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(bo)的(de)相(xiang)關(guan)物理量


   物體(ti)沿直線或(huo)曲線在(zai)某一(yi)平(ping)衡位(wei)(wei)置(zhi)附(fu)近做(zuo)周(zhou)期性往(wang)復運動(dong)，稱(cheng)為(wei)(wei)機械振(zhen)(zhen)(zhen)動(dong)。日常(chang)生(sheng)活中隨處可見振(zhen)(zhen)(zhen)動(dong)現象，如鐘擺的(de)往(wang)復運動(dong)、旗幟的(de)擺動(dong)、聲帶的(de)振(zhen)(zhen)(zhen)動(dong)等(deng)。常(chang)見的(de)表(biao)征振(zhen)(zhen)(zhen)動(dong)的(de)參數有：波(bo)(bo)長，任一(yi)質(zhi)點(dian)經歷一(yi)次(ci)完整振(zhen)(zhen)(zhen)動(dong)時波(bo)(bo)所(suo)傳播的(de)距(ju)離(li)，通(tong)常(chang)用符(fu)號λ表(biao)示，單(dan)位(wei)(wei)為(wei)(wei)m（米）；波(bo)(bo)速，波(bo)(bo)在(zai)單(dan)位(wei)(wei)時間(jian)內(nei)所(suo)傳播的(de)距(ju)離(li)，通(tong)常(chang)用符(fu)號c表(biao)示，單(dan)位(wei)(wei)為(wei)(wei)m/s（米/秒）；頻率(lv)，質(zhi)點(dian)在(zai)1s內(nei)進行(xing)全振(zhen)(zhen)(zhen)動(dong)的(de)次(ci)數，通(tong)常(chang)用f表(biao)示，單(dan)位(wei)(wei)為(wei)(wei)Hz（赫茲）；周(zhou)期，質(zhi)點(dian)次(ci)全振(zhen)(zhen)(zhen)動(dong)所(suo)需的(de)時間(jian)，通(tong)常(chang)用T表(biao)示，單(dan)位(wei)(wei)為(wei)(wei)s（秒）；振(zhen)(zhen)(zhen)幅，質(zhi)點(dian)離(li)開平(ping)位(wei)(wei)置(zhi)的(de)最(zui)大距(ju)離(li)，通(tong)常(chang)用A表(biao)示。


  上(shang)述(shu)波長(chang)(chang)、波速、頻率(lv)(lv)三者之間關系為(wei)(wei)：λ= c/f 由上(shang)式(shi)可知，頻率(lv)(lv)一定時，波速越大(da)，波長(chang)(chang)就越長(chang)(chang)；而波速一定時，率(lv)(lv)越低，波長(chang)(chang)就越長(chang)(chang)。周(zhou)期和頻率(lv)(lv)描述(shu)的(de)是振動的(de)快慢，兩者大(da)小與(yu)周(zhou)期互為(wei)(wei)倒數。振幅描述(shu)的(de)是振動的(de)強(qiang)弱。


2. 機械波


  振動(dong)(dong)(dong)在(zai)介(jie)質(zhi)或空(kong)間中(zhong)的(de)(de)傳(chuan)播(bo)過程叫作波(bo)(bo)(bo)(bo)(bo)(bo)動(dong)(dong)(dong)，簡稱波(bo)(bo)(bo)(bo)(bo)(bo)，可(ke)分為機(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)(bo)(bo)(bo)(bo)與(yu)電磁波(bo)(bo)(bo)(bo)(bo)(bo)兩種。本書(shu)中(zhong)僅涉及機(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)(bo)(bo)(bo)(bo)。振動(dong)(dong)(dong)在(zai)彈(dan)性(xing)介(jie)質(zhi)中(zhong)的(de)(de)傳(chuan)播(bo)稱為機(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)(bo)(bo)(bo)(bo)，如(ru)固體(ti)、液體(ti)、氣體(ti)均可(ke)視為彈(dan)性(xing)介(jie)質(zhi)。機(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)(bo)(bo)(bo)(bo)的(de)(de)頻率(lv)范圍(wei)很寬(kuan)，從10-4Hz到102Hz，跨(kua)越(yue)16個(ge)數(shu)量級其(qi)中(zhong)人類聽(ting)覺(jue)所能感知的(de)(de)范圍(wei)在(zai)20~20000Hz。人們把能牽動(dong)(dong)(dong)聽(ting)覺(jue)神(shen)經的(de)(de)機(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)(bo)(bo)(bo)(bo)稱為聲波(bo)(bo)(bo)(bo)(bo)(bo)，當(dang)聲波(bo)(bo)(bo)(bo)(bo)(bo)頻率(lv)低于20Hz時，稱為次聲波(bo)(bo)(bo)(bo)(bo)(bo)；當(dang)聲波(bo)(bo)(bo)(bo)(bo)(bo)頻率(lv)于20000Hz時，稱為超聲波(bo)(bo)(bo)(bo)(bo)(bo)。


圖 1.jpg


  為簡(jian)單(dan)闡(chan)述機械波是(shi)如何產生(sheng)(sheng)(sheng)(sheng)和傳(chuan)播(bo)的(de)(de)(de)(de)，建立(li)如圖所彈性(xing)(xing)(xing)介質(zhi)(zhi)(zhi)(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)間以(yi)小彈簧(huang)連接(jie)在一起(qi)，這(zhe)(zhe)種(zhong)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)間以(yi)彈性(xing)(xing)(xing)力(li)連接(jie)在起(qi)的(de)(de)(de)(de)介質(zhi)(zhi)(zhi)(zhi)(zhi)稱(cheng)為彈性(xing)(xing)(xing)介質(zhi)(zhi)(zhi)(zhi)(zhi)。外力(li)F首先對(dui)(dui)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)A產生(sheng)(sheng)(sheng)(sheng)作用，A偏離均衡點(dian)(dian)，此時(shi)(shi)附(fu)近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)將對(dui)(dui)A產生(sheng)(sheng)(sheng)(sheng)力(li)的(de)(de)(de)(de)作用，迫使(shi)其回到(dao)(dao)均衡點(dian)(dian)。而(er)當(dang)A回到(dao)(dao)均衡點(dian)(dian)時(shi)(shi)，其他質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)對(dui)(dui)其不產生(sheng)(sheng)(sheng)(sheng)作用，但是(shi)由于慣性(xing)(xing)(xing)的(de)(de)(de)(de)存在，A具(ju)有一定的(de)(de)(de)(de)速度(du)，不會(hui)(hui)停留在均衡點(dian)(dian)，反而(er)繼續(xu)向(xiang)前(qian)方運動(dong)，并(bing)沿(yan)相反方向(xiang)離開(kai)均衡點(dian)(dian)。一旦離開(kai)均衡點(dian)(dian)，A又會(hui)(hui)受到(dao)(dao)附(fu)近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)對(dui)(dui)它相反的(de)(de)(de)(de)彈性(xing)(xing)(xing)力(li)，使(shi)A再次回到(dao)(dao)均衡點(dian)(dian)。導致(zhi)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)A在均衡點(dian)(dian)來回往復產生(sheng)(sheng)(sheng)(sheng)振(zhen)(zhen)(zhen)動(dong)。與此同時(shi)(shi)，A附(fu)近(jin)(jin)的(de)(de)(de)(de)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)也(ye)會(hui)(hui)受到(dao)(dao)同樣力(li)的(de)(de)(de)(de)作用使(shi)它們離開(kai)均衡點(dian)(dian)，并(bing)在各(ge)自的(de)(de)(de)(de)均衡點(dian)(dian)附(fu)近(jin)(jin)運動(dong)。這(zhe)(zhe)樣彈性(xing)(xing)(xing)介質(zhi)(zhi)(zhi)(zhi)(zhi)中單(dan)一質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)(zhen)動(dong)引起(qi)鄰近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)(zhen)動(dong)，鄰近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)(zhen)動(dong)又會(hui)(hui)引起(qi)更遠質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)(zhen)動(dong)最終由近(jin)(jin)及(ji)遠地(di)向(xiang)各(ge)個方向(xiang)傳(chuan)播(bo)，從(cong)而(er)形成(cheng)機械波。


  超(chao)聲波(bo)(bo)(bo)是一種以波(bo)(bo)(bo)動(dong)(dong)(dong)(dong)形式在(zai)介質中(zhong)傳播(bo)的(de)機(ji)(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)，提到了(le)機(ji)(ji)械波(bo)(bo)(bo)傳播(bo)所必需(xu)的(de)兩(liang)個條件：做機(ji)(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)的(de)波(bo)(bo)(bo)源和能(neng)夠傳播(bo)機(ji)(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)的(de)介質。振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)與(yu)波(bo)(bo)(bo)動(dong)(dong)(dong)(dong)是相互關聯的(de)，振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)產生波(bo)(bo)(bo)動(dong)(dong)(dong)(dong)，而波(bo)(bo)(bo)動(dong)(dong)(dong)(dong)是振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)的(de)傳播(bo)。波(bo)(bo)(bo)動(dong)(dong)(dong)(dong)時介質中(zhong)的(de)質點會在(zai)各自(zi)的(de)平衡位置附近(jin)做往復(fu)運動(dong)(dong)(dong)(dong)，并不隨波(bo)(bo)(bo)前進(jin)，在(zai)波(bo)(bo)(bo)動(dong)(dong)(dong)(dong)中(zhong)由各質點的(de)位移(yi)連續變(bian)化將振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)能(neng)量傳播(bo)出去(qu)。