Search for: All records

This work uses in situ nonlinear ultrasound measurements to study the relationship between the acoustic nonlinearity parameter β and the low cycle fatigue behavior of stainless steel 316L. The measured β shows a rapid decrease during hardening followed by a transition to a slower decrease in β as a function of fatigue cycles. Measurements show this trend is consistent at two different strain amplitudes. By comparing our results with prior work on dislocation characterizations in the same material, we hypothesize that the transition in slopes of β coincides with the planar-to-wavy transition that occurs at the end of hardening. Further, measurement results show that the parameter Δβt-c, the difference between β measured after the tension and compression portions of the fatigue cycle, depends on strain amplitude. The dependence of Δβt-c on strain amplitude is related to fatigue life through a power law relationship, similar to slip irreversibility. Overall, the results provided in this work suggest that β correlates with characteristics of low cycle fatigue, and thus supports the idea that in situ NLU measurements can eventually be used as a quantitative measure to predict fatigue life. 

Lattice materials provide unusual thermal and vibrational properties but not within the same structure. Thermal and vibrational multifunctionality is, however, crucial for thermomechanical applications such as automotive, aerospace, building, transportation, and energy infrastructure. In applications involving mobility, both high heat transfer and low mass are desired. Although there have been various efforts to design multifunctional lattice materials, the focus has largely remained on quasi‐static mechanical and thermal properties or mechanical and vibrational properties. Herein, designs of realizable lattice materials are reported, which are inherently thermally resistive, with vastly improved thermal conductance and omnidirectional phononic band gaps. By redesigning the truss structures to serve as interconnected heat pipes, a three‐order‐of‐magnitude improvement in the specific thermal conductance is found. Nodal masses at truss junctions are further used to obtain full vibrational band gaps. It is shown that it is possible to independently tune vibrational and thermal properties within the same structure. This work provides background for the design and fabrication of multifunctional lattice materials that simultaneously prevent structural vibrations and enhance heat conduction.