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The results of the experiments confirms that the torque-force graphs are made of passive and active sections. If we could determine a generalizable relation between the two sections, which would enable the programming of screwdriving machines in mass production in such a way that, based on the measured torque and considering passive resistances, a defined torque or angle could be applied to reduce the scatter of preload forces.

Classical analysis methods have shown that flexural, in-plane, deflections due to shear strain in the flange pack of preloaded bolted joints produce bending moments and tensile loads on bolts within the joint. These bending moments and tensile loads are most noticeable in joints that are required to support large in-plane loads and torsional moments. The shear loads on the bolt associated with the flexural deflections can result in the bolt head, or nut, slipping relative to the flanges. This slippage will in turn result in mechanical loosening of the joint. The bending moments associated shear loads and tensile loads produced by the combination of both out-of-plane and in-plane external loads and torsional moments are in addition to the bolt preload. These additional loads, combined with a high initial bolt preload, can cause yielding of the bolt, which can also result in relaxation of the initial preload. This article reviews earlier work in determining the tensile bolt stresses induced in preloaded bolts by the external loads and presents methods of calculating the amount of preload relaxation that could occur from each mechanism discussed.

The attenuation of bolt preload is a critical factor leading to bolt fatigue failure, whereas the study of the nonlinear attenuation behavior of preload and its mechanism during installation is an inevitable challenge in engineering practice. The attenuation of the preload of a bolt is mainly related to the stiffness of the bolt body as well as the stiffness of the connected parts. This study aimed to develop an experimental system to analyze the nonlinear attenuation behavior of preload during bolt tightening. First, a simulation system replicating the bolt installation process was constructed in a laboratory setting, incorporating blade and pitch bearing specimens identical to those used in a 10 MW wind turbine, restoring the stiffness coupling characteristics of the “composite-metal bearing” heterogeneous interface at the blade root through a 1:1 full-scale simulation system for the first time. Second, ultrasonic preload measurement equipment was employed to monitor preload variations during the bolt tightening process. Finally, the instantaneous preload decay rate of the wind turbine blade-root bolts and the over-draw coefficient were quantified. Experiments have shown that the preload decay rate of commonly used M36 leaf root bolts is 11–16%. If a more precise value is required, each bolt needs to be calibrated. These findings provide valuable insights for optimizing bolt installation procedures, enabling precise preload control to mitigate fatigue failures caused by abnormal preload attenuation.

A high-frequency, piezoelectric thin-film sensor was successfully deposited on a nickel-based superalloy bolt by radio frequency magnetron sputtering to develop a smart, nickel-based superalloy bolt. Ultrasonic response characterization, high accuracy, and repeatability of ultrasonic measurement of axial preload in nickel-based superalloy smart bolts are reported here and were fully demonstrated. The axial preload in the nickel-based superalloy smart bolt was directly measured by the bi-wave method (TOF ratio between transverse and longitudinal-mode waves) without using the traditional integration of a longitudinal and shear transducer. A model concerning the bolt before and after tensioning was established to demonstrate the propagation and displacement distribution of the ultrasonic waves inside a nickel-based superalloy smart bolt. The measured A-scan signal presented significantly favorable features including a mixture of transverse and longitudinal mode waves, a pure and broad frequency spectrum which peaked at 17.14 MHz, and high measurement accuracy below 3% for tension of 4 kN–20 kN. For the temporal ultrasonic signal, the measurement envelopes were narrower than for the counterpart of the simulation, justifying the ‘filtration’ advantage of the high-frequency sensor. Both the TOF change of the single longitudinal-mode wave and the TOF ratio between transverse- and longitudinal-mode waves increased linearly with preload force in the range of 0 kN to 20 kN. Compared with the commercial piezoelectric probe, the proposed probe, based on the combination of a high-frequency, piezoelectric thin-film sensor and a magnetically mounted transducer connector, exhibited high tolerance to temperatures as high as 320 °C and high repeatability free from some interference factors such as bolt detection position change and couplant layer thickness. The results indicate that this system is a promising axial preload measurement system for high-temperature fasteners and connectors, and the proposed sensor is a practical, high-frequency ultrasonic sensor for non-destructive testing.

Fluid administration leads to a significant increase in cardiac output in only half of ICU patients. This has led to the concept of assessing fluid responsiveness before infusing fluid. Pulse pressure variation (PPV), which quantifies the changes in arterial pulse pressure during mechanical ventilation, is one of the dynamic variables that can predict fluid responsiveness. The underlying hypothesis is that large respiratory changes in left ventricular stroke volume, and thus pulse pressure, occur in cases of biventricular preload responsiveness. Several studies showed that PPV accurately predicts fluid responsiveness when patients are under controlled mechanical ventilation. Nevertheless, in many conditions encountered in the ICU, the interpretation of PPV is unreliable (spontaneous breathing, cardiac arrhythmias) or doubtful (low Vt). To overcome some of these limitations, researchers have proposed using simple tests such as the Vt challenge to evaluate the dynamic response of PPV. The applicability of PPV is higher in the operating room setting, where fluid strategies made on the basis of PPV improve postoperative outcomes. In medical critically ill patients, although no randomized controlled trial has compared PPV-based fluid management with standard care, the Surviving Sepsis Campaign guidelines recommend using fluid responsiveness indices, including PPV, whenever applicable. In conclusion, PPV is useful for managing fluid therapy under specific conditions where it is reliable. The kinetics of PPV during diagnostic or therapeutic tests is also helpful for fluid management.

Introduction: Different implant–abutment connections have been developed to reduce mechanical and biological failure. The most frequent complications are loss of preload, screw loosening, abutment or implant fracture, deformations at the different interfaces, and bacterial microleakage. Aim: To review the evidence indicating whether the implant–abutment connection type is significant regarding the following issues: (1) maintenance of the preload in static and dynamic in vitro studies; (2) assessment of possible deformations at the implant–abutment interfaces, after repeated application of the tightening torque; (3) evaluation of the sealing capability of different implant connections against microleakage. Materials and Methods: In June 2020, an electronic literature search was performed in Medline, EBSCO host, and PubMed databases. The search was focused on the ability of different implant connections to maintain preload, resist deformation after tightening and retightening, and prevent microleakage. The related titles and abstracts available in English were screened, and the articles that fulfilled the inclusion criteria were selected for full-text reading. Results: The literature search conducted for this review initially resulted in 68 articles, among which 19 articles and 1 systematic review fulfilled the criteria for inclusion. The studies were divided according to the three proposed objectives, with some studies falling into more than one category (maintenance of preload, surface abutment–implant deformation, and resistance to microleakage). Conclusions: Conical abutment appears to result in fewer mechanical complications, such as screw loosening or fractures, and higher torque preservation. After SEM evaluation, damage was observed in the threads of the abutment screws, before and after loading in internal and external connections. Internal hexagon implants and predominantly internal conical (Morse taper) implants showed less microleakage in dynamic loading conditions. We suggest further studies to guarantee excellence in methodological quality.

In this study, a preload monitoring method using impedance signatures obtained from a piezoelectric-based smart interface is presented for bolted girder connections. Firstly, the background theory of the piezoelectric-based smart interface and its implementation into the health monitoring of bolted connections are outlined. A simplified electro-mechanical (EM) impedance model of a smart interface-embedded bolted connection system is formulated to interpret a mechanistic understanding of the EM impedance signatures under the effect of bolt preload. Secondly, finite element modeling of a bolted connection is carried out to show the numerical feasibility of the presented method, and to predetermine the sensitive frequency band of the impedance signatures. Finally, impedance measurements are conducted on a lab-scaled bolted girder connection, to verify the predetermined sensitive frequency range and to assess the bolt preload changes in the test structure.

Early management of sepsis and septic shock is crucial for patients’ prognosis. As the Emergency Department (ED) is the place where the first medical contact for septic patients is likely to occur, emergency physicians play an essential role in the early phases of patient management, which consists of accurate initial diagnosis, resuscitation, and early antibiotic treatment. Since the issuing of the Surviving Sepsis Campaign guidelines in 2016, several studies have been published on different aspects of sepsis management, adding a substantial amount of new information on the pathophysiology and treatment of sepsis and septic shock. In light of this emerging evidence, the present narrative review provides a comprehensive account of the recent advances in septic patient management in the ED.

Background For complex patients in the intensive care unit or in the operating room, many questions regarding their haemodynamic management cannot be answered with simple clinical examination. In particular, arterial pressure allows only a rough estimation of cardiac output. Transpulmonary thermodilution is a technique that provides a full haemodynamic assessment through cardiac output and other indices. Main body Through the analysis of the thermodilution curve recorded at the tip of an arterial catheter after the injection of a cold bolus in the venous circulation, transpulmonary thermodilution intermittently measures cardiac output. This measure allows the calibration of pulse contour analysis. This provides continuous and real time monitoring of cardiac output, which is not possible with the pulmonary artery catheter. Transpulmonary thermodilution provides several variables beyond cardiac output. It estimates the end-diastolic volume of the four cardiac cavities, which is a marker of cardiac preload. It provides an estimation of the systolic function of the combined ventricles. It is more direct than the pulmonary artery catheter, but does not allow the distinct estimation of right and left cardiac function. It is easier and faster to perform than echocardiography, but does not provide a full evaluation of the cardiac structure and function. Transpulmonary thermodilution has the unique advantage of being able to estimate at the bedside extravascular lung water, which quantifies the volume of pulmonary oedema, and pulmonary vascular permeability, which quantifies the degree of a pulmonary capillary leak. Both indices are helpful for guiding fluid strategy, especially in case of acute respiratory distress syndrome. Conclusions Transpulmonary thermodilution provides a full cardiovascular evaluation that allows one to answer many questions regarding haemodynamic management. It belongs to the category of “advanced” devices that are indicated for the most critically ill and/or complex patients.

The rotational performance of the spindle-bearing system has critical influence upon the geometric shape and surface roughness of the machined parts. The effects of preload and preload method on the rotational performance of the spindle-bearing system is explored experimentally to reveal the role of preload and preload method in spindle rotational performances under different speeds. A test rig on which both the rigid preload and elastic preload can be realized, equipped with variable preload spindle-bearing system, is developed. Based on the mechanical model, the relationship of the axial preload and negative axial clearance of the spindle-bearing system is provided. Rotating sensitive radial error motion tests are conducted for evaluating synchronous and asynchronous radial errors of the variable preload spindle-bearing system under different rotating speeds and preload methods. The change regularity of synchronous and asynchronous radial errors with preloads under different rotating speeds are given. The results show that the preload plays an important role on the rotational performance of spindle-bearing system. The rigid preload is more efficient in achieving better rotational performance than elastic preload under the same rotating speed. Furthermore, this article significantly guides the preload designing and assembling of the new spindle-bearing system.