Tightening Conditions Research Articles

Analysis of bolt load uniformity in raised flange connection

Aiming at the problem of uneven preload of raised flange, a model considering elastic interaction is established to study the uniformity of bolt load under raised flange connection. Firstly, the elastic interaction coefficient method of bolt flange connection structure is extended to multiple times, and the initial preload of all bolts at each tightening step is determined by analytical model; secondly, a three-dimensional finite element model of bolt flange connection structure is established, and the correctness of the finite element model is verified by comparing with the literature test, and the influence of tightening sequence and tightening steps on bolt preload is explored; finally, the results of raised flange under symmetrical tightening conditions with and without considering elastic interaction are compared and analyzed. The results show that when the tightening method is symmetrical tightening and the tightening steps are three steps, the elastic interaction of each bolt is the smallest, and the final preload uniformity is better; on this basis, the results of the model considering elastic interaction further improve the uniformity of the final preload and are closer to the target preload. The problem of bolt preload dispersion caused by elastic interaction is solved, and the research results can provide guidance for the safety and reliability design of bolt flange connection structure.

Development of a test bench for ventilation masks through 2D and 3D printing processes

ObjectiveMask choice is a key parameter in adaptation of ventilation through continuous positive airway pressure i.e. sleep apnea syndrome golden standard treatment. Two parameters of mask poor tolerance are cutaneous over pressure and unintentional leaks. The aim of this study was to create a test bench for masks to compare and localize cutaneous pressure areas, while monitoring leak flow. MethodsThe test bench is made of an artificial head on which customs-made pressure sensors were placed. The artificial head and the sensors were developed with various additive manufacturing technologies. Sensors measured electrical capacity variations (%VC) positively correlated with cutaneous pressure. For 4 different masks, different harness tightening conditions were tested. A flowmeter was used to monitor total leaks. ResultsWhen displayed on the nasal bridge of the artificial head, sensors detected tightening conditions: average of + 2%VC when harness was tight. This increase varied according to masks [1; 3]%VC and the sensors position [1.3; 2.2]%VC. ConclusionThis bench test allowed us to compare masks between them. Indeed it allowed us to localize and compare high pressure areas according to the mask. These data could be helpful for physicians and health professionals in the choice of the mask and for manufacturers in the development process

Ensuring the economic security of the country in the new geopolitical realities

The issue of ensuring Russia’s economic security is an important and priority task, especially in the tightening conditions of the consolidated sanctions policy of the European Union countries and the United States. The process of developing measures that allow Russian economy to develop sustainably and effectively counter the growing geopolitical threats is complex and requires a comprehensive and honest assessment, including the import dependence degree of business, the degree and level of involvement in global supply chains, the development level of domestic production, etc. For each assessment area, indicators should be identified that have a preventive nature and make it possible to detect a growing potential threat. In the research theoretical provisions on economic security are considered; existing threats to economic security in geopolitical realities are formulated; indicators presented by the Federal State Statistics Service are identified that allow assessing the threat degree; directions for ensuring economic security are developed.

Analysis of self-tapping screw joints in fibre glass reinforced PEI polymer used in the automotive industry

This article presents a study of the joining of polyetherimide (PEI) polymer parts reinforced with fibre glass which has great application in the automotive sector. A simulation model based on the finite element method is proposed. For the modelling of the polymeric material, the three-network viscoplastic (TNV) rheological model was used, with very adequate results and producing a good fit with the experimental data. In addition, a methodology is proposed that allows simplifying a three-dimensional to an axisymmetric model, which implies a notable reduction in computational cost. In addition, the work includes an experimental analysis that evaluates the tightening torque under conditions of assembly repetitiveness, relaxation over time and influence of thermal cycles. These scenarios have a different influence depending on the geometry of the self-tapping screw used. Regarding repetitiveness, it has been verified that PF-30 (CELOspArk®) loses 17.16% while in Δ-PT (DELTA PT®) it loses up to 41.93% in the tenth repetition. In contrast, in the relaxation over time scenario, the PF-30 loses 13.38% and the Δ-PT loses 17.82%. Finally, regarding the thermal cycles, cooling allows to slightly delay the loss of tightening torque in both screws in a similar way; however, in the heating stage, 36.89% is lost with PF-30 and only 14.66% with Δ-PT. This study represents an improvement in the knowledge of the joining processes of self-tapping screws with polymeric materials of an engineering nature. The simulation model can be easily adapted to other materials and other geometries, and the experimental study offers a vision of the evolution of tightening conditions in realistic operating scenarios.

Millennials and Early Retirement: An Exploratory Study

The article explores the extent to which working conditions and health factors shape Millennials’ preferences to retire early in the European context. On the one hand, Millennials’ approach to life and work potentially implies a preference to retire early. Yet, on the other hand, the ongoing trend of tightening conditions and penalizing early retirement, as well as the expected decrease in living standards in old age for Millennial cohorts, restricts options and discourages early retirement. The results indicate that Millennials across Europe do not explicitly express a wish to retire early. This holds true most prominently for Millennials who are healthy and satisfied with their job. The analysis employs a classification decision tree model as the main method.

Monitoring a Bolted Vibrating Structure Using Multiple Acoustic Emission Sensors: A Benchmark

The dataset presented in this work, called ORION-AE, is made of raw AE data streams collected by three different AE sensors and a laser vibrometer during five campaigns of measurements by varying the tightening conditions of two bolted plates submitted to harmonic vibration tests. With seven different operating conditions, this dataset was designed to challenge supervised and unsupervised machine/deep learning as well as signal processing methods which are developed for material characterization or structural health monitoring (SHM). One motivation of this work was to create a common benchmark for comparing data-driven methods dedicated to AE data interpretation. The dataset is made of time series collected during an experiment designed to reproduce the loosening phenomenon observed in aeronautics, automotive, or civil engineering structures where parts are assembled together by means of bolted joints. Monitoring loosening in jointed structures during operation remains challenging because contact and friction in bolted joints induce a nonlinear stochastic behavior.

Comparison of loosening behavior of bolted joints using plain and spring washers with full-threaded and plain shank bolts

Bolted joints tend to loosen under dynamic loads. Plain and spring washers are most common to control loosening. Initial tightening torque applied on the joint, at the time of assembly, also plays an important role. It is also known that bolts with shanks snugly fitting in the hole help in the control of loosening. In the present study comparison of plain and spring washer with the case of using no washer, and comparison of the bolt with plain shank with full-threaded bolt have been carried out. The result shows that plain washer is slightly effective to prevent loosening than that of spring washer with a threaded bolt. Whereas, the combination of Plain washer and bolt with plain shank is most effective. It shows that use of plain washer significantly controls loosening, under the three initial tightening conditions of the joint 20% under-tightened, 10% under-tightened and tightened up to rated torque.

Mechanical behavior of loose high-strength bolted connections with thin sheet steels

High-strength bolted connections have attracted increasing attention over the past few decades because they can safely transfer the design load. However, the effect of the preload loss on the mechanical behavior of the bolted connections has not been investigated sufficiently, This paper presents an experimental investigation of the bearing capacity of high-strength bolted connections with loose bolts (lacking pretension force). The tests investigated ninety specimens with loose bolts and six specimens without loose bolts for comparison. The results showed that bolt fracture was the only failure mode for all of the tested connections under uniaxial tension. The global behavior of the tested connections exhibited four stages, and the features of each stage were summarized. The connections with different tightening conditions exhibited a similar trend in terms of strain development around the bolt holes. The effect of the slip coefficient, position and number of loose bolts, and the plate thickness is elucidated through parametric studies. It is found that the yield load of high-strength bolted connections may be affected by the pretension force and the slip coefficient, while the effect of the slip coefficient gradually decreases with the increasing number of loose bolts. The experimental results are compared to the calculated ultimate bearing resistance according to the GB 50017, Eurocode 3, and AISC 360-16 standards. It is found that the resistance prediction of the standards may be too conservative for the prediction of the ultimate bearing capacity of loose high-strength bolted connections when bolt fracture governs failure. Practical design recommendations in the algebraic form are presented and verified to predict the yield load and ultimate bearing capacity of loose high-strength bolted connections.

Study on the Load Conversion of Bolt-Nut Fasteners between Tightening and Service Conditions

At present, the common method to realize the pre-tightening effect of threaded fasteners is by applying an accurate tightening torque on them. However, when removing the tightening torque, the load characteristics will have a transient conversion, so that the pre-tightening loads will be significantly different from the tightening condition. For the aim of understanding the pre-tightening effect under the service condition, it is important to model the load conversion between tightening and service conditions. Based on the most basic mechanical equilibrium analysis, the load characteristics of bolt-nut fasteners under a round of the tightening and service conditions were studied. The torque equilibrium equations were built respectively, the load conversion between two conditions was analyzed and an approximate relationship between the applied tightening torque under the tightening condition and the pre-tightening torque under the service condition was obtained. In the meanwhile, a dynamic strain measuring system was proposed to accurately determine the pre-tightening loads in real time. Results verified that the thread torque and the bearing friction torque balance each other and act as pre-tightening torques under the service condition. The final pre-tightening loads can be roughly estimated to be larger than half of the difference in tightening torques by wrenches, but smaller than half of the sum of tightening torques, or can be accurately measured through dynamic strain measurements. • We study on bolt-nut fasteners , load characteristics under tightening and service conditions. • We model the relationship between the pre-tightening torque and the applied tightening torque. • We verify that the pre-tightening torque is apparently determined by the friction on the contacting interface.

Robustness of polyisobutylene for friction coefficients between bearing surfaces of bolted joints

In bolted joints, clamp force must be accurately controlled to secure their reliability. However, the clamp force varies widely in each tightening because friction coefficients at thread surfaces and bearing surfaces vary in each tightening due to lubricants, configuration error of bolts, surface roughness, and surface hardness, among other things. In this study, we investigated the robustness of polyisobutylene and ISO VG46 machine oil during the tightening process for several parameters of tightening conditions. We especially focused on variations of the friction coefficient between bearing surfaces at an appropriate target clamp force of M8 bolt/nut assemblies and change rates of the friction coefficients from the middle to the end of the appropriate target clamp force. Results showed that the friction coefficients at the target clamp force varied widely if ISO VG46 machine oil was used as a lubricant. In contrast, the variations of the friction coefficients in which polyisobutylene was used for tightening were small. Results also showed that the friction coefficients invariably decreased about 20% from the middle to the end of the target clamp force if ISO VG46 machine oil was used for the lubricant. However, if polyisobutylene was used, the friction coefficients were almost constant for all tightening instances.

Youth, the Labor Market, and the Expansion of Higher Education

This article presents data about the aspirations of youth in relation to education and work, and it attempts to forecast the likelihood of fulfilling those aspirations. We have found that youth prefer enrolling in institutions of higher education to other educational trajectories; this is true of children whose parents have different socioprofessional statuses. Young people choose education because they want to obtain work that corresponds to their interests and aptitudes, is high-paying and prestigious, and makes it easy to find work in our country and to become a competent worker. However, most students in the ninth and eleventh grades had not made a decision about their future occupation or could not explain the reasons for their choice, and some were not sure of the correctness of their choice. [The Russian secondary school system goes through eleventh grade—Trans.] The authors do not share the belief that youth are behaving irresponsibly in charting their own future, but we do note a lack of appropriate communication between the labor market and its prospective personnel resources. Study of the opportunities for youth to realize their aspirations leads us to conclude that there is persistent differentiation in education, defined as an inequality of opportunities. The increase of a scarce resource (the number of places available in institutions of higher education) primarily increased the opportunities available to “strong” groups. With tightening conditions in the labor market, workers who received a pseudo-education will be replaced by qualified specialists. Differentiation in education will manifest itself in the labor market even more strongly than before. In conclusion, we draw attention to the fact that the aspirations of youth in educational institutions is consistent with global trends, and their positive motivation to work is the guarantee of progress and an important value component of social well-being.

Thermal Stress Cracking of Slide-Gate Plates in Steel Continuous Casting

The slide-gate plates in a cassette assembly control the steel flow through the tundish nozzle, and may experience through-thickness cracks, caused by thermal expansion and/or mechanical constraint, leading to air aspiration and safety concerns. Different mechanisms for common and rare crack formation are investigated with the aid of a three-dimensional finite-element model of thermal mechanical behavior of the slide-gate plate assembly during bolt pretensioning, preheating, tundish filling, casting, and cooling stages. The model was validated with previous plant temperature measurements of a ladle plate during preheating and casting, and then applied to a typical tundish-nozzle slide-gate assembly. The formation mechanisms of different types of cracks in the slide-gate plates are investigated using the model and evaluated with actual slide-gate plates at POSCO. Common through-thickness radial cracks, found in every plate, are caused during casting by high tensile stress on the outside surfaces of the plates, due to internal thermal expansion. In the upper plate, these cracks may also arise during preheating or tundish filling. Excessive bolt tightening, combined with thermal expansion during casting may cause rare radial cracks in the upper and lower plates. Rare radial and transverse cracks in middle plate appear to be caused during tundish filling by impingement of molten steel on the middle of the middle plate that generates tensile stress in the surrounding refractory. The mechanical properties of the refractory, the bolt tightening conditions, and the cassette/plate design are all important to service life.

Influence of a micro-thread at cervical position and a cylindrical intermediate zone on the mechanical behaviour of dental implants: A three-dimensional finite element analysis.

The purpose of this work is to analyse the influence on the biomechanical behaviour of dental implants of a micro-thread at their cervical part as well as of a cylindrical geometry at an intermediate zone. Stresses and strains in the elements involved, that is, bone, implant, screw and abutment, have to be considered in detail. Three different three-dimensional finite element models are generated to analyse the behaviour of the various components under the so-called tightening and operating conditions. For the modelling, material specifications for the cancellous bone and cortical bone, on one hand, and titanium properties for the implant, screw and abutment, on the other, are implemented. The tightening condition was fixed according to the stresses in the screw. The operating conditions were simulated by applying a force of 150 N, taking into account ISO 14801:2007 standard. The maximum stress under tightening conditions occurs always in the screw, while under operating conditions it is produced at the screw or the abutment, although considerable stress values are also present in the implant. In all the models, the maximum stress at the junction between the implant and the bone occurs within the cortical bone. Implants provided with micro-thread at the cervical position are advantageous over homogeneously threaded implants since lower stresses in both the implant and the adjacent bone are produced. A cylindrical intermediate portion on the implant surface does not present special advantage over the implants with continuous external thread under tightening and operating conditions.

Experimental study of loosening behavior of plain shank bolted joint under dynamic loading

Purpose – Bolted joints are commonly used to connect structural members. These joints can be disassembled whenever required. Various types of washers are used between nut and the connected member to keep the joints tight. However, these joints often become loose over time under dynamic loading conditions. The purpose of this paper is to know the reasons of loosening of bolted joints and to identify the main parameters that contribute to the bolt loosening, and to verify them with previous work. Design/methodology/approach – This work studies loosening of bolted joint in a test rig under varying tightening torque as well as for various types of washers used as the number of load cycles increases. Four trial runs are taken for each case considered and the average results are found out to minimize possible sources of errors. For the purpose, a specifically made test rig is used which is capable of applying harmonic load on the bolted joint by the lever action. Findings – The study compares the loosening of bolted joint with and without washer, and also under different initial tightening conditions. This study has shown the suitability of the test rig, methodology and parameters for study of loosening in bolted joints. This study presents an indigenous test, capable of applying harmonic load on bolted joint. Originality/value – The results establish that the methodology and parameters selected were appropriate for the purpose of study of loosening of bolted joints. This study has provided a base line for further work to understand the loosening of bolted joints.

Auditory Evaluation of Sounds Radiated from a Vibrating Plate Inside a Damped Cavity: Adjustment of the Frequency Resolution of Vibro-Acoustical Computing

The issue of adjusting vibro-acoustical computational cost is especially important when enhancing the sound quality of a mechanical structure using simulation. Simulation parameters must be specified so as to: i) reduce computational cost, and ii) satisfy perceptual constraints. For a simple plate-cavity system, the adjustment of computational cost is investigated in the framework of evaluating the influence of variable structural parameters (cavity absorption, thickness and tightening conditions of the plate) on the auditory perception of sounds radiated inside the cavity. By concentrating on such a simple system, we eventually aim at achieving some recommendations adaptable to different vibrating structures of our environment – in the areas of transport and building – made up of plane elements coupled with enclosures. Considering stationary sounds, this study deals with the adjustment of a major frequency computation parameter, i.e. frequency resolution. The specification of the frequency resolution for vibro-acoustical simulations has a great influence on the spectral envelope of the sounds synthesized afterwards. Here, we modify the spectral envelope of real sounds in order to reproduce the envelope of spectra of synthesized sounds that would be computed in a simulation using a given frequency resolution. The adjustment process pursues the following objective: determining a frequency resolution for which certain perceptual outcomes relative to modified real sounds remain similar to those concerning the original real sounds. These perceptual constraints are pertinent regarding the issue of adjusting vibro-acoustical computational cost. These constraints notably concern the merits of the stimuli and are translated into two adjustment criteria. The results of a first experiment, an auditory evaluation of partial corpora of modified stimuli, highlight that, for the plate-cavity system under consideration, 4 Hz may be an adjusted frequency resolution. The consequences of using this frequency resolution are then further assessed through a second experiment, an auditory evaluation of the complete corpus of modified stimuli. A wider range of perceptual results (perceptual spaces, preference spaces and merits) obtained for the modified sounds and the original sounds are compared. It is shown that both adjustment criteria are fulfilled for the adjusted frequency resolution equal to 4 Hz.

Fatigue Characteristics of Bolted Joint under Transverse Vibration ~Influence of Bolt Tightening Conditions on Transverse Fatigue Strength~

Fatigue tests under transverse vibration were performed for three separate tightening conditions to investigate the grip length and the engaging thread length in this study. The relationships between the apparent fatigue limit (the highest amplitude of transverse vibration force which can be applied to the bolted joint without generating fatigue) and the real fatigue limit of bolt material also were investigated. Results showed that apparent transverse fatigue limit decreased if the grip length was long. And relationships of the apparent fatigue limit and the real fatigue limit were different in each tightening conditions depending on the bending moment at the root of the first thread.

Machined and plastic copings in three-element prostheses with different types of implantabutment joints: a strain gauge comparative analysis

ObjectiveUsing strain gauge (SG) analysis, the aim of this in vitro study was quantify the strain development during the fixation of three-unit screw implant-supported fixed partial dentures, varying the types of implant-abutment joints and the type of prosthetic coping. The hypotheses were that the type of hexagonal connection would generate different microstrains and the type of copings would produce similar microstrains after prosthetic screws had been tightened onto microunit abutments.Materials and methodsThree dental implants with external (EH) and internal (IH) hexagonal configurations were inserted into two polyurethane blocks. Microunit abutments were screwed onto their respective implant groups, applying a torque of 20 Ncm. Machined Co-Cr copings (M) and plastic prosthetic copings (P) were screwed onto the abutments, which received standard wax patterns. The wax patterns were cast in Co-Cr alloy (n=5), forming four groups: G1) EH/M; G2) EH/P; G3) IH/M and G4) IH/P. Four SGs were bonded onto the surface of the block tangentially to the implants, SG 1 mesially to implant 1, SG 2 and SG 3 mesially and distally to implant 2, respectively, and SG 4 distally to implant 3. The superstructure’s occlusal screws were tightened onto microunit abutments with 10 Ncm torque using a manual torque driver. The magnitude of microstrain on each SG was recorded in units of microstrain (µε). The data were analyzed statistically by ANOVA and Tukey’s test (p<0.05).ResultsMicrostrain values of each group were: G1= 338.1±223.0 µε; G2= 363.9±190.9 µε; G3= 415.1±53.5 µε; G4= 363.9±190.9 µε. No statistically significant difference was found between EH and IH, regardless of the type of copings (p>0.05). The hypotheses were partially accepted.ConclusionsIt was concluded that the type of hexagonal connection and coping presented similar mechanical behavior under tightening conditions.

508 軸直角方向振動を受けるボルト締結体の疲労強度設計法(締結・接合部の力学・プロセスと信頼性評価(2),ものづくりにおける基礎研究と先端技術の融合)

In transverse fatigue of a bolted joint, the apparent fatigue limits (the highest amplitude of transverse vibration force which can be applied to the bolted joint without generating fatigue) vary according to the bolt tightening conditions even if the bolt size and the property class are the same. Hence, it is necessary to develop a guideline to safety and appropriately design bolted joints under transverse vibration. In this study, a method to predict the apparent fatigue limit of the bolted joint using the fatigue limit of a bolt material has been developed.

ボルト締結体における軸直角方向疲労強度予測法

In transverse fatigue of a bolted joint, althogh the real fatigue limit (the highest nominal stress at the root of the first thread of bolt without generating fatigue failure) is the same for bolts with the same size and property class, the apparent fatigue limits (the highest amplitude of transverse vibration force which can be applied to the bolted joint without generating fatigue failure) vary according to the bolt tightening conditions. Hence, it is necessary to develop a guideline for safety and design of bolted joints under transverse vibration. In this study, the relationship between the apparent fatigue limit and the real fatigue limit has been experimentally revealed. The method to predict the apparent fatigue limit using the real fatigue limit has been developed.

PS14 軸直角方向振動下におけるボルト締結体の疲労強度予測(フェロー賞対象ポスターセッション)

In transverse fatigue of a bolted joint, although the real fatigue limit is the same for bolts with the same size and property class, the apparent fatigue limits (the highest amplitude of transverse vibration force witich can be applied to the bolted joint without generating fatigue) vary according to the bolt tightening conditions. Hence, it is necessary to develop a guideline to accurately design bolted joints under transverse vibration. In this study, the relationships between the apparent fatigue limit and the real fatigue limit has been experimentally revealed. And then method to predict the apparent fatigue limit using the real fatigue limit has been developed.