Improving Linear Weld Density in Ultrasonically Consolidated Parts

Ultrasonic consolidation is a novel additive manufacturing process with immense potential for fabrication of complex shaped three-dimensional metallic objects from metal foils. The proportion of bonded area to unbonded area along the layer interface, termed linear weld density (LWD), is perhaps the most important quality attribute of ultrasonically consolidated parts. Part mechanical properties largely depend on LWD and a high level of LWD must be ensured in parts intended for load-bearing structural applications. It is therefore necessary to understand what factors influence LWD or defect formation and devise methods to enhance bond formation during ultrasonic consolidation. The current work examines these issues and proposes strategies to ensure near 100% LWD in ultrasonically consolidated aluminum alloy 3003 parts. The work elucidates the effects of various process parameters on LWD and a qualitative understanding of the effects of process parameters on bond formation during ultrasonic consolidation is presented. The beneficial effects of using elevated substrate temperatures and its implications on overall manufacturing flexibility are discussed. A preliminary understanding of defect morphologies and defect formation is presented, based on which a method (involving surface machining) for minimizing defect incidence during ultrasonic consolidation is proposed and demonstrated. Finally, trade-offs between part quality and build time are discussed.Mechanical Engineerin

Economics of Managing Invasive Species in Tropical and Sub-Tropical Areas of the U.S.A.: Case Study Development

Resource /Energy Economics and Policy,

Maximum Height to Width Ratio of Freestanding Structures Built Using Ultrasonic Consolidation

Ultrasonic consolidation (UC) is a process whereby metal foils can be metallurgically bonded at or near room temperature. The UC process works by inducing high-speed differential motion (~20kHz) between a newly deposited layer and a substrate (which consists of a base plate and any previously deposited layers of material). This differential motion causes plastic deformation at the interface, which breaks up surface oxides and deforms surface asperities, bringing clean metal surfaces into intimate contact, where bonding occurs. If the substrate is not stiff enough to resist deflection during ultrasonic excitation of newly deposited layers, then it deflects along with the newly deposited layer, resulting in no differential motion and lack of bonding. Geometric issues which control substrate stiffness and deflection were investigated at Utah State University by building a number of free-standing rib structures with varying dimensions and orientations. Each structure was built to a height where lack of bonding between the previously deposited layers and the newly deposited layer caused the building process to fail, a height to width ratio (H/W) of approximately 1:1. The parts were then cut, polished, and viewed under a microscope. An ANSYS model was created to investigate analytically the cause of this failure. It appears build failure is due to excessive deflection of the ribs around a 1:1 H/W, resulting in insufficient differential motion and deformation to achieve bonding. Preliminary results show, when the H/W reaches 1:1, the von Mises stress is found to be tensile along portions of the bonding interface, which eliminates the compressive frictional forces necessary for plastic deformation and formation of a metallurgical bond. These tensile stresses are shown to be concentrated at regions near the edges of the newly deposited foil layer.Mechanical Engineerin

Connectivity strategies to enhance the capacity of weight-bearing networks

The connectivity properties of a weight-bearing network are exploited to enhance it's capacity. We study a 2-d network of sites where the weight-bearing capacity of a given site depends on the capacities of the sites connected to it in the layers above. The network consists of clusters viz. a set of sites connected with each other with the largest such collection of sites being denoted as the maximal cluster. New connections are made between sites in successive layers using two distinct strategies. The key element of our strategies consists of adding as many disjoint clusters as possible to the sites on the trunk $T$ of the maximal cluster. The new networks can bear much higher weights than the original networks and have much lower failure rates. The first strategy leads to a greater enhancement of stability whereas the second leads to a greater enhancement of capacity compared to the original networks. The original network used here is a typical example of the branching hierarchical class. However the application of strategies similar to ours can yield useful results in other types of networks as well.Comment: 17 pages, 3 EPS files, 5 PS files, Phys. Rev. E (to appear

Effect of soil and crop management practices on sodicity stress alleviation and rice productivity under water scarce condition

The prominent issue faced by the farmers of Cauvery Delta regionin Tamil Nadu particularly Tiruchirapalli District is the lack of timely release of water for rice nursery preparation and transplanting. Hence wet seeding of rice is recommended for timely cultivation. On the other hand, sodic nature of the soil warrants rice cultivation only. Therefore, the present investigation was carried out to study the different soil and crop management practices on alleviating sodicity stress and improving rice (variety ADT 3) productivity under water-scarce conditions. The experiment was laid in a split plot design with six mainplots,including rice wet seeding, daincha (Sesbania aculeata) application as green manure, anti-oxidant microbial consortia (AOMC) spray and four sub-plots with graded levels of NPK based on soil test values with three replication. Results showed that the daincha incorporation @ 6.25 t/ha followed by rice wet seeding + AOMC spray @1.5 % with 125 % soil test based NPK had significantly increased thechlorophyll content, SPAD values, proline content and grain and straw yields which remained on par with daincha incorporation @ 6.25 t/ha followed by rice wet seeding + AOMC spray @1.5 % with 100 % soil test based NPK.Significantly lower ESP at 5% level and higher phosphatase activity in soil was also recorded by daincha incorporation @ 6.25 t/ha followed by rice wet seeding + AOMC spray @1.5 % with 125 % and 100 % soil test based NPK. Gross return, net return and B:C ratio were also higher in the plot, which received daincha incorporation @6.25 t/ha followed by rice wet seeding + AOMC spray @1.5 % with 100 % soil test based NPK. The present study reveals that the inclusion of ectophytic microbial population spray in rice plants and the management practices helps the crop to tolerate the sodicity stress under water-scarce condition by maintaining required physiological functions like proline synthesis and enzyme activities etc which need to be further explored at the genotypic level.