Kenichi Hirai

A Challenge of Modeling Thermo-Mechanical Response of Silica-Phenolic Composites under High Heating Rates

We have been building up a brand new ablation analysis code which is intended to predict simultaneously thermo-chemical and thermo-mechanical response of the SilicaPhenolic (SiFRP) ablator. In this paper, the model is applied to the RTG tests, FTE tests and the laser heating tests for model validation. The comparison to the SiFRP’s actual thermomechanical behavior shows that the present model gives better match by introducing the dependence of the elastic coefficient on the pore pressure in the high temperature region.

Dual-Component Sensor Design for In Situ Ablation Measurement

In this study, a novel ablation sensor capable of measuring surface recession and thermal decomposition in an ablative heat shield was developed by implementing two measurement principles into a single sensor unit. The proposed dual-component ablation sensor includes a surface-recession sensor and char sensor. The surface-recession sensor was designed using an ablative rod with embedded optical fibers, and the char sensor was designed using polyimide tubes and resistive wire with a low-temperature coefficient. In application, the surface-recession sensor detects thermal-emission transitions from the ablative material to shock layer, and the char sensor acts as an electric circuit that changes its resistance as the polyimide tubes carbonize. In this study, the proposed ablation sensor was miniaturized for possible flight-measurement application. To test the operational principles of the proposed design, a prototype ablation sensor was embedded in a polyimide-impregnated carbon-based ablative material, and ...

In-Situ Measurement of Ablation Fronts of A Low Density Ablator With An Ablation Sensor

An ablation sensor which can measure receded and thermally decomposed fronts of an ablative heatshield is developed by implementing two measurement principles into a single sensor unit. Difficulties in our previously proposed prototype sensor are overcome by fabricating an ablative rod on which optical fibers can be placed, and by producing a resistive circuit composed only of a polymeric material and resistive wire with low temperature coefficients. The present ablation sensor is tested in an arcjet wind tunnel by embedding it into a polyimide impregnated carbon based ablative material. The results demonstrate that the two ablation fronts can be measured simultaneously by using the proposed sensor concept.

In Situ Ablation Measurement for an Ablative Heat Shield Using an Embedded Sensor

An ablation sensor which can measure surface recession and thermal decomposition in an ablative heat shield was developed. In this sensor, the two measurement principles are implemented into a miniaturized unit. For the surface-recession detection, an ablative rod with embedded optical fibers were used, and for the thermal decomposition rate measurement, polyimide tubes with resistive wire were adopted. During operation, the surface-recession sensor component detects thermal-emission transitions from the ablative material to shock layer, and the char sensor component works as an electric circuit that changes its resistance along with the polyimide tube’s carbonization. The proposed ablation sensor was tested in an arcjet experiment and results showed that the measurement principles for surface recession and thermal-decomposition rates were successfully demonstrated.

Post-Test Sample Analysis of Fiber Reinforced Plastic Using Arcjet

Coking phenomenon for silica fiber reinforced plastic(SFRP) exposed to aerodynamic heating is examined experimentally and numerically. The SFRP material with the nominal virgin density of 1.70 g/cm 3 is heated in an arcjet wind tunnel. The spatial distribution of in-depth gas permeability and material density is measured for post-test arcjet sample. Thermal response analysis is made by evaluating thermophysical parameters for the SFRP material. Comparison of the density and permeability distribution gives a fair agreement between measurement and calculation, suggesting that coking effect could be negligibly small for the case of the high density ablator examined in the present study. Nomenclature A : cross sectional area of unsealed portion of test specimen for permeability measurement