Lorenzo Valdevit
University of California, Irvine
Conference Proceedings
Publication Types:
A Cellular Periodic Material Design for Enhanced Seismic Protection of Low-Rise Buildings
Abstract
In most recent earthquakes, traditional seismic design demonstrated its effectiveness in reducing casualties through ductile structural mechanisms, but allowed for extensive structural damages that accounted for tremendous economic losses. This evidence raised awareness for the need of an increased level of resiliency, mostly in low-rise buildings. Seismic isolation is a protection system that proved to be successful in prevent damages and maintaining operability. However, high costs and sever testing protocols currently discourage the extensive application of this technology to low-rise buildings. In this study, an architected periodic cellular material with unprecedented characteristic is proposed as a low-cost alternative to traditional technologies to produce seismic isolation devices for implementation in residential, retail and office buildings. Results from preliminary numerical analysis demonstrate the range of performance of this novel architected material in comparison with traditional materials. The scalability of the architected material is also addressed with the aim of investigating the feasibility of using tests on small assemblies of the constituent unit-cells instead of full scale tests to assess the structural performance of the isolators.
Use of architected materials for the design of seismic isolation devices
Abstract
The development of a novel class of materials that can be used for the seismic isolation protection systems is presented. The material is an architected cellular material obtained as periodic reproduction of a unit cell in all spatial directions. The mechanical properties of the constitutive unit-cell are tailored through an optimal design of the spatial configuration of voids and solids (cellular architecture) for a given solid constituent. The presented material can be designed at different scales in order to obtain unprecedented combinations of mechanical properties, such as high stiffness and strength in the vertical direction combined with high flexibility and dissipative capability in the lateral directions. Compact-shape, light-weight isolators overcoming traditional isolators’ limitations may be obtained through optimization of the unit cell properties. A mechanistic model of the isolator is provided after calibration on randomized parametric nonlinear Finite Element analysis of the unit cell. Keywords: Seismic isolation; periodic architected material; mechanistic model.
3D Manufacturing of Micro and Nano-Architected Materials
Abstract
Reducing mass without sacrificing mechanical integrity and performance is a critical goal in a vast range of applications. Introducing a controlled amount of porosity in a strong and dense material (hence fabricating a cellular solid) is an obvious avenue to weight reduction. The mechanical effectiveness of this strategy, though, depends strongly on the architecture of the resulting cellular material (i.e., the topology of the introduced porosity). Recent progress in additive manufacturing enables fabrication of macro-scale cellular materials (both single-phase and hybrid) with unprecedented dimensional control on the unit-cell and sub-unit-cell features, potentially producing architectures with structural hierarchy from the nano to the macro-scale. As mechanical properties of materials often exhibit beneficial size effects at the nano-scale (e.g., strengthening of metals and toughening of ceramics), these novel manufacturing approaches provide a unique opportunity to translate these beneficial effects to the macro-scale, further improving the mechanical performance of architected materials. The enormous design space for architected materials, and the strong relationship between the topological features of the architecture and the effective physical and mechanical properties of the material at the macro-scale, present both a huge opportunity and an urgent need for the development of suitable optimal design strategies. Here we present a number of strategies for the advanced manufacturing, characterization and optimal design of a variety of lightweight architected materials with unique combinations of mechanical properties (stiffness, strength, damping coefficient…). The urgent need to form strong synergies among the fields of additive manufacturing, topology optimization and architectureproperties relations is emphasized throughout.
Glass-Blown Pyrex Resonator with Compensating Ti Coating for Reduction of TCF
Abstract
This paper demonstrates that the Thermal Coefficient of resonant Frequency (TCF) of a micro glass-blown Pyrex spherical resonator can be substantially reduced by the application of a titanium (Ti) coating. Finite Elements Analysis (FEA) is used to demonstrate that the temperature dependence of the Young’s modulus of the shell material is the dominant parameter affecting the TCF of the resonator, clearly suggesting the use of a metallic compensating layer. Experimental characterization demonstrates that the TCF of a Pyrex glass-blown resonator is reduced by 70% (from 73 ppm/°C to 24 ppm/°C) by the application of a 1.33 μm thick layer of Ti. It is predicted by FEM that for a Ti layer thickness on the order of 2.5 μm the TCF will fall below 10 ppm an acceptable value for high performance resonators. This investigation is a step forward in the quest to employ the desirable properties of micro-blown resonators, such as high symmetry, manufacturing tolerances and environmental robustness.
Ceramic and hybrid micro-architected materials for high temperature applications
Abstract
This article presents an innovative additive manufacturing approach for fully optimized ceramic and hybrid (ceramic/polymer) hierarchical micro-architected materials for extreme environments. The developed materials combine high-temperature capabilities, extremely low thermal conductivity, high stiffness and strength per unit weight, sufficient toughness and great resistance to oxidation. Processing involves 3D printing of a ceramic architecture, followed by bisque firing and sintering. When sufficient porosity remains after sintering (~50%), infiltration by a polymeric matrix is possible, resulting in a cellular architecture where the constituent material is a fully dense ceramic/polymer hybrid with exceptional ductility. After characterizing the microstructure and mechanical properties of the constituent material (ceramic and hybrid), we demonstrate the fabrication of a truss-core sandwich panel. Both the internal architecture and the external shape can be controlled at will in the manufacturing process. Multifunctional Thermal Protection Systems (TPS) for the next generation of high-speed aircraft (particularly hypersonics) are the prototypical, albeit not the only, application.
A novel modeling platform for characterization and optimal design of micro-architected materials
Abstract
Recent advances in multi-scale manufacturing enable fabrication of hollow-truss based lattices with dimensional control spanning seven orders of magnitude in length scale (from ~50nm to ~10cm), offering tremendous potential for multifunctionality. Topology optimization is essential to realize the full potential of these micro-architected materials. This paper presents a novel optimal design and modeling platform, consisting of four interconnected tools: (i) a geometric modeling algorithm; (ii) a meshing algorithm; (iii) an optimal design code; and (iv) a communication interface with a commercial Finite Elements program (Abaqus). The powerfulness of the proposed platform is demonstrated for the optimization of specific stiffness in pyramidal hollow micro-lattices.
A resonant tuning fork sensor with unprecedented combination of resolution and range
Abstract
This paper presents a double-ended tuning fork (DETF) force sensor with a resolution of 7nN and a range of 0.12N. The resonator has a scale factor of 216 kHz/N, a Q-factor exceeding 60,000 at 3mTorr ambient pressure and a zero-load resonant frequency of 47.6 kHz. The sensor and the complete readout circuit are fully embedded in a compact 65 mm × 52 mm printed circuit board (PCB). The PCB is mounted on a micro-stage and coupled with an off-the-shelf displacement actuator to realize an economical, versatile and robust micro mechanical test frame with unprecedented combination of force and displacement resolutions and ranges.
The design space of Superalloy-based actively cooled combustor walls for Mach 7-12 hypersonic vehicles
Abstract
The walls of combustion chambers used for air-breathing hypersonic vehicles are subject to substantial thermo-mechanical loads, and require active cooling by the fuel in conjunction with advanced material systems. Solutions based on metallics are preferable to ceramic matrix composites due to their lower cost and greater structural robustness. Previous work suggested that a number of metallic materials (e.g. Nickel, Copper and Niobium alloys) could be used to fabricate actively cooled sandwich structures that withstand the thermo-mechanical loads for a Mach 7, hydrocarbon-powered vehicle (albeit with different weight efficiencies). However, this conclusion changes when the Mach number is increased. This work explores the feasibility of the Nickel superalloy MARM246 for a wide range of Mach numbers (7–12). Since hydrocarbon fuels are limited to Mach 7–8, Hydrogen is used as the coolant of choice. A previously derived analytical model (appropriately modified for gaseous coolant) is used to explore the design space. The relative importance of each design constraint is assessed, resulting in the distillation of essential guidelines for optimal design.
Metallic structural heat pipes as sharp leading edges for Mach 7 vehicles
Abstract
Sharp leading edges on hypersonic vehicles experience very large heating loads and consequent high temperatures. One strategy for for accommodating these effects is to provide very high effectively thermal conductivity which allows heat to be transferred from the hot leading edge to large cool surfaces for radiation into space. Heat pipes integrated within metallic leading edges provide this function, as well as being easy to manufacture and highly robust compared to other material choices. This paper will examine the feasibility of metallic leading edge heat pipes for hypersonic vehicles in Mach 7 flight. Using temperatures and heat fluxes calculated elsewhere, analytic approximations of the temperature distributions and stresses in a prototypical system are analyzed. The analysis is supplemented and confirmed by finite element calculations. Feasibility of the system is assessed by simple calculations on the operational limits of heat pipes.
Design and implementation of actively cooled panels for scramjets
Abstract
The operating conditions of scramjet engines demand designs that include active cooling by the fuel and the use of lightweight materials that withstand extreme heat fluxes and structural loads. An optimization tool has previously been introduced to direct the development of advanced materials that outperform existing high temperature alloys and compete with ceramic matrix composites. This analysis presents verification and accretion of the analytical design tool through a combination of numerical and experimental techniques. Selected computational fluid dynamics (CFD) analyses have been performed to verify critical thermal assumptions. A high-power CO2 laser provides heat fluxes representative of hypersonic flight conditions.
Design of actively cooled panels for scramjets
Abstract
The operating conditions of scramjet engines demand designs that include active cooling by the fuel and the use of lightweight materials that withstand extreme heat fluxes under oxidizing conditions. The goal of this analysis is to provide an optimization tool that can be used to direct the development of advanced materials that outperform existing high temperature alloys and compete with ceramic matrix composites. For this purpose an actively cooled plate has been optimized for minimum weight under three primary constraints. (i) Resistance to pressure loads arising from fuel injection and combustion, as well as thermal loads associated with the combustion temperature. (ii) A temperature distribution in the structure during operation that does not exceed material limits, subject to a reasonable pressure drop. (iii) A maximum temperature in the fuel (JP-7) low enough to prohibit coking. It is shown that all design requirements typical of Mach 5-7 hypersonic vehicles can be met by a small subset of material systems. Those made using C/SiC composites are the lightest. Others made using Nb alloys and (thermal barrier coated) superalloys are somewhat heavier, but might prevail in a design selection because of their structural robustness, facility of fabrication and cost-effectiveness.