1,721,115 research outputs found
Experimental, numerical, and analytical investigations on the charge weld evolution in extruded profiles
No full textCharge welds are unavoidable product defects generated during the continuous extrusion of metallic materials that extend to a certain variable length and that are marked by lower mechanical properties than the base material. The portion of the profile containing the charge welds thus needs to be scrapped and an accurate prediction of this portion becomes mandatory, not only for the final user of the profile, in order to avoid in-service product failures, but also for extruders and die makers in order to increase the process efficiency. In the present work, four case studies carried out in the years by the authors on the prediction of the charge weld extension are reviewed and systematically compared in terms of experimental and numerical results. Data are furthermore compared with the predictions of analytical models reported in literature for the scrap length calculation and of an industrial empirical rule based on the extrusion ratio. Final aim of the work is to highlight potentials and limits of each predictive method and to assess their applicability in the everyday industrial practice
Verification of a stress gradient theory for the fatigue life predicition of components in case of pure push-pull and pure torsion conditions
No full textA relevant number of theories has been proposed
in the last 50 years for calculation of the fatigue
limits of components containing notches or more
general geometrical discontinuities. Beyond the
most classical ones, some methods
correlate the life to the relative stress gradient, allowing to overcome the limits of the
factors Kt and Kf not definable for generally
complex shaped components. On this direction, a
recent and very promising formulation has been
proposed [11,12] to predict the local S/N curve on
the base of a Finite Elements Analysis of the
stress gradient and on an empirical formulation of
the support factor nx.Aim of the present study is to validate the present
theory in the case of shafts in pure torsion and in
push-pull, comparing the predicted values with
experimental data obtained in two different test
campaigns
Asessment of a local S/N curve theory for the fatigue life calculation on experimental data
No full textABSTRACT: A theory for the fatigue life calculation based on local S/N curves, computed from the finite element results,
has been analysed by the comparison with experimental data. In a first analysis, a good agreement in the general trend of data
as function of the relative stress gradient, c’, has been observed. This means that an exponential decreasing of the slope K
and the number of cycle at the fatigue limit ND over the stress gradient was observed. Nevertheless, an absolute error
following an exponential low came out from the comparison of the experimental versus the predicted values of K and ND.
This low should be computed for each analysed data set, requiring, however, more than two generally data set as indicated in
the original theory, and used to refine the proposed formulas to calculate K and ND
Multi-goal optimization of a carry-mould
No full textA common engineering task is the optimization of components that are part of multibody
assemblies, in which it is difficult to extrapolate and define the boundary conditions
to be applied for the component optimization. This work presents a procedure for multi-goal
optimization of components that are integrated in multipart engineering systems. The efficiency
of the procedure is illustrated by means of a test case, a carry-mould that is part of a multicomponent
blowing machinery. Target goals of the optimization process were the minimization
of moment of inertia and of global mass and the maximum allowable displacement in a number
of control points
Innovative method for rapid development of shoes and footwear
No full textIn the present work, a novel set of software tools for the rapid development of shoes and footwear is presented aimed at strongly reducing the design time and then the time-to-market of the products. These tools are mainly based on an implementation of Constrained Free Form Deformation techniques and on the use of modern surface scanning methods. The proposed approach allows, in many cases, to avoid the mathematical surface reconstruction and to quickly generate the complex geometries that CAM systems will process in order to generate the tool paths for mold manufacturing
HOW ACCURATELY PRE-OPERATIVE PLANNING MATCHES THE ACHIEVED SURGERY: A FINITE ELEMENT STUDY
No full textPre-operative planning trains the surgeon in the workshop environment. The final objective of the early researches
along this line is to arrange a set of instruments to predict the primary stability in the pre-operative planning moving
toward a less and minimally invasive surgical technique. Nevetheless, even assuming a perfect surgical planning, there
is still the practical problem of correct positioning of the stem in the femur during surgery. An erroneous initial
positioning could lead to the implant instability promoting the ultimate failure of the implant [1,2]. Initial excessive
relative micromotions at the bone-implant interface may inhibit the bony in-growth and secondary long term fixation
[3,4]. To achieve a good level of primary stability the surgery technique play therefore a fundamental role.
Aim of the present study was to asses the sensitivity of the relative bone-implant micromotions, stresses and strains to
the surgical parameters as planned and achieved by the surgeon respectively before and after the operation. For this
purpose, the subject-specific finite element (FE) model of a cadaveric femur, accounting for patient and surgeon, was
derived from pre-operative and post-operative CT scans. The specific aim was to verify if finite element models based
on pre-clinical planning correctly match the achieved implant stability conditions
Experimental assessment of hot-work tool steels performances under the creep-fatigue regime
Full text linkIn the present research an innovative testing method, specifially developed to characterize the tool steels under creep-fatigue conditions, was carried out an a TQ1 hot-work tool steel. The experimental campaign consisted of different testing conditions and part of the specimens were nitrided to account for the specific surface state of the tools. Tests were performed on a 10tons MTS fatigue machine equipped with a heating furnace. A creep-fatigue loading type was applied to the specimens, i.e. a cyclic load with a dwell-time, in order to properly reproduce the conditions acting on a hot forging or extrusion tool. Then, under a constant temperature of 520°C, the effects of four different load levels and 2 different values of dwell-times were evaluated. In addition, selected test conditions were replicated with the specimens not nitrided with the aim to evalute and quantify the influence of the superficial treatment. Final results were presented in terms of fatigue curves of the TQ1 and compared to the performances of the H11 tool steel tested in a previous research by the same authors
Multi-objective Optimization of the Extrusion Process
No full textIn the paper a multi-objective optimization of a porthole extrusion die used to manufactured a thick AA7003 round tube is presented. Eight competitive objective functions were selected aimed at increasing the seam weld quality, the die lifetime, the production rate and at restraining the die yielding and the peak process load with respect to an initial already optimized solution. Six geometric input variables were included in the optimization procedure (welding chamber and bridges height, ports width, undercut on ports, die entry angle, mandrel-bridges fillet radius) together with the ram speed. The multi-objective optimization was performed by means of modeFRONTIER® using meta-models generated over a selected set of experimental and numerical training designs
Accuracy of the planned vs achieved position of a cementless hip stem: a finite element study
No full textThe implant of an hip stem into the femoral medullary cavity consists of three steps: the resection of the femoral head,
the rasping of the femoral canal and the placement of the stem. Priority for cemtless hip implants, in order to achieve a
good level of primary stability, is the accuracy with which the stem is positioned in the host bone. An erroneous initial
positioning could lead to the implant instability promoting the ultimate failure of the implant 1. Initial excessive relative
micromotions at the bone-implant interface may inhibit the bony in-growth and secondary long term fixation 2,3.
The final objective of the early researches along this line is to arrange a set of instruments to predict the primary
stability in the pre-operative planning moving toward a less and minimally invasive surgical technique. Nevetheless,
even assuming a perfect surgical planning, there is still the practical problem of correct positioning of the stem in the
femur during surgery.
Aim of the present study was to asses the sensitivity of the relative bone-implant micromotions, stresses and strains to
the implant position as planned and achieved by the surgeon respectively before and after the operation. For this
purpose, the subject-specific finite element (FE) model of a cadaveric femur, accounting for patient and surgeon, was
derived from pre-operative and post-operative CT scans. The overall aim was to verify if the pre-clinical planning
correctly matches the achieved implant stability conditions and hence if it can be considered as a powerful tool to train
the surgeon in taking the appropriate clinical decisions
MODELLAZIONE NUMERICA DI ARTICOLAZIONI CEDEVOLI PER DITA DI MANI ROBOTICHE
No full textAbstract
In the present work, the flexural stiffness of a close-wound cylindrical spring for a novel joint of
robotic hands is developed by means of the finite element (FE) method. In the first step, the FE model
of the spring has been generated and verificated to guarantee its numerical accuracy. Experimental
measurements and theoretical results on close-wound springs in the same geometrical configurations
here analysed were used as benchmark to compare predictions of the developed FE models. A good
agreement was found in terms of stiffness (Nmm/rad) between numerical versus experimental and
theoretical analysis at the same rotation (90°) with a root mean square error respectively of 11% and
8%
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