| 1. |
- Das, Atanu Kumar, et al.
(författare)
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Formability study of bake hardening steel and its correlation with microstructure
- 2022
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Ingår i: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture. - : SAGE Publications Ltd. - 0954-4054 .- 2041-2975. ; 236:6-7, s. 882-893
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, the bake hardening (BH 240) steel sheet’s formability behavior is studied experimentally based on the Nakajima test method. A forming limit diagram is successfully constructed using universal sheet metal forming machine by offline measuring the strains of deformed specimens. In-process strain measurement based on a digital image correlation technique is also performed for a few selected samples to compare the results with manual strain measurement techniques. All the deformed specimens are also characterized to correlate the sample geometries with hardness values and microstructure. It is observed that the hardness value gradually decreases with an increase in sample width for all the deformed specimens up to the width of 150 mm, except for full-width sample of 200 mm. Microstructural analysis reveals that the morphology of ferrite grains changes with the sample geometry in all the deformed specimens. Microstructural characterization at the top surface of the specimen demonstrates that the aspect ratio of grains is maximum for a 25 mm width sample due to uni-axial stretching. It is also noted that grain’s aspect ratio is close to one (minimum) for a 200 mm width sample due to almost equi-biaxial elongation in grains. It is also observed that the aspect ratio of grains obtained from specimen cross-section indicates that the ratio increases gradually from 25 to 200 mm width samples.
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| 2. |
- Tiloca, Marco, et al.
(författare)
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DISH: DIstributed SHuffling against selective jamming attack in IEEE 802.15.4e TSCH networks
- 2018
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Ingår i: ACM transactions on sensor networks. - : Association for Computing Machinery (ACM). - 1550-4867 .- 1550-4859. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- The MAC standard amendment IEEE 802.15.4e is designed to meet the requirements of industrial and critical applications. In particular, the Time Slotted Channel Hopping (TSCH) mode divides time into periodic, equally-sized, slotframes composed of transmission timeslots. Then, it combines timeslotted access with multi-channel and channel hopping capabilities, providing large network capacity, high reliability and predictable latency, while ensuring energy efficiency. Since every network node considers the same timeslots at each sloframe and selects physical channels according to a periodic function, TSCH produces a steady channel utilization pattern. This can be exploited by a selective jammer to entirely thwart communications of a victim node, in a way that is stealthy, effective and extremely energy efficient. This paper shows how a selective jamming attack can be successfully performed even though TSCH uses the IEEE 802.15.4e security services. Furthermore, we propose DISH, a countermeasure which randomly permutes the timeslot and channel utilization patterns at every slotframe in a consistent and completely distributed way, without requiring any additional message exchange. We have implemented DISH for the Contiki OS and tested its effectiveness onTelosB sensor nodes. Quantitative analysis for different network configurations shows that DISH effectively contrasts selective jamming with negligible performance penalty.
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