Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

Active noise control (ANC) is achieved by introducing a cancelling "antinoise" wave through an appropriate array of secondary sources. These secondary sources are interconnected through an electronic system using a specific signal processing algorithm for the particular cancellation scheme. ANC has application to a wide variety of problems in manufacturing, industrial operations, and consumer products. The emphasis of this paper is on the practical aspects of ANC systems in terms of adaptive signal processing and digital signal processing (DSP) implementation for real-world applications. In this paper, the basic adaptive algorithm for ANC is developed and analyzed based on single-channel broad-band feedforward control. This algorithm is then modified for narrow-band feedforward and adaptive feedback control. In turn, these single-channel ANC algorithms are expanded to multiple-channel cases. Various online secondary-path modeling techniques and special adaptive algorithms, such as lattice, frequency-domain, subband, and recursive-least-squares, are also introduced. Applications of these techniques to actual problems are highlighted by several examples.

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Active noise control: a tutorial review

The problem of updating a structural model and its associated uncertainties by utilizing dynamic response data is addressed using a Bayesian statistical framework that can handle the inherent ill-conditioning and possible nonuniqueness in model updating applications. The objective is not only to give more accurate response predictions for prescribed dynamic loadings but also to provide a quantitative assessment of this accuracy. In the methodology presented, the updated (optimal) models within a chosen class of structural models are the most probable based on the structural data if all the models are equally plausible a priori. The prediction accuracy of the optimal structural models is given by also updating probability models for the prediction error. The precision of the parameter estimates of the optimal structural models, as well as the precision of the optimal prediction-error parameters, can be examined. A large-sample asymptotic expression is given for the updated predictive probability distribution of the uncertain structural response, which is a weighted average of the prediction probability distributions for each optimal model. This predictive distribution can be used to make model predictions despite possible nonuniqueness in the optimal models.

Updating Models and Their Uncertainties. I: Bayesian Statistical Framework

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test...

Metal Additive Manufacturing: A Review of Mechanical Properties

Past, present and future of nonlinear system identification in structural dynamics

/pdf/modal-analysis-theory-and-testing-1dak9eyuuo.pdf

Modal Analysis Theory and Testing

On the difference in material structure and fatigue properties of nylon specimens produced by injection molding and selective laser sintering

This paper describes and analyzes fracture toughness and crack propagation of selective laser molten (SLM) components made from Ti6Al4V powder particles The main goal of this research is to gain more insight in the fracture mechanisms of this relatively new material and to improve the static and dynamic behavior of cracked SLM-Ti components At first, the SLM process parameters are optimized until the relative material density equals 997% This is close to the relative density of vacuum arc remelted mill annealed standard oxygen titanium which is used as a reference for all experiments A distinctive difference in phase morphology and texture of the microstructure is noticed between the SLM and the reference titanium The fine acicular martensite phase of the SLM-Ti results in more brittle behavior and inferior fracture toughness On the other hand, the fine grained microstructure leads to a large number of grain boundaries acting as obstacle points for crack propagation Consequently, crack growth properties do not significantly differ between both Microstructural analysis of the crack growth and final failure areas on the fractured surfaces is performed to study the failure mechanisms in more detail

Analysis of Fracture Toughness and Crack Propagation of Ti6Al4V Produced by Selective Laser Melting

On the potential of tuned resonators to obtain low-frequency vibrational stop bands in periodic panels

Three types of multibody models are presented for the investigation of the internal dynamics of a drive train in a wind turbine. The first approach is limited to the analysis of torsional vibrations only. Then a rigid multibody model is presented with special focus on the representation of the bearings and gears in the drive train. The generic model implementation can be used for parallel as well as planetary gear stages with both helical and spur gears. Examples for different gear stages describe the use of the presented formulations. Furthermore, the influence of the helix angle and the flexibility of the bearings on the results of eigenmode calculations are discussed. The eigenmodes of a planetary stage are classified as rotational, translational or out-of-plane modes. Thirdly, the extension to a flexible multibody model is presented as a method to include directly the drive train components' flexibilities. Finally, a comparison of two different modelling techniques is discussed for a wind turbine's drive train with a helical parallel gear stage and two planetary gear stages. In addition, the response calculation for a torque input at the generator demonstrates which eigenmodes can be excited through this path. Copyright © 2005 John Wiley & Sons, Ltd.

https://lirias.kuleuven.be/bitstream/123456789/157841/1/04PP087.pdf

Paul Sas

Papers

Modal Analysis Theory and Testing

On the difference in material structure and fatigue properties of nylon specimens produced by injection molding and selective laser sintering

Analysis of Fracture Toughness and Crack Propagation of Ti6Al4V Produced by Selective Laser Melting

On the potential of tuned resonators to obtain low-frequency vibrational stop bands in periodic panels

Analysis of internal drive train dynamics in a wind turbine