超聲波是由機械振動引起、在介質中沿一定方向傳播的一種機械波針對在線亞洲日產一區二區:超聲波自身特性和在各類常見介質中傳播時的特點進行基本把握，有助于我們正確應用超聲探傷技術、解決實際檢測過程中的各種問題。在超聲探傷中，常常涉及部分幾何聲學的反射、折射定律及波型轉換，以及物理聲學中波的疊加、干涉和衍射等規律或概念。本章主要介紹不銹鋼管缺陷探傷中的常用無損探傷技術、超聲波物理特性以及探傷規范相關基礎內容。

1. 振動及波的相關物理(li)量(liang)

   物體沿直線或(huo)曲線在(zai)某一平衡位(wei)置附近做周期性往(wang)復運動(dong)，稱為機械振動(dong)。日(ri)常(chang)(chang)生活中隨處(chu)可見(jian)振動(dong)現象，如鐘擺的(de)(de)往(wang)復運動(dong)、旗幟的(de)(de)擺動(dong)、聲帶的(de)(de)振動(dong)等。常(chang)(chang)見(jian)的(de)(de)表(biao)(biao)征振動(dong)的(de)(de)參數有：波(bo)(bo)長(chang)，任一質(zhi)(zhi)點(dian)經(jing)歷(li)一次完整振動(dong)時波(bo)(bo)所(suo)傳播(bo)的(de)(de)距(ju)離，通(tong)常(chang)(chang)用符(fu)(fu)號λ表(biao)(biao)示，單(dan)位(wei)為m（米）；波(bo)(bo)速，波(bo)(bo)在(zai)單(dan)位(wei)時間(jian)內所(suo)傳播(bo)的(de)(de)距(ju)離，通(tong)常(chang)(chang)用符(fu)(fu)號c表(biao)(biao)示，單(dan)位(wei)為m/s（米/秒）；頻率，質(zhi)(zhi)點(dian)在(zai)1s內進行全振動(dong)的(de)(de)次數，通(tong)常(chang)(chang)用f表(biao)(biao)示，單(dan)位(wei)為Hz（赫茲）；周期，質(zhi)(zhi)點(dian)次全振動(dong)所(suo)需的(de)(de)時間(jian)，通(tong)常(chang)(chang)用T表(biao)(biao)示，單(dan)位(wei)為s（秒）；振幅，質(zhi)(zhi)點(dian)離開(kai)平位(wei)置的(de)(de)最(zui)大距(ju)離，通(tong)常(chang)(chang)用A表(biao)(biao)示。

  上述波(bo)長、波(bo)速、頻率三者(zhe)之間關(guan)系為：λ= c/f 由上式可知，頻率一定時，波(bo)速越(yue)(yue)大，波(bo)長就(jiu)(jiu)越(yue)(yue)長；而波(bo)速一定時，率越(yue)(yue)低，波(bo)長就(jiu)(jiu)越(yue)(yue)長。周期(qi)和(he)頻率描述的(de)是(shi)(shi)振動的(de)快慢，兩者(zhe)大小與周期(qi)互為倒數。振幅描述的(de)是(shi)(shi)振動的(de)強(qiang)弱。

2. 機(ji)械波

  振動在介質或空(kong)間中的(de)傳(chuan)播(bo)過程叫作波(bo)動，簡稱(cheng)波(bo)，可分為(wei)(wei)機(ji)械波(bo)與電磁波(bo)兩(liang)種(zhong)。本(ben)書中僅(jin)涉及機(ji)械波(bo)。振動在彈性介質中的(de)傳(chuan)播(bo)稱(cheng)為(wei)(wei)機(ji)械波(bo)，如固體、液(ye)體、氣(qi)體均可視為(wei)(wei)彈性介質。機(ji)械波(bo)的(de)頻(pin)率范(fan)圍很(hen)寬，從10-4Hz到102Hz，跨越16個(ge)數(shu)量級其中人(ren)類聽(ting)覺所能感知的(de)范(fan)圍在20~20000Hz。人(ren)們把(ba)能牽動聽(ting)覺神(shen)經的(de)機(ji)械波(bo)稱(cheng)為(wei)(wei)聲(sheng)波(bo)，當(dang)聲(sheng)波(bo)頻(pin)率低于20Hz時，稱(cheng)為(wei)(wei)次(ci)聲(sheng)波(bo)；當(dang)聲(sheng)波(bo)頻(pin)率于20000Hz時，稱(cheng)為(wei)(wei)超聲(sheng)波(bo)。

  為簡單闡述機(ji)械波是如(ru)何產(chan)(chan)生(sheng)和傳播的(de)(de)(de)，建(jian)立如(ru)圖(tu)所彈(dan)(dan)(dan)性(xing)(xing)(xing)介(jie)質(zhi)模型。圖(tu)2-1中(zhong)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)間以小彈(dan)(dan)(dan)簧連接(jie)在一起(qi)，這種質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)間以彈(dan)(dan)(dan)性(xing)(xing)(xing)力連接(jie)在起(qi)的(de)(de)(de)介(jie)質(zhi)稱(cheng)為彈(dan)(dan)(dan)性(xing)(xing)(xing)介(jie)質(zhi)。外力F首(shou)先對質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)A產(chan)(chan)生(sheng)作(zuo)用(yong)(yong)，A偏離(li)(li)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，此時附(fu)近(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)將對A產(chan)(chan)生(sheng)力的(de)(de)(de)作(zuo)用(yong)(yong)，迫使(shi)其(qi)回(hui)到(dao)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。而當A回(hui)到(dao)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時，其(qi)他(ta)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)對其(qi)不產(chan)(chan)生(sheng)作(zuo)用(yong)(yong)，但是由(you)于慣性(xing)(xing)(xing)的(de)(de)(de)存在，A具有(you)一定的(de)(de)(de)速度，不會停留在均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，反而繼續向前方(fang)運(yun)動(dong)，并(bing)沿相反方(fang)向離(li)(li)開(kai)(kai)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。一旦離(li)(li)開(kai)(kai)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，A又會受到(dao)附(fu)近(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)對它(ta)(ta)相反的(de)(de)(de)彈(dan)(dan)(dan)性(xing)(xing)(xing)力，使(shi)A再次回(hui)到(dao)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。導致(zhi)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)A在均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)來回(hui)往復產(chan)(chan)生(sheng)振動(dong)。與(yu)此同時，A附(fu)近(jin)的(de)(de)(de)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)也會受到(dao)同樣力的(de)(de)(de)作(zuo)用(yong)(yong)使(shi)它(ta)(ta)們離(li)(li)開(kai)(kai)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，并(bing)在各(ge)自的(de)(de)(de)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)附(fu)近(jin)運(yun)動(dong)。這樣彈(dan)(dan)(dan)性(xing)(xing)(xing)介(jie)質(zhi)中(zhong)單一質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振動(dong)引起(qi)鄰(lin)近(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振動(dong)，鄰(lin)近(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振動(dong)又會引起(qi)更遠(yuan)(yuan)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振動(dong)最終由(you)近(jin)及遠(yuan)(yuan)地向各(ge)個方(fang)向傳播，從(cong)而形成機(ji)械波。

  超(chao)聲(sheng)波(bo)(bo)是一種以(yi)波(bo)(bo)動(dong)形式在(zai)(zai)介質(zhi)中傳(chuan)(chuan)播(bo)(bo)的機(ji)械(xie)振(zhen)(zhen)動(dong)，提到了(le)機(ji)械(xie)波(bo)(bo)傳(chuan)(chuan)播(bo)(bo)所必需的兩個條件：做(zuo)機(ji)械(xie)振(zhen)(zhen)動(dong)的波(bo)(bo)源和(he)能(neng)夠傳(chuan)(chuan)播(bo)(bo)機(ji)械(xie)振(zhen)(zhen)動(dong)的介質(zhi)。振(zhen)(zhen)動(dong)與波(bo)(bo)動(dong)是相(xiang)互(hu)關聯(lian)的，振(zhen)(zhen)動(dong)產生波(bo)(bo)動(dong)，而波(bo)(bo)動(dong)是振(zhen)(zhen)動(dong)的傳(chuan)(chuan)播(bo)(bo)。波(bo)(bo)動(dong)時介質(zhi)中的質(zhi)點會在(zai)(zai)各自的平衡位置附近做(zuo)往(wang)復運動(dong)，并不隨波(bo)(bo)前進，在(zai)(zai)波(bo)(bo)動(dong)中由各質(zhi)點的位移連續(xu)變(bian)化將振(zhen)(zhen)動(dong)能(neng)量(liang)傳(chuan)(chuan)播(bo)(bo)出去(qu)。