The microstructures of materials dictate their macroscopic mechanical behavior (i.e., plasticity and fracture).  Our group studies the links between microstructure and mechanical behavior through novel experiments and computational modeling in order to develop predictive and extensible mechanical models.  We perform microscale tests in situ SEM using a mini test stage and in situ neutron diffraction, both of which allow for the quantification of deformation on the scale of grains.  We compare the experimental results with microstructural finite element representative volume element (FE-RVE) models and crystal plasticity models developed in our group.  The hybrid experimental-computational approach allows for the identification of deformation and failure mechanisms of different metals, which enables the development of physically based, predictive plasticity and fracture models.

Selected Publications

 

It is well-known that the ductile fracture behavior, and often plasticity behavior, of metals depends on stress state.  Thus, to efficiently use these materials, predictive models that describe the failure of these materials under realistic complex loading states are needed.  Our lab uses a combined experimental-computational approach to investigate and model large deformation and fracture behavior.  In particular, we use a custom-built dual-actuator mechanical test frame along with specially designed test specimens to measure the multiaxial deformation behavior of a range of metals, from advanced high strength steels to additively manufactured alloys.  Based on experiments and simulations, we develop computational plasticity and fracture models for these materials.

Selected Publications

 

In additive manufacturing (AM) of metals, 3D components are built in a layer-by-layer fashion using different processes including powder-based, laser-based processes of powder bed fusion (PBF) and directed energy deposition (DED).  In both processes, a 3-dimensional component is sliced into 2-dimensional layers.  Powder feedstock is delivered to a location within the 2D layer, melted with a laser, and fuses to the layer below upon cooling and solidification.  AM technology allows for the fabrication of design-driven components rather than manufacturing process-dependent geometries. However, an understanding of the mechanics of materials made by AM is required for the adoption of AM in load-bearing applications.  Our group works to understand the multiaxial mechanical behavior of materials made by AM through combined experimental and computational methods.

Selected Publications

 

Additively manufactured components are subjected to complex thermal histories, beginning with rapid solidification and followed by thermal cycling with the addition of layers. This processing can result in porosity (defects), location-dependent microstructures, and thus, location-dependent and anisotropic mechanical properties (elasto-plastic deformation and fracture) that differ significantly from those of conventionally processed materials. We perform research toward developing a fundamental understanding of the connections among the processing (thermal history), microstructure, and mechanical properties additively manufactured metallic materials, using both experimental characterization and computational simulations, and develop computational models that describe these relationships.

Selected Publications


Functionally graded materials (FGMs) have the potential to expand the design space within additive manufacturing (AM) for spatially tailored properties within single components. In FGMs, material properties vary spatially due to intentional changes in chemistry or microstructure within a single component.  Our group studies metallic FGMs fabricated using directed energy deposition (DED) additive manufacturing.  With DED AM, the ratios of powder metal feedstock being fed into the melt pool can be varied, allowing for targeted changes in chemistry, and therefore, properties, as a function of location.  We use a combination of experimental characterization and computational simulations to analyze the microstructure, chemistry, phase composition, and mechanical properties of FGM systems, and use the resulting information to inform future gradient pathway designs. 

Selected Publications


Alloys currently used in additive manufacturing (AM) are primarily limited to those designed for welding and casting, thus, they are not optimized for the complex thermal histories seen in AM of rapid solidification followed by repeated thermal cycling with the addition of layers. Understanding and designing advanced alloys for AM requires knowledge of non-equilibrium microstructure as a function of alloying elements and thermal history. We are working to develop an approach for predicting microstructure, which can then be applied to develop alloys specifically tailored for AM. For this, we use a combined experimental/computational approach, which makes use of CALPHAD modeling.