Two explosively loaded cylindrical shell experiments were conducted to provide experimental data for benchmarking numerical codes. Each shell was subjected to internal high-explosive detonations, which caused it to expand outwardly at strain rates on the order of 104 s–1. At approximately 150 percent strain, multiple plastic instabilities appeared on the surface of these shells in a quasi-periodic pattem. These instabilities continued to develop into bands of localized shear and eventually formed cracks before causing the shell to fragment. Diagnostic equipment on these experiments included a Fabry-Perot interferometer and a fast-framing camera. The experiments and the data obtained from the diagnostic equipment are discussed and illustrated.]]>

Pipeline steels have been widely used in a long-distance transportation of large amounts of crude oil or natural gas under high pressure due to their high transportation efficiency, low energy loss and production cost. For high pressure gas transmission pipelines made from high-strength steels an important problem is to know their fracture behavior in a long running process. In this paper, fracture toughness of X80 pipeline steel was measured by V-notch Charpy impact test at -20 and\linebreak -60 ℃. OM, SEM, EDS and EBSD were used to analyze its fracture mechanism. Experimental results show that the maximum impact load is slightly influenced by temperature, but with the decrease of temperature, crack forming work, crack propagating work and energy absorbed by crack arresting decrease significantly. During fracture process, the intensive tensile stress in the sample would induce the deformation bands formed around the fracture surface and grains elongated along the direction vertical to the main crack, but original austenite grain boundaries are hardly deformed, it would cause stress concentration and then produce intergranular fracture. Generally, brittle second phase particles could act as crack sources under intensive internal stress. In the crack propagation process, grains near the main crack are deformed and elongated tempestuously, resulting in their breaking and new grains with high angle grain boundary (HAGB) formed. Therefore, the grain size decreases and the fraction of HAGB increases in the crack propagation region. Temperature has great influence on the plastic deformation behavior of pipeline steel during facture process. At -20 ℃, the tested steel has good plasticity and the grains are refined during deformation, but at -60 ℃, they are difficult to deform and refine. Consequently, the grain size near crack propagation zones in the sample impacted at -20 ℃ is much smaller than the original grain size, but in -60 ℃ impacted sample the grain sizes has little difference.

采用金相显微镜和扫描电子显微镜对厚规格X80管线钢微观组织和-25℃落锤撕裂试验断口形貌进行观察,研究了X80管线钢的断裂行为与组织之间的关系。研究发现,钢板从表面到厚度中心,针状铁素体体积分数逐渐降低,并出现较多的粒状贝氏体、多边形和准多边形铁素体。具有较高针状铁素体体积分数的钢板,其落锤撕裂剪切面积也越高,多边形和准多边形铁素体以及大尺寸MA岛的存在能够导致解理断裂的产生,不利于钢板的低温断裂韧性。在裂纹扩展的过程中,主裂纹附近组织出现变形,导致脆硬性的MA岛周围出现微孔,微孔与微孔之间随着组织变形相互连接而形成微裂纹。二次裂纹通常在针状铁素体周围出现转折或停滞,说明针状铁素体有利于阻碍裂纹的扩展,提高钢板的断裂韧性。

We present an electro-magnetic (EM) setup in order to collapse thick-walled cylinders, for the investigation of spontaneous formation of multiple adiabatic shear bands. The EM setup is based on a pulsed current generator using a capacitor bank system. The cylindrical specimen is part of an assembly of coaxial cylinders, where the inner and outer cylinders, each attached to an opposite pole, are short-circuited. Upon capacitor discharge, a high current flows through the cylinders, in opposite directions, creating repulsive magnetic forces between them. The outer cylinder is driven outwards and the inner cylinder is driven inwards - in a collapsing manner. This work presents the design procedure of the specimens' geometry using numerical simulations, and some preliminary experimental results for SS304L steel specimens. The spatial distribution of the multiple adiabatic shear bands in these specimens is in good agreement with that reported in the literature for explosively driven experiments with the same material. Our numerical simulations of the collapsing cylinder show good agreement with the experimental results for both global behavior and shear band distribution. (C) 2011 Elsevier Ltd.

Recent studies have revealed microscopic amorphous lamella resulting from inelastic deformation in the ballistic impact of boron carbide ceramic. The possibility that these deformation features are a consequence of adiabatic shear deformation in the impact event is explored. An early theory of adiabatic shear that was limited to the response of rigid-plastic deformation is expanded to include elastic strain energy. The study reveals that elastic strain energy is commonly a small, but not negligible, contribution to impact-induced adiabatic shear in metals. Elastic strain energy is paramount in brittle solids. Relations are developed from the theory to predict the nominal width and spacing of adiabatic shear-bands in brittle solids. Comparisons of the theoretical predictions are consistent with observations of impact-induced deformation features in boron carbide. (C) 2011 Elsevier Ltd.

The complex structural transformation in crystals under static pressure or shock loading has been a subject of long-standing interest to materials scientists and physicists. The polymorphic transformation is of particular importance for iron (Fe), due to its technological and sociological significance in the development of human civilization, as well as its prominent presence in the earth's core. The martensitic transformation α→ε (bcc→hcp) in iron under shock-loading, due to its reversible and transient nature, requires non-trivial detective work to uncover its occurrence. Here we reveal refined microstructural fingerprints, needle-like colonies and three sets of {112}<111> twins with a threefold symmetry, with tell-tale features that are indicative of two sequential martensitic transformations in the reversible α→ε phase transition, even though no ε is retained in the post-shock samples. The signature orientation relationships are consistent with previously-proposed transformation mechanisms, and the unique microstructural fingerprints enable a quantitative assessment of the volume fraction transformed.