Konstantinos Tsembelis

Canadian Nuclear Safety Commission | CNSC · Operational Engineering Assessment Division

In order to address the risks associated with the operation of ageing pressure boundary components, many assessments incorporate probabilistic analysis tools for alleviating excessive conservatism of deterministic methodologies. In general, deterministic techniques utilize conservative bounding values for all critical parameters. Recently, various...

In order to address the risks associated with the operation of ageing pressure boundary components, many assessments incorporate probabilistic analysis methodologies for alleviating excessive conservatism of deterministic methodologies. In general, deterministic techniques utilize conservative upper bound values for all critical parameters. Equally...

It is important to characterize the fracture toughness of a CANDU® pressure tube to determine whether a tube containing a known or postulated flaw is fit-for-service. In an ongoing effort to study the relationship between small- and large-scale tests of Zr-2.5Nb pressure tube material, the current work examines the use of the crack tip opening angl...

Experimental and theoretical results for light flash temperatures are presented for impacts on soda-lime glass by iron projectiles. The experiments were performed with a 2MV Van de Graaff, where iron dust particles (0.14–0.63μm in diameter) impacted soda-lime glass at a velocity range of 5–20kms−1. Theoretical calculations were based on the assumpt...

A method is presented for obtaining materials parameters, for quartz sand, over a wide range of strain rates. This involves the use of a modified Kolsky bar and plate impact experiments. Data were analysed based on the determination of longitudinal and lateral stresses in the Kolsky method. These values were combined with the longitudinal stress da...

Materials blasted into space from the surface of early Earth may preserve a unique record of our planet's early surface environment. Armstrong et al. (2002) pointed out that such materials, in the form of terrestrial meteorites, may exist on the Moon and be of considerable astrobiological interest if biomarkers from early Earth are preserved within...

The shock response of geological materials is of interest to many industries, in particular oil and gas exploration. The porous inhomogeneous composition of geological materials complicates characterisation under dynamic loading. The behaviour of dry limestone has been investigated under the condition of uniaxial strain using a plate impact facilit...

Porous and granular materials are widely found in a number of environments. One of the most important groups both geographically and in the construction industry are the sands. A review of the response of sand (42% porous) over a wide range of strain rates is presented. Factors such as water content and density variation are addressed. In addition...

Hydrocodes are widely used to predict or simulate highly dynamic and transient events such as blast and impact. Codes such as GRIM, CTH or AUTODYN are well developed and involve complex numerical methods and in many cases a large computing infrastructure. In this paper we present a simple 1-D Langrangian hydrocode developed at the University of Cam...

We characterise the pressures achieved in spherical particle impact, as a precursor to investigating the possibility of shock-driven DNA modification in sandstone targets, which could occur at lower pressures than those previously established to cause extinction e.g. for {B. subtilis} [1, 2]. Hypervelocity impact experiments at 5 km/s using spheric...

The goal of this study was to apply and compare different computational compaction models to the dynamic compaction of porous silicon dioxide (SiO2) powder. Three initial specific volumes were investigated in this study, V00=1.3, 4 and 10 cm3/g, where the solid material specific volume is V0=0.4545 cm3/g. Two hydrodynamic codes, KO and CTH, were us...

Plate impact experiments have been performed to assess the behaviour of a heavy proprietary Tungsten alloy in the longitudinal orientation by means of manganin gauges. The Hugoniot curve is compared and contrasted against published data on pure Tungsten and a number of Tungsten alloys.

A series of plate impact experiments has been performed to assess the dynamic behaviour of dry Yorkshire sandstone up to 8 GPa. Standard manganin gauges were inserted between samples in order to determine the principal Hugoniot curve. A VISAR system was used to measure the free surface velocity of the target. This work is in part of a research prog...

A computational analysis of the dynamic compaction of porous silica is presented and compared with experimental measurements. The experiments were conducted at Cambridge University's one-dimensional flyer plate facility. The experiments shock loaded samples of silica dust of various initial porous densities up to a pressure of 2.25 GPa. The computa...

A series of plate impact experiments has been performed to assess the dynamic behaviour of micro-concrete (70% fine-grain dolerite powder and 30% cement paste by weight) in both longitudinal and lateral directions. Information was obtained for the Hugoniot curve and dynamic shear stress properties. Hugoniot results are compared with published data...

Plate impact experiments have been performed in forward and reverse impact configurations on dry, quartz sand to obtain Hugoniot data. In the forward configuration, manganin gauges were placed both in surrounding anvils and in the sand. Gauges placed directly in or near the sand gave anomalously high stress values compared with stresses measured in...

The in-material longitudinal and lateral stress histories in a filled, silica-based glass (Schott SF-57) have been measured during plate impact experiments using embedded manganin stress gauges. Longitudinal stress histories are presented and used to provide the principal Hugoniot for the material. Lateral stress measurements show a two-wave struct...

A series of impact experiments were conducted at Cambridge University, Cavendish Laboratory to experimentally determine the Hugoniot of various densities of porous silica dust. The densities investigated were 0.1, 0.25, and 0.77 g cm-3. The experiments were conducted up to ca. 2.3 GPa in the Silica. Individual experimental results and the resulting...

A series of plate impact experiments has been performed to assess the dynamic behaviour of concrete in the longitudinal stress direction. Information was obtained on the Hugoniot curve and release states. Hugoniot results are compared with published data on cement paste, mortar, micro-concrete and full-size concrete from the UK, Germany and the US....

A series of plate impact experiments have been performed on quartz sand of 230 µm average grain size, at various levels of water saturation to obtain Hugoniot data. Manganin stress gauges were inserted in anvils surrounding the sand samples. Shock-velocity was calculated from the time of arrival and the Hugoniot data was inferred using impedance ma...

The dynamic compaction characteristics of a porous silicon dioxide ( Si O ₂) powder are reported. The initial specific volumes of the samples were either V₀₀=1.30 , 4.0, or 10.0 cm ³/ g whereas the silicon dioxide has a matrix specific volume of V₀=0.455 cm ³/ g . The impact velocity ranges fro...

A series of plate impact experiments has been performed to assess the dynamic behaviour of micro-concrete (70% crushed dolerite and 30% cement paste by weight) in both longitudinal and lateral directions. Information was obtained for the Hugoniot curve and dynamic shear stress properties. Hugoniot results are compared with published data on cement...

A series of plate impact experiments has been performed to assess the dynamic behaviour of silica gel in the longitudinal orientation by means of manganin gauges and VISAR using the Cavendish facility. This series is part of a preliminary program to assess the survivability of biological materials during a terrestrial impact event.

This paper describes research to develop an equation of state to describe the behaviour of a highly porous silica powder. It shows that whilst molecular modelling techniques can be readily applied to develop a description of a compact material the description of the compaction process is more problematic. An empirical model, based upon the Lennard-...

A new method has been developed for determining the main laws of the deformation of soft soils under conditions of dynamic loading with amplitudes of up to several gigapascals. The method is based on the results of high-strain-rate tests under uniaxial deformation conditions, which were obtained using a modified Kolsky method and the plane shock wa...

A series of plate impact experiments was performed on cement paste and mortar. Longitudinal stresses were measured using embedded manganin stress gauges up to ca. 18 GPa. Data are then compared to those obtained in previous studies on concrete varied on aggregate size using a plate reverberation technique and velocity interferometry.

A series of plate impact experiments on low-density silica powder have been conducted at the Cavendish Laboratory's single stage gas gun facility. The experiments were conducted at impact velocities ranging from 600 to 1200 m s-1 to determine the powder's low-pressure shock response. Density of powder was 0.1 g cm-3 on average. Attempts to model th...

Failure fronts or ``waves'' in brittle materials have been the subject of extensive research. This is a phenomenon where a damage front propagates behind the main shock wave and reduces the strength. It is reported to be observed by means of embedded lateral gauges where it manifests itself as a two-step structure. Such profiles were obtained when...

The lateral stress in materials has been measured, under shock wave loading, using manganin gauges mounted normal to the direction of shock propagation. Generally the sample has been sectioned along the direction of impact and adhered again with the gauge in this plane. A series of previous papers have reported a two-step structure in the lateral g...

A series of plate impact experiments was performed on granite from the Stone Mountain in Atlanta, Georgia. Longitudinal stresses were measured by means of embedded manganin gauges and the Hugoniot was established up to ca. 10 GPa. The results are then compared and contrasted to data for other geologic materials.

Silicone Elastomer, (``Sylgard 184 ®''), samples were mounted between copper plates. Manganin stress gauges were placed within the front copper plate, halfway through the Sylgard and at the interface between the Sylgard and the rear copper plate. A series of experiments was performed in which the front plate was impacted by copper plates projected...

A series of plate impact experiments on cement paste (grout) has been performed to assess the dynamic strength of this material. Lateral stresses have been directly measured by means of embedded manganin stress gauges. In combination with longitudinal stresses, measured previously 1, these results have been used to obtain shear strength under shock...

The detonation velocity following type II deflagration-to-detonation transitions (DDT) has been observed to be markedly different to that which would be expected were the charges directly initiated. In charges of pentaerythritol tetranitrate (PETN) velocities as high as 5.6 mm μs−1 have been observed compared to 3.7 mm μs−1 which is both predicted...

A series of plate impact experiments was performed on Dolerite (diabase) igneous rock. Longitudinal stresses were measured using embedded manganin stress gauges up to ca. 11 GPa. In addition, lateral stresses were also measured up to ca. 7 GPa. In combination with the longitudinal stresses, these results have been used to obtain the material shear...

A series of plate impact experiments has been performed to determine the shock loading behavior of cement paste (grout) with water to cement ratio of 0.35 by weight and no aggregates. Hugoniot stress data were collected by means of embedded manganin gauges up to 5 GPa. Results are then compared to those obtained in previous studies on concrete vari...

Plate impact experiments have been performed on two igneous rocks of differing grain size. Shock stresses have been measured by means of embedded manganin stress gauges, up to ca. 12 GPa. In the coarser grained material data was obtained from both copper impactors on rock and the reverse situation. Results are compared and contrasted to the existin...

Plate impact experiments have been performed on two igneous rocks of different grain size. Shock stresses have been measured using embedded manganin stress gauges, up to ∼12 GPa. In the coarser grained material data was obtained by impacting rock flyer plates onto previously characterized targets. Results are compared and contrasted to the existing...

The Johnson-Holmquist brittle material model has been implemented into the AUTODYN hydrocode and used for Lagrangian simulations of hypervelocity impact of spherical projectiles onto soda-lime glass targets. A second glass model (based on a shock equation of state and the Mohr-Coulomb strength model) has also been used. Hydrocode simulations using...

A series of plate impact experiments has been performed to determine the shock loading behaviour of cement with water to cement ratio of 0.35 and no aggregates. Hugoniot stress data were collected by means of embedded manganin gauges over a range of approximately 0.5 to 5 GPa. The results of these data are compared to those obtained in previous stu...

Experiments have been performed on the dust accelerator facilities at the University of Kent at Canterbury (UK) and the Max-Planck-Institut für Kernphysik (Germany) in which the production of plasma from impacts of micron and sub-micron particles at velocities from 1 to 90 km s−1 has been measured. Various projectile and target materials have been...

We present the initial results of an implementation of the Johnson-Holmquist 2 (JH-2) model within the AUTODYN-2D™ hydrocode using a Lagrangian grid. The code results were compared to the results of a hypervelocity impact (HVI) programme on to soda-lime glass carried out at the Unit for Space Sciences and Astrophysics at the University of Kent. The...

Hydrocodes are widely used to predict or simulate highly dynamic and transient events such as blast and impact. Codes such as GRIM, CTH or AUTODYN are well developed and involve complex numerical methods and in many cases require a large computing infrastructure. In this paper we present a simple 1-D Langrangian hydrocode developed at the Universit...