Effect Of Root Radius Research Articles

Effects of root radius and pitch difference on fatigue strength and anti-loosening performance for high strength bolt–nut connections

The fatigue strength improvement and anti-loosening performance are studied experimentally and analytically for JIS M16 bolt–nut connections. Three different root radii are considered coupled with three different pitch differences. The enlarging the bolt root radius improves the fatigue limit of the bolt by more than 30% because both stress amplitude and mean stress can be reduced. Furthermore, suitable pitch difference improves the fatigue limit by more than 25%. This is because under no pitch difference the crack initiation always occurs at No.1 or No.2 threads close to the bolt head causing the final failure; however, under a suitable pitch difference the crack initiation occurs at No.6 or No.7 threads far away from the bolt head. Good anti-loosening performance can be expected for the bolt–nut connections having enlarged root radius because the prevailing torque [Formula: see text] = 19 Nm and the residual prevailing torque [Formula: see text] are not smaller compared to other special bolt–nut connections.

Fatigue damage evolution and finite element simulation of the samples under different notch morphology

Based on the theory of continuous damage mechanics and the principle of irreversible thermodynamics, the damage evolution model of low cycle fatigue is investigated. By programming the damage evolution model as UMAT subroutine in ABAQUS, the fatigue damage and crack initiation life of notch materials under specific loads are simulated, and the crack initiation location is determined. Furthermore, the effects of root radius, depth and opening angle on crack initiation life are investigated. The results show that the crack initiation occurs easily in the notch root where the damage is the most serious and the plastic strain accumulates fastest under cyclic loading. With the increase of notch depth and root radius, the crack initiation life decreases. For V-notched specimens, when the notch depth remains unchanged, the crack initiation life will decrease with the increase of the opening angle.

1310 ねじ谷底の丸みを考慮したメートル台形ねじおよび管用ねじの断面積の理論式(GS-11 ねじ,潤滑機器)

1310 ねじ谷底の丸みを考慮したメートル台形ねじおよび管用ねじの断面積の理論式(GS-11 ねじ,潤滑機器)

Stress concentration at the root of a screw thread (Effects of root radius and friction coefficient)

In general, the stress at the first root of the ridge in a bolt seems to be beyond the yield stress. But the fastened parts which are made of ductile material have generally enough strength, since the regions deformed plastically may be limited around the root. In the case of evaluating the strength for dynamic load and cyclic load (fatigue strength) or the strength of the bolt made of high strength material, however, the stress concentration factor at the root of the ridge must be estimated correctly. In this paper, an analysis is carried out with a high accuracy for the case of bolt being both tensioned and fastened in order to obtain elementary knowledges concerning the stress concentration of the screw thread. The effects of the root radius and the friction coefficient of the contact surfaces upon the stress concentration at the root of screw thread are examined on the basis of the results by an axi-symmetric FEM which can deal with a three-body elastic contact problem.

The effect of root radius on the direction of crack extension under combined mode loading

The “energy density theory” of G. Sih is extended to investigate the direction of initial crack extension at the tip of blunt cracks (notches) in combined Mode 1-Mode 2 loading. Three different governing strain energy density functions are postulated for comparison, and each is applied to the ideally sharp and the blunt notch cases. It is found that the sharp and blunt notch solutions agree in the limits of pure Mode 1 loading, but their difference grows as K1/K2 value is decreased and becomes most conspicuous in the limit of pure Mode 2 loading. It is also found that the above solution difference is greatest near the crack tip and diminishes at a large distance from the crack tip. For both the sharp and blunt notch solutions, the deviatoric strain energy density function predicts a larger absolute value of the critical angle θc than does the total strain energy density function. The results are compared with those obtained by using the classical method of “maximum tangential (tensile) stress” for predicting the crack trajectories.

Effects of root radius, stress, crack growth and rate on fracture instability

Of various criteria for fracture at the root of a notch, the energy, local stress, and displacement criteria have limited validity. More appropriate is the history of both stress and strain over a small region ahead of the crack, as required for fracture by the coalescence of holes. Expressions are given for crack initiation, growth, and subsequent instability in anti-plane strain of a non-hardening material. Instability is shown to depend primarily on those strain increments arising from crack grow that constant load rather than on those from increasing load at constant crack length. Thus final instability conditions are similar for single and double-ended cracks, round notches, and cracks cut under constant load. Round notches may give instability, restabilization, and final instability. The growth and coalescence of holes in front of a crack in a linearly viscous material is studied for both tensile and anti-plane-strain cracks. The absence of residual strain eliminates instability, but the crack continually accelerates.