| As the second largest economy in the world,the road transport industry plays an important role in our country.With the growth of road transport scale,transport vehicles have more load,faster speed,increasing transport efficiency,overcoming harsh road environment and other changing trends,the safety of life and property face unprecedented challenges.Brake system is the security of transport vehicles,in which the drum brake is an important part of the truck braking system,in the truck braking by thermal fatigue and wear role to produce thermal fatigue cracks,resulting in drum brake failure,serious life threatening,drum brakes and the material used in grey cast iron problems are increasingly prominent.In addition,China’s annual drum brake usage of more than 30 million,frequent replacement of drum brakes will cause billions to tens of billions of resources worth of waste.Therefore,to improve the service life of the drum brake,improve the drum brake gray cast iron material resistance to thermal fatigue and wear performance has practical significance and significant application value.The failure of grey cast iron truck drum brakes is a complex problem caused by multiple factors that cannot be solved by changing a single factor alone.Observations and studies of the surface characteristics of living organisms in nature have revealed that in order to adapt to nature,organisms have evolved a body surface structure with excellent functionality due to the combined effect of multiple coupled factors such as structure,material and morphology.In this paper,based on the principle of coupling bionics,the coupling bionic unit is prepared on the surface of grey cast iron by laser fusion,and the unit coupling element forms a"soft-hard"structure with the base material coupling element,the relationship between laser energy and drum brake wall thickness is investigated,the laser parameters for processing grey cast iron truck drum brakes are optimised,and the effect of different tissue grey cast iron base material coupling elements on the drum brake is analysed.The influence of the coupling elements of different grey cast iron base materials on the laser coupling bionic treatment was analysed,the degree of improvement of the coupling bionic units on the thermal fatigue and wear performance of grey cast iron with different structures was summarised,the influence of the morphological coupling element characteristics on the thermal fatigue and wear performance of grey cast iron drum brakes was investigated,a combined coupling bionic model for the failure characteristics of grey cast iron truck drum brakes was designed,and a number of coupling bionic grey cast iron drum brakes were trialed for bench testing and loading tests.The coupling bionic unit is an important part of the"soft-hard"bionic coupling element,and the depth to width ratio,the number of pores and cracks in the cell are directly related to the degree of performance improvement of the drum brake.Firstly,it is verified that the thickness of the sample has a great influence on the laser processing element.The temperature field distribution in the laser melting region is analyzed by finite element simulation,and the thermal impedance of the sample with different thickness is calculated and compared.Then,the laser parameters of gray cast iron drum brake of processing truck were optimized by orthogonal test,and a structural coupling element with a depth-width ratio of 0.722 and no obvious pores and cracks was obtained.The processing parameters were current 140A,pulse width 8ms,frequency 4Hz,scanning speed 1.2mm/s,defocusing amount 9.8mm.Then,the relationship between laser energy and samples with different thickness was fitted,and the laser power density of the processed drum brake was determined to be 150.8W/mm~2.The microhardness of the high quality unit is much higher than that of the base material because of the superfine structure of cementite,martensite and residual austenite.The microhardness of the melting zone is 133%higher than that of the base material,and the microhardness of the phase transformation zone is 90%higher than that of the base material.The influence of the parent material coupling elements on the thermal fatigue and wear resistance of coupling bionic grey cast iron needs to be investigated,as different manufacturers and batches of grey cast iron drum brakes on the market have different tissue compositions and varying properties.Firstly,the effects of different graphite types,carbon contents,pearlite contents and interlamellar spacing on the thermal fatigue and wear properties of grey cast iron are investigated,and secondly,the extent to which the coupling bionic units enhance the thermal fatigue and wear resistance of grey cast iron of different tissues is investigated and their mechanism of action is analysed.Within the scope of this study,for different graphite types of grey cast iron,type A graphite has the best thermal fatigue resistance,type C and D graphite has the highest number of thermal fatigue cracks,type D graphite has the longest main crack length,the unitary has the greatest enhancement of thermal fatigue resistance for type D graphite,type C graphite has the best wear resistance,type D graphite has the worst wear resistance,and the unitary has the greatest enhancement of wear resistance for type D graphite For grey cast iron with different carbon content,the higher the carbon content,the worse the thermal fatigue resistance,the higher the carbon content,the stronger the lubricating effect of graphite,the better the wear resistance of the parent material;for grey cast iron with different pearlite content and interlamellar spacing,the higher the pearlite content,the better the thermal fatigue resistance and wear resistance,the smaller the interlamellar spacing,the better the thermal fatigue resistance and wear resistance,with 98%pearlite content and 152nm pearlite interlamellar spacing.After laser treatment,the influence of pearlite is reduced and the difference between the experimental results of each sample is reduced.The failure of grey cast iron drum brakes is caused by the combined effect of thermal fatigue and wear resulting in non-uniform regional damage.Therefore,the degree of improvement of the bionic surface against thermal fatigue and wear with different morphological coupling element features was first investigated,and the most suitable morphological coupling element feature for the drum brake was selected respectively.It was found that the best thermal fatigue resistance was achieved at a cell distribution spacing of 2 mm,but with the highest wear weight loss,and the best wear resistance was achieved at a unit distribution spacing of 4 mm;the best resistance to thermal fatigue cracking from the vertical direction was achieved at a distribution angle of 0°,and the best resistance to thermal fatigue and wear was achieved at a distribution angle of 45°.In view of the failure characteristics of grey cast iron drum brakes in actual working conditions,a combined coupling bionic model is designed and its resistance to thermal fatigue and wear is investigated,combined with finite element analysis of its mechanism of action.The best thermal fatigue and wear resistance was found to be achieved by the anti-crack ring+45°angle characteristic volume model.The results of the bench tests showed that the life of the bionic drum brake was improved by 33%,47%and 42%respectively,and the practical application of the drums in the loading tests showed that the service life of the bionic drum brake was improved by at least 50%. |
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