Development of Design Charts for Bolts Preloaded up to the Plastic Range

Motosh, Nabil

doi:10.1115/1.3439041

Cited by 112 publications

(79 citation statements)

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“…However, the scatter of this factor is too high to give an accurate prediction of the initial load for given torque, especially for critical joint applications. In order to obtain the relation between torque and initial load precisely, a more accurate equation provided by Motosh 14 neglecting the helix angle of threads is as follows…”

Section: Theoretical Relation Between Torque and Initial Loadmentioning

confidence: 99%

Finite element analysis of relationship between tightening torque and initial load of bolted connections

Zhou

Wang

2015

Advances in Mechanical Engineering

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Proper initial load is necessary to ensure the stability of the bolted connections. In order to apply appropriate torque, the relationship between tightening torque and initial load should be determined. In this study, a detailed threedimensional finite element model of bolted joints was established with consideration of helix angle, pitch, thread type, tooth-type angle, and other details. The process of pre-tightening of bolted joints was simulated to validate the finite element model. The curves for the relationship between the torque and initial load obtained from finite element analysis agree well with those calculated from theoretical equations. Then, the influence of the friction coefficient, pitch, elastic modulus, assembly clearance, and strain-hardening exponent on the relationship was studied. The results show that the friction coefficient between nut and joint has great influence on the relationship between torque and initial load, that is, the larger the friction coefficient, the smaller the initial load of bolt at the same tightening torque. In contrast, the pitch, assembly clearance, Young's modulus, and strain-hardening exponent have little influence on torque-initial load relation. The method used in this study provides a theoretical basis for accurately determining the tightening torque for bolted joints. Bolted joints are widely used in mechanical structures as they are easy to be assembled and disassembled. Threaded joints must be tightened when installed so that the connected components are compressed while the bolt is stretched. The force acting on the bolt introduced by pre-tightening is named initial load. Keywords1 The purpose of pre-tightening is to strengthen reliability and compactness of the connections. However, an excessive initial load will lead to yield and even fracture in the bolt; on the other hand, an insufficient initial load cannot provide the adequate clamping force which is required for maintaining the integrity of the joint and eventually causes structure loosening and failure. So, determining an appropriate initial load is quite important for bolted connections. It is hard to measure the initial load during the assembly process, so the common practice is using torque wrench to regulate the tightening torque. Thus, determining the relationship between the tightening torque and initial load is of remarkable significance in maintaining the reliability of the bolted joints.

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Section: Theoretical Relation Between Torque and Initial Loadmentioning

confidence: 99%

Finite element analysis of relationship between tightening torque and initial load of bolted connections

Zhou

Wang

2015

Advances in Mechanical Engineering

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“…The most commonly used assumption of the bearing pressure distribution is a uniform distribution. 3,13 In that case, r b is calculated to be equation (7). Another simple assumption of the bearing pressure distribution is a linear decreasing distribution, which gives the expression of r b as equation (8).…”

Section: Appendixmentioning

confidence: 99%

Calculation of the effective bearing contact radius for precision tightening of bolted joints

Gong

Liu

Ding

2016

Advances in Mechanical Engineering

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Torque control is usually the only method for tightening bolts in some precision assembly applications. However, the scatter of the torque-tension relationship may significantly decrease the accuracy of the preload, which conflicts with the high requirement for mechanical accuracy in such precision assemblies. An important, but often ignored, factor affecting the accuracy of the torque-tension relationship is the effective bearing contact radius. In this article, a threedimensional finite element model of a typical bolted joint was developed to obtain the actual bearing pressure distribution, based on which the effective bearing contact radius can be further calculated. Then, a parametrical study was conducted to systematically investigate the effects of various geometrical, material, and frictional factors on the effective bearing contact radius. Based on the numerical results, a comprehensive and quantitative evaluation of the relative accuracy of each traditional method of calculating the effective bearing contact radius was made. In particular, it was found that the effective bearing contact radius, calculated based on the assumption of uniform bearing pressure distribution, was always relatively accurate regardless of the geometrical, material, and frictional conditions considered. This study will be helpful in increasing the accuracy of preload, thus ensuring mechanical accuracy and quality for precision assemblies.

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“…Motash informó que sólo el 10% del torque aplicado al ajuste inicial de un sistema de rosca se mantiene para inducir la precarga mientras que el 90% sirve para superar la fricción entre los componentes de acoplamiento (14). Por otra parte encontró que las fuerzas cíclicas que se producen al momento de ajustar y aflojar el tornillo disminuyen la fricción entre las roscas durante la aplicación del torque, esto se debe al desgaste de la microrugosidades entre las superficies de contacto, en consecuencia aumenta la precarga axial.…”

Section: Revisión De Literaturaunclassified

Condiciones favorables para el desempeño de prótesis sobre implantes utilizando conexiones externas

Arias

Vasquez

Suarez

2014

Rev Estomatol Herediana.

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para el desempeño de pró-tesis sobre implantes utilizando conexiones externas. Rev Estomatol Herediana. 2012; 22(2):121-128 RESUMEN La presente revisión tiene por objetivo mostrar las principales consideraciones favorables para distribuir las fuerzas de tensión a través del eje longitudinal del implante y evitar complicaciones protésicas en el sistema de conexión externa, prolongando la supervivencia o éxito del implante. Las complicaciones en el sistema de conexión externa son la fractura del pilar e implante, aflojamiento y fractura del tornillo y reabsorción ósea de la cresta alveolar. Para evitar estas complicaciones se busca una óptima precarga, estabilidad antirotacional y sentamiento pasivo. Estas propiedades son elementales para disminuir la tensión ante fuerzas de compresión, torsión y fricción. Otras consideraciones a tener en cuenta son la oclusión, el polígono de estabilización y el diseño protésico. Favorable conditions for the performance of implant-supported prosthesis using external connection. ABSTRACTThis review aims to show the main favorable considerations to distribute the tensile forces along the long axis of the implant and to avoid prosthetic complications focusing on the external connection system, in this way extending the implant survival or success. Complications in the external connection system are the abutment and implant fracture, screw loosening and fracture and loss of the marginal bone. In order to avoid these complications it is needed to obtain an optimal preload, antirotational stability and passive fit, which are fundamental properties for the reduction of the tension due to compression, frictional and torsion forces. Beside those, other considerations that must be taken into account are occlusion, the staggered placement of dental implants and prosthetic design. IntroducciónDesde que a mediados del siglo XX el Dr. Branemark descubriera que el titanio se adhería firmemente al hueso, los implantes han sufrido una gran evolución (1). La conexión externa fue el primer sistema en ser creado, su uso ha sido el más extendido, sin embargo ha dado lugar a un importante número de complicaciones (2). Para mitigar estos problemas, la conexión externa, la conexión transmucosa y los tornillos de retención han sido sometidos a una serie de modificaciones (3).En la actualidad existen diversos elementos que sirven para disipar la tensión a través de los componentes protésicos y sistemas de implantes, además se busca un óptimo asentamiento entre la interfase de la plataforma del implante y el pilar a través del macrodiseño del implante, torque, precarga, diseño y material del tornillo.El sistema de conexión externa posee un dispositivo antirotacional, inicialmente la función de este dispositivo diseñado como hexagono era proporcionar un mecanismo de torque rotacional que asegure y facilite la transferencia del implante en su montura durante la colocación quirúrgica en el hueso, la altura del hexágono era de 0,7 mm pero debido al aflojamiento o fractura del tornillo ante diversas fuerzas te...

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Development of Design Charts for Bolts Preloaded up to the Plastic Range

Cited by 112 publications

References 0 publications

Finite element analysis of relationship between tightening torque and initial load of bolted connections

Finite element analysis of relationship between tightening torque and initial load of bolted connections

Calculation of the effective bearing contact radius for precision tightening of bolted joints

Condiciones favorables para el desempeño de prótesis sobre implantes utilizando conexiones externas

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