JP3726067B2 - Ultrasonic flaw detection method and ultrasonic flaw detection apparatus - Google Patents

Description

【００１３】
また、本発明においては、前記被試験体が中ぐり軸であり、前記探触子の出力面を、次式に基づく座標点Ｔ_ijを統合して求めるものとすることができる；
【数５】

【００１４】
さらに、本発明においては、前記探触子の出力面と前記ターゲットポイントとの間を前記超音波が屈折する際における、前記小領域の各相互間の位相変化の差を調整するものとすることができる。
この場合、より高精度な探傷検査を実現できる。
【００１５】
本発明においては、次式を満たすように前記探触子の出力面を前記ターゲットポイントに近づけて、前記位相変化の差を調整するものとすることができる；
【数６】

【００１６】
本発明の超音波探傷装置は、被試験体に超音波を入射し被試験体から反射してくる反射波（エコー）を検出する探触子を備える超音波探傷装置であって、 前記探触子が、前記被試験体の検査面上のある点（ターゲットポイント）から、前記被試験体の超音波入射面を複数に分割した小領域を経由して、前記超音波が屈折しながら伝搬する方向を算出し、音響的距離が相対的に等しい点の座標を統合してなる出力面を有することを特徴とする。
【００１７】
本発明の超音波探傷装置においては、前記探触子の出力面と前記ターゲットポイントとの間を前記超音波が屈折する際に、前記小領域の各相互間の位相変化の差を調整する位相差調整手段をさらに備えるものとすることができる。
【００１８】
【発明の実施の形態】
以下、図面を参照しつつ説明する。以下の実施例では、本発明を鉄道車両の輪軸の探傷検査に適用した場合について説明する。
図１は、本発明に係る超音波探傷方法の概要を説明するための輪軸周りの断面図である。
図２（Ａ）は同探触子から発生した超音波の伝搬状態を説明するための軸方向断面図であり、図２（Ｂ）は径方向断面図であり、図２（Ｃ）は受信されるエコーの波形図である。
【００１９】
図１に示す輪軸１１は、車軸１２に車輪１３が圧入されたものである。図１では、車軸１２の端部側（ジャーナル部１２Ａ及び車輪圧入部１２Ｂ）を拡大して示している。ジャーナル部１２Ａは軸受け１４を介して車軸箱（図示されず）に取り付けられ、車輪圧入部１２Ｂには車輪１３が嵌合わされている。車輪圧入部１２Ｂの軸表面が輪座面である。本実施例の車軸１２は、中ぐり孔１５を有する中ぐり車軸である。中ぐり車軸は、例えば３００系新幹線以降の鉄道車両に用いられており、ばね下荷重を軽減できる、あるいは、探傷検査に好適である等の利点を有する。
【００２０】
図２（Ａ）及び（Ｂ）に分かり易く示すように、本発明に係る探触子は、出力面が３次元曲面状をした曲面振動子２３を備えている。この曲面振動子２３は、従来の探触子（図１４参照）と同様に、くさび材（シュー材）２５やダンパー材（図示されず）と一体化したものである。図１及び図２（Ａ）に示すように、曲面振動子２３の出力面から発生した超音波ビームは、くさび材２５を通って車軸１２内を斜めに進行する。そして、この超音波ビームは、車軸１２のキズ（探傷点）１２Ｘにおいて集束し、且つ、超音波の位相が揃うようになっている。そのため、曲面振動子２３で受信される反射エコーは、図２（Ｃ）に示すように、リンギングが少なく、クリアーな波形を得ることができる。
【００２１】
以下、このような３次元曲面状の出力面を有する曲面振動子２３の形状解析について述べる。
まず、図３を参照して、曲面振動子の形状設計法の概要について説明する。
図３は、本発明に係る曲面振動子の形状設計法を説明するための模式的斜視図である。
【００２２】
（ａ）最初に、次の（ａ１）〜（ａ３）の手順で、曲面振動子２３の出力面の各点と車軸１２表面の超音波ビームの集束点（ターゲットポイント；この場合キズ１２Ｘ）との音響的な距離が一致するように設定する。
（ａ１）車軸１２の内面にメッシュＭを切る（複数の小領域へ仮想的に分割する）。
（ａ２）メッシュＭの各点とターゲットポイント１２Ｘを結ぶ直線（図３中の点線）を考える。
（ａ３）この直線から、曲面振動子２３への超音波経路と伝搬時間を算出し、曲面振動子２３の出力面の曲面形状を求める。
【００２３】
（ｂ）次に、超音波ビームがターゲットポイント１２Ｘで反射するまでの伝搬経路を考え、拡散に伴う振幅の変化、屈折時の振幅変化・位相変化の差から、トータルとして振動子全面で位相が一致するように、振動子の形状を補正して最終的な曲面形状を算出する。
【００２４】
次いで、振動子の出力面の形状解析について詳しく説明する。本実施例では、前述の中ぐり車軸用の探触子の形状解析について述べる。
図４〜図１３は、本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
以下の説明では、超音波が波線理論にしたがって伝搬すると仮定して解析を進める。
【００２５】
まず、図４（Ａ）に示すように、中ぐり車軸内筒面上にトランスデューサー（探触子）の寸法程度の領域を設定し、前記（ａ）で述べたように、その領域をメッシュに分割する。そして、分割された各メッシュの中点とターゲットポイントとを通り、各メッシュの中点からの音響的距離が等しくなる点（すなわち伝搬時間が等しくなる点）の集合を求めて、これをトランスデューサーの形状とする。すなわち、図４（Ｂ）により詳細に示すように、車軸表面上にとったターゲットポイントを点Cとし、車軸内面に設けた各メッシュＭの中点を点Ｐ_ij（周方向ｉ番目、長手方向ｊ番目）とする。
【００２６】
トランスデューサーの一点Ｔ_ijから放射された超音波ビームが点Ｐ_ijを通り、点Ｃに到達するまでの伝搬時間ｔ_ijは、トランスデューサー前面の音響伝達媒質（シュー材）の音速をｖ_c、車軸の音速ｖ_sとすると、次の「数７」で表される；
【数７】

したがって、この伝搬時間ｔ_ijが任意の一定時間ｔ₀になるとすると、次の「数８」が得られる；
【数８】

この「数８」を満たす点の集合が、求めるトランスデューサーの形状（振動子の出力面形状）となる。
【００２７】
いま、車軸の内径をｒ_a、外径をｒ_b、基準点からターゲットまでの距離をｚ_b、メッシュの周方向間隔（ラジアン）をΔα、長手方向間隔（距離）をΔｚとし、点Ｐ_ijにおける法線ベクトルをｎ_ijとする。ターゲットポイントＣ、各メッシュの中点Ｐ_ij、法線ベクトルｎ_ij、各メッシュの中点からターゲットポイントまでのベクトルＰ_ijＣは、それぞれ次の「数９」で与えられる（図４（Ｂ）参照）；
【数９】

【００２８】
図５に示すように、直線ＰＣと法線ベクトルｎ_ijを含む面をＳとすると、トランスデューサーの一点Ｔ_ijから放射された超音波は、Ｓ面内で屈折する。このとき入射角をθ_i、屈折角をθ_rとすると、これらの角度の間にはスネルの法則から次式
【数１０】

の関係がある。ここで、直線ＰＣ、ＰＴの単位ベクトルをそれぞれｌ_ij、ｍ_ijとし、
【数１１】

とおく。
【００２９】
そして、これら単位ベクトルｌ_ij、ｍ_ijと法線ベクトルｎ_ijとの内積・を計算すると、次の「数１２」及び「数１３」の関係式が得られる；
【数１２】

【数１３】

【００３０】
さらに、「数１１」、「数１２」、「数１３」より
【数１４】

が得られるとともに、「数１２」、「数１４」より
【数１５】

が得られる。
【００３１】
また、「数１１」より、単位ベクトルｌ_ijの内積・として
【数１６】

が得られる。そして、「数１６」と「数１５」より
【数１７】

が得られるとともに、「数１７」と「数１０」より
【数１８】

が得られる。
【００３２】
次に、幾何学的にδ＜０でなければならないので、
【数１９】

となる。このとき、
【数２０】

より、γ＜０である条件を満たす。
【００３３】
また、「数１０」及び「数１８」より
【数２１】

となる。よって、次の「数２２」が得られる；
【数２２】

以上より、δ、γ、θ_iの全てが既知となり、単位ベクトルｌ_ijが求められる。
【００３４】
ここで、
【数２３】

とすると
【数２４】

であり、したがって「数８」より
【数２５】

となる。
【００３５】
以上よりベクトルＰ_ijＴ_ijが決まり、求めるＴ_ijの座標は
【数２６】

となる。
【００３６】
ここで求めたＴ_ijの座標、つまり設計すべきトランスデューサーの出力面の形状は、第一次近似的なもの（音響的な距離に基づいて設計したもの）である。そのため、さらに高精度の設計のためには、境界面での屈折時の位相変化の差を考慮する必要がある。そこで、キズをターゲットポイントとした場合の、受信振幅と位相変化の差を考慮したトランスデューサーの出力面の形状の補正について述べる。
【００３７】
（Ｉ）伝搬距離に伴う減衰
ここでは、トランスデューサーの一メッシュ点（ポイントトランスデューサー）から放射された超音波が球面波となって伝搬し、その後、キズで反射して再びトランスデューサーの同一点で受信した際の受信振幅について解析する。超音波振幅の減衰は、拡散による減衰、屈折時の減衰、及び、伝搬媒質による減衰等に関係するが、ここでは設計形状に関係しない伝搬媒質の減衰は無視して解析する。
【００３８】
反射ターゲットとして微小球反射源を考える。まず、球面波の拡散による振幅の減少について解析する。
超音波を集束する探触子としては、２種類のタイプが考えられる。一つは前述のシュー付きタイプであり、もう一つはシューなしで液体などの接触媒質に直接接触するタイプである。シュー付きのタイプは、検査時にシューと車軸の間に約０．２ｍｍ程度の油層のギャップを設けるが、このギャップは薄いので存在を無視する。
【００３９】
ポイントトランスデューサーから出たビームがターゲットに到達するまでの経路は、図６のように表すことができる。
ここで、最大入射角になる面上での超音波の拡がりを考える。トランスデューサーの一点から放射した超音波は、拡がりながら伝搬する。この拡がりの大きさは、シューと車軸との境界面において、弧ＡＢであるとする（図７（Ａ）参照）。さらに、車軸中を伝わった波が微小球反射源に到達したときの拡がりの大きさが弧ＣＤであるとする（図７（Ｂ）参照）。すると、スネルの法則により入射角θ_iと屈折角θ_rの間には、次の「数２７」が成り立つ；
【数２７】

【００４０】
「数２７」の両辺を微分すると、
【数２８】

であり、したがって
【数２９】

が成り立つ。
【００４１】
そこで、図７（Ａ）のように、虚像の探触子位置をＯ₁とし、Ｏ₁Ｂ＝ｒ₁´とすると
【数３０】

であり、扇Ｏ₁ＡＢ∽扇Ｏ₁Ａ´Ｂ´であるから
【数３１】

となる。
【００４２】
一方、入射角が最大となる面と垂直な面上では、超音波のみかけの入射角は０°となる。そのため、放射時の新たな超音波の拡がりはなく、図７（Ｂ）に示すように、扇ＯＣＤ∽扇ＯＣ´Ｄ´となる。したがって、微小曲面ＡＢＣＤ上での超音波の振幅をＡ₀とすると、微小球反射源における微小曲面Ａ´Ｂ´Ｃ´Ｄ´上での振幅Ａ₁は、
【数３２】

となる。ここで、Ｋ₁はシューから車軸への透過率である。
【００４３】
微小球反射源での反射、すなわち半球面上に散乱し、車軸の入射位置に戻ってきた超音波の振幅（これをＡ₂とする）は、球面状散乱であるので伝搬距離ｒ₂に反比例し、
【数３３】

となる（図８参照）。ここで、Ｋ₂は固体−空気境界面での反射率とする。
なお、微小球の半径は、理想的には小さいほど解析しやすいが、無限小にすると反射波の振幅が０になるので、ここでは簡単のため微小球の半径を単位の１とする。この微小球に入射した超音波は、上半球面上に散乱すると考え、上式「数３３」の比例関係を等号で関係付けることにする。すなわち、次式が成り立つ；
【数３４】

【００４４】
ここで、車軸からシューに透過する超音波の伝わりを考える。シューから車軸への透過の場合と同様に解析すると、探触子位置（探傷面からｒ₁の位置）における超音波の振幅（Ａ₃とする）は、
【数３５】

となる。ここで、弧Ｅ´Ｆ´と弧Ｇ´Ｈ´は、それぞれ振動子位置における最大入射角を含む面上、及び、最小入射角を含む面上での超音波の拡がりの大きさである（図９（Ａ）、（Ｂ）参照）。さらに、Ｋ₃は車軸からシューへの透過率である。
【００４５】
したがって、全行程における超音波の受信振幅は、
【数３６】

で与えられる。なお、この振幅Ａ₃は前述したように相対的な振幅を表している。
【００４６】
（ＩＩ）各境界面における透過率・反射率
前述と同様に、シュー付きのタイプのものでは、カップラント層の存在を無視する。しかし、カップラント層の存在を無視しても、シューと車軸は固体接触していないので、接触面で互いにすべりが許される。そのため、境界面でのせん断応力と接線方向変位の連続性はないものとする。
【００４７】
シューから固体境界面に縦波を入射した場合でもシューなしタイプと同様に扱え、図１０に示すように、反射波・透過波が発生する。ここで、入射角をθ_l1、縦波の屈折角をθ_l2、横波の屈折角をθ_t2とし、入射波（縦波）の音速をｖ_l1、透過波縦波の音速をｖ_l2、横波の音速をｖ_t2とする。そして、密度をρとし、Lameの定数をμ、λで表すと、次の「数３７」が得られる；
【数３７】

【００４８】
さらに、各波の反射率・透過率は、次の「数３８」で表すことができる；
【数３８】

したがって、横波の透過率Ｋ₁（＝Ｔｔ／Ｌｉ）は、
【数３９】

となる。
【００４９】
固体と気体の境界面に横波が入射した場合は、図１１に示すような反射波が発生する。このとき、各波の反射率は、次の「数４０」で表すことができる；
【数４０】

したがって、横波の反射率Ｋ₂（＝Ｔｒ／Ｔｉ）は、
【数４１】

となる。なお、ここでは微小球反射源に入射する場合を扱うので、入射角は常に０°（垂直入射）である。したがってＫ₂＝−１となる。
【００５０】
車軸からシューへと横波を入射した場合は、図１２に示すのような反射波・透過波が発生する。このとき、各波の反射率・透過率は、次の「数４２」で表すことができる；
【数４２】

この場合も、シューから車軸への入射と同様に、せん断応力と接線変位は連続でないとする。透過率（縦波）Ｋ₃（＝Ｌｔ／Ｔｉ）は、
【数４３】

となる。
以上で、Ｋ₁、Ｋ₂、Ｋ₃が決定できる。
【００５１】
（ＩＩＩ）位相変化
系としての透過率・反射率の総合特性をＫとし、その実数部をＫ_Re、虚数部をＫ_Imとする。ポイントトランスデューサー各点での受信振幅は、次の「数４４」で表すことができる；
【数４４】

【００５２】
「数４４」は、さらに
【数４５】

と表すことができる。なお、「数４５」において、Ｋ₀は系の透過率・反射率の総合特性値であり、αは系の総合位相変化の値である。いま、シュー内の波長（シューなしタイプではカップラント内での波長）をλ_cとすると、トランスデューサーのメッシュの各小領域での位相ずれを補正するためには、
【数４６】

だけトランスデューサーを近づければよい（図１３参照）。
【００５３】
なお、本実施例では、中ぐり軸を例に挙げて説明したが、本発明は通常の中実軸にも適用することが可能である。さらに、被検査物の形状や材質等に応じて、屈折時の位相変化の差も適宜補正することが可能である。
【００５４】
【発明の効果】
以上の説明から明らかなように、本発明によれば、探傷検出感度を向上し、
より高精度の探傷検査を行うことができる。
【図面の簡単な説明】
【図１】本発明に係る超音波探傷方法の概要を説明するための輪軸周りの断面図である。
【図２】図２（Ａ）は同探触子から発生した超音波の伝搬状態を説明するための軸方向断面図であり、図２（Ｂ）は径方向断面図であり、図２（Ｃ）は受信されるエコーの波形図である。
【図３】本発明に係る曲面振動子の形状設計法を説明するための模式的斜視図である。
【図４】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図５】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図６】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図７】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図８】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図９】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図１０】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図１１】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図１２】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図１３】本実施例に係る振動子の出力面の形状解析を説明するための説明図である。
【図１４】従来の探傷検査で用いられる探触子の一例を模式的に示す側面図である。
【図１５】図１５（Ａ）は同探触子から発生した超音波の伝搬状態を説明するための軸方向断面図であり、図１５（Ｂ）は径方向断面図であり、図１５（Ｃ）は受信されるエコーの波形図である。
【符号の説明】
１１ 輪軸 １２ 車軸
１２Ａ ジャーナル部 １２Ｂ 車輪圧入部
１３ 車輪 １５ 中ぐり孔
２１ 探触子 ２３ 曲面振動子
２５ くさび材（シュー材）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flaw detection method for examining the presence or absence of scratches on a test object using ultrasonic waves, and an ultrasonic flaw detection apparatus to which this flaw detection method is applied. In particular, the present invention relates to an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus that can improve the flaw detection sensitivity and perform a highly accurate flaw detection inspection.
[0002]
[Prior art and problems to be solved by the invention]
Conventional techniques and problems will be described by taking a flaw detection inspection of a wheel shaft of a railway vehicle as an example.
The wheel shaft of a railway vehicle is an important part that supports the entire vehicle. The wheel axle is an integrated body in which the left and right wheels are press-fitted into the axle. A vehicle equipped with a wheel shaft generates frictional force and minute relative slip at the fitting portion (wheel seat) between the wheel shaft and the wheel during operation. These factors can cause a decrease in fatigue strength and can cause cracks from the axle surface. In order to detect this crack at an early stage, the axle is regularly inspected.
[0003]
For the flaw detection inspection for the crack check, most of the conventional non-destructive methods using ultrasonic waves are performed as follows, for example.
FIG. 14 is a side view schematically showing an example of a probe used in a conventional flaw detection inspection.
FIG. 15A is an axial sectional view for explaining a propagation state of ultrasonic waves generated from the probe, FIG. 15B is a radial sectional view, and FIG. FIG.
[0004]
As shown in FIG. 14, the probe 1 includes a planar vibrator 3 made of a piezoelectric body. The flat vibrator 3 is attached to the inclined surface of the back portion of a wedge material (shoe material) 5 made of a synthetic resin such as acrylic. A damper material 7 made of a high specific gravity member such as tungsten is attached to the back surface of the planar vibrator 3.
[0005]
The probe 1 is used by placing the wedge material 5 against the surface of a device under test (boring axle) 10. At this time, oil is applied between the wedge material 5 and the surface of the DUT 10 (the inner surface of the bore of the axle) in order to improve the transmission of ultrasonic waves. When an electric pulse is applied to the planar vibrator 3 from a pulse generator (not shown), an ultrasonic beam is generated. The ultrasonic beam travels diagonally through the test object 10 through the wedge material 5. Then, the echo reflected from the scratch 10X of the device under test 10 returns to the probe 1 again to be converted into an electric signal and detected as an electric waveform.
[0006]
By the way, since the conventional probe 1 uses the planar vibrator 3, as shown in FIG. 15A, the generated ultrasonic beam is refracted on the inner surface of the bore of the axle 10 and then slightly spreads. Propagate. Further, since the inner surface of the boring hole has an arc shape, as shown in FIG. 15B, the refraction angle increases as the ultrasonic wave enters the outside of the axle 10, and the size of the probe 1 and the axle The degree of spreading of the ultrasonic beam on the axle surface varies depending on the inner diameter and the outer diameter of 10. Therefore, there are problems that the ultrasonic energy density is low and the flaw detection sensitivity is difficult to increase.
[0007]
Further, in the flaw detection inspection of the wheel seat surface of the axle 10, the press-fitting echo is reflected in addition to the scratch echo. This press-fitting echo is an echo reflected by a minute contact state between the axle and the wheel in the wheel seat. In the conventional planar vibrator 3, since the press-fitting echo is mixed with the scratch echo, the detected electrical waveforms are overlapped as shown in FIG. 15C. Therefore, it is difficult to distinguish between the press-in echo and the original scratch echo depending on how the press-in echo groups overlap. On the other hand, when the probe 1 is operated, in order to reduce the wave number, the damper material 7 is pasted on the back surface of the planar vibrator 3 to effect the damping, so that the reverberation of the vibration is immediately stopped. I am doing so. However, when damping is applied in this way, there arises a problem that the ultrasonic wave itself to be transmitted and received becomes weak.
[0008]
In order to distinguish the scratch echo from the press-in echo with high accuracy, it is useful to concentrate the ultrasonic beam to increase the detection sensitivity of the scratch echo and reduce the overlap of the waves of the press-in echo so as not to generate a large press-in echo.
The present invention has been made paying attention to the above-mentioned viewpoint, and an object thereof is to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus capable of improving flaw detection sensitivity and performing a highly accurate flaw detection inspection. .
[0009]
[Means for Solving the Problems]
In the ultrasonic flaw detection method as a premise of the present invention, ultrasonic waves are incident on a test object from a probe, and a reflected wave (echo) reflected from the test object is detected to detect the test object. an ultrasound flaw detection method, the Ru is three-dimensionally point focus the ultrasound at the test points of the test object.
[0010]
In the ultrasonic flaw detection method of the present invention, ultrasonic flaw detection is performed by detecting a reflected wave (echo) reflected from the test object by injecting ultrasonic waves from the probe to the test object. A method is provided in which a certain point (target point) on an inspection surface of the test object is set, an ultrasonic incident surface of the test object is divided into a plurality of small regions, and each small point is formed from the target point. Calculating the direction in which the ultrasonic wave propagates while being refracted through a region, obtaining the coordinates of points with relatively equal acoustic distances, and integrating the coordinates of the points to obtain the output surface of the probe; A probe having the output surface is used to focus the ultrasonic wave three-dimensionally at the target point.
[0011]
According to the present invention, the ultrasonic energy density can be increased and the flaw detection sensitivity can be improved by focusing the ultrasonic wave three-dimensionally at the flaw detection point (target point) of the test object. Accurate flaw detection inspection can be performed.
When the present invention is applied to a crack inspection of a wheel shaft of a railway vehicle, it is possible to increase the detection sensitivity of scratch echoes and reduce the overlap of waves of press-in echoes.
[0012]
In the present invention, the device under test may be an axis, and the output surface of the probe may be obtained by integrating points satisfying the following formula;
[Expression 4]

[0013]
In the present invention, the DUT may be a boring axis, and the output surface of the probe may be obtained by integrating coordinate points T _ij based on the following equation:
[Equation 5]

[0014]
Furthermore, in the present invention, when the ultrasonic wave is refracted between the output surface of the probe and the target point, a difference in phase change between the small regions is adjusted. Can do.
In this case, more accurate flaw detection inspection can be realized.
[0015]
In the present invention, the output surface of the probe is brought close to the target point so as to satisfy the following formula, and the difference in phase change can be adjusted;
[Formula 6]

[0016]
The ultrasonic flaw detector of the present invention is an ultrasonic flaw detector provided with a probe that detects a reflected wave (echo) that is incident on a test object and that is reflected from the test object. The child propagates while refracting the ultrasonic wave from a certain point (target point) on the inspection surface of the DUT through a small area obtained by dividing the ultrasonic incident surface of the DUT. A direction is calculated, and an output surface is formed by integrating coordinates of points having relatively equal acoustic distances.
[0017]
In the ultrasonic flaw detector according to the present invention, when the ultrasonic waves are refracted between the output surface of the probe and the target point, the difference in phase change between the small regions is adjusted. Phase difference adjusting means may be further provided.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, it demonstrates, referring drawings. In the following embodiments, a case where the present invention is applied to a flaw detection inspection of a wheel shaft of a railway vehicle will be described.
FIG. 1 is a cross-sectional view around the wheel axis for explaining the outline of the ultrasonic flaw detection method according to the present invention.
2A is an axial sectional view for explaining a propagation state of ultrasonic waves generated from the probe, FIG. 2B is a radial sectional view, and FIG. FIG.
[0019]
A wheel shaft 11 shown in FIG. 1 is obtained by press-fitting a wheel 13 into an axle 12. In FIG. 1, the end side (journal portion 12A and wheel press-fitting portion 12B) of the axle 12 is shown enlarged. The journal portion 12A is attached to an axle box (not shown) via a bearing 14, and a wheel 13 is fitted to the wheel press-fitting portion 12B. The shaft surface of the wheel press-fitting portion 12B is a wheel seat surface. The axle 12 of this embodiment is a boring axle having a boring hole 15. The boring axle is used in, for example, railway vehicles of the 300 series Shinkansen and later, and has advantages such as being able to reduce the unsprung load or being suitable for flaw detection inspection.
[0020]
2A and 2B, the probe according to the present invention includes a curved vibrator 23 whose output surface has a three-dimensional curved surface shape. The curved vibrator 23 is integrated with a wedge material (shoe material) 25 and a damper material (not shown), as in a conventional probe (see FIG. 14). As shown in FIGS. 1 and 2A, the ultrasonic beam generated from the output surface of the curved vibrator 23 travels obliquely in the axle 12 through the wedge material 25. The ultrasonic beam is focused at a flaw (flaw detection point) 12X of the axle 12 and the phases of the ultrasonic waves are aligned. Therefore, as shown in FIG. 2C, the reflected echo received by the curved vibrator 23 has little ringing and can obtain a clear waveform.
[0021]
Hereinafter, the shape analysis of the curved vibrator 23 having such a three-dimensional curved output surface will be described.
First, an outline of the shape design method of the curved vibrator will be described with reference to FIG.
FIG. 3 is a schematic perspective view for explaining the shape design method of the curved vibrator according to the present invention.
[0022]
(A) First, according to the following procedures (a1) to (a3), each point on the output surface of the curved vibrator 23 and the focal point of the ultrasonic beam on the surface of the axle 12 (target point; scratch 12X in this case) Are set so that their acoustic distances match.
(A1) The mesh M is cut on the inner surface of the axle 12 (virtually divided into a plurality of small areas).
(A2) Consider a straight line (dotted line in FIG. 3) connecting each point of the mesh M and the target point 12X.
(A3) From this straight line, the ultrasonic path and propagation time to the curved vibrator 23 are calculated, and the curved surface shape of the output surface of the curved vibrator 23 is obtained.
[0023]
(B) Next, the propagation path until the ultrasonic beam is reflected at the target point 12X is considered, and the phase of the entire surface of the vibrator as a whole is calculated from the difference in amplitude due to diffusion and the difference in amplitude / phase change during refraction. The final curved surface shape is calculated by correcting the shape of the vibrator so as to match.
[0024]
Next, the shape analysis of the output surface of the vibrator will be described in detail. In the present embodiment, the shape analysis of the above-described boring axle probe will be described.
4 to 13 are explanatory diagrams for explaining the shape analysis of the output surface of the vibrator according to the present embodiment.
In the following description, the analysis proceeds on the assumption that ultrasonic waves propagate according to the wave line theory.
[0025]
First, as shown in FIG. 4 (A), an area about the size of the transducer (probe) is set on the inner cylindrical surface of the boring axle, and the area is meshed as described in (a) above. Divide into Then, a set of points that pass through the midpoint of each divided mesh and the target point and have the same acoustic distance from the midpoint of each mesh (that is, the points at which the propagation times are equal) is obtained, and this is set as the transducer. The shape of That is, as shown in more detail in FIG. 4B, the target point taken on the axle surface is a point C, and the middle point of each mesh M provided on the axle inner surface is a point P _ij (i-th circumferential direction, longitudinal direction). jth).
[0026]
The propagation time t _ij until the ultrasonic beam radiated from one point T _{ij of the} transducer passes through the point P _ij and reaches the point C is the velocity of sound of the acoustic transmission medium (shoe material) in front of the transducer v _c , When the sound velocity v _s of the axle, it is expressed by the following "Equation 7";
[Expression 7]

Therefore, if this propagation time t _ij is an arbitrary fixed time t ₀ , the following “Equation 8” is obtained;
[Equation 8]

A set of points satisfying this “Equation 8” is a transducer shape to be obtained (an output surface shape of the vibrator).
[0027]
_Here , the inner diameter of the axle is r _a , the outer diameter is r _b , the distance from the reference point to the target is z _b , the mesh circumferential interval (radian) is Δα, the longitudinal interval (distance) is Δz, and the point P _ij Let n _ij be the normal vector at. The target point C, the midpoint P _{ij of} each mesh, the normal vector n _ij , and the vector P _ij C from the midpoint of each mesh to the target point are respectively given by the following “Equation 9” (FIG. 4B). reference);
[Equation 9]

[0028]
As shown in FIG. 5, when a plane including the straight line PC and the normal vector n _ij is S, the ultrasonic wave radiated from one point T _{ij of the} transducer is refracted in the S plane. At this time, when the incident angle is θ _i and the refraction angle is θ _r , the following equation is obtained between these angles from Snell's law:

There is a relationship. Here, the unit vectors of the straight lines PC and PT are defined as l _ij and m _ij , respectively.
[Expression 11]

far.
[0029]
Then, by calculating the inner product of the unit vectors l _ij and m _ij and the normal vector n _ij , the following relational expressions of “Equation 12” and “Equation 13” are obtained;
[Expression 12]

[Formula 13]

[0030]
Furthermore, from "Equation 11", "Equation 12", and "Equation 13"

From "Equation 12" and "Equation 14"

Is obtained.
[0031]
Further, from “Equation 11”, the inner product of unit vector l _ij is given by

Is obtained. From “Equation 16” and “Equation 15”,

From "Equation 17" and "Equation 10"

Is obtained.
[0032]
Second, geometrically δ <0, so
[Equation 19]

It becomes. At this time,
[Expression 20]

Therefore, the condition that γ <0 is satisfied.
[0033]
From “Equation 10” and “Equation 18”,

It becomes. Thus, the following “Equation 22” is obtained;
[Expression 22]

From the above, all of δ, γ, and θ _i are known, and the unit vector l _ij is obtained.
[0034]
here,
[Expression 23]

Then, [Equation 24]

Therefore, from [Equation 8], [Equation 25]

It becomes.
[0035]
From the above, the vector P _ij T _ij is determined, and the coordinates of T _ij to be obtained are:

It becomes.
[0036]
The coordinates of T _ij obtained here, that is, the shape of the output surface of the transducer to be designed is a first-order approximation (designed based on the acoustic distance). Therefore, in order to design with higher accuracy, it is necessary to consider the difference in phase change during refraction at the boundary surface. Therefore, the correction of the shape of the output surface of the transducer in consideration of the difference between the reception amplitude and the phase change when the scratch is the target point will be described.
[0037]
(I) Attenuation with propagation distance Here, the ultrasonic wave radiated from one mesh point (point transducer) of the transducer propagates as a spherical wave, and then is reflected by a scratch and again at the same point of the transducer. Analyze the received amplitude when receiving with. The attenuation of the ultrasonic amplitude is related to attenuation due to diffusion, attenuation during refraction, attenuation due to the propagation medium, and the like, but here, the attenuation of the propagation medium not related to the design shape is ignored and analyzed.
[0038]
Consider a microsphere reflection source as a reflection target. First, the decrease in amplitude due to spherical wave diffusion is analyzed.
There are two types of probes that focus ultrasonic waves. One is the above-mentioned type with a shoe, and the other is a type that directly contacts a contact medium such as a liquid without a shoe. In the type with a shoe, an oil layer gap of about 0.2 mm is provided between the shoe and the axle at the time of inspection. However, since this gap is thin, the existence is ignored.
[0039]
The path until the beam emitted from the point transducer reaches the target can be expressed as shown in FIG.
Here, the spread of the ultrasonic wave on the surface having the maximum incident angle is considered. The ultrasonic wave radiated from one point of the transducer propagates while spreading. The size of the spread is assumed to be an arc AB at the boundary surface between the shoe and the axle (see FIG. 7A). Furthermore, it is assumed that the magnitude of the spread when the wave transmitted through the axle reaches the microsphere reflection source is the arc CD (see FIG. 7B). Then, according to Snell's law, the following “Equation 27” holds between the incident angle θ _i and the refraction angle θ _r ;
[Expression 27]

[0040]
Differentiating both sides of “Equation 27”,
[Expression 28]

Therefore, [Equation 29]

Holds.
[0041]
Therefore, as shown in FIG. 7A, if the probe position of the virtual image is O ₁ and O ₁ B = r ₁ ′,

, And the because it is fan-O ₁ AB∽ fan O ₁ A'B' [number 31]

It becomes.
[0042]
On the other hand, the apparent incident angle of ultrasonic waves is 0 ° on a plane perpendicular to the plane having the maximum incident angle. Therefore, there is no spread of new ultrasonic waves at the time of radiation, and as shown in FIG. 7B, a fan OCD / fan OC′D ′ is obtained. Therefore, when the amplitude of the ultrasonic wave on the minute curved surface ABCD is A ₀ , the amplitude A ₁ on the minute curved surface A′B′C′D ′ in the microspherical reflection source is
[Expression 32]

It becomes. Here, K ₁ is the transmittance from the shoe to the axle.
[0043]
Reflection at the microsphere reflection source, that is, the amplitude of the ultrasonic wave scattered on the hemisphere and returned to the incident position on the axle (referred to as A ₂ ) is spherical scattering, and is therefore inversely proportional to the propagation distance r ₂ . And
[Expression 33]

(See FIG. 8). Here, K ₂ is the reflectance at the solid-air interface.
Note that the smaller the radius of the microsphere, the easier it is to analyze. However, when the radius is infinitely small, the amplitude of the reflected wave becomes 0. Therefore, for the sake of simplicity, the radius of the microsphere is set to 1. The ultrasonic wave incident on the microsphere is considered to be scattered on the upper hemisphere, and the proportional relationship of the above equation “Expression 33” is related by an equal sign. That is, the following equation holds:
[Expression 34]

[0044]
Here, let us consider the transmission of ultrasonic waves transmitted from the axle to the shoe. Analyzing in the same manner as in the case of transmission from the shoe to the axle, the amplitude of the ultrasonic wave (referred to as A ₃ ) at the probe position (position r ₁ from the flaw detection surface) is
[Expression 35]

It becomes. Here, the arc E′F ′ and the arc G′H ′ are the magnitudes of the spread of ultrasonic waves on the plane including the maximum incident angle and the plane including the minimum incident angle at the transducer position, respectively ( (See FIGS. 9A and 9B). Further, K ₃ is the transmittance from the axle to the shoe.
[0045]
Therefore, the reception amplitude of the ultrasonic wave in the whole process is
[Expression 36]

Given in. The amplitude A ₃ represents a relative amplitude as described above.
[0046]
(II) Transmittance / reflectance at each interface As in the case described above, the presence of the coupling layer is ignored for the type with a shoe. However, even if the presence of the coupling layer is ignored, since the shoe and the axle are not in solid contact, they are allowed to slide on the contact surface. Therefore, it is assumed that there is no continuity between shear stress and tangential displacement at the boundary surface.
[0047]
Even when a longitudinal wave is incident on the solid boundary surface from the shoe, it can be handled in the same manner as the shoeless type, and a reflected wave and a transmitted wave are generated as shown in FIG. Here, the incident angle is θ _l1 , the refraction angle of the longitudinal wave is θ _l2 , the refraction angle of the transverse wave is θ _t2 , the sound velocity of the incident wave (longitudinal wave) is v _l1 , the sound velocity of the transmitted wave longitudinal wave is v _l2 , and the transverse wave. Is set to v _t2 . If the density is ρ and the Lame constant is expressed by μ and λ, the following “Expression 37” is obtained;
[Expression 37]

[0048]
Furthermore, the reflectance and transmittance of each wave can be expressed by the following “Equation 38”;
[Formula 38]

Therefore, the transmissivity K ₁ (= Tt / Li) of the transverse wave is
[39]

It becomes.
[0049]
When a transverse wave enters the boundary surface between the solid and the gas, a reflected wave as shown in FIG. 11 is generated. At this time, the reflectance of each wave can be expressed by the following “Equation 40”;
[Formula 40]

Therefore, the reflectance K ₂ (= Tr / Ti) of the transverse wave is
[Expression 41]

It becomes. Here, since the case where the light is incident on the microsphere reflection source is handled, the incident angle is always 0 ° (perpendicular incidence). Therefore, K ₂ = −1.
[0050]
When a transverse wave enters the shoe from the axle, a reflected wave / transmitted wave as shown in FIG. 12 is generated. At this time, the reflectance and transmittance of each wave can be expressed by the following “Equation 42”;
[Expression 42]

Also in this case, it is assumed that the shear stress and the tangential displacement are not continuous as in the case of the incident from the shoe to the axle. Transmittance (longitudinal wave) K ₃ (= Lt / Ti) is
[Expression 43]

It becomes.
Thus, K ₁ , K ₂ , and K ₃ can be determined.
[0051]
(III) Assume that the total characteristic of transmittance and reflectance as a phase change system is K, the real part is K _Re , and the imaginary part is K _Im . The received amplitude at each point of the point transducer can be expressed by the following “Equation 44”;
(44)

[0052]
"Equation 44" is

It can be expressed as. In “Equation 45”, K ₀ is the total characteristic value of transmittance and reflectance of the system, and α is the value of the total phase change of the system. Now, if the wavelength in the shoe (wavelength in the coupling for the shoeless type) is λ _c , in order to correct the phase shift in each small area of the transducer mesh,
[Equation 46]

It is only necessary to bring the transducer closer (see FIG. 13).
[0053]
In this embodiment, the boring shaft has been described as an example. However, the present invention can also be applied to a normal solid shaft. Furthermore, the difference in phase change during refraction can be corrected as appropriate according to the shape, material, etc. of the object to be inspected.
[0054]
【The invention's effect】
As is clear from the above description, according to the present invention, the flaw detection sensitivity is improved,
More accurate flaw detection inspection can be performed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view around a ring axis for explaining an outline of an ultrasonic flaw detection method according to the present invention.
2A is an axial sectional view for explaining a propagation state of ultrasonic waves generated from the probe, FIG. 2B is a radial sectional view, and FIG. C) is a waveform diagram of received echoes.
FIG. 3 is a schematic perspective view for explaining a shape design method of a curved vibrator according to the present invention.
FIG. 4 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 5 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 6 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 7 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 8 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 9 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 10 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 11 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 12 is an explanatory diagram for explaining shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 13 is an explanatory diagram for explaining the shape analysis of the output surface of the vibrator according to the embodiment.
FIG. 14 is a side view schematically showing an example of a probe used in a conventional flaw detection inspection.
15A is an axial sectional view for explaining a propagation state of ultrasonic waves generated from the probe, FIG. 15B is a radial sectional view, and FIG. C) is a waveform diagram of received echoes.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Wheel shaft 12 Axle 12A Journal part 12B Wheel press-fit part 13 Wheel 15 Boring hole 21 Probe 23 Curved vibrator 25 Wedge material (shoe material)

Claims (7)

An ultrasonic flaw detection method in which ultrasonic waves are incident on a test object from a probe and a reflected wave (echo) reflected from the test object is detected to detect the test object.
Set a point (target point) on the inspection surface of the DUT,
Dividing the ultrasonic incident surface of the DUT into a plurality of small regions,
Calculate the direction in which the ultrasonic wave propagates while being refracted from the target point via the small areas, and obtain the coordinates of the points where the acoustic distance is relatively equal,
The coordinates of the points are integrated to obtain the probe output surface,
An ultrasonic flaw detection method characterized in that a probe having the output surface is used to three-dimensionally focus the ultrasonic wave at the target point. The test object is axial, the output surface of the probe, an ultrasonic flaw detection method according to claim 1, wherein the determination by integrating the points satisfying the following equation;

The test object is boring axis, the output surface of the probe, an ultrasonic flaw detection method according to claim 1, wherein the determination by integrating the coordinate points Tij based on the following equation;

Definitive when refracted the ultrasound between the target point and the output surface of the probe, one of claims 1 to 3, characterized in that for adjusting a difference in phase change between the mutually the small region The ultrasonic flaw detection method according to claim 1. The ultrasonic flaw detection method according to claim 4 , wherein the phase change difference is adjusted by bringing an output surface of the probe close to the target point so as to satisfy the following equation;

An ultrasonic flaw detector comprising a probe for detecting a reflected wave (echo) reflected from a test object by applying an ultrasonic wave to the test object,
The probe refracts the ultrasonic wave from a certain point (target point) on the inspection surface of the device under test through a small area obtained by dividing the surface of the ultrasonic wave of the device under test into a plurality of parts. An ultrasonic flaw detector characterized by having an output surface that calculates the propagation direction while integrating the coordinates of points with relatively equal acoustic distances. When the ultrasonic wave is refracted between the output surface of the probe and the target point, it further comprises a phase difference adjusting means for adjusting a difference in phase change between the small regions. The ultrasonic flaw detector according to claim 6 .

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