Laser-shock-induced spall failure is studied in thin aluminum targets at strain rates from 2 to 5 · 10 6 s -1 . Targets were prepared from high-purity aluminum in the recrystallized condition and a low-impurity aluminum alloy containing 3 wt pct magnesium in both recrystallized and cold-rolled conditions. The effects of material and microstructure on spall fracture morphology are investigated. Recrystallized pure aluminum produced spall fracture surfaces characterized by transgranular ductile dimpling. Recrystallized aluminum-magnesium alloy with a 50-lm grain size produced less ductile spall surfaces, which were dominated by transgranular fracture, with some isolated transgranular ductile dimpling at fast strain rates. Transgranular ductile dimpling regions disappeared in recrystallized alloy specimens with a 23-lm grain size tested at faster rates. Cold-rolled alloy material produced spall failure surfaces consisting of brittle intergranular and transgranular fractures. Measured spall strength increases with increasing ductile fracture character. Spall failure preferentially follows grain boundaries, making grain size an important factor in spall fracture surface character.

Material microstructure is a significant determinant of the tensile stress at which materials fail. Using a high-energy laser to drive shocks in thin slabs, we have explored the role material microstructure plays on the spall strength of high-purity and alloyed aluminum at strain rates of (2–7.5)×106s−1. Slabs of pure recrystallized Al and recrystallized or cold worked Al+3wt% Mg were shock driven using the Z-Beamlet Laser at Sandia National Laboratories. Velocity interferometer measurements determined the spall strength of the materials, and postshot target analysis explored the microscopic fracture morphology. We observed the greatest spall strength for large-grained, recrystallized high-purity aluminum, with the dominant failure mode being ductile and transgranular. We observe for the first time at these strain rates fracture features for a fine-grained Al+3wt% Mg that were a combination of brittle intergranular and ductile transgranular fracture types. Postshot analysis of target cross sections and hydrocode simulations indicate that this mixed-mode failure results from spall dynamics occurring on spatial scales on the order of the grain size. Differences in spall strength between these Al samples were experimentally significant and correlate with the damage morphologies observed.

Articles you may be interested inHigh repetition rate laser-induced breakdown spectroscopy using acousto-optically gated detection Rev. Sci. Instrum. 85, 073104 (2014) This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Abstract. We conducted laser-induced spall experiments aimed at studying how a material's micro structure affects the tensile fracture characteristics at high strain rates (>10* s''). We used the ZBeamlet Laser at Sandia National Laboratory to drive shocks and to measure the spall strength of aluminum targets with various microstructures. The targets were recrystallized, high-purity aluminum (Al-HP RX), recrystallized aluminum + 3 wt.% magnesium (Al-3Mg RX), and cold-worked aluminum + 3 wt.% magnesium (Al-3Mg CW). The Al-3Mg RX and Al-3Mg CW are used to explore the roles that solid-solution alloying and cold-work strengthening play in the spall process. Using a line-VISAR (Velocity Interferometer System for Any Reflector) and analysis of recovered samples, we were able to measure spall strength and determine failure morphology in these targets. We find that the spall strength is highest for Al-HP RX. Analysis reveals that material grain size plays a vital role in the fracture morphology and spall strength results.

Vortex Induced Motion (VIM) of a Spar platform is an important consideration in the design of Spar moorings and risers. During the design phase, the VIM characteristics of a Spar configuration are evaluated by hydrodynamic model testing. The basis for hydrodynamic model testing is that geometric and dynamic similitude between prototype and model parameters is preserved. Reynolds number and Froude number scaling are the two relevant scaling parameters for Spar VIM model testing. However, simultaneously satisfying Reynolds and Froude scaling for the model and prototype conditions is practically impossible. This leads to compromises in model test Reynolds number scaling and inherent uncertainties in extrapolating the model test VIM predictions to full-scale design conditions. Hence measurement of full-scale Spar VIM responses provides valuable data for validation of design assumptions. BP’s integrity management efforts for its Gulf of Mexico deep water production facilities include monitoring of the environmental conditions, and response of the hull, mooring and riser systems. Field measured data for VIM of BP’s Horn Mountain Truss Spar, presented in this paper, shows that the Horn Mountain Truss Spar VIM response is within original design assumptions. The maximum VIM measured in the field (A/D ≈ 0.26) is well below the acceptable design value of A/D = 0.5. The field data is analyzed and results presented in the form of Spar VIM response time traces, Spar VIM response versus Reduced Velocity and variation of period of VIM oscillation with Spar offsets. The field data shows VIM response characteristics consistent with model test observations.

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