Failure modes of bolt and nut assemblies under tensile loading

Bolt and nut assemblies under tension loading can either fail by bolt fracture or thread failure. The latter failure mode is arguably undesired because it leads to failure at a comparatively low deformation level. Moreover, incipient thread failure is challenging to detect in the case of overtightening since the bolt remains in the bolt hole after this type of failure occurs. The failure mode of bolt and nut assemblies is determined by several well-known factors such as the thread engagement length and the relative strength of the bolt and nut. However, one factor that has received limited attention in the literature is the placement of the nut along the threaded portion of the bolt shank. We have performed a series of direct tension tests on various single M16 bolt and nut assemblies, where the placement of the nut was varied. Some of the assemblies experienced that placing the nut close to the thread run-out, i.e., near the unthreaded portion of the bolt shank, led to thread failure, whereas placing the nut sufficiently far from the thread run-out led to bolt fracture. We carried out finite element simulations of the tests in order to further investigate the mechanisms occurring during failure. In the case where the nut was located close to the thread run-out, the simulations revealed that necking of the bolt shank affected the effective overlap of the internal and external threads. This effect seemed to contribute to thread failure in both tests and simulations.

“…8) Deformed threads at three stages throughout a simulation with = 9 mm. The numbers 1 to 3 in the bottom frame label the pairs of engaged threads [3]. Fig.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…| 172 R e t r a c t e d Fig. 9) Force-displacement curves obtained from two replicate tests with = 9 mm and the corresponding simulation [3].…”

Section: Simulation Resultsmentioning

confidence: 99%

Section: Test Specimens and Setupmentioning

confidence: 99%

Section: Geometry Mesh and Boundary Conditionsmentioning

confidence: 99%

Section: Geometry Mesh and Boundary Conditionsmentioning

confidence: 99%

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Retracted: 01.01: Placement of nut determining failure mode of bolt and nut assemblies

Grimsmo

Aalberg²,

Langseth

et al. 2017

Fracture simulation of fully and partially threaded bolts under tension

Yang¹,

Veljković

2021

The tensile behaviour of bolts has direct effects on the performances of structural bolted joints. Conventional studies mainly focus on the stiffness and strength of bolt assemblies, whereas the deformation and fracture behaviour of fully and partially threaded bolts under tension is rarely investigated. This paper presents a numerical investigation of the fracture behaviour of fully and partially threaded bolts based on the experimental results in literature [5]. Firstly, a combined linear and power stress‐strain relation is used to describe the post‐necking stress‐strain relations of fully and partially threaded bolts. Direct tension tests on fully and partially threaded bolts are modelled using ABAQUS with the explicit solver. The fracture criterion proposed by Bao and Wierzbicki [10] is used to simulate the bolt tensile fracture and thread stripping failure. Numerical results indicate that the large deformation behaviour and the failure mode of fully and partially threaded bolts under tension could be accurately predicted combining the calibrated post‐necking stress‐strain relations and the Bao‐Wierzbicki fracture criterion with suitable parameters.

Numerical analysis of ring flange connection with defined surface area

Lu¹,

Xin

Veljković

2021

Ring flange connections with preloaded high strength bolts are most commonly used to connect two segments of steel tubular towers. Behaviour and durability of ring flange connections is influenced by various factors, including stiffness of ring flanges, fabrication and execution imperfections, welding technology and welding details of the ring flange/segment connection, type of bolts, pretension technique and control of accomplished pretension force in bolts. This paper focuses on ring flange connections with defined contacts compared to the “full ring flange connection”. No imperfections are considered. Behaviour of the ring flange connections is investigated by advanced finite element analysis (FEA). The realistic geometry of bolted connection, ductile damage material model and element removal are used in the advanced FE model with explicit numerical solver. In addition, the influence of two types of high strength bolts, fully‐threaded and partial‐threaded bolts, on the mechanical behaviour of connections is considered. The failure modes and tensile stiffness are compared using different analytical models. Finally, recommendations for calculation of the tensile resistance of the connection and the bolt force with defined surface area are provided.