Mohsen Seifi, Matt Dahar, Ron Aman, Ola Harryson, Jack Beuth and John Lewandowski have published a paper in a special issue on Additive Manufacturing in the March issue of Journal of Materials (JOM) entitled: Evaluation of Orientation Dependence of Fracture Toughness and Fatigue Crack Propagation Behavior of As-Deposited ARCAM EBM Ti-6Al-4V.

Abstract— This preliminary work documents the effects of test orientation with respect to build and beam raster directions on the fracture toughness and fatigue crack growth behavior of as-deposited EBM Ti-6Al-4V.  Although ASTM standards exist for determining the orientation dependence of various mechanical properties in both cast and wrought materials, these standards are evolving for materials produced via Additive Manufacturing (AM) techniques.  The present work was conducted as part of a larger America Makes funded project to begin to examine the effects of process variables on the microstructure and fracture and fatigue behavior of AM Ti-6Al-4V. In the fatigue crack growth tests, the fatigue threshold, Paris law slope, and overload toughness were determined at different load ratios, R, while fatigue precracked samples were tested to determine the fracture toughness. The as-deposited material exhibited a fine-scale basket-weave microstructure throughout the build and although fracture surface examination revealed the presence of unmelted powders, disbonded regions and isolated porosity, the resulting mechanical properties were in the range of those reported for cast and wrought Ti-6Al-4V. Remote access and control of testing was also developed at CWRU to improve efficiency of fatigue crack growth testing.

The published paper can be accessed: 

M. Seifi, M. Dahar, R. Aman, O. Harrysson, J. Beuth, J.J. Lewandowski, JOM 67 (2015) 597.

 

Jun Yi, Wei-Hua Wang and Prof. Lewandowski published at paper in Acta Materialia (2015) 87, pp. 1-7, entitled: Sample size and preparation effects on the tensile ductility of Pd-based metallic glass nanowires. 

Abstract—Glass materials, including metallic glasses (MGs), typically fracture in tension at room temperature in a globally elastic manner. Although homogeneous tensile plasticity and necking of nanoscale MGs have been reported, controversy exists regarding possible contributions from specimen preparation and testing techniques. Here, we show the separate effects of sample size reduction and extrinsic effects on the homogeneous tensile plas- ticity and necking of Pd40Cu30Ni10P20 glassy wires tested at room temperature. An intrinsic transition from catastrophic shear fracture to plasticity and necking was obtained in this glass when its diameter approached the estimated length scale of the shear-band nucleus size (i.e. 500 nm). A further reduction in the wire diameter to 267 nm produced homogeneous flow and complete ductile necking, with a true fracture strain in excess of 2.0. Our theoretical analysis shows that the plasticity of nanoscale MG wires with diameters smaller than a critical length scale is mediated by shear trans- formations catalyzed by local shear dilatation, and the predicted critical length scale for the brittle-to-ductile transition of the glassy wires is con- sistent with our experimental results. Extrinsic effects introduced during sample preparation and/or testing produce entirely different results and are reviewed in the light of previous work.

The published paper can be accessed here.

Francesca Fabe, a junior at Beaumont High School, collaborated with PhD student, Janet Gbur on her AP Biology project investigating the fatigue of dental arch wires. The project, “Beta Titanium vs. Nitinol Archwires: Which material can withstand longer periods of fatigue before failing?” has been accepted into the NEOSF, BEST Medicine, and District V science fairs.

 

Freshman, Ilana Roth, sophomore, Kimaya Gupte (both pictured above) joined the group in January and will be working with PhD student, Janet Gbur on the mechanical characterization of various wires used in biomedical applications. Kimaya is a BME major from Portland, Oregon and is investigating the flex fatigue behavior of dental arch wires. Ilana is an engineering major from New Jersey and is investigating the rotating bending behavior of fine Nitinol wires. Nicole Corbin also recently joined the group and is a senior Materials Science and Engineering student working with Nitinol sheet for her senior design project.

John Bobanga recently completed his Masters degree and is now employed at NSWC in Washington DC as a Safety Systems Engineer. He is responsible for identifying and eliminating safety hazards in the various stages of development while meeting deadlines for delivery of fleet systems.