Hall-Petch relationship in Mg alloys: A review

Enhancement of cross-plane thermal conductivity and mechanical strength via vertical aligned carbon nanotube@graphite architecture

We investigate spall damage of a mild carbon steel under high strain-rate loading, regarding the effects of peak stress, strain rate, and pulse duration on spall strength and damage, as well as related microstructure features, using gas gun plate impact, laser velocimetry, and electron backscatter diffraction analysis. Our experiments demonstrate strong dependences of spall strength on peak stress and strain rate, and its weak dependence on pulse duration. We establish numerical relations between damage and peak stress or pulse duration. Brittle and ductile spall fracture modes are observed at different loading conditions. Damage nucleates at grain boundaries and triple junctions, either as transgranular cleavage cracks or voids.

Spall damage of a mild carbon steel: Effects of peak stress, strain rate and pulse duration

Anisotropic deformation of extruded magnesium alloy AZ31 under uniaxial compression: A study with simultaneous in situ synchrotron x-ray imaging and diffraction

Intragranular void formation in shock-spalled tantalum: Mechanisms and governing factors

Dynamic fracture of C/SiC composites under high strain-rate loading: microstructures and mechanisms

We investigate deformation and damage of a magnesium alloy, AZ91, under high strain rate ( ∼ 10 5 s − 1 ) loading via planar impact. The soft-recovered specimens are examined with electron back-scatter diffraction (EBSD). EBSD analysis reveals three types of twinning: { 10 1 ¯ 2 } extension, { 10 1 ¯ 1 } contraction, and { 10 1 ¯ 1 } – { 10 1 ¯ 2 } double twinning, and their number density increases with increasing impact velocity. The extension twins dominate contraction and double twins in size and number. Dislocation densities of the recovered specimens are evaluated with x-ray diffraction, and increase with increasing impact velocity. X-ray tomography is used to resolve three-dimensional microstructure of shock-recovered samples. The EBSD and tomography results demonstrate that the second phase, Mg17Al12, plays an important role in both deformation twinning and tensile cracking. Deformation twinning appears to be a common mechanism in deformation of magnesium alloys at low, medium and high strain rates, in addition to dislocation motion.

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Deformation and spallation of a magnesium alloy under high strain rate loading

Dynamic split Hopkinson pressure bar experiments with in situ synchrotron x-ray imaging and diffraction are conducted on a rolled magnesium alloy at high strain rates of ~5500 s −1 . High speed multiscale measurements including stress–strain curves (macroscale), strain fields (mesoscale), and diffraction patterns (microscale) are obtained simultaneously, revealing strong anisotropy in deformation across different length scales. {10 1 ¯ 2} extension twinning induces homogenized strain fields and gives rise to rapid increase in strain hardening rate, while dislocation motion leads to inhomogeneous deformation and a decrease in strain hardening rate. During the early stage of plastic deformation, twinning is dominant in dynamic compression, while dislocation motion prevails in quasi-static loading, manifesting a strain-rate dependence of deformation.

Simultaneous multiscale measurements on dynamic deformation of a magnesium alloy with synchrotron x-ray imaging and diffraction

Gas-gun experiments are carried out to study the mechanical properties and fracture behavior of a textured Mg–3Al–1Zn alloy under high strain rate. The impact direction (ID) is either perpendicular or parallel to crystallographic {0001} planes, referred to as ID ∥ 〈 c 〉 and ID ⊥ 〈 c 〉 , respectively. Shock compression and spallation are achieved with different specimen-to-flyer plate thickness ratios. The Hugoniot elastic limits and spall strengths are estimated as 0.32–0.35 GPa and 0.9–0.92 GPa, respectively, showing weak anisotropy. The deformed specimens are characterized with scanning electron microscope and X-ray computed tomography. Abundant { 10 1 2 } extension twins are activated and the strain hardening rate exhibits a sharp increase and then decrease for the ID ⊥ 〈 c 〉 specimen, while a small number of twins are observed and the hardening rate decreases monotonically for the ID ∥ 〈 c 〉 specimen. As a result of the anisotropic distribution of the β -Mg17Al12 phase, cracks are generally distributed in the mid-part and connected together for the ID ⊥ 〈 c 〉 case, while the distribution of cracks in the ID ∥ 〈 c 〉 specimen is relatively discrete along the ID and parallel to the rolling plane.

L. Lu

Papers

Dynamic fracture of C/SiC composites under high strain-rate loading: microstructures and mechanisms

Deformation and spallation of a magnesium alloy under high strain rate loading

Simultaneous multiscale measurements on dynamic deformation of a magnesium alloy with synchrotron x-ray imaging and diffraction

Mechanical properties and fracture behavior of Mg–3Al–1Zn alloy under high strain rate loading