Single point incremental forming suffers from process window limitations which are strongly determined by the maximum achievable forming angle. Forming consecutive, intermediate shapes can contribute to a significantly enlarged process window by allowing steeper maximum wall angles for a range of part geometries. In this paper an experimentally explored multi-step toolpath strategy is reported and the resulting part geometries compared to simulation output. Sheet thicknesses and strains achieved with these multi-step toolpaths were verified and contribute to better understanding of the material relocation mechanism underlying the enlarged process window.

Incremental Sheet Forming (ISF) is a relatively new class of sheet forming processes that allow the manufacture of complex geometries based on computercontrolled forming tools in replacement (at least partially) of dedicated tooling. This paper studies the straining behaviour in the Single Point Incremental Forming (SPIF) variant (in which no dedicated tooling at all is required), both on experimental basis using Digital Image Correlation (DIC) and on numerical basis by the Finite Element (FE) method. The aim of the paper is to increase understanding of the deformation mechanisms inherent to SPIF, which is an important issue for the understanding of the high formability observed in this process and also for future strategies to improve the geometrical accuracy. Two distinct large-strain FE formulations, based on shell and first-order reduced integration brick elements, are used to model the sheet during the SPIF processing into the form of a truncated cone. The prediction of the surface strains on the outer surface of the cone is compared to experimentally obtained strains using the DIC technique. It is emphasised that the strain history as calculated from the DIC displacement field depends on the scale of the strain definition. On the modelling side, it is shown that the mesh density in the FE models plays a similar role on the surface strain predictions. A good qualitative agreement has been obtained for the surface strain components. One significant exception has however been found, which concerns the circumferential strain evolution directly under the forming tool. The qualitative discrepancy is explained through a mechanism of through-thickness shear in the experiment, which is not fully captured by the present FE modelling since it shows a bending-dominant accommodation mechanism. The effect of different material constitutive behaviours on strain prediction has also been investigated, the parameters of which were determined by inverse modelling using a specially designed sheet forming test. Isotropic and anisotropic yield criteria are considered, combined with either isotropic or kinematic hardening. The adopted constitutive law has only a limited influence on the surface strains. Finally, the experimental surface strain evolution is compared between two cones with different forming parameters. It is concluded that the way the plastic zone under the forming tool accommodates the moving tool (i.e. by through-thickness shear or rather by bending) depends

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Articles you may be interested inEnhancement of fatigue endurance in ferroelectric PZT ceramic by the addition of bismuth layered SBT Effects of W doping and annealing parameters on the ferroelectricity and fatigue properties of sputtered Bi 3.25 La 0.75 Ti 3 O 12 films It is well known that doping can greatly affect the ferroelectric properties of Bi 4 Ti 3 O 12 : however, the mechanisms of the doping effect, especially doping at the B site, are not well understood. The effect of B-site doping with different ion sizes and valences on the remanent polarization and fatigue endurance was investigated to clarify the mechanism of B-site doping. The experimental results indicated that both the radius of doping ion and the concentration of oxygen vacancies have no certain relation with the enhancement of remanent polarization. However, oxygen vacancies play an important role in fatigue endurance in doped Bi 4 Ti 3 O 12 . The effect of B-site doping is briefly discussed.

The simulation of a resin flow through a porous medium by FE-models has become a very important aspect for the design of a high-performance RTM produced composite part. The key parameter to perform RTM flow simulations is the fibre reinforcement permeability. Unfortunately, permeability measurements are not yet fully standardized and thus many different set-ups have been proposed. A major problem in comparing different set-ups has always been the fact that there exists no reliable reference material on which a comparative permeability measurement can be performed. This paper presents a solid test specimen, produced with a stereolithography technique, which can be used as a reference sample for calibration of test rigs and for comparison of results from different test rigs. Since the permeability properties of the specimen do not vary from test to test, an excellent repeatability of the experiments is obtained and any measured difference must be attributed to the set-up.

Although combination chemoimmunotherapy shows promising clinical results for cancer treatment, this approach is largely restricted by variable objective response rate and severe systemic adverse effects of immunotherapeutic antibody and chemotherapeutic drugs. Therefore, an in situ-formed therapeutic silk-chitosan composite scaffold is fabricated in this study to allow local release of the chemotherapeutic drug doxorubicin (DOX) and JQ1 (small molecular inhibitor used for the extraterminal protein BRD4 and bromodomain) with control release kinetics. DOX-JQ1@Gel contains a pH-degradable group that releases therapeutics in a weak acidic tumor microenvironment. The released DOX could directly kill tumor cells or lead to immunogenic cell death, thereby triggering the response of antitumor immunity. Meanwhile, chemotherapy-triggered antigen release and JQ1-mediated PD-L1 checkpoint blockade cumulatively contribute to trigger the response of antitumor immunity. Finally, the DOX-JQ1@Gel is locally injected to evaluate its synergistic cancer therapeutic effect, which is expected to improve objective response rate of immunotherapy and minimize systemic side effects. Graphical Abstract