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1

Effect of pre-cut hole diameter on deformation mechanics in multi-stage incremental hole flanging of deep drawing quality steel

Gandla Praveen Kumar, Kurra Suresh, Prasad K. Sajun, Panda Sushanta Kumar, Singh Swadesh Kumar

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

260--282

EN

Incremental hole flanging (IHF) is a relatively new sheet metal forming process to produce intricate shapes without using dedicated punches and dies. The present work focuses on understanding the mechanics of the multi-stage IHF process through experimental studies and the finite element approach. The IHF experiments were performed on deep drawing quality steel sheets with a pre-cut hole diameter of 45 mm, 50 mm, 60 mm, and 70 mm. The cylindrical flanges were formed in four stages with an initial wall angle of 60° to a final angle 90° with an angle increment of 10° in each stage. The maximum and minimum hole expansion ratio was found to be 2.06 and 1.17 respectively. The fracture was observed in a blank of 45 mm pre-cut hole diameter in the third stage at 40 mm depth. The fracture forming limit diagram (FFLD) was determined from incrementally formed varying wall angle conical and pyramidal frustums. Consequently, six different ductile damage models incorporating Hill48 anisotropy plastic theory were successfully calibrated. The Ayyada model showed good agreement with experimental FFLD as compared to all other models. The fracture limit determined experimentally and using the Ayyada model was implemented in the finite element simulation of the IHF process to predict the formability in terms of in-plane strain distribution, forming forces, and thickness distribution. The predicted results matched accurately with the experimental data within a 6% error for all investigated conditions. Noticeably, the strain path in IHF had three deformation modes viz. plane strain, bi-axial stretching, and uni-axial tension, which was comprehended using texture analyses. Finally, irrespective of the initial pre-cut hole diameter, the surface roughness was found to decrease with the number of stages of the IHF process.

2

Evaluation of brain injury criteria based on reliability analysis

Hazay Máté, Bojtar Impre

Acta of Bioengineering and Biomechanics

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2021

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Vol. 23, no. 1

173--185

EN

Purpose: Among the proposed brain injury metrics, Brain Injury Criteria (BrIC) is a promising tool for performing safety assessment of vehicles in the future. In this paper, the available risk curves of BrIC were re-evaluated with the use of reliability analysis and new risk curves were constructed for different injury types based on literature data of tissue-level tolerances. Moreover, the comparison of different injury metrics and their corresponding risk curves were performed. Methods: Tissue-level uncertainties of the effect and resistance were considered by random variables. The variability of the tissue-level predictors was quantified by the finite element reconstruction of 100 frontal crash tests which were performed in Simulated Injury Monitor environment. The applied tests were scaled to given BrIC magnitudes and the injury probabilities were calculated by Monte Carlo simulations. New risk curves were fitted to the observed results using Weibull and Lognormal distribution functions. Results: The available risk curves of diffuse axonal injury (DAI) could be slightly improved, and combined AIS 4+ risk curves were obtained by considering subdural hematoma and contusion as well. The performance of several injury metrics and their risk curves were evaluated based on the observed correlations with the tissue-level predictors. Conclusions: The cumulative strain damage measure and the BrIC provide the highest correlation (R2 = 0.61) and the most reliable risk curve for the evaluation of DAI. Although the observed correlation is smaller for other injury types, the BrIC and the associated reliability analysis-based risk curves seem to provide the best available method for estimating the brain injury risk for frontal crash tests.

3

The probability of traumatic brain injuries based on tissue-level reliability analysis

Hazay Máté, Bojtár Imre

Acta of Bioengineering and Biomechanics

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2019

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Vol. 21, no. 1

141--152

EN

Motor vehicle crashes are one of the leading causes of traumatic brain injuries. Restraint systems of cars are evaluated by crash tests based on human tolerance data, however, the reliability of data currently used has been questioned several times in the literature due to the neglect of certain types of effects, injury types and uncertainties. Our main goal was to re-evaluate the currently applied risk curve by taking the previously neglected effects into account. Methods: In this paper, the probability of traumatic brain injury was determined by reliability analysis where different types of uncertainties are taken into account. The tissue-level response of the human brain in the case of frontal crashes was calculated by finite element analyses and the injury probability is determined by Monte Carlo simulations. Sensitivity analysis was also performed to identify which effects have considerable contribution to the injury risk. Results: Our results indicate a significantly larger injury risk than it is predicted by current safety standards. Accordingly, a new risk curve was constructed which follows a lognormal distribution with the following parameters: μLN = 6.5445 and LN = 1.1993. Sensitivity analysis confirmed that this difference primarily can be attributed to the rotational effects and tissue-level uncertainties. Conclusions: Results of the tissue-level reliability analysis enhance the belief that rotational effects are the primary cause of brain injuries. Accordingly, the use of a solely translational acceleration based injury metric contains several uncertainties which can lead to relatively high injury probabilities even if relatively small translational effects occur.

4

Regression Points in Non-Intrusive Polynomial Chaos Expansion Method and D-Optimal Design

Szepietowska K., Magnain B., Lubowiecka I., Florentin E.

Machine Dynamics Research

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2017

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Vol. 41, No. 2

5--16

EN

The paper addresses selected issues of uncertainty quantification in the modelling of a system containing surgical mesh used in ventral hernia repair. Uncertainties in the models occur due to variability of abdominal wall properties among others. In order to include them, a nonintrusive regression-based polynomial chaos expansion method is employed. Its accuracy depends on the choice of regression points. In the study, a relation between error of mean, standard deviation, 95th percentile and location of regression points is investigated in the models of implants with a single random variable. This approach is compared with a classic choice of points based on the D-optimality criterion.

5

Numerical prediction of high explosive ignition under low velocity impact

Gruau C., Picart D.

Foundations of Civil and Environmental Engineering

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2008

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No. 12

33-48

EN

In the framework of low velocity impact studies, dedicated to safety analyses of plastic bonded explosives (PBX), we propose a numerical tool, designed for predicting the ignition of a HMX (high melting point explosive) based composition. The major results are the use of a concrete-like constitutive law for the PBX and an efficient implementation of an ignition criterion. It has been shown that the calculation tool is able to accurately predict the results when the ignition is diluted. For localized ignition into shear bands or macro cracks, some differences between numerical and experimental results have been discussed..

6

Finite element simulations of floating ice - engineering structure interactions

Staroszczyk R.

Archives of Hydro-Engineering and Environmental Mechanics

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2003

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Vol. 50, nr 3

251-268

EN

In this paper the problem of interaction between a coherent floating ice cover and a rigid engineering structure is considered. It is assumed that the ice cover, of horizontal dimensions considerably larger than the dimensions of the structure, is driven by wind and water current drag forces. During the interaction process of a quasi-static character, ice is assumed to behave as a creeping material, with a rheology described by the viscous fluid flow law. The ice cover is treated as a plate which sustains both bending due to the vertical reaction of the underlying water and the action of horizontal forces, which gives rise to the development of creep buckles in the plate and subsequently leads to the flexural failure of ice. An approximate solution to the problem is constructed by employing the finite element method. The results of numerical simulations illustrate the magnitudes of the forces exerted on the structure and their dependence on the wind direction and the structure geometry. In addition, the ice plate deflection in the vicinity of the structure is illustrated, and the values of the critical time at which the plate starts to fail by creep buckling are determined to show their dependence on the ice thickness, temperature, and type.

7

FE-simulations of rapid silo flow with a polar elasto-plastic constitutive model

Tejchman J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1998

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Vol. 2, No 3

473-501

EN

The paper presents results on numerical modelling of rapid flow of granular materials in a model silo with convergent smooth walls. The calculations were performed with a finite element method based on a polar elasto-plastic constitutive relation by Muhlhaus (1995). The relation differs from the conventional theory of plasticity by the presence of Cosserat rotations and couple stresses using a mean grain diameter as a characteristic length. The characteristic length causes that numerical results do not depend upon the mesh discretisation. The model tests on rapid silo flow of glass beads performed by Renner in a glass hopper with a large wall inclination from the bottom were numerically simulated. The plane strain FE-calculations were performed by taking into account inertial forces and linear viscous damping. A satisfactory agreement between numerical and experimental results was obtained. Advantages and limitations of a continuum approach for simulations of rapid silo flow were outlined.