19 research outputs found
Key Characteristics of Carbonized Corncob through Hydrothermal and Pyrolysis Conversion Techniques for Further Activation
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Localized Preheating Approaches for Reducing Residual Stress in Additive Manufacturing
No full textUniform preheating can be used to limit residual stress in the solid freeform
fabrication of relatively small parts. However, in additive manufacturing processes,
where a feature is deposited onto a much larger part, uniform preheating of the entire
assembly is typically not practical. This paper considers localized preheating to reduce
residual stresses, building on previous work using a defined thermal gradient through the
part depth as a metric for predicting maximum final residual stress. The building of thinwalled structures is considered. Two types of localized preheating approaches are
compared, appropriate for use in laser- or electron beam-based additive manufacturing
processes. In evaluating the effectiveness of each approach, a simplified
thermomechanical model is used that can be related directly to analytical
thermomechanical models for thermal stresses in unconstrained thin plates. Results are
presented showing that one of the methods yields temperature profiles likely to yield
reduced residual stresses at room temperature. Mechanical model results confirm this,
showing a significant reduction in maximum stress values. A more complete
thermomechanical simulation of thin wall fabrication is used to verify the trends seen in
the simplified model results.Mechanical Engineerin
Potential of Fermentable Sugar Production from Napier cv. Pakchong 1 Grass Residue as a Substrate to Produce Bioethanol
No full textAbstractBioethanol is one of the most significant renewable fuels. The major sources of bioethanol production are food crops such as corn, sugarcane, rice, wheat and sugar beet. However, utilization of food crops to produce bioethanol could affect the food sources and disrupt the food to population ratio. To overcome these issues, the utilization of lignocellulosic materials such as wheat straw, grass and crop residues to produce bioethanol has been developed for second-generation fuel, since those resources are abundant, cheap and renewable. Napier Pakchong 1 grass (NPG) residue is a lignocellulosic waste obtained from the process of biogas production that can be used as an alternative material for bioethanol production. This research aims to study on the potential of fermentable sugar production from NPG residue. The materials were pretreated with different concentrations of sodium hydroxide (NaOH), followed by enzymatic hydrolysis for saccharification. The results suggested that pretreatment with 3.0% (w/v) NaOH solution at 121̊C for 60 minutes provided the highest lignin removal of 86.1% (w/w) and enriched cellulose fraction from 36.4 to 75.6% (w/w). The enzymatic hydrolysis was conducted by varying enzyme loading volume and total solid contents (TS) at pH 4.8, 50̊C for 72h. The hydrolysis with enzyme loading volume of 2.0 ml/g of substrate and 10% (w/v) of TS were optimal for saccharification giving the reducing sugar yield of 768 mg/g of pretreated biomass or equal to 64 g/L and glucose yield of 522 mg/g of pretreated biomass or equal to 43 g/L. The reducing sugar will be used as a starting material for yeast to produce bioethanol
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Melt Pool Size and Stress Control for Laser-Based Deposition Near a Free Edge
No full textThermomechanical models developed in this research address two experimental
observations made during the deposition of thin-walled structures by the LENSTM process. The
first observation (via thermal imaging) is of substantial increases in melt pool size as a vertical
free edge is approached under conditions of constant laser power and velocity. The second
observation (via neutron diffraction) is of large tensile stresses in the vertical direction at vertical
free edges, after deposition is completed and the wall is allowed to cool to room temperature. At
issue is how to best control melt pool size as a free edge is approached and whether such control
will also reduce observed free edge stresses. Thermomechanical model results are presented
which demonstrate that power reduction curves suggested by process maps for melt pool size
under steady-state conditions can be effective in controlling melt pool size as a free edge is
approached. However, to achieve optimal results it is important that power reductions be
initiated before increases in melt pool size are observed. Stress simulations indicate that control
of melt pool size can reduce free-edge stresses; however, the primary cause of these stresses is a
constraint effect which is independent of melt pool size.This research was supported by the National Science Foundation Division of Design,
Manufacture and Industrial Innovation, through the Materials Processing and Manufacturing
Program, award number DMI-0200270.Mechanical Engineerin
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Process Scaling and Transient Melt Pool Size Control in Laser-Based Additive Manufacturing Processes
No full textThis modeling research considers two issues related to the control of melt pool size in
laser-based additive manufacturing processes. First, the problem of process size scale is
considered, with the goal of applying knowledge developed at one processing size scale (e.g. the
LENSTM process, using a 500 watt laser) to similar processes operating at larger scales (e.g. a 3
kilowatt system under development at South Dakota School of Mines and Technology). The
second problem considered is the transient behavior of melt pool size due to a step change in
laser power or velocity. Its primary application is to dynamic feedback control of melt pool size
by thermal imaging techniques, where model results specify power or velocity changes needed to
rapidly achieve a desired melt pool size. Both of these issues are addressed via a process map
approach developed by the authors and co-workers. This approach collapses results from a large
number of simulations over the full range of practical process variables into plots process
engineers can easily use.This research was supported by the National Science Foundation Division of Design,
Manufacture and Industrial Innovation, through the Materials Processing and Manufacturing
Program, award number DMI-0200270.Mechanical Engineerin
