An Improved Stiffness Model for Bolted Joints

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Sayed A. Nassar ◽  
Antoine Abboud
Keyword(s):  
Joint Stiffness ◽  
Effective Area ◽  
Accurate Estimate ◽  
Diameter Ratio ◽  
Bolted Joints ◽  
Plate Material ◽  
Reliable Prediction ◽  
Novel Approach ◽  
Stiffness Model ◽  
Initial Assembly

An improved stiffness model is proposed for bolted joints made of similar and dissimilar plates. A novel approach is used to obtain an expression for the effective area used for determining the joint stiffness. More accurate estimate of the joint stiffness provides a more reliable prediction of the joint behavior both during its initial assembly, as well as under subsequently applied tensile loads in service. The effect of the grip length-to-diameter ratio, joint sizes, underhead contact radii ratio, hole clearance, and plate material/thickness ratio are investigated. Experimental data are used for determining the envelope angle α in the proposed analytical model. Finite element modeling is used for evaluating the accuracy of the proposed stiffness model.

New Formulation of Bolted Joint Stiffness

2008 ◽  
Author(s):  
Sayed A. Nassar ◽  
Antoine Abboud
Keyword(s):  
Joint Stiffness ◽  
Effective Area ◽  
Accurate Estimate ◽  
Diameter Ratio ◽  
Bolted Joint ◽  
Reliable Prediction ◽  
Novel Approach ◽  
Fea Modeling ◽  
New Formulation ◽  
External Loads

New formulation is proposed for a more accurate estimate of bolted joint stiffness. In this study, a novel approach is used to obtain an expression for an effective area to be used for determining the clamped parts stiffness. A more accurate estimate of the joint stiffness would naturally provide a more reliable prediction of the bolted assembly response to external loads. The effects of the grip length-to-diameter ratio, joint dimensions, and the contact radii ratio of the joint plates are investigated and analyzed. Experimental data and finite element (FEA) modeling are provided to evaluate the accuracy of the proposed formulation of joint stiffness.

A New Approach for Determining Joint Stiffness of Bolted Joints

2014 ◽  
Vol 670-671 ◽  
pp. 1041-1044 ◽  
Author(s):  
Xi Wang Wang ◽  
Xiao Yang Li ◽  
Lin Lin Zhang ◽  
Xiao Guang Wang
Keyword(s):  
Accurate Determination ◽  
Joint Stiffness ◽  
Fatigue Loading ◽  
Bolted Joints ◽  
Analytical Models ◽  
Bolted Connection ◽  
New Approach ◽  
Axisymmetric Model ◽  
Force Equilibrium

Joint member stiffness in a bolted connection directly influence the safety of a design in regard to both static and fatigue loading as well as in the prevention of separation in the connection. Thus, the accurate determination of the stiffness is of extreme importance to predict the behavior of bolted assemblies. In this paper, An analytical 3D axisymmetric model of bolted joints is proposed to obtain the joint stiffness of Bolted Joints. Considering many different analytical models have been proposed to calculate the joint stiffness, the expression based force equilibrium can be a easy way to choose the best expression for the joint stiffness as a judgment criteria.

Accurate Evaluation of Bolt and Clamped Members Stiffnesses Of Bolted Joints

2021 ◽  
Author(s):  
Rashique Iftekhar Rousseau ◽  
Abdel-Hakim Bouzid ◽  
Zijian Zhao
Keyword(s):  
Finite Element ◽  
Joint Stiffness ◽  
Element Model ◽  
Fe Analysis ◽  
Bolted Joints ◽  
Analytical Models ◽  
Fe Modeling ◽  
Bolted Joint ◽  
A New Technique ◽  
External Loads

Abstract The axial stiffnesses of the bolt and clamped members of bolted joints are of great importance when considering their integrity and capacity to withstand external loads and resist relaxation due to creep. There are many techniques to calculate the stiffnesses of the joint elements using finite element (FE) modeling, but most of them are based on the displacement of nodes that are selected arbitrarily; therefore, leading to inaccurate values of joint stiffness. This work suggests a new method to estimate the stiffnesses of the bolt and clamped members using FE analysis and compares the results with the FE methods developed earlier and also with the existing analytical models. A new methodology including an axisymmetric finite element model of the bolted joint is proposed in which the bolts of different sizes ranging from M6 to M36 are considered for the analysis to generalize the proposed approach. The equivalent bolt length that includes the contribution of the thickness of the bolt head and the bolt nominal diameter to the bolt stiffness is carefully investigated. An equivalent bolt length that accounts for the flexibility of the bolt head is proposed in the calculation of the bolt stiffness and a new technique to accurately determine the stiffness of clamped members are detailed.

scholarly journals Nonlinear Axial Stiffness Characteristics of Axisymmetric Bolted Joints

1990 ◽  
Vol 112 (3) ◽  
pp. 442-449 ◽  
Author(s):  
I. R. Grosse ◽  
L. D. Mitchell
Keyword(s):  
Finite Element ◽  
Linear Theory ◽  
Design Theory ◽  
Joint Stiffness ◽  
Bolted Joints ◽  
Axial Stiffness ◽  
Outer Diameter ◽  
Bolted Joint ◽  
Element Analysis ◽  
Stiffness Characteristics

A critical assessment of the current design theory for bolted joints which is based on a linear, one-dimensional stiffness analysis is presented. A detailed nonlinear finite element analysis of a bolted joint conforming to ANSI standards was performed. The finite element results revealed that the joint stiffness is highly dependent on the magnitude of the applied load. The joint stiffness changes continuously from extremely high for small applied loads to the bolt stiffness during large applied loads, contrary to the constant joint stiffness of the linear theory. The linear theory is shown to be inadequate in characterizing the joint stiffness. The significance of the results in terms of the failure of bolted joints is discussed. A number of sensitivity studies were carried out to assess the effect of various parameters on the axial joint stiffness. The results revealed that bending and rotation of the joint members, interfacial friction, and the bolt/nut threading significantly influence the axial stiffness characteristics of the bolted joint. The two-dimensional, axisymmetric finite element model includes bilinear gap elements to model the interfaces. Special orthotropic elements were used to model the bolt/nut thread interaction. A free-body-diagram approach was taken by applying loads to the outer diameter of the joint model which correspond to internal, uniformly distributed line-shear and line-moment loads in the joint. A number of convergence studies were performed to validate the solution.

A Proposed Model for Predicting Clamp Load Loss Due to Gasket Creep Relaxation in Bolted Joints

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Basil A. Housari ◽  
Ali A. Alkelani ◽  
Sayed A. Nassar
Keyword(s):  
Joint Stiffness ◽  
Closed Form Solution ◽  
Load Level ◽  
Form Solution ◽  
Bolted Joints ◽  
Experimental Procedure ◽  
Proposed Model ◽  
Gasket Material ◽  
Improved Model ◽  
Over Time

An improved mathematical model is proposed for predicting clamp load loss due gasket creep relaxation in bolted joints, taking into consideration gasket behavior, bolt stiffness, and joint stiffness. The gasket creep relaxation behavior is represented by a number of parameters which has been obtained experimentally in a previous work. An experimental procedure is developed to verify the proposed model using a single-bolt joint. The bolt is tightened to a target preload and the clamp load loss due to gasket creep relaxation is observed over time under various preload levels. The experimental and analytical results are presented and discussed. The proposed model provides a prediction of the residual clamp load as a function of time, gasket material and thickness, bolt stiffness, and joint stiffness. The improved model can be used to simulate the behavior of creep relaxation in soft joints as the joint stiffness effect is considered. Additionally, a closed form solution is formulated to determine the initial clamp load level necessary to provide the desired level of a steady state residual clamp load in the joint, by taking the gasket creep relaxation into account.

EFFECTIVE DYNAMIC STIFFNESS MODEL AND ITS EFFECTS ON ROBOT SAFETY AND PERFORMANCE

2013 ◽  
Vol 37 (3) ◽  
pp. 395-403
Author(s):  
Dongjun Shin ◽  
Zhan Fan Quek
Keyword(s):  
Dynamic Stiffness ◽  
Joint Stiffness ◽  
Optimization Strategy ◽  
Design Guideline ◽  
Controller Gain ◽  
Stiffness Model ◽  
Effective Dynamic ◽  
Stiffness Characteristics ◽  
And Performance ◽  
The Impact

Due to the limited control bandwidth of pneumatic artificial muscles, joint stiffness characteristics and their effects on safety and performance of human-friendly robots should be considered in the frequency domain. This paper introduces the concept of effective dynamic stiffness and validates its model with the Stanford Safety Robot. Experimental results show that the dynamic stiffness demonstrates limited effects on the impact acceleration given the same impact velocity and controller gain, whereas it significantly affects control performance of position tracking due to pressure-induced non-linearities. A stiffness optimization strategy for safety and performance is discussed as a design guideline of human-friendly robots.

Fastener Tightening Beyond Yield

2004 ◽  
Author(s):  
Sayed A. Nassar ◽  
Payam H. Matin
Keyword(s):  
Equilibrium Point ◽  
Joint Stiffness ◽  
Cyclic Loads ◽  
Clamping Force ◽  
Bolted Joint ◽  
Permanent Set ◽  
Clamp Force ◽  
Service Load ◽  
The Mean ◽  
Initial Assembly

The effect of fastener tightening beyond yield on the amount of clamp load loss, due to the application of a separating force, is investigated for a system in which the bolted joint remains within its elastic range. After the initial assembly, the joint is subsequently subjected to a tensile separating force, which increases the tensile stress in the fastener further into the plastic range. Simultaneously, the separating force reduces the clamping force. Upon the removal of the separating service load from the system, the system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the tension in the fastener is reduced due to its plastic elongation. The reduction in fastener tension translates to a partial, yet permanent, reduction in the clamping force. Excessive loss of the clamp load is a failure mode that may lead to joint leakage, loosening, or fatigue failure. Additionally, the loss of the clamp force reduces the mean stress, which may significantly affect the fatigue performance of the system under subsequent cyclic loads. A discretized non-linear model is established in order to describe the fastener behavior, and to determine the clamp load loss due to the permanent set in the fastener. The effect of two non-dimensional variables on the amount of clamp load loss is investigated. The first variable is the fastener-to-joint stiffness ratio, and the second is the ratio of initial fastener tension to its yield strength. Analytical results are presented for a range of stiffness ratios that simulates both soft and hard joint applications.

Torsional Stiffness Model of an Industrial Robotic Joint Using Fractal Theory

2019 ◽  
Author(s):  
Jingjing Xu ◽  
Zhifeng Liu ◽  
Yongsheng Zhao ◽  
Qiang Cheng ◽  
Yanhu Pei ◽  
...  
Keyword(s):  
Prediction Accuracy ◽  
Fractal Theory ◽  
Great Influence ◽  
Joint Stiffness ◽  
Equilibrium Analysis ◽  
Torsional Stiffness ◽  
Tangential Stiffness ◽  
Proposed Model ◽  
Stiffness Model ◽  
Rv Reducer

Abstract It is known that mechanical connections have great influence on the dynamic characteristic of the assembly. In existing methods, the torsional stiffness of the robotic joint is calculated only considering the stiffness of components of the system, which largely reduces the prediction accuracy of the joint stiffness. In the paper, to predict the joint stiffness more accurately, a model is proposed considering influences of the stiffness of all connections existed in a joint system. The normal and tangential stiffness of the contact surface of each connection are calculated by combining the equilibrium analysis of the force and the fractal theory. Then the total stiffness of one robotic joint can be modelled by putting the torsional stiffness of all connections and that of the RV reducer and gear pair in parallel. To verify the proposed model, its simulation result is compared to the stiffness based on the previous technique without considering the influence of connections. The comparison result shows that the proposed model can improve the stiffness-prediction accuracy. This study can be extended to the stiffness modeling of other joint systems and provides a theoretical basis for the dynamic analysis of the robotic system.

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