Fatigue strength evaluation for bolt-nut connections having slight pitch difference considering incomplete threads of nut

Proceedings of 4th International Conference on Fracture Fatigue and Wear, FFW 2015, Ghent University, Belgium, 27-28 August 2015The high strength bolts and nuts are widely used in various fields. In this study the effect of slight pitch difference is considered when the nut pitch is αμm larger than the bolt pitch. In the first place, the fatigue experiment is conducted with varying pitch difference. The results show that the fatigue life is extended to about 1.5 times by introducing the suitable pitch difference under the high stress amplitude. Next, the detail observation is performed on the fractured specimens including the fractured positions and the crack configurations. It is found that the fractured positions and the crack distributions vary depending on the pitch difference. Finally, to clarify the improvement mechanism of the fatigue strength, the finite element method is applied to calculate the stress amplitude and mean stress at each bolt threads, and the incomplete threads at the nut ends are also considered to obtain the accurate analytical results

Convenient and accurate formulas for stress intensity factor distribution of semi-elliptical surface crack

In this paper, the stress intensity factor (SIF) formula FISE along the crack front of a semi-elliptical surface crack is studied. The exact SIF solution FISE is used by solving the hypersingular integral equation of the body force method discussed in the previous paper. To obtain the accurate formula, the SIF ratio FISE/FIE is focused considering the exact solution FIE of an elliptical crack. By applying the least squares method to the ratio FISE/FIE, accurate and convenient formula is proposed. The proposed formulas may provide the accurate SIF distributions for the aspect ratio a/b=1–4 better than 0.2% accuracy

Contact Analysis and Simulation of Rolled Plastic Film Used for Roof Ventilation in Japanese Greenhouses

Greenhouses are capable of producing a variety of high-value crops year-round. A novel Japanese greenhouse design is gaining popularity because of its automated roll-up ventilation system that is integrated into the roof. However, due to the frequent movement of the roll-up system, the plastic film deteriorates rapidly and typically lasts for only three or four months. In order to better understand the film deterioration, we studied the mechanics involved at the point of contact between the film and the metal greenhouse frame. We found that film deformation and failure were closely related to stretching and creasing, and these processes were observed at the microscopic level. An experimental device was developed to further study the damage to greenhouse film due to the roll-up movement. We concluded that the reduction in film thickness due to static loading or rolling contact was the best predictor of future film damage

Failure Analysis for Coming out of Shaft from Shrink-Fitted Ceramics Sleeve

This paper deals with failure analysis for coming out of the steel shaft from ceramic sleeve connected by shrink fitting. Only low shrink fitting ratio can be applied because of the brittleness of the ceramic sleeve. However, the steel shafts may be loosening out from the ceramic sleeve under such low shrink fitting ratio. In this study, the coming out behavior of the shaft during rotation is analyzed by the finite element method. The roller rotation is replaced by shifted load in the circumferential direction on the fixed roller. It is found that the load rotation can be approximated by the discrete load shifting at the interval angle θ0 = 12° within 1% error. The effect of the shrink fitting ratio on the coming out of the shaft is discussed as well as several other parameters, such as Young\u27s modulus of the shaft, the friction coefficient, magnitude of the load, and geometry of the shaft. Furthermore, it is found that the shear stress distribution at the shrink-fitted area may be useful for evaluating whether the coming out occurs or not

Stress and deformation of ceramic rolls to produce high quality zinc coated steel sheet

Several ceramic rolls can be used efficiently to produce high quality zinc coated steel sheet used for automobiles. Those ceramics rolls may provide a longer life and reduce the cost for the maintenance because of its large heat resistance and large wear resistance. One example may be seen in sink rolls used in molten zinc bath to manufacture zinc coated steel sheet. Since the rolls are subjected to large thermal stress and mechanical loading, care should be taken for the risk of fracture due to the ceramic brittleness. Moreover, since the sleeve and shafts can be connected only by using small shrink fitting ratio，another failure risk should be considered for the separation of those components [25, 26]. In this paper, therefore, the mechanical and thermal stress and separation condition will be investigated considering the separation of the connected portion. Here, by using the finite volume method the heat transfer coefficient is discussed and by using the finite element method the thermal stress is considered.12th International Conference on Damage Assessment of Structures 10–12 July 2017, Kitakyushu, Japa

Effect of Pitch Difference on Anti-loosening Performance and Fatigue Strength for High Strength Bolts and Nuts

A slight pitch difference is considered between the bolt and nut in this study. Here, the pitch ofnut is α μm larger than the pitch of bolt. In the first place, the distance δ, of nut screwed onto bolt withoutany prevailing torque, is experimentally and analytically obtained for each level of α. Then, the relationshipbetween axial force and prevailing torque during tightening process is tested. According to the obtainedtorque-axial force relationship, for four different levels of α, the loosening experiment based on NAS3350(National Aerospace Standard) is performed, and the loosening and dropping status of the nuts areinvestigated. Considering both the anti-loosening ability and the clamping ability of the nut, the desirablerange of α is discussed. After that, according to the loosening experiment results, three levels of α areselected to make a further study about the effect of the pitch difference on the fatigue life of bolt. The fatigueexperiment is performed and the S-N curves are obtained. Finally, the finite element method is used to makea simulation of the fatigue experiment and the mean stress and stress amplitude at each thread bottom of boltare analyzed.13th International Conference on Fracture, June 16–21, 2013, Beijing, Chin

Intensity of singular stress fields of wedge-shaped defect in human tooth due to occlusal force before and after restoration with composite resins

Wedge-shaped defects are frequently observed on the cervical region of the human tooth. Previously, most studies explained that improper tooth-brushing causes such defects. However, recent clinical observation suggested that the repeated stress due to occlusal force may induce the formation of these wedge-shaped defects. In this study, therefore, two-dimensional human tooth models are considered with and without a wedge-shaped defect by applying the finite element method. To evaluate large stress concentrations accurately, a method of analysis is discussed in terms of the intensity of singular stress fields appearing at the tip of the sharp wedge-shaped defect. The effects of the position and direction of occlusion on the intensity of singular stress fields are discussed before and after restoration with composite resins

Semi-automatic retractable handrail utilizing opening/closing movement of sliding door supporting elderly people to walk independently

The purpose of this research is to install a handrail on the sliding doors used in hospitals and nursing facilities to support senior and people with disabilities to walk by themselves. The semi-automatic lifting equipment is utilized for the retractable handrail to make sure people in bad health are able to open the door using a weak force. To design the handrail for this purpose, the theoretical formula for opening force is derived. Then the simulation is performed with varying geometry conditions confirming the results are in good agreement with the experiment results. The opening force is designed to be less than the target value previously reported. The sliding door developed in this study is useful for elderly people walking by themselves safely.Peer Reviewe

Laparoscopic resection of two peritoneal loose bodies on the rectosigmoid colon

Laparoscopic examination of a 77-year-old woman revealed two peritoneal loose bodies connected to fatty appendices on the rectosigmoid colon and resected at the stalks. The peritoneal loose bodies were found to be fat-containing masses on preoperative magnetic resonance imaging, and postoperative pathological examination revealed fat degeneration tissue with or without fibrous outer layers