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(zhen)動及波(bo)的相(xiang)關(guan)物理量

   物體沿直線或曲線在某一(yi)平衡(heng)位(wei)置(zhi)附近做周期(qi)性往復運(yun)動(dong)(dong)(dong)(dong)，稱為機械振動(dong)(dong)(dong)(dong)。日(ri)常生(sheng)活中(zhong)隨處可見(jian)振動(dong)(dong)(dong)(dong)現象，如鐘擺的(de)(de)(de)往復運(yun)動(dong)(dong)(dong)(dong)、旗幟的(de)(de)(de)擺動(dong)(dong)(dong)(dong)、聲帶的(de)(de)(de)振動(dong)(dong)(dong)(dong)等。常見(jian)的(de)(de)(de)表征(zheng)振動(dong)(dong)(dong)(dong)的(de)(de)(de)參數有(you)：波(bo)(bo)長，任(ren)一(yi)質點(dian)經歷一(yi)次(ci)完整(zheng)振動(dong)(dong)(dong)(dong)時波(bo)(bo)所傳播(bo)(bo)的(de)(de)(de)距離(li)，通常用符號λ表示，單位(wei)為m（米）；波(bo)(bo)速，波(bo)(bo)在單位(wei)時間內所傳播(bo)(bo)的(de)(de)(de)距離(li)，通常用符號c表示，單位(wei)為m/s（米/秒(miao)(miao)）；頻率，質點(dian)在1s內進行全(quan)振動(dong)(dong)(dong)(dong)的(de)(de)(de)次(ci)數，通常用f表示，單位(wei)為Hz（赫茲）；周期(qi)，質點(dian)次(ci)全(quan)振動(dong)(dong)(dong)(dong)所需的(de)(de)(de)時間，通常用T表示，單位(wei)為s（秒(miao)(miao)）；振幅，質點(dian)離(li)開平位(wei)置(zhi)的(de)(de)(de)最大(da)距離(li)，通常用A表示。

  上述(shu)波(bo)長(chang)、波(bo)速、頻(pin)率(lv)三(san)者之間關系為：λ= c/f 由(you)上式可知，頻(pin)率(lv)一(yi)定(ding)時(shi)，波(bo)速越大，波(bo)長(chang)就(jiu)越長(chang)；而(er)波(bo)速一(yi)定(ding)時(shi)，率(lv)越低，波(bo)長(chang)就(jiu)越長(chang)。周期(qi)和頻(pin)率(lv)描述(shu)的是振(zhen)動(dong)的快慢(man)，兩者大小(xiao)與(yu)周期(qi)互為倒數。振(zhen)幅描述(shu)的是振(zhen)動(dong)的強弱。

2. 機械(xie)波

  振(zhen)動在介(jie)(jie)質(zhi)或(huo)空間中(zhong)(zhong)的(de)傳播(bo)過程叫作波(bo)動，簡稱(cheng)波(bo)，可(ke)分為(wei)機(ji)械波(bo)與電(dian)磁波(bo)兩種。本書(shu)中(zhong)(zhong)僅涉及機(ji)械波(bo)。振(zhen)動在彈性介(jie)(jie)質(zhi)中(zhong)(zhong)的(de)傳播(bo)稱(cheng)為(wei)機(ji)械波(bo)，如固(gu)體(ti)(ti)、液體(ti)(ti)、氣體(ti)(ti)均可(ke)視為(wei)彈性介(jie)(jie)質(zhi)。機(ji)械波(bo)的(de)頻率(lv)范圍(wei)很寬，從10-4Hz到102Hz，跨越(yue)16個數(shu)量級(ji)其中(zhong)(zhong)人類聽覺所(suo)能感知的(de)范圍(wei)在20~20000Hz。人們(men)把能牽(qian)動聽覺神經的(de)機(ji)械波(bo)稱(cheng)為(wei)聲波(bo)，當聲波(bo)頻率(lv)低于20Hz時，稱(cheng)為(wei)次聲波(bo)；當聲波(bo)頻率(lv)于20000Hz時，稱(cheng)為(wei)超聲波(bo)。

  為簡單闡述機(ji)械波(bo)是如何(he)產(chan)(chan)生(sheng)和傳播的(de)(de)，建(jian)立如圖所彈(dan)(dan)性(xing)(xing)(xing)介質(zhi)模型。圖2-1中質(zhi)點(dian)(dian)(dian)(dian)(dian)間以小彈(dan)(dan)簧連(lian)(lian)接(jie)在(zai)一(yi)起，這(zhe)種質(zhi)點(dian)(dian)(dian)(dian)(dian)間以彈(dan)(dan)性(xing)(xing)(xing)力連(lian)(lian)接(jie)在(zai)起的(de)(de)介質(zhi)稱為彈(dan)(dan)性(xing)(xing)(xing)介質(zhi)。外力F首先對(dui)(dui)質(zhi)點(dian)(dian)(dian)(dian)(dian)A產(chan)(chan)生(sheng)作(zuo)用(yong)，A偏離(li)(li)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，此時(shi)(shi)附近質(zhi)點(dian)(dian)(dian)(dian)(dian)將對(dui)(dui)A產(chan)(chan)生(sheng)力的(de)(de)作(zuo)用(yong)，迫(po)使其回(hui)到(dao)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。而(er)當A回(hui)到(dao)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，其他質(zhi)點(dian)(dian)(dian)(dian)(dian)對(dui)(dui)其不產(chan)(chan)生(sheng)作(zuo)用(yong)，但是由于慣性(xing)(xing)(xing)的(de)(de)存在(zai)，A具(ju)有一(yi)定的(de)(de)速度，不會(hui)停留在(zai)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，反(fan)而(er)繼續向前方運動(dong)(dong)(dong)(dong)，并(bing)沿相反(fan)方向離(li)(li)開均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。一(yi)旦離(li)(li)開均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，A又會(hui)受到(dao)附近質(zhi)點(dian)(dian)(dian)(dian)(dian)對(dui)(dui)它相反(fan)的(de)(de)彈(dan)(dan)性(xing)(xing)(xing)力，使A再(zai)次(ci)回(hui)到(dao)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。導致質(zhi)點(dian)(dian)(dian)(dian)(dian)A在(zai)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)來回(hui)往復(fu)產(chan)(chan)生(sheng)振(zhen)動(dong)(dong)(dong)(dong)。與此同時(shi)(shi)，A附近的(de)(de)質(zhi)點(dian)(dian)(dian)(dian)(dian)也會(hui)受到(dao)同樣力的(de)(de)作(zuo)用(yong)使它們離(li)(li)開均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，并(bing)在(zai)各(ge)自的(de)(de)均(jun)(jun)(jun)(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)附近運動(dong)(dong)(dong)(dong)。這(zhe)樣彈(dan)(dan)性(xing)(xing)(xing)介質(zhi)中單一(yi)質(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)引起鄰近質(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)，鄰近質(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)又會(hui)引起更(geng)遠質(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)(dong)(dong)最終(zhong)由近及(ji)遠地向各(ge)個方向傳播，從而(er)形成(cheng)機(ji)械波(bo)。

  超聲波(bo)是(shi)一種(zhong)以波(bo)動(dong)(dong)形(xing)式在介(jie)質中(zhong)(zhong)傳播(bo)(bo)(bo)的機(ji)械(xie)振(zhen)動(dong)(dong)，提到了機(ji)械(xie)波(bo)傳播(bo)(bo)(bo)所必需的兩(liang)個條件：做(zuo)機(ji)械(xie)振(zhen)動(dong)(dong)的波(bo)源(yuan)和能夠傳播(bo)(bo)(bo)機(ji)械(xie)振(zhen)動(dong)(dong)的介(jie)質。振(zhen)動(dong)(dong)與波(bo)動(dong)(dong)是(shi)相互(hu)關聯的，振(zhen)動(dong)(dong)產生波(bo)動(dong)(dong)，而(er)波(bo)動(dong)(dong)是(shi)振(zhen)動(dong)(dong)的傳播(bo)(bo)(bo)。波(bo)動(dong)(dong)時介(jie)質中(zhong)(zhong)的質點會在各自的平衡位(wei)置(zhi)附近做(zuo)往復運動(dong)(dong)，并不(bu)隨波(bo)前(qian)進，在波(bo)動(dong)(dong)中(zhong)(zhong)由各質點的位(wei)移連續(xu)變化(hua)將振(zhen)動(dong)(dong)能量傳播(bo)(bo)(bo)出去(qu)。