Results 1 - 10 of 60362
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[en] Polymer gel (PG) dosimetry enables three dimensional (3D) measurement of complex dose distributions. However, PGs are strongly reactive with oxygen and other contaminations, limiting their applicability by the need to use specific container materials. We investigate different 3D printing materials and printing techniques for their compatibility with PG. Suitable 3D printing materials may provide the possibility to perform PG dosimetry in complex-shaped phantoms. 3D printed and PG-filled test vials were irradiated homogenously. The signal response was evaluated with respect to homogeneity and compared to the signal in already validated reference vials. In addition, for the printing material VeroClear™ (StrataSys, Eden Prairie, USA) different methods to remove support material, which was required during the printing process, were investigated. We found that the support material should be used only on the outer side of the container wall with no direct contact to the PG. With the VeroClear™ material a homogenous signal response was achieved with a mean deviation of relative to the reference vials. In addition, the homogeneous irradiation of an irregularly-shaped gel container designed with the same printing material and technique also lead to a homogenous PG response. Furthermore, a small field irradiation of an additional test-vial showed an accurate representation of steep dose gradients with a deviation of the maximum position of relative to the reference vial. (note)
[en] Highlights: • Metamaterials with stiff micro-structured fibers in a soft polymeric matrix were designed and fabricated with dual-material 3D printing • The metamaterials were able to show some degree of strain-stiffening behavior instead of the typical strain-softening mechanical response of polymeric materials • This dual-material 3D printed metamaterial can be used to fabricate patient-specific tissue-mimicking phantoms with accurate mechanical behavior • The mechanical response of the micro-structured metamaterials can be controlled by tuning the design parameters of the stiff fiber • The effect of design parameters were investigated by sensitivity analysis Patient-specific tissue-mimicking phantoms are becoming available with the advent of additive manufacturing. Phantoms currently in use are focused on the geometrical accuracy and mechanical properties under small deformation. Mimicking the mechanical properties at large deformation is challenging because of the inherent difference between the mechanical behaviors of polymeric materials and that of human tissues. In this study, the mechanical behavior of soft tissues under a uniaxial tension is mimicked by dual-material 3D printed meta-materials with stiff micro-structured fibers embedded in a soft polymeric matrix. Although the two base materials are strain-softening polymers, some of the designed meta-materials demonstrate certain degree of strain-stiffening behavior. Further investigation shows how the stress–strain curve of the meta-materials can be controlled by the design parameters. Sensitivity analysis is used to study the effects of each parameter. General design guidelines are proposed based on the results of the experiments. Dual-material 3D printed meta-materials have great potential in fabricating patient-specific phantoms with accurate mechanical properties that are associated with the gender, age, ethnicity, and other physiological/pathological characteristics. Mechanically accurate phantoms can play an important role in a variety of biomedical applications, including validation of computational models, testing of medical devices, surgery planning, medical education and training, and doctor-patient interaction.
[en] Nano powders of MgO, Al_2O_3 and SiO_2 were made by high energy ball milling. The simultaneous synthesis and consolidation of non-conductor's MgAl_2O_4-Mg_3Al_2Si_3O_12 composites from milled 4MgO, _2Al_2O_3 and 3SiO_2 powders was investigated by a high-frequency induction heating process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nano structured MgAl_2O_4-Mg_3Al_2Si_3O_12 composites were produced with a simultaneous application of 80 MPa pressure and an induced current within 1 min. The relative density and fracture toughness of the composite were 98% and 3.2 MPam1/2, respectively. The fracture toughness of the MgAl_2O_4-Mg_3Al_2Si_3O_12 composite was higher than that of monolithic MgAl_2O_4.
[en] In this paper, we report a simple and precise method to rapidly replicate master structures for fast microchannel fabrication by double replica moulding of polydimethylsiloxane (PDMS). A PDMS mould was surface-treated by vapour phase deposition of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS), which resulted in an anti-stiction layer for the improved release after PDMS casting. The deposition of FDTS on an O2 plasma-activated surface of PDMS produced a reproducible and well-performing anti-stiction monolayer of fluorocarbon, and we used the FDTS-coated moulds as micro-masters for rapid replication of micro-structures, avoiding the necessity to have to use other, more costly and fragile master materials. Our protocol has been shown to reliably fabricate PDMS-based microfluidic devices in a low-cost and efficient manner. The replicas were further employed as micro-contract stamps to fabricate polymer-based waveguides.
[en] Most automotive powertrain parts made of castings have surface defects such as pores. However, detecting pores inside small diameter bores is a challenge because of the limited dimensional accessibility. Adding to this difficulty is the auto industry's desire to conduct the porosity inspection in-line, i.e. within the machining production cycle time of a part. A technique or equipment that meets these requirements currently does not exist. In order to meet these demands, it is necessary to develop an entire new methodology to inspect the inner surface of small diameter bores. This paper presents an innovative methodology to inspect the porosity of the inner surface of small bores and to provide their characteristics such as size and location. A prototype measurement system was built and tested in the lab. Experimental results showed the proposed method to be reliable and consistent
[en] Full text: The ability of processing through laser beams different kind of powders for direct production of components with complex geometries by 3D printing has been gaining an impressive and growing attention for specific industrial applications. The process which can be distinguished as Selective Laser Sintering or Selective Laser Melting is even considered, more generally, as Additive Manufacturing where layer by layer material is built by interaction between a laser beam and a powder bed. All effects occurring during the interaction between the laser beam and the powder properties are usually neglected and phenomenological approaches are rather followed. From the work here presented some considerations related to the defect observed during the employment of the Additive Manufacturing process such as: balling, pores production, thermal stresses, micro-structural inhomogeneities, presence of unprocessed powder, capillary instability and so on will be discussed. With this aim, laser parameters (power, spot size, duration, wavelength) both, in plane laser scanning and vertical powder bed translation features (speed, pattern and spacing) power properties (size, density, distribution, composition and layer thickness) already reported in literature will be introduced. In such a way a deep insight view about the effects played by these parameter will be reported in order to provide some indications on the manifold mechanisms involved. Although non equilibria processes can be considered, thermal effects will be taken into account in first approximation. The rapid heating of the powder due to the laser beam energy transfer process followed by a rapid cooling rate can provide a local latent heat during the solidification process and induce unexpected phases of the final manufactured component. On these bases and taking into account other hypothesis connected to the underneath heat diffusion of the growing up piece of manufacture, heat accumulation effects and sharp decrease of the melted material viscosity, the presence of different kind of defects can be foreseen. In this manner the generated 3D component features and the production parameters used in this survey will be considered for drawing a relationship between fundamental mechanisms occurring during the laser ablation process and the Additive Manufacturing technique. (author)
[en] Description is given of a hot pressing process providing homogeneous ceramic, refractory or metallic materials of uniform or composite structure with dimensions that can reach and even overstep a squared meter. In view of the setting of the materials inside a container of versatile shape then introduced into the processing module, said materials can be pre-conditionned, their chemical and mechanical insulation during sintering can be obtained, within a controlled atmosphere and the elimination of the initial heterogeneities resulting from cold pressing also obtained. A new press with a working area of large dimensions is then described
[fr]On decrit un procede de frittage sous charge permettant d'obtenir des materiaux ceramiques, refractaires ou metalliques homogenes, de structure uniforme ou composite dont les dimensions peuvent atteindre ou depasser le metre carre. La mise en place du materiau dans un container deformable place ensuite dans le module de traitement permet un preconditionnement des materiaux, leur isolement chimique et mecanique lors du frittage, la creation d'une atmosphere controlee, l'elimination des inhomogeneites de depart dues a la compression a froid. On decrit une nouvelle presse dont la zone de travail est de grande dimension
[en] Since the fundamental works of FREKNEL/1/ and KUCZYNSKI/2/ on sintering of glass many investigators have tackled this topic. The present communication should be a further contribution to this problem. Plate glass was used, the properties of which have been determined. Pieced of this glass have been crushed to powder and the fraction 0,5-0,315 mm was separated using the appropriate sieves. The powder was very carefully cleaned and treated with an ultrasonic apparatus in order to remove the finest particles and dust. The investigation of sintering kinetics shown that the process of sintering of a glass is governed by viscous flow
[en] The problem of parameter identification of Ivensen's equation of sintering kinetics was considered. For this reason, the analysis of corresponding algorithms is carried out and the combination of the gradient algorithm Gauss-Newton algorithm and the method of linearization of Ivensen's equation is proposed