For decades,the preparation of polyisoprene rubber that can match the comprehensive properties of natural rubber(NR)has been pursued.While sacrificial bonds have been used to promote the strength and toughness of rubb...For decades,the preparation of polyisoprene rubber that can match the comprehensive properties of natural rubber(NR)has been pursued.While sacrificial bonds have been used to promote the strength and toughness of rubbers,little is known about their effects on fatigue resistance,which is important in dynamic environments.Herein,terminal block and randomly functionalized polyisoprene rubbers tethered with di-alanine,tri-alanine and tetra-alanine were prepared.The results showed that the flow activation energy,aggregates ordering and energy dissipation of the hydrogen-bonded aggregates increase with the elongation of oligopeptide length(XA,X=2,3,4),therefore resulting in enhanced mechanical strength and toughness of corresponding samples.Comparably,the tear strengths are barely affected by oligopeptide lengths in block samples,but promoted from dipeptide to tetrapeptide in random samples,probably due to the well dispersed oligopeptide aggregates.Most importantly,it is found that the tight binding aggregates of oligopeptides are critical for the excellent fatigue resistance,which is absent in polyisoprene and natural rubber.The loose aggregates dissociate and recombine repeatedly under cyclic loading and the tight aggregates keep the network integrated and robust.Interestingly,the largest hysteresis of PIP-4A-V with the longest oligopeptide length give the lowest heat generation,which is contrary to the traditional sacrificial bonds.Overall,the oligopeptide aggregates have repeatable energy dissipation properties and cycle life comparable to or even surpassing those of the linked proteins in NR,resulting in similar tensile strength,fracture toughness,and better fatigue resistance relative to NR.This deep insight on the role of oligopeptide aggregates is very useful for the engineering rubbers served in dynamic environments.展开更多
Thermal fatigue behaviors of two forged hot-work die steels subjected to cyclic heating （650 ℃）-water quenching were investigated. A martensitic hot-work die steel containing 10% Cr （HHD）, showing superior oxidat...Thermal fatigue behaviors of two forged hot-work die steels subjected to cyclic heating （650 ℃）-water quenching were investigated. A martensitic hot-work die steel containing 10% Cr （HHD）, showing superior oxidation resistance and thermal fatigue resistance to the commercial martensitic hot-work die steel （Uddeholm DIEVAR ）, was developed. The maximal crack length in HHD was 35% shorter than that in DIEVAR after 2000 thermal cycles, and the hot yield strength at 650℃ of HHD was 14% lower than that of DIEVAR prior to thermal fatigue testing, which is 30% higher after 1500 cycles. It is found that cracks initiated and propagated along the oxide layers in the grain boundaries, suggesting that the oxidation-induced thermal fatigue cracks can significantly reduce the mechanical performance and service life for the hot- work die steel. High-temperature oxidation behavior is crucial for thermal fatigue crack formation, while high-temperature yield strength and ductility play a less important role.展开更多
基金financially supported by the Natural Science Foundation of Jiangsu Province(BK20211243)Jiangsu Provincial Key Research and Development Program(BE2022708)+1 种基金the Tribology Science Fund of State Key Laboratory of Tribology in Advanced Equipment(SKLTKF21B15)the Open Fund of State Key Laboratory of Solid Lubrication,Lanzhou Institute of Chemical Physics(LSL-2107).
基金financially supported by the National Natural Science Foundation of China(No.51973126)the State Key Laboratory of Polymer Materials Engineering(No.sklpme20222-11)。
文摘For decades,the preparation of polyisoprene rubber that can match the comprehensive properties of natural rubber(NR)has been pursued.While sacrificial bonds have been used to promote the strength and toughness of rubbers,little is known about their effects on fatigue resistance,which is important in dynamic environments.Herein,terminal block and randomly functionalized polyisoprene rubbers tethered with di-alanine,tri-alanine and tetra-alanine were prepared.The results showed that the flow activation energy,aggregates ordering and energy dissipation of the hydrogen-bonded aggregates increase with the elongation of oligopeptide length(XA,X=2,3,4),therefore resulting in enhanced mechanical strength and toughness of corresponding samples.Comparably,the tear strengths are barely affected by oligopeptide lengths in block samples,but promoted from dipeptide to tetrapeptide in random samples,probably due to the well dispersed oligopeptide aggregates.Most importantly,it is found that the tight binding aggregates of oligopeptides are critical for the excellent fatigue resistance,which is absent in polyisoprene and natural rubber.The loose aggregates dissociate and recombine repeatedly under cyclic loading and the tight aggregates keep the network integrated and robust.Interestingly,the largest hysteresis of PIP-4A-V with the longest oligopeptide length give the lowest heat generation,which is contrary to the traditional sacrificial bonds.Overall,the oligopeptide aggregates have repeatable energy dissipation properties and cycle life comparable to or even surpassing those of the linked proteins in NR,resulting in similar tensile strength,fracture toughness,and better fatigue resistance relative to NR.This deep insight on the role of oligopeptide aggregates is very useful for the engineering rubbers served in dynamic environments.
基金supported by the Project 985-High Properties Materials of Jilin University.
文摘Thermal fatigue behaviors of two forged hot-work die steels subjected to cyclic heating （650 ℃）-water quenching were investigated. A martensitic hot-work die steel containing 10% Cr （HHD）, showing superior oxidation resistance and thermal fatigue resistance to the commercial martensitic hot-work die steel （Uddeholm DIEVAR ）, was developed. The maximal crack length in HHD was 35% shorter than that in DIEVAR after 2000 thermal cycles, and the hot yield strength at 650℃ of HHD was 14% lower than that of DIEVAR prior to thermal fatigue testing, which is 30% higher after 1500 cycles. It is found that cracks initiated and propagated along the oxide layers in the grain boundaries, suggesting that the oxidation-induced thermal fatigue cracks can significantly reduce the mechanical performance and service life for the hot- work die steel. High-temperature oxidation behavior is crucial for thermal fatigue crack formation, while high-temperature yield strength and ductility play a less important role.
