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(ji)波的相(xiang)關(guan)物理量

   物體(ti)沿直線或曲線在某一(yi)平(ping)(ping)衡位(wei)(wei)(wei)置(zhi)附近(jin)做(zuo)周期性往復運(yun)動(dong)(dong)(dong)(dong)(dong)，稱為(wei)(wei)機械振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)。日常生活中隨(sui)處可見振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)現象，如鐘擺的往復運(yun)動(dong)(dong)(dong)(dong)(dong)、旗(qi)幟的擺動(dong)(dong)(dong)(dong)(dong)、聲帶的振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)等。常見的表(biao)(biao)征(zheng)振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)的參數有：波長，任(ren)一(yi)質(zhi)點(dian)經歷一(yi)次(ci)完整振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)時波所傳播的距離(li)(li)，通(tong)常用(yong)(yong)符(fu)號(hao)λ表(biao)(biao)示(shi)，單(dan)位(wei)(wei)(wei)為(wei)(wei)m（米）；波速，波在單(dan)位(wei)(wei)(wei)時間內(nei)所傳播的距離(li)(li)，通(tong)常用(yong)(yong)符(fu)號(hao)c表(biao)(biao)示(shi)，單(dan)位(wei)(wei)(wei)為(wei)(wei)m/s（米/秒(miao)）；頻率，質(zhi)點(dian)在1s內(nei)進行(xing)全振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)的次(ci)數，通(tong)常用(yong)(yong)f表(biao)(biao)示(shi)，單(dan)位(wei)(wei)(wei)為(wei)(wei)Hz（赫茲）；周期，質(zhi)點(dian)次(ci)全振(zhen)(zhen)動(dong)(dong)(dong)(dong)(dong)所需(xu)的時間，通(tong)常用(yong)(yong)T表(biao)(biao)示(shi)，單(dan)位(wei)(wei)(wei)為(wei)(wei)s（秒(miao)）；振(zhen)(zhen)幅，質(zhi)點(dian)離(li)(li)開(kai)平(ping)(ping)位(wei)(wei)(wei)置(zhi)的最大距離(li)(li)，通(tong)常用(yong)(yong)A表(biao)(biao)示(shi)。

  上(shang)述波長(chang)(chang)、波速(su)、頻率(lv)(lv)三者之間關系為(wei)：λ= c/f 由上(shang)式可(ke)知，頻率(lv)(lv)一(yi)定(ding)(ding)時(shi)，波速(su)越大，波長(chang)(chang)就越長(chang)(chang)；而波速(su)一(yi)定(ding)(ding)時(shi)，率(lv)(lv)越低，波長(chang)(chang)就越長(chang)(chang)。周(zhou)期(qi)和頻率(lv)(lv)描(miao)述的(de)是振(zhen)動的(de)快慢，兩者大小與周(zhou)期(qi)互為(wei)倒數。振(zhen)幅描(miao)述的(de)是振(zhen)動的(de)強弱。

2. 機械波

  振動(dong)(dong)(dong)(dong)在(zai)介質(zhi)或空間中(zhong)的(de)傳播過程叫(jiao)作(zuo)波(bo)動(dong)(dong)(dong)(dong)，簡稱(cheng)波(bo)，可分(fen)為(wei)機(ji)械(xie)(xie)(xie)波(bo)與電磁波(bo)兩種。本(ben)書中(zhong)僅涉及(ji)機(ji)械(xie)(xie)(xie)波(bo)。振動(dong)(dong)(dong)(dong)在(zai)彈(dan)性介質(zhi)中(zhong)的(de)傳播稱(cheng)為(wei)機(ji)械(xie)(xie)(xie)波(bo)，如固體、液體、氣體均可視為(wei)彈(dan)性介質(zhi)。機(ji)械(xie)(xie)(xie)波(bo)的(de)頻(pin)率范圍(wei)(wei)很(hen)寬，從10-4Hz到102Hz，跨越16個數量級其中(zhong)人類聽(ting)覺所(suo)能(neng)感(gan)知的(de)范圍(wei)(wei)在(zai)20~20000Hz。人們把能(neng)牽動(dong)(dong)(dong)(dong)聽(ting)覺神經的(de)機(ji)械(xie)(xie)(xie)波(bo)稱(cheng)為(wei)聲波(bo)，當聲波(bo)頻(pin)率低(di)于20Hz時，稱(cheng)為(wei)次聲波(bo)；當聲波(bo)頻(pin)率于20000Hz時，稱(cheng)為(wei)超聲波(bo)。

  為(wei)簡單闡述機(ji)械波(bo)是(shi)(shi)如(ru)何產(chan)(chan)生和傳播的(de)(de)，建立如(ru)圖(tu)所彈(dan)性介質(zhi)(zhi)(zhi)(zhi)(zhi)模型。圖(tu)2-1中質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間以小彈(dan)簧(huang)連接在(zai)(zai)(zai)一起(qi)，這(zhe)種質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間以彈(dan)性力(li)連接在(zai)(zai)(zai)起(qi)的(de)(de)介質(zhi)(zhi)(zhi)(zhi)(zhi)稱為(wei)彈(dan)性介質(zhi)(zhi)(zhi)(zhi)(zhi)。外力(li)F首先(xian)對(dui)(dui)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A產(chan)(chan)生作用(yong)，A偏離(li)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)，此時(shi)(shi)附(fu)(fu)(fu)近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)將對(dui)(dui)A產(chan)(chan)生力(li)的(de)(de)作用(yong)，迫使其(qi)回到(dao)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)。而當(dang)A回到(dao)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，其(qi)他質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對(dui)(dui)其(qi)不產(chan)(chan)生作用(yong)，但是(shi)(shi)由(you)于慣性的(de)(de)存(cun)在(zai)(zai)(zai)，A具有(you)一定的(de)(de)速度，不會(hui)停(ting)留在(zai)(zai)(zai)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)，反而繼續(xu)向(xiang)前方(fang)運(yun)動(dong)(dong)(dong)(dong)，并沿相反方(fang)向(xiang)離(li)開(kai)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)。一旦(dan)離(li)開(kai)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)，A又會(hui)受(shou)到(dao)附(fu)(fu)(fu)近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對(dui)(dui)它(ta)相反的(de)(de)彈(dan)性力(li)，使A再次回到(dao)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)。導致質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A在(zai)(zai)(zai)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)來回往復產(chan)(chan)生振(zhen)動(dong)(dong)(dong)(dong)。與此同時(shi)(shi)，A附(fu)(fu)(fu)近的(de)(de)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)也會(hui)受(shou)到(dao)同樣力(li)的(de)(de)作用(yong)使它(ta)們離(li)開(kai)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)，并在(zai)(zai)(zai)各自的(de)(de)均(jun)(jun)衡點(dian)(dian)(dian)(dian)(dian)(dian)附(fu)(fu)(fu)近運(yun)動(dong)(dong)(dong)(dong)。這(zhe)樣彈(dan)性介質(zhi)(zhi)(zhi)(zhi)(zhi)中單一質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)引起(qi)鄰(lin)近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)，鄰(lin)近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)又會(hui)引起(qi)更遠質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)最終由(you)近及(ji)遠地向(xiang)各個方(fang)向(xiang)傳播，從而形(xing)成機(ji)械波(bo)。

  超聲(sheng)波(bo)(bo)(bo)是(shi)一種以波(bo)(bo)(bo)動(dong)形式在介(jie)質(zhi)中(zhong)傳(chuan)播的(de)(de)機(ji)(ji)械振動(dong)，提到了(le)機(ji)(ji)械波(bo)(bo)(bo)傳(chuan)播所(suo)必需的(de)(de)兩個條(tiao)件：做機(ji)(ji)械振動(dong)的(de)(de)波(bo)(bo)(bo)源和能(neng)夠傳(chuan)播機(ji)(ji)械振動(dong)的(de)(de)介(jie)質(zhi)。振動(dong)與(yu)波(bo)(bo)(bo)動(dong)是(shi)相互關聯的(de)(de)，振動(dong)產生波(bo)(bo)(bo)動(dong)，而(er)波(bo)(bo)(bo)動(dong)是(shi)振動(dong)的(de)(de)傳(chuan)播。波(bo)(bo)(bo)動(dong)時介(jie)質(zhi)中(zhong)的(de)(de)質(zhi)點(dian)會在各自的(de)(de)平衡位置附近做往(wang)復運動(dong)，并不隨波(bo)(bo)(bo)前進，在波(bo)(bo)(bo)動(dong)中(zhong)由各質(zhi)點(dian)的(de)(de)位移連續變(bian)化將(jiang)振動(dong)能(neng)量傳(chuan)播出去。