A. James Clark School of Engineering

Permanent URI for this communityhttp://hdl.handle.net/1903/1654

The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

Browse

Subject: search.filters.subject.Sintering

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Tailorable Energy Absorbing Cellular Materials via Sintering of Dry Powder Printed Hollow Glass Microspheres
    (2024-05-01) Wereley, Norman; Park, Jungjin; Howard, John; DeMay, Matthew; Edery, Avi; Wereley, Norman
    This article examines amorphous glass-based foams as lightweight core materials for crash-resistant structures that offer tailorable energy absorption capabilities. Hollow glass microspheres (HGMs) of different densities are layered using dry powder printing (DPP), an additive manufacturing process, and subsequently sintered to consolidate these microspheres into a cellular foam structure. The tailoring of energy absorption is achieved in these foams by layering hollow microspheres with different densities and different thickness ratios of the layers. The mechanical response to quasi-static uniaxial compression of the bilayer foams is also investigated. Bilayer samples exhibit a distinctive two-step stress-strain profile that includes first and second plateau stress, as opposed to a single constant density which does not. The strain at which the second plateau occurs can be tailored by adjusting the thickness ratio of the two layers. The resulting stress-strain profiles demonstrate tailorable energy absorption. Tailorability is found to be more significant if the density values of each layer differ greatly. For comparison, bilayer samples are fabricated using epoxy at the interface instead of the co- sintering process. Epoxy-bonded samples show a different mechanical response from the co-sintered sample with a different stress-strain profile. Designing the bilayer foams enables tailoring of the stress-strain profile, so that energy-absorption requirements can be met for a specific impact condition. The implementation of these materials for energy absorption, crashworthiness, and buoyancy applications will be discussed.
  • Thumbnail Image
    Item
    ASSESSMENT OF PROPERTIES OF TRANSIENT LIQUID PHASE SINTERED (TLPS) INTERCONNECTS BY SIMULATION AND EXPERIMENTS
    (2017) Greve, Hannes Martin Hinrich; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Growing power densities of electronic products and application of electronic systems in high temperature environment increase the temperature requirements on electronic packaging systems. Conventional interconnect technology was designed for devices based on silicon semiconductor technology limited to 175 °C and below. The introduction of wide bandgap semiconductor materials such as silicon carbide and gallium nitride expands the potential application temperature range to 500 °C beyond the range of conventional electronic packaging solutions. Transient Liquid Phase Sintering (TLPS) is a promising high temperature, high strength, low cost interconnect technology solution. TLPS is a liquid-assisted sintering process during which a low melting temperature constituent melts, surrounds, and diffuses with a high melting temperature constituent. A shift towards higher melting temperatures occurs as the low melting temperature phase is transformed into high melting temperature intermetallic compounds (IMCs). In this work, three TLPS sinter paste systems based on the copper-tin (Cu-Sn), nickel-tin (Ni-Sn), and copper-nickel-tin (Cu-Ni-Sn) material systems are designed. A novel process for their application as electronic interconnects is developed. Processing and thermal aging studies are performed to determine times to process completion characterized by high-temperature capability of the joints. Microstructural convergence durations are studied for each of the material systems. A modeling approach is developed to model realistic joint geometries with varying types, sizes, and distributions of metal particles and voids in intermetallic matrices. These are used to predict the constitutive (elastic-plastic) stress-strain responses and thermal properties of these systems by simulation. The constitutive models derived by this approach are compared to constitutive properties determined experimentally by Iosipescu shear samples with TLPS joints. The thermal properties of TLPS joints are determined experimentally by transient thermal response analyses. Failure mechanisms driven by thermal and thermo-mechanical stressors are predicted and verified, and mitigation techniques are developed.
  • Thumbnail Image
    Item
    SIZE MODIFICATION AND COATING OF TITANIUM DIOXIDE USING A PREMIXED HYDROGEN/AIR FLAME
    (2006-08-22) Lee, Seungchan; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A study was conducted of the effect of flame processing on the size distribution of titania nanoparticles, and a flame process was developed for producing TiO2/SiO2 coreshell particles from aqueous suspensions of TiO2 and SiO2 nanoparticles. Both were performed using a premixed hydrogen/air flame. At the adiabatic flame temperature of 2400 K, the number mean diameter of titania primary particle increased considerably from an initial value of 44 nm to 96 nm, presumably by atomic diffusion, and viscous flow coalescence. Moreover, the majority of product particles from this high flame temperature were smooth and spherical. Based on the results of size modification experiments, coating experiments were performed. The dominant morphology observed in the product particles from coating experiments was silica coated titania. The silica coating was very smooth and dense. The total particle size and the shell volume of the product particles were in reasonable agreement with values predicted from the atomized droplet size distribution and the droplet concentration.