Lawrence Livermore researchers have adapted theoretical models to predict and demonstrate the failure behavior of miniaturized three-dimensional (3D) lattices, seen in trestle bridges and similar structures. Additive manufacturing—also known as 3D printing—allows researchers to miniaturize these types of structures to considerably smaller length scales than was possible before. Laboratory researchers Mark Messner (now at Argonne National Laboratory) and Holly Carlton published these studies in the May 1, 2017, edition of Acta Materialia.
Messner used a newly developed equivalent continuum model to predict failure behavior in lattice structures with different topologies. Understanding the dominant failure mode is critical to using lightweight microtrusses because of the mode’s influence on a structure’s energy absorption capacity. Messner’s method predicts a tradeoff between yield-dominated and catastrophic buckling–dominated failure modes at a critical relative density. This predicted density depends on several modeling assumptions that are strongly influenced by the manufacturing process.
To experimentally investigate deformation in lattice structures, Carlton coupled quasistatic compression tests with in situ tomography at Lawrence Berkeley National Laboratory’s Advanced Light Source. These experiments on miniaturized 3D-printed unit cell lattice structures captured real-time deformation, specifically showing a transition in failure mode from catastrophic buckling to yielding at a low relative density, thus validating Messner’s model predictions. These findings have implications for how scientists and engineers design and fabricate architected structures for future applications.
Contact: Holly Carlton (925) 422-2765 (carlton4@llnl.gov).
Livermore researchers have measured the effects of drug exposure on heart tissue using “heart-on-a-chip” technology—an engineered chip that models the human heart. This research, published in the April 18, 2017, edition of Lab on a Chip, seeks to shorten new-drug trials and ensure that potentially lifesaving drugs are safe and effective.
The paper describes the successful recording of both electrical signals and cellular beating from normal heart cells grown on a Livermore-developed multielectrode array. (See rendering above.) This design is the first capable of simultaneously mapping both the electrophysiology and contraction frequency of the cells. The tissue was exposed to the stimulant norepinephrine, resulting in increases in the cells’ electrical signal and beating, replicating what happens in the human body. The researchers state that the chip can benefit pharmaceutical companies not only by serving as an early alert for cardiac problems caused by a drug but also by providing experimental information about drug functions so that better compounds can be designed. The technology may also reduce the need for human and animal testing.
The heart-on-a-chip uses cultured human cardiac cells, which naturally and spontaneously grow to form a layer of heart tissue that begins to beat after only two days in culture. Over time, the researchers demonstrated that the platform could measure heart tissue growth, electrophysiology, and heartbeat simultaneously and in real time. The Laboratory Directed Research and Development Program funded the project as part of its iCHIP (in vitro chip-based human investigational platform) effort. Livermore collaborated with Harvard Medical School in the research.
Contact: Elizabeth Wheeler (925) 423-6245 (wheeler16@llnl.gov).
Lawrence Livermore researchers recently proposed a technique to obtain structural information about lithium under conditions at which traditional crystallographic methods are insufficient, possibly solving a decades-long puzzle. Although lithium is considered a typical, simple metal, its crystal structure at ambient pressure and low temperature has remained unknown.
In a paper appearing in the May 23, 2017, edition of Proceedings of the National Academy of Sciences, the researchers describe measuring oscillations of lithium’s crystal magnetic moment in an external magnetic field. The team performed theoretical analysis showing the spectrum of oscillation resonances to be quite distinctive for different lithium structures. A comparison with previous experimental data indicates that the low-temperature phase of lithium is incompatible with the previously attributed structure of nine hexagonal stacking layers.
Lithium and its compounds have several industrial applications, including heat-resistant glass and ceramics, grease lubricants, flux additives for metal production, and lithium-ion batteries—uses that represent more than three-quarters of lithium production. For years, however, scientists have tried to understand lithium’s strange behavior and structure. Calculations to determine the lowest energy equilibrium structure require enormous precision. In addition, the element’s light atomic mass results in significant dynamics even at low temperature and a relatively weak response to x rays and neutrons—the traditional methods for determining crystal structure. Furthermore, the transition to the low-temperature phase is gradual and breaks the single-crystal structure. This recent breakthrough by Laboratory researchers enables more-precise analysis of lithium.
Contact: Stanimir Bonev (925) 422-4347 (bonev2@llnl.gov).