration, percentage of longitudinal reinforcement and tie spacing in improving the confinement and behaviour of UHPC columns. In order to determine the behaviour of UHPC column, half scaled specimens of original short column with four different tie configurations were used. The configurations considered for the study included a double legged ties (A), welded ties with bars running centrally across the length and width (B), ties with inclined bars connecting two adjacent mid-points (C) and ties with bars connecting two adjacent sides at one-third distances (D). For the same tie configuration, the transverse reinforcement ratios are varied by changing the diameter of the ties. The specimens were tested under quasi static reverse cyclic loading under a constant axial load. The test results were represented and compared in terms of load-deflection envelope, ductility and cracking patterns. Tie configuration C exhibited better performance in stiffness and ductility, when compared with other configurations. For same parameters, “B” and “D” configuration displayed better behaviour than “A” configuration. This variation in performance was due to increase in transverse reinforcement percentage and the consequent effectiveness of core confinement. Transverse reinforcement percentage of “B” and “C” configurations is less than “D” configuration. The enhancements of properties of “B” and “C” configurations are better than “D” configuration. It was due to the effective core confinement of “B” and “C” configuration. For the same tie configuration, ultimate load, initial stiffness and relative ductility increases with increase in transverse reinforcement percentage. UHPC columns with “C” type tie configuration can effectively use in moderate and high seismic areas and its performance can be improved by increasing the transverse reinforcement ratio.

Origins of improved elongation to fracture in cyclic bending under tension of AA6022-T4 sheets as revealed using crystal plasticity modeling

Plastic instabilities can be suppressed by imposing cyclic bending during tension to increase elongation-to-fracture (ETF) of metallic sheets. This work is a combined experimental and modeling study into the origins of the improved ETF in cyclic bending during tension facilitated by a continuous-bending-under-tension (CBT) test. Load-displacement is measured during the CBT test under an optimized combination of band depth and pull speed process parameters for aluminum alloy (AA) 6022-T4. Monotonic and load reversal response of the alloy is also characterized under strain histories that resemble the history in CBT. Electron-backscattered diffraction and neutron diffraction are employed to characterize the initial microstructure and texture evolution of the alloy after CBT and simple tension (ST). Monotonic, load reversal, and texture data are used to adjust and verify the parameters of an elasto-plastic self-consistent crystal plasticity-based finite element model for simulating CBT. Additionally, a flow stress curve based on a bulge test is used to calibrate the model to capture the large strain hardening behavior of the alloy. The model is then used to simulate the CBT test while predicting the load-displacement and texture evolution data. The model successfully reproduced the succession of spikes and plateaus during CBT validating the prediction of the extrapolated hardening. After the validation, the development of stress and strain is probed through the sheet thickness to determine the underlying profiles as well as along the sheet to elucidate the location and onset of failure axially. The model reveals the development of more strain and dislocation density at the surface then at the center of the sheet and correctly predicts the strain localizations. Comparisons of texture evolution and mechanical fields developed in ST and CBT reveal very similar mechanical states in the sheet. These results in combination with experimental results suggest that the origins of improved ETF during CBT pertain primarily to the incremental deformation structural effects and secondary to the microstructural evolution effects.

Multi-directional T-EMSD-based p-y model for recent loading history effects on lateral response of short pile and caisson in undrained clays

Rigid foundations supporting offshore wind turbines (OWT) like short piles and caissons can sustain multi-directional lateral loading. Moreover, the monotonic and cyclic response of these foundations can be affected by recent loading history aligned along directions different from the present one. To represent such recent loading history effects, a multi-directional p-y model is proposed for rigid foundations in undrained clays. The model is constructed by extending the uni-directional p-y model previously proposed by the authors based on Total-displacement-loading Extended Mobilisable Strength Design (T-EMSD) approach, and thus considering site-specific soil stress-strain relations and foundation geometries. The crux of the extension is to combine bounding surface plasticity and radial mapping with a moving projection center. The former effectively couples p-y response along orthogonal directions, while the latter is crucial for representing the influences of loading direction reversal and recent loading history effects. The proposed p-y model is evaluated against existing centrifuge tests and finite element analysis (FEA) of this work. Lastly, the proposed p-y model and FEA are used in parallel to highlight the effects of loading path rotation on monotonic and cyclic accumulative foundation response. These comparative analyses indicate that the proposed p-y model can reasonably represent recent loading history effects.

Plastic deformation of ultra-thin pure titanium sheet subject to tension-compression loadings

Measurement of the Bauschinger effect of ultra-thin metallic sheet by the conventional tension-compression (TC) test is challenging due to the premature buckling during compression. In this study, a test method based on a multi-layered sandwich specimen is newly introduced to suppress the buckling in the uniaxial compression. Theoretical calibration is conducted for obtaining accurate flow stress under compression by correcting the effects of adhesive and friction induced by supporting side plates. Also, strains during the TC tests are measured by the digital image correlation (DIC) technique. From the proposed TC test with the sandwich specimen, plastic deformation of 0.1-mm-thick ultra-thin pure titanium sheet was investigated under reverse loading. Finally, the constitutive model based on the distortional hardening concept is newly developed and calibrated to reproduce the Bauschinger effect of the investigated ultra-thin sheet subject to TC loadings.

A Grid-Edge-Inspired and Community-Oriented Control Framework: Utility perspective on centralized and decentralized control

Technology advancements in renewable generation, power electronic devices, and advanced computing expedite a decarbonized, decentralized, and digitalized grid. These advancements also enable a role transition for traditional utility customers, enabling the role of “prosumers” who provide power to the grid with distributed energy resources (DERs) that exceed their demand and who adjust the timing of their energy consumption to energy pricing. Although this role change can alleviate stresses on the grid and support a clean generation future, it sparks multiple challenges for the power industry, spanning system operation to future grid planning. One class of problems relates to visibility. Utility operators usually do not have oversight over rooftop solar photovoltaics (PVs) or site batteries. These behind-the-meter (BTM) DERs tend to cluster in neighborhoods, which can cause or exacerbate issues with reverse power flow, power quality, and load masking. In turn, these problems increase the risk of relay miscoordination and power interruptions during normal grid operations. Aging grid infrastructure adds an additional layer of uncertainty to the operational characteristics of the nonvisible generation stack, and electrification adds a layer on top of that, with the increasing penetration of electric vehicles adding stochastic loads to the system. These challenges are not only operational, they also relate to the near- and long-term planning of the grid. Because planners cannot anticipate where and when the new DER interconnections will be requested by customers, requests may overturn the original grid upgrade plan and reshape resource distribution.