Computing a flattest, undercut-free parting line for a convex polyhedron, with application to mold design

AbstractA parting line for a polyhedron is a closed curve on its surface, which identifies the two halves of the polyhedron for which mold-boxes must be made. A parting line is undercut-free if the two halves that it generates do not contain facets that obstruct the de-molding of the polyhedron. Computing an undercut-free parting line that is as “flat” as possible is an important problem in mold design. In this paper, algorithms are presented to compute such a parting line for a convex polyhedron, based on different flatness criteria

Synthesis, structural elucidation and antimicrobial effectiveness of coordination entities of cobalt (II) and nickel (II) derived from 9,17-diaza-2,6,11,15-tetrathia-1,7,10,16-(1,2)-tetrabenzenacyclooctadecaphan-8,17-diene

9,17-Diaza-2,6,11,15-tetrathia-1,7,10,16-(1,2)-tetrabenzenacyclooctadecaphan-8,17-diene, macrocycle was synthesized, thereafter formulation and designing strategies applied for the preparation of coordination entities of Co(II) and Ni(II). Coordination behaviour of N2S4 donor macrocycle towards metal ion(s) was assessed by physiochemical measurements and spectral investigations viz. elemental analysis, molar conductance, magnetic susceptibility measurements, infrared, UV-Vis, 1H and 13 C NMR, mass spectroscopy, electron paramagnetic resonance (EPR), cyclic voltammetry and molecular modeling. Side-by-side comparison of the spectral findings exposed different geometrical aspects of macrocycle and coordination entities. Cyclic voltammogram showed fully oxidized and reduced species in one unified experiment. Macrocycle and coordination entities were screened for antimicrobial effectiveness (antifungal properties against Aspergillus-niger)

Impact and Implication of Thermal Conditioning on the Mechanical behavior of FRP Composites

Fiber reinforced composites are used extensively on a very large scale. They are subject to change in temperature and loading conditions constantly. In the experimental study, we have tried to assess the impact of temperature and conditioning time on the mechanical behaviour of glass fiber reinforced composites. Interface is the most significant part of composite structure which regulates the load transfer from matrix to fiber. Its strength is measured in terms of ILSS (Inter Laminar Shear Strength). Short beam shear tests are done at ambient and 60⁰C for conditioning times 30 minutes, 1 hour and 3 hours .The results show that at high temperature, there is initial increase in the strength of interface up to 30 minutes followed by weakening as conditioning time increases to 1 hour. This again is followed by strengthening of the interface as conditioning time extends to 3 hours. Understanding the effect of conditioning time might help us in optimization of the mechanical properties. Composite material may contain randomly spaced microvoids, incipient damage sites and microcracks with statistically distributed sizes and directions. Therefore, the local strength in the material varies in a random fashion. The failure location as well as degree of damage induced in the material will also vary in an unpredictable mode. The fractured surfaces are photographed by SEM analysis and studied. As temperature increases, the mode of failure approaches matrix cracking, fiber breakage and debonding. Each test is carried out at six different crosshead speeds, 5mm /min, 10mm/min, 50mm/min, 100mm/min, 200mm/min, and 500mm/min. ILSS decreases as crosshead speed is increased. FTIR analysis of composite specimens was carried out to interpret the reaction between matrix and fiber at the interface. DSC analysis was done to understand the deflection of glass transition temperature with the change in temperature and conditioning time. There are a lot of conflicts over this subject and this study has tried to highlight the major factors which need to be focussed upon for further improvement in the field of composites

Algorithms for generating multi-stage molding plans for articulated assemblies

Plastic products such as toys with articulated arms, legs, and heads are traditionally produced by first molding individual components separately, and then assembling them together. A recent alternative, referred to as in-mold assembly process, performs molding and assembly steps concurrently inside the mold itself. The most common technique of performing in-mold assembly is through multi-stage molding, in which the various components of an assembly are injected in a sequence of molding stages to produce the final assembly. Multi-stage molding produces better-quality articulated products at a lower cost. It however, gives rise to new mold design challenges that are absent from traditional molding. We need to develop a molding plan that determines the mold design parameters and sequence of molding stages. There are currently no software tools available to generate molding plans. It is difficult to perform the planning manually because it involves evaluating large number of combinations and solving complex geometric reasoning problems. This dissertation investigates the problem of generating multi-stage molding plans for articulated assemblies. The multi-stage molding process is studied and the underlying governing principles and constraints are identified. A hybrid planning framework that combines elements from generative and variant techniques is developed. A molding plan representation is developed to build a library of feasible molding plans for basic joints. These molding plans for individual joints are reused to generate plans for new assemblies. As part of this overall planning framework, we need to solve the following geometric subproblems -- finding assembly configuration that is both feasible and optimal, finding mold-piece regions, and constructing an optimal shutoff surface. Algorithms to solve these subproblems are developed and characterized. This dissertation makes the following contributions. The representation for molding plans provides a common platform for sharing feasible and efficient molding plans for joints. It investigates the multi-stage mold design problem from the planning perspective. The new hybrid planning framework and geometric reasoning algorithms will increase the level of automation and reduce chances of design mistakes. This will in turn reduce the cost and lead-time associated with the deployment of multi-stage molding process

Minimum accommodation for aerobrake assembly, phase 2

A multi-element study was done to assess the practicality of a Space Station Freedom-based aerobrake system for the Space Exploration Initiative. The study was organized into six parts related to structure, aerodynamics, robotics and assembly, thermal protection system, inspection, and verification, all tied together by an integration study. The integration activity managed the broad issues related to meeting mission requirements. This report is a summary of the issues addressed by the integration team

CASTonCAST: Superficies arquitectónicas complejas a partir de componentes prefabricados apilables

[EN] This article introduces the CASTonCAST system for the design and production of architectural freeform shapes from precast stackable components. This system is composed of two complementary parts: a novel manufacturing technique of precast stackable building components and a new geometric method for the design of freeform shapes by means of stackable solid tiles. This paper describes both parts of the system by means of physical prototypes and geometric studies. Guardar / Salir Siguiente >[ES] Este artículo presenta el sistema CASTonCAST para el diseño y la producción de superficies arquitectónicas complejas a partir de componentes prefabricados apilables. Este sistema está compuesto por dos partes complementarias: una innovadora técnica de fabricación de componentes prefabricados apilables y un nuevo método geométrico para el diseño de superficies complejas a partir de baldosas sólidas apilables. Este trabajo describe las dos partes del sistema mediante prototipos físicos y estudios geométricosWe would like to give special thanks to the LafargeHolcim Foundation for Sustainable Construction for supporting this project with two international awards: 1st Europe Next Generation award 2011 and 3rd Holcim Innovation award 2012. Furthermore, we would like to thank the Architectural Association School of Architecture and in particular our tutors Yusuke Obuchi and Robert Stuart-Smith for their encouragement and support during this research. Finally, we would like to thank Rafel Jaume Deyà for his helpful advice on the geometric method.Enrique, L.; Cepaitis, P.; Ordoñez, D.; Piles, C. (2016). CASTonCAST: Architectural freeform shapes from precast stackable components. VLC arquitectura. Research Journal. 3(1):85-102. doi:10.4995/vlc.2016.4291.SWORD8510231De Larrard, F. Why rheology matters. Concrete International, 1999, 21(8).Khoshnevis, B., Hwang, D., Yao, K. T., & Yeh, Z. (2006). Mega-scale fabrication by Contour Crafting. International Journal of Industrial and Systems Engineering, 1(3), 301. doi:10.1504/ijise.2006.009791Lasemi, A., Xue, D., & Gu, P. (2010). Recent development in CNC machining of freeform surfaces: A state-of-the-art review. Computer-Aided Design, 42(7), 641-654. doi:10.1016/j.cad.2010.04.002Liu, Y., Pottmann, H., Wallner, J., Yang, Y.-L., & Wang, W. (2006). Geometric modeling with conical meshes and developable surfaces. ACM Transactions on Graphics, 25(3), 681. doi:10.1145/1141911.1141941Lim, S., et al. Fabricating construction components using layer manufacturing technology. Global Innovation in Construction Conference, Loughborough University, Leicestershire, September 2009.Lloret, E., et al. Complex concrete structures: Merging existing techniques with digital fabrication. Computer-Aided Design, 2014.Podolny, W. and Muller, J.M., Construction and Design of Pre-stressed Concrete Segmental Bridges. New York: John Wiley & Sons, 1982.Pottmann, H., Schiftner, A., Bo, P., Schmiedhofer, H., Wang, W., Baldassini, N., & Wallner, J. (2008). Freeform surfaces from single curved panels. ACM Transactions on Graphics, 27(3), 1. doi:10.1145/1360612.1360675Pottmann, H., Liu, Y., Wallner, J., Bobenko, A., & Wang, W. (2007). Geometry of multi-layer freeform structures for architecture. ACM SIGGRAPH 2007 papers on - SIGGRAPH ’07. doi:10.1145/1275808.1276458Pronk, A., Rooy, I.V. and Schinkel, P. Double-curved surfaces using a membrane mold. IASS Symposium 2009: Evolution and trends in design, analysis and construction of shell and spatial structures. Valencia, Sept. 2009.Schmieder, M. and Mehrtens, P. Cladding freeform surfaces with curved metal panels: a complete digital production chain. Advances in Architectural Geometry. Wien: Springer, 2012.Vaudeville, B., et al. How irregular geometry and industrial process come together: a case study of the "Fondation Louis Vuitton Pour la Création", Paris. Advances in Architectural Geometry. Wien: Springer, 2012

A New 2d Coordination Polymer Based on Zinc(Ii), 1,2,3-Benzenetricarboxylic Acid And 4,4ʹ-Bis(Imidazol-1-Ylmethyl)Biphenyl: Synthesis and Crystal Structure

The solvothermal reaction of zinc(II) nitrate with 1,2,3-benzenetricarboxylic acid (1,2,3-H3BTC) and 4,4ʹ-bis(imidazol-1-ylmethyl)biphenyl (BIBPh) produced a crystalline solid {[Zn3(BIBPh)3(BTC)2]∙H2O}n. The product has been structurally characterised and investigated by X-ray diffraction, IR and thermogravimetric methods. The polymer has a bidimentional structure and crystallizes in the P21/c space group of the monoclinic system with the following unit cell parameters: a= 14.8687(16), b= 36.915(4), c= 13.8378(16) (Å), β= 105.584(6)°. The asymmetric unit of the crystal structure contains three zinc(II) ions, three BIBPh ligands and two BTC3- monodentate ligands with all three deprotonated carboxylate groups that balance the overall charge. All zinc centers have similar coordination environment: each metal ion is four coordinated exhibiting a slightly distorted tetrahedral coordination, where two positions are occupied by oxygen atoms of the carboxylic acid and the other two by nitrogen atoms of imidazole subunits

Process–Structure–Properties in Polymer Additive Manufacturing

Additive manufacturing (AM) methods have grown and evolved rapidly in recent years. AM for polymers is an exciting field and has great potential in transformative and translational research in many fields, such as biomedical, aerospace, and even electronics. Current methods for polymer AM include material extrusion, material jetting, vat polymerisation, and powder bed fusion. With the promise of more applications, detailed understanding of AM—from the processability of the feedstock to the relationship between the process–structure–properties of AM parts—has become more critical. More research work is needed in material development to widen the choice of materials for polymer additive manufacturing. Modelling and simulations of the process will allow the prediction of microstructures and mechanical properties of the fabricated parts while complementing the understanding of the physical phenomena that occurs during the AM processes. In this book, state-of-the-art reviews and current research are collated, which focus on the process–structure–properties relationships in polymer additive manufacturing