Load Cases Research Articles

Numerical analysis of failure mechanics of concrete under true dynamic triaxial loading using a four-phase meso-model

In the present paper, the failure mechanics of concrete under true triaxial dynamic loading is investigated. A four-phase concrete meso-model is developed. The meso-model consists of aggregate, mortar, interfacial transition zone (ITZ) and macropores. A finite element (FE) model of a split Hopkinson pressure bar is also created to apply true triaxial dynamic loading. The development of cracks in concrete is presented for the uniaxial, biaxial and triaxial loading cases. The presence of local discontinuity is modelled, and its effect on the failure of concrete is extensively investigated and discussed. In the last, the effect of aggregate distribution is also analysed. It is found that the internal structure of concrete changes the stress distribution from true triaxial to compression or extension triaxial, which is the prime cause of internal cracking.

Total elbow arthroplasty in England.

The aim of this study was to review the provision of total elbow arthroplasties (TEAs) in England, including the incidence, the characteristics of the patients and the service providers, the types of implant, and the outcomes. We analyzed the primary TEAs recorded in the National Joint Registry (NJR) between April 2012 and December 2022, with mortality data from the Civil Registration of Deaths dataset. Linkage with Hospital Episode Statistics-Admitted Patient Care (HES-APC) data provided further information not collected by the NJR. The incidences were calculated using estimations of the populations from the Office for National Statistics. The annual number of TEAs performed by surgeons and hospitals was analyzed on a national and regional basis. A total of 3,891 primary TEAs were included. The annual incidence of TEA was between 0.72 and 0.82 per 100,000 persons before 2020 and declined to 0.4 due to a decrease in elective TEAs during the COVID-19 pandemic, with a slight recovery in 2022. Older patients, those of white ethnicity and females, were more likely to undergo TEA. Those who underwent elective TEA had a median wait of between 89 (IQR 41 to 221) and 122 days (IQR 74 to 189) in the years before 2021, and this increased to 183 days (IQR 66 to 350) in 2021. The number of TEAs performed by surgeons per annum remained unchanged, with a median of two (IQR 1 to 3). The median annual number of TEAs per region was three to six times higher than the median annual case load of the highest volume hospital in a region. Patients in the lowest socioeconomic group had a higher rate of serious adverse events and mortality (11%) when undergoing TEA for acute trauma. In England, TEA is more common in older age groups, those of white ethnicity, and females. The COVID-19 pandemic affected the incidence of elective TEA and waiting times, and the provision of TEA has not yet recovered. The Getting it Right First Time recommendation of centralizing services to one centre per region could result in up to a six-fold increase in the number of TEAs being performed in some centres.

Advancements in Biofiller-Reinforced PLA Composites for 3D Printing: A Review

Additive manufacturing is key in realizing highly complex and high-performance composite materials. Among all the various kinds of functionality that could be added to a composite component, continuous fiber-reinforced composites have been drawing much attention because of their attractive combination of properties. The comprehensive spectrum of knowledge that ranges from the basics concerned with structure, morphology, synthesis, physical, and chemical properties finally reaches to this analytical study of advanced composites. Most generally, such a composite is structured on a thermoplastic or thermoset polymer matrix that embeds the load-carrying reinforcing fibers; probably best known are carbon, glass, and aramid fibers. These composites, which involve fibers continuously reinforcing, have high strength relative to their weight. They are also anisotropic, meaning they have qualities that vary from one direction to another – something which might be customisable for specific load cases. They warp and shrink less during their life in an outside environment than conventionally made bioplastics due to a fact that short fibers can provide reinforcement to them. This 3-D printing object is manufactured by special additive manufacture technology during the manufacturing process after compounding and extruding the fiber-reinforced composite filament. The final properties of 3D printed parts could be tailorable through changing variables such a fiber type, fiber length, volume fraction, polymer matrix material, orientation of fibers, and printing process parameters. These continuous fiber-reinforced 3D printed composites could achieve tensile strengths up to one GPa, have stiffness values reaching even a rating of countless Gpa, and have ad thicknesses in the range from about 1.4–1.8 g/cm³. This finding could be applied in basically all major industries, from aerospace and the automotive industry to sports gear. Such conclusions from the analysis may be useful in the selection of appropriate materials and techniques while even guiding the development of new applications with respect to such advanced composite materials.

A theoretical framework for predicting the heterogeneous stiffness map of brain white matter tissue

Finding the stiffness map of biological tissues is of great importance in evaluating their healthy or pathological conditions. However, due to the heterogeneity and anisotropy of biological fibrous tissues, this task presents challenges and significant uncertainty when characterized only by single-mode loading experiments. In this study, we propose a new theoretical framework to map the stiffness landscape of fibrous tissues, specifically focusing on brain white matter tissue. Initially, a finite element (FE) model of the fibrous tissue was subjected to six loading cases, and their corresponding stress-strain curves were characterized. By employing multiobjective optimization, the material constants of an equivalent anisotropic material model were inversely extracted to best fit all six loading modes simultaneously. Subsequently, large-scale FE simulations were conducted, incorporating various fiber volume fractions and orientations, to train a convolutional neural network capable of predicting the equivalent anisotropic material properties solely based on the fibrous architecture of any given tissue. The proposed method, leveraging brain fiber tractography, was applied to a localized volume of white matter, demonstrating its effectiveness in precisely mapping the anisotropic behavior of fibrous tissue. In the long-term, the proposed method may find applications in traumatic brain injury, brain folding studies, and neurodegenerative diseases, where accurately capturing the material behavior of the tissue is crucial for simulations and experiments.

A Comparative Analysis of Active Control vs. Folding Wing Tip Technologies for Gust Load Alleviation

As part of the Ultra High Aspect Ratio Wing Advanced Research and Designs (U-HARWARD) project, funded by CS2JU, various gust load alleviation (GLA) technologies have been developed and studied. GLA plays a crucial role in the development of new generation ultra-high aspect ratio wings (UHARWs), as it reduces gust loads, thereby decreasing the structural weight of the wing and, consequently, the entire aircraft. This weight reduction enhances overall aircraft efficiency, enabling a higher aspect ratio. GLA technologies are categorized into passive systems, which require no active intervention, and active systems, where control surfaces redistribute the aerodynamic loads. In this study, passive GLA was implemented using a folding wing tip (FWT) developed by the University of Bristol, while active GLA employed a Static Output Feedback controller developed by Politecnico di Milano. Both approaches were compared against a baseline aircraft configuration. A flutter assessment confirmed that FWT does not introduce aeroelastic instabilities, ensuring the aircraft remains flutter-free across its flight envelope. A thorough comparison of load envelopes, based on nearly 2000 load cases across different flight points and mass configurations, was conducted in compliance with CS25 regulations, examining both positive and negative gust conditions. The results show a possible 15% reduction in the dynamic load envelope for both passive and active solutions. Using NeOPT, a hybrid finite element (FE) model was developed, with a detailed global FEM (GFEM) for the wingbox and stick elements for other components. Linear gust analyses in Nastran, with the hinge locked and released, provided high-fidelity results, comparing wing failure indexes and demonstrating the effectiveness of the FWT solution.

Barriers and Facilitators in Implementation of Nutritional Benefit Transfer to Tuberculosis Patients

Abstract Background Malnutrition & Tuberculosis (TB) form a vicious cycle. Nikshay Poshan Yojana (NPY) is a key strategy for a TB free India, that seeks to provide financial assistance for nutritional support to TB patients. The study is a qualitative study to identify operational challenges and facilitators in implementation of NPY Methods In Depth Interview (IDI) of 18 Senior Treatment Supervisor (STS) at Tuberculosis Unit (TU) and 19 Tuberculosis Health Visitor (TB HV) at Designated Microscopy Centre’s (DMC) was done. For further insights, the STS, at District Tuberculosis Centre, Lucknow was also interviewed. Informal discussion was done with about 50 Tuberculosis patients. We explored providers perspective on impact of NPY on other duties/services, case load, hours dedicated to NPY, practice protocols, record keeping and data management, compliances, capacity building needs, quality protocols, key enablers, motivating factors, challenges, best practices and beneficiary’s perspectives on quality of life, facilitators and challenges in availing services. Results Motivating leadership, supportive staff, good working relationship and seamless communication, teamwork, use of technology, supportive supervision & collaboration and support of NGO for private sector were the key facilitators. Barriers comprised system level barriers (Budget constraints, issues with NIKSHAY software and bank account), provider level barriers (shortage of human resource, nonfunctional tablets) and patient level barriers (stigma and bank account related challenges). The encouraging finding was majority of recipients, responding that they used the incentive to purchase ration, vitamin supplements etc. Conclusions NPY is having its intended benefit but there are barriers that need to be resolved for successful roll out. The study yield suggestions for removing barriers and found a set of innovations that can be replicated across other settings with high Tuberculosis burden Key messages • Malnutrition and Tuberculosis form a vicious cycle. Nutritional support to TB patients improves treatment outcome and can save lives. • Operational research on implementation of NPY offers insights for successful roll out of this key initiative across other resource limited settings in developing countries.

A Transition State Theory-Based Continuum Plasticity Model Accounting for the Local Stress Fluctuation

Based on the transition state theory, a continuum plasticity theory is developed for metallic materials. Moreover, the nature of local stress fluctuation within a material point is considered by incorporating the probability distribution of the stresses. The model is applied to investigate the mechanical behaviors of 316 L stainless steel under various loading cases. The simulated results closely match the results obtained by the polycrystal plasticity model and experiments. The mechanical behaviors associated with strain rate sensitivity, temperature dependence, stress relaxation, and strain creep are correctly captured by the model. Furthermore, the proposed model successfully characterizes the Bauschinger effect, which is challenging to capture with a conventional continuum model without additional assumptions. The proposed model could be further employed in the design, manufacturing, and service of engineering components.

Weight Minimization of Truss Using Strain Energy Density and Genetic Algorithm for Single and Multiple Load Cases

Weight Minimization of Truss Using Strain Energy Density and Genetic Algorithm for Single and Multiple Load Cases

Computational Analysis of the Micromechanical Stress Field in Undamaged and Damaged Unidirectional Fiber-Reinforced Plastics Using a Modified Principal Component Analysis

This study investigated the internal stress distribution of unidirectional fiber-reinforced plastics (UD-FRP) at the micro level using principal component analysis (PCA). The composite material was simulated using a representative volume element model together with the embedded cell approach. Two fundamental quasi-static load cases, transverse and longitudinal tensile deformation, were considered. The experimental results show that mechanical failure occurred at 2.15 ± 0.06% transverse tensile strain and at 1.52 ± 0.07% longitudinal tensile strain. Furthermore, the undamaged state and a combination of matrix and interface damage, as well as fiber breakage, were simulated. From the simulations, the octahedral shear stress and octahedral normal stress were computed at the integration points of the matrix elements, constituting what is known as the octahedral stress field. A modification on the PCA to obtain mesh-independent eigenvalues is presented and was used to investigate the effects of damage events on the octahedral stress field. The results indicate that each damage mechanism had a distinct signature in the redistribution of the stress field, characterized by specific changes in the eigenvalues and orientation of the principal component (θ1). Furthermore, the PCA suggests that the accumulation of matrix damage began to be relevant at the 1% strain, while fiber breakage began at an average longitudinal strain of 0.98 ± 0.12%. Additionally, it is shown that the first principal component served as an indicator of the predominant stress state of the stress field. This investigation suggests that the PCA can provide valuable insights regarding the complex damage mechanisms of UD-FRP that may not be captured by conventional mechanical analysis.

Experimental and Numerical Research on Fracture Properties of Mass Concrete Under Quasi-Static and Dynamic Loading

The dynamic fracture behavior of mass concrete is crucial to the dynamic analysis and safety evaluation of concrete dams subjected to strong earthquake shocks in the framework of fracture mechanics. In the presented research, cylindrical specimens with a ring of preset cracks were cast by three-graded mass concrete, and direct tension tests were performed with two loading rates considered, i.e., 10−6/s for quasi-static loading and 10−3/s for dynamic loading. The load–crack mouth opening displacement (P-CMOD) curves were obtained, from which the fracture toughness, fracture energy, and characteristic length of the mass concrete were obtained. In this process, the influence of the eccentricity in the tests was compensated by the numerical modeling of the tests. Next, the crack propagation process of the mass concrete was modeled using the extended finite element method. From the test results, it is found that, under quasi-static loading, the crack generally propagates along the interface between the aggregates and the matrix, while, under dynamic loading, more aggregates are fractured. As compared to the case of quasi-static loading, the energy absorption capacity, fracture energy, and fracture toughness increase for dynamic loading, while the characteristic length decreases. Moreover, the numerically predicted P-CMOD curves agree reasonably well with the experimental measurements.

Predicting the variability of the dynamics of bolted joints using polynomial chaos expansion

Friction and contact occurring in bolted joints can lead to highly nonlinear dynamics. Moreover, joints are prone to high sample-to-sample variability as well as low test-to-test repeatability. Notably, experimental work is increasingly highlighting the most influential sources of uncertainties. Nevertheless, randomness due to some uncertainties, such as surface imperfections, cannot be completely eliminated. Others, such as the actual applied bolt load, can be laborious to control. In this work, we aim to computationally predict the variability of numerical models of joints given such uncertainties. We perform the dynamic analysis using the Multi-Harmonic Balance Method (MHBM) to compute the forced, periodic response of the system. For probabilistic surrogate modeling, we use Polynomial Chaos Expansion (PCE). We show that PCE can be successful in studying the impact of ISO tolerances and uncertain bolt loads in the practical case where only a few numerical samples can be generated. We also show that an empirical error metric is unreliable and a validation error metric must be used. In addition, we assess using PCE to propagate uncertainties due to mesoscale imperfections, and highlight that unsuccessful PCE models indicate sensitive structural designs.

Experimental and numerical investigations into torsional-flexural behaviours of railway composite sleepers and bearers

Abstract Fibre-reinforced foamed urethane (FFU) composite sleepers and bearers are safety-critical components installed in complex railway switches and crossings. Not only does they need to provide vertical track support, the composite sleepers and bearers must also endure longitudinal and lateral actions stemming from complex wheel and rail interactions. In reality, the railway bearers at crossing noses are susceptible to coupling torsional-flexural loading. The complex non-linear behaviours have never been investigated numerically nor experimentally. It is thus necessary to comprehend torsional-flexural behaviours of FFU composite sleepers and bearers through finite element and experimental approaches. 3D finite element modelling of FFU composite beams have been established to predict the non-linear coupling behaviours. Three specimens of FFU beams have been prepared for robust experiments under each load case. Our studies exhibit excellent agreement between numerical and experimental results. The ductile failure behaviours (post yield point) have been observed from the experiments. Considerable effects of load eccentricity on the flexure–torsion behaviours of the composite members can also be noted. In addition, the load-eccentricity curves have been identified to portray the non-linear behaviour of the railway components under coupling flexural and torsional loadings. The new insights considering their load–displacement relationships, modes of failure and damage, flexural and torsional interactions are the precursors for railway engineers to design and adopt FFU composite sleepers and bearers in practice where complex wheel/rail interface generally causes coupling torsional and vertical loading conditions.

First Principles Variational Formulation and Analytical Solutions for Third Order Shear Deformable Beams with Simple Supports using Fourier Series Method

The Fourier series method for solving bending problems of third-order shear deformable beams (TSBD) is presented in this paper. The theory accounts for transverse shear deformation and is suitable for moderately thick beams. Transverse shear stress-free conditions are valid at the beam surfaces for TSDB. The field equations are two coupled ordinary differential equations in terms of two unknown displacement functions – transverse deflection w(x) and warping function For simply supported ends considered, the loading and unknown functions w(x) and are represented in Fourier series that satisfies the boundary conditions. The problem is reduced to a system of algebraic equations in terms of the Fourier coefficients wn and which is solved to obtain wn and Axial and transverse displacements fields, axial bending stress and transverse shear stress are then determined for the cases of point load at midspan, uniformly and linearly distributed loads over the span. The results are identical with previous results obtained by other scholars who used Ritz variational methods and other mathematical tools. For moderately thick beams under uniform load with l/h = 4, the results obtained for is 0.516% greater than the exact result by Timoshenko and Goodier while for thick beams under uniform load with l/h = 2, the result for is 1.96% greater than the exact result by Timoshenko and Goodier. Similar acceptable variation was obtained for for beams under linearly distributed load with the variations being less than 2% for l/h = 2. However, unacceptable variations of 68.37% were found for in thick beams under point load, for l/h = 2.0. The variation for however reduced to 12.513% for moderately thick beams under point load for l/h =4.

Evaluation of wind-induced response of high-rise structure with TMD system by real-time hybrid simulation test with motor-driven shaking table

Due to the difficulty in constructing the small-scaled model of tuned mass damper (TMD) system to meet the requirement of dynamic similarity law, it is hard to evaluate the vibration control effect of passive TMD system on the wind-induced response of high-rise structure by wind tunnel test. The Real-Time Hybrid Simulation (RTHS) test could provide a suitable solution to this problem by increasing the size of the scaled TMD model to overcome the limitation in dynamic similarity law. A RTHS test system with a linear electric motor-driven shaking table was developed by the interface with model interface toolkit in general real time system operating environment. Taking the Guangzhou New TV Tower with a passive TMD system as an example, the Finite Element (FE) model of Guangzhou New TV Tower was selected as the numerical substructure and TMD system was selected as the experimental substructure, the RTHS test was conducted at a sampling frequency of 250 Hz to estimate the wind-induced response of this high-rise structure with a TMD system in various dynamic wind loading cases. To reduce the time delay effect generated by the nonlinear interaction between motion control system and experimental substructure, the adaptive time series (ATS) compensator for time delay compensation was proposed in the RTHS test. The RTHS results were also compared with the numerical simulation results using the FE model of the investigated object. The RTHS test with additional ATS time delay compensator can obtain more accurate experimental results. The effectiveness of the proposed RTHS test system was testified to be powerful test system to evaluate the wind-induced response of high-rise structures with complex passive TMD system.

A frequency-dependent model for bone remodeling using a micromorphic porous medium subjected to harmonic mechanical loading

In this paper, the bone tissue was modeled as a linear viscoelastic material saturated with interstitial fluid. We considered a specific case of harmonic loading and related the mechanical stimuli to the loading frequency. In this way, we could include the inertial effect in the model while not having to deal with the perturbation during each loading period. Two types of mechanical signals were considered: strain energy and dissipation energy. A parametric study revealed the dependency of the two signals on loading frequency and material property. The evolution of the apparent mass density supported the parametric study’s findings. Under the three different frequency loadings, the strain energy-stimulated samples experienced identical remodeling scenarios. The samples stimulated with dissipation energy, on the other hand, exhibited a strong frequency dependence. An additional study was performed to investigate the effect of long-term variations in the loading frequency on the remodeling process. This demonstrated the model’s capabilities in designing and evaluating load regimes for rehabilitation following a bone injury or bone reconstruction.

The influence of anomalies in supporting structures on the validation of finite-element blade bearing models

Finite-element analysis is the only means to determine the load distribution of large slewing bearings considering flexible bearing rings and supporting structures. For reliable results, the plausibility of the models need to be validated. Previous attempts on validating a finite-element model of a slewing bearing against measurement results have indicated a huge dependence of the deformation on tolerances in the supporting structures. This dependence has not yet been explored in research in favor of a focus on tolerances of the bearing itself. The present work explores different irregularities of the flange that connects to the outer ring of the bearing and their effects on bearing deformation. The results show that single dents or bulges on the flange and inclined flanges of the adapter ring significantly change the load distribution and contact angles of the bearing. They also aggravate the risk of truncation. For the calculated fatigue life however, the bearings seem to be robust to these uncertainties for the shown load cases. The dimensions of the investigated tolerances are verified by comparing the resulting deformations of the bearing outer ring against experimental data.

DMATCH: A novel integrated testing method for floating wind turbine dynamics – Potential error and its impact

With floating offshore wind turbines (FOWT) steadily advancing towards large-scale deployments in deep water, the traditional wave basin model testing method shows its shortage to fulfill the testing requirement. To enhance the effectiveness of model tests for FOWT, this paper introduces a distributed model testing method, dMATCH (distributed-Mooring-Aerodynamics-Testing-Control-Hydrodynamics). The dMATCH method separates the experiment into aerodynamic testing in the wind tunnel and hydrodynamic testing in the wave basin, achieving integrated coupling through real-time data transmission using a data exchange system. Errors in sensor acquisition and actuator actuation during data communication may impact the accuracy of experiments. To investigate the potential error and its impact within dMATCH, an integrated model testing system in the wave basin was constructed. Four load cases were established, introducing varying magnitudes of normally distributed random errors to simulate acquisition and actuation inaccuracies. The investigation revealed a positive correlation between errors in experimental results and those in acquisition and actuation. As error increased, result fluctuations became more pronounced. Within the current experimental framework, acquisition error had a greater influence on results compared to actuation error, with aerodynamic thrust being more sensitive to error than the pitch and surge motions of platform. When acquisition and actuation errors were controlled below 5%, the relative RMSE of the results remained below 5%. The dMATCH method proposed in this paper offers a new approach for integrated model testing of FOWT, and the study of potential error impact is crucial to ensuring the reliability of this innovative testing method.

When confidence reveals more than recognition performance does: The case of context load.

Context in which events are embedded is often hypothesized to serve as an independent cue for retrieval. This means that any effects of context need to obey two basic principles of cue-dependent memory: Memory retrieval should be augmented when, first, encoding context is reinstated and, second, this context uniquely specifies individual items stored in memory. Both of these regularities are well supported for recall tests, but they remain contentious in recognition tests. Here, in three experiments, we assess whether unique and nonunique contexts affect memory processes when reinstated during recognition. However, rather than focusing on measures of recognition performance, we looked at confidence judgments collected during recognition that should be particularly sensitive to recollective effects resulting from context cuing. Experiments 1 and 2, using old/new and forced-choice recognition tests, respectively, documented positive effects of context reinstatement on confidence in correct recognition identifications, but only for contexts uniquely associated with individual items. These effects emerged even when there were no reliable context effects in recognition performance measures. Experiment 3 showed the same effect of context reinstatement, moderated by context load, when spontaneous recognition of a previous study episode occurred during restudy. These results demonstrate the role of context as an independent retrieval cue both in deliberate and spontaneous recognition. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Probabilistic risk analysis of local verification of Load Model 1 in Eurocode for Soil-Steel Composite bridges in Sweden

Bridges must be designed to ensure safety for all users. At the same time, the design should be performed with an appropriate risk level. In Sweden, Soil-Steel Composite bridges (SSCB) are the most common bridge type. For SSCB, local verification of Load Model 1 in Eurocode is most often governing the design. The objective of this study was to investigate whether local verification of LM1 load case could be modified without decreasing the agreed risk level in Eurocode. Weight in motion measurements from real traffic were extrapolated with Rice formula. Monte Carlo simulations were used to simulate the 1000-year return period event to obtain the acceptable risk level as prescribed in Eurocode. The results show that the local verification of LM1 is conservative, considering the acceptable risk level in Eurocode. With a modified implementation of local verification, this paper shows that a potential saving of up to 14% in terms of economic cost and CO2-equivalents is possible. A modified implementation of local verification of LM1 in Eurocode for SSCB is proposed, which could reduce the climate impact by up to 14% associated to the construction of new SSCB in Sweden.

Wear analysis of material measures and stylus probes in repetitive tactile calibration

Tactile industrial measuring instruments are frequently calibrated with material measures defined in ISO 5436–1 to ensure their function, determine their measurement uncertainty and assess the capability of measuring processes. Since these process needs to be repeated on a regular basis, the long-term stability of both material measures and the stylus is essential to enable a repeatable and reliable measurement. Since the tactile sampling of a material measure involves a mechanical interaction, there is the potential for wear when repetitive measurements are performed. We present a comprehensive experimental study on the effects of wear for different stylus instruments – including a reference plane scanning system and multiple skidded scanning systems. Multiple measurement methods are used to determine the state of the stylus and the surface of the material measure, both before and after their mechanical interaction. The impact of the wear on the accuracy of the results can be described, as can the connection between the wear and the hardness of the skidded probe. The study found that significant wear effects on surfaces with even >500 HV become qualitatively visible much earlier than they can be quantitatively detected, with extreme load cases of >1000 repetitive measurements at the same position being necessary to produce major wear influences. Thus, regular visual inspections in case of extensive repetitive measurements can be recommended, just as well as a low measuring force and a reduction of the number of measurements for measurement capability analysis to 12 measurements.