Effect Of Cooling Mode On Mechanical Properties Of Granite After Microwave Irradiation

With the rapid development of China’s economy,the construction of a large number of infrastructure also promotes the development and renewal of hard rock crushing technology.Among them,microwave assisted mechanical rock fragmentation technology is considered as a potential and feasible rock fragmentation method.Microwave irradiation makes the rock produce certain pre-damage,so as to achieve the purpose of weakening the rock strength,improve the life of the tool head of large tunneling equipment,reduce the number of tool head frequent stuck machine and ensure the smooth development of the project.However,the degree of rock damage caused by microwave heating is affected by many factors,among which the cooling mode is one of the important factors affecting the strength deterioration of rock after microwave irradiation.Based on this,to explore different cooling methods on rock strength after microwave irradiation damage law,hebei hirayama granite as the research object,selected specimens of compressional wave velocity,surface temperature of the basic physical and mechanical parameters,such as to the dynamic compressive strength and the static compressive strength for mechanical strength index,and then to study the cooling way after the microwave irradiation rock mechanics characteristics and the influence law of strength damage.The main conclusions are as follows:(1)When the microwave irradiation time was constant,the increase of microwave power significantly increased the surface temperature of the specimen,and the heating rate showed a trend of first slow and then fast with the increase of microwave heating power.Under the conditions of two cooling methods,the surface temperature of granite underwent three stages of rapid cooling,slow decline and constant temperature,and the cooling rate of granite under soaking cooling was significantly higher than that of natural cooling,that is,the surface temperature of granite specimens tended to be stable before that of natural cooling.(2)Damage factors under different cooling methods based on various static load parameters show an increasing trend with the increase of microwave power,while damage factors based on peak stress can better describe the influence of cooling methods on the strength reduction degree of rock after microwave irradiation.The influence degree of the cooling mode expressed by the damage factor based on the velocity of p-wave on the strength reduction of rock after microwave radiation is quite different from the reality.(3)After microwave irradiation,the static peak stress and elastic modulus of granite under the two cooling modes decrease with the increase of microwave power.In the process of soaking cooling,the peak strain of granite after soaking cooling is obviously smaller than that of natural cooling,because water cooling can show strong cold quenching effect under high microwave power heating.As a result,the peak strain after soaking cooling shows a completely different law from natural cooling.(4)The dynamic compressive strength and elastic modulus of granite specimens under the two cooling methods decrease with the increase of microwave power,while the dynamic peak strain of granite specimens after cooling decreases significantly with the increase of microwave power.Compared with the dynamic mechanical parameters of rock after natural cooling,the dynamic impact compression strength and strain of rock under soaking cooling are lower than those under room temperature cooling,while the dynamic elastic modulus of rock shows a trend of being larger than that under room temperature cooling.(5)At the same power level,the dynamic peak stress and peak strain of granite increase with the increase of strain rate,showing an obvious strain rate effect.With the increase of microwave power,the sensitivity of dynamic peak stress of granite to strain rate becomes less obvious.When the microwave power is constant,the strain rate increases with the increase of the impact pressure,but there is no obvious correlation between the dynamic elastic modulus of the granite and the strain rate after microwave irradiation.(6)Combined with the analysis results of microwave energy utilization rate,it can be found that the energy efficiency is the best when the microwave power is 4.0kW.At the same time,the strength value of granite cooled by immersion under 4.0kW microwave power heating is almost equal to that of granite cooled by natural cooling under 5.3kW microwave power heating.That is,in practical engineering practice,under the premise of ensuring construction progress and personnel safety,"Microwave heating under low microwave power+immersion cooling sharply" this combination can not only achieve high microwave power by natural cooling after heated by the effect of rock strength degradation,also can reduce energy consumption,shortening the time of microwave according to rock after cooling,at the same time in the crushing process can reduce the occurrence of rock bits.This paper mainly studied the effect mechanism of cooling methods on the mechanical properties of rock after microwave irradiation,compared and analyzed the influence degree of different cooling methods on the strength deterioration of rock after microwave irradiation,and clarified the relationship between the dynamic mechanical properties of rock under different cooling methods and microwave power and strain rate.Based on this,it provides a reference for the application of microwave assisted mechanical rock breaking technology to the treatment of high temperature environment caused by actual excavation.