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亞洲歐美色綜合一區二區在線: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(de)相關物(wu)理量


   物體沿直線或曲線在某一(yi)平衡位(wei)(wei)置附(fu)近做(zuo)周期(qi)性往復運動(dong)(dong)，稱為機械振(zhen)(zhen)動(dong)(dong)。日常(chang)生活中隨處可見(jian)振(zhen)(zhen)動(dong)(dong)現象，如鐘(zhong)擺(bai)的(de)(de)往復運動(dong)(dong)、旗幟的(de)(de)擺(bai)動(dong)(dong)、聲帶的(de)(de)振(zhen)(zhen)動(dong)(dong)等(deng)。常(chang)見(jian)的(de)(de)表(biao)(biao)征振(zhen)(zhen)動(dong)(dong)的(de)(de)參數(shu)(shu)有：波(bo)長，任一(yi)質(zhi)點經歷(li)一(yi)次完整振(zhen)(zhen)動(dong)(dong)時波(bo)所(suo)傳播的(de)(de)距(ju)離(li)，通常(chang)用(yong)(yong)符號λ表(biao)(biao)示(shi)，單(dan)位(wei)(wei)為m（米）；波(bo)速，波(bo)在單(dan)位(wei)(wei)時間內所(suo)傳播的(de)(de)距(ju)離(li)，通常(chang)用(yong)(yong)符號c表(biao)(biao)示(shi)，單(dan)位(wei)(wei)為m/s（米/秒(miao)）；頻率(lv)，質(zhi)點在1s內進行全振(zhen)(zhen)動(dong)(dong)的(de)(de)次數(shu)(shu)，通常(chang)用(yong)(yong)f表(biao)(biao)示(shi)，單(dan)位(wei)(wei)為Hz（赫茲）；周期(qi)，質(zhi)點次全振(zhen)(zhen)動(dong)(dong)所(suo)需的(de)(de)時間，通常(chang)用(yong)(yong)T表(biao)(biao)示(shi)，單(dan)位(wei)(wei)為s（秒(miao)）；振(zhen)(zhen)幅，質(zhi)點離(li)開平位(wei)(wei)置的(de)(de)最大距(ju)離(li)，通常(chang)用(yong)(yong)A表(biao)(biao)示(shi)。


  上述(shu)波(bo)長(chang)、波(bo)速(su)、頻(pin)率(lv)(lv)(lv)三者(zhe)之間關系(xi)為：λ= c/f 由(you)上式(shi)可(ke)知，頻(pin)率(lv)(lv)(lv)一定時，波(bo)速(su)越(yue)大，波(bo)長(chang)就越(yue)長(chang)；而波(bo)速(su)一定時，率(lv)(lv)(lv)越(yue)低(di)，波(bo)長(chang)就越(yue)長(chang)。周期(qi)和頻(pin)率(lv)(lv)(lv)描述(shu)的(de)(de)是振(zhen)動的(de)(de)快慢(man)，兩者(zhe)大小與周期(qi)互為倒數。振(zhen)幅描述(shu)的(de)(de)是振(zhen)動的(de)(de)強弱。


2. 機械波


  振動在介質或空間(jian)中的(de)傳(chuan)播過(guo)程叫作(zuo)波(bo)動，簡稱(cheng)波(bo)，可分為(wei)(wei)機(ji)(ji)械(xie)(xie)波(bo)與(yu)電磁波(bo)兩種。本書中僅涉及機(ji)(ji)械(xie)(xie)波(bo)。振動在彈(dan)性介質中的(de)傳(chuan)播稱(cheng)為(wei)(wei)機(ji)(ji)械(xie)(xie)波(bo)，如(ru)固體(ti)(ti)、液體(ti)(ti)、氣體(ti)(ti)均可視為(wei)(wei)彈(dan)性介質。機(ji)(ji)械(xie)(xie)波(bo)的(de)頻(pin)(pin)率范圍很寬，從10-4Hz到102Hz，跨越16個(ge)數量級其(qi)中人類聽(ting)覺所能(neng)感知的(de)范圍在20~20000Hz。人們(men)把能(neng)牽動聽(ting)覺神經的(de)機(ji)(ji)械(xie)(xie)波(bo)稱(cheng)為(wei)(wei)聲(sheng)波(bo)，當(dang)(dang)聲(sheng)波(bo)頻(pin)(pin)率低(di)于(yu)20Hz時，稱(cheng)為(wei)(wei)次聲(sheng)波(bo)；當(dang)(dang)聲(sheng)波(bo)頻(pin)(pin)率于(yu)20000Hz時，稱(cheng)為(wei)(wei)超聲(sheng)波(bo)。


圖 1.jpg


  為(wei)簡單闡(chan)述機械(xie)波是(shi)如何(he)產(chan)生(sheng)和傳(chuan)播的(de)(de)(de)(de)，建立如圖所(suo)彈(dan)性介質(zhi)(zhi)(zhi)(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)間以(yi)(yi)小彈(dan)簧連接在(zai)(zai)(zai)一(yi)(yi)起(qi)(qi)，這種質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)間以(yi)(yi)彈(dan)性力(li)(li)連接在(zai)(zai)(zai)起(qi)(qi)的(de)(de)(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)(li)F首先(xian)對質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)A產(chan)生(sheng)作(zuo)用(yong)，A偏(pian)離均(jun)衡(heng)點(dian)(dian)(dian)(dian)，此(ci)時(shi)附(fu)近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)將對A產(chan)生(sheng)力(li)(li)的(de)(de)(de)(de)作(zuo)用(yong)，迫使其(qi)回到(dao)(dao)均(jun)衡(heng)點(dian)(dian)(dian)(dian)。而(er)當A回到(dao)(dao)均(jun)衡(heng)點(dian)(dian)(dian)(dian)時(shi)，其(qi)他質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)對其(qi)不產(chan)生(sheng)作(zuo)用(yong)，但是(shi)由于慣性的(de)(de)(de)(de)存在(zai)(zai)(zai)，A具有一(yi)(yi)定的(de)(de)(de)(de)速度，不會停留在(zai)(zai)(zai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)，反(fan)而(er)繼續向前方運動(dong)(dong)，并沿(yan)相(xiang)反(fan)方向離開均(jun)衡(heng)點(dian)(dian)(dian)(dian)。一(yi)(yi)旦離開均(jun)衡(heng)點(dian)(dian)(dian)(dian)，A又(you)會受到(dao)(dao)附(fu)近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)對它相(xiang)反(fan)的(de)(de)(de)(de)彈(dan)性力(li)(li)，使A再(zai)次(ci)回到(dao)(dao)均(jun)衡(heng)點(dian)(dian)(dian)(dian)。導(dao)致質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)A在(zai)(zai)(zai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)來回往復產(chan)生(sheng)振(zhen)動(dong)(dong)。與(yu)此(ci)同(tong)時(shi)，A附(fu)近的(de)(de)(de)(de)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)也會受到(dao)(dao)同(tong)樣力(li)(li)的(de)(de)(de)(de)作(zuo)用(yong)使它們離開均(jun)衡(heng)點(dian)(dian)(dian)(dian)，并在(zai)(zai)(zai)各自的(de)(de)(de)(de)均(jun)衡(heng)點(dian)(dian)(dian)(dian)附(fu)近運動(dong)(dong)。這樣彈(dan)性介質(zhi)(zhi)(zhi)(zhi)(zhi)中單一(yi)(yi)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)引起(qi)(qi)鄰近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)，鄰近質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)又(you)會引起(qi)(qi)更(geng)遠(yuan)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)最終(zhong)由近及遠(yuan)地(di)向各個(ge)方向傳(chuan)播，從而(er)形成機械(xie)波。


  超聲波是(shi)一種以波動(dong)(dong)形式在介(jie)質中傳播(bo)的(de)(de)(de)(de)機(ji)械振(zhen)(zhen)動(dong)(dong)，提到了(le)機(ji)械波傳播(bo)所(suo)必需的(de)(de)(de)(de)兩(liang)個條件：做機(ji)械振(zhen)(zhen)動(dong)(dong)的(de)(de)(de)(de)波源(yuan)和(he)能(neng)夠傳播(bo)機(ji)械振(zhen)(zhen)動(dong)(dong)的(de)(de)(de)(de)介(jie)質。振(zhen)(zhen)動(dong)(dong)與波動(dong)(dong)是(shi)相互關聯的(de)(de)(de)(de)，振(zhen)(zhen)動(dong)(dong)產生波動(dong)(dong)，而波動(dong)(dong)是(shi)振(zhen)(zhen)動(dong)(dong)的(de)(de)(de)(de)傳播(bo)。波動(dong)(dong)時介(jie)質中的(de)(de)(de)(de)質點會在各自的(de)(de)(de)(de)平(ping)衡(heng)位置附近做往復運動(dong)(dong)，并不隨波前進，在波動(dong)(dong)中由(you)各質點的(de)(de)(de)(de)位移連續變化將振(zhen)(zhen)動(dong)(dong)能(neng)量傳播(bo)出去。