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

Abstract

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.

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

“…In this study, a three-dimensional (3D) finite element model of a typical bolted joint structure is built, and the torque control strategy by directly applying a moment to the nut is simulated. [14][15][16] Then, the effective bearing contact radius is calculated based on the FEA results of bearing pressure distribution…”

The Study of Aircraft Accidents Causes by Computer Simulations

“…This publication presents detailed results of the numerical and experimental tests involving a shank with a thread and cooperating nut, which are the elements of an aircraft fuel system assembly ( Figure 2). The various aspects of numerical analyses of threaded connection are approached in scientific research [18][19][20][21][22]. Whereas the authors have not encountered a strength analysis of a threaded connection with modelled operational wear and tear in the source literature.…”

Modelagem e simulação do processo de aparafusamento

“…Hwang (2013): Este artigo apresentou um estudo do aperto de fixadores usados na porta deslizante de uma minivan comercial leve, através de experimentos e simulações numéricas. Yu et al (2015): Através de um modelo 3D de elementos finitos, foi estudado a relação torque e força de união em uma junta aparafusada, a partir da variação de diversos parâmetros como coeficiente de atrito, passo de rosca, folga de montagem e módulo de elasticidade.…”

“…Os trabalhos de Hwang (2013) e Yu et al (2015) serão abordados, a seguir, de forma mais detalhada, já que eles fornecerão dados importantes para o modelo e os comparativos realizados neste trabalho.…”

“…Os resultados das simulações do modelo de aparafusamento se mostraram coerentes com a realidade e conceitos já consagrados, como, por exemplo, apresentados em Yu et al (2015). Ao aumentar o coeficiente de atrito do parafuso, os valores de torque total aumentam e os valores de força de união, em uma mesma (2015), os resultados mostraram excelente concordância entre todas as abordagens.…”