采用脉冲红外成像法的表面下暗藏物蓄热系数的测量

Thermal effusivity measurement of subsurface heterogeneous materials using pulsed thermography

近年来,脉冲红外成像无损评估方法已成功应用于航空航天、汽车制造、新材料等领域。但是对于很多应用,仅发现材料中存在缺陷是不够的,还需要对表面下缺陷热特性进行识别。实验设计制作了一个不锈钢平底孔试件,为了模拟表面下不同性质的暗藏物,在平底孔内分别埋入水、油、石蜡及空气。在试件表面施加均匀脉冲面热源后,试件表面及表面下暗藏物的热物理特性将影响热波的传导。提出了一种使用脉冲红外成像技术测量均匀固体材料下暗藏物质蓄热系数的实验方法。描述并分析了基于两层结构的一维热传导模型和界面热反射系数的计算方法,设计并进行了验证实验,通过对实验获得的材料表面温度变化的热图序列进行处理和分析,计算得到试件中不同暗藏物质的蓄热系数。

Pulsed thermography can be used to recognize the characterizations of surface hidden heterogeneities. In order to simulate the situation of hidden heterogeneities, a self-designed 20 mm thick stainless steel plate was machined with eight circular holes on the back side, and the holes were intentionally filled with different materials： water, oil, air and wax. The experimental method of pulsed thermography was provided to measure the thermal effusivity of heterogeneous materials, which were hidden in a uniform solid. For a two-layer sample, a theoretical 1-dimensional model of temperature evolution with time after excitation was presented and analyzed. A practical data processing criteria based on the theoretical 1-dimensional model was given for acquired IR image sequences after a heating pulse applied on the surface of the stainless steel. At last, the calculation results were deduced for four different materials in one stainless steel samples and compared with known characteristics of materials. It is shown that the proposed method can be used for non-destructive characterizations and identifications of subsurface defects.