JP4150564B2

JP4150564B2 - Degradation evaluation method for fiber reinforced plastic and strength measuring device for fiber reinforced plastic

Info

Publication number: JP4150564B2
Application number: JP2002277397A
Authority: JP
Inventors: 崇二木; 幹男竹本
Original assignee: Ajinomoto Co Inc
Current assignee: Ajinomoto Co Inc
Priority date: 2002-09-24
Filing date: 2002-09-24
Publication date: 2008-09-17
Anticipated expiration: 2022-09-24
Also published as: JP2004117035A

Description

【０００１】
【発明の属する技術分野】
本発明は、非破壊検査に関し、詳しくは、簡便かつ正確に繊維強化プラスチックの劣化の程度を評価し得る方法および装置に関する。
【０００２】
【従来の技術】
繊維強化プラスチックを検査する従来技術として、アルミ繊維や炭素繊維のような導電性材料を埋め込み、電位差を測定する方法(例えば、特許文献１参照)、光ファイバーを埋め込み赤外線や可視光線で評価する方法(例えば、特許文献２参照)がある。しかし、これらの方法は特殊なファイバーを別途埋め込む必要があり、既に使用されている貯槽など既設の設備には適用しがたい。
【０００３】
また他の検査方法としてアコースティックエミッションを用いる方法(ASTM E1067-96)、超音波強度の減衰による方法(例えば、特許文献３、非特許文献１参照)がある。しかし、前者は液の増減を繰り返す必要があることから使用中の設備についての検査が不可能なこと、および検査費用が高価であること、後者は超音波の発信、受信手段の接触状態に測定結果が左右されやすいことなどの問題がある。このため繊維強化プラスチック製耐食貯槽の検査は未だに目視点検によるところが主であり、劣化状態の判断は推測によるところが多い。
【０００４】
このような状況の下、有機材料の劣化を目視によらず非破壊的に検査・判断する手法として、超音波発振手段と超音波受信手段とを有機高分子製物品の表面に設置し、超音波発振手段から発振された超音波が有機高分子製物品中を伝搬して超音波受信手段にて受信されるまでに要する伝搬時間を測定し、伝搬時間の経時的変化から有機高分子製品の劣化度を診断する方法が提案されている（例えば、特許文献４参照）。
【０００５】
【特許文献１】
特開昭60-044857号公報
【特許文献２】
特開2001-116687号公報
【特許文献３】
特開平7-301624号公報
【特許文献４】
特開平11-337532号公報
【非特許文献１】
プラスチックス, Vol. 41, No.11
【０００６】
【発明が解決しようとする課題】
上記特許文献４（特開平11-337532号公報）に記載の方法では、使用する超音波の種類を規定していない。しかし、波動の種類および周波数によっては、被検体の劣化している部位を超音波が透過しない可能性があるため、劣化を確実に推定できない可能性がある。また、繊維強化プラスチックの場合、内部に様々な方向で繊維が混在しており、波動の伝播や反射が不規則になり、波動の種類、周波数によっては、波動を検出しても劣化の程度を反映しない。
【０００７】
本発明は、上記の問題点を解決し、簡便に精度よく繊維強化プラスチックの劣化度を評価することを課題とする。
【０００８】
また、本発明は、繊維強化プラスチック製の薬液貯槽など使用中の既存設備において好適に用いることができる、繊維強化プラスチックの劣化度評価方法およびそのための装置を提供することを課題とする。
【０００９】
【課題を解決するための手段】
上記課題を解決するために本発明者らは鋭意研究を進めたところ、低周波数帯域での板波Ｓ₀モードの伝播速度が繊維強化プラスチックの強度と相関性があるなどの知見を見出し、さらに貯槽などの設備において上記板波を測定するに足る程度にまで強く励起させる簡便な機構を考案し、本発明を完成させた。すなわち、本発明は、次の通りである。
【００１０】
〔１〕被検体である繊維強化プラスチックでの板波Ｓ₀モードの群速度を測定し、予め求めておいた板波Ｓ₀モードの群速度と繊維強化プラスチックの強度との相関関係と照合し、被検体の強度から被検体の劣化度を評価する方法であり、前記板波Ｓ ₀ モードの群速度の測定は、実質的に前記被検体の板厚および前記板波Ｓ ₀ モードの周波数に依存せず前記被検体の弾性率および密度に依存する低周波数帯域における板波Ｓ ₀ モードの群速度を測定することを特徴とする、繊維強化プラスチックの劣化度評価方法。
〔２〕易折導電体を圧折して被検体である繊維強化プラスチックに板波を励起すると共に、易折導電体の圧折によりスイッチがオフとなる電気回路の電気的変化を検知して板波の励起時点（Ｔ₁）を特定し、
励起された板波を受信子で受信して、板波励起時点（Ｔ₁）から受信子に最初に振動が受信された板波受信時点（Ｔ₂）までに要した時間（Ｔ）を求め、板波の励起源から受信子までの距離（Ｌ）を時間（Ｔ）で除して、被検体での板波Ｓ₀モードの群速度を算出し、算出された被検体での板波Ｓ₀モードの群速度を、予め求めておいた板波Ｓ₀モードの群速度と繊維強化プラスチックの強度との相関関係と照合し、被検体の強度から被検体の劣化度を評価する、繊維強化プラスチックの劣化度評価方法。
〔３〕易折導電体が、黒鉛を主成分とする棒状の導電体である、上記〔２〕に記載の繊維強化プラスチックの劣化度評価方法。
〔４〕易折導電体が、シャープペンシルの芯である、上記〔２〕に記載の繊維強化プラスチックの劣化度評価方法。
〔５〕被検体である繊維強化プラスチックでの板波Ｓ₀モードの群速度を測定し、予め求めておいた板波Ｓ₀モードの群速度と繊維強化プラスチックの強度との相関関係と照合し、被検体の強度を求める方法であり、前記板波Ｓ ₀ モードの群速度の測定は、実質的に前記被検体の板厚および前記板波Ｓ ₀ モードの周波数に実質的に依存せず前記被検体の弾性率および密度に依存する低周波数帯域における板波Ｓ ₀ モードの群速度を測定することを特徴とする、繊維強化プラスチックの強度測方法。
〔６〕易折導電体を圧折して被検体である繊維強化プラスチックに板波を励起すると共に、易折導電体の圧折によりスイッチがオフとなる電気回路の電気的変化を検知して板波の励起時点（Ｔ₁）を特定し、
励起された板波を受信子で受信して、板波励起時点（Ｔ₁）から受信子に最初に振動が受信された板波受信時点（Ｔ₂）までに要した時間（Ｔ）を求め、板波の励起源から受信子までの距離（Ｌ）を時間（Ｔ）で除して、被検体での板波Ｓ₀モードの群速度を算出し、算出された被検体での板波Ｓ₀モードの群速度を、予め求めておいた板波Ｓ₀モードの群速度と繊維強化プラスチックの強度との相関関係と照合し、被検体の強度を求める、繊維強化プラスチックの強度測定方法。
〔７〕繊維強化プラスチックの被検体に板波を励起すると共に板波が励起した時点で電気回路をオフにする励起スイッチ手段と、前記励起スイッチ手段からの板波を受信する受信子と、演算処理を行う演算装置と、演算結果を表示する表示手段と、板波Ｓ₀モードの群速度と繊維強化プラスチックの強度との相関データが記憶された記憶手段と、を備え、前記励起スイッチ手段は、易折導電体と、易折導電体および被検体に接触する介在導電体とを有する電気回路を形成しており、易折導電体が圧折することにより、前記介在導電体を介して被検体に板波が励起されると共に、易折導電体が介在導電体から離れて当該電気回路のスイッチをオフにし、当該電気回路の電気的変化により板波励起時点（Ｔ₁）が検知され、
前記演算装置で、板波の励起時点（Ｔ₁）および板波が最初に受信子に到達した時点である受信時点（Ｔ₂）から、板波が励起源から受信子まで到達するのに要した時間（Ｔ）が算出され、さらに時間（Ｔ）と板波の励起源から受信子までの距離（Ｌ）とから、励起源から受信子まで伝達した板波のＳ₀モードの群速度を算出し、記憶手段内の相関データに照合して被検体の強度を算出する、
繊維強化プラスチックの強度測定装置。
〔８〕前記演算装置が、算出された被検体の強度を、予め定められた所定の基準値と比較して、被検体の劣化度を求める算出手段を有する、上記〔７〕に記載の繊維強化プラスチックの強度測定装置。
〔９〕易折導電体がシャープペンシルの芯であり、介在導電体が導電箔である、上記〔７〕または〔８〕に記載の繊維強化プラスチックの強度測定装置。
【００１１】
【発明の実施の形態】
本発明の繊維強化プラスチック（以下「ＦＲＰ」という）の劣化度評価方法は、被検体に板波を励起し、低周波数帯域での板波Ｓ₀モードの群速度Ｃｅを測定し、求められた群速度Ｃｅと被検体の強度との相関関係から被検体の劣化の程度を評価する。本発明により、ＦＲＰの劣化度評価方法、ＦＲＰの強度測定方法、板波Ｓ₀モードの群速度Ｃｅを測定する方法、およびこれらに用いられる装置が提供される。
【００１２】
図１は板波の説明図である。板波は板状の弾性体中を伝播する弾性波動であって、図１に示すようにＳモードすなわち対称モードと、Ａモードすなわち非対称モードの二つに大別でき、さらにそれぞれが無数の高次モードを有する。また、図２は、アルミニウムについて板波の群速度を計算した計算結果であり、板波の群速度の周波数および板厚に対する依存性を示すものである。
【００１３】
板波は、それぞれのモードが弾性率、密度、板厚、周波数に依存した群速度を示す。しかし、図２に示すように、板波Ｓ₀モードの群速度は、低周波数帯域において板厚、周波数によらずほぼ一定の群速度Ｃｅとなり（図２中Ｃｅの線上を楕円で印した部分）、材料の弾性率および密度のみに依存して速度が変わる。すなわち、この振動は、材料表面のみならず材料内部の弾性率や密度を反映して伝播し、かつ周波数によらずほぼ一定の群速度を示すという性質を有する。薬液貯槽などにおけるＦＲＰの劣化は、例えば薬液など腐食性物質による樹脂の加水分解などによって生じる。ＦＲＰの劣化は、破壊強さの低下とともに弾性率の低下を招き、この結果板波Ｓ₀モードの群速度も低下する。したがって、低周波数帯域での板波Ｓ₀モードの群速度を測定することにより、周波数や被検体の厚さの影響を最小限に抑え、より正確に被検体であるＦＲＰの強度を推定することができる。本発明においては、弾性率などの強度を表す指標としては、好ましくは曲げ強さ（試験方法：ＪＩＳＫ７０５５）などが用いられる。曲げ強さは、ＦＲＰの強度を表す指標とし得るものであり、また試験片が反っていても試験可能であり、例えば円筒状貯槽などのように側筒部が平坦ではないものからも試験片を容易に調製することができる。
【００１４】
予め様々な強度を有するＦＲＰ試験片を用いて、低周波数帯域での板波Ｓ₀モードの群速度と、曲げ強さなどで表される強度との相関関係を求めておくことにより、被検体についての上記群速度を測定して、被検体の強度を求めることができる。より具体的には、例えば、新品の試験片や意図的に劣化させた試験片、または使用済みのＦＲＰ製貯槽などから切り出した試験片などの繊維強化プラスチックの曲げ強さおよび低周波数帯域における板波Ｓ₀モードの群速度の相関を求めておく。そして、被検体での低周波数帯域における板波Ｓ₀モードの群速度を求め、先にも求めた相関関係から被検体の曲げ強さが求められる。さらに、被検体の曲げ強さを、本来要求される所定の曲げ強さまたは新品の曲げ強さなどと比べることにより、被検体の劣化の程度、すなわち劣化度を推定することができる。
【００１５】
本発明のＦＲＰ劣化度評価方法は、ＦＲＰ製の耐食貯槽などの劣化度評価に好適に用いることができる。ＦＲＰ材料の劣化は主に薬液に接触する貯槽の内表面から生じる。したがって、例えば、表面波を測定した場合、表面波は表面の弾性率、密度のみに依存するため、板波の励起、検出は劣化した内表面で行わなければ劣化を充分に推定することができない。すなわち、この場合には、貯槽内に試験者が入らなければならないことになるのが殆どである。また、縦波超音波を用いるとＦＲＰのような複合材料の場合には、内部の層界面で反射が生じ、受信波の判別が難しい。
【００１６】
これに対して、本発明は低周波数帯域における板波Ｓ₀モードを用いており、この弾性波は材料の厚さ方向全てに伝播するため、板波の励起、検出は材料の内外表面のいずれで行ってもよい。すなわち、貯槽で試験を行う場合、貯槽の外表面で板波の励起・受信を行って測定しても貯槽を構成するＦＲＰの劣化度を的確に把握することができる。したがって、本発明の方法によれば、劣化度評価試験を行うために、貯槽の内容物を抜き出し内部に試験者が入って試験を行わずとも、貯槽の外側から測定作業をして劣化度評価を的確に行うことができる。
【００１７】
また、図２に示されるように、低周波数帯域での板波Ｓ₀モードの群速度Ｃｅは、板波の中で最も伝播速度が速い。したがって、最初に受信された波動（以下、「初動波」という場合がある）をＣｅと判定してよく、複数の波動の中から容易に目的の波動を検出できる。
【００１８】
上記のように、本発明のＦＲＰ劣化度評価方法では、低周波帯域での板波Ｓ₀モードの群速度Ｃｅを測定する。板波Ｓ₀モードは比較的振幅の小さい弾性波動であり、励起には強力な励起手段が必要である。一般的に超音波などの弾性波動を発生させる手段としては圧電素子による方法があるが、圧電素子では、本発明の測定方法に適用できるほど充分な振幅で板波Ｓ₀モードを励起することは容易ではない。
【００１９】
そこで、本発明の群速度測定方法では、易折導電体を被検体に押しつけて圧折し、被検体に対して板波を励起する。易折導電体とは、試験者が被検体に押しつけることによって折れる程度の強度を持つ導電体のことである。易折導電体として好ましくは、黒鉛を主成分とする棒状体または針状体などが挙げられ、特に好ましくは、シャープペンシルの芯などが挙げられる。シャープペンシルの芯は上記のように圧折することにより板波を励起することができるものであり、かつ製品として入手が容易で品質の安定性もある。また、針状体またはシャープペンシルの芯であれば音源の入力点が小さいので板波の群速度を測定において誤差を小さくすることができる。
【００２０】
さらに、本発明における群速度測定方法では、上記のように板波を励起させると共に板波の励起時点を検知するために、易折導電体が圧折されることによりスイッチがオフとなる電気回路を備える励起スイッチ手段が用いられる。励起スイッチ手段は、易折導電体と、易折導電体および被検体に接触する介在導電体とを有する電気回路で構成される。介在導電体としてはアルミ箔などの金属泊を好適に用いることができる。アルミ箔などのような導電箔は薄いため、易折導電体が折れた際に生じる衝撃を被検体に十分に伝えることができる。
【００２１】
易折導電体を圧折することにより、前記介在導電体を介して被検体に板波が励起されると共に、易折導電体が介在導電体から離れて電気回路のスイッチがオフになり、その電気的変化を検知して、板波の励起時点（Ｔ₁）が特定される。電気的な変化の検知は、電気回路がオフにされたことを検知できる指標であれば特に限定されず、電圧、電流などを測定する手段を設けることにより容易に検知できる。すなわち、上記のような、励起スイッチ手段を用いることにより、簡便に板波を発生させることができ、またその励起時点の特定も容易にかつ正確に行うことができる。
【００２２】
励起された板波は受信子で受信する。上記のとおり、板波のうち低周波数帯域のＳ₀モード波の伝播速度が最も速い。したがって、受信子に最初に振動が受信された板波を低周波数帯域として検知する。そして、板波の発生時点（Ｔ₁）から受信時点（Ｔ₂）までの時間（Ｔ）と、板波の励起源から受信子までの距離（Ｌ）とを求める。より具体的には、易折導電体と介在伝導体の接触点が板波の励起源であり、励起源から受信子の中心までの距離を（Ｌ）とする。以下の式（I）により低周波数帯域における板波Ｓ₀モードの群速度Ｃｅが求められる。
Ｃｅ＝Ｌ／Ｔ・・・（I）
【００２３】
被検体での板波Ｓ₀モードの群速度を、予め求めておいた板波Ｓ₀モードの群速度と繊維強化プラスチックの強度との相関関係と照合し、被検体の強度から被検体の劣化度を評価する。
【００２４】
本発明のＦＲＰ劣化度評価方法が好ましく適用される繊維強化プラスチックとしては、例えば、ビスフェノール型ビニルエステル樹脂、ノボラック型ビニルエステル樹脂、イソフタル酸ポリエステル樹脂、フェノール樹脂、フラン樹脂などが挙げられる。また、ＦＲＰに用いられる強化繊維としては、ガラス繊維、炭素繊維などが例示される。さらに、ＦＲＰの製造方法としては、フィラメントワインディング法、ハンドレイアップ法などが例示される。
【００２５】
次に、本発明の一実施形態について図面を参照しつつより具体的に説明する。図３は、板波Ｓ₀モードの検知装置を示す図である。図３に示す板波Ｓ₀モードの検知装置は、アルミ箔２、棒状黒鉛３、直流電源５、抵抗６、Ａ／Ｄコンバーター７、受信子８、波形表示装置１０からなり、繊維強化プラスチック材料１が被検体のＦＲＰ板である。
【００２６】
まず、板波Ｓ₀モードの検知対象とする被検体である繊維強化プラスチック材料１に対し、アルミ箔２を密着させる。棒状黒鉛３をアルミ箔に接触させ、棒状黒鉛３、箔２、直流電源５および抵抗６からなる回路を形成する。抵抗６の両端に作用する電圧Ｖ₁をＡ／Ｄコンバーター７で測定する。箔の上で棒状黒鉛３を圧折し、板波を発生させる。板波発生点である棒状黒鉛３の先端から任意の距離Ｌだけ離れた地点に設置した受信子８により板波を電圧値Ｖ₂として検出し、Ａ／Ｄコンバーター７で測定する。Ａ／Ｄコンバーター７を介して得られたＶ₁、Ｖ₂は波形表示装置１０に表示される。
【００２７】
図４は、波形表示装置に表示される板波の励起、受信信号を示す図である。棒状黒鉛３を圧折すると、図３に示す繊維強化プラスチック材料1に板波が生じると共に、回路２−３−６−５が切断されるため、電圧Ｖ₁が降下する。したがって、電圧Ｖ₁が降下しはじめる時間Ｔ₁は、棒状黒鉛３が圧折し、板波が励起された時間であると判断できる。
【００２８】
棒状黒鉛３の圧折で様々なモードの板波が発生する。板波はそれぞれのモードにおいて、材料の弾性率、厚さおよび周波数に依存する群速度を示すが、このうち低周波数帯域におけるＳ₀モードは板波として最も速く、かつ厚さ、周波数によらず材料の弾性率のみに依存するほぼ一定の群速度Ｃｅを示す。したがって、板波Ｓ₀モードの低周波数成分が受信子８に最初に速度Ｃｅで到達する。
【００２９】
すなわち、図４中、受信子８から発生した信号Ｖ₂の電圧が変化しはじめる時間であるＴ₂は、板波Ｓ₀モードの低周波数成分が受信子８に到達する時間であると判断できる。したがって、棒状黒鉛３の先端と受信子８の中心との間の距離をＬとすると、板波Ｓ₀モードの低周波数成分の群速度Ｃｅは次式（I'）より求められる。
Ｃｅ＝Ｌ／（Ｔ₂−Ｔ₁）・・・・・・・（Ｉ'）
波形表示装置１０のモニターには、Ｔ₁、Ｔ₂、Ｔ、Ｌ、Ｃｅの各データが表示される。
【００３０】
図５に示す装置は、本発明のＦＲＰの強度測定装置であり、図３の検知装置と異なる点を中心に説明する。図５の装置では、板波の励起手段として、シャープペンシル４が用いられ、シャープペンシルの芯４１を圧折して板波を励起させる。また、図５の装置では、演算装置９、記憶装置１１、表示モニター１２を備える。Ａ／Ｄコンバーター７からの信号は演算装置９に入力され、群速度Ｃｅが算出される。さらに演算装置９では、算出された群速度Ｃｅが、記憶装置１１に記憶されているＦＲＰの曲げ強度と群速度Ｃｅとの相関関係と照合され、被検体１の曲げ強度が算出される。また、演算装置９では、予め、望ましい曲げ強度または新品のＦＲＰ試験片の曲げ強度などを基準値として記憶装置１１に入力しておき、これと実測から求められた被検体１の曲げ強度を対比して、被検体１の劣化度を求めることができる。所定の基準値以下、例えば新品のＦＲＰ試験片の５０％以下の強度しかないものは交換する必要があるというように、判定手段を設けることもできる。演算の結果、劣化度などのデータは表示モニター１２に表示される。
【００３１】
図３および図５に例示されるように、本発明の装置は、簡便なものであり、携帯が容易である。したがって、屋外での測定などにも好適に用いることができる。
【００３２】
次に、群速度ＣｅからＦＲＰの劣化度を判定する基準の設定方法について、ＦＲＰ製耐食貯槽を具体例として挙げて説明する。本発明者は、使用済みである繊維強化プラスチック製耐食貯槽から切り抜いた試験片および新規に作成した繊維強化プラスチック製試験片など、複数の繊維強化プラスチック製の試験片１〜２１を用意し、図５に示した装置を用い、これら試験片における群速度Ｃｅを測定した。表１中、試験片９〜２１については貯槽に貯められていた内容物を示す。また、表１中、「液相」とあるのは貯槽の液相部位から試験片を採取し、気相とあるのは貯槽の気相部位から採取したことを示す。
【００３３】
次に、上記試験片から短冊状に切り抜いた試験片に対しＪＩＳＫ７０５５に基づき曲げ試験を実施し、曲げ強さσｂを得た。ここで、繊維強化プラスチックは異方性材料であるので、強度、弾性率は繊維の配向方向の影響を受け、またこの影響により群速度Ｃｅも波動伝播方向により異なる。本試験では、板波の伝播方向、および曲げ試験片の長手方向を貯槽の側胴部の周方向となるようにした。表１には各種の試験片の種類と実験により得られたＣｅ、σｂを示す。また表１に示した結果の群速度Ｃｅと曲げ強さσｂをグラフに示した結果を図６に示す。
【００３４】
【表１】

【００３５】
ここで、表1に示したＦＲＰ製試験片は、樹脂の種類、ガラス繊維の積層方法（ガラス繊維の配向方向）、ＦＲＰの作成方法などが異なるものが含まれるが、図６よりＣｅとσｂはほぼ線形の関係、すなわち次式（II）で表される関係となることが明らかとなった。
σｂ＝αＣｅ＋β ・・・・・（II）
【００３６】
ここで、式（II）のα、βは実験結果から求められる任意の常数である。例えば、表１に示した結果より最小二乗法にてα、βを求めた結果、α＝0.1725、β＝−485.05であり、式（II）は次式（III）の関係となる。
σｂ＝0.1725Ｃｅ − 485.05 ・・・・・（III）
【００３７】
劣化度について判断するための基準値を定めるには、例えば、薬液等の影響で強度が低下した場合の許容曲げ強さσｂｃを任意に定め、式（II）よりσｂｃに対応するＣｅの許容値Ｃｅｃを求める。具体的には、許容曲げ強さσｂｃを表１に示した新品の試験片１の半分である210.9MPaと定めると、式（III）より、Ｃｅｃ＝4037.1 m/sとなる。
【００３８】
図６に示されるように、ＦＲＰの種類、薬液槽内の内容物の種類などが異なっていても、Ｃｅとσｂとの相関関係は薬液貯槽の劣化度評価に十分対応し得る。なお、図６は例示であり、さらにデータの集積を重ねることにより、より精度の高い劣化度評価が可能である。
【００３９】
次に、稼働中である繊維強化プラスチック製耐食貯槽の劣化判定方法を説明する。図７に示すように、貯槽に図５の装置２、３、４、８で示した板波の群速度測定装置を設置する。ここで、群速度測定装置は貯槽の内表面、外表面のいずれに設置してもよいが、貯槽の外表面に設置すれば貯槽の在液時でも評価が可能である。また群速度測定装置の設置場所は、貯槽の在液時に液圧の影響により最も応力が集中するマンホールやノズル周辺が望ましい。
【００４０】
被検体である繊維強化プラスチック製耐食貯槽に設置された群速度測定装置より求められた群速度Ｃｅが、判定基準Ｃｅｃを上回る場合は継続使用可能、また下回る場合は継続使用不可と判断する。
【００４１】
【発明の効果】
本発明により、繊維強化プラスチックの劣化を、簡便かつ正確に評価することができる。また、本発明の方法及び装置は、繊維強化プラスチック製の耐食貯槽などの使用中の設備についての劣化度評価に極めて好適に用いることができる。また、本発明により、低周波数帯域の板波Ｓ₀モードの群速度を、簡便かつ正確に測定することができる。
【図面の簡単な説明】
【図１】板波についての簡単な説明図である。
【図２】アルミニウムを例として、板波の群速度の周波数および板厚に対する依存性を示す図である。
【図３】板波Ｓ₀モードの検知装置を示す図である。
【図４】板波励起手段と受信子から得られた信号を示す図である。
【図５】ＦＲＰの強度測定装置を示す図である。
【図６】繊維強化プラスチック製試験片の板波群速度Ｃｅ（音速）と曲げ強度σｂの相関を示す図である。
【図７】本発明を、被検体である繊維強化プラスチック製耐食貯槽について実施する様子を示す図である。
【符号の説明】
１繊維強化プラスチックからなる被検体
２導電性を有する箔（アルミ箔）
３棒状黒鉛
４シャープペンシル
４１板波発生手段であるシャープペンシルの芯
５直流電源
６抵抗
７Ａ／Ｄコンバーター
８板波受信子
９演算装置
１０波形表示装置
１１記憶装置
１２表示モニター
１５薬液貯槽
Ｃｅ板波Ｓ₀モードの低周波数帯域における群速度
Ｌ板波が伝播する距離であるシャープペンシルの芯４１の先端と受信子の中心間の距離
Ｖ₁ 抵抗６間に作用する電圧
Ｖ₂ 板波受信子８が発生する電圧
Ｔ板波Ｓ₀モードの伝播時間
Ｔ₁ 板波Ｓ₀モードが発生するシャープペンシルの芯４１が圧折した時刻
Ｔ₂ 板波Ｓ₀モードが板波受信子８に到達した時刻[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nondestructive inspection, and more particularly, to a method and an apparatus that can easily and accurately evaluate the degree of deterioration of a fiber reinforced plastic.
[0002]
[Prior art]
As conventional techniques for inspecting fiber reinforced plastics, a method of measuring a potential difference by embedding a conductive material such as aluminum fiber or carbon fiber (see, for example, Patent Document 1), and a method of evaluating an embedded optical fiber with infrared or visible light ( For example, see Patent Document 2). However, these methods need to embed special fibers separately and are difficult to apply to existing facilities such as storage tanks that are already in use.
[0003]
Other inspection methods include a method using acoustic emission (ASTM E1067-96) and a method using attenuation of ultrasonic intensity (see, for example, Patent Document 3 and Non-Patent Document 1). However, because the former requires repeated increase / decrease of liquid, it is impossible to inspect the equipment in use, and the inspection cost is expensive, and the latter is measured by the ultrasonic wave transmission and the contact state of the receiving means. There are problems such as the result being easily influenced. For this reason, the inspection of the fiber reinforced plastic corrosion-resistant storage tank is still mainly performed by visual inspection, and the judgment of the deterioration state is often based on speculation.
[0004]
Under such circumstances, as a method for nondestructively inspecting and judging deterioration of organic materials without visual observation, ultrasonic oscillating means and ultrasonic receiving means are installed on the surface of an organic polymer article. The propagation time required for the ultrasonic wave oscillated from the sound wave oscillating means to propagate through the organic polymer article and be received by the ultrasonic wave receiving means is measured. A method for diagnosing the degree of deterioration has been proposed (see, for example, Patent Document 4).
[0005]
[Patent Document 1]
JP 60-044857 A [Patent Document 2]
JP 2001-116687 [Patent Document 3]
Japanese Patent Laid-Open No. 7-301624 [Patent Document 4]
Japanese Patent Laid-Open No. 11-337532 [Non-Patent Document 1]
Plastics, Vol. 41, No.11
[0006]
[Problems to be solved by the invention]
In the method described in Patent Document 4 (Japanese Patent Laid-Open No. 11-337532), the type of ultrasonic wave to be used is not defined. However, depending on the type and frequency of the wave, there is a possibility that the ultrasonic wave may not pass through the deteriorated part of the subject, so there is a possibility that the deterioration cannot be reliably estimated. Also, in the case of fiber reinforced plastic, fibers are mixed in various directions inside, and the propagation and reflection of waves are irregular, and depending on the type and frequency of waves, the degree of deterioration can be reduced even if waves are detected. Does not reflect.
[0007]
This invention solves said problem and makes it a subject to evaluate the deterioration degree of a fiber reinforced plastic simply and accurately.
[0008]
Another object of the present invention is to provide a method for evaluating the degree of deterioration of fiber reinforced plastic and an apparatus therefor, which can be suitably used in existing facilities such as a chemical liquid storage tank made of fiber reinforced plastic.
[0009]
[Means for Solving the Problems]
The present inventors to solve the above problems was promoted extensive studies, the propagation speed of the Lamb wave S ₀ mode at low frequency band found knowledge, such as there is correlation with the strength of the fiber reinforced plastic, further A simple mechanism has been devised to excite the plate wave in a storage tank or the like to the extent sufficient to measure the plate wave, and the present invention has been completed. That is, the present invention is as follows.
[0010]
(1) measuring the Lamb wave S ₀ mode group velocity of the fiber-reinforced plastic is a subject against a correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode In this method, the degree of degradation of the subject is evaluated from the strength of the subject , and the group velocity in the plate wave S ₀ mode is measured substantially by the plate thickness of the subject and the frequency of the plate wave S ₀ mode. characterized in that said measuring a group velocity of plate wave S ₀ mode in the low frequency band which depends on the elastic modulus and density of the object, the degradation evaluation method of a fiber reinforced plastic independent.
[2] Folding the easily foldable conductor to excite a plate wave in the fiber reinforced plastic, which is the subject, and detecting an electrical change in the electric circuit where the switch is turned off by the foldable conductor Specify the excitation time (T ₁ ) of the plate wave,
The excited plate wave is received by the receiver, and the time (T) required from the plate wave excitation time (T ₁ ) to the plate wave reception time (T ₂ ) at which the vibration is first received by the receiver is obtained. The plate wave S ₀ mode group velocity at the subject is calculated by dividing the distance (L) from the plate wave excitation source to the receiver by the time (T), and the plate wave at the calculated subject is calculated. the group velocity of the S ₀ mode, against the correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode, evaluating the deterioration degree of the object from the intensity of the subject, the fiber Degradation evaluation method for reinforced plastics.
[3] The method for evaluating the degree of deterioration of the fiber-reinforced plastic according to [2], wherein the easily foldable conductor is a rod-shaped conductor having graphite as a main component.
[4] The method for evaluating the degree of deterioration of the fiber-reinforced plastic according to [2], wherein the easily foldable conductor is a mechanical pencil core.
[5] measured Lamb wave S ₀ mode group velocity of the fiber-reinforced plastic is a subject against a correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode is a method for determining the intensity of the subject, the measurement of the group velocity of the plate wave S ₀ mode, essentially the said essentially independent on the thickness and the frequency of the plate waves S ₀ mode of the subject and measuring a group velocity of plate wave S ₀ mode in the low frequency band which depends on the elastic modulus and density of the object, the strength of the fiber reinforced plastic measuring method.
[6] Exciting the foldable conductor to excite a plate wave in the fiber reinforced plastic, which is the subject, and detecting an electrical change in the electrical circuit where the switch is turned off by the foldable conductor. Specify the excitation time (T ₁ ) of the plate wave,
The excited plate wave is received by the receiver, and the time (T) required from the plate wave excitation time (T ₁ ) to the plate wave reception time (T ₂ ) at which the vibration is first received by the receiver is obtained. The plate wave S ₀ mode group velocity at the subject is calculated by dividing the distance (L) from the plate wave excitation source to the receiver by the time (T), and the plate wave at the calculated subject is calculated. the S ₀ mode group velocity, against the correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode, obtains the intensity of the subject, the strength measuring method of the fiber-reinforced plastic.
[7] Excitation plate means for exciting a plate wave to a fiber reinforced plastic object and turning off the electric circuit when the plate wave is excited; a receiver for receiving the plate wave from the excitation switch means; an arithmetic unit that performs processing, and display means for displaying the calculation results, a storage unit correlation data between the intensity of the group velocity and the fiber-reinforced plastic plate wave S ₀ mode is stored, wherein the excitation switching means An electric circuit having an easily foldable conductor and an interposable conductor in contact with the easily foldable conductor and the subject. As the plate wave is excited in the specimen, the easily foldable conductor is separated from the intervening conductor to switch off the electric circuit, and the plate wave excitation time point (T ₁ ) is detected by the electrical change of the electric circuit,
In the arithmetic unit, it is necessary for the plate wave to reach the receiver from the excitation source from the excitation time (T ₁ ) of the plate wave and the reception time (T ₂ ), which is the time when the plate wave first reaches the receiver. And the group velocity of the S ₀ mode of the plate wave transmitted from the excitation source to the receiver is calculated from the time (T) and the distance (L) from the excitation source of the plate wave to the receiver (L). Calculate, and compare the correlation data in the storage means to calculate the intensity of the subject,
Fiber reinforced plastic strength measurement device.
[8] The fiber according to [7] , wherein the arithmetic device includes a calculation unit that compares the calculated intensity of the subject with a predetermined reference value determined in advance to obtain a degree of deterioration of the subject. Strength measuring device for reinforced plastic.
[9] The fiber-reinforced plastic strength measuring apparatus according to [7] or [8] above, wherein the easily foldable conductor is a mechanical pencil core and the intervening conductor is a conductive foil.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The method for evaluating the degree of degradation of the fiber reinforced plastic (hereinafter referred to as “FRP”) of the present invention was obtained by exciting a plate wave to a subject and measuring the group velocity Ce of the plate wave S ₀ mode in a low frequency band. The degree of deterioration of the subject is evaluated from the correlation between the group velocity Ce and the strength of the subject. The present invention, the deterioration evaluation method of FRP, the strength measuring method of the FRP, a method of measuring a group velocity Ce plate wave S ₀ mode, and the apparatus used in these are provided.
[0012]
FIG. 1 is an explanatory view of a plate wave. A plate wave is an elastic wave propagating in a plate-like elastic body, and can be broadly divided into an S mode, ie, a symmetric mode, and an A mode, ie, an asymmetric mode, as shown in FIG. It has the following mode. FIG. 2 is a calculation result of calculating the plate wave group velocity for aluminum, and shows the dependence of the plate wave group velocity on the frequency and plate thickness.
[0013]
The plate wave shows a group velocity in which each mode depends on the elastic modulus, density, plate thickness, and frequency. However, as shown in FIG. 2, the group velocity in the plate wave S ₀ mode is a substantially constant group velocity Ce regardless of the plate thickness and frequency in the low frequency band (the portion marked with an ellipse on the line of Ce in FIG. 2). ), The speed varies depending only on the modulus and density of the material. That is, this vibration propagates reflecting not only the surface of the material but also the elastic modulus and density inside the material, and exhibits a substantially constant group velocity regardless of the frequency. Degradation of FRP in a chemical storage tank or the like is caused by, for example, hydrolysis of a resin by a corrosive substance such as a chemical liquid. FRP degradation can lead to decrease in elastic modulus with decreasing fracture strength, the group velocity of this result Lamb wave S ₀ mode is also reduced. Thus, by measuring the group velocity of plate wave S ₀ mode in a low-frequency band, to minimize the effect of the thickness of the frequency and the subject, to estimate the FRP strength is more accurately a subject Can do. In the present invention, as an index representing strength such as elastic modulus, preferably bending strength (test method: JIS K7055) is used. The bending strength can be used as an index representing the strength of FRP, and can be tested even when the test piece is warped. For example, the test piece can be used even when the side tube portion is not flat, such as a cylindrical storage tank. Can be easily prepared.
[0014]
Using FRP specimens with pre different intensities, by previously seeking the group velocity of plate wave S ₀ mode in a low-frequency band, a correlation between the intensity represented by such as bending strength, the subject The above group velocity can be measured to determine the strength of the subject. More specifically, for example, a plate in a low frequency band and bending strength of fiber reinforced plastic such as a new test piece, a purposely deteriorated test piece, or a test piece cut out from a used FRP storage tank or the like. previously obtained correlation group velocity of the wave S ₀ mode. Then, a group velocity of plate wave S ₀ mode in the low frequency band in a subject, the bending strength of the specimen is determined from the correlation obtained in earlier. Further, the degree of deterioration of the subject, that is, the degree of degradation can be estimated by comparing the bending strength of the subject with a predetermined bending strength originally required or a new bending strength.
[0015]
The FRP deterioration degree evaluation method of the present invention can be suitably used for deterioration degree evaluation of an FRP corrosion-resistant storage tank or the like. The deterioration of the FRP material mainly occurs from the inner surface of the storage tank in contact with the chemical solution. Therefore, for example, when measuring a surface wave, the surface wave depends only on the elastic modulus and density of the surface. Therefore, unless the excitation and detection of the plate wave are performed on the deteriorated inner surface, the deterioration cannot be sufficiently estimated. . That is, in this case, it is almost always necessary for a tester to enter the storage tank. When longitudinal wave ultrasonic waves are used, in the case of a composite material such as FRP, reflection occurs at the inner layer interface, and it is difficult to discriminate received waves.
[0016]
In contrast, the present invention is a plate wave S ₀ mode in the low frequency band, for propagating the acoustic waves in all the thickness direction of the material, the excitation of the plate wave, detection inside or outside surface of the material You may go on. That is, when the test is performed in the storage tank, the deterioration degree of the FRP constituting the storage tank can be accurately grasped even if measurement is performed by exciting and receiving plate waves on the outer surface of the storage tank. Therefore, according to the method of the present invention, in order to conduct a deterioration degree evaluation test, the contents of the storage tank are extracted and a tester enters the inside to perform the measurement work from the outside of the storage tank and perform the deterioration degree evaluation. Can be performed accurately.
[0017]
Further, as shown in FIG. 2, the group velocity Ce plate wave S ₀ mode at low frequency band, most propagation speed is high in the plate wave. Therefore, the first received wave (hereinafter sometimes referred to as “initial wave”) may be determined as Ce, and the target wave can be easily detected from a plurality of waves.
[0018]
As described above, in the FRP deterioration evaluation method of the present invention measures the group velocity Ce plate wave S ₀ mode in the low frequency band. Plate wave S ₀ mode is a relatively small elastic wave amplitude, it is necessary strong excitation means for exciting. Generally, there is a method using a piezoelectric element as a means for generating an elastic wave such as an ultrasonic wave. However, in the piezoelectric element, it is not possible to excite the plate wave S ₀ mode with an amplitude sufficient to be applicable to the measurement method of the present invention. It's not easy.
[0019]
Therefore, in the group velocity measurement method of the present invention, the easy-folding conductor is pressed against the subject to be collapsed, and a plate wave is excited with respect to the subject. The easy-folding conductor is a conductor having a strength that can be broken when the tester presses against the subject. The foldable conductor is preferably a rod-like body or a needle-like body mainly composed of graphite, and particularly preferably a mechanical pencil core or the like. The mechanical pencil core can excite a plate wave by being folded as described above, and is easily available as a product and has stable quality. Moreover, since the input point of a sound source is small in the case of a needle-like body or a mechanical pencil core, an error can be reduced in measuring the plate wave group velocity.
[0020]
Furthermore, in the group velocity measurement method according to the present invention, an electric circuit in which the switch is turned off when the easily foldable conductor is collapsed to excite the plate wave and detect the excitation point of the plate wave as described above. Excitation switch means comprising The excitation switch means is composed of an electric circuit having an easy-folding conductor and an interposing conductor that contacts the easily-folding conductor and the subject. As the intervening conductor, a metal stay such as an aluminum foil can be suitably used. Since the conductive foil such as an aluminum foil is thin, the impact generated when the easily foldable conductor is broken can be sufficiently transmitted to the subject.
[0021]
By folding the foldable conductor, a plate wave is excited on the subject via the intervening conductor, the foldable conductor is separated from the interposable conductor, and the switch of the electric circuit is turned off. By detecting an electrical change, the plate wave excitation time (T ₁ ) is specified. The detection of the electrical change is not particularly limited as long as it is an index that can detect that the electrical circuit is turned off, and can be easily detected by providing means for measuring voltage, current, and the like. That is, by using the excitation switch means as described above, a plate wave can be easily generated, and the excitation point can be identified easily and accurately.
[0022]
The excited plate wave is received by the receiver. Above As, the fastest propagation speed of the S ₀ mode wave in a low frequency band of the plate wave. Therefore, the plate wave whose vibration is first received by the receiver is detected as a low frequency band. Then, the time (T) from the generation time (T ₁ ) of the plate wave to the reception time (T ₂ ) and the distance (L) from the excitation source of the plate wave to the receiver are obtained. More specifically, the contact point between the easily foldable conductor and the intervening conductor is a plate wave excitation source, and the distance from the excitation source to the center of the receiver is (L). Group velocity Ce plate wave S ₀ mode in the low frequency band is determined by the following formula (I).
Ce = L / T (I)
[0023]
The Lamb wave S ₀ mode group velocity in a subject, against a correlation between the intensity of the group velocity and the fiber-reinforced plastic pre Lamb had asked S ₀ mode, subject degradation in the intensity of the subject Assess degree.
[0024]
Examples of the fiber reinforced plastic to which the FRP degradation evaluation method of the present invention is preferably applied include bisphenol type vinyl ester resin, novolac type vinyl ester resin, isophthalic acid polyester resin, phenol resin, furan resin and the like. Examples of reinforcing fibers used for FRP include glass fibers and carbon fibers. Furthermore, examples of the method for producing FRP include a filament winding method and a hand lay-up method.
[0025]
Next, an embodiment of the present invention will be described more specifically with reference to the drawings. 3 is a diagram showing the detection device of the plate wave S ₀ mode. Lamb wave S ₀ mode of the sensing device shown in FIG. 3, the aluminum foil 2, the rod-shaped graphite 3, the DC power source 5, resistors 6, A / D converter 7, the receivers 8, made from the waveform display device 10, a fiber-reinforced plastic material Reference numeral 1 denotes a subject FRP plate.
[0026]
First, with respect to fiber-reinforced plastics material 1 is subject to be detected plate wave S ₀ mode, adhering the aluminum foil 2. The bar-shaped graphite 3 is brought into contact with the aluminum foil to form a circuit composed of the bar-shaped graphite 3, the foil 2, the DC power source 5 and the resistor 6. The voltage V ₁ acting on both ends of the resistor 6 is measured by the A / D converter 7. The bar-shaped graphite 3 is crushed on the foil to generate a plate wave. A plate wave is detected as a voltage value V ₂ by a receiver 8 installed at a point separated by an arbitrary distance L from the tip of the bar-shaped graphite 3, which is a plate wave generation point, and measured by the A / D converter 7. V ₁ and V ₂ obtained via the A / D converter 7 are displayed on the waveform display device 10.
[0027]
FIG. 4 is a diagram showing plate wave excitation and reception signals displayed on the waveform display device. When the bar-shaped graphite 3 is folded, a plate wave is generated in the fiber reinforced plastic material 1 shown in FIG. 3 and the circuit 2-3-6-5 is cut, so that the voltage V ₁ drops. Therefore, it can be determined that the time T ₁ when the voltage V ₁ starts to drop is the time when the bar graphite 3 is collapsed and the plate wave is excited.
[0028]
Plate waves of various modes are generated by the bending of the bar-shaped graphite 3. Plate wave in each mode, the elastic modulus of the material, exhibit group velocity which depends on the thickness and frequency, fastest as S ₀ mode Lamb wave in these low frequency band, and a thickness, regardless of the frequency It shows a substantially constant group velocity Ce that depends only on the elastic modulus of the material. Therefore, the low frequency component of the plate wave S ₀ mode first reaches the receiver 8 at the speed Ce.
[0029]
That is, in FIG. 4, T ₂ , which is the time when the voltage of the signal V ₂ generated from the receiver 8 starts to change, can be determined as the time for the low frequency component of the plate wave S ₀ mode to reach the receiver 8. . Therefore, when the distance between the tip of the bar-shaped graphite 3 and the center of the receiver 8 is L, the group velocity Ce of the low frequency component of the plate wave S ₀ mode is obtained from the following equation (I ′).
Ce = L / (T ₂ −T ₁ ) (I ′)
The T ₁ , T ₂ , T, L, and Ce data are displayed on the monitor of the waveform display device 10.
[0030]
The apparatus shown in FIG. 5 is an FRP intensity measuring apparatus according to the present invention, and will be described focusing on differences from the detecting apparatus of FIG. In the apparatus of FIG. 5, a mechanical pencil 4 is used as a plate wave excitation means, and the plate wave is excited by collapsing the core 41 of the mechanical pencil. 5 includes an arithmetic device 9, a storage device 11, and a display monitor 12. A signal from the A / D converter 7 is input to the arithmetic unit 9, and a group velocity Ce is calculated. Further, in the arithmetic unit 9, the calculated group velocity Ce is collated with the correlation between the bending strength of the FRP stored in the storage device 11 and the group velocity Ce, and the bending strength of the subject 1 is calculated. Further, in the arithmetic unit 9, a desired bending strength or a bending strength of a new FRP test piece is previously input as a reference value to the storage device 11, and this is compared with the bending strength of the subject 1 obtained from the actual measurement. Thus, the degree of deterioration of the subject 1 can be obtained. It is also possible to provide a judging means so that it is necessary to replace those having a strength of not more than a predetermined reference value, for example, 50% or less of a new FRP test piece. As a result of the calculation, data such as the degree of deterioration is displayed on the display monitor 12.
[0031]
As illustrated in FIGS. 3 and 5, the apparatus of the present invention is simple and easy to carry. Therefore, it can be suitably used for outdoor measurement and the like.
[0032]
Next, a reference setting method for determining the degree of FRP degradation from the group velocity Ce will be described using a FRP corrosion-resistant storage tank as a specific example. The present inventor prepared a plurality of test pieces 1 to 21 made of fiber reinforced plastic, such as a test piece cut out from a used fiber reinforced plastic corrosion-resistant storage tank and a newly created test piece made of fiber reinforced plastic. Using the apparatus shown in FIG. 5, the group velocity Ce in these test pieces was measured. In Table 1, about the test pieces 9-21, the content stored in the storage tank is shown. In Table 1, “Liquid phase” means that the test piece was collected from the liquid phase part of the storage tank, and “gas phase” means that it was collected from the gas phase part of the storage tank.
[0033]
Next, a bending test was performed based on JIS K7055 with respect to the test piece cut out in a strip shape from the above test piece to obtain a bending strength σb. Here, since the fiber reinforced plastic is an anisotropic material, the strength and elastic modulus are affected by the orientation direction of the fiber, and the group velocity Ce also varies depending on the wave propagation direction due to the influence. In this test, the propagation direction of the plate wave and the longitudinal direction of the bending test piece were set to be the circumferential direction of the side body portion of the storage tank. Table 1 shows the types of test pieces and Ce and σb obtained by experiments. FIG. 6 is a graph showing the group velocity Ce and the bending strength σb of the results shown in Table 1.
[0034]
[Table 1]

[0035]
Here, the FRP test pieces shown in Table 1 include those with different types of resins, glass fiber lamination methods (glass fiber orientation directions), FRP creation methods, and the like. From FIG. 6, Ce and σb It became clear that is a substantially linear relationship, that is, a relationship represented by the following formula (II).
σb = αCe + β (II)
[0036]
Here, α and β in the formula (II) are arbitrary constants obtained from experimental results. For example, as a result of obtaining α and β by the least square method from the results shown in Table 1, α = 0.1725, β = −485.05, and the formula (II) is represented by the following formula (III).
σb = 0.1725Ce-485.05 (III)
[0037]
In order to determine the reference value for determining the degree of deterioration, for example, an allowable bending strength σbc when the strength is reduced due to the influence of a chemical solution or the like is arbitrarily determined, and an allowable value of Ce corresponding to σbc from Equation (II) Find Cec. Specifically, when the allowable bending strength σbc is determined to be 210.9 MPa, which is half of the new test piece 1 shown in Table 1, Cec = 4037.1 m / s from the formula (III).
[0038]
As shown in FIG. 6, even if the type of FRP, the type of contents in the chemical solution tank, and the like are different, the correlation between Ce and σb can sufficiently correspond to the deterioration degree evaluation of the chemical solution storage tank. Note that FIG. 6 is an example, and by further accumulating data, it is possible to evaluate the degree of deterioration with higher accuracy.
[0039]
Next, a method for determining deterioration of a fiber-reinforced plastic corrosion-resistant storage tank that is in operation will be described. As shown in FIG. 7, the plate wave group velocity measuring device shown by the

devices

2, 3, 4, and 8 of FIG. 5 is installed in the storage tank. Here, the group velocity measuring device may be installed on either the inner surface or the outer surface of the storage tank, but if it is installed on the outer surface of the storage tank, the evaluation can be performed even when the storage tank is present. Also, the group velocity measuring device is preferably installed in the vicinity of a manhole or nozzle where stress is most concentrated due to the influence of the hydraulic pressure when the storage tank is present.
[0040]
When the group velocity Ce obtained from the group velocity measuring device installed in the corrosion-resistant storage tank made of fiber reinforced plastic, which is the subject, exceeds the determination criterion Cec, it is determined that continuous use is possible, and when the group velocity Ce is below, it is determined that continuous use is not possible.
[0041]
【The invention's effect】
According to the present invention, it is possible to easily and accurately evaluate deterioration of a fiber reinforced plastic. Moreover, the method and apparatus of the present invention can be used very suitably for evaluating the degree of deterioration of equipment in use such as a corrosion-resistant storage tank made of fiber reinforced plastic. Further, the present invention, the group velocity of plate wave S ₀ mode in the low frequency band can be easily and accurately measured.
[Brief description of the drawings]
FIG. 1 is a simple explanatory diagram of a plate wave.
FIG. 2 is a diagram showing the dependence of the plate wave group velocity on the frequency and plate thickness using aluminum as an example.
3 is a diagram showing the detection device of the plate wave S ₀ mode.
FIG. 4 is a diagram showing signals obtained from plate wave excitation means and a receiver.
FIG. 5 is a view showing an FRP intensity measuring apparatus.
FIG. 6 is a diagram showing a correlation between a plate wave group velocity Ce (sonic velocity) and a bending strength σb of a fiber-reinforced plastic test piece.
FIG. 7 is a diagram showing a state in which the present invention is carried out on a corrosion-resistant storage tank made of fiber reinforced plastic which is a subject.
[Explanation of symbols]
1 Subject made of fiber reinforced plastic 2 Conductive foil (aluminum foil)
3 Rod-shaped graphite 4 Mechanical pencil 41 Mechanical pencil core 5 as a plate wave generating means DC power supply 6 Resistance 7 A / D converter 8 Plate wave receiver 9 Arithmetic device 10 Waveform display device 11 Storage device 12 Display monitor 15 Chemical solution storage tank Ce Plate Group velocity L in the low frequency band of the wave S ₀ mode Distance between the tip of the mechanical pencil core 41 and the center of the receiver V _1, which is the distance that the plate wave propagates V _{1 The} voltage V ₂ plate wave receiver 8 has reached the time T _2, the plate wave S ₀ mode Lamb wave receiving element 8 the core 41 of the pencil is圧折the voltage T Lamb wave S ₀ mode propagation time T ₁ plate wave S ₀ mode occurs for generating Times of Day

Claims

Measuring the group velocity of plate wave S ₀ mode fiber-reinforced plastic is a subject against a correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode, the subject It is a method to evaluate the degree of deterioration of the subject from the intensity of
Measurement of group velocity of the plate wave S ₀ mode, in the low frequency band substantially the dependence on the elastic modulus and density of the subject without depending on the thickness and the frequency of the plate waves S ₀ mode of the subject plate wave S ₀ mode feature that deterioration evaluation method of a fiber reinforced plastic to measure the group velocity of.

The foldable conductor is crushed to excite a plate wave in the fiber reinforced plastic that is the subject, and an electrical change in the electric circuit that is turned off due to the foldable conductor fold is detected to detect the plate wave. Identify the excitation time point (T ₁ )
The excited plate wave is received by the receiver, and the time (T) required from the plate wave excitation time (T ₁ ) to the plate wave reception time (T ₂ ) at which the vibration is first received by the receiver is obtained. The plate wave S ₀ mode group velocity at the subject is calculated by dividing the distance (L) from the plate wave excitation source to the receiver by the time (T), and the plate wave at the calculated subject is calculated. the group velocity of the S ₀ mode, against the correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode, evaluating the deterioration degree of the object from the intensity of the subject, the fiber Degradation evaluation method for reinforced plastics.

The degradation-evaluating method for fiber-reinforced plastic according to claim 2, wherein the easily foldable conductor is a rod-shaped conductor mainly composed of graphite.

The degradation evaluation method of the fiber reinforced plastic according to claim 2, wherein the easily foldable conductor is a mechanical pencil core.

Measuring the group velocity of plate wave S ₀ mode fiber-reinforced plastic is a subject against a correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode, the subject is the strength of a determined Mel method,
The measurement of the group velocity in the plate wave S ₀ mode is substantially independent of the plate thickness of the subject and the frequency of the plate wave S ₀ mode and is low depending on the elastic modulus and density of the subject. and measuring a group velocity of plate wave S ₀ mode in the frequency band, the strength of the fiber reinforced plastic measuring method.

The foldable conductor is crushed to excite a plate wave in the fiber reinforced plastic that is the subject, and an electrical change in the electric circuit that is turned off due to the foldable conductor fold is detected to detect the plate wave. Identify the excitation time point (T ₁ )
The excited plate wave is received by the receiver, and the time (T) required from the plate wave excitation time (T ₁ ) to the plate wave reception time (T ₂ ) at which the vibration is first received by the receiver is obtained. The plate wave S ₀ mode group velocity at the subject is calculated by dividing the distance (L) from the plate wave excitation source to the receiver by the time (T), and the plate wave at the calculated subject is calculated. the S ₀ mode group velocity, against the correlation between the intensity of the group velocity and the fiber-reinforced plastic obtained beforehand had been plate wave S ₀ mode, obtains the intensity of the subject, the strength measuring method of the fiber-reinforced plastic.

An excitation switch means for exciting a plate wave to a fiber reinforced plastic object and turning off the electric circuit when the plate wave is excited, a receiver for receiving the plate wave from the excitation switch means, and performing arithmetic processing comprising an arithmetic unit, and display means for displaying the calculation results, a storage unit correlation data between the intensity of the group velocity and the fiber-reinforced plastic plate wave S ₀ mode is stored, and
The excitation switch means forms an electric circuit having an easily foldable conductor and an easily foldable conductor and an intervening conductor that comes into contact with the subject. with plate wave to the subject through the body it is excited, turns off the switch of the electric circuit Ekiorishirube collector is separated from the intermediate conductor plate wave excitation point by an electrical change of the electrical circuits (T ₁ ) Is detected,
In the arithmetic unit, it is necessary for the plate wave to reach the receiver from the excitation source from the excitation time (T ₁ ) of the plate wave and the reception time (T ₂ ), which is the time when the plate wave first reaches the receiver. And the group velocity of the S ₀ mode of the plate wave transmitted from the excitation source to the receiver is calculated from the time (T) and the distance (L) from the excitation source of the plate wave to the receiver (L). Calculate, and compare the correlation data in the storage means to calculate the intensity of the subject,
Fiber reinforced plastic strength measurement device.

The strength of the fiber reinforced plastic according to claim 7 , wherein the arithmetic device has a calculation unit that compares the calculated strength of the subject with a predetermined reference value that is determined in advance to obtain a degree of deterioration of the subject. measuring device.

The fiber reinforced plastic strength measuring device according to claim 7 or 8 , wherein the easy-folding conductor is a mechanical pencil core and the intervening conductor is a conductive foil.