High-speed photographic studies of blast wave impact phenomena

An exploding wire technique (EWT) is described, which provides high rates of loading by producing cylindrical blast waves of high reflection pressure with short duration. These waves have been used for internal impact of hollow polymeric cylindrical specimens. The EWT overcomes the small size restrictions of other high strain rate testing methods like the Split-Hopkinson pressure bar technique and drop weight. [Continues.

Strain rate behaviour of thermoplastic polymers

Polymers are increasingly used in structures that have to withstand impact conditions. This thesis describes an investigation of strain rate properties at room temperature of four engineering polymers; polyethylene (high density, HDPE and ultra high molecular weight, UHMWPE), nylatron and polyetheretherketone (PEEK 150g). A split Hopkinson pressure bar (SHPB) system was used to study the response of these polymers in compression tests at high strain rates up to 10' S-1. Stress equilibrium in SHPB samples was studied theoretically by examining multiple reflection effects during the initial elastic loading of the polymers; this study proved very useful in the analysis of SHPB tests. To cover a wide range of strain rate, compression studies were also made at low strain rates (10-3 _10-2 S-1) using a Hounsfield screw machine. Viscoelastic models have been applied to these results. These models fit quite well with the experimental results of HDPE, UHMWPE, and nylatron, but not to the PEEK due to the yield drop in the stress - strain curves, especially at high strain rates. An exploding wire technique was used as an axial impulsive loading system for hollow cylindrical samples. An image converter camera at framing intervals of 21ls or 10 Ils recorded the radial expansion of the cylinder. The expanding cylinder was used as a driving system for a new technique called the freely expanding ring method, which was used to obtain the stress - strain behaviour of polymeric thin rings placed as a sliding fit on the cylinder. This method produced very high tensile strain rates up to fracture (> 10' S-1). Comparisons have been made between results obtained from the quasi-static, SHPB, and expanding ring tests. The freely expanding ring and SHPB results were in good agreement indicating similar tensile and compressive high strain rate behaviour. The mechanical properties of the above polymers are strongly dependent on strain rate. The Young's modulus and the flow stress increase with increasing strain rate. Nylatron showed high strain rate strain softening at high strain, this was due to the high temperature rise during loading, when the transition temperature (Tg) of the material (50 QC) was exceeded. However, the other materials showed continuous hardening behaviour. Plots of the flow stress at 5% and 10% strain vs log strain rate showed a linear increase up to a strain rate of about 103 S-1. Above 103 s-1, the stress rose more rapidly, but then showed significant drops for nylatron and PEEK. These drops in stress are probably due to both micro crack initiation in the sample and also high temperatures around the crack tips

Constitutive relation development through the FIRE test

The importance of well-developed constitutive models for predicting deformation behavior of materials at high strain rates cannot be overstated. The study and development of these constitutive models is pertinent to several fields, yet the test methods utilized to probe this high strain-rate realm are limited in both number and standardization. In an effort to augment current high rate tests, new technologies have been leveraged to revive an old, under-utilized test method - the axisymmetric expanding ring. The combination of Photon Doppler Velocimetry (PDV) and one of several ring launch techniques allows the successful testing and instrumentation of samples loaded in tension without wave effects at strain rates exceeding 10^4 s^-1. Design and construction of the embodiment of this test at OSU, dubbed the Fully Instrumented Ring Expansion (FIRE) system, will be discussed. The key difficulties to implementation of the test are examined, along with our efforts to overcome them and preliminary results

Features of particle synthesis at metal wire dispersion

Features of particle synthesis under simultaneous dispersion of copper and nickel wires were investigated using a molecular dynamics method. The dynamics of wire dispersion, the size and phase composition of synthesized particles depend on the internal structure of dispersed metal wires and the distance between them. The main mechanism of particle synthesis was agglomeration of sputtered clusters, which predominated over the atom deposition from the gas phase on the particle surface. Synthesized particles were characterized by a nonuniform distribution of chemical elements along their cross section. The subsurface region had a higher concentration of copper in comparison with the particle volume. The molecular dynamics simulation of the metal wire dispersion allows finding optimal loading parameters for the synthesis of particles with desirable size and internal structure

Ankara bombing : distribution of injury patterns with radiological imaging

Purpose: To describe and explain the blast injuries and imaging findings in the Ankara terrorist explosion that took place on October 10, 2015. Material and methods: A total of 77 patients who underwent radiologic imaging were classified as primary, secondary, tertiary, and quaternary, according to the injury type. The patients were evaluated based on body regions, such as head and neck, thorax, abdomen, lower extremity, and upper extremity. Results: Blast lung injury was identified in one patient and tympanic membrane perforation in seven patients, as the primary injury. Sixty-two of 77 patients had secondary blast injuries caused by shrapnel. The blast injuries were observed in the head and neck (16/77, 20.7%), thorax (11/77, 14.2%), abdomen (16/77, 20.7%), lower extremity (48/77, 62.3%), and upper extremity (5/77, 6.4%). Vascular injuries were seen in eight cases, of which seven were in the lower extremities. Conclusions: The most common blast injury pattern was of a secondary type in the current study. Lower extremities were the significantly more affected body region, probably due to the bomb exploding at ground level. In mass casualty events, radiologic imaging is located at the centre of patient management

Off-fault tensile cracks: A link between geological fault observations, lab experiments, and dynamic rupture models

We examine the local nature of the dynamic stress field in the vicinity of the tip of a semi-infinite sub-Rayleigh (slower than the Rayleigh wave speed, c_R) mode II crack with a velocity-weakening cohesive zone. We constrain the model using results from dynamic photoelastic experiments, in which shear ruptures were nucleated spontaneously in Homalite-100 plates along a bonded, precut, and inclined interface subject to a far-field uniaxial prestress. During the experiments, tensile cracks grew periodically along one side of the shear rupture interface at a roughly constant angle relative to the shear rupture interface. The occurrence and inclination of the tensile cracks are explained by our analytical model. With slight modifications, the model can be scaled to natural faults, providing diagnostic criteria for interpreting velocity, directivity, and static prestress state associated with past earthquakes on exhumed faults. Indirectly, this method also allows one to constrain the velocity-weakening nature of natural ruptures, providing an important link between field geology, laboratory experiments, and seismology