Premature Failure Research Articles

PD-Free Design of Insulation Systems: An Application to Laminated Busbars

The reliability of components of industrial electrical assets fed by power electronics might be at risk due to the type and extent of electrothermal stresses. The move of power electronics toward higher levels of voltage, switching frequency, slew rate, and specific power increases the risk of partial discharge inception and thus of accelerated extrinsic aging and premature failure. The reaction to this challenge is to embrace the concept of partial discharge-free (PD-free) design and operation. This paper presents a PD-free approach to the design of laminated busbars, considering both AC and DC insulation subsystems, and focusing on surface insulation. The availability of a recently proposed model to estimate the inception field is a key tool. The model is validated through PD measurements performed on a laminated busbar, using new automatic software that can identify the type of source generating PD. Combined with electric field calculations, the model provides estimates of the PD inception voltage which are almost coincident with the measurement results. Inception voltages in the order of 10 kV and 20 kV have been observed for AC and DC excitation, respectively. In the case of DC supply, tests at different ambient temperatures, 25 °C and 60 °C, indicate that the inception voltage does not change significantly with temperature. Disposability, scalability to any voltage/power, and capability to work, potentially, for any other type of insulation system, are interesting features of the proposed approach, which are discussed in the paper.

Use of bore-epoxy anchorage system with CFRP laminates for shear strengthening of RC beams: An experimental and analytical investigation

Shear strengthening of reinforced concrete (RC) beams with externally bonded reinforcement (EBR) using carbon fiber reinforced polymer (CFRP) plates and sheets have become a widely accepted practice. To avoid the associated premature debonding failure, this study presents an experimental and analytical investigation on the use of bore-epoxy as an anchorage system for CFRP plates and sheets bonded on both sides of shear deficient RC beams of rectangular cross-sections. Nine (9) RC beams were prepared and strengthened with CFRP plates and sheets as EBR with bore-epoxy anchorage system considering different bore diameters and tested under four point bending. The results indicate that RC beams strengthened with bore-epoxy anchorage system have high shear strength as compared with the unstrengthened control beam and those strenghtended with the conventional EBR approach (without boring). The increase in the shear strength over the control beam was found to be up to 67 % and 121 % for cases of CFRP plates and sheets, respectively. Moreover, the increase of shear strength in comparison with the conventional EBR method ranged from 9.33 % to 20.36 % for CFRP plates and from 12.97 % to 36.10 % for CFRP sheets. Consistently, the contribution of bore-epoxy on the shear strength increased with the increase of bore diameter. Consequently, the existing formulas in the ACI440.2 R for predicting the shear strength of FRP strengthened RC beams were modified to incorporate the improvement made by the proposed bore-epoxy approach. The revised models predicted the experimental shear strength of RC beams, strengthened with bore-epoxy, with a good level of accuracy with average mean absolute percentage error (MAPE) = 6.07 %, 14.71 %, normalized mean square error (NMSE) = 0.097, 0.16, and coefficient of determination R2 = 0.912, 0.974 for plates and sheets, respectively.

Cellular Immunity Against BK Polyomavirus in Kidney Transplant Recipients: A Comprehensive Review.

BK polyomavirus (BKPyV) is an important opportunistic viral infection that complicates kidney transplantation. Uncontrolled viral replication may result in BKPyV-associated nephropathy (BKPyVAN), a major cause of premature allograft damage and failure. In the continued absence of proven treatments, management relies on the empirical reduction of immunosuppression to facilitate an effective host immune response to clear the virus. This may be complicated by the risk of allograft rejection. There is compelling evidence that cellular immune responses are key to establishing control after viral reactivation. Measurable peripheral BKPyV-specific T cell responses temporally correlate with declining viral loads and subsequent clearance. Conversely, these responses are delayed or absent in BKPyVAN. How these peripheral findings correspond to the intragraft response, and whether BKPyV-specific T cells contribute to the immunopathology of BKPyVAN, remains poorly understood. Molecular techniques have provided some insights; however, these have been unable to fully discriminate BKPyVAN from cellular rejection to date. Furthermore, the contributions of components of innate cellular immunity, such as natural killer cells, are not known. Herein, we review the role of cellular immunity in BKPyV infection in kidney transplant recipients. We discuss advances in the understanding of how the development, phenotype, and functionality of these responses may determine the balance between viral control and immunopathology, and how this knowledge is being translated into tools to prognosticate and guide individualized immunosuppression reduction. Lastly, we consider how further elucidation of these responses may inform the design of therapies that would revolutionize how BKPyV is managed after transplantation.

Non-HLA Autoantibodies Against Angiotensin II Receptor 1 (AT1R) and Endothelin A Receptor (ETAR) in Pediatric Kidney Transplantation

Antibody-mediated rejection (AMR) is the leading cause of premature kidney transplant failure. The role of alloantibodies against Human Leukocyte Antigens (HLA) has been a primary focus in AMR. More recently autoantibodies and alloantibodies against the angiotensin II receptor type 1 (AT1R) and the endothelin A receptor (ETAR) have been linked to poor allograft outcomes in kidney transplantation. Nevertheless, evidence supporting routine testing remains insufficient. ELISA testing for anti-AT1R and anti-ETAR antibodies was performed in a pediatric renal transplant cohort. We selected 12 pediatric recipients who had undergone protocol biopsies and antibody measurements at 6 and 24 months post-transplant. Immunohistochemistry was performed on biopsies for AT1R and ETAR as well as the adhesion molecules ICAM-1 and VCAM-1. The analysis showed that ICAM-1 and VCAM-1 expression was significantly increased, along with the presence of circulating antibodies, in patients at 24 months post-transplant compared to patients without circulating antibodies. The presence of anti-AT1R and anti-ETAR antibodies does not seem to influence the expression of their receptors in the transplanted organ. Instead, the increase in adhesion molecules may precede the development of histological damage. Therefore, enlarging the cohort and extending long-term observation would help to understand the impact of anti-AT1R and anti-ETAR antibodies after transplantation.

Tuning Interfacial Characteristics of Epoxy Composites Towards Simultaneous High Thermal and Dielectric Properties

AbstractAchieving excellent thermal and dielectric performance is crucial to prevent premature insulation failure of epoxy in high‐frequency transformers. However, interfaces introduced by embedding micro/nano fillers in epoxy have opposite effects on these properties. Here, the interfacial characteristics of micro‐BN/nano‐Al2O3 epoxy is tailored composites by modifying nano‐Al2O3 with functional amine groups, leading to simultaneous improvements in thermal conductivity and high‐frequency breakdown strength. After modification, thermal conductivity increased from 0.193 to 0.490 W m−1 K−1 at 25 °C, and breakdown strength improved from 85.4 to 94.8 kV mm−1 at 10 kHz. The findings revealed the coexistence of overlapping interfaces between micro‐BN and chemical interfaces between modified Al2O3‐NH2 and matrix in composites. Contrary to the overlapping interface, the chemical interface played a more pivotal role in macroscopic performance. Calculations based on a covalent bonding interfacial model demonstrated that this in‐situ tight interface facilitated phonon transport, thereby enhancing thermal conductivity. Besides the physical structure, an increase in electrostatic potential in the chemical interface also impeded charge migration, resulting in an improved breakdown strength. The synergistic effect of the chemical interface on thermal and dielectric properties presents a promising design strategy for developing high‐performance epoxy composites.

Investigation of Abnormal Level Control Oscillations in a BWR Feedwater System

In the long-term operation of nuclear power plants, the aging of systems, structures, and components can lead to maintenance issues that must be dealt with to maintain cost-effective plant operations. One common issue affecting the currently operated boiling water reactors is the onset of unexpected level oscillations in feedwater heaters. This phenomenon can cause excessive cycling of drain valves and lead to premature failures. In this work, we develop a dynamic model of a set of feedwater heaters to determine the root cause of oscillations observed in an operating plant. Simulation results of various transient scenarios were used to investigate the effects of the controller parameters, boundary conditions, and possible valve and instrument issues. The analysis led to the conclusion that the most likely causes of the observed self-sustained oscillations in the system are the nonlinear behaviors of the drain valve and the level transmitter induced by degraded equipment condition. A partial plug of the pressure line used for level sensing in the system can account for a significant deadtime in the level transmitter, a nonlinear effect shown to induce self-sustained oscillatory behaviors.

Sanding Performance and Wear Mechanism of Precision-Shaped Abrasive Belts for Medium-Density Fiberboard

Sanding in medium-density fiberboard (MDF) often encounters unstable quality and premature failure, primarily because there is currently no abrasive belt specifically suitable for MDF sanding characteristics. We designed two precision-shaped abrasive belts (PSAs) for MDF and herein report on the characteristics. The material removal process for PSA was divided into three phases; the most stable, phase II, represents the effective working period. Compared to the contrast accumulated abrasive belt, PSAs achieve 16.12 and 11.10 times higher surface quality based on the mean value of roughness parameter Sa, achieving 1.34- and 2.0-, and 15.61- and 8.54-times-higher stability in material removal and surface quality based on the mean deviation. Wear patterns on PSAs include large abrasive wear, micro-abrasive fall-off, fracture, and wear, avoiding premature failure due to blockage and promoting long-term and efficient sanding. The uniform shape, height, and distribution of particles in PSAs results in excellent sanding performance. This study provides the foundation for further research on sanding mechanisms and PSA design for MDF.

Bending Failure Behavior of Thin-walled Composite Tube Structures

Abstract The bending failure, failure load and failure mode of thin-walled circular tubes made of carbon fiber reinforced resin matrix composites were investigated by experiments and numerical simulation. Three typical failure modes of circular tubes under bending load were observed in experiments, and the characteristics and mechanisms of different failure modes were analyzed. The results show that interlaminar shear induces the generation and propagation of microcracks at the interface of circular tubes, which accelerates the failure of circular tubes. In the bending failure process, because the interlayer performance of the round pipe is relatively low, it is the weak link of the structure, and the pipe wall is the first to produce interlayer delamination and splitting failure under the action of shear stress, resulting in structural instability and premature fracture failure. The lay-up and initial defects of thin-walled round pipe have great influence on the bending failure mode and failure load.

Fast and Efficient Mitigation of Coupled Axial-Torsional Drillstring Vibrations through State-Feedback Linear-Quadratic-Integral (LQI) Control

Summary In the exploitation of subsurface hydrocarbon and geothermal energy, more than 50% of total expenses are typically attributed to drilling and well completion. Coupled triaxial vibrations in the drilling system, excited by various mechanical, hydraulic, and geological sources, are major causes of premature downhole tool failures, excessive bit damage, compromised hole quality, reduced rate of penetration (ROP), and increased nonproductive time. Drillstring dynamic models, shock absorption tools, and controllers have been developed since the 1960s to understand and mitigate detrimental vibrations in the drilling system, aiming for smoother and more efficient operations. With advancements in measurement/logging while drilling technologies, rig equipment, mud pulse/wired pipe telemetry, and the digitalization of drilling engineering, a foundation has been established for proactive drilling vibration detection, analysis, and control to achieve efficient and safe drilling. In this study, a reduced-order axial-torsional drillstring dynamic model with soft string lateral contacts is first developed. Nonlinear drilling boundary conditions and inputs, such as bit-rock interactions (BRIs) with torque-on-bit (TOB) velocity-weakening effects, wellbore-drillstring contacts/friction, drillstring gravity, mud buoyancy, and more, are defined within the modeling framework. Equilibrium states and linearization of the model are derived for any given weight-on-bit (WOB) and rotational speed (RPM) setpoints, 3D well trajectories, and drillstring dimensions. A linear-quadratic-integral (LQI) controller is developed and tested for drillstring vibration suppression using a 6,562 ft (2000 m) drillstring model. In comparison to commercially available controllers for stick/slip mitigation, which are designed based on impedance matching and only address the decoupled drillstring torsional dynamics, the proposed state-feedback LQI controller emphasizes the coupling between the axial and torsional drillstring dynamics by simultaneously controlling WOB and RPM. Simulation results demonstrate that the LQI controller can suppress stick/slip and stabilize downhole WOB within 7 seconds, while a commercial drilling controller takes more than 35 seconds to achieve the same. Additionally, valuable insights and potential future directions for nonlinear drillstring vibration mitigation and drilling controller design are provided. With its fast drilling dysfunction stabilization time, small downhole RPM/WOB overshoots, minimal rig control inputs, robustness against drilling nonlinearities, and high efficiency, the proposed multi-input-multi-output state-feedback drilling controller holds great potential for application in proactive drilling vibration control, drilling automation, and real-time drilling optimization.

Testing the strength of thin feather-edge monolithic multilayered zirconia crowns: A pilot study with a novel acoustic test

Intoduction: Limited research has explored the mechanical characteristics of recently introduced multilayered monolithic zirconia (MZC) crowns with feather-edge margins design. Moreover, most of the conventional techniques for evaluating the mechanical behavior of brittle dental ceramics rely on destructive tests, making it impossible to precisely evaluate real strength values due to premature crack initiation detection failure. Objectives: The main objective of the study was to assess the load capacity of translucent multilayered monolithic zirconia crowns with feather-edge margin thicknesses of 0.4 mm and 0.5 mm. Additionally, the research introduced a novel non-destructive acoustic emission testing (AET) technique in the laboratory to identify early cracks in dental ceramics. Methods: Forty multilayered zirconia crowns produced using computer-aided design and computer-aided manufacturing (CAD/CAM) technology were evenly divided into two groups, each with distinct feather-edge margin thicknesses: 0.5 mm (group 1) and 0.4 mm (group 2). These crowns were securely cemented onto customized polymethyl methacrylate (PMMA) dies using a universal restorative glass ionomer. Subsequently, the crowns underwent a compressive axial loading test, controlled by an innovative AET crack detection system rooted in the principles of non-destructive laboratory testing. Fractographic analysis was conducted to determine the location of crack or eventual fracture. Results: The proportion of MZCs with a crack was statistically higher than the proportion with a fracture in the whole sample (p<0.001). In addition, the results showed that the crowns in group 1 exhibited higher loading values than those in group 2. The mean loading capacity in group was 911.2 N ± 614.7 N. Two locations of crack and fracture were registered: occlusal and marginal. No statistical association was observed between the two groups for the location of cracks or fractures. Conclusions: The feather-edge crowns with a 0.5 mm margin thickness had a higher loading capacity than those with a 0.4 mm. However, the latter supports loads that exceed occlusal force in the oral cavity suggesting that 0.4 mm feathered edge MZCs may be a valid and less invasive alternative to thicker margins. The novel load-to-fracture AET setup proved effective in detecting early crack initiation, suggesting it as a promising method for assessing the mechanical properties of brittle materials prior to failure, potentially impacting the field of dentistry. However more advanced research is needed to enhance the accuracy of the proposed technique. Clinical implications: The examined MZC demonstrates the ability to withstand occlusal forces in a patient’s mouth, offering clinical practitioners the option of embracing minimally invasive dentistry through the use of 0.4 mm feather-edge MZC in their treatment options. Furthermore, the positive results from the innovative acoustic emission testing technique, facilitating early crack detection, indicate a promising future for studying the behavior of brittle materials in dental laboratory testing.

Experimental and numerical study of corrugated anchors for CFRP plates

Carbon fibre reinforced polymer (CFRP) plates are promising materials for cables and prestress tendons in structural engineering for the excellent tensile performance, light in weight and anti-corrosion character. Anchoring has always been the main challenge of this high-performance material due to its anisotropy and brittleness. Corrugated anchors are high-efficiency friction-based anchorage devices. Nevertheless, premature failure of the CFRP plates can still be observed with this type of anchors, and the anchor efficiency for the corrugated anchors needs further improvement. This paper proposes a novel configuration of corrugated anchors. Experimental tests are then carried out to investigate the influence of the pre-tensioning bolt load and adhesive layer. Consequently, numerical analysis is conducted to reveal the anchoring mechanism. The results indicate the traditional corrugated anchors lead to non-uniform stress distribution in the CFRP plate, and with the proposed configuration the anchor efficiency can be increased up to 100%.

Influence of Engine Oil Degradation on Sliding Bearings, with Special Focus on Different Degrees of Nitration

Bismuth (Bi) can be considered for use as a green substitute for lead in bearing applications. However, accelerated Bi oxidation can occur during operation, creating a brittle surface and resulting in premature seizure failure. Thus, the aim of this study was to evaluate the influence of engine oil degradation, especially nitration processes, on the oxidation of Bi. Tailor-made artificially aged oils with different degrees of nitration were produced and utilized in static bearing oxidation tests. By means of X-ray photoelectron spectroscopy (XPS), the Bi surfaces were analyzed regarding their chemical compositions after the tests. The results were correlated with the respective oil conditions determined via conventional parameters as well as high-resolution mass spectrometry. The findings obtained revealed a direct correlation between the amount of Bi-oxide and the nitration values of the oil, proving there was a positive impact of nitration products on the oxidation of the Bi surfaces. A comparison with the Bi content in the oils demonstrated a protective effect of the oxide layer as the Bi content declined with an increase in nitration. Overall, valuable insight into understanding the impact of oil condition on engine parts is given, and the importance of testing engine parts with aged lubricants is emphasized.

Full robustness-based decision-making computational approach for RC structures subjected to multiple hazards

Existing RC structures show accidental loadings vulnerabilities because of inadequate design detailing causing in premature failure. The installation of a certain reinforcement measure on the susceptible structure is a common option to mitigate these fragility. At this time, reinforcement measures aided by the participation of stakeholders are crucial to combat multiple hazards. However, previous studies did not necessarily dealt with the integration multi-hazard loss, multi-uncertainty, and dependence configuration in a performance-based engineering decision-making framework, to retrofit selection from the robustness of structures perspective. In this paper, an efficient fuzzy full robustness-based decision-making framework is proposed to tackle the challenge of integration of multi-uncertainty and dependence, and further to avoid biased strategies. This framework contained Probabilistic Multi-hazards Fuzzy Global Vulnerability (PMFGV), Loss (PMFGL), and Robustness Assessment (PMFRA) for structures, by incorporating the fuzzy theory and Vine-Copula tree structure. The mentioned robustness index can be used as a reference indicator in the rehabilitation and retrofitting planning. The PMFRA-based making-decision methodology is applied to RC structures with three design schemes, which were established the platform OpenSEEsPy. Results confirm that the established assessment framework is effective in evaluating actual RC structures’ robustness. The fuzzy full robustness index for the frame S-RC, SS-RC, and RS-RC, was < 0.327, 0.421, 0.470 > , < 0.400, 0.503, 0.523 > , < 0.356, 0.453, 0.507 > , respectively. Whether the robustness-cost-based or the Cumulative Prospect Theory-based, the robustness of the reinforcement strategy with the installation of secondary beam (SS-RC) outdistance that of the additional reinforcement ratio (RS-RC). Such parameters are suggested as reasonable and meaningful making-decision index for selecting the optimal retrofitting schemes for structures subjected to multiple hazards, which leads to a balance between the enhancement of full robustness and reduction of life cost.

Experimentally optimized anchored-FRP method: A high-strength, cost-effective and ease-to-install technique for concrete rehabilitation

Conventional EB-and NSM-FRP techniques tend to prematurely fail in FRP delamination, suggesting inefficient utilization of the FRP materials. Various anchorage systems have been developed by integrating FRP anchors with FRP patches or groove bond to maximize the utilization of FRP materials. This study proposes a simpler but robust method that can make full use of FRP materials while minimizing the need for groove excavation, FRP patches, epoxy adhesive and surface preparations. The reinforcement was achieved by externally bonding FRP reinforcement to the concrete surface, with bent anchors being embedded into the strengthened elements. 51 experiments were conducted to demonstrate the potentials of the proposed method, which successfully prevented premature debonding failure, thereby offering robust rehabilitation solutions with a reduction of up to 42 % in epoxy usage compared to current methodologies. The results also suggested the impact of key parameters, such as cross-sectional area, embedment depth, and multi-reinforcement arrangement, on the effectiveness of the proposed FRP technique. Based on the experimental findings, discussions and recommendations were presented to facilitate the continued advancement of the proposed FRP methodology, aiming to fully develop FRP strength and minimize the need for FRP materials and epoxy adhesive in comparison to the current anchored FRP methods.

Underwater Structurally‐Colored Adhesives for Visualized Adhesion Monitoring in Aqueous Media

AbstractAssessment of the local strain/stress changes of adhesives is highly desirable for their service to avoid premature failure. However, monitoring local strain/stress variations in adhesives in practical settings remains challenging, especially in aqueous media. Here, an underwater structurally‐colored adhesive for visualized local strain/stress monitoring in aqueous media is reported. The structurally‐colored adhesive is obtained by shearing composites of poly(butyl acrylate‐co‐acrylic acid) copolymer and carboxylated polystyrene colloidal particles. The resultant structurally‐colored adhesive exhibits underwater adhesive strength (i.e., 238 kPa for stainless steel substrates) to various substrates (e.g., metals and plastics) thanks to hydrophobic segments and carboxyl groups. Notably, they can shift color in response to external force, enabling real‐time visual monitoring of localized strain/stress changes. As a proof of concept, the structurally‐colored adhesive can be used to seal a leaking hole on a bottle or tube, and it can precisely visualize the localized pressure distribution, providing critical information on the adhesion performance and the local pressure. These distinctive properties make the structurally‐colored adhesive suitable for application in wet environments as a real‐time visual pressure tracking device.

The impact of the filling technique with two sealers in bulk or associated with gutta-percha on the fatigue behavior and failure patterns of endodontically treated teeth.

The present in vitro study aimed to evaluate the fatigue behavior of teeth filled with a calcium silicate-based sealer (Bio-C Sealer, BC) or an epoxy resin-based sealer (AH Plus, AH), in bulk or associated with gutta-percha as main core material. Seventy-two sound human maxillary anterior teeth were initially selected. Sixty of them, were randomly chosen, and had their root canals prepared using nickel-titanium reciprocating instruments, being again randomly assigned to five experimental groups (n = 12): C+ (control + prepared but not filled); BC-B (BC in bulk); BC-GP (BC+ gutta-percha); AP-B (AH in bulk); AP-GP (AH+ gutta-percha). An additional negative control group (C-) was considered (n = 12), consisting only on sound teeth, without preparation and filling. The specimens were submitted to a survival analysis after the cyclic fatigue test. Sound teeth (C-) presented the best fatigue performance (P < 0.05), being similar only to the AP-GP group (P > 0.05). Despite that, all experimental groups showed similar fatigue behavior (P > 0.05) to C+ (BC-B = BC-GP = AP-B = AP-GP = C+). Based on that, it can be seen that the use of gutta-percha, as a main core material, associated with the AH Plus sealer, reestablished the mechanical fatigue performance of endodontically treated teeth comparable to sound teeth, still consisting on the most promising approach to rehabilitate such scenario. Teeth filled in bulk, had discreetly higher risk of premature failures and inferior fatigue performance.

Fracture Analysis of 316L Specimens Fabricated via Material Extrusion Additive Manufacturing: Influence of Building Orientation and Notch Acuity

ABSTRACTThree‐point bending tests were performed on notched specimens extracted from cuboids of 316L stainless steel produced via material extrusion additive manufacturing. The cuboids were printed vertically and horizontally on the printing platform to account for the building orientation effect on the mechanical performance. For each orientation, three notch sizes were considered. Overall, the specimens printed with building direction parallel to the loading direction outperformed the others. A significant notch size effect was observed in these specimens since the sharpest notch provoked a decrease in the peak load reached by the specimens in comparison with larger notches. On the contrary, this effect was less relevant among the other specimens, which presented a conspicuous amount of residual porosity that contributed to the premature failure. Further investigations were carried out to correlate the building orientation to the density of the parts and, ultimately, to the investigated mechanical properties. The ASED and TCD criteria were also applied to assess their accuracy in the failure prediction of the tested specimens.

Bearing Characteristics of Deep Cement Mixing Integrated Drilling, Mixing and Jetting Piles Based on Numerical Simulation

The Deep Cement Mixing Integrated Drilling, Mixing and Jetting (DMJ) technique has been developed through the installation of high-pressure spray holes at the mixing blades, with the objective of enhancing the bearing capacity of deep-mixed piles in the Yellow River floodplain. In order to enhance the bearing capacity of the foundation, variable-modulus piles and capped piles were incorporated within the DMJ piles. Engineering applications have demonstrated that DMJ piles can effectively address the issue of foundation reinforcement in the Yellow River floodplain region, minimize the wastage of cement, and reduce the environmental pollution associated with waste slurry. Nevertheless, a comprehensive study of the relevant factors is still lacking in the available literature. This study addresses this gap by conducting a numerical simulation of these two types of DMJ piles based on the preliminary field test data, with the objective of analyzing both the single-pile-bearing characteristics and the composite foundation-bearing characteristics. Furthermore, the study seeks to optimize the DMJ pile’s structure based on the simulation results. The findings demonstrate that the premature failure of a single pile during the bearing process can be averted if the modulus of the pile core reaches a minimum of 0.3 GPa or if the pile cap thickness exceeds 1 m. The utilization of large-diameter drilling, stirring and spraying piles can markedly enhance the bearing capacity of the composite foundation and mitigate the differential settlement of pile and soil. The spacing of the pile has been identified as a significant factor influencing the differential settlement of pile and soil. Consequently, this study also examines the impact of pile spacing on the differential settlement of piles and soil.

Load transfer behavior of 3D printed concrete formwork for ribbed slabs under eccentric axial loads

3D printed concrete (3DPC) has primarily been used for non-structural applications, with limited exploration into its potential for structural load-bearing applications. This is mainly due to the layered structure of 3DPC and the lack of compatibility of conventional reinforcement strategies to be integrated within the 3D concrete printing process. The post-tensioning of 3DPC structures presents an effective solution to improve the load-carrying capacity and cracking behavior of 3DPC. However, understanding the load transfer behavior and failure modes of 3DPC structures under a particular post-tensioning configuration are crucial to determine the permissible post-tensioning load for a structure without premature failure and to understand the distribution of stresses within the concrete structure under post-tensioning loads. The current study aims to investigate the load transfer behavior and failure mode of a 30 mm thick 3DPC formwork designed for one-way ribbed slabs when subjected to end-anchorage post-tensioning. For this purpose, a series of mechanical characterization and load transfer experiments were conducted on ribbed 3DPC formwork. The mechanical characterization investigations involved examining the compressive and flexural strength, as well as the elastic modulus of 3DPC, under various loading orientations relative to the print path. In the load transfer experiments, the end anchorage post-tensioning system was simulated by applying the axial load to the specimen via end plates bonded to the specimen. The variable parameters of the load transfer experiments were the boundary conditions, the eccentricity of the axial load from the neutral axis, and the topology of the ribbed 3DPC formwork. A digital image correlation system was used to study the axial and transverse strain evolution during the load transfer experiments. The experimental results showed that, regardless of the eccentricity of the applied load, the ribbed 3DPC formwork specimens exhibited higher axial load capacity when the load was applied near the bottom flange rather than the top flange. This was because of the reduced effective cross-sectional area for compression when the load was positioned near the top flanges, a consequence of the selected formwork topology, where top flanges were discontinuous to allow for pouring of the cast concrete within the formwork.

Addressing thermal challenges in hydrodynamic bearings: A contemporary review of strategies and technologies

Hydrodynamic bearings are integral components in various industrial sectors, including aerospace, defense technologies, and power generation units etc. Advancements in modern technology have driven the evolution of bearings to withstand the high temperatures, increased speeds, and additional load demands of contemporary operations. Some of the prime consequences of high temperatures include thermal deformation, misalignment, viscosity degradation, reduced oil film thickness, reduced load carrying capacity and premature failure due to bearing seizure. Researchers have rigorously addressed the persistent thermal challenges posed to hydrodynamic bearings, achieving significant advancements over the years. Key developments include innovative bearing pad designs, optimal materials, coating technologies, advanced computational software, novel lubrication methods, and efficient monitoring techniques. The introduction of materials with tailored properties such as high heat conductivity, high strength, and low-friction coatings has greatly enhanced bearing performance. Additionally, advanced computational software like ANSYS CFX, Fluent, and COMSOL, adaptive lubrication methods, and real-time temperature sensors have significantly improved the performance of critical systems, including hydro power plants. This review paper summarizes significant developments and investigations carried out to mitigate thermal effects in hydrodynamic bearings, and hence provides a comprehensive in depth details of the subject matter. Even though there has been a lot of progress in the field of hydrodynamic bearings, continuous research is important to tackle issues related to sustainability, industry-specific obstacles, developing technologies, and dynamic operating conditions.