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Experimental instrumentation helps understand variation in mechanical behavior

A) Microtensile specimens milled from a thin sheet of steel near a welded junction, B) pin loaded test specimen with local reduction in cross section near a grain boundary, C) stress-strain curve and D) deformed grains surrounding the boundary of interest.The mechanical performance of materials can be explicitly related to local grain structures at the microscopic scale and smaller. Using advanced experimental instrumentation, direct measurements of mechanical properties can now be taken from targeted regions within a microstructure. An external study is currently underway at CEMAS between researchers at MicroTesting Solutions LLC (MTSL) and Battelle to help understand the variation in mechanical behavior across a weld junction between dissimilar metals. Weld interface microstructures can be quite complex at the local level, being composed of multiple graded heat affected zones surrounding a unique weld zone.

Dr. Robert Wheeler, of MTSL, has worked with CEMAS staff to interface special testing equipment with a Focused Ion Beam/Scanning Electron Microscope (FIB/SEM) to enable microtensile loading of small scale specimens having lateral gauge dimensions on the order of about10 microns. The FIB/SEM instrument is also used fabricate the micro-scale samples as shown in the figure. Conducting tests In-situ, within the microscope, allows direct visualization of elastic and plastic responses over the entirety of the micro-volume being deformed. These experiments enable precise correlation of atomic level slip events that contribute to plastic flow with the observed stress-strain curve.

CEMAS houses all the advanced instrumentation required to fabricate microsamples, test these samples in-situ with concurrent imaging and then further characterize deformed regions via post mortem TEM techniques.” - Dr. Robert Wheeler, MicroTesting Solutions LLC