薄壁试件脉冲热像法深度检测模型分析

Analysis of depth testing model for thin board specimen in pulsed thermography

脉冲热像法作为红外热像检测中具有定量分析能力的方法,其主要检测模型温差函数法在薄壁试件的缺陷深度检测时存在失效问题.为找出建模过程中的缺陷,以理想脉冲激励下一维有限形式的解析解替代原温差函数模型中的近似解,在温差曲线和温差导数曲线中,对模型中的核心参数峰值温差时间和峰值斜率时间的使用特性进行了比较分析.结果显示:峰值温差时间由参考点决定,而不由测试点决定,峰值温差时间不具备对缺陷深度的定量检测能力;峰值斜率时间的适用范围受到测试点与参考点实际深度之比的限制,根据给出的适用性判据公式求得该比值的上限在0.5附近,判据公式可作为使用峰值斜率时间的理论依据.

Pulsed thermography（PT） is always considered as a quantitative testing approach in infrared thermal imaging.One of its main models called temperature-contrast function（TCF） method is usually found invalidated in defect depth measurement when meets a thin sample.To exhibit the existing fault during TCF modeling,one-dimensional finite analytical solutions were used to carry out calculations instead of the approximate solution adopted in original TCF model under an ideal impulse excitation.Two kernel parameters,named as peak temperature-contrast time（PCT） and peak temperature-contrast slope time（PST）,were detailedly analyzed both in temperature-contrast curve and its derivative line.Comparison was made in their detecting abilities.The results show that PCT is governed by background＇s depth,not by test point＇s depth,so this parameter isn＇t suitable for a quantitative test;and PST is also manifested to have service restriction in a depth ratio between the two points（test point/reference point）.The upper limit of this depth ratio（approximately 0.5） was obtained by a criterion equation as a theoretical reference when PST was chosen in applications.