Shock instabilities

It is well known that adiabatic shocks in ordinary gases are stable to both tranverse and longitudinal perturbations, but this need not be true if there are significant thermal effects due to chemical reactions or cooling processes. For example, detonation waves in gases are observed to form cellular structures if the chemical reaction is sufficiently temperature sensitive and a similar instability occurs in radiative shocks in the ISM if their speed exceeds 150 km s^–1. This means that interstellar shocks will be subject to this radiative instability in many cases. The temperature sensitivity of the nuclear reactions in Type I supernovae is also such that we would expect detonation waves in these objects to have a cellular structure.     

太原盆地震群的几个特征

在分析１９６６年—１９８５年间太原盆地发生的１４起震群序列资料的基础上。叙述了这些震群分布区的新构造特征、空间分布特征、震群活动区特征、震群迁移特征、震群的震源深度、震群所反映的现代局部应力场等。     

The application of CFRP to strengthen buried steel pipelines against subsurface explosion

Multiple explosions in the route of oil and gas transmission pipelines during recent years demonstrate that terrorist attacks and sabotages have unfortunately increased. The present investigation is carried out numerically in order to minimize the amount of damages imposed on steel pipelines under close-in explosions. This research presents a novel concept, using CFRP (Carbon Fiber Reinforced Polymer) to strengthen the wall of steel pipelines against these incidents. For this purpose, a full coupled 3D finite element model developed using a combined Eulerian-Lagrangian method. The simplified Johnson-Cook material model, the JWL equation of state, and the ideal gas equation of state were employed for modeling the pipe material behavior, charge detonation, and air, respectively. Mechanical behavior of the composite wrap was simulated using an anisotropic material model and the damage initiation criteria were based on Hashin's theory. In addition, soil mass behavior was modeled applying a Drucker-Prager strength criterion with piecewise hardening and hydro tensile limit accompanied by Mie-Grüneisen equation of state. Several comparisons carried out between the results from present investigation and those from field and empirical studies and good agreements were observed. The results show that using a proper thickness of CFRP wrap for every particular circumstance can significantly improve the performance of steel pipelines under blast loads. For instance, in the current example, maximum equivalent strains developed in the most of the studied pipelines decreased by over 30% (up to 64%) with the application of 4-mm-thickness CFRP wrap. The present study contributes to protective design of steel pipelines.     

Concepts of blast hole pressure applied to blast design

Blast hole pressure is the starting point for many blast design calculations, but the way in which it is usually derived, from measured detonation velocity, indicates that more thought is needed as to its true meaning and implication. The general impression is given that the energy in the hole is defined by velocity of detonation (VoD), but this is rarely the case. VoD is defined by the energy released in the detonation driving zone between the shock front and the sonic (or CJ) surface, and for commercial explosives it is normal for reaction not to be complete within this zone. Reaction and energy delivery continues behind it, not reflected by VoD. Thus it would be more appropriate to use the theoretical VoD, not the measured VoD, to derive the starting pressure, since this would reflect the energy input of full reaction. In decoupled situations, the derivation of pressure at the blast hole wall using a polynomial decay concept is also of debatable value, and an alternative is offered.     

Parameterization of the porous-material model for sand with different levels of water saturation

The experimental results for the mechanical response of sand (at different levels of saturation with water) under shock-loading conditions generated by researchers at Cavendish [Bragov AM, Lomunov AK, Sergeichev IV, Tsembelis K, Proud WG. The determination of physicomechanical properties of soft soils from medium to high strain rates, November 2005, in preparation; Chapman DJ, Tsembelis K, Proud WG. The behavior of water saturated sand under shock-loading. In: Proceedings of the 2006 SEM annual conference and exposition on experimental and applied mechanics, vol. 2, 2006.p.834–40] are used to parameterize our recently developed material model for sand [Grujicic M, Pandurangan B, Cheeseman B. The effect of degree of saturation of sand on detonation phenomena associated with shallow-buried and ground-laid mines. J Shock Vib 2006;13:41–61]. The model was incorporated into a general-purpose non-linear dynamics simulation program to carry out a number of simulation analyses pertaining to the detonation of a landmine buried in sand and to the interactions of the detonation products, mine fragments and sand ejecta with various targets. A comparison of the computed results with their experimental counterparts revealed a somewhat improved agreement with the experimental results in the case of the present model as compared to the agreement between the widely used porous-material/compaction model for sand and the experiments.     

Subgrade fatigue life effects due to a pressurized void

The effect on the fatigue life of a subgrade beneath a uniformly loaded cement concrete runway, when detonation gases have formed a void in the subgrade is considered. The research models numerically the runway and the subgrade and considers the void when empty, partially filled, and filled. The void may or may not be pressurized. Pressurizing the void reduces the downward vertical runway surface displacements. In only two of the 90 numerical models considered did pressurizing the void increase the subgrade fatigue life. In the subgrade outside the cone of disturbance, the fatigue life was significantly reduced.