Phenomenological aspects of a modified fragmentation test using small quantities of explosive

This paper describes the phenomenological aspects of a modified fragmentation test which utilizes an annulus of high explosive in contact with the inner wall of a cylinder of material under test. The shock interactions within the cylinder wall on detonation of the explosive are modelled using a one-dimensional Lagrangian computer code. Predictions of fragment velocities are made in this work. The velocities are found to be influenced by the spallation of the cylinder and this effect can be accounted for in the model by using the position of the spall surfaces which have been obtained from experimental firings of cylinders.

The fragment velocities are found to be much lower than those predicted for a conventional fragmentation test which utilizes a cylinder completely filled with high explosive and this suggests that the post-fragmentation damage of the fragments on recovery from the modified fragmentation test will be small. Experimental evidence from the steel cylinders tested in this work shows that the fragmentation mechanisms operating at the initiation of the test are similar to those reported for a conventional fragmentation test.     

Cleavage Stress Required to Produce Fracture Path Deflection in Cold-Drawn Prestressing Steel Wires

Cold-drawn prestressing steel wires exhibit strength anisotropy in the form of fracture path deflection towards a direction approaching the wire axis, or cold drawing line, as a consequence of the pearlitic microstructure orientation induced by the manufacturing procedure. Such a crack path deflection is initiated at certain nuclei (fracture origins) at which axial cracking appears in the cold drawing direction (or wire axis) in the form of micro-cleavage units that produce in the load-displacement curve a macroscopic phenomenon of pop-in. This paper shows that such fracture initiators appear at a certain distance from the fatigue pre-crack tip at which a local maximum of the cleavage stress is located.     

The effect of metal wires on the fracture of a brittle-matrix composite

The behaviour of stainless steel, work-hardened nickel and annealed nickel wires bridging a crack in a brittle-matrix has been studied as a function of the length and orientation of the wire. The pull-out stress for stainless steel wire in epoxy resin increases less than linearly with wire length, following the behaviour predicted by Takaku and Arridge [6]. Wires inclined at 20° and 40° to the tensile axis gave pull-out stresses some 30% higher than wires parallel to the tensile axis, this increase being attributed mainly to enhanced friction on the bent wire near its point of exit from the matrix. Work-hardened nickel wires fractured when their length exceeded a critical value, and the critical length was significantly shorter for inclined wires than for wires parallel to the tensile axis. In contrast, annealed nickel wires, no matter how long, did not fracture but pulled out at a limiting stress which was slightly higher for inclined wires than for wires parallel to the tensile axis. The results show that, in some cases, there does not exist a critical length above which an embedded wire will fracture rather than pull out of the matrix.     

壁厚对HR2钢柱壳爆轰加载下膨胀断裂行为的影响

通过对6、12 mm两种不同壁厚的HR2钢柱壳进行爆轰加载实验,对其断裂碎片的宏观形貌、断口的微观形貌以及横截面的变形微观结构进行系统表征,研究了金属柱壳在爆轰加载下的膨胀断裂机理。结果表明,在膨胀断裂过程中壳壁厚度的增大导致HR2钢柱壳由纯剪切断裂变为拉剪混合的断裂模式。断裂碎片的微观结构分析结果表明,柱壳的断裂实际上是剪切裂纹从样品内部剪切带形核并扩展、和拉伸裂纹沿柱壳外表面的形核扩展的共同作用及竞争的结果。薄壁柱壳断裂由样品内裂纹沿剪切带的形核和扩展主导发生剪切断裂,而厚壁柱壳中内侧的裂纹沿剪切带的形核和扩展,但是最外侧则为环向拉应力主导发生拉伸断裂,因此表现出拉剪结合的断裂模式。     

Effect of heat treatment on small scale fragmentation of aluminium alloy

Abstract

Small scale explosions, using a detonator, of 7075 aluminium alloy cylinders, 15–100 mm outside diameter, were carried out to investigate the effects of heat treatment on fragmentation. This was the finest for the strongest as received alloy and coarsest for the softest overaged alloy. This effect was similar to that seen in investigations of the fragmentation of steel. Cylinders of 50 and 100 mm in diameter did not fragment but plastically deformed with maximum deformation at the cylinder bottom. Fragmentation of 33 and 42 mm diameter cylinders produced long fragments typical of the break-up of thick walled cylinders. At smaller diameters, break-up gave fragments of several shapes, finer fragments being largely associated with the smallest diameter cylinders and the highest strength alloys. Results followed those seen in large scale studies of cylinder break-up and suggest the possibility of using small scale fragmentation experiments in the investigation of the effects of composition, heat treatment and processing on natural fragmentation.     

Explosive Deformation and Fracture of Thick-Wall Cylinders

Deformation and fracture behavior of thick-wall cylinders under the action of detonation products was considered. Upon the outflow of the detonation products from the bore filled with explosive, spalling effects in the end of the cylinder and regular vortex structures over its thickness were noted.     

On the Critical Point of Tungsten

Experimental results of exploding tungsten wire experiments with heating rates of 10¹⁰ to 10¹¹ Ks^–1 are interpreted using a one-dimensional hydrodynamic model. The vaporization dynamics under these conditions are discussed. It is shown that for the wires used the superheating of the liquid phase is small and vaporization starts close to the binodal line of the phase diagram. Due to inertia, a volume vaporization takes place in a thin surface layer, while in the bulk of the column formed by the exploding wire a pressure of the order of 10 kbar is maintained. Sufficiently uniform density and temperature distributions are formed in the liquid core surrounded by the two-phase layer. This behavior of vaporizing wires was used to obtain the thermal expansion coefficient of liquid tungsten along with its critical point parameters.     

Fragmentation model for expanding cylinder

A two-dimensional energy-based model of fragmentation of rapidly expanding cylinder under plane strain conditions is proposed. The model allows us to estimate the average fragment length and the number of fragments produced by ductile fracture of the cylinder. Comparison of obtained results with published experimental data on the fragmentation of the aluminum rings and cylinders shows that they are in good agreement.     

A radially cracked,cylindrical fracture toughness specimen

A new fracture toughness specimen in the shape of a hollow circular cylinder has been characterized, allowing more economical and representative use of as-formed cylinders in toughness tests. Several configurations of a cylinder with radial cracks parallel to the axis of revolution are described with respect to crack mouth compliance and stress intensity factor. Specimen geometries useful for fracture toughness tests are analyzed in detail, based on results derived from finite-element codes. Results of experiments using 707S-T6 aluminum and uranium alloys of known toughness showed good agreement with the analytical results.     

The influence of the drawing parameters and temperature rise on the prediction of chevron crack formation in wire drawing

The objective of the present work is to predict the formation of chevron crack in copper wire drawing process. The first part of this paper is to determine the chevron crack formation initiated by a central burst inside the wire material using experimental tests. These results are compared with results from a series of numerical simulations using the Cockcroft?CLatham fracture criterion. The second part of this work concerns the determination of a curve that divides the chevron and safe zones for a better wire drawing process. The conditions of central burst defects formation along the wire axis depend on drawing parameters and friction coefficient between the die and the wire. The friction coefficient is defined as a linear function of temperature rise which is measured close to the wire-die interface. The obtained results show that the friction coefficient depending on temperature rise during wire drawing has an impact on the damage of copper wire.     

Preparation and magnetic properties of cylindrical NiFe films and antidot arrays

Continuous NiFe (Permalloy) cylindrical films and arrays of cylindrical NiFe antidots 7 nm thick have been prepared by sputtering onto cylindrical aluminum wires and onto wires anodized to form a porous anodic alumina layer. The antidots are arranged in a close-packed pattern determined by the hexagonal pore arrangement in the porous alumina, with period 103 nm and diameter 42 nm. Hysteresis loops were measured at different angles with respect to the cylinder axis and indicate an easy plane normal to the radius of the wire. The antidots enhance the coercivity compared to the continuous cylindrical film.     

The dependence of the optoelectrical properties of silver nanowire networks on nanowire length and diameter

We have characterized the optoelectrical properties of networks of silver nanowires as a function of nanowire dimension by measuring transmittance (T) and sheet resistance (R(s)) for a large number of networks of different thicknesses fabricated from wires of different diameters (D) and lengths (L). We have analysed these data using both bulk-like and percolative models. We find the network DC conductivity to scale linearly with wire length while the optical conductivity is approximately invariant with nanowire length. The ratio of DC to optical conductivity, often taken as a figure of merit for transparent conductors, scales approximately as L/D. Interestingly, the percolative exponent, n, scales empirically as D2, while the percolative figure of merit, Π, displays large values at low D. As high T and low R(s) are associated with low n and high Π, these data are consistent with improved optoelectrical performance for networks of low-D wires. We predict that networks of wires with D = 25 nm could give sheet resistance as low as 25 Ω/□ for T = 90%.     

Strength and Fracture Behavior of Ultrathin Pt Wires

Ultrathin metallic wires having defects may show much lower strength compared to the strength of the wire material. To characterize ultrathin Pt wires having the nominal diameter of 625 nm, tensile test of the wires was performed by developing a testing platform and a gripping technology. Fracture stress determined by the tensile test showed much higher value compared with that of bulk Pt. However, the fracture stress of some of the wires was lower than the yield stress of the wire determined by the bending test. From the observation of the fracture surfaces, it was found that the lower fracture stress of the wires was due to the defects in the wires and such wires showed brittle fracture behavior.     

加速膛孔径对冲击片换能元换能特性的影响

加速膛在冲击片换能元中起着剪切飞片和提供飞片加速通道的功能,其孔径对飞片速度形态有重要的影响。本文中,研究不同加速膛孔径对冲击片换能元在不同回路参数条件下的爆发电流和飞片速度的影响规律,并且与数值模拟计算结果进行对比。结果表明,在相同的短路电流峰值和桥箔条件下,加速膛孔径对桥箔的爆发电流没有明显影响,但是对飞片速度有较大影响。加速膛孔径增加,飞片面积增加,飞片速度相应减小;但是飞片面积存在着一个最大值S_max,当加速膛孔的面积大于S_max时,飞片的面积会保持为一定值,不再随着加速膛孔径的增加而变化,此时加速膛失去剪切飞片的功能,只是保留了提供飞片加速通道的功能,从而导致飞片速度不再发生变化。对于文中的起爆回路和桥区尺寸为0.3 mm×0.3 mm×0.005 mm的铜桥箔来讲,可以近似认为S_max=0.3²πmm²,对应的加速膛孔径约为0.60 mm。研究结果为加速膛的孔径设计范围提供依据。     

FLOW PATTERNS THROUGH TUBE BUNDLES AND PARTICULATE FOULING ONTO CYLINDERS

The shear-stress distributions around cylinders in tube bundles were measured by means of the limiting current method and the flow inside the bundle was also visualized. In the case of the staggered bundle, the shear-stress distributions had two peaks by the effect of the jet streams generated at the front row spacing and the adjacent cylinder. While in the bundle with in-line arrangement, the front stagnant point was shifted about 30° downward and the traverse streams among the rows were observed. This traverse streams caused asymmetry of the shear-stress distributions with respect to the main flow axis.

These results were discussed in connection with the fouling experiments investigated in dusty air. Particle deposition around cylinders could be qualitatively predicted from the shear-stress distributions, namely particles tend to deposit at positions where are less shear-stress in both tube arrangements. The size of particle deposited on the wake zone was coarser than that near the stagnant point behind the third row in both arrangements.     

氢气瓶爆炸原理及其防范措施探讨

通过对一起氢气瓶爆炸事故处理,总结了处置潜在爆炸危险气瓶的成功方案,应用事故树分析方法,结合生产装置实际情况和前后爆炸的3只气瓶,探讨分析了引起氢气瓶爆炸的直接原因,有针对性的提出了防止同类事故发生的措施.     

FLOW PATTERNS THROUGH TUBE BUNDLES AND PARTICULATE FOULING ONTO CYLINDERS

ABSTRACT

The shear-stress distributions around cylinders in tube bundles were measured by means of the limiting current method and the flow inside the bundle was also visualized. In the case of the staggered bundle, the shear-stress distributions had two peaks by the effect of the jet streams generated at the front row spacing and the adjacent cylinder. While in the bundle with in-line arrangement, the front stagnant point was shifted about 30° downward and the traverse streams among the rows were observed. This traverse streams caused asymmetry of the shear-stress distributions with respect to the main flow axis.

These results were discussed in connection with the fouling experiments investigated in dusty air. Particle deposition around cylinders could be qualitatively predicted from the shear-stress distributions, namely particles tend to deposit at positions where are less shear-stress in both tube arrangements. The size of particle deposited on the wake zone was coarser than that near the stagnant point behind the third row in both arrangements.     

船用螺旋桨的爆破拆解

论述了船用螺旋桨爆破拆解的基本原理及实施过程，提出了一套完整线状聚能切割器的设计程序及轮毂的水压控制爆破拆解的设计原则。     

A practical in situ wire: a composite wire with many in situ processed Nb3Sn cores of an internal diffusion type

As a superconducting in situ wire for practical use, we propose a new type of composite wire with fine cores consisting of in situ processed wires of an internal diffusion type. These Nb₃Sn wires have merit in a simple fabrication process and a high stability compared with ordinary multifilamentary Nb₃Sn wires. Expected properties of the new type of Nb₃Sn wires were estimated based on a series of experimental results for a single in situ Nb₃Sn wire used as a fine core. A quantitative reliability of the new design estimation was examined by comparing the theoretical values with observed data on the electromagnetic properties of a test wire.     

End Effects in the Three-Omega Method to Measure Gas Thermal Conductivity

A two-dimensional analytical solution is derived for the three-omega method for measurement of thermal conductivity of materials with a fine wire. The analytical solution includes the wire heat capacity and the effect of heat losses from the ends of the wire. To derive the solution, finite Fourier transforms are applied in the direction parallel to the wire axis. The solution is compared with a one-dimensional solution and experimental data. It is found that heat losses from the wire ends have a significant effect on the 3ω components at low frequency and tend to be less important at high frequency. Moreover, it is shown that two-dimensional effects will be severe for nano-scale wires, even if the wire length-to-diameter ratio is very large.