CHALLENGES IN ENGINEERING DESIGN EDUCATION: VERTICAL AND LATERAL LEARNING
Alex Czekanski, Maher Al-Dojayli and Tom Lee
Abstract – Engineering practice and design in particular have gone through several changes during the last two decades whether due to scientific achievements including the evolution in novel engineering materials, computational advancements, globalization and economic constraints as well as the strategic needs which are the drive for innovative engineering. All these factors have impacted and shaped to certain extent the educational system in North America and Canada in particular. Currently, high percentage of the engineering graduates would require extensive training in industry to be able to conduct reliable complex engineering designs supported by scientific verification and validation, understand the complete design stages and phases, and identify the economic and cultural impact on such designs. This task, however, faces great challenges without educational support in such vastly changing economy.
Lots of attention has been devoted to engineering design education in the recent years to incorporate engineering design courses supported by team design projects and capstone projects. Nevertheless, the lack of integrated education system towards engineering design programs can undermine the benefits of such efforts. In this paper, observations and analysis of the challenges in engineering design are presented from both academic and industrial points of view. Furthermore, a proposed vertical and lateral engineering education program is discussed. This program is structured to cover every year of the engineering education curricula, which emphasizes on innovative thinking, design strategies, support from and integration with other technical engineering courses, the use of advanced analysis tools, team collaboration, management and leadership, multidisciplinary education and industrial involvement. Its courses have just commenced for freshmen engineering students at the newly launched Mechanical Engineering Department at the Lassonde School of Engineering, York University.
DESIGN OF KOLSKY BAR TO CHARACTERIZE THE DYNAMIC RESPONSE OF ELASTOMERS UNDER HIGH STRAIN RATE
M.S. Chaudhry, R. Carrick and A. Czekanski
Abstract The need for dynamic characterization of elastomers under high strain rate is increasing with the intensification of their use in a wide variety dynamic applications. The most common experiment used to study the dynamic behavior of materials in the strain rate regimes of 100/s – 1000/s is the Kolsky bar apparatus. There are no standard guidelines for the design and construction of a Kolsky bar apparatus and special considerations must be taken when it is to be used to characterize low strength materials such as elastomers. Design considerations such as uniform deformation, equilibrated stress, effect of axial and radial inertia are discussed. The correct selection of the specimen geometry is of vital importance in order to ensure stress equilibrium is reached. To determine the dimensions of the specimens and bars, a selection criterion has been discussed. Moreover, precise strain recording instruments are needed to capture the micro-level strains propagated through the bars. In this paper, the overall design requirements and guidelines of a Kolsky bar apparatus for soft materials are discussed. Finally a design for dynamic characterization of elastomers is presented based on the modifications needed for its use with soft materials.
FINITE ELEMENT MODELLING OF A MODIFIED KOLSKY BAR DEVELOPED FOR HIGH STRAIN RATE TESTING OF ELASTOMERS
Elastomers are finding a wide variety of dynamic applications in aerospace, automobile and biomedical industries. The response of these complex material is based on the loading conditions and the strain rate at which the loading is applied. To suit the designer’s requirement, there is an ever increasing need to characterize this application specific, dynamic behavior under high strain rates. The Kolsky bar apparatus, also known as the Split Hopkinson Bar, is the most common apparatus used to test engineering materials at strain rates between 100/s and 10000/s. In this paper a modified Kolsky bar to characterize soft material is numerically modeled using Finite Element Method. The focus of the study is to numerically analyze the modifications made to a conventional Kolsky bar to specifically test nonlinear hyperelastic, soft materials. The challenge for testing low strength materials is the impedance mismatch between the bar and specimen interfaces, which results in a very weak distorted signal. One of the solution is to use a hollow transmission bar instead of solid one. With the use of FEM it can be numerically verified that using a hollow bar increases the amplitude of the transmitted signal up to several times. It is known that the rise time of the elastic wave can be increased by using a copper pulse shaper. Different dimensions of pulse shaper are modeled and the effect on the incident pulse is analyzed. The main aim of this study is to provide a detailed numerical analysis on the testing parameters, and to model one way wave propagation in Kolsky bar experiment for hyperelastic materials. The constitutive equations used to model the parts of the apparatus are also discussed.
ON THE CONTINUUM MECHANICS APPROACH FOR THE ANALYSIS OF SINGLE WALLED CARBON NANOTUBES
M.S. Chaudhry, A. Czekanski
Abstract – Today carbon nanotubes have found various applications in structural, thermal and almost every field of engineering. Carbon nanotubes provide great strength, stiffness resilience properties. Evaluating the structural behavior of nanoscale materials is an important task. In order to understand the materialistic behavior of nanotubes, atomistic models provide a basis for continuum mechanics modelling. Although the properties of bulk materials are consistent with the size and depends mainly on the material but the properties when we are in Nano-range, continuously change with the size. Such models start from the modelling of interatomic interaction. Modelling and simulation has advantage of cost saving when compared with the experiments. So in this project our aim is to use a continuum mechanics model of carbon nanotubes from atomistic perspective and analyses some structural behaviors of nanotubes. It is generally recognized that mechanical properties of nanotubes are dependent upon their structural details. The properties of nanotubes vary with the varying with the interatomic distance, angular orientation, radius of the tube and many such parameters. Based on such models one can analyses the variation of young’s modulus, strength, deformation behavior, vibration behavior and thermal behavior. In this study some of the structural behaviors of the nanotubes are analyzed with the help of continuum mechanics models. Using the properties derived from the molecular mechanics model a Finite Element Analysis of carbon nanotubes is performed and results are verified. This study provides the insight on continuum mechanics modelling of nanotubes and hence the scope to study the effect of various parameters on some structural behavior of nanotubes.
AWARENESS OF SELF AND THE ENGINEERING FIELD: STUDENT MOTIVATION, ASSESSMENT OF ‘FIT’ AND PREPAREDNESS FOR ENGINEERING EDUCATION
Claudia Bennett, Minha R. Ha, Julian Bennett and Aleksander Czekanski
Abstract – Understanding factors that influence incoming students’ preparedness and success is critical in improving educational efficacy. Students’ prior experiences, assumptions, and habits influence their engagement in process of learning to become competent design engineers. A thematic analysis of students’ reasons for pursuing an engineering major revealed such decisions to be based on self-assessed personal fit. This paper indicates four common types of personal fit as described by students: matching skillsets, desirable activities, meaningful impact, and exploratory intrigue. From these, two key factors emerged: an awareness of self (ie. skills, interests, values) and an awareness of the engineering field (ie. nature of its work, its value to society, its value to the individual). These factors were influenced by: prior academic performance in core courses, authoritarian influence and the presence of engineers within their social networks. The paper also discusses incoming students’ perception of design engineering attributes as revealed in their survey responses. We argue that efforts are needed to provide students, before and during university, with opportunities to engage with career engineers or engineering exercises in order for them to be able to accurately establish an understanding of the engineering field, negotiate expected learning outcomes, master effective strategies to succeed, assess their strengths and limitations. The data are drawn from a larger study on student motivation and learning process in design engineering education.
BUILDING A MORE COMPLETE DESIGN EXPERIENCE: PHILOSOPHIES AND REFLECTIONS FROM A SECOND YEAR MECHANICAL ENGINEERING DESIGN PROJECT COURSE
Roger Carrick, Alex Czekanski, and Minha R. Ha
Abstract – For undergraduate engineering students, earlier exposure to and training in the design engineering process hold much value for an enriched experience and an in-depth understanding of engineering design. Simultaneously, students in their earlier years require more guidance and frequent feedback to inform their own expectations of learning objectives, as well as develop effective learning strategies. This paper focuses on the design and implementation of a second year Mechanical Engineering “Mini-Design Project” course, which had four main goals: (1) provide students with their first “complete” design experience, allowing them to take a project from problem to produced solution; (2) integrate knowledge and skills from other courses in the curriculum; (3) allow for the enhancement of under-represented CEAB graduate attributes, particularly design and teamwork; and (4) prepare students for high performance in their capstone projects. Several learning needs were addressed: Effective teamwork skills, effective project management, and systematic practice of engineering design with an emphasis on the process. Students were placed in teams of 4-5 and given a design problem with specified evaluation criteria, and strict restrictions on construction materials. Students were given milestones throughout the term that encouraged them to follow the design process, as well as build, test and evaluate their designs. Mechanisms for creating and supporting design teams are described, and students’ feedback and comments on these mechanism are discussed.
Finite Element Analysis of Pulseshaping Technique in Kolsky Compression Bar for Elastomers
S.chaudhry and A. Czekanski
Abstract: The modified design of a Kolsky bar to test elastomers, has been numerically modeled and analyzed. The main outcome of the study is to quantify the effect of using pulse shaping techniques and the misalignment in the bars. Alignment of the bars is a critical requirement of a valid Kolsky bar setup. The effect of non-parallel impacting faces of the bars and offset of the striker from the central axis on the incident pulse has been analyzed. Some basic alignment requirements for a valid Kolsky setup has been established. A comprehensive modelling methodology is presented to model the working components of the setup, including a copper pulse shaper. The incident is shaped due to plastic deformation taking place in the copper pulse shaper. This effect has been analyzed for the variation in pulse shaper geometry size and impacting velocities of the striker.
HIGH STRAIN RATE RESPONSE OF CARBON NANOTUBES BASED ELASTOMER COMPOSITES
S. Chaudhry and A. Czekanski
Abstract – Summary The article investigates the response of nanoparticle reinforced elastomer composites under dynamic impact. The preparation, characterization and testing methodology of polydimethylsiloxane based elastomers reinforced with multi walled carbon nanotubes is discussed in detail. Under quasi-static condition the presence of CNT network resulted in an enhanced stiffness. When subjected to high strain rates of compressive loading the presence of CNTs influenced the stress – strain curve characteristics (e.g. transition point from strain hardening to softening region) while greatly improving the energy storing capabilities. To test under high rates of strain, some necessary modification were also made to the dynamic testing apparatus (Kolsky bar/Split Hopkinson bar).
TOPOLOGY OPTIMIZATION USING BERNSTEIN BASIS POLYNOMIALS
Andrew Lambe and Aleksander Czekanski
Abstract – Summary A new method for density-based topology optimization is presented in which the density field is parametrized using Bernstein polynomial basis functions on a finite-element mesh. This parametrization permits a continuous variation of the density between mesh elements to suppress checkerboards without a filter. In addition, rather than refining the design variable mesh, the material boundary is more accurately captured by elevating the order of the basis functions. Standard meshing techniques may be used to define the design variable mesh, even with complex domain shapes, and different meshes may be used to define the design variables and the finite element analysis. Results are presented for two structural topology design problems.
EFFECT OF THE SURFACE ON HYPERELASTIC PROPERTIES OF MATERIALS AT SMALLER SCALES
Taisiya Sigaeva and Aleksander Czekanski
Summary In this work, well-known continuum models in the framework of hyperelasticity are generalized for certain applications where the scale of the problem decreases to nano-level. At this length scale, the surface and residual surface stresses have a critical effect on the overall deformation of the bulk material. The proposed models employ the Gurtin-Murdoch theory to represent the surface effect as a residually prestressed thin hyperelastic film of separate elasticity, perfectly bonded to the bulk. Obtained results demonstrate remarkable changes in the effective mechanical properties of materials at smaller scales that are not captured by classical theories.
EFFECT OF FDM PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF THERMOPLASTIC ELASTOMER SUBJECT TO HIGH-STRAIN RATES
M.S. Chaudhry and A. Czekanski
Abstract – 3D printed products have been used extensively in product development cycle to test kinematic functionality and design verification. Now, aerospace  and medical   industries are exploiting the advantages offered by additive manufacturing as it outgrows its roots of rapid prototyping. Fused deposition modeling (by Stratasys Inc.) is a process of 3D printing in which a thermoplastic material is extruded in layers to create a three dimensional object. The finished 3D part takes the form of a vertically stacked laminated composite with a network of fibers and voids. FDM process produces parts with unique characteristics. Moreover, overall quality and performance of a 3D printed part is also affected by the build parameters such as printing direction, percentage amount of infill and resolution (layer height); recently huge amounts of attention have been paid to analyzing and characterizing their effects  . A similar study done by Sood et al.  investigated the influence of layer thickness, raster angles, infill width and air voids on the bonding and distortion within the 3D printed part and its meso-structural configuration. Further they investigated the effect of these parameters on the compressive strength of the specimens and analyzed the importance of fiber-to-fiber bonding . Compressive strength is also shown to be affected by the anisotropic behavior due to build direction, showing a reduced strength in transverse direction as compared to axial .
ON THE EFFECTIVE PROPERTIES OF 3D METAMATERIALS
M. Abdelhamid and A. Czekanski
We developed a continuum-based model for the octet-truss unit cell in order to describe the effective mechanical properties (elastic modulus) of the lattice structure. This model is to include different geometric parameters that impact the structural effects; these parameters are: lattice angle, thickness to diameter ratio, diameter to length ratio, ellipticity, and loading direction. All these geometric parameters are included in the stiffness matrix, and the impact of each parameter on the stiffness tensor is investigated. Furthermore, the Gurtin-Murdoch model of surface elasticity is used to include the size effect in the stiffness tensor, as well as anisotropy of this model is investigated.
PERFORMANCE OF 3-D PRINTED THERMOPLASTIC POLYURETHANE UNDER QUASI-STATIC AND HIGH-STRAIN RATE LOADING
S. Chaudhry, M. Al-Dojayli and A. czekanski
As 3-D printed materials are being embraced by the manufacturing industries, understanding the response mechanism to high strain rate events becomes a concern to meet requirements for a specific application. In order to improve the mechanical performance of a 3-D printed part, it is necessary to quantify the impact of various printing parameters on the mechanical properties. Initial studies have shown that a difference in 3-D printed material is expected due to the effect of manufacturing parameters such as anisotropy relating to printing direction, infill pattern, infill percentage, layer height and orientation of the part being printed. The main focus of the study is to characterize the effect of the previously mentioned printing parameters under quasi-static and high strain rate (100 – 1000 /s). In this strain rate regime, the most common apparatus used is the Split Hopkinson pressure bar (also known as Kolsky bar). It consists of a cylindrical metallic bar that has a striker, input and output bar. While the specimen is fixated between the input and output bar, the striker bar is accelerated and triggers the incident bar. As a result, an elastic wave is generated which travels towards the specimen/input bar interface, where some part of it is reflected and the rest is transmitted. The Kolsky bar is adjusted by using a hollow transmitter tube and pulse shaper. Due to an impedance mismatch between the samples and bar material, the amplitude of the transmitted pulse is low. Using a hollow transmitter bar increases this amplitude due to area mismatch between the specimen and tube. Using a pulse shaper between the striker and input bar, the rise time of the elastic compressive wave increases and assists in achieving a constant rate of loading. The compressive stress strain curves were obtained under high strain rates to determine the strain rate effect. To measure the response under static testing conditions, a commercial load frame was used. A comprehensive comparison of dynamic compressive response of samples was performed to characterize the effect of printing parameters.
ADAPTIVE TOPOLOGY OPTIMIZATION USING A CONTINUOUS APPROXIMATION OF MATERIAL DISTRIBUTION
A. Lambe and A. Czekanski
Structural topology optimization seeks to distribute material in a design domain to produce the stiffest structure for a given mass or the lightest structure for a given strength. In the density-based approach to topology optimization, the design domain is divided into small elements and an optimization algorithm determines whether each element in the optimal design contains solid material or void. Solutions obtained using this method may suffer from a variety of issues, such as a checkerboard pattern of solid and void elements, large transition regions between solid and void parts of the structure, and dependence of the final solution on the initial mesh. Typically, these issues are mitigated using filters, projection functions, or a combination of the two. However, applying these techniques requires the user to select a few parameter values and the optimal design strongly depends on the selected parameters. This work presents an alternative approach to addressing the aforementioned issues in density-based topology optimization. Rather than assigning a separate design variable to each element in the domain, a continuous approximation of the density field is used. This field is interpolated using finite element shape functions with the scaling coefficients of these shape functions acting as design variables in the optimization problem. Although this technique is known to produce an optimal design that is free of checkerboard patterns, it leads to a large transition region at the boundary of the structure whose size depends on the size of the finite elements used. To systematically reduce the size of this transition region, the finite element mesh is locally refined near the structural boundary and the design is optimized again. Because the mesh implicitly controls the size of the transition region, local refinement and optimization continue until the smallest cells in the mesh reach an acceptable resolution. A local refinement indicator is developed to identify and refine cells lying in the transition region. Local isotropic mesh refinement is used to maintain reasonable cell sizes over most of the design domain and, consequently, keep the computational cost of both the finite element analysis and the optimization down. Anisotropic mesh refinement may also be used with a suitable indicator, though it is not demonstrated here.