Search Results (18)

The integrity of bolted components primarily relies on the quality of interfacial contact, which is achieved by maintaining prescribed bolt torque levels. However, challenges arise from corrosion-induced bolt head damage, potentially compromising the bolt preload, and quantifying such effects remains unanswered. Many studies often compare bolt corrosion’s effects to bolt loosening as both affect the interfacial contact stresses to some extent. This technical study aimed to investigate whether a correlation exists between the impact of bolt head damage and the different levels of bolt torque. Guided wave ultrasonic testing (UT) was implemented for this investigation. Laboratory experiments were conducted to monitor the transmission of ultrasonic signals across the bolted interface first during the bolt-tightening process. Once the highest bolt torque was achieved, the process was repeated for a simplified corrosion scenario, simulated by artificially damaging the bolt head in a controlled manner. The analysis focused on studying the transmission of signal energy for both scenarios. The findings revealed different trends for the signal energy transmission during bolt tightening, which are subjective to the inspection frequency. On the contrary, even at an advanced level of bolt head damage corresponding to 16% mass loss, no clear or monotonic trend was observed in the total transmitted energy. While the total energy remained relatively stable across all inspection frequencies, distinct waveform changes, such as energy redistribution and the emergence of additional wave packets, were observed. The findings emphasize the need for more advanced waveform-based analysis techniques to detect and interpret subtle changes caused by bolt degradation. Full article

In hydraulics, threaded plugs are used to close various manufacturing holes and other fluid channels. They are preloaded to ensure sufficient sealing force. Since the range of recommended thread and underhead friction coefficients for preloaded threaded connections in the literature is very wide, they are not suitable for accurate determination of the preload–torque relationships of plug–valve connections. In the study, two non-standard plugs with metric threads were equipped with strain gauges and repeatedly tightened three times in valve housings under lubricated and unlubricated conditions. The preload and tightening torque were measured. (1) Although the plug–valve connections had a similar geometry with the same surface roughness of the contacting surfaces, the average overall friction coefficient (uniform thread and underhead friction coefficient) and torque coefficient differed between the two connections in the unlubricated and lubricated conditions by 16% and 18%, respectively. This indicates that even small geometrical differences can have a considerable influence on these coefficients. The overall friction and torque coefficients were between 8% and 17% higher in the unlubricated condition than in the lubricated condition (not statistically proven). (2) The overall friction and torque coefficients decreased with repeated tightening under lubricated conditions. This influence decreased with the number of tightening repetitions. (3) Consideration of the minimum and maximum thread and underhead friction coefficients given in VDI 2230 would lead to an error in the estimated preload of −15% to +86%. In conclusion, for accurate determination of the preload–torque relationship of the plug–valve connections, measurements considering repeated tightening are crucial. These should be performed for each type and size of plug–valve connection separately. To minimize the repeated tightening influence, it is recommended to re-tighten the connections several times before leaving production. Full article

Screws are a versatile method of fixation and are often used in orthopaedic surgery. Various specialised geometries are often used for bone screws to optimise their fixation strengths in limited spaces at the expense of manufacturing costs. Additionally, ongoing research is looking to develop systems/models to automatically optimise bone screw tightening torques. For both applications, it is desirable to have a test rig for inserting screws in a regulated, instrumented, and repeatable manner. This work presents such a test rig primarily used for the validation of optimal torque models; however, other applications like the above are easily foreseeable. Key features include controllable insertion velocity profiles, and a high rate measurement of screw torque, angular displacement, and linear displacement. The test rig is constructed from mostly inexpensive components, with the primary costs being the rotational torque sensor (approx. 2000 €), and the remainder being approximately 1000 €. This is in comparison to a biaxial universal testing machine which may exceed 100,000 €. Additionally, the firmware and interface software are designed to be easily extendable. The angular velocity profiling and linear measurement repeatability of the test rig is tested and the torque readings are compared to an off-the-shelf static torque sensor. Full article

Our study presents a novel design for a cable-driven robotic arm, emphasizing low cost, low inertia movement, and long-term cable durability. The robotic arm shares similar specifications with the UR5 robotic arm, featuring a total of six degrees of freedom (DOF) distributed in a 1:1:1:3 ratio at the arm base, shoulder, elbow, and wrist, respectively. The three DOF at the wrist joints are driven by a cable system, with heavy motors relocated from the end-effector to the shoulder base. This repositioning results in a lighter cable-actuated wrist (weighing 0.8 kg), which enhances safety during human interaction and reduces the torque requirements for the elbow and shoulder motors. Consequently, the overall cost and weight of the robotic arm are reduced, achieving a payload-to-body weight ratio of 5:8.4 kg. To ensure good positional repeatability, the shoulder and elbow joints, which influence longer moment arms, are designed with a direct-drive structure. To evaluate the design’s performance, tests were conducted on loading capability, cable durability, position repeatability, and manipulation. The tests demonstrated that the arm could manipulate a 5 kg payload with a positional repeatability error of less than 0.1 mm. Additionally, a novel cable tightener design was introduced, which served dual functions: conveniently tightening the cable and reducing the high-stress concentration near the cable locking end to minimize cable loosening. When subjected to an initial cable tension of 100 kg, this design retained approximately 80% of the load after 10 years at a room temperature of 24 °C. Full article

Electrical accidents caused by bolt looseness in transformers have been frequently reported in recent years. The monitoring, and warning of, axial force as an indicator of looseness is one of the key issues affecting the operation and maintenance of transformers. Traditional ultrasonic testing and a patch-type ultrasonic method, using piezoelectric probes and coupling agents, showed poor repeatability and accuracy in detecting the bolt pre-tightening force, because of the uncertainty of the contact interface produced via manual operation. A permanent thin-film pressure sensor (PMTS), which provides accurate and in-situ stress detection, is more suitable for bolts, to reveal the pretightening force. The key is depositing a nano-zinc oxide (ZnO) piezoelectric film with an excellent measurement performance, which could be tuned using deposition parameters. This paper investigates the effects of the current and bias voltage on the crystal structure and performance of ZnO piezoelectric films. The results show that the crystallinity degree and resistance decrease with the increase in bias voltage, while the target current could increase the crystallinity. However, a high current also brings large particles in the coating surface, which greatly decrease the resistance. The cause is expected to be related to the ion energy, which could be affected by the bias voltage and current. The PMTS deposited with an optimized bias voltage and current revealed excellent measurement performance, and is expected to be applied to the bolt, to detect the pretightening force. Full article

Recently, there has been an increase in the number of reports on textile-based dry electrodes that can detect biopotentials without the need for electrolytic gels. However, these textile electrodes have a higher electrode skin interface impedance due to the improper contact between the skin and the electrode, diminishing the reliability and repeatability of the sensor. To facilitate improved skin–electrode contact, the effects of load and holding contact pressure were monitored for an embroidered textile electrode composed of multifilament hybrid thread for its application as a surface electromyography (sEMG) sensor. The effect of the textile’s inter-electrode distance and double layering of embroidery that increases the density of the conductive threads were studied. Electrodes embroidered onto an elastic strap were wrapped around the forearm with a hook and loop fastener and tested for their performance. Time domain features such as the Root Mean Square (RMS), Average Rectified Value (ARV), and Signal to Noise Ratio (SNR) were quantitatively monitored in relation to the contact pressure and load. Experiments were performed in triplicates, and the sEMG signal characteristics were observed for various loads (0, 2, 4, and 6 kg) and holding contact pressures (5, 10, and 20 mmHg). sEMG signals recorded with textile electrodes were comparable in amplitude to those recorded using typical Ag/AgCl electrodes (28.45 dB recorded), while the signal-to-noise ratios were, 11.77, 19.60, 19.91, and 20.93 dB for the different loads, and 21.33, 23.34, and 17.45 dB for different holding pressures. The signal quality increased as the elastic strap was tightened further, but a pressure higher than 20 mmHg is not recommended because of the discomfort experienced by the subjects during data collection. Full article

Using the MTS816 rock mechanics servo tester, an acoustic emission monitoring system and high-speed digital photographic equipment, uniaxial compression tests were conducted on granite specimens containing single fracture slabs after repeated treatment (treatment times 1, 5, 10, 15 and 20) with three types of high temperature (250, 350 and 450 °C) water cooling, respectively, to analyze the basic mechanical parameters, acoustic emission change characteristics and fracture evolution of the specimens during the uniaxial compression process. It is shown that the heating temperature and the number of treatments not only have a deteriorating effect on the basic mechanical parameters of the specimens but also have an important effect on the changes in the basic parameters of acoustic emission at different compression stages. At 250 °C, the acoustic emission characteristics of the specimens at the initial tightening stage tended to decrease (N = 1 and 5 times) then, increase (N = 10 and 15 times) and then decrease (N = 20 times) as the number of treatments increased. At the same set temperature, the percentage of the bottom amplitude value of the acoustic emission of the specimen gradually decreases, and the percentage of the high amplitude value gradually increases as the number of treatments increases. After the specimen undergoes one and five treatments at 250 °C, the maximum acoustic emission energy value changes less, the maximum acoustic emission energy value decreases with the increase of treatment times in an approximately exponential function, the specimen is transformed from the brittle damage mode to the plastic damage mode and the effect of the prefabricated fracture on the damage of the specimen gradually disappears. Full article

A sodium channel blocker mexiletine (MEX) is used to treat chronic pain, myotonia and some arrhythmias. Mutations in the pore domain (PD) of voltage-gated sodium channels differently affect tonic block (TB) and use-dependent block (UDB) by MEX. Previous studies identified several MEX-sensing residues in the hNav1.5 channel and demonstrated that the channel block by MEX increases with activation of the voltage-sensing domain III (VSD_III), whereas MEX stabilizes the activated state of VSD_III. Structural rationales for these observations are unclear. Here, Monte Carlo (MC) energy minimizations were used to dock MEX and its more potent analog, Thio-Me2, into the hNav1.5 cryo-EM structure with activated VSDs and presumably inactivated PD. Computations yielded two ensembles of ligand binding poses in close contacts with known MEX-sensing residues in helices S6_III, S6_IV and P1_IV. In both ensembles, the ligand NH₃ group approached the cation-attractive site between backbone carbonyls at the outer-pore bottom, while the aromatic ring protruded ether into the inner pore (putative UDB pose) or into the III/IV fenestration (putative TB pose). In silico deactivation of VSD_III shifted helices S4–S5_III, S5_III, S6_III and S6_IV and tightened the TB site. In a model with activated VSD_III and three resting VSDs, MC-minimized energy profile of MEX pulled from the TB site towards lipids shows a deep local minimum due to interactions with 11 residues in S5_III, P1_III, S6_III and S6_IV. The minimum may correspond to an interim binding site for MEX in the hydrophobic path to the TB site along the lipid-exposed sides of repeats III and IV where 15 polar and aromatic residues would attract cationic blockers. The study explains numerous experimental data and suggests the mechanism of allosteric modification of the MEX binding site by VSD_III. Full article

The aim of this study was to evaluate the stability of prosthetic screws after applying cyclic loadings in an “all-on-four” rehabilitation model with the OT Bridge system. The model was tested both with and without anterior screws. Four implant analogues following the “all-on-four” concept were inserted in an edentulous mandibular resin model. An OT Bridge system with a Cr–Co prosthetic framework was fabricated. Depending on the presence or absence of one or two anterior screws on the implant analogues, three groups were created, i.e., Gr.1: three tightening screws, Gr.2: two tightening screws, Control Group: four tightening screws. Each single group underwent subsequent 400,000 cyclic loads, simulating approximately a year of chewing by using a dynamometer machine. This cycle was repeated five times for each group, and preload loss values were evaluated on each prosthetic screw after each cycle. All the data obtained were analyzed by one-way ANOVA and Student’s t-test. No statistically significant differences after intragroup analysis were found. A statistically significant difference within the Gr.1 between the screws in positions 33 and 36, equal to 15.2% (p-value = 0.0176), was found. The OT Bridge seems a useful system to maintain the retention of a prosthesis during mechanical stress conditions even in the absence of one screw in an “all-on-four” rehabilitation. This could represent a good solution to solve the esthetic problem of the screw buccal access hole for fixed solutions. Full article

The stability and integrity of the abutment-implant connection, by means of a screw, is fallible from the moment the prosthetic elements are joined and is dependent on the applied preload, wear of the components and function. One of the main causes of screw loosening is the loss of preload. The loosening of the screw-abutment can cause complications such as screw fracture, marginal gap, peri-implantitis, bacterial microleakage, loosening of the crown and discomfort of the patient. It is also reported that loosening of the screw/abutment may lead to a failure of osseointegration. It is necessary to evaluate and quantify, with in vitro studies, the torque loss before and after loading in the different connections. Aim: evaluate the influence of implant- abutment connection design in torque maintenance after single tightening, multiple tightening and multiple tightening followed by mechanical cycling. Materials and Methods: 180 Klockner implants divided in 4 groups: 15 SK2 external connection, 25 Ncm tightening torque; 15 KL external connection, 30 Ncm tightening torque; 15 Vega internal connection, 25 Ncm tightening torque; 15 Essential internal connection, 30 Ncm tightening torque. In each group removal torque values (RTV) were evaluated with a digital torque meter, in 3 distinct phases: after one single tightening, 10 multiple tightenings and 10 multiple tightenings and cyclic loading (500 N × 1000 cycles). Results: After one single tightening, and for all connections, RTV were lower than those of insertion, but only for Essential and Vega internal connections this result was statistically significant. After multiple tightening, RTV were significantly lower in all connections. After repeated tightening followed by cyclic loading, mean RTV were significantly lower, when compared to insertion torque. The multiple tightening technique resulted in higher RTV than the single tightening technique, except for Vega implant. The multiple tightening followed by cyclic load, compared to the other phases, was the one that generated the lowest RTV, for all connections. Conclusions: The connection design, in our study, did not seem to influence the maintenance of preload. Loading influenced the loss of preload, in the sense that significantly decreased the removal torque values. The multiple re-tightening technique resulted in higher removal torque values than the single tightening technique. Clinically, our results recommend to retighten retaining screws, a few minutes after insertion. Full article

Uncontrolled hemorrhage remains a leading cause of death in both emergency and military medicine. Tourniquets are essential to stopping hemorrhage in these scenarios, but they suffer from subjective, inconsistent application. Here, we demonstrate how tourniquet application can be automated using sensors and computer algorithms. The auto-tourniquet self-tightens until blood pressure oscillations are no longer registered by the pressure sensor connected to the pneumatic pressure cuff. The auto-tourniquet’s performance in stopping the bleed was comparable to manual tourniquet application, but the time required to fully occlude the bleed was longer. Application of the tourniquet was significantly smoother, and less variable, for the automatic tourniquet compared to manual tourniquet application. This proof-of-concept study highlights how automated tourniquets can be integrated with sensors to provide a much more consistent application and use compared to manual application, even in controlled, low stress testing conditions. Future work will investigate different sensors and tourniquets to improve the application time and repeatability. Full article

Rail clips are essential components of rail fastening systems that clamp the rails to sleepers. Fatigue damage of rail clips has been recently reported in railway lines. However, there has been a lack of research investigating this fatigue issue. The KR-type rail fastening system has been recently developed and used in some domestic railways. This study aimed at evaluating the structural behavior and fatigue performance of the KR-type rail clip. The assembly test performed in the laboratory showed that the stresses induced in the rail clips after tightening, particularly at the stress concentration locations, exceeded the yield stress, indicating that the rail clip could be vulnerable to fatigue cracking when combined with the stress range during repeated trainloads. The finite element analysis results, which revealed a good correlation with the experiments, were used to evaluate the fatigue performance of the rail clip by adopting the modified Goodman fatigue criteria. The fatigue evaluation results indicated that when the vertical rail displacement during train operation exceeded 2 mm, the rail clips could potentially suffer from fatigue failure. Full article

Calculating Repeating Thermal Bridges (RTBs) for Timber Frame (TF) closed panels that could occur in Offsite Manufactured (OSM) Modern Methods of Construction (MMC), such as exterior walls for nearly-to-zero operational energy dwellings to be constructed in Wales, United Kingdom (UK) is discussed in this paper. Detailed calculations for linear RTBs due to the TF components are often neglected when evaluating thermal transmittance (known as U-values hereafter). The use of standard TF fractions does not allow the designer to perceive their detrimental impact on RTBs and consequent U-values for exterior walls. With the increase of the thermal performance of exterior walls and as such lower U-values due to ever-tightening Building Regulations, specifically related to the energy use and carbon emissions from the space heating of dwellings, then the impacts of RTBs requires more investigation. By not calculating the potential of linear RTB at the design stage could lead to a performance gap where assumed U-values for exterior walls differ from manufacture to onsite. A TF detail from the Welsh manufacture has been chosen as a case study, to develop and apply a methodology using manufacturing drawings to evaluate TF fraction and their effect on the thermal performance. Full article

Background: To compare the loss of preload in absence of loading and after a fixed number of cyclic loadings on 7-mm distal cantilever in two different connection systems using all-on-four prosthetic model. Methods: Two equal models of an edentulous mandible rehabilitated with all-on-four technique with two types of abutment system (MUA and OT-Bridge) supporting a hybrid prosthesis, were used. Initial torque values of the prosthetic fixing screw, after ten minutes from initial screw tightening and after 400,000 repeated loadings were registered using a mechanical torque gauge. Differences between initial and final torque values were reported for each anchoring system and the two systems were finally compared. Results: No statistically significant differences regarding the loss of preload between MUA and OT-Bridge system were found after 400,000 cyclic loadings; however, in MUA system it was found between anterior and posterior implant screws. A significant difference in preload loss was found only for MUA system comparing the initial screw torque to that measured after 10 min from the tightening in absence of cyclic loadings. Conclusions: Within the limits of the present study, MUA and OT-Bridge may be considered reliable prosthetic anchoring systems able to tolerate repeated cyclic occlusal loads on distal cantilever in all-on-four rehabilitation model without any significant loss of preload in screw tightening. Full article

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. Full article