Bolt Body Research Articles

A Parametric Study of Ridge-cut Explosive Bolts using Hydrocodes

Explosive bolts are one of pyrotechnic release devices, which are highly reliable and efficient for a built-in release. Among them, ridge-cut explosive bolts which utilize shock wave generated by detonation to separate bolt body produce minimal fragments, little swelling and clean breaks. In this study, separation phenomena of ridge-cut explosive bolts or ridge-cut mechanism are computationally analyzed using Hydrocodes. To analyze separation mechanism of ridge-cut explosive bolts, fluid-structure interactions with complex material modeling are essential. For modeling of high explosives (RDX and PETN), Euler elements with Jones-Wilkins-Lee E.O.S. are utilized. For Lagrange elements of bolt body structures, shock E.O.S., Johnson-Cook strength model, and principal stress failure criteria are used. From the computational analysis of the author’s explosive bolt model, computational analysis framework is verified and perfected with tuned failure criteria. Practical design improvements are also suggested based on a parametric study. Some design parameters, such as explosive weights, ridge angle, and ridge position, are chosen that might affect the separation reliability; and analysis is carried out for several designs. The results of this study provide useful information to avoid unnecessary separation experiments related with design parameters.

Separation characteristics study of ridge-cut explosive bolts

Explosive bolts are one type of reliable and efficient pyrotechnic release devices used for many applications. Although numerous explosive bolts have been designed and utilized, most design processes rely on experience based on repetitive experiments. In order to provide a better understanding of the separation behavior of explosive bolts, separation behavior analysis environments for the ridge-cut explosive bolts are established. Ridge-cut explosive bolts, which are separated by ridge-cut mechanism or spallation, are analyzed using AUTODYN. From the behavior analysis of explosive bolts whose design was based on the author's prior experience, the numerical analysis method is verified, including appropriate failure criteria. Utilizing the proposed methodology, the separation characteristics of ridge-cut explosive bolts according to confinement conditions, and especially the gap distance between the bolt body and the fixture, are studied. A degradation in separation reliability due to tight gap distance is observed in separation experiments. This separation phenomenon is specifically clarified by the separation behavior analysis. Based on the numerical study of separation characteristics, some design improvements considering manufacturing tolerance are proposed here.

Stress wave propagation in supporting bolts: A test for bolt support quality

A test method for the non-destructive determination of bolt length, anchoring length, and bolt body force is described. This addresses the problems of low accuracy, limited number of data, and untimely warning signs encountered with existing test methods. Numerical simulations of the bolt, resin, and rock system show that the length accuracy when using the velocity wave is lower than when using the acceleration wave. It is accepted practice to use the acceleration wave for length tests because of improved signal to noise ratios of the waveforms. Laboratory and in situ underground tests showed that the precision of the measurements meets field requirements. Using this method the anchor properties of each single bolt and, thus, the safety of the entire roadway support may be evaluated.

볼트 몸체 특정 부위 팽창을 이용한 풀림 방지 볼트 연구

The present work has suggested the design methods of the bolt body for making the anti-releasing bolts and provided the changed properties of the bolt body after explosion. To prove this work, two models of the anti-releasing bolts, M10 and M20, are produced and the expansion properties of each model are experimentally obtained. This study verify that the expansion of the bolt body is reproducible and the expansion rate could be controlled by the combination of the design factors and the anti-releasing characteristics could be quantified. It also could provide the data that would be needed to make the bolts with the anti-releasing effect.

Longevity enhancement of bolted joints for aircrafts

New designs of bolted joints with bolt countersunk heads having high longevity in comparison with the used ones were proposed. One type of joint has the bolt heads with the reduced surface taper of the bolt head and in a joined part. Two other types have a spherical head surface, which is in contact with a tapered countersink surface. The rise in the fatigue life is achieved owing to the balance of the radial tension along the contact surfaces of the head and the countersink. Designs of a washer from the direction of a nut are proposed. These washers have ring bulges of wedge-shaped cross section that form areas of plastic deformations around a bolt body during the bolt tightening and reduce the concentration of contact stresses close to an edge of the contact surfaces of the bolt and joined parts. Procedures of fatigue tests were developed. Results of tests of the proposed bolted joints supporting their high longevity are presented. Findings of experimental investigations verify the efficiency of the application of proposed types of bolted joints in the designs of aircrafts.

せん断荷重を受ける多数ボルト締結体の力学特性の評価

When subjected to external forces, bolted joints behave in a complex manner especially in the case of the joints being clamped with multiple bolts. Friction type joints are widely used for the joints subjected to shear loads. Bearing type joints, which support the shear load on the surface of bolt body, are used less frequently, since its mechanical behavior is too complicated to accurately estimate the load capacity. In this study, mechanical behavior of multi-bolted joints subjected to shear loads is comprehensively analyzed by three-dimensional FEM. Load distribution patterns of the bearing type joint are compared to those of the friction type joint. It has been found that the shear load, which is applied to the bearing type joint, distributes with a concave shape along the load direction as the number of bolts is increased and a fair amount of the shear load is supported by friction. Additionally, a simple method that calculates the shear load distribution is proposed using elementary theory of solid mechanics, which can estimate the shear load distribution with sufficient accuracy for the case of small friction coefficient.

틸팅차량용 차체의 Hybrid 복합재 접합체결부의 정적 및 피로 파괴 평가

Fatigue fracture behavior of a hybrid bolted joint was evaluated in comparison to the case of static fracture. Two kinds of specimens were fabricated for the mechanical tests; a hybrid bolted joint specimen for the shear test and a hybrid joint part specimen applied in the real tilting car body for the bending test. Characteristic fracture behaviors of those specimens under cyclic loads were obviously different from the case under static loads. For the hybrid bolted joint specimen, static shear loading caused the fracture of the bolt body itself in a pure shear mode, whereas cyclic shear loading brought about the fracture at the site of local tensile stress concentration. For the hybrid joint part specimen, static bend loading caused the shear deformation and fracture in the honeycomb core region, while cyclic bend loading did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.

Roof Bolts Broken Mechanism and Their Reasonable Construction Structures

Since the broken phenomenon is always appeared in the roof of mine roadway, it largely affects the roadway’s roof stability. With Material Mechanics theory, the authors expound bolt tail subjected to no center load action and roof bolt broken mechanism while roadway is supported with bolts. By theoretical analysis and Lab test, the paper puts forward a kind of new type bolts which may prevent bolt tails from being broken, bolt construction structure’s pattern, and bolt made technology. It is illustrated that the reasonable grading relationship between bolt body’s iameter and bolt tail’s screw diameter. At same time, the authors compare disturbed values of the thick tail metal bolt and common bolt under the load action. It is verified that roof bolt broken problem may be solved with new type’s thick tail bolt. Therefore, the new type bolts have a wide application in the future.

볼트결합부를 포함한 구조물의 정적 및 동적 해석을 위한 유한요소 모델링

Many studies on the finite element modeling for bolted joints have proceeded, but the structures with bolted joints are complicated in shape and it is difficult to find out the characteristics according to joint condition. Usually, experimental methods have been used for bolted joint analysis. A reliable and practical finite element modeling technique for structure with bolted joints is very important for engineers in industry. In this study, three kinds of model are presented; a detailed model, a practical model and a simple model. The detailed model is modeled by using 3-D solid element and gap element, and the practical model is modeled by using shell element (a portion of bolt head) and beam element (a portion of bolt body), the simple model is modeled by simplifying practical model without using gap elements. Among these models, the simple model has the least degree of freedom and show the effect of memory reduction of 59%, when compared with the detailed model.