Static and dynamic performance of Ti foams

Titanium (Ti) foams of different densities 1622-4100 Kgm-3 made by a powder sintering technique were studied as to their structural and mechanical properties. The foams were tested under static and dynamic loading. The material was tested quasi statically and dynamically under strain rates in the range of 0.001-2500 s-1 and under different loading modes. It was found that strain rate sensitivity is more pronounced in lower density foams. Experiments were complimented by virtual testing. Based on the Voronoi tessellations a computational method was developed to generate stochastic foam geometries. Statistical control was applied to produce geometries with the microstructural characteristics of the tested material. The generated structures were numerically tested under different loading modes and strain rates. Voronoi polyhedrals were used to form the porosity network of the open cell foams. The virtually generated foams replicated the geometrical features of the experimentally tested material. Meshes for finite element simulations were produced. Existing material models were used for the parent material behaviour (sintered Ti) and calibrated to experiments. The virtual foam geometries of different densities were numerically tested quasi statically under uniaxial, biaxial and triaxial loading modes in order to investigate their macroscopic behaviour. Dynamic loading was also applied for compression. Strain rate sensitive and insensitive models were used for the parent material model in order to examine the influence of geometry and material strain rate sensitivity under high rates of deformation. It was found that inertial effects can enhance the strain rate sensitivity for low density foams and numerical predictions for the generated foam geometries were in very good agreement with experimental results. Power laws were established in scaling material properties with density. The study includes: 1. Information on the material behaviour and data for macroscopically modelling this type of foams for a range of densities and under different strain rates. 2. A proposed method for virtually generating foam geometries at a microscopic scale and examine the effect of geometrical characteristics on the macroscopic behaviour of foams.</p

Dimensional considerations on the mechanical properties of 3D printed polymer parts

Additive manufacturing offers a useful and accessible tool for prototyping and manufacturing small volume functional parts. Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are amongst the most commonly used materials. Characterising 3D printed PLA and TPU is potentially important for both designing and finite element modelling of functional parts. This work explores the mechanical properties of additively manufactured PLA/TPU specimens with consideration to design parameters including size, and infill percentage. PLA/TPU specimens are 3D-printed in selected ISO standard geometries with 20%, 60%, 100% infill percentage. Tensile and compression test results suggest that traditional ISO testing standards might be insufficient in characterising 3D printed materials for finite element modelling or application purposes. Infill percentage in combination to design size, may significantly affect the mechanical performance of 3D printed parts. Dimensional variation may cause inhomogeneity in mechanical properties between large and small cross section areas of the same part. The effect was reduced in small cross section parts where reducing the nominal infill had less effect on the resulting specimens. The results suggest that for 3D printed functional parts with significant dimensional differences between sections, the material properties are not necessarily homogeneous. This consideration may be significant for designers using 3D printing for applications, which include mechanical loading

Introduction to industrial design and product case studies

This paper describes the practical elements included in the first term of a second-year engineering module which was developed in alignment with CDIO standards. The students were assigned into teams based on their course of study (i.e. electronics, biomedical, and sports engineering). Each team would be free to choose, research, and evaluate three products with some relevance to their field. Aspects such as technology, regulations and user reviews would have to be considered within the analysis. The scientific principles involved in the products would have to be explained in reasonable depth and aspects such as product end-of-life management (sustainability) also mentioned. Multiple sources would have to be used such as scientific articles, product specifications, regulations, and online reviews. The students would have to use available resources without necessarily having the actual physical product at hand. Once the teams had gained insight on the products they would have to either choose one of the products to improve, or decide to design a new product, (relevant to their discipline). The teams would have to produce a report and a demonstrator of their designs by the end of term. The demonstrator would have to be a physical representation with some functionality that can effectively communicate the proposed concept. The students were expected to use the tools and experience gained during previous and prerequisite modules, for designing and prototyping. The report was also expected to contain references to the indicative reading. The module would be an opportunity to build upon previous knowledge obtained through both, core and specialized modules. Additionally, a research element was included both in terms of the students looking into the cutting-edge technologies of their subject but also in trying to push those boundaries. This study aims at describing the module rationale, and reflecting upon inclusivity, and pedagogical effectiveness

Generating 3D porous structures using machine learning and additive manufacturing

Complex structures, often found in nature, may be difficult to replicate or integrate with human-made designs. Generative machine learning may be a useful tool in extracting and transferring complex structure features. A generative adversarial network (GAN) was trained using x-ray microtomography images of porous and lattice structures. Three types of cellular materials were used. Two-dimensional images were generated by the generative network at two resolutions. A bag of features approach was used to sequence the generated images of porous structures. The combination of 2D GAN method and similarity based stacking resulted in 3D structures. The approach aimed at economising on computational cost whilst ensuring a degree of continuity through the structure. The original and generated open cell porous structure images were binarized and 3D surfaces were created using imaging tools. The surfaces were transformed into solid geometries, using computer aided design tools and exported for 3D printing. The compressive behaviour of the specimens was compared. The method generated qualitatively similar structures of consistent relative densities. However the relative density and compressive response of the generated structures diverged in relation to the reduction in resolution. The method shows promise for biomimicking, or generating hybrid natural-artificial structures, based on training sets

Modelling Stochastic Foam Geometries for FE Simulations Using 3D Voronoi Cells

A method for generating realistic foam geometries is developed for modelling the structure of stochastic foams. The method employs 3D Voronoi cells as pores. The virtual geometries are subjected to loading with the use of finite element methods and the results are compared to experimental data for open cell Titanium foams. The method applies statistical control to geometrical characteristics and it's used to either replicate or virtually generate prototype foam structures

Reverse engineering and introduction to engineering design

This paper describes practical elements during two terms of a first-year module within which CDIO standards are implemented. The aim of this practical module is for students to practice their fundamental knowledge and develop the required skills to complete projects that are structured according to industry standards. Several skills are involved in working within a professional engineering environment, beyond the strictly technical knowledge. The intention is to make the students also aware of these skills. During the first term of year one, the module includes a team-based reverse engineering project. Students are assigned to teams and given an appliance. They are expected to conceptually and physically deconstruct the device and analyze the relevant aspects of both of its parts and as a whole. Aspects would include scientific principles related to function, design considerations, the context of use, etc. The teams will then propose improvements on individual parts and the device as a whole, in terms of either function, price, manufacturing, or sustainability. The work is presented to the class and compiled into a group report. During the second term, the students are trained in design software (Autodesk Fusion 360 CAD, CAE, CAM), including basic finite element simulation, and are given two design tasks. The first is to use laser cutting to design a small wooden bridge based on certain specifications (e.g., dimensions, load-bearing), including some aesthetic elements, using limited resources (i.e., material allowance). The second is to design and optimize (in terms of mass) a support structure of certain dimensions and load-bearing capacity. The structures are then manufactured and assembled, i.e., laser-cut, and 3D printed correspondingly, weighted and tested for their load-bearing capacity. Assessment is based on a relevant portfolio. Throughout the two terms, lectures are delivered on project management and product development, as well as case studies by guest lecturers of various engineering fields. The module has been very well received with high student ratings in relevant surveys

Integrated cad and reverse engineering to enhance conception and design

his paper details the adoption of a methodology of integrating CAD with reverse engineering to enhance the conception and design skills of first year engineering students. The students are given an engineered device to reverse engineer via physical deconstruction and redesign via CAD as a group. The aim of administering this methodology is two-fold; firstly, to ensure students from various engineering backgrounds (Mechanical, Electronic, Biomedical and Sport Engineering) reverse engineer devices relevant to their discipline and specifically work on CAD models of these devices to enhance relatability. Secondly, to ensure students appreciate and adopt the underpinning practices involved in the design and conception of engineering devices. As opposed to dictating specifications, the redesign of the device is left at the discretion of the students to encourage a student-centred approach whereby the students take on an active role in the learning process. Additionally, designing and deconstructing the same device as part of a group ensures higher student engagement. This paper demonstrates the efficacy of the adopted approach by providing various examples of students’ Reverse Engineering/CAD outputs as well as assessment statistics. The paper also details the online support provided in addition to the on-site teaching to aid optimum learning in a blended learning environment

Static and dynamic performance of Ti foams

Titanium (Ti) foams of different densities 1622-4100 Kgm-3 made by a powder sintering technique were studied as to their structural and mechanical properties. The foams were tested under static and dynamic loading. The material was tested quasi statically and dynamically under strain rates in the range of 0.001-2500 s-1 and under different loading modes. It was found that strain rate sensitivity is more pronounced in lower density foams. Experiments were complimented by virtual testing. Based on the Voronoi tessellations a computational method was developed to generate stochastic foam geometries. Statistical control was applied to produce geometries with the microstructural characteristics of the tested material. The generated structures were numerically tested under different loading modes and strain rates. Voronoi polyhedrals were used to form the porosity network of the open cell foams. The virtually generated foams replicated the geometrical features of the experimentally tested material. Meshes for finite element simulations were produced. Existing material models were used for the parent material behaviour (sintered Ti) and calibrated to experiments. The virtual foam geometries of different densities were numerically tested quasi statically under uniaxial, biaxial and triaxial loading modes in order to investigate their macroscopic behaviour. Dynamic loading was also applied for compression. Strain rate sensitive and insensitive models were used for the parent material model in order to examine the influence of geometry and material strain rate sensitivity under high rates of deformation. It was found that inertial effects can enhance the strain rate sensitivity for low density foams and numerical predictions for the generated foam geometries were in very good agreement with experimental results. Power laws were established in scaling material properties with density. The study includes: 1. Information on the material behaviour and data for macroscopically modelling this type of foams for a range of densities and under different strain rates. 2. A proposed method for virtually generating foam geometries at a microscopic scale and examine the effect of geometrical characteristics on the macroscopic behaviour of foams.This thesis is not currently available in ORA

Rate Dependence of the Compressive Response of Ti Foams

Titanium foams of relative density ranging from 0.3 to 0.9 were produced by titanium powder sintering procedures and tested in uniaxial compression at strain rates ranging from 0.01 to 2,000 s−1. The material microstructure was examined by X-ray tomography and Scanning Electron Microscopy (SEM) observations. The foams investigated are strain rate sensitive, with both the yield stress and the strain hardening increasing with applied strain rate, and the strain rate sensitivity is more pronounced in foams of lower relative density. Finite element simulations were conducted modelling explicitly the material’s microstructure at the micron level, via a 3D Voronoi tessellation. Low and high strain rate simulations were conducted in order to predict the material’s compressive response, employing both rate-dependant and rate-independent constitutive models. Results from numerical analyses suggest that the primary source of rate sensitivity is represented by the intrinsic sensitivity of the foam’s parent material