Interactive mechanism and friction modelling of transient tribological phenomena in metal forming processes: A review

The accurate representation of tribological boundary conditions at the tool–workpiece interface is crucial for analysis and optimization of formability,material flow,and surface quality of components during metal forming processes.It has been found that these tribological conditions vary spatially and historically with process parameters and contact conditions.These time-dependent tribological behaviours are also known as transient tribological phenomena,which are widely observed during forming processes and many other manufacturing application scenarios.However,constant friction values are usually assigned to represent complex and dynamic interfacial conditions,which would introduce deviations in the relevant predictions.In this paper,transient tribological phenomena and the contemporary understanding of the interaction between friction and wear are reviewed,and it has been found that these phenomena are induced by the transitions of friction mechanisms and highly dependent on complex loading conditions at the interface.Friction modelling techniques for transient behaviours for metal forming applications are also reviewed.To accurately describe the evolutionary friction values and corresponding wear during forming,the advanced interactive friction modelling has been established for different application scenarios,including lubricated condition,dry sliding condition(metal-on-metal contact),and coated system.

Bioaccumulation and the expression of hepatic cytochrome P450 genes in marine medaka(Oryzias melastigma)exposed to difenoconazole

This study was conducted to assess the effects of difenoconazole（DFZ）, a triazole fungicide,on the hepatic biotransformation system and its bioaccumulation in marine medaka（Oryzias melastigma）. Fish were exposed to DFZ（1, 10, 100, 1000 ng/L） for 180 days. The results showed that：（1） The m RNA levels of hepatic CYP1A1, CYP1 B, CYP1C1, CYP27 B and CYP3A40 were up-regulated, but those of CYP3A38 and CYP27A1 were down-regulated.（2） The activity of ethoxyresorufin-O-deethylase（EROD） and the content of reduced glutathione（GSH） in the liver were increased in the DFZ-treated groups, and glutathione S-transferase（GST） activity was increased in the 100 and 1000 ng/L groups.（3） DFZ was accumulated in the muscle and the biological concentration factors in the 10, 100, and1000 ng/L groups were respectively 149, 81 and 25. These results suggested that long-term exposure to DFZ at low concentrations would result in a bioaccumulation of this compound and disturb the biotransformation system.

Experimental and modelling study of interaction between friction and galling under contact load change conditions

The galling process remains one of the least understood phenomena in metal forming.The transfer of material from a work-piece onto the tool surface can cause an evolutionary increase in friction coefficient(COF)and thus the use of a constant COF in finite element(FE)simulations leads to progressively inaccurate results.For an aluminium work-piece,material transfer,which has history and pressure dependency,is determined by a dynamic balance between the generation and ejection of wear particles acting as a‘third body’abrasive element at the contact interface.To address this dynamic interactive phenomenon,pin-on-disc tests between AA6082 and G3500 were performed under step load change conditions.The COF evolutions,morphologies of the transfer layer and its cross-section were studied.It has been found that contact load change will disequilibrate and rebuild the dynamic balance and high load will increase the generation and ejection rate of third body and vice versa.Moreover,based on the experimental results,an interactive model was developed and presented to simulate the dynamic formation process of the aluminium third body layer under load change conditions,enabling multi-cycle simulations to model the galling distribution and friction variation.

Experimental and modelling studies of the transient tribological behaviour of a two-phase lubricant under complex loading conditions

The transient tribological phenomenon and premature lubricant breakdown have been widely observed in metal forming,leading to excessive friction at the contact interfaces.In this research,the transient tribological behaviour of a two-phase lubricant were studied under complex loading conditions,featuring abrupt interfacial temperature,contact load,and sliding speed changes,thus representing the severe interfacial conditions observed in warm/hot metal forming applications.The strong experimental evidence indicates that the evolution of friction was attributed to the physical diminution and chemical decomposition effects.As such,a visco-mechanochemical interactive friction model was developed to accurately predict the transient tribological behaviour of the two-phase lubricant under complex loading conditions.The new friction model exhibited close agreements between the modelling and experimental results.

Exposure to difenoconazole inhibits reproductive ability in male marine medaka(Oryzias melastigma)

Difenoconazole（DFZ） is a triazole fungicide which has been detected in the aquatic environment, including estuaries and embayments. However, few studies addressing the reproductive toxicity and transgenerational effects of DFZ on marine fishes are available.The present study was conducted to investigate the effects of DFZ on male marine medaka（Oryzias melastigma）. After exposure of the embryo to 1, 10, 100 and 1000 ng/L DFZ for180 days, the gonadosomatic index was significantly decreased in the 1000 ng/L treatment.The number of sperm was reduced while the abundances of spermatocytes and spermatogonia in the testes were increased in all the treatments. The m RNA levels of salmontype gnrh（sgnrh）, the luteinizing hormone（lhβ） and the follicle-stimulating hormone（fshβ）genes in the brain all exhibited a significant down-regulation, the expression of androgen receptors（arα and arβ） was decreased and that of estrogen receptor β and cytochrome P450 aromatase（cyp19 B） was increased in the testes. The expression levels of cyp19 A and cyp19 B were increased in the liver. The decrease of ars m RNA levels might be one of the reasons causing the reduction of sperm. The down-regulation of sgnrh, lhβ and fshβ m RNA levels suggested that DFZ might impact the spermatogenesis via the brain–pituitary–gonad pathway. The decrease of the fertilization success, the hatch ability and the swim-up success in the F1 generation indicated that DFZ pollution at environmental levels might cause a decrease of wild fish populations.