Asymmetric and Skin-Mimicking Hydrogels with Wide Temperature Tolerance and Superior Elasticity for High-Performance Strain Sensors.

Wide temperature tolerance and superior mechanical properties are highly required for composite hydrogels in electronic applications such as electronic skins and soft robotics. In this work, a unique polyacrylamide-based and double-network hydrogel system is designed and fabricated by introducing graphene oxide and glycerol to improve mechanical properties as well as antifreezing and antiheating properties. Maximum stress of the graphene oxide-incorporated hydrogel increases rapidly to 500.0 kPa which is much higher than that of polymetric acrylamide/carboxymethylcellulose sodium hydrogel (281.7 kPa), probably due to the inhibition from graphene oxide in generation and propagation of cracks. With constantly adding glycerol, total elongation and antifreezing and heating properties of the composite hydrogels increase gradually. Especially, sample with 20 vol % of glycerol not only shows stable conductivity and wide temperature tolerance (-50 to 50 °C) but also has ideal strength-toughness match (597.6 kPa and 1263.4%), suggesting that synergistic effect of different layers in the asymmetric structure plays an active role in improvement of mechanical properties.

Analysis of MnS Inclusions Formation in Resulphurised Steel via Modeling and Experiments.

Controlling the formation of MnS inclusions during solidification influences the mechanical properties and machinability of the resulfurized steel. A coupled segregation-nucleation-growth model was developed by the finite-difference method involving solute redistribution, heterogeneous nucleation and growth kinetics. Laboratory solidification experiments were performed under various cooling rates in resulphurised 49MnVS steel. In this work, the influence of cooling rate on solute redistribution and growth size of MnS inclusions were simulated using the current coupled model, and the calculated results can provide a valuable reference for MnS formation. Increasing of the cooling rate led to early precipitation and refinement of formed MnS inclusions. Based on the simulation results and experimental data, mathematical relationships between the growing size of MnS with the cooling rate in the low ductility temperature region and in the whole solidification were obtained.

Morphology Study on Inclusion Modifications Using Mg⁻Ca Treatment in Resulfurized Special Steel.

In resulfurized special steel, MnS and Al2O3 are two main inclusions that deteriorate fatigue life and machinability. It is important that these two inclusions should be well controlled to increase steel quality and usage performance. In the present study, a Mg⁻Ca treatment was employed to modify the MnS and Al2O3 inclusions in resulfurized steels to reduce detrimental effects on fatigue life and machinability. In the laboratory study, Ni⁻Mg alloy was added to 16MnCrS5 and 49MnVS3 steels. Both Al2O3 and CaO⁻Al2O3 were gradually modified to MgO·Al2O3 and MgO, being surrounded by MnS, that is, a complex inclusion with an oxide core and sulfide outer layer was formed. The amount of the complex inclusion increased with Mg content. In the hot forging experiment, non-Mg treated inclusions were in the morphology of long strip, while those with Mg treatment were seen to be less deformed with spherical morphology of low aspect ratio in which case inclusions had less effect on steel mechanical properties. The Mg⁻Ca treatment was also applied to the manufacture of resulfurized special steel in steel plants. The scanning electron microscope⁻energy dispersive spectrometer and statistical results agreed well with those in the laboratory studies.