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The theory of critical distances (TCD) is one of the most promising approaches to the prediction of material fracture, in which the stress concentration effect is taken into account. To date, the TCD has proven itself as a successful method for assessing the fatigue, static and dynamic strength of components with stress concentrators. However, for dynamic loading the theory was verified only on a small list of materials. This paper confirms that the application of the theory of critical distances to specimens made of structural steel 08X18H10T with different geometry features under dynamic deformation is a successful technique for estimating dynamic strength, and it allows a substantial reduction in the program of experiments in determining the ultimate loads. [ABSTRACT FROM AUTHOR]

A new recovery method for investigating material response to shockless (ramped) loading paths is described. The work makes use of a laser generated plasma piston that produces ramped loading at high strain rates (>≈107/s). Large sample sizes are utilized to prevent reflected wave interactions. The overall deformation path is characterized by two transients: one at very high strain rate on the 5–10 nanosecond time scale and one at a lower strain rate occurring over a 1–2 microsecond timescale. It was found that a sufficiently large region of material experiences shockless loading conditions enabling recovery based characterization. The presence of two strain transients makes the method more applicable to comparative assessments between shockless and shock loading conditions. [ABSTRACT FROM AUTHOR]

In the current study we are developing an experimental fracture material property test method specific to dynamic fragmentation. This test method allows the study of fracture fragmentation in a reproducible laboratory environment under well-controlled loading conditions. Motion and fragmentation of the specimen are diagnosed using framing camera, VISAR and soft recovery methods. Fragmentation properties of several steels, nitinol, tungsten alloy, copper, aluminum, and titanium have been obtained to date. The values for fragmentation toughness, and failure threshold will be reported, as well as effects in these values as the material strain-rate is varied through changes in wall thickness and impact conditions. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

One of the current challenges facing researchers in the field of dynamic properties of materials is the need for a predictive modeling capability for damage and fragmentation. A series of small-scale, explosively-driven experiments were designed and executed in order to gain a better understanding of the nucleation and growth of damage under explosive loading. The interaction of varying obliquity detonation waves with the test articles was of particular interest. The material in these tests experiences a combination of hydrostatic and deviatoric stresses that is spatially and temporally varying. Variations in shot geometries and explosive load causes direct variations in the nature of the resulting damage fields in the recovered samples. The characterization of a number of samples from a test series of tantalum discs will be presented and compared to numerical analyses of the experiments. Insights gained from the post-mortem examination of the discs and the accompanying simulations will be presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Accurate material constitutive modeling is critical for the quality and reliability of the simulation of dynamic impact processes. Under dynamic loading ductile structural components can experience very large deformation that, in terms of equivalent plastic strain, can be well beyond the strain at which necking would occur in uniaxial tensile tests. Unfortunately, the material flow curve for ductile metals can only be measured over a limited strain range while at large strain it is either extrapolated or corrected in some way. In this paper the role of the approximation of the material flow law in the post-necking range is investigated with particular reference to the Taylor test. Result seems to indicate that the flow law governs the shape of the mushroom region while temperature and strain rate have a more important role in the resulting deformed shape of the intermediate and rear portion of the specimen geometry. In particular, the temperature effect exponent in the J&C expression can be calibrated based on the final length of the impacted cylinder. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

High-strength constructional 38KhN3MFA steel and 02H18К9M5-BИ maraging steel were tested to determine the yield stress under dynamic loading. The 38KhN3MFA steel was used as central test material to work out the experimental technique. For both kinds of steel the results obtained in the plane shock tests under uniaxial strain condition show approximately the identical yield stress values as those obtained in Taylor tests. Cracking of maraging steel occurs along the shock-induced austenite bands where microhardness is much smaller than that for the rest of the matrix. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]