Method for Estimating Thread Strength Reduction of Damaged Parent Holes with Inserts

During normal assembly and disassembly of bolted-joint components, thread damage and/or deformation may occur. If threads are overloaded, thread damage/deformation can also be anticipated. Typical inspection techniques (e.g. using GO-NO GO gages) may not provide adequate visibility of the extent of thread damage. More detailed inspection techniques have provided actual pitch-diameter profiles of damaged-hardware holes. A method to predict the reduction in thread shear-out capacity of damaged threaded holes has been developed. This method was based on testing and analytical modeling. Test samples were machined to simulate damaged holes in the hardware of interest. Test samples containing pristine parent-holes were also manufactured from the same bar-stock material to provide baseline results for comparison purposes. After the particular parent-hole thread profile was machined into each sample a helical insert was installed into the threaded hole. These samples were tested in a specially designed fixture to determine the maximum load required to shear out the parent threads. It was determined from the pristine-hole samples that, for the specific material tested, each individual thread could resist an average load of 3980 pounds. The shear-out loads of the holes having modified pitch diameters were compared to the ultimate loads of the specimens with pristine holes. An equivalent number of missing helical coil threads was then determined based on the ratio of shear-out loads for each thread configuration. These data were compared with the results from a finite element model (FEM). The model gave insights into the ability of the thread loads to redistribute for both pristine and simulated damage configurations. In this case, it was determined that the overall potential reduction in thread load-carrying capability in the hardware of interest was equal to having up to three fewer threads in the hole that bolt threads could engage. One- half of this potential reduction was due to local pitch-diameter variations and the other half was due to overall pitch-diameter enlargement beyond Class 2 fit. This result was important in that the thread shear capacity for this particular hardware design was the limiting structural capability. The details of the method development, including the supporting testing, data reduction and analytical model results comparison will be discussed hereafter

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

An alternative to the plasma emission model: Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts

1.5D PIC, relativistic, fully electromagnetic (EM) simulations are used to model EM wave emission generation in the context of solar type III radio bursts. The model studies generation of EM waves by a super-thermal, hot beam of electrons injected into a plasma thread that contains uniform longitudinal magnetic field and a parabolic density gradient. In effect, a single magnetic line connecting Sun to earth is considered, for which several cases are studied. (i) We find that the physical system without a beam is stable and only low amplitude level EM drift waves (noise) are excited. (ii) The beam injection direction is controlled by setting either longitudinal or oblique electron initial drift speed, i.e. by setting the beam pitch angle. In the case of zero pitch angle, the beam excites only electrostatic, standing waves, oscillating at plasma frequency, in the beam injection spatial location, and only low level EM drift wave noise is also generated. (iii) In the case of oblique beam pitch angles, again electrostatic waves with same properties are excited. However, now the beam also generates EM waves with the properties commensurate to type III radio bursts. The latter is evidenced by the wavelet analysis of transverse electric field component, which shows that as the beam moves to the regions of lower density, frequency of the EM waves drops accordingly. (iv) When the density gradient is removed, electron beam with an oblique pitch angle still generates the EM radiation. However, in the latter case no frequency decrease is seen. Within the limitations of the model, the study presents the first attempt to produce simulated dynamical spectrum of type III radio bursts in fully kinetic plasma model. The latter is based on 1.5D non-zero pitch angle (non-gyrotropic) electron beam, that is an alternative to the plasma emission classical mechanism.Comment: Physics of Plasmas, in press, May 2011 issue (final accepted version

Investigation for a suitable screw of a briquetting machine

[Abstract]: Briquetting is a well-established technology. But its crucial part is the screw wear, which has a great influence on the cost of production. The aim of this study is to look for the suitable parameters of screw, which can make this technology attractive to the people. With this objective, the study of existing Bangladeshi screw and a few newly designed screws has been done. Four different types of new screw have been constructed, the design and idea of which are taken from the experience of the Institute of Energy in Vietnam. The remarkable features of the screw are that it is short in length and the thread is not made as an integral part of the base of screw. Different types of pitch and height of screw have been used for this stud

Hexapod Design For All-Sky Sidereal Tracking

In this paper we describe a hexapod-based telescope mount system intended to provide sidereal tracking for the Fly's Eye Camera project -- an upcoming moderate, 21"/pixel resolution all-sky survey. By exploiting such a kind of meter-sized telescope mount, we get a device which is both capable of compensating for the apparent rotation of the celestial sphere and the same design can be used independently from the actual geographical location. Our construction is the sole currently operating hexapod telescope mount performing dedicated optical imaging survey with a sub-arcsecond tracking precision.Comment: Accepted for publication in PASP, 10 page

Investigation of tool geometry effect and penetration strategies on cutting forces during thread milling

The application of thread milling is increasing in industry because of its inherent advantages over other thread cutting techniques. The objective of this study is to investigate the effect of milling cutter tool geometry on cutting forces during thread milling. The proposed method can compare the performance of milling cutters in spite of the different number of tooth. The best thread milling cutter among the studied tools was determined from the cutting forces point of view. Furthermore, this study also pinpoints the best penetration strategy that provides minimum cutting forces. Lower cutting force variations will lead to fewer vibrations of the tool which in turn will produce accurate part.Postdoc de V Sharma financé par la région Bourgogn

Carbon electrode development program Final report, 3 Nov. 1964 - May 1965

Solar arc positive carbon electrodes with improved joint strength and minimized arc sputterin

Analysis of API 5C3 failure prediction formulae for casing and tubing

Due to the increasing demand for oil and gas, coupled with the fact that oil reserves are becoming rather scarce, the petroleum industry is pushed to drill and complete deeper wells. Threaded connections are often the weakest link in this process and are therefore the subject of research and optimization. At first, this paper presents a brief overview of the design characteristics of today’s premium connections. Secondly, the failure mechanisms of Oil Country Tubular Goods (OCTG) are discussed. At last, an in-depth analysis of the API 5C3 formulae is given. Four formulas for collapse are given in API 5C3, each valid for a specific D/t range. With increasing yield strength of the steel, the difference between the yield strength collapse and the plastic collapse gets larger. Also, the elastic collapse zone gets bigger, so stronger materials with relatively large D/t ratios will collapse in the elastic zone instead of the plastic or transition zone. These four formulas can be approached by a third-order polynomial equation that is valid for all D/t ratios