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The paper presents experimental studies of an asymmetric multi-bolted connection at the preloading state. Design assumptions and structure of a stand for testing forces in bolts in a multi-bolted connection were introduced. The tightening process was conducted with a wrench, monitoring the values of the forces in the bolts using a calibrated measuring system based on resistance strain gauges. The measurement data was processed using the Matlab R2018b Simulink program. Two methods of bolt tightening were tested: in one pass (in which the bolts were tightened in a specific sequence and each bolt was tightened immediately to the full preload value) and in several passes (in which the bolts were also tightened sequentially but the full preload value was applied to the bolts in three tightening cycles). The influence of the method and sequence of bolt tightening on the distribution of force values in bolts during and at the end of the preloading state was investigated. The results were statistically processed and summarized in the form of diagrams showing the distributions of normalized force values in the bolts for all the considered tightening cases. The tests were carried out for the selected connection and an assembly method was proposed which would make it possible to achieve the most even distribution of the force values in the bolts at its end, and thus before the connection exploitation state.

In the paper, experimental studies of an asymmetric preloaded seven-bolted connection are presented. The tightening process of the connection was carried out with a wrench, monitoring the values of the bolt forces with a calibrated strain gauge measuring system. Two methods of bolt tightening were tested: in one and several passes. After all bolts were tightened, the selected bolts were removed, simulating bolt failure under the loading conditions of the connection. The influence of the method and sequence of bolt tightening on the distribution of bolt forces values after the introduction of failure states of some bolts was investigated. The results were statistically processed and presented in the form of graphs showing the distributions of normalised bolt forces values for all the considered failure cases.

Unplanned machine downtimes lead to higher costs through reduced productivity. Machine availability is amongst others limited by the failure of wear-induced preload loss of ball screws. Therefore, attempts are made to monitor the preload. The high complexity and required robustness of preload monitoring leads to a low spreading in industry so far. This paper investigates the capability of sensor fusion based on principal component analysis to monitor preload loss of single nut ball screws. Features are investigated using different preload levels of the ball screw by selecting different ball-diameters. It is shown that this approach reliably detects the preload levels. [ABSTRACT FROM AUTHOR]

Aiming at the problem of batch breaking of bolts at the blade root of wind turbine in a wind farm, to analyze whether the fracture was caused by fatigue damage, the method of finite element simulation and field test was used. The stiffness behavior of the blade bolt connection system and fatigue life of the blade bolt were studied. The fatigue life calculation results of blade bolts were combined with the fracture analysis of blade bolts to confirm that the fracture of blade bolt was caused by fatigue damage. A method of reducing the stiffness of blade bolts to improve their fatigue life was proposed, and the optimization scheme of fine bolt was designed, implemented and verified on site. The results show that the fatigue fracture location of blade bolt is mainly within ± 45 degrees of leading edge, which is consistent with the simulation results. The improved fine-rod bolt scheme reduces the stress amplitude of the blade bolt by about 13%, which improves the fracture of blade bolt obviously in the field application. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aim of this study is to design and test a new, simple, and reusable linear variable differential transformer (LVDT)-based in situ bolt preload monitoring system (L-PMS) during fastening of a truck wheel assembly. Instead of measuring the elongation of a bolt, the distance between the end surfaces of both the bolt and nut was monitored via the L-PMS. The distance obtained from the L-PMS was experimentally correlated with the actual preload measured by a washer-type load cell. Since the variation of the distance is related to the stiffness of the bolt and clamped parts, a finite element analysis was also conducted to predict the sensitivity of L-PMS. There was a strong linear relationship between the distance and bolt preload after the bolt and nut were fully snugged. However, a logarithm-shaped nonlinear relationship was irregularly observed before getting snugged, making it difficult to define a clear relationship. In order to tackle this issue, an arc-shaped conductive line was screen-printed onto the surface of the clamped parts using a conductive carbon paste. The results show that a resistance variation of the conductive line during fastening enables to determine the snug point, so the L-PMS combined with resistance measurement results in an approximately ±6% error in the measurement of bolt preload. The proposed L-PMS offers a simple but highly reliable way for measuring bolt preload during fastening, which could be utilized in a heavy-truck production line.

Background In mechanically ventilated patients, changes in breathing patterns may affect the preload, causing stroke volume fluctuation. Pulse pressure variation (PPV) and systolic pressure variation (SPV) are dynamic means of the hemodynamic monitoring in ventilated patients. No study on PPV and SPY in children has been reported to date. Objective To study changes in PPV and SPY values in mechanically ventilated children. Method A descriptive cross􀁏sectional study was done at the Pediatric Critical Care Unit (PICU), Cipto Mangunkusumo Hospital, Jakarta. Subjects were mechanically ventilated children aged > 12 months. Echocardiography was performed in all patients to determine the cardiac index. Arterial pressure was measured by connecting an arterial line to a vital signs monitor. PPV and SPV were calculated using the standard formulas. Bivariate correlation tests were performed between cardiac index and PPV and between cardiac index and SPV. Receiver operator characteristic (ROC) curve analysis was done to determine the optimum PPV and SPV cut-off points to predict normal cardiac index (2:3.5 L/minute/m2). Results Eighteen patients were enrolled in the study, yielding 48 measurements. Mean cardiac index was 2.9 (SD 1-2.6) L/minute/m2. Median PPV was 18.9 (range 4.1-45.5)% and SPV was 12.1 (range 3.8- 18.9)%. We found strong negative correlations between PPY and cardiac index (r= ; p = ) and SPY and cardiac index (r= ; p = ). To predict nonnal cardiac index, the optimum cut-off point was 11.4% for PPV (100% sensitivity, 100% specificity) and 9.45% for SPV (91.7% sensitivity, 100% specificity). Conclusion In mechanically ventilated children, cardiac index is negatively correlated with PPV and SPV.

The aim of this study is to design and test a new, simple, and reusable linear variable differential transformer (LVDT)-based in situ bolt preload monitoring system (L-PMS) during fastening of a truck wheel assembly. Instead of measuring the elongation of a bolt, the distance between the end surfaces of both the bolt and nut was monitored via the L-PMS. The distance obtained from the L-PMS was experimentally correlated with the actual preload measured by a washer-type load cell. Since the variation of the distance is related to the stiffness of the bolt and clamped parts, a finite element analysis was also conducted to predict the sensitivity of L-PMS. There was a strong linear relationship between the distance and bolt preload after the bolt and nut were fully snugged. However, a logarithm-shaped nonlinear relationship was irregularly observed before getting snugged, making it difficult to define a clear relationship. In order to tackle this issue, an arc-shaped conductive line was screen-printed onto the surface of the clamped parts using a conductive carbon paste. The results show that a resistance variation of the conductive line during fastening enables to determine the snug point, so the L-PMS combined with resistance measurement results in an approximately ±6% error in the measurement of bolt preload. The proposed L-PMS offers a simple but highly reliable way for measuring bolt preload during fastening, which could be utilized in a heavy-truck production line. [ABSTRACT FROM AUTHOR]

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.