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Lattice Design Optimization: Crowdsourcing Ideas in the Classroom
Get PDFCrowdsourcing is a powerful method of generating ideas, particularly when there are many
possible solutions to a particular problem with no obvious process towards arriving at the optimum
one. In this paper, results of a crowdsourcing exercise conducted in a 30-student classroom are
reported. Students were tasked with using lattice design concepts to minimize the weight of a beam
under bending, tension and torsion. Using the nTopology software, they approached the problem
in three steps: (1) Selection/design of a unit cell, (2) Distribution of cell size, and (3) Optimization
of the thickness of individual members. The first two steps were design decisions made by the
students, the last step used nTopology's native solver. This work shares insights gained both in
lattice design itself, as well as on the use of crowdsourcing in the classroom, particularly in the
context of the rapidly evolving field of Design for Additive Manufacturing.Mechanical Engineerin
Hierarchy in fracture as a stochastic process: Model, implementation and validation
No full textLinear Elastic Fracture Mechanics (LEFM), Cohesive Zone Models (CZMs) and damage mechanics all address the problem of predicting failure in structures using continuum treatments of the materials involved. Each of these approaches has a distinct set of limitations, some of which are: LEFM is applicable only for problems involving elastic materials, or at best, small-scale yielding. CZMs, while being applicable to a wide range of failure behaviors, have tenuous physical origins and the estimation of the required parameters is challenging. Damage mechanics approaches do not explicitly account for the existence of the crack. The overarching goal of this thesis is the development of a failure model that is free of the limiting assumptions of LEFM, does not postulate alternate behavioral models like the CZM and explicitly accounts for the existence of the crack, unlike damage mechanics. To demonstrate the need for the proposed failure modeling approach, and to verify its validity, solder alloys are selected as an ideal subject for study, on account of their complex constitutive, microstructural and failure behavior. In the first part of this thesis, solder behavior is characterized experimentally by performing extensive constant-strain-rate and creep tests on solder interconnections. Special care is taken to ensure the validity of the estimated stress and strain quantities. Viscoplastic constitutive models are developed to describe the behavior of these solders. Existing failure modeling approaches for describing fatigue failure in solder joints are examined closely. The developed constitutive model is used to estimate failure parameters for a failure model inspired by Cohesive Zone Modeling and Weibull functions. A novel failure modeling approach is developed. This approach is inspired by two facts that are backed by experimental evidence: cracks grow by specific mechanisms and are the end result of a dissipative process, and fracture has an inherent hierarchy. The second of these facts permits the interpretation of fracture as a stochastic process, where each potential path for the crack is assigned a certain probability with it being the path for failure. A key mathematical result developed in an area of research called Information Theory is borrowed to quantify this probability of failure and relate it to the irrecoverable energy that is expended in the creation of new surfaces. The proposed failure model is implemented in finite elements and the smeared approach is selected to represent cracks. The key issue of mesh dependence is discussed and it is shown that reasonable mitigation of mesh sensitivity in the models is obtained by the incorporation of a characteristic length measure. The failure model is then implemented in commercial finite element code by means of a user subroutine that calculates the probability of failure at each point. To alleviate the computational expense associated with simulating typical fatigue problems over several thousand cycles, the subroutine extrapolates relevant quantities. Finally, thermomechanical cycling tests are performed on a microelectronics Chip Scale Package (CSP). Extensive failure analysis is carried out in addition to the conventional Weibull analysis and the growth of the fatigue crack through the joint is tracked periodically. Finite element simulations using the constitutive and failure models developed in this work are validated against these experimentally obtained results and satisfactory agreement is obtained
Capillary Action in Additive Manufactured Channels for Thermal Management
No full textabstract: Due to the vast increase in processing power and energy usage in computing, a need for greater heat dissipation is prevalent. With numerous applications demanding cheaper and more efficient options for thermal management, new technology must be employed. Through the use of additive manufacturing, designs and structures can be created that were not physically possible before without extensive costs. The goal is to design a system that utilizes capillary action, which is the ability for liquids to flow through narrow spaces unassisted. The level of detail required may be achieved with direct metal laser sintering (DMLS) and stereolithography (SLA) 3D printing. (abstract
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Bio-Inspired Design of Next Generation Honeycomb Sandwich Panel Cores
No full textabstract: Honeycomb sandwich panels have been used in structural applications for several decades in various industries. While these panels are lightweight and rigid, their design has not evolved much due to constraints imposed by available manufacturing processes and remain primarily two-dimensional extrusions sandwiched between facings. With the growth in Additive Manufacturing, more complex geometries can now be produced, and advanced design techniques can be implemented into end use parts to obtain further reductions in weight, as well as enable greater multi-functionality. The question therefore is: how best to revisit the design of these honeycomb panels to obtain these benefits?
In this work, a Bio-Inspired Design approach was taken to answer this question, primarily since the hexagonal lattice is so commonly found in wasp and bee nests, including the well-known bee’s honeycomb that inspired these panel designs to begin with. Whereas prior honeycomb panel design has primarily focused on the hexagonal shape of the unit cell, in this work we examine the relationship between the various parameters constituting the hexagonal cell itself, specifically the wall thickness and the corner radius, and also examine out-of-plane features that have not been previously translated into panel design. This work reports findings from a study of insect nests across 70 species using 2D and 3D measurements with optical microscopy and X-ray tomography, respectively. Data from these biological nests were used to identify design parameters of interest, which were then translated into design principles. These design principles were implemented in the design of honeycomb panels manufactured with the Selective Laser Sintering process and subjected to experimental testing to study their effects on the mechanical behavior of these panels.Dissertation/ThesisMasters Thesis Manufacturing Engineering 202
Evaluation of Properties of Triply Periodic Minimal Surface Structures Using ANSYS
Get PDFabstract: The advancements in additive manufacturing have made it possible to bring life to designs
that would otherwise exist only on paper. An excellent example of such designs
are the Triply Periodic Minimal Surface (TPMS) structures like Schwarz D, Schwarz
P, Gyroid, etc. These structures are self-sustaining, i.e. they require minimal supports
or no supports at all when 3D printed. These structures exist in stable form in
nature, like butterfly wings are made of Gyroids. Automotive and aerospace industry
have a growing demand for strong and light structures, which can be solved using
TPMS models. In this research we will try and understand some of the properties of
these Triply Periodic Minimal Surface (TPMS) structures and see how they perform
in comparison to the conventional models. The research was concentrated on the
mechanical, thermal and fluid flow properties of the Schwarz D, Gyroid and Spherical
Gyroid Triply Periodic Minimal Surface (TPMS) models in particular, other Triply
Periodic Minimal Surface (TPMS) models were not considered. A detailed finite
element analysis was performed on the mechanical and thermal properties using ANSYS
19.2 and the flow properties were analyzed using ANSYS Fluent under different
conditions.Dissertation/ThesisMasters Thesis Mechanical Engineering 201
Effects of Increasing Layer Thickness in the Laser Powder Bed Fusion of Inconel 718
Get PDFabstract: With the advancement of the Additive Manufacturing technology in the fields of metals, a lot of interest has developed in Laser Powder Bed (LPBF) for the Aerospace and Automotive industries. With primary challenges like high cost and time associated with this process reducing the build time is a critical component. Being a layer by layer process increasing layer thickness causes a decrease in manufacturing time. In this study, effects of the change in layer thickness in the Laser Powder Bed Fusion of Inconel 718 were evaluated. The effects were investigated for 30, 60 and 80 μm layer thicknesses and were evaluated for Relative Density, Surface Roughness and Mechanical properties, for as-printed specimens not subjected to any heat treatment. The process was optimized to print dense pasts by varying three parameters: power, velocity and hatch distance. Significant change in some properties like true Ultimate Tensile Testing (UTS), %Necking and Yield Stress was observed.Dissertation/ThesisMasters Thesis Manufacturing Engineering 201
Thermal Resistance Measurements of Triply Periodic Minimal Surface Structures (TPMS) of the Thermogalvanic Brick
No full textabstract: The presence of huge amounts of waste heat and the constant demand for electric energy makes this an appreciable research topic, yet at present there is no commercially viable technology to harness the inherent energy resource provided by the temperature differential between the inside and outside of buildings. In a newly developed technology, electricity is generated from the temperature gradient between building walls through a Seebeck effect. A 3D-printed triply periodic minimal surface (TPMS) structure is sandwiched in copper electrodes with copper (I) sulphate (Cu2SO4) electrolyte to mimic a thermogalvanic cell. Previous studies mainly concentrated on mechanical properties and the electric power generation ability of these structures; however, the goal of this study is to estimate the thermal resistance of the 3D-printed TPMS experimentally. This investigation elucidates their thermal resistances which in turn helps to appreciate the power output associated in the thermogalvanic structure. Schwarz P, Gyroid, IWP, and Split P geometries were considered for the experiment with electrolyte in the thermogalvanic brick. Among these TPMS structures, Split P was found more thermally resistive than the others with a thermal resistance of 0.012 m2 K W-1. The thermal resistances of Schwarz D and Gyroid structures were also assessed experimentally without electrolyte and the results are compared to numerical predictions in a previous Mater's thesis.Dissertation/ThesisMasters Thesis Mechanical Engineering 202
An Investigation into the Stiffness Response of Lattice Shapes under Various Loading Conditions
Get PDFabstract: One of the fundamental aspects of cellular material design is cell shape selection. Of particular interest is how this selection can be made in the context of a realistic three-dimensional structure. Towards this goal, this work studied the stiffness response of periodic and stochastic lattice structures for the loading conditions of bending, torsion and tension/compression using commercially available lattice design optimization software. The goal of this computational study was to examine the feasibility of developing a ranking order based on minimum compliance or maximum stiffness for enabling cell selection. A study of stochastic shapes with different seeds was also performed. Experimental compression testing was also performed to validate a sample space of the simulations. The findings of this study suggest that under certain circumstances, stochastic shapes have the potential to generate the highest stiffness-to-weight ratio in the test environments considered.Dissertation/ThesisMasters Thesis Mechanical Engineering 201
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