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Impact behaviour of safety shoe high strength steel parts

Peixinho N., Mendonça J.

Engineering Transactions

2018

Vol. 66, iss. 2

175--185

This study presents results on the dynamic response of safety toe cap models made of high-strength steel. The structural response to impact loading conditions under normative requirements was properly related to tap the potential of lightweight design for significant reduction of thickness. A fully martensitic steel grade was selected, and numerical models were used to study extensive plastic deformation and strain-rate dependence. Material properties were modelled using the Cowper-Symonds models. The numerical simulation was developed using ANSYS explicit dynamics software and was compared to an experimental standard testing of final prototypes. The numerical modelling approach analysed different friction models seeking to better describe collapsing behaviour. A local stiffening toe cap model with high energy absorption efficiency was validated.

OGLE-2017-BLG-1434Lb: Eighth q<1×10-4 Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function

Udalski A., Ryu Y.-H., Sajadian S., Gould A., Mróz P., Poleski R., Szymański M. K., Skowron J., Soszyński I., Kozłowski S., Pietrukowicz P., Ulaczyk K., Pawlak M., Rybicki K., Iwanek P., Albrow M. D., Chung S. -J., Han C., Hwang K.-H., Jung Y. K., Shin I.-G., Shvartzvald Y., Yee J. C., Zang W., Zhu W., Cha S.-M., Kim D.-J., Kim H.-W., Kim S.-L., Lee C.-U., Lee D.-J, Lee Y., Park B.-G., Pogge R. W., Bozza W., Dominik M., Helling C., Hundertmark M., Jørgensen U. G., Longa-Peña P., Lowry S., Burgdorf M., Campbell-White J., Ciceri S., Evans D., Jaimes R. F., Fujii Y. I., Haikala L. K., Henning T., Hinse T. C., Mancini L., Peixinho N., Rahvar S., Rabus M., Skottfelt J., Snodgrass C., Southworth J., von Essen C.

Acta Astronomica

2018

Vol. 68, No. 1

1--42

We report the discovery of a cold Super-Earth planet (mp=4.4±0.5 M⊕) orbiting a low-mass (M=0.23±0.03 M⊙) M dwarf at projected separation a⊥=1.18±0.10 a.u., i.e., about 1.9 times the distance the snow line. The system is quite nearby for a microlensing planet, DL=0.86±0.09 kpc. Indeed, it was the large lens-source relative parallax πrel=1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax" πE∝(πrel/M)1/2 that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q<1×10-4. We apply a new planet-detection sensitivity method, which is a variant of "V/Vmax", to seven of these eight planets to derive the mass-ratio function in this regime. We find dN/d lnq ∝ qp, with p=1.05+0.78 -0.68, which confirms the "turnover" in the mass function found by Suzuki et al. relative to the power law of opposite sign n=-0.93±0.13 at higher mass ratios q≳2×10-4. We combine our result with that of Suzuki et al. to obtain p=0.73+0.42 -0.34.

Quasi-static and dynamic properties of the intervertebral disc : experimental study and model parameter determination for the porcine lumbar motion segment

Araujo A. R. G., Peixinho N., Pinho A. C. M., Claro J. C. P.

Acta of Bioengineering and Biomechanics

2015

Vol. 17, no. 4

59--66

Purpose: The study of axial loading is essential to determine the properties of intervertebral disc. The objectives of this work are (1) to quantify the mechanical properties of porcine lumbar intervertebral discs under static and cyclic compressive loading, and (2) to determine the parameters of a five-parameter rheological model for porcine and compare them with those obtained for human lumbar intervertebral discs. Methods: Thus, the porcine lumbar motion segments were subjected to quasi-static and dynamic compression tests. The quasi-static tests were used to obtain the static stiffness coefficient at different strain rates, while the data from the cyclic compressive tests were used to both determine the dynamic stiffness coefficient and to be fitted in a 5-parameter model, in order to simulate the creep response of the porcine intervertebral discs. Results: The results demonstrated that dynamic stiffness coefficient of porcine discs is between four and ten times higher than the static stiffness coefficient, depending on load applied. The parameters of the rheological model suggested a low permeability of nucleus and endplate during the fast response of porcine discs. In addition, the fast response in terms of displacement is four times higher than those documented for human discs. Conclusions: This study revealed that care must be taken on the comparison between porcine and human discs, since they present different behaviour under quasi-static and dynamic compressive loading.

Numerical Simulation of Impact Behaviour of Structures with Internal Pressurization for Crash-Adaptive Concept

Noversa M., Peixinho N.

Engineering Transactions

2013

Vol. 61, iss. 3

185--195

This study presents an alternative approach for the absorption of impact energy that uses the internal pressurization of structures in the framework of a crash-adaptive response. Numerical simulations were conducted on the axial impact of thin-walled tubular structures with circular cross-section that serves as an approximation to a front crash box of a motor vehicle.The main objective of this work consists in studying the effect of internal pressurization of tubular structures in a crashworthiness application, as well as the possibility to obtain a reduction in wall thickness thus improving weight efficiency. A numerical study is presented for an internal pressure of 20 bar and tubular structures of circular section and 1.14 mm thickness. Numerical simulations were performed by making use of the LS-DYNA explicit dynamics software, while considering for the material a stainless steel alloy that is a material with interest for crashworthiness applications and manufacturing requisites due to its balance between strength, ductility, and energy absorption. The results obtained allow the conclusion, that with respect to internal pressurization it is feasible to reduce the wall thickness and have an impact resistance identical to the original while improving overall efficiency.