Evaluating Thermal Conductivity Of The Coating And Structural Damage Of Stone Curtain Walls Based On The Relative Method

The detection,characterization and evaluation of material surface properties are very important to the service safety of components.It is difficult to evaluate the service performance of the surface layer of components because of the particularity of surface structure and the connection between the surface layer and substrate.However,this kind of measurement is necessary due to the importance of surface function and surface safety.In this paper,evaluations on the thermal conductivity of the coating and the safety performance of building surface layer were studied based on an indirect evaluation,so called relative method.The evaluation of ceramic coatings,especially thermal barrier coatings,has been a hotspot in the field of surface and interface science.Thermal conductivity is one of the important indexes to evaluate the thermal insulation performance of thermal barrier coatings.Although the testing methods of thermal conductivity of block materials have been quite mature,none of the existing methods can directly measure the thermal conductivity of coatings.Measurement by conventional method involves two problems:i)it is difficult to peel off a ceramic coating from a substrate,ii)even if the coating can be peeled off,it is still hardly used as standard specimen in test.Therefore,the accurate measurement of thermal conductivity of coatings becomes a difficult problem.In view of the difficulty of directly testing thermal conductivity of ceramic coating,the theoretical relationship between thermal conductivities of coating,matrix and composite were established in this study,and then the thermal conductivity of the coating could be obtained through the thermal conductivities of matrix and composite,so as to establish an effective indirect method for testing thermal conductivity of coatings.The thermal conductivity of 8YSZ thermal barrier coatings was tested from 32℃to 1000℃by this method,and the impact of temperature on the thermal conductivity of 8YSZ coatings was investigated.The results showed that:i)the thermal conductivity of coating obtained by the relative method was close to the existing literature reports,which proved the accuracy and feasibility of the relative method to evaluate the thermal conductivity of coating.ii)with the increasing testing temperature,the thermal conductivity value of 8YSZ coatings displayed nonlinearity feature,i.e.decreased from 1.4 to 1.3(W m^-1 K^-1)in the temperature range of 32³00℃and then increased up to 1.58 W m^-1 K^-1 at 1000℃.The huge stock of building curtain walls is aging day by day.Because of the failure of structural bonding,the falling of curtain walls threatens the safety of public property.However,due to the hidden damage node,its safety performance evaluation is not perfect.In this study,the dynamic relative method was adopted to obtain the relationship between the degree and location of the structural damage and its vibration characteristic parameters,so as to establish a method to evaluate the safety performance of curtain wall through the relative comparison of vibration characteristic parameters.In this paper,the dry hanging stone curtain wall was chosen as the research object.Pendant damages were set with different quantity and position and the natural frequency and modal shape of stone panels under different circumstances are measured.The results show that:i)the natural frequency of the panel is correlated with the degree of connection damage,and the panel with relatively low natural frequency has a higher risk of falling.ii)the panel modal shape is correlated with the damage position of the connection,and the relative amplitude of the damage node is large.At the same time,the laser vibration frequency method is put forward to improve the efficiency of curtain wall on-site detection,and the influence of test point selection on the accuracy of detection was studied.