Search

赤外線応力測定は、非接触で、かつ、その場での観察が可能な非破壊評価手法の一つとして、CFRP(炭素繊維強化プラスチック)に適用されてきている。この応力測定を定量化する場合に必要となる1方向CFRP材の熱弾性係数すなわち応力変化と温度変化の係数を、赤外線応力画像システムを用いて測定すると共に、支配方程式に基づく理論的方法で得た値と比較を行い、測定値の妥当性を検討して、良好に一致する結果を得た。この過程で、80度C程度までの温度域では、熱膨張係数の温度依存性と比熱の温度依存性は打ち消し合うように作用し、CFRPの赤外線応力測定に有利な状況となっていることも判明した。次に、一般的に構造物に応用される形態である多方面に積層されたCFRP積層板に対する赤外線応力測定について、主に板厚方向の熱伝導の考慮の必要性を実験・解析の比較により検討した。この結果、積層板の各層での熱弾性効果による発生熱量の違いにより生じる板厚方向の熱伝導を考慮する必要のある場合があることが判明した。更に、実際の測定に際して影響を及ぼす要因である位相差の原因についても検討した。また、CFRP試験片レベルでの非破壊評価へ適用したいくつかの事例について記述した。, The infrared stress measurement technique was applied to the qualitative measurement of stress in Carbon Fiber Reinforced Plastic (CFRP) composites; the main advantages of this measurement method being its in-situ and non-contact nature. As a first step, thermoelastic constants were obtained for unidirectional CFRP (UD-CFRP) using the infrared stress measurement system. The resulting values were compared with thermoelastic constants derived using basic equations. As a consequence, the reliability of the measured thermoelastic constants was established and the effectiveness of this measurement system for quantitative stress measurement was confirmed. The temperature dependency of the transverse coefficient of thermal expansion and specific heat at constant stress in UD-CFRP were also demonstrated to have a tendency to cancel one another out so as to decrease the temperature dependency of the thermoelastic constant. Such a finding was considered to be an advantage of the infrared stress measurement technique for CFRP. In addition, other influential factors on measurement were examined. Regarding the infrared stress measurement for multi-ply CFRP laminates, one important issue is to evaluate the effect of heat conduction from internal plies where heat is produced as a result of the thermoelastic effect. Although the heat flux from internal plies as a result of the thermoelastic effect and applied loading has the same frequency, the infrared stress measurement system allows the surface temperature amplitude to be synchronized with the loading. The heat conduction effect for multi-ply CFRP laminates was evaluated numerically based on an analytical equation and FEA (Finite Element Analysis). These calculated values were compared with those obtained from infrared stress measurement. A high degree of coincidence between theoretical, FEA, and experimental results was obtained. It was clearly shown that thermal conduction must be considered in the infrared stress measurement of multi-ply CFRP should the surface layer be a ply with a low thermoelastic constant. Finally, some examples of applications of this technique to the non-destructive evaluation of CFRP laminates have also been presented., 資料番号: AA0001987000, レポート番号: NAL TR-1396