| Under the action of alternating stress?strain?,such as tire products,the material properties will continue to decline due to the development of fatigue damage during use,therefore,fatigue performance is one of the main indicators for evaluating the performance of rubber composite.Short fiber reinforced rubber?SFRR?composite is one of the most high-performance composite materials with the most application potential which thanks to the high modulus,high tear strength of the fiber and the high elasticity of the rubber.The introduction of fibers increases the interface between phases,and its fatigue behavior is different from that the pure rubber material.The interface layer between rubber and fibers becomes the key to affect its fatigue performance.Therefore,the construction of interface layers with different characteristics to characterize the interface characteristics of SFRR composites and to explore the relationship between interface characteristics and fatigue behavior can provide theoretical guidance for the design of high-performance SFRR composites with higher values and high service life.In this paper,a SFRR material with an effective in-situ interface layer was prepared based on a two-step method;Using the compound coating of maleic anhydride grafted polybutadiene liquid rubber?MLPB?,epoxy resin?EP?and2-ethyl-4-methylimidazole?2E4MZ?to adjust the interface characteristics.SFRR materials relative debonding energy?RDE?and relative modified debonding energy?RMDE?are used to describe the interface bonding performance.Atomic force microscopy?AFM?was used to characterize the interface characteristics;The formation mechanism of in-situ interface layer and the adjustment method of interface characteristics were studied.The relationship between interface characteristics and fatigue life and the effect of effective interface layer on the crack growth rate of SFRR were studied.The main results of the thesis research are as follows:?1?Based on the two-step method,the aramid fiber?AF?was complex modified?T-AF?and the surface was coated with styrene-butadiene latex?VPL?or MLPB.The interface adhesion between AF and styrene-butadiene rubber?SBR?was improved.Observed the obvious interfacial layer of the modified composite by AFM,and calculated the RDE,RMDE and the attenuation rate of RMDE during fatigue by tensile stress-strain curve.The three were used to characterize the strain energy required for fiber and rubber matrix to debond during stretching,additional strain energy required for debonding of the interface layer produced after fiber modification during stretching,and the amount of damage to the interface layer produced during fiber modification during fatigue.The proportional relationship between RDE and RMDE values and the load-controlled tensile fatigue life can be used to qualitatively evaluate the fatigue life of the rubber composites.The RDE value of SBR/CB/T-AF/MLPB prepared by two-step modification of AF was higher than that of SBR/CB/AF by more than 100%,and the fatigue life was increased by 195%.The results showed that the fatigue performance of SFRR composites can be improved by establishing a tough interface layer with a certain modulus that can absorb a large amount of strain energy.?2?Establishing a good interface layer can significantly improve the fatigue performance of SFRR materials,but how to build and how to control the characteristics of the interface layer needs further research.MLPB,epoxy resin E51and 2E4MZ were used to prepare the coating agent dispersion.The complexed aramid fiber was coated,added to an internal mixer and co-compacted with SBR to prepare a composite material with an in-situ interface layer.The results showed that esterification reactions occurred between coating agents,and an in-situ interface layer was formed on the fiber surface.The optimum processing technology for preparing the in-situ interface layer is that the mixer temperature and mixer speed are150°C and80 r·min-1,respectively,the RDE value of composites increases by 100 k J·m-3.Compared with traditional coating method,the composite material processed after curing of the coating agent has doubled the increase in RDE value.?3?Further adjust the interface characteristics of SFRR composite materials by adjusting the total amount and mutual ratio of the coating agents MLPB and E51.The results showed that when the ratio of coating agent to fiber content was 6:4,the ratio of the coating agent to the in-situ interface layer was higher,the interface adhesion strength was well,and the RDE and RMDE values were the highest,and the RDE value was doubled.The action mechanism of MLPB and EP on interface adhesion in coating agent is different,the former mainly provides groups co-vulcanized with rubber,while the latter is capable of coating and fixing MLPB at the interface,while providing a mold for the interface layer.The final study found that when E51/MLPB was 1/5 and 2/4,the composites had the highest RDE and RMDE values,the best interface bonding strength,and the better mechanical properties.?4?The interface characteristics?interface thickness and interface layer hardness?of different composites were characterized by Shore hardness tester and AFM,and the influence of interface characteristics on fatigue properties of composites was investigated.It was found that there was a good proportional relationship between RDE,RMDE and fatigue life.The SFRR material with more MLPB content and less E51 content in coating agent has larger RDE and RMDE values?higher interface toughness?,longer fatigue life,and can increase more than three times the original life.Higher toughness and thicker interface layers are beneficial to improve the fatigue life of composites.The crack growth rate of composite was measured,it was found that a plateau region appears on crack growth rate curve of the composite with modified interface layer,and the crack growth rate did not increase with the increase of tear energy in this plateau region.After shifting the curve to a plateau region,it basically conforms to the power law relationship between the crack growth rate and tear energy of rubber materials.The SFRR material with the highest fatigue life formula has a plateau size of 1116 k J·m-2. |
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