Browsing by Subject "Additive manufacturing"

Now showing 1 - 4 of 4

Open Access
An analytical approach to the design of multiple mode rectangular cavity waveguide filters
(Institute of Electrical and Electronics Engineers Inc., 2017) Kelleci, C.; Atalar, Abdullah
The multiple mode rectangular cavity structure with square corner cuts is revisited. An attempt to predict the physical dimensions of the cavity for dual mode second-order and triple mode third-order filters is made. Analytic expressions are formed to be used in the design process. The classical triple mode cavity filter structure is altered to give a finite frequency transmission zero either in the lower or upper sideband of the center frequency. The concept is illustrated with example designs. A novel additive manufacturing technique is used to fabricate a selected filter structure. The experimental results are in agreement with the expectations.
Open Access
Computational homogenization of fatigue in additively manufactured microlattice structures
(Springer, 2023-02) Mozafari, Farzin; Temizer, İlker
A novel computational approach to predicting fatigue crack initiation life in additively manufactured microlattice structures is proposed based on a recently developed microplasticity-based constitutive theory. The key idea is to use the concept of (micro)plastic dissipation as the driving factor to model fatigue degradation in additively manufactured metallic microlattice. An ad-hoc curve-fitting procedure is proposed to calibrate the introduced material constitutive parameters efficiently. The well-calibrated model is employed to obtain fatigue life predictions for microlattices through a diverse set of RVE-based finite element fatigue simulations. The model’s predictive capabilities are verified by comparing the simulation results with experimental fatigue data reported in the literature. The overall approach constitutes a unified setting for fatigue life prediction of additively manufactured microlattice structures ranging from low- to high-cycle regimes. It is also shown that the model can be applied to technologically relevant microlattices with mathematically-created complex microstructure topologies.
Open Access
Process modeling for projection based stereo lithography
(2015-08) Zulfiqar, Ali
Stereo lithography is a widely used additive manufacturing process, where a three dimensional object is fabricated directly from a solid computer model. This thesis develops a projection type SLA (PSLA) test bed using a digital micro mirror device. The goal is to improve the dimensional accuracy and surface quality of the polymer parts through detailed process modeling and gain predictive ability about the duration of the printing process. For that purpose; (i) process parameters of the PSLA system have been analyzed, (ii) material properties of different polymers have been identiffed through experimental techniques, and a curing process model has been established, and (iii) some case studies have been conducted. The information deduced from the system is used to set the continuous movement speed of the vertical axis to obtain "layerless printing" of parts where the surface quality is signiffcantly improved compared to conventional layer-by-layer printing. The results show that the process planning approach used in this thesis can produce highly accurate parts. Experiments on more challenging part designs such as high aspect ratio and micro scale parts have also been conducted, and limits of the three dimensional printing system have been determined.
Open Access
The universality of self-organisation: a path to an atom printer?
(Springer Science and Business Media Deutschland GmbH, 2023-04-07) Ilday, S.; Ilday, F. Ömer
More than 30 years ago, Donald Eigler and Erhard Schweizer spelt the letters IBM by positioning 35 individual xenon atoms at 4 K temperature using a scanning tunnelling microscope. The arrangement took approximately 22 h. This was an outstanding demonstration of control over individual atoms. Since then, 3D printers developed into a near-ubiquitous technology. Nevertheless, with typical resolutions in the micrometres, they are far from the atomic scale of control that the IBM demonstration seemed to herald. Even the highest resolution achieved with ultrafast lasers driving two-photon polymerisation barely reaches 100 nm, three orders of magnitude distant from the atomic scale. Here, we adopt a long-term view when we ask about the possibility of a 3D atom printer, which can build an arbitrarily shaped object of macroscopic dimensions with control over its atomic structure at room temperature and within a reasonable amount of time. After discussing the state-of-the-art technology based on direct laser writing, we identify three fundamental challenges to overcome. The first is the fat fingers problem, which refers to laser wavelengths being much larger than the size of the atoms. The second one is complexity explosion, namely, the number of processing step scales with the inverse cube of the resolution, leading to prohibitively long processing times. The third challenge is the increasing strength of random fluctuations as the size of the smallest volume element to be printed approaches the atomic scale. This requires control over the fluctuations, which we call mischief of fluctuations. Although direct-writing techniques offer sufficient resolution, speed, and excellent flexibility for the mesoscopic scale, each of the three fundamental problems above appears enough to render the atomic scale unreachable. Each of these arise out of a need to control each atom individually and with precision. In contrast, the three challenges of direct writing are not fundamental limitations to self-organisation, this chapter proposes a potential path to a 3D atom printer, where laser-driven self-organisation can complement direct-writing techniques by bridging the atomic and mesoscopic scales.