Steam generation via explosive fragmentation of ice

The possibility of generating steam by means of the explosive fragmentation of ice, which takes place under the conditions of strong nonuniform compression, is considered. Water films with thicknesses of up to several microns can form during the mutual friction of ice grains and their quasi-liquid flow in a fragment generator. Depending on a pressure level in the generator, the total amount of water in these films can reach several hundred liters per cubic meter of ejected ice micro-and nanofragments. High-rate ejection of the ice-water mixture from the generator is accompanied by a jumplike drop in the pressure that can lead to boiling of the water film with the formation of a partly dissociated steam.     

PAFRAG modeling of explosive fragmentation munitions performance

A technique for predicting performance of explosive fragmentation munitions presented in this work is based on integrating three-dimensional axisymmetric hydrocode analyses with analyses from a newly developed fragmentation computer code PAFRAG. The validation of the PAFRAG code fragmentation model was accomplished using the existing munition arena test data. After having established the crucial parameters of the model, a new explosive fragmentation munition was designed and optimized. Upon fabrication of the developed munition, the performance of the new charge was tested in a series of small-scale experiments including the flash radiography, the high-speed photography, and the sawdust fragment recovery. Considering relative simplicity of the model, the accuracy of the PAFRAG code predictions is rather remarkable.     

Gas evolution during the explosive fragmentation of ice

It is possible in principle that hydrogen and oxygen can evolve during the explosive instability of ice leading to its disintegration into micro-and nanofragments, which takes place under the conditions of strong nonuniform compression in the region of high pressures. The nature of the anticipated phenomenon can be related to the electron-and ion-induced sputtering and dissociation of nanodimensional ice fragments. Electrons and ions can be generated in the course of an explosive instability in ice, which is developed as a result of fractoemission, triboemission, and secondary electron emission. The yield Y of hydrogen, oxygen, and related radicals is expected to depend as Y ∝ P ² on the threshold pressure P at which the explosive instability of ice is manifested.     

Anisotropic dynamic damage and fragmentation of rock materials under explosive loading

This paper describes the development of a constitutive model for predicting dynamic anisotropic damage and fragmentation of rock materials under blast loading. In order to take account of the anisotropy of damage, a second rank symmetric damage tensor is introduced in the present model. Based on the mechanics of microcrack nucleation, growth and coalescence, the evolution of damage is formulated. The model provides a quantitative method to estimate the fragment distribution and fragment size generated by crack coalescence in the dynamic fragmentation process. It takes account of the experimental facts that a brittle rock material does not fail if the applied stress is lower than its static strength and certain time duration is needed for fracture to take place when it is subjected to a stress higher than its static strength. Numerical results are compared with those from independent field tests.     

Standoff detection of high explosive materials at 50 meters in ambient light conditions using a small Raman instrument

We have designed and demonstrated a standoff Raman system for detecting high explosive materials at distances up to 50 meters in ambient light conditions. In the system, light is collected using an 8-in. Schmidt-Cassegrain telescope fiber-coupled to an f/1.8 spectrograph with a gated intensified charge-coupled device (ICCD) detector. A frequency-doubled Nd : YAG (532 nm) pulsed (10 Hz) laser is used as the excitation source for measuring remote spectra of samples containing up to 8% explosive materials. The explosives RDX, TNT, and PETN as well as nitrate- and chlorate-containing materials were used to evaluate the performance of the system with samples placed at distances of 27 and 50 meters. Laser power studies were performed to determine the effects of laser heating and photodegradation on the samples. Raman signal levels were found to increase linearly with increasing laser energy up to approximately 3 x 10(6) W/cm2 for all samples except TNT, which showed some evidence of photo- or thermal degradation at higher laser power densities. Detector gate width studies showed that Raman spectra could be acquired in high levels of ambient light using a 10 microsecond gate width.     

Analysis of the single-fiber fragmentation test

An analysis of the single-fiber fragmentation test was investigated.An approximate solution for the stress fields of a fiber embedded in a polymer matrix of different elastic moduli was obtained by the Eshelby method. The fiber was modeled as a prolate spheroid. The axial stress of the fiber increases with increasing aspect ratio and fiber-matrix shear modulus ratio and decreases with increasing matrix and fiber Poisson's ratios. Using this analysis, the fracture stress of a single-fiber fragmentation specimen was derived. The applied stress at fiber fracture decreases monotonically with increasing aspect ratio of the fragmented fiber and increases with increasing fiber and matrix Poisson's ratios. This model is in qualitative agreement with published experimental data.     

An evaluation of arsenic release from monolithic solids using a modified semi-dynamic leaching test

Quicklime and quicklime-fly ash-based stabilization/solidification (S/S) effectiveness was evaluated by performing semi-dynamic leaching tests (American Nuclear Society 16.1). Artificial soil samples, contaminated with arsenic trioxide (As2O3) as well as field soil samples contaminated with arsenic (As) were tested. The artificial soils were prepared by mixing amounts of kaolinite or montmorillonite with fine quartz sand. The S/S effectiveness was evaluated by measuring effective diffusion coefficients (De) and leachability indices (LX). Treatment was most effective in kaolinite-based artificial soils treated with quicklime and in quicklime-fly ash treated field soils. The experimental results indicate that De values were lowered as a result of S/S treatment. Upon treatment LX values were higher than 9, suggesting that S/S treated soils are acceptable for "controlled utilization". Based on a model developed by de Groot and van der Sloot [G.J. de Groot, H.A. van der Sloot, in: T.M. Gilliam, C.C. Wiles (Eds.), Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes, vol. 2, ASTM STP 1123, ASTM, PA, 1992, p. 149], the leaching mechanism for all of the treated soils was found to be controlled by diffusion. The effect of soluble silica (Si) on As leachability was also evaluated. When soluble Si concentration was less than 1 ppm, As leachability was the lowest. The controlling mechanism of As immobilization whether sorption, precipitation, or inclusion was also evaluated. It was determined that precipitation was the dominant mechanism.     

Evaluation of explosive properties of organic peroxides with a modified Mk III ballistic mortar

Ballistic mortar tests using the Mk III F mortar have been carried out to examine a procedure for assessing the explosive hazard of organic peroxides. The explosive properties of an organic peroxide can be evaluated from two series of experiments, for propagation and power of explosion, and for shock sensitivity. Among seven organic peroxides tested, tert-butyl peroxybenzoate and dibenzoyl peroxide have shown high shock sensitivity and explosive powers of 40 and 25% of TNT, respectively. Di-tert-butyl peroxide showed medium sensitivity and the power of 30% of TNT. Cumyl hydroperoxide, 80% in cumene, dibenzoyl peroxide, 75% with water, dicumyl peroxide and dilauroyl peroxide did not propagate explosion.     

On the numerical implementation of a shear modified GTN damage model and its application to small punch test

Gurson-type models have been widely used to predict failure during sheet metal forming process. However, a significant limitation of the original GTN model is that it is unable to capture fracture under relatively low stress triaxiality. This paper focused on the fracture prediction under this circumstance, which means shear-dominated stress state. Recently, a phenomenological modification to the Gurson model that incorporates damage accumulation under shearing has been proposed by Nahshon and Hutchinson. We further calibrated new parameters based on this model in 22MnB5 tensile process and developed the corresponding numerical implementation method. Lower stress triaxiality were realized by new-designed specimens. Subsequently, the related shear parameters were calibrated by means of reverse finite element method and the influences of new introduced parameters were also discussed. Finally, this shear modified model was utilized to model the small punch test (SPT) on 22MnB5 high strength steel. It is shown that the shear modification of GTN model is able to predict failure of sheet metal forming under wide range of stress state.     

Fracture toughness prediction of aged CF8M using small punch test

Following Ref. 1 , this technical note presents a method to predict the thermal ageing effect on fracture toughness of cast stainless steel CF8M from the small punch test using finite element (FE) damage analysis. A procedure is given to extract tensile properties and multi‐axial fracture strain locus of aged CF8M from the small punch test using FE analysis. It is further shown that fracture toughness of aged CF8M can be predicted from the small punch test using FE damage analysis. Comparison with experimental data shows good agreement.     

Comparison of nondestructive microfailure evaluation of fiber-optic Bragg grating and acoustic emission piezoelectric sensors using fragmentation test

Nondestructive evaluation of microfailure mechanisms in two-diameter SiC fibers/epoxy composites is investigated using a directly embedded fiber-optic sensor attached with an acoustic emission piezoelectric (AE-PZT) sensor. Interfacial shear strength by fragmentation test, and optical failure observation inside microcomposite can contribute to analyze two sensors quantitatively. Although fiber Bragg grating (FBG) sensor exhibits sudden wavelength shift due to plastic deformation by larger diameter SiC fiber breakage, AE-PZT monitors much more precise microfailure process, such as the fiber break or matrix cracking. Since the FBG sensor can measure the strain at only a single point, whether it can detect a fiber break in single-fiber composite specimen depends on its proximity to the failure location. In addition, micro-strain measurement at one single point may not provide enough information on the whole microfailure process including multiple fiber breakage and matrix crack. It can be considered that FBG sensor can be somewhat effective in measuring the continuous micro-strain change due to the internal disturbance such as resin curing, whereas AE-PZT sensor can be effective in detecting the microfailure by elastic wave propagation through the composite materials.     

Development of a new methodology for estimating the CTOD of structural steels using the small punch test

The small punch test (SPT) is very convenient for estimating tensile mechanical properties, being the estimation of fracture toughness still a controversial subject of debate. One of the new strategies developed is the use of notched specimens. In this paper, two different grades of CrMoV steels were employed to analyse the evolution of the notch mouth opening displacement of the small punch sample (δSPT). Complete and interrupted tests were performed on specimens with longitudinal non-through notches with a notch length to thickness ratio of 0.3. A numerical model was also developed for corroborating the experimental results. A material-independent relationship between δ_SPT and the punch displacement (d) was found: δ_SPT = 0.217d. Since crack length measurement is not possible on SPT samples, the value of δ_SPT at crack growth onset (δ_{SPT_ini}) was used for comparison with the CTOD values for crack initiation in the standard tests (δ_ini). Crack growth onset in the SPT specimens was verified by observation after splitting them in two halves, as well as comparing the numerical curves (without damage model) and the experimental ones. Larger values have been obtained by means of the SPT, due to the lower constraint of the test. However, the developed methodology seems to be suitable when dealing with ductile steels, although other different materials are needed to be tested.     

A method to measure fracture toughness of the fiber/matrix interface using the single-fiber fragmentation test

A fracture mechanics model was developed for determining the fracture toughness of the fiber/matrix (F/M) interface based on a modified test procedure for the single fiber fragmentation test (SFFT). After loading the specimen until the first fiber fracture and instantaneous debonding events occur, the specimen is unloaded and loaded again until the debond propagates. The critical load for debond propagation is measured and is used with a fracture mechanics analysis to determine the interface fracture toughness. The analysis considers also friction between the fiber and matrix in the debonded region. To obtain the necessary data for calculation of residual radial stress at the F/M interface due to matrix cure shrinkage, simultaneous measurements of dynamic modulus and cure shrinkage were conducted on the matrix (vinylester) during cure. Tests employing E-glass/vinylester SFFT specimens provided fracture toughness values of G_cd = 62 J/m² (frictionless) and 48 J/m² (friction).     

Analysis of styrene-butadiene-styrene polymer modified bitumen using fluorescent microscopy and conventional test methods

This paper presents a laboratory study of modified bitumen containing styrene-butadiene-styrene (SBS) copolymer. Polymer modified bitumen (PMB) samples have been produced by mixing a 50/70 penetration grade unmodified (base) bitumen with SBS Kraton D1101 copolymer at five different polymer contents. The fundamental characteristics of the SBS PMB samples have been determined using conventional methods. The morphology of the samples as well as the percent area (%) distribution of SBS polymers throughout the base bitumen have been characterized and determined by means of fluorescence microscopy and Qwin Plus image analysis program, respectively. The mechanical properties of the hot-mix asphalt (HMA) containing SBS PMBs have also been analyzed and compared with HMA incorporating base bitumen. The effect of polymer addition on the short and long term aging characteristics of HMA have been evaluated by indirect tensile strength (ITS) test. The results indicated that polymer modification improved the conventional properties (penetration, softening point, etc.) and the mechanical properties (Marshall, ITS, etc.) of the base bitumen. It was also concluded that at low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed. Moreover, it was found out that the polymer addition minimizes the short and long term aging of HMA.     

Phenomenological aspects of the double yield of polyethylene and related copolymers under tensile loading

The double yield point is shown to be a common feature to polyethylene and ethylene copolymers, regardless of the crystallinity level. Particular attention has been paid to the influence of draw temperature and strain rate which unambiguously indicate a combination of two thermally activated rate processes. Various thermal treatments have been investigated in order to check the influence of the crystal thickness distribution and the chain topology on the yield behaviour. Isothermal crystallization at high temperature is shown to have little effect compared with variations of crystallinity, temperature and strain rate in the case of compression-moulded samples. On the other hand, a strong effect has been observed in the case of solution crystallization which is well known to affect the chain-folding topology. The results are fairly consistent with the previous proposal by Takayanagi that (1) two processes govern the plastic deformation of the crystalline lamellae in semi-crystalline polymers, and (2) these processes are closely related to the viscoelastic relaxations in the crystal. The crystalline lamellae may deform plastically through sliding of crystalline blocks (brittle process) and/or homogeneous shear (ductile process). In order to account for the dependency of the brittle-to-ductile transition on the copolymer structure and crystallization method, a molecular model is put forward on the basis of the chain topology concepts borrowed from our former investigations on the tensile drawing and the melting behaviour of ethylene copolymers.