This paper presents an ultrasonic method for tracking the decomposition front in ablating silica-phenolic thermal protection system material. The method exploits diffuse ultrasonic backscatter from the material microstructure to account for the temperature-dependent change of the speed of sound. The method is demonstrated in a series of ablation tests performed at a heat flux of $1350{\mathrm{W}/\mathrm{cm}}^2$ provided by an oxy-acetylene torch. Validation of the method is performed using machining, ultrasound, and micro–computed tomography scanning of the ablated samples. The measurement error in all tests does not exceed 1 mm. Analysis of the data suggests that, during the active ablation phase, temperature rise in the virgin material zone is low and the speed of sound correction is not required, whereas the main advantage of the method comes during the heat soak-back phase. Performed thermo-acoustic characterization of silica phenolic shows a linear dependence between the speed of sound and temperature up to 210°C. This finding opens a way to use the backscatter for estimation of temperature distribution in the virgin material. Finally, the study presents the measurement of acoustic attenuation to provide a reference for the application of the method to additional thermal protection materials, except silica phenolic.

本文提出了一种超声方法，用于追踪烧蚀硅酚热防护体系材料中的分解前沿。该方法利用了材料微观结构中的扩散超声反向散射，可以解释声速随温度变化的情况。该方法在热通量为的条件下进行的一系列烧蚀测试中得到了证明。$1350{\mathrm{w\; ^}/\mathrm{厘米}}^{\mathrm{2个}}$由氧-乙炔炬提供。该方法的验证是通过对烧蚀样品进行机加工，超声和显微计算机断层扫描来进行的。所有测试中的测量误差均不超过1毫米。数据分析表明，在主动消融阶段，原始材料区域的温度升高较低，并且不需要进行声音校正的速度，而该方法的主要优势在于回热阶段。硅酚的热声表征显示出声速与最高210°C的温度之间存在线性关系。这一发现为利用反向散射估算原始材料中的温度分布开辟了一条途径。最后，