Advantage of Elliptical Confidence Limit Method for Bolted Joint Tightening Reliability

2015 ◽  
Author(s):  
Soichi Hareyama ◽  
Ken-ichi Manabe
Keyword(s):  
Process Control ◽  
Yield Point ◽  
Confidence Limit ◽  
Equivalent Stress ◽  
Bolted Joints ◽  
Bolted Joint ◽  
Tightening Torque ◽  
Axial Tension ◽  
Control Capability ◽  
Joint Tightening

The calibrated wrench method is often used for tightening. When tightening bolted joints, it is important to apply high initial axial tension. However, since the axial tension is indirectly applied in this method, it varies and is widely distributed in the case of tightening carried out in the production line of a factory, for example. However, the calibrated wrench method is still widely used because of the simple tool used and easy standardization. Conventionally, this type of distribution has been considered to lie within a rhombus. In our previous paper, we analyzed and discussed the case when the distribution of the tightening torque and the equivalent stress of the bolted joint are considered to be independent random variables; in this case, the distribution becomes elliptical. Using this feature, a higher target tightening torque can be set than before. Finally, we established a procedure for the analysis and calculation of the optimum tightening torque for bolted joints. To ensure sufficient long-term tightening reliability to prevent breakage and loosening, a high initial axial tension and high equivalent stress can be realized using this proposed method. In this study, we analyze and discuss the case of differences in the tightening work condition (process control capability) and the tightening design condition. The tightening work coefficient a depends on the management state, the tightening working posture, and the process control capability of a tool or shop floor at a production site. According to the results of our trial calculation in Appendix A, the improvement ratio of the proposed target tightening torque is approximately 8.3% compared with the conventional method for dry friction and approximately 7.5% in the case of oily friction. Furthermore, in bolted joint tightening design, the tightening conditions under which the design conditions are satisfied are derived analytically. For the tightening design conditions of (1) a minimum axial stress of at least 50% at the yield point, and (2) an equivalent stress of 70% to 90% at the yield point, both the conventional and proposed areas of the confidence limit are obtained by precise analysis. Although the permitted limit of the tightening design condition cannot be realized by the conventional method, it can be realized by the proposed elliptical confidence limit method. Finally, we establish a method for maintaining the tightening reliability that involves applying high axial tension by increasing the target design tightening torque using the elliptical confidence limit.

Improvement of Axial Tension Distribution of Bolted Joints Tightened by Calibrated Wrench Method From Viewpoint of Quality and Process Control Using Elliptical Confidence Limit

2019 ◽  
Author(s):  
Soichi Hareyama ◽  
Ken-ichi Manabe ◽  
Satoshi Kobayashi
Keyword(s):  
Process Control ◽  
Statistical Method ◽  
Confidence Limit ◽  
Bolted Joints ◽  
Independent Random Variables ◽  
Tension Stress ◽  
Bolted Joint ◽  
Tightening Torque ◽  
Tension Distribution ◽  
Axial Tension

Abstract When tightening a large number of bolted joints, the calibrated wrench method is used. Since this method is indirect, the axial tension varies greatly in many cases. However, the calibrated wrench method is still widely used because of the simplicity of the tool and easy standardization. When the tightening torque and axial tension are considered to be two independent random variables, the axial tension (stress) is distributed within an elliptical confidence limit. Conventionally, it is thought that the shape of this distribution is a rhombus. Considering the permitted limit for a working load (stress) on a bolted joint, the elliptical variation has a larger margin to the yield point than that of a conventional rhombus. On the basis of this feature, we show in this paper that a higher tightening target torque and a higher axial tension can be set than before. By applying the elliptical confidence limit, one can obtain higher tightening torque and initial axial tension than the conventional values within a smaller range of variations. In this study, in the case of tightening a large number of bolted joints at factories and so forth, tightening reliability is considered as a problem associated with quality or process control and a probabilistic statistical method is investigated. Finally, we carry out analysis to establish the optimum tightening torque for bolted joints.

Improving Tightening Reliability on Bolted Joints for Calibrated Wrench Method (An Analysis on Optimum Tightening Torque by Confidence Limit Ellipse)

2013 ◽  
Author(s):  
Soichi Hareyama ◽  
Ken-ichi Manabe ◽  
Makoto Nakashima
Keyword(s):  
Conventional Method ◽  
Confidence Limit ◽  
Equivalent Stress ◽  
Plastic Region ◽  
Bolted Joints ◽  
Independent Random Variables ◽  
Bolted Joint ◽  
Tightening Torque ◽  
Axial Tension ◽  
Improvement Effect

On tightening bolted joints, the calibrated wrench method is used in manufacturing industries for a large amount of tightening work. It is important to give high initial axial tension in respect of tightening reliability, self-loosening prevention, the prevention from fatigue breakage, etc. In this method the axial tension of a bolt is controlled by grasping the wrench torque. However, since the axial tension grasp of this method is indirect, it varies greatly in lot of tightening. Therefore, the calibrated wrench method is not so accurate from the viewpoint of axial tension control. Turn-of-nut method, torque gradient control method and plastic-region tightening, etc. are developed as the methods of getting high initial axial tension with sufficient accuracy. But the calibrated wrench method is still widely used because of the simple tool and easy standardization. In this paper, the statistical distribution of the magnitude of the combined stress (equivalent stress) by shear strain energy criterion in bolted joint, which are tightened by the calibrated wrench method is formulated. Tightening torque and equivalent stress coefficients are considered to be two independent random variables. We show that the equivalent stress obtained by those products is distributed in a confidence limit ellipse. It is thought that distribution of this kind is conventionally varied in a rhombus. However, this proposed method shows that the distribution is varied inside the confidence limit ellipse. Now, when considering the permitted limit for working load stress on a bolted joint, ellipse-like variation has big margin to yield point than the shape of a conventional rhombus. Using this feature, we show that higher tightening target torque value can be set than before by this method. Finally, this research established the analysis and calculating routine for the optimum tightening torque on bolted joints. The merit and effect of this proposed method are as follows. 1) The optimum tightening torque can be raised by about 13% than conventional method by using the experimental thread characteristic values in this research. 2) In a large amount of tightening work, the axial tension distribution (tightening coefficient Q) and distribution of equivalent stress (tightening stress coefficient S) are presumed. The predicted value of the distribution of the Q is about 1.73, which has the 20% improvement effect compared to the conventional method. Also the distribution of the S is about 1.58, which has the similar improvement effect of 18%. As a rapid calculation, the nomograph of the optimum tightening torque can be obtained by combining the tightening torque and axial tension (axial stress) as well as the distribution of equivalent stress with dimensionless data of screw shape and strength. The example of nomograph on metric coarse screw is shown. In order to maintain the tightening reliability in bolted joints, standardization of the tightening work in a production site is very important. We think that this method is useful for establishment of the job standard (technical engineering standard).

Experimental Study to Verify Elliptical Confidence Limit Method for Bolted Joint Tightening

2016 ◽  
Author(s):  
Soichi Hareyama ◽  
Ken-ichi Manabe ◽  
Takayuki Shimodaira ◽  
Takashi Naganawa
Keyword(s):  
Confidence Limit ◽  
Axial Stress ◽  
Equivalent Stress ◽  
Independent Random Variables ◽  
Screw Thread ◽  
Tightening Torque ◽  
Axial Tension ◽  
Rectangular Area ◽  
Shear Strain Energy ◽  
Joint Tightening

The calibrated wrench method is often used for tightening. When tightening bolted joints, it is important to apply high axial tension. However, since the axial tension is indirectly applied in this method, it varies and has a distribution in the case of tightening carried out in the production line of a factory, for example. However, the calibrated wrench method is still widely used because of the simple tool and easy standardization. In our previous papers, we analyzed and discussed the main points of this research by a theoretical approach as discussed below. Conventionally, this type of distribution has been considered to lie within a rhombus (more precisely, within a rectangular area). However, when considering the tightening torque and axial tension as independent random variables, the distribution becomes elliptical. The same idea applies to the relation between the tightening torque and the equivalent stress for a bolt axis based on shear strain energy theory. On the other hand, regarding the variation in the tightening torque (tightening work coefficient a) actually applied to a bolt, it was reported by Bickford, Kawasaki, and others that it can vary by 15% or more from the target (indicated) tightening torque. However, the torques for wrenches used at actual assembly sites or under lubricated conditions were not reported. Therefore, it is necessary to experimentally verify that the relation between the tightening torque and the axial tension (axial stress) and equivalent stress of a bolt axis is distributed in an ellipse. Furthermore, the screw-thread characteristics (torque coefficient, equivalent stress coefficient, coefficient of friction, etc.) during the tightening process should be clarified by an experimental approach and observation. Thus, in this study, in experiments under dry (as-obtained) and lubricated (Loctite 263) conditions, the tool (preset-type and dial-type torque wrenches) and bolt strength classification (8.8 and 10.9) were changed, and the screw-thread characteristics were observed during actual bolt tightening and the characteristics under different conditions were analyzed. It was clearly shown that the tightening torque and the axial tension (axial stress) of a bolt axis and the equivalent stress vary with an elliptical distribution rather than a rhombic distribution. Finally, the validity of the tightening theory based on the elliptical confidence limit method was also verified experimentally.

scholarly journals Identification of Pre-Tightening Torque Dependent Parameters for Empirical Modeling of Bolted Joints

2021 ◽  
Vol 11 (19) ◽  
pp. 9134
Author(s):  
Yu Tian ◽  
Hui Qian ◽  
Zhifu Cao ◽  
Dahai Zhang ◽  
Dong Jiang
Keyword(s):  
Experimental Data ◽  
Thin Layer ◽  
Empirical Equation ◽  
Model Updating ◽  
Bolted Joints ◽  
Empirical Modeling ◽  
Bolted Joint ◽  
Tightening Torque ◽  
Torque Wrench ◽  
Interface Parameters

The vibration characteristics of bolted structures are crucially affected by the pre-tightening torque. An approach for identifying the pre-tightening torque dependent stiffness parameters of bolted joints is proposed in this paper. Firstly, the interface of the bolted joint is characterized by the thin layer element with the isotropic material property, and the parameter value of the property is assigned relative to the distance from the center of the bolt; the influence of the bolt is ignored. Secondly, the model updating method is adopted to identify the parameters of thin layer elements using experimental data, and modal data under different values of pre-tightening torque in the range of 2 N·m~22 N·m are obtained; the torque wrench is used to determine the pre-tightening torque in the modal test. Finally, after identifying the material parameters using partial experimental data on pre-tightening torque range, the empirical equation of the interface parameters with the pre-tightening torque parameter is obtained by curve fitting and the rest of the experimental data are used to verify the accuracy of the fitted empirical equations. It is concluded that this method can obtain all the parameters of the equivalent thin layer elements within a certain range of pre-tightening torque, which can provide a reference for the empirical modeling of bolted structures, improve modeling efficiency and reflect the characteristic performance of real structural dynamics.

2301 Improving Research of Tightening Reliability on Bolted Joints : A Study on Optimum Tightening Torque Using Ellipse of Confidence Limit

2010 ◽  
Vol 2010.10 (0) ◽  
pp. 191-194
Author(s):  
Soichi HAREYAMA ◽  
Kazuo NAGASHIMA ◽  
Makoto NAKASHIMA ◽  
Ryuji TAKADA ◽  
Takayuki SHIMODAIRA ◽  
...  
Keyword(s):  
Confidence Limit ◽  
Bolted Joints ◽  
Tightening Torque

scholarly journals Effect of Washer Type on Bearing Strength of Bolted-Joint Laminated Composites

2012 ◽  
Vol 21 (6) ◽  
pp. 096369351202100
Author(s):  
Yusuf Arman
Keyword(s):  
Laminated Composites ◽  
Bolted Joints ◽  
Bolted Joint ◽  
Tightening Torque ◽  
Bearing Strength ◽  
Failure Loads ◽  
Glass Fibre Reinforced ◽  
Load Displacement ◽  
Damage Tolerant ◽  
Composite Samples

There are various parameters for bolted joints used in so many industries. The main objective of this work was to investigate the influence of washer type as a bolting parameter on the bearing strength of bolted joints in laminated composites. Therefore, by using three different washer types; flat washer, spring washer and tooth lock washer, an experimental study was performed. Quasi-isotropic glass-fibre reinforced epoxy laminated composites were used in the study. Four different tightening torques ( T = 2, 3, 4, 5 Nm) were chosen for the bolted joints in the experiments, for each washer type. E/W ratio was chosen as 0.25, 0.5, 0.75 and 1 in order to investigate damage modes of composite samples. It was applied tensile test, through a centroidal axis, on each specimen. From these tests, load-displacement curves of the specimens were drawn. The maximum failure loads and bearing strengths of the bolted joints were obtained from the load-displacement curves. From the experimental results, it is noted that bearing strength of the specimens with flat washer is higher than the specimens with tooth lock and spring washer, respectively. Also, it is concluded that higher tightening torque increases the bearing strength, and E/W ratio should be determined as larger than 0.25 for a damage tolerant design in terms of bearing strength.

scholarly journals Progressive fatigue damage analysis of composite bolted joint using equivalent stress model

2019 ◽  
Vol 103 (1) ◽  
pp. 003685041987423 ◽  
Author(s):  
Fang Liu ◽  
Ming Xie ◽  
Yanjun Ji ◽  
Mengzhen Zhou
Keyword(s):  
Fatigue Life ◽  
Composite Structures ◽  
Progressive Failure ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
Field Variable ◽  
Bolted Joints ◽  
Bolted Joint ◽  
Damage State ◽  
Fatigue Model

Composite bolted joints are quite necessary for composite structures connection, which has become the main limit for the use of composites in main load-bearing structures. In this article, a fatigue model of composite bolted joint based on equivalent stress is established by programming in ABAQUS USDFLD subroutine to simulate the progressive failure of composite bolted joints. By introducing three-dimensional Tsai–Hill static failure criterion, equivalent stress is calculated for investigating effects of multiaxial stress on fatigue life. In the subroutine of progressive failure for fatigue model, fatigue life of composite bolted joint and damage state of elements that are meshed in the process of modelling are connected by defining field variable. Different fatigue modes are predicted here by changing stress amplitude and ratio loading, in which simulation results agree well with that obtained in corresponding experiments.

Mechanical Behaviors of Bolted Joint in Various Clamping Configurations

1998 ◽  
Vol 120 (3) ◽  
pp. 226-231 ◽  
Author(s):  
T. Fukuoka ◽  
T. Takaki
Keyword(s):  
Stress Concentration ◽  
Bolted Joints ◽  
Elastic Contact ◽  
Bolted Joint ◽  
Mechanical Behaviors ◽  
Stress Concentrations ◽  
Tightening Torque ◽  
Pitch Error ◽  
Manufacturing Errors ◽  
Multi Body

In a bolted joint, failures usually initiate at the first root of the bolt thread. However, rupture around the bolt head is sometimes reported for a tap bolt because of high stresses produced by tightening torque applied to the bolt head. It is also well known that manufacturing errors of internal threads in a tapped hole are generally much larger than those of external threads, thus leading to the failures concerned. In this paper, mechanical behaviors of bolted joints in various clamping configurations are analyzed using FEM as multi-body elastic contact problem, and the effects of nominal diameter, friction and pitch error upon stress concentrations are evaluated for through bolts, studs, and tap bolts. It is then quantitatively estimated on the effectiveness of “recessed internal threads” for reducing the stress concentration occurred around the far end of bolt hole. In addition, the tightening process and strength of a bottoming stud, which have seldom been studied despite favorable performance in preventing stress concentration at the runout of threads, are also investigated.

Representation of bolted joints in a structure using finite element modelling and model updating

2020 ◽  
Vol 14 (3) ◽  
pp. 7141-7151 ◽  
Author(s):  
R. Omar ◽  
M. N. Abdul Rani ◽  
M. A. Yunus
Keyword(s):  
Finite Element ◽  
Dynamic Behaviour ◽  
Model Updating ◽  
Complex Structure ◽  
Bolted Joints ◽  
Model Parameters ◽  
Fe Model ◽  
Bolted Joint ◽  
Fe Modelling ◽  
Joint Structure

Efficient and accurate finite element (FE) modelling of bolted joints is essential for increasing confidence in the investigation of structural vibrations. However, modelling of bolted joints for the investigation is often found to be very challenging. This paper proposes an appropriate FE representation of bolted joints for the prediction of the dynamic behaviour of a bolted joint structure. Two different FE models of the bolted joint structure with two different FE element connectors, which are CBEAM and CBUSH, representing the bolted joints are developed. Modal updating is used to correlate the two FE models with the experimental model. The dynamic behaviour of the two FE models is compared with experimental modal analysis to evaluate and determine the most appropriate FE model of the bolted joint structure. The comparison reveals that the CBUSH element connectors based FE model has a greater capability in representing the bolted joints with 86 percent accuracy and greater efficiency in updating the model parameters. The proposed modelling technique will be useful in the modelling of a complex structure with a large number of bolted joints.

scholarly journals Experimental study of lateral resistance of bolted joints using Japanese cedar (Cryptomeria japonica) treated with resin impregnation

2020 ◽  
Vol 66 (1) ◽  
Author(s):  
Keita Ogawa ◽  
Satoshi Fukuta ◽  
Kenji Kobayashi
Keyword(s):  
Short Pulse ◽  
Japanese Cedar ◽  
Bolted Joints ◽  
Bolted Joint ◽  
Yield Load ◽  
Short Pulse Laser ◽  
Resin Impregnation ◽  
Lateral Resistance ◽  
Ultraviolet Wavelength ◽  
Resistance Performance

Abstract The development of wooden joints possessing high resistance performance has become an important issue for the construction of newer buildings. This study attempts to strengthen the lateral resistance of bolted joints using the previously reported plasticizing technique. This technique consists of two processing stages: incising the surface of the wood using an ultraviolet wavelength short-pulse laser and impregnating the resin into the incised area. This technique makes it possible to plasticize only a local part of the wood surface. Bolted joint specimens were assembled using plasticized wood around the bolt hole, and the lateral tests were conducted. Acrylic monomer and urethane prepolymer were used as the impregnating resins and their incision depths were set as 4 and 10 mm. When the lateral load acted parallel to the grain, changes in the lateral resistance characteristics were observed, especially for the stiffness and yield load. For example, when acryl was used, and the incision depth was 10 mm, an increment of 73% in the yield load was observed, as compared to the non-impregnated specimens. The specimen groups impregnated with acryl exhibited greater changes in their properties than those using urethane. When loaded perpendicular to the grain, an increase in properties were observed; however, these increments were lower than those of the groups loaded parallel to the grain.

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