Verification of structural simulation results of metal-based additive manufacturing by means of neutron diffraction

AbstractMetal-based additive processes are characterized by numerous transient physical effects, which exhibit an adverse influence on the production result. Hence, various research approaches for the optimization of e. g. the structural part behavior exist for layered manufacturing. Increasingly, these approaches are based on the finite element analysis to be able to understand the complexity. Hereby it should be considered that the significance of the calculation results depends on the quality of modeling the process in the simulation environment. Based on a selected specimen, the current work demonstrates in which way the numerical accuracy of the residual stress state can be analyzed by utilizing the neutron diffraction. Thereby, different process parameter settings were examined

Experimental and Numerical Study of Low-Velocity Impact Damage in Sandwich Panel with UHMWPE Composite Facings

This paper is concerned with the low-velocity impact (LVI) response behaviour of sandwich composite panels (SCPs) with ultra-high molecular weight polyethylene (UHMWPE) composite facings and Polyvinyl Chloride (PVC)/Polyethylene Terephthalate (PET) foam cores. A series of LVI tests with SCPs subjected to 50 J, 80 J and 110 J were conducted to examine their impact characteristics and damage mechanisms. LVI-induced internal damage in the SCPs were characterised by compute micro-tomography (μCT) analysis. The effects of UHMWPE areal density and foam type on the LVI responses and associated failure modes of the panels were also examined. The experimental results showed that the SCP with a PET foam core exhibited higher impact strength and energy absorption performance than those of the panel with a PVC foam core. In addition, a finite element (FE) model incorporating the Puck’s failure criteria, cohesive law and crushable foam plasticity model was developed and validated to predict the intra- and inter-laminar damages of SCPs. Finally, several failure mechanisms (fibre failure, matrix cracking and local delamination) of SCPs during LVI was thoroughly discussed. The results show the UH170-PET specimen has the best impact resistance and energy absorption performance. The parametric analysis of the areal density and foam type has revealed that these parameters can be optimised for the best LVI resistance of SCPs. These findings are helpful for designing lightweight foam-based sandwich composite structures with superior impact resistance

Study of the interlayer adhesion and warping during material extrusion-based additive manufacturing of a carbon nanotube/biobased thermoplastic polyurethane nanocomposite

Unformatted preprint version of the submitted articleA thermoplastic bio-polyurethane from renewable sources (TPU) and the nanocomposite developed by mixing it with carbon nanotubes (CNT) are investigated as potentially adequate for Material Extrusion-based Additive Manufacturing (EAM). Thermal and rheological features are studied from the perspective of their liaisons with printing adequacy and conditions. As predicted by rheology, both samples show good performance in filament elaboration and flow in the nozzle. Warpage is observed for TPU, but not for the nanocomposite, which is due to the effect of CNT nanoparticles on polymer chains dynamics. At the studied printing velocities, interlayer adhesion strength is independent of printing velocity implying that there is no significant chain orientation which can induce changes in the TPU entanglements. The nanocomposite shows a lower welding strength, notwithstanding both have the same chain entanglements density. This is explained by considering that the higher viscosity of TPU/CNT, as compared to TPU, reduces the melt diffusion coefficient.We would like to thank the financial support provided by the BIODEST project. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 778092. This work has also received funding from MINECO through project MAT2017-83014-C2-1-P and from the Basque Government through grant IT1309-19

Influence of printing conditions on structure in FDM prototypes

Osnovni nedostatak prototipova nastalih 3D tiskanjem metodom taloženja (FDM) je nehomogenost strukture koja proizlazi iz osnovnog principa te tehnike. Cilj je ovoga rada pokazati kako promjena radne temperature i rasporeda na osnovnoj ploči utječe na strukturu FDM prototipova. Kako bi se odredio utjecaj obradne temperature na strukturu nastajanja FDM prototipova, primijenjene su različite temperature glave i omotača kod tiskanja uzoraka. Uzorci su analizirani kompjuterskom tomografijom da bi se odredile promjene u strukturi slojeva, dimenzijama i dijelu nepopunjenog volumena u njima. Dobiveni rezultati pokazuju da raspodjela materijala u cjelokupnom volumenu skeniranih uzoraka nije ravnomjerna. Ustanovljeno je da na homogenost strukture koju predstavlja obujam neispunjenog područja, djeluje čak i oblik izrađenog dijela. U budućnosti se ovaj pristup može koristiti kao standardna metoda za procjenu kvalitete.The main insufficiency of prototypes made by 3D printing with FDM (Fused Deposition Modelling) method is structure inhomogeneity resulting from the basic principle of this technique. The aim of the paper is to show how the structure of the FDM prototypes, by changing of processing temperature and layout on base plate, is affected. In order to define the processing temperatures influence on building structure of the FDM prototypes, various head and envelope temperatures in printing of specimens were applied. The samples were analysed by computed tomography to determine changes in layers structure, dimensions and the portion of unfilled volume in specimen. Obtained results show that material distribution in the whole volume of scanned specimens is not uniform. It was found out that structure homogeneity represented by the volume of non-filled area is affected by even the shape of fabricated part. This approach can be in the future used as a standard method for quality evaluation

Innovative techniques to devise 3D-printed anatomical brain phantoms for morpho-functional medical imaging

Introduction. The Ph.D. thesis addresses the development of innovative techniques to create 3D-printed anatomical brain phantoms, which can be used for quantitative technical assessments on morpho-functional imaging devices, providing simulation accuracy not obtainable with currently available phantoms. 3D printing (3DP) technology is paving the way for advanced anatomical modelling in biomedical applications. Despite the potential already expressed by 3DP in this field, it is still little used for the realization of anthropomorphic phantoms of human organs with complex internal structures. Making an anthropomorphic phantom is very different from making a simple anatomical model and 3DP is still far from being plug-and-print. Hence, the need to develop ad-hoc techniques providing innovative solutions for the realization of anatomical phantoms with unique characteristics, and greater ease-of-use. Aim. The thesis explores the entire workflow (brain MRI images segmentation, 3D modelling and materialization) developed to prototype a new complex anthropomorphic brain phantom, which can simulate three brain compartments simultaneously: grey matter (GM), white matter (WM) and striatum (caudate nucleus and putamen, known to show a high uptake in nuclear medicine studies). The three separate chambers of the phantom will be filled with tissue-appropriate solutions characterized by different concentrations of radioisotope for PET/SPECT, para-/ferro-magnetic metals for MRI, and iodine for CT imaging. Methods. First, to design a 3D model of the brain phantom, it is necessary to segment MRI images and to extract an error-less STL (Standard Tessellation Language) description. Then, it is possible to materialize the prototype and test its functionality. - Image segmentation. Segmentation is one of the most critical steps in modelling. To this end, after demonstrating the proof-of-concept, a multi-parametric segmentation approach based on brain relaxometry was proposed. It includes a pre-processing step to estimate relaxation parameter maps (R1 = longitudinal relaxation rate, R2 = transverse relaxation rate, PD = proton density) from the signal intensities provided by MRI sequences of routine clinical protocols (3D-GrE T1-weighted, FLAIR and fast-T2-weighted sequences with ≤ 3 mm slice thickness). In the past, maps of R1, R2, and PD were obtained from Conventional Spin Echo (CSE) sequences, which are no longer suitable for clinical practice due to long acquisition times. Rehabilitating the multi-parametric segmentation based on relaxometry, the estimation of pseudo-relaxation maps allowed developing an innovative method for the simultaneous automatic segmentation of most of the brain structures (GM, WM, cerebrospinal fluid, thalamus, caudate nucleus, putamen, pallidus, nigra, red nucleus and dentate). This method allows the segmentation of higher resolution brain images for future brain phantom enhancements. - STL extraction. After segmentation, the 3D model of phantom is described in STL format, which represents the shapes through the approximation in manifold mesh (i.e., collection of triangles, which is continuous, without holes and with a positive – not zero – volume). For this purpose, we developed an automatic procedure to extract a single voxelized surface, tracing the anatomical interface between the phantom's compartments directly on the segmented images. Two tubes were designed for each compartment (one for filling and the other to facilitate the escape of air). The procedure automatically checks the continuity of the surface, ensuring that the 3D model could be exported in STL format, without errors, using a common image-to-STL conversion software. Threaded junctions were added to the phantom (for the hermetic closure) using a mesh processing software. The phantom's 3D model resulted correct and ready for 3DP. Prototyping. Finally, the most suitable 3DP technology is identified for the materialization. We investigated the material extrusion technology, named Fused Deposition Modeling (FDM), and the material jetting technology, named PolyJet. FDM resulted the best candidate for our purposes. It allowed materializing the phantom's hollow compartments in a single print, without having to print them in several parts to be reassembled later. FDM soluble internal support structures were completely removable after the materialization, unlike PolyJet supports. A critical aspect, which required a considerable effort to optimize the printing parameters, was the submillimetre thickness of the phantom walls, necessary to avoid distorting the imaging simulation. However, 3D printer manufacturers recommend maintaining a uniform wall thickness of at least 1 mm. The optimization of printing path made it possible to obtain strong, but not completely waterproof walls, approximately 0.5 mm thick. A sophisticated technique, based on the use of a polyvinyl-acetate solution, was developed to waterproof the internal and external phantom walls (necessary requirement for filling). A filling system was also designed to minimize the residual air bubbles, which could result in unwanted hypo-intensity (dark) areas in phantom-based imaging simulation. Discussions and conclusions. The phantom prototype was scanned trough CT and PET/CT to evaluate the realism of the brain simulation. None of the state-of-the-art brain phantoms allow such anatomical rendering of three brain compartments. Some represent only GM and WM, others only the striatum. Moreover, they typically have a poor anatomical yield, showing a reduced depth of the sulci and a not very faithful reproduction of the cerebral convolutions. The ability to simulate the three brain compartments simultaneously with greater accuracy, as well as the possibility of carrying out multimodality studies (PET/CT, PET/MRI), which represent the frontier of diagnostic imaging, give this device cutting-edge prospective characteristics. The effort to further customize 3DP technology for these applications is expected to increase significantly in the coming years

A review of composite product data interoperability and product life-cycle management challenges in the composites industry

A review of composite product data interoperability and product life-cycle management challenges is presented, which addresses “Product Life-cycle Management”, developments in materials. The urgent need for this is illustrated by the life-cycle management issues faced in modern military aircraft, where in-service failure of composite parts is a problem, not just in terms of engineering understanding, but also in terms of the process for managing and maintaining the fleet. A demonstration of the use of ISO 10303-235 for a range of through-life composite product data is reported. The standardization of the digital representation of data can help businesses to automate data processing. With the development of new materials, the requirements for data information models for materials properties are evolving, and standardization drives transparency, improves the efficiency of data analysis, and enhances data accuracy. Current developments in Information Technology, such as big data analytics methodologies, have the potential to be highly transformative

Material Design, Processing, and Engineering Requirements for Magnetic Shape Memory Devices

For magnetic shape memory (MSM) alloys, a magnetic field stimulates a shape change. We use the shape change to build devices such as micro-actuators, sensors, and microfluidic pumps. Currently, (as a novel technology,) devices suffer from some material and magnetic driver shortcomings. Here we address the issues related to operating temperature, repeatability, failure, and magnetic driver development. To increase the operating temperature of the MSM material, we alloyed Fe and Cu to Ni-Mn-Ga. We showed that the element-specific contribution to the valence electron density as parameter systematically determines the effect of each element on the variation of the martensite transformation temperature of the 10M phase. To stabilize the material, we developed a micro-shotpeening process that adds stresses to the material surface, thereby inducing a fine twin microstructure. The treatment allowed nearly full magnetic-field-induced strain, and extended fatigue life of the material from only one thousand cycles in the electropolished state to more than one million cycles in the peened state. We measured the effect of the peening process on material actuation when in MSM pump configuration. In the polished state, the deformation was stochastic, with a sharp-featured, faceted shrinkage. In the treated state, the deformation was smooth and repeatably swept along the surface akin to a wave. To actuate the MSM micropump without electromotor, we developed a linear electromagnetic actuation device and evaluated its effectiveness in the switching mechanism of the material. By compressing the magnetic field between opposing coils, we generated a strong magnetic field, which caused a localized region to switch at selected poles. In the next iteration of the drive, we inserted the MSM sample between two linear pole arrangements of high pitch density to approximate a moving vertical field. The incremental stepping of the vertical field between poles caused translation of the switched region. The results of this dissertation demonstrate the suitability of MSM alloys for high-precision, persistent, and reliable actuators such as micropumps

Analysis, Design and Fabrication of Micromixers, Volume II

Micromixers are an important component in micrototal analysis systems and lab-on-a-chip platforms which are widely used for sample preparation and analysis, drug delivery, and biological and chemical synthesis. The Special Issue "Analysis, Design and Fabrication of Micromixers II" published in Micromachines covers new mechanisms, numerical and/or experimental mixing analysis, design, and fabrication of various micromixers. This reprint includes an editorial, two review papers, and eleven research papers reporting on five active and six passive micromixers. Three of the active micromixers have electrokinetic driving force, but the other two are activated by mechanical mechanism and acoustic streaming. Three studies employs non-Newtonian working fluids, one of which deals with nano-non-Newtonian fluids. Most of the cases investigated micromixer design