Load Cases Research Articles

Lightweight Potential of Anisotropic Plate Lattice Metamaterials

Additive manufacturing enables the production of lattice structures, which have been proven to be a superior class of lightweight mechanical metamaterials whose specific stiffness can reach the theoretical limit of the upper Hashin–Shtrikman bound for isotropic cellular materials. To achieve isotropy, complex structures are required, which can be challenging in powder bed additive manufacturing, especially with regard to subsequent powder removal. The present study focuses on the Finite Element Method simulation of 2,5D anisotropic plate lattice metamaterials and the investigation of their lightweight potential. The intentional use of anisotropic structures allows the production of a cell architecture that is easily manufacturable via Laser Powder Bed Fusion (LPBF) while also enabling straightforward optimization for specific load cases. The work demonstrates that the considered anisotropic plate lattices exhibit high weight-specific stiffnesses, superior to those of honeycomb structures, and, simultaneously, a good de-powdering capability. A significant increase in stiffness and the associated surpassing of the upper Hashin–Shtrikman bound due to anisotropy is achievable by optimizing wall thicknesses depending on specific load cases. A stability analysis reveals that, in all lattice structures, plastic deformation is initiated before linear buckling occurs. An analysis of stress concentrations indicates that the introduction of radii at the plate intersections reduces stress peaks and simultaneously increases the weight-specific stiffnesses and thus the lightweight potential. Exemplary samples illustrate the feasibility of manufacturing the analyzed metamaterials within the LPBF process.

"Spanish flu," encephalitis lethargica, and COVID-19: Progress made, lessons learned, and directions for future research.

One hundred years ago, an influenza pandemic swept across the globe that coincided with the development of a neurological condition, named "encephalitis lethargica" for the occurrence of its main symptom, the sudden onset of sleepiness that either developed into coma or gradually receded. Between 1917 and 1920, mortality of the flu was >20 million and of encephalitis lethargica approximately 1 million. For lessons to be learned from this pandemic, it makes sense to compare it with the COVID-19 pandemic, which occurred 100 years later. Biomedical progress had enabled testing, vaccinations, and drug therapies accompanied by public health measures such as social distancing, contact tracing, wearing face masks, and frequent hand washing. From todays' perspective, these public health measures are time honored but not sufficiently proven effective, especially when applied in the context of a vaccination strategy. Also, the protective effects of lockdowns of schools, universities, and other institutions and the restrictions on travel and personal visits to hospitals or old-age homes are not precisely known. Preparedness is still a demand for a future pandemic. Clinical trials should determine the comparative effectiveness of such public health measures, especially for their use as a combination strategy with vaccination and individual testing of asymptomatic individuals. It is important for neurologists to realize that during a pandemic the treatment possibilities for acute stroke and other neurological emergencies are reduced, which has previously led to an increase of mortality and suffering. To increase preparedness for a future pandemic, neurologists play an important role, as the case load of acute and chronic neurological patients will be higher as well as the needs for rehabilitation. Finally, new chronic forms of postviral disease will likely be added, as was the case for postencephalitic parkinsonism a century ago and now has occurred as long COVID.

Transient surrogate modeling of modally reduced structures with discontinuous loads and damping

AbstractIn this work, a surrogate model for structural, transient and discontinuously excited finite element method simulations is developed. This allows to reduce the computational effort of repeated calculations of identical models under different load cases. The architecture of the surrogate combines fully connected neural network layers with long short-term memory layers. For the reproduction of different damping ratios, a categorical variable is added to the continuous input data. Based on a recursive flow of the predicted data back to the input layer, long-term dependencies do not vanish due to short-input sequences. The system dimension is reduced by applying the model-order reduction technique for modal decomposition. The high accuracy of the surrogate and the reduction of computational costs are shown on an academic example of a cantilever beam and a real-world example of a robot. The advantages of our approach are illustrated in comparison with state-of-the-art surrogates for transient finite element analysis. By using the surrogate proposed in this study, oscillations due to discontinuous excitation of mechanical structures can be reproduced. For this purpose, only short-input sequences are necessary since the excitation of the oscillations does not have to be part of the input sequence during the whole duration of the oscillations. Due to the categorical variable for the damping ratio, the surrogate can account for the influence of different damping in parameter studies.

Transmissibility-based operational modal analysis: A unified scheme and uncertainty quantification

The transmissibility-based Operational Modal Analysis (OMA) technique has attracted substantial research interest over the past two decades due to its capability to extract structural modal parameters in the presence of non-white excitation. The transmissibility function used in OMA can be categorized as Response Transmissibility (RT) and Power Spectral Density Transmissibility (PSDT). Modal parameters can be identified by combining RTs from multiple load cases or PSDTs from multiple transfer outputs. Nevertheless, the mathematical formulations and implementation procedures of the various RT-based and PSDT-based methods exhibit significant differences. Furthermore, the uncertainty associated with modal parameter estimates is rarely assessed in these methods. This work aims to propose a scheme that unifies various transmissibility-based OMA algorithms through a consistent parametric formulation. Within this scheme, a universal parametric model and a standardized implementation procedure are developed to accommodate two types of transmissibility in both time and frequency domains and six OMA algorithms; additionally, a generalized framework for quantifying the uncertainties associated with modal parameter estimates is provided. The proposed scheme is finally validated using a planar truss structure.

The stacking sequence optimisation of a filament wound composite bicycle frame using the data-driven evolutionary algorithm EvoDN2

ABSTRACT This work focusses on identifying the optimal stacking sequence for composite tubes in mountain bike frames using a data-driven model combined with evolutionary algorithms. The objective is to find a frame that is sufficiently stiff while meeting the requirements of weight, strength, and minimum tube wall thickness. The decision variables are the ply winding angles and the ply thicknesses of each tube. The study performs designs for two load cases – Starting and Uphill – and explores two types of winding: the gradual winding of individual layers (1ply) and the winding of layers between predefined inner and outer layers with variable thicknesses (TW). Additionally, the design process is applied to frames made of isotropic materials, such as steel, aluminium, and titanium, using the same methodology to allow for comparison of results. The article demonstrates the successful application of this methodology to common sports equipment, suggesting its potential for beneficial use in other common composite frame structures.

Structural Optimization of an Unmanned Ground Vehicle as Part of a Robotic Grazing System Design

Unmanned ground vehicles (UGVs) have gained increased attention in different fields of application; therefore, their optimization requires special attention. Lowering the mass of a UGV is especially important to increase its autonomy, agility, and payload capacity and to reduce dynamic forces. This contribution deals with optimizing a UGV unit prototype that, when connected with similar units, forms a moving electric fence for animal grazing. Together, these units form a robotic system that is intended to solve the critical problem of lack of human capacity in herding and grazing. This approach employs topology optimization (TO) and finite element analysis (FEA) to lower the mass of a UGV unit and validate the design of its structural components. To our knowledge, no optimization of this type of UGV has been reported in the literature. Here, we present the results of a case study in which a set of four load cases served as a basis for the optimization of the UGV frame. Response surface analysis (RSA) was used to identify the worst load cases, while substructuring was used to allow for more detailed meshing of the frame portion that was subjected to TO. Thereby, we demonstrate that the prototype of the UGV unit can be built using standard parts and that TO and FEA can be efficiently used to optimize the load-carrying structure of such a specific vehicle.

Finite element analysis of implanted lumbar spine: Effects of open laminectomy plus PLF and open laminectomy plus TLIF surgical approaches on L3-L4 FSU

Several finite element (FE) studies reported performances of various lumbar fusion surgical approaches. However, comparative studies on the performance of Open Laminectomy plus Posterolateral Fusion (OL-PLF) and Open Laminectomy plus Transforaminal Interbody Fusion (OL-TLIF) surgical approaches are rare. In the current FE study, the variation in ranges of motions (ROM), stress-strain distributions in an implanted functional spinal unit (FSU) and caudal adjacent soft structures between OL-PLF and OL-TLIF virtual models were investigated. The implanted lumbar spine FE models were developed from subject-specific computed tomography images of an intact spine and solved for physiological loadings such as compression, flexion, extension and lateral bending. Reductions in the ROMs of L1-L5 (49 % to 59 %) and L3-L4 implanted FSUs (91 % to 96 %) were observed for both models. Under all the loading cases, the maximum von Mises strain observed in the implanted segment of both models exceeds the mean compressive yield strain for the vertebra. The maximum von Mises stress and strain observed on the caudal adjacent soft structures of both the implanted models are at least 22 % higher than the natural spine model. The findings indicate the risk of failure in the implanted FSUs and higher chances of adjacent segment degeneration for both models.

Exploring the relationship between case volume and intracranial aneurysm treatments with flow-diverters and flow-disruptors: Insights from the 2020 to 2021 Database of the German Society for Interventional Radiology National Registry in Germany.

Intracranial aneurysm treatment using flow-diverters and flow-disruptors requires a higher level of expertise when compared to more traditional methods. Our hypothesis was that the procedural success and the rate of complications are dependent on the annual case load of a center. Conducting a retrospective analysis on the Database of the German Society for Interventional Radiology for the years 2020 to 2021, we examined flow-diverter and flow-disruptor procedures. We categorized centers into four groups according to their annual case load and proceeded to analyze success rates, complication rates, and fluoroscopy times across these centers. No statistically significant differences were observed among the groups in both flow-diverter and flow-disruptor cases concerning fluoroscopy time and the incidence of technical complications. However, within the subgroup of flow-disruptor cases, centers with lower case load exhibited significantly higher rates of hemorrhagic and clinically relevant complications. Additionally, it was noted that the rate of therapeutic success in the flow-diverter group significantly increased in centers with higher case volumes. Our findings support the intention towards centralization of medical care especially for complex neuroendovascular procedures. Furthermore, our findings are an argument to further develop a standardized educational and procedural algorithm based on defined case numbers and training modules for complex neurovascular procedures as already implemented by the Database of the German Society for Interventional Radiology.

Exploring the Practice of Victim-Offender Mediation, to Proceed or Retrieve: The Case of Ghana

In contrast to the State-centred perspective, which is based on criminal jurisprudence and holds that crime is committed against the State rather than the victim, the primary party. Victim-Offender Mediation (VOM), also known as restorative justice or transformative justice, aims to resolve some criminal offenses amicably. It appears the State is ignoring the victim's needs, restoration, interests, fears, and desires in order to proceed with the prosecution as it sees fit to settle its disputes in the strict criminal justice system. Outcomes sometimes appears unsatisfactory to victims, offenders, families, and the public. The paper conducts a theoretical and historical examination of VOM from a global as well as a Ghanaian viewpoint. Despite a few minor difficulties, it notes that VOM has been embraced by many states all over the world because the benefits far outweigh the drawbacks. Additionally, it has been noted that Ghana's judicial system supports the use of VOM. In particular, the Courts Act, 1993, the Alternative Dispute Resolution Act, 2010, and the Court- Connected ADR Practice Manual, 2010 call for the encouragement, promotion, and facilitation of amicable settlements of offenses that do not amount to felonies and do not qualify as serious offenses. The practice of VOM in Ghana has not only helped victims receive restorative justice and emotional healing, improving access to justice for the poor and vulnerable, but has also contributed to reducing the load and pressure of cases placed on the courts, which causes the wheel of justice to turn grind slowly. As a result, rather than eliminating VOM in Ghana, efforts must be made to strengthen and institutionalize it.

Method of accumulation of preload loss of bolted joints due to rotational self-loosening caused by cyclic, transversal excitation

This paper presents a new method to experimentally characterize the rotational self-loosening behavior of bolted joints. Furthermore, a method to calculate the preload loss due to certain relative displacements of the clamped parts was developed. The method obtains all required calculation parameters from the experimental tests performed and neither needs further experimental determination of friction coefficients nor numerical simulations to predict the preload loss. The method accumulates the preload loss of load cycles. Thereby, it can be used to estimate the time a machine can operate until a critical amount of preload is lost. Non-linear dependencies of the preload loss to the displacement amplitude and the remaining preload are considered. The calculation method also applies to load cases with variable load amplitudes. This is validated experimentally.

Experimental investigation of microchannel heat sink performance under non-uniform heat load conditions with different flow configurations

Cooling methods for multiple hotspots with high heat flux pose a reliability threat to electronic devices. This study investigates the microchannel-based heat sink performance under various non-uniform heat load conditions for different geometry with three different flow configurations (I, U and Z). An in-house designed Heater Array Unit (HAU) facilitates the generation of both uniform and non-uniform heat loads using a heater power supply. Two different microchannel geometries were employed, namely, microchannel-1 (MC-1) with channel and fin widths of 0.6 mm and 0.33 mm, respectively, and MC-2 with dimensions of 0.64 mm and 0.572 mm. Each microchannel incorporates three manifold configurations (I, U, and Z). Each flow configuration is regulated by flow control valves. Various non-uniform heat load patterns were considered, including streamline, non-streamline, and across-streamline conditions. To assess the thermal performance of the heat sinks the parameters used are thermal resistance (Rth), Nusselt number (Nu), and temperature non-uniformity (Ѱ). Experimental findings indicate that the MC-2 design with an I flow configuration is more suitable for uniform heat load conditions. On the contrary, for some non-uniform heat load cases MC-1 also showed up as a suitable design over MC-2.

Experimental investigation on adaptive concrete slabs equipped with integrated fluidic actuators

One possible approach for saving structural mass and related emissions is to design adaptive load-bearing structures, i.e. actively reducing deformations under changing loads through actuation. This paper describes the application of a methodology based on influence matrices to identify a feasible actuator size for actuator placement in reinforced concrete slabs under multiple load cases. The design is implemented in a physical prototype comprising a concrete slab with a clear span of 2 m x 2 m, being equipped with fluidic actuators that are controlled via a cascade controller. Experimental tests show that the displacement response of the adaptive slab under twice the design load can be kept equal to that of the passive slab under the design load. Thus, proof of concept is provided that considerable material savings can be achieved by employing integrated fluidic actuators in two-way slabs.

Abstract PO1-09-05: Reversing Rural Disparity Through Increased Access to Breast Care Using Model of Academic-Community Collaboration

Abstract Background: Rural disparity in Breast Cancer (BC) often relates to poor geographic access. We are small county in rural North Carolina with historically poor outcomes, including more advanced stages of BC at presentation, higher mastectomy rates, and higher BC-specific mortality rates than elsewhere. Beginning in 2002 we increased access to care by construction of a 19-bed Critical Access Hospital. With a higher median age population (10 years older), and cancer as the number one cause of death (30% of all deaths), we began to increase access to services with focus on cancer. Two decades later, we still do not provide all aspects of care locally, but through a model of collaboration we have increased access to all aspects of cancer care. Breast Cancer is the most common, and this report details the reversal in disparity seen rurally based on our model of collaboration with both a regional community cancer program and academic cancer program. Methods: We partnered with academic and community cancer centers in nearby counties to increase access to imaging, cancer specialists, radiation therapy and chemotherapy services, and support services for breast care. When we could not provide these services locally, we helped navigate patients to these other facilities to improve access. We invited dedicated breast surgeon from community cancer program to attend clinic weekly in our area. We created virtual breast-specific tumor boards to discuss 100% of cases prospectively, with improved access to pathologists, geneticists, fellowship-trained imaging specialists, breast surgeons and other multi-disciplinary care members (reconstructive surgery, PT/OT, integrative medicine, GYN). We became cancer accredited with both COC and NAPBC. We compare metrics pre/post-improvements. Results: Baseline: 1. Mortality rates: (2002-2006) 5-year BC mortality rates in our region averaged 32.3/100,000 population which was in the top quartile for the state, 30% higher than the state average. 2. Stages at presentation: 47% of BC stages were early (stages 0/1) in our service region compared to 62% elsewhere (NCDB data). Stage IV represented 6% in our region versus 4% elsewhere. 2500 mammograms/year at hospital at baseline. 3. Surgery/Radiation Therapy: Mastectomy rates averaged >50% in region, with correspondingly lower breast conserving rates than elsewhere due to lack of access to breast surgeons and radiation therapy services locally. Closest RT facility 80 miles. 4. Distances to high quality breast care averaged 150 miles. Closest Academic/Community Cancer Program 2-hour drive (one way). Post Collaboration: 1. Mortality rates: (2015-2019), 5-year BC mortality rates in our region averaged 16.3/100,000 population which is in the lowest quartile, 20% lower than the state average. 2. Stages at presentation: 74% of BC stages are early (stages 0/I) in our region versus 68% elsewhere. Stage IV now below parity with 3% locally versus 4% nationally. More than 5100 mammograms/year done currently at local hospital. 3. Surgery/Radiation Therapy: Mastectomy rates average 21%, with partial mastectomy rates of 79% in our area versus 70% elsewhere (NAPBC data) with RT services available locally. 4. Distances to quality breast care average 20 miles, and we are nationally accredited program in breast care as a critical access hospital. Analytic case load is now triple baseline numbers. Conclusion: We reversed the trend in rural disparity in breast cancer outcomes through model of collaboration. We increased screening rates locally, doubling the number of screening/diagnostic exams, increased the percentage of early stage at diagnosis, halved our mastectomy rates, and reduced BC-specific mortality 50% relative to baseline (and now 20% lower than state). We are now at parity with most BC-specific quality metrics reflecting a huge shift in rural disparity, which could only be achieved rurally through collaboration. Reversing Rural Disparity Through Increased Access to Breast Care Using Model of Academic-Community Collaboration This table depicts the changes in our region over time, which have brought us to parity with Breast Care nationally. Citation Format: Charles Shelton, Antonio Ruiz. Reversing Rural Disparity Through Increased Access to Breast Care Using Model of Academic-Community Collaboration [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-09-05.

Mechanical anisotropy induced by the competition between twinning and basal slip of AZ31 magnesium alloy under biaxial tension

The mechanical behavior of a hot-rolled Mg AZ31 plate was studied under biaxial tensions along two perpendicular loading axes of x and y in the ND-TD plane, with the x-axis aligned at a 45° counterclockwise angle from the TD (ND and TD refer to the normal direction and transverse direction). A complex strain partitioning in two loading axes is observed with the variation of stress ratio σxx:σyy. For σxx:σyy= 1:1 and 1:1.5, the strains along the x- and y-axes, εxx and εyy, are both positive. However, With the stress ratio of σxx:σyy= 1:3, εyy remains positive, while εxx becomes negative. Interestingly, for σxx:σyy = 1:2, εxx changes from negative during the early stage of loading to positive upon failure. Crystal plasticity simulations and theoretical calculations reveal that the observed strain transition. The reasons for the strain transition with stress ratio is related to the competition between {101¯2} twinning and basal slip. For {101¯2} twinning, the accommodated strains by most of the twins are εxx>0 and εyy>0 for all the stress ratios considered. For basal slip, most of the basal variants accommodate a positive y-axis strain, while for loading cases with low stress ratios, most of the basal variants result in a negative x-axis strain. As the stress ratio decreases, basal slip becomes more active, while the activity of {101¯2} twinning gradually decreases, leading to the observed strain transition. For σxx:σyy = 1:2, the transition from negative to positive is related to the increasing activity of {101¯2} twinning with strain. Theoretical calculations reveal that the competition of basal slip and {101¯2} twinning under biaxial tension is determined by the variation of their Schmid factors with σxx:σyy.

A two-scale method to include essential behavior of bolted connections in structures including elevated temperatures

A two-scale method is proposed to simulate the essential behavior of bolted connections in structures including elevated temperatures. It is presented, verified, and validated for the structural behavior of two plates, connected by a bolt, under a variety of loads and elevated temperatures. The method consists of a global-scale model that simulates the structure (here the two plates) by volume finite elements, and in which the bolt is modelled by a spring. The spring properties are provided by a small-scale model, in which the bolt is modelled by volume elements, and for which the boundary conditions are retrieved from the global-scale model. To ensure the small-scale model to be as computationally efficient as possible, simplifications are discussed regarding the material model and the modelling of the threads. For the latter, this leads to the experimentally validated application of a non-threaded shank with its stress area. It is shown that a non-linear elastic spring is needed for the bolt in the global-scale model, so the post-peak behavior of the structure can be described efficiently. All types of bolted connection failure as given by design standards are simulated by the two-scale method, which is successfully validated (except for net section failure) by experiments, and verified by a detailed system model, which models the structure in full detail. The sensitivity to the size of the part of the plate used in the small-scale model is also studied. Finally, multi-directional load cases, also for elevated temperatures, are studied with the two-scale method and verified with the detailed system model. As a result, a computationally efficient finite element modelling approach is provided for all possible combined load actions (except for nut thread failure and net section failure) and temperatures. The two-scale method is shown to be insightful, for it contains a functional separation of scales, revealing their relationships, and consequently, local small-scale non-convergence can be handled. Not presented in this paper, but the two-scale method can be used in e.g. computationally expensive two-way coupled fire-structure simulations, where it is beneficial for distributed computing and densely packed bolt configurations with stiff plates, for which a single small-scale model may be representative of several connections.

Mining and Medicine in 1872-1954: The Doctors of Waratah Hospital, Tasmania, Part 2

The published clinical case load of the doctors of the Waratah Hospital, Tasmania between 1901 and 1920 is described with emphasis firstly on the accidents occurring in the mines, and the subsequent support of the victims over a twenty year period, then secondly on the infectious diseases in the community in the era before antibiotics and vaccines.

Evaluation of an experimental kelp farm’s structural behavior using regression modelling and response amplitude operators derived from in situ measurements

An experimental kelp farming system for exposed ocean conditions was designed, deployed, planted with kelp and instrumented for evaluation of its dynamic response to ocean waves, tides, and currents. The farm featured a novel “lattice” mooring design and anchor lines and cultivation lines (horizontal lines used as kelp growth substrate) made of fiberglass rods. The farm was deployed at a site in Saco Bay, Maine with 13 m (MLLW) water depth. There the farm was exposed to waves with heights up to 5.9 m. Anchor line tension, tide and wave height time series were gathered and processed into response amplitude operators (RAOs) and least squared error linear regression models enabling recognition of meaningful patterns between the forcing factors and the mooring response. Mean mooring line tensions were shown to increase nonlinearly with tide. Anchor line tension response amplitudes were shown to exhibit high sensitivity to both low and high frequency wave forcing. Numerical free-release test simulations suggested natural frequencies in heave of 0.91 Hz, indicating that tension response sensitivities at high frequency could be the result of resonance. Low frequency tension response disproportionate to the low frequency wave forcing could be explained by wave forcing on kelp cultivation arrays modulated by wave group envelopes. Instances of high magnitude, potentially damaging peak tensions, deemed shock loads, were prevalent in most load cases. Anchor line tension dynamics including RAO and shock load magnitudes were shown to be sensitive to mooring stiffness (ratio of tension to resulting elongation) and, in some cases, significant wave amplitude. Patterns of anchor line response indicated that additional mooring elasticity or geometric compliance and use of floatation with less sensitivity to high frequency waves could help avoid the cause of and costly consequences of amplified high frequency loading and high amplitude shock loading. RAOs and regression model results also indicated a subdued response in frequencies associated with ocean swell waves, suggesting desirable performance in waves most dominant in extreme storm events. With the proposed improvements, the farm system design suggests merit as a robust and durable macroalgae biomass production platform.

Heliostat Consortium: Gap Analysis on State of the Art in Wind Load Design

Abstract Wind loads are a major driver of heliostat cost. Standardized methods and tools are needed for a more detailed understanding of the static and dynamic loads of a heliostat design. This will enable cost reduction of wind-dependent heliostats to avoid unnecessarily conservative heliostat designs and increase field efficiency and reliability to reduce the risk of component failures due to high-wind events. Gaps related to wind load include lack of site characterization for wind measurements, insufficient critical load cases for heliostat design, Insufficient understanding of turbulence impacts on heliostat tracking error, lack of knowledge on wind load under various heliostat array configurations, and underexplored heliostat field wind load reduction and operating strategies. Recommended pathway forward is to develop wind load and site characterization guidelines for heliostat design and develop heliostat field wind load models with optical performance impacts.

Radiation exposure of patients during endourological procedures.

Considering the existing gaps in the literature regarding patient radiation dose (RD) and its associated risks, a systematic review of the literature on RD was conducted, focusing on percutaneous nephrolithotomy (PCNL), extracorporeal shock wave lithotripsy (SWL), and ureteroscopy (URS). Two authors conducted a literature search on PubMed, Web of Science, and Google Scholar to identify studies on RD during endourological procedures. Two thousand two hundred sixty-six articles were screened. Sixty-five publications met the inclusion criteria using the PRISMA standards. RD was generally highest for PCNL, reaching levels up to 33mSv, 28,700 mGycm2, and 430.8mGy. This was followed by SWL, with RD reaching up to 7.32mSv, 13,082 mGycm2, and 142mGy. URS demonstrated lower RD, reaching up to 6.07mSv, 8920 mGycm2, and 46.99mGy. Surgeon experience and case load were inversely associated with RD. Strategies such as optimizing fluoroscopy settings, implementing ultrasound (US), and following the ALARA (As Low As Reasonably Achievable) principle minimized RD. This is the first systematic review analyzing RD, which was generally highest during PCNL, followed by SWL and URS. There is no specific RD limit for these procedures. Implementation of strategies such as optimizing fluoroscopy settings, utilizing US, and adhering to the ALARA principle proved effective in reducing RD. However, further research is needed to explore the factors influencing RD, assess their impact on patient outcomes, and establish procedure-specific reference levels for RD.

M‐AGC tangent visco‐plastic operator with hardening/softening, and application to the visco‐plastic relaxation analysis of stable and unstable problems using fracture‐based geomechanical interfaces

AbstractA previous perfect visco‐plastic constitutive formulation of the Perzyna type incorporating the concepts of prescribed stress increments and m‐AGC tangent operator (m‐Assumed algorithmic generalized compliance tangent operator) is extended to the case of Hardening/Softening (H/S). This extension is possible thanks to the closed‐form solution developed for the evolution of the loading function during a visco‐plastic time step. The formulation is then applied to constitutive modeling of zero‐thickness interfaces on the basis of a well‐established fracture‐based elasto‐plastic formulation, which in this manner is extended to visco‐plasticity. The resulting model is implemented in the finite element (FE) and small‐strain context by using both a standard Newton Raphson scheme for physical visco‐plasticity in which visco‐plastic time corresponds to physical time, and a Visco‐Plastic Relaxation (VPR) scheme, in which time corresponds to a fictitious time governing the transition from the elastic to the inviscid elasto‐plastic response. The numerical implementation is verified satisfactorily for common loading cases at interfaces such as pure tension (mode I) opening and shear‐compression (mixed‐mode) cracking/sliding, showing that the visco‐plastic results match the predictions of the fracture mechanics inviscid model in the long term. In addition, it is also shown that the VPR strategy developed is capable of providing temporary stability while the equilibrium path is recovered during instability events such as a snap‐back in the load‐displacement curve. This feature opens the door to a number of potential advanced applications of the formulation developed in the geomechanical context.