• 021-55264716,18
  • info@behinfoolad.ir
مطالعه آزمایشگاهی در مورد تاثیر شکل پیچ و مهره بر استحکام خستگی اتصال پیچ و مهره ای
  • 7
  • خرداد

مطالعه آزمایشگاهی در مورد تاثیر شکل پیچ و مهره بر استحکام خستگی اتصال پیچ و مهره ای

IOP Conference Series: Materials Science and Engineering

 

 

 

 

 

 

PAPER • OPEN ACCESS

 

Experimental study on the effect of shape of bolt and nut on fatigue strength for bolted joint

To cite this article: T Matsunari et al 2018 IOP Conf. Ser.: Mater. Sci. Eng. 372 012016

 

 

 

View the article online for updates and enhancements.

 

Related content

X Liu, N-A Noda, Y Sano et al.

 

Sumio Takahashi, Katsunori Okajima and Akio Hasegawa

 

S Kubo, K Tateishi, N-A Noda et al.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This content was downloaded from IP address 84.241.55.30 on 20/01/2020 at 10:25

 

 

 

 

 

 

 

 

 

 

Experimental study on the effect of shape of bolt and nut on fatigue strength for bolted joint

 

T Matsunari1, K Oda2,5, N Tsutsumi2, T Yakushiji 3, N A Noda4 and Y Sano4

1Graduate School of Engineering, Oita University, 700 Dannoharu, Oita 870-1192, Japan

2Division of Mechanical Engineering, Oita University, 700 Dannoharu, Oita 870-1192, Japan

3National Institute of Technology, Oita College, 1666 Maki, Oita 870-0152, Japan 4Mechanical Engineering Department, Kyushu Institute of Technology, 1-1 Sensui- cho Tobata-ku, Kitakyushu-shi, 804-8550, Japan

 

E-mail: oda-kazuhiro@oita-u.ac.jp

 

Abstract. In this study, the effect of curvature radius of the thread bottom and the pitch difference between of M16 bolt and nut on fatigue strength for bolted joint is considered experimentally. The M16 bolt-nut specimens having the two kinds of thread bottom radii and the pitch differences are prepared. The S-N curves for bolted specimens with different thread shapes are obtained by the stress-controlled fatigue test (stress ratio R>0). The experimental results are compared and discussed in terms of stress analysis. The finite element method is used to make a simulation of the fatigue experiment and the mean stress and stress amplitude at each thread bottom of bolt are analysed. It is found that the initiation and propagation of crack

are  changed  by introducing the  pitch difference  of α=15 μm,  from the  crack  observation in

cross section of the bolt specimens after the experiment. Furthermore, the fatigue life can be extended by increasing curvature radius of thread bottom and introducing the pitch difference.

 

 

1. Introduction

The bolted connection is one of the most important mechanical components and is used frequently.  For instance, since about 1,000 bolts and nuts joints are used in a single car, high fatigue strength at low cost is required. Damage of the bolt-nut joint is due to high stress concentration at the bolt thread bottoms and its strength is reduced. To ensure the safety and reliability of the bolted joint, researches on anti-loosening performance have been actively conducted [1-3]. However, there are not many studies on fatigue strength improvement of bolted connections. It is not easy to improve the fatigue strength of standard shape of bolt-nut joint because high stress concentration always occurs at the bottom of bolt thread.

Focusing on the stress relaxation at the thread bottom due to the shape change of the bolt [4-7] and the material difference of the fatigue strength [8], several studies have been conducted to improve the fatigue strength of the bolted joint. The effect of the pitch difference between the nut and the bolt on the stress concentration at the screw thread of the bolt has been studied previously and it is reported that the fatigue strength can be improved by changing the contact state between the bolt and the nut [9- 14]. In particular, Noda et al [9-13] analysed the effects of anti-loosening and stress reduction for the bolt-nut joint with small pitch difference, and showed that the fatigue life of the bolted joint can be

 

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Published under licence by IOP Publishing Ltd                             1

 

 

 

improved by using the pitch difference of a=15 mm. However, the studies on the conventional pitch difference were limited to the improvement of fatigue life for the standard shape bolt thread.

In this study, a more detailed fatigue test is systematically carried out for a new bolt specimen with small pitch difference a and large thread bottom radius r. Here, the standard bolt-nut joint has a=0 and r=r0. Then, from the S-N curves obtained for the bolted specimens, the improved fatigue lives are discussed. To clarify the effects of the thread bottom radius and the pitch difference, stress amplitude and average stress at each bolt thread are analysed by the finite element method (FEM). By comparing the experimental results with the results computed using FEM, the mechanism of improvement in fatigue life of bolted specimen is examined.

 

2. Fatigue experiment to investigate the fatigue life

 

    1. Specimens and experimental conditions

In this study, the Japanese Industrial Standard (JIS) M16 bolt-nut joints of strength grade 8.8 are used. The bolt is made from chromium-molybdenum steel SCM435, and the nut is the quenched and tempered medium carbon steel S45C, and their properties are indicated in table 1. Figure 1 shows schematic diagram of bolted joint. Numbers -3, -2 … 7, 8 in figure 1 correspond to the bottom of each thread. The fatigue experiment device assembly drawing is illustrated in figure 2. The Servo Fatigue Testing Machine (392 kN) is used at a cycle frequency of 5 or 10 Hz in this test. The bolt specimen is subjected to a mean tensile force of 30 kN. Since the area AR of the bolt cross section is 141 mm2, the

stress-controlled fatigue experiment is conducted under the corresponding mean tensile stress

کد رهگیری وضعیت پروژه خود را وارد کنید.