A new finite element model was developed to predict the density distribution in an Alumix 321 powder metallurgy compact. The model can predict the density distribution results of single-action compaction from 100 to 500 MPa compaction pressure. The model can also determine the amount of springback experienced by a compact upon ejection from the die at 100 and 300 MPa compaction pressure. An optical densitometry method, along with the creation of a compaction curve, was used to experimentally predict density distributions found within compacts, and found results that were consistent with both literature and finite element simulation. Further powder characterization included testing apparent density and flow rate of the powder. A literature review was also conducted and the results of which have been organized by three categories (powder type, material model, and finite element code) for easy reference by future powder researchers.

Lattice structures are widely used in nowadays industries in combination with additive manufacturing technology to obtain components with a limited weight and tuneable mechanical properties. However, industries still find challenging a complete implementation of these metamaterials in the product development due to the complexity given by an accurate prediction of the mechanical and fatigue properties. To overcome this limitation, analytical and numerical techniques are developed, to help designers to achieve the desired performances. Finite Element simulations are a common tool utilized in this sense, where solid models can provide accurate results. Nevertheless, the implementation of this technique requires high computational costs, often not compatible with an iterative design process where versions of the component are constantly updated considering the feedback provided by actors having different backgrounds and product interactions. Accurate and computationally efficient simulations strategies are thus required. The proposed thesis investigates three possible simulations ideas able to describe the mechanical properties of the lattice-based components. Two main properties are studied: the lattice structure elastic behaviour, which is important to determine the in-service behaviour of the designed component and the fatigue resistance, which defines the component service duration. Homogenization technique is the first numerical method analysed and it is pivoted on the idea of substituting the intricate lattice geometries with a solid fictitious material displaying the same elastic properties. In this framework, a case study is analysed, where the design process of a total hip replacement prosthetic device is developed. The workflow starts with a preliminary experimental campaign on lattice specimens with the aim of determining the printing quality, the mechanical properties, and the biological characteristics. In this phase, a verification of the homogenization predictions is performed. On this base, the best specimens’ configurations are selected to design and manufacture the prosthetic device. The second simulation technique leverages on the observation of the onedimensional nature of the strut-based lattice structures. Lattice structures’ behaviour can thus be simulated through the usage of truss and beam elements, depending on the stretching or bending dominated nature of the lattice topologies. Based on this observation, two different paths are followed, the first one aiming to improve the fatigue life of lattice components by acting of their orientation in the printing chamber. It is known that printing orientation influences the surface quality of the components and, in lattice struts this effect can be directly linked to a variation in the fatigue life. An optimization algorithm is thus developed, aiming to optimize the fatigue resistance of the manufactured components. Following this idea, a control and an optimized lattice batch are printed and an improvement in the fatigue resistance is found, even if not as large as expected by the simulations. Improvements in the predictions can be observed if the as-build geometry of the struts is considered. The second path is devoted to the computation of the corrective coefficients able to properly describe the elastic properties of bending dominated lattice structures. One-dimensional simulations are normally too severe for bending dominated lattice topologies, and a compensation has to be provided to match the elastic properties calculated trough computational efficient beam models and lattice ones. To address this problem, an optimization routine is developed, where the compensation factors are computed comparing the elastic properties of the beam models and a homogenised solid model taken as reference. A benchmark testing between the beam model, - built with the so computed compensation coefficients - a homogenised, and a solid model is developed. Compensated beam models are found to be able to improve the predictions of lattice structures elastic properties if compared to the homogenization techniques, showing a comparable computational time. Nevertheless, a reduced accuracy is found in presence of dense lattice structures, where the hypothesis of one-dimensional is weaker. The third analysed simulation method aims to obtain a precise fatigue life estimation at the expense of computational time. Starting from an as-build geometry reconstructed trough CT-scan analysis, a finite element simulation built with solid elements is performed. To reduce the computational cost, an innovative finite element theory is adopted, the Finite Cell Method. A two-step simulation is performed, and thanks to the usage of the average strain energy density method, the fatigue life estimation can be obtained. An excellent agreement is found; however, a complete validation is required for this method before its safe implementation in the design process.

Die surface shape may improve the flow of materials, reduce stress concentration of the products, and decrease the processing load to extend the life of die. The objective of this paper is to show that how to design the die surface shape of T-shape protrusion hydroforming with different diameters. A finite element code DEFORM 3D is used to simulate the process of THF, including adaptive simulation to predict the internal pressurization in the tube, and utilize flow net distribution to predict the axial feeding stroke and counter punch (CP) movement. After the amendment to the loading path, the flowability and appearance of the product quality will achieve the best results. Experiments of T-shape warm hydroforming of magnesium alloy AZ61 tubes are. The forming temperature is set as 250¢J. The simulated loading paths are used. From the comparisons of product shape, thickness distribution between analytical and experimental values, the validity of this analytical model is verified.. Keywords: Tube hydroforming, Finite element simulation, Die surface design.

Magnesium alloy tubes have good formability at elevated temperatures. In this study, a finite element code DEFORM 3D is used to simulate the result of T-shape hydroforming at working temperatures 150¢J and 250¢J with magnesium alloy AZ61 tubes and then conducts the hydroforming experiments. By modifying the loading paths, products with uniform thickness and branch height are obtained 49mm. The results of simulation are compared with the experimental results to verify the validity of this modeling. On the other hand, the effects of the die fillet radius on tube formability during y-shape hydroforming are discussed. With the right die fillet radius r1¡×10mm and the left die fillet radius r2¡×30mm, a better formability of the tube is obtained.

abstract: Ordered buckling of stiff films on elastomeric substrates has many applications in the field of stretchable electronics. Mechanics plays a very important role in such systems. A full three dimensional finite element analysis studying the pattern of wrinkles formed on a stiff film bonded to a compliant substrate under the action of a compressive force has been widely studied. For thin films, this wrinkling pattern is usually sinusoidal, and for wide films the pattern depends on loading conditions. The present study establishes a relationship between the effect of the load applied at an angle to the stiff film. A systematic experimental and analytical study of these systems has been presented in the present study. The study is performed for two different loading conditions, one with the compressive force applied parallel to the film and the other with an angle included between the application of the force and the alignment of the stiff film. A geometric model closely resembling the experimental specimen studied is created and a three dimensional finite element analysis is carried out using ABAQUS (Version 6.7). The objective of the finite element simulations is to validate the results of the experimental study to be corresponding to the minimum total energy of the system. It also helps to establish a relation between the parameters of the buckling profile and the parameters (elastic and dimensional parameters) of the system. Two methods of non-linear analysis namely, the Newton-Raphson method and Arc-Length method are used. It is found that the Arc-Length method is the most cost effective in terms of total simulation time for large models (higher number of elements).The convergence of the results is affected by a variety of factors like the dimensional parameters of the substrate, mesh density of the model, length of the substrate and the film, the angle included. For narrow silicon films the buckling profile is observed to be sinusoidal and perpendicular to the direction of the silicon film. As the angle increases in wider stiff films the buckling profile is seen to transit from being perpendicular to the direction of the film to being perpendicular to the direction of the application of the pre-stress. This study improves and expands the application of the stiff film buckling to an angled loading condition. / Dissertation/Thesis / M.S. Mechanical Engineering 2010

No description available.

Transmissibility is the most common metric used for isolator characterization. However, engineers are becoming increasingly concerned about energy transmission through an isolator at high frequencies and how the compliance of the machine and foundation factor into the performance. In this study, the transfer matrix approach for isolator characterization is first reviewed. Two methods are detailed for determining the transfer matrix of an isolator using finite element simulation. This is accomplished by determining either the mobility or impedance matrix for the isolator and then converting to a transfer matrix. One of the more useful metrics to characterize the high frequency performance of an isolator is insertion loss. Insertion loss is defined as the difference in transmitted vibration in decibels between the unisolated and isolated cases. Insertion loss takes into account the compliance on the source and receiver sides. Accordingly, it has some advantages over transmissibility which is a function of the damping and mounted resonant frequency. A static analysis is to preload the isolator so that stress stiffening is accounted for. This is followed by modal and forced response analyses to identify the transfer matrix of the isolator. In this paper, the insertion loss of spring isolators is examined as a function of several geometric parameters including the spring diameter, wire diameter, number of active coils, and height. Results demonstrate how modifications to these parameters affect the insertion loss and the first surge frequency.

Nowadays, physical inactivity has become a global problem. According to the research, about 5.3 million deaths all over the world in 2008 could be attributed to inactivity [1]. However, it is enough to do a little exercise every day to reduce the risk of premature deaths by as much as 30 percent. Due to the increasing working pressure, people do not have enough time to go to gym and do exercises, which means that the design of multi-functional fitness chair is necessary so that people can do exercise at home at any time.There have already been many similar household fitness products in the market, but most of them take up large space and the training part is very simple. In comparison, the multi-function fitness chair designed in this thesis combines several fitness equipment together in one chair, so it would save a lot of space, and yet provides possibility to perform versatile exercise.The product was designed in Autodesk Inventor 2015, and finite element analysis was performed in Inventor 2015 and for checking the strength and safety of the design.

The current design code governing bridge structure resistance to vessel impact loads in the U.S. is the American Association of State Highway and Transportation Officials' (AASHTO) Guide Specification and Commentary for Vessel Collision Design of Highway Bridges. The code stipulated method, based on Meir-Dornberg's equivalent static load method, is usually not warranted because of insufficient data on the impact load histories and wide scatter of the impact force values. The AASHTO load equations ignore certain fundamental factors that affect the determination of impact forces and bridge dynamic responses. Some examples of factors that are omitted during standard impact force analysis are: impact duration, pier geometry, barge-barge and barge-pier interactions, and structural characteristics of bridges. The purpose of this research is to develop new methods and models for predicting barge impact forces on piers. In order to generate research information and produce more realistic flotilla impact data, extensive finite element simulations are conducted. A set of regression formulas to calculate the impact force and time duration are derived from the simulation results. Also, a parametric study is performed systematically to reveal the dynamic features of barge-bridge collisions. A method to determine the quasi upper bound of the average impact force under any given scenarios is preposed. Based on the upper bounds of the average impact forces, an impact spectrum procedure to determine the dynamic response of piers is developed. These analytical techniques transform the complex dynamics of barge-pier impact into simple problems that can be solved through hand calculations or design charts. Furthermore, the dependency of the impact forces on barge-barge and barge-pier interactions are discussed in detail. An elastoplastic model for the analysis of multi-barge flotillas impacting on bridge piers is presented. The barge flotilla impact model generates impact force time-histories for various simulation cases in a matter of minutes. The results from the proposed model are compatible with the respective impact time-histories produced by an exhuaustive finite element simulation. All of the proposed methods and loading functions in this study are illustrated through design examples. Accordingly, the research results may help engineers to enhance bridge resistance to barge impacts and also lead to economic savings in bridge protection design.

The walker is regarded as a promising solution to provide additional support to maintain balance or stability while walking for elderly people. Significant assistance in improving mobility technology have been observed from literature review. However, the walkers available in the market is possible to optimize in design and include additional functionality, including getting out of the seat at home with caregiver aid, emergency care aided system. Considering falling down is a public healthcare problem, we designed the emergency aided system to rescue them [1].   In this paper, we proposed a multiple function elderly mobility and emergency aid system, was developed and modelled by Inventor 2015, and finite element analysis. Simulation was then created to get the value of safety factor, and make comparison base on the results from structural calculation. Finally, the application of few features of the improved walker was illustrated.