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香蕉視頻app下載蘋果版: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)的相關物理量


   物體(ti)沿直線或曲線在某一(yi)平衡位置附近做(zuo)周期性往復(fu)運動(dong)，稱為機械振(zhen)(zhen)動(dong)。日(ri)常生活中(zhong)隨(sui)處(chu)可見振(zhen)(zhen)動(dong)現象，如(ru)鐘擺(bai)的(de)(de)(de)(de)往復(fu)運動(dong)、旗幟的(de)(de)(de)(de)擺(bai)動(dong)、聲帶的(de)(de)(de)(de)振(zhen)(zhen)動(dong)等。常見的(de)(de)(de)(de)表(biao)征振(zhen)(zhen)動(dong)的(de)(de)(de)(de)參數有：波長，任一(yi)質(zhi)(zhi)(zhi)點(dian)經歷一(yi)次完整振(zhen)(zhen)動(dong)時波所傳(chuan)播(bo)的(de)(de)(de)(de)距離(li)(li)，通(tong)(tong)常用符(fu)號(hao)λ表(biao)示(shi)，單位為m（米）；波速，波在單位時間內(nei)所傳(chuan)播(bo)的(de)(de)(de)(de)距離(li)(li)，通(tong)(tong)常用符(fu)號(hao)c表(biao)示(shi)，單位為m/s（米/秒）；頻率，質(zhi)(zhi)(zhi)點(dian)在1s內(nei)進行(xing)全振(zhen)(zhen)動(dong)的(de)(de)(de)(de)次數，通(tong)(tong)常用f表(biao)示(shi)，單位為Hz（赫(he)茲）；周期，質(zhi)(zhi)(zhi)點(dian)次全振(zhen)(zhen)動(dong)所需的(de)(de)(de)(de)時間，通(tong)(tong)常用T表(biao)示(shi)，單位為s（秒）；振(zhen)(zhen)幅，質(zhi)(zhi)(zhi)點(dian)離(li)(li)開平位置的(de)(de)(de)(de)最大(da)距離(li)(li)，通(tong)(tong)常用A表(biao)示(shi)。


  上述波(bo)(bo)長(chang)(chang)、波(bo)(bo)速、頻率三者(zhe)之間關(guan)系(xi)為(wei)：λ= c/f 由上式可知，頻率一(yi)(yi)定(ding)時(shi)，波(bo)(bo)速越(yue)大(da)，波(bo)(bo)長(chang)(chang)就(jiu)越(yue)長(chang)(chang)；而波(bo)(bo)速一(yi)(yi)定(ding)時(shi)，率越(yue)低(di)，波(bo)(bo)長(chang)(chang)就(jiu)越(yue)長(chang)(chang)。周期(qi)(qi)和頻率描(miao)述的是振動的快慢，兩者(zhe)大(da)小(xiao)與周期(qi)(qi)互為(wei)倒數。振幅描(miao)述的是振動的強弱。


2. 機械波(bo)


  振動(dong)在(zai)介質或空間中的(de)(de)(de)傳播(bo)(bo)過程叫(jiao)作(zuo)波動(dong)，簡稱(cheng)(cheng)波，可分為(wei)(wei)(wei)機(ji)(ji)械(xie)(xie)波與電磁(ci)波兩種。本書中僅涉及機(ji)(ji)械(xie)(xie)波。振動(dong)在(zai)彈性介質中的(de)(de)(de)傳播(bo)(bo)稱(cheng)(cheng)為(wei)(wei)(wei)機(ji)(ji)械(xie)(xie)波，如(ru)固體(ti)、液體(ti)、氣體(ti)均可視為(wei)(wei)(wei)彈性介質。機(ji)(ji)械(xie)(xie)波的(de)(de)(de)頻(pin)率范圍很寬，從10-4Hz到102Hz，跨越16個數量級其中人類聽覺(jue)所(suo)能感知(zhi)的(de)(de)(de)范圍在(zai)20~20000Hz。人們把能牽動(dong)聽覺(jue)神(shen)經的(de)(de)(de)機(ji)(ji)械(xie)(xie)波稱(cheng)(cheng)為(wei)(wei)(wei)聲(sheng)(sheng)波，當聲(sheng)(sheng)波頻(pin)率低(di)于20Hz時，稱(cheng)(cheng)為(wei)(wei)(wei)次(ci)聲(sheng)(sheng)波；當聲(sheng)(sheng)波頻(pin)率于20000Hz時，稱(cheng)(cheng)為(wei)(wei)(wei)超聲(sheng)(sheng)波。


圖 1.jpg


  為簡單(dan)闡述機(ji)械(xie)波(bo)是(shi)如何(he)產(chan)生和傳播(bo)的(de)(de)(de)，建立如圖(tu)所(suo)彈性介(jie)質(zhi)(zhi)(zhi)(zhi)模型。圖(tu)2-1中(zhong)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間以小彈簧連接(jie)在(zai)一(yi)(yi)起，這(zhe)種質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間以彈性力連接(jie)在(zai)起的(de)(de)(de)介(jie)質(zhi)(zhi)(zhi)(zhi)稱為彈性介(jie)質(zhi)(zhi)(zhi)(zhi)。外力F首先對質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A產(chan)生作用，A偏離(li)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，此(ci)時附近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)將對A產(chan)生力的(de)(de)(de)作用，迫使(shi)(shi)其(qi)(qi)回(hui)到(dao)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。而當A回(hui)到(dao)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)時，其(qi)(qi)他質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對其(qi)(qi)不(bu)產(chan)生作用，但(dan)是(shi)由(you)于慣性的(de)(de)(de)存在(zai)，A具有(you)一(yi)(yi)定的(de)(de)(de)速度，不(bu)會(hui)停留在(zai)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，反(fan)而繼續向(xiang)前方(fang)運動(dong)(dong)，并(bing)沿(yan)相反(fan)方(fang)向(xiang)離(li)開(kai)(kai)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。一(yi)(yi)旦離(li)開(kai)(kai)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，A又會(hui)受到(dao)附近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對它相反(fan)的(de)(de)(de)彈性力，使(shi)(shi)A再次回(hui)到(dao)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。導致質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A在(zai)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)來回(hui)往復產(chan)生振(zhen)動(dong)(dong)。與此(ci)同(tong)時，A附近(jin)的(de)(de)(de)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)也會(hui)受到(dao)同(tong)樣力的(de)(de)(de)作用使(shi)(shi)它們(men)離(li)開(kai)(kai)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，并(bing)在(zai)各自(zi)的(de)(de)(de)均衡(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)附近(jin)運動(dong)(dong)。這(zhe)樣彈性介(jie)質(zhi)(zhi)(zhi)(zhi)中(zhong)單(dan)一(yi)(yi)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振(zhen)動(dong)(dong)引起鄰近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振(zhen)動(dong)(dong)，鄰近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振(zhen)動(dong)(dong)又會(hui)引起更遠質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)振(zhen)動(dong)(dong)最(zui)終由(you)近(jin)及遠地向(xiang)各個方(fang)向(xiang)傳播(bo)，從而形成機(ji)械(xie)波(bo)。


  超聲波(bo)是一(yi)種以(yi)波(bo)動形式(shi)在(zai)介質(zhi)中傳播(bo)的(de)(de)機(ji)(ji)械(xie)(xie)振(zhen)動，提到了機(ji)(ji)械(xie)(xie)波(bo)傳播(bo)所必需的(de)(de)兩個條件：做機(ji)(ji)械(xie)(xie)振(zhen)動的(de)(de)波(bo)源(yuan)和能夠(gou)傳播(bo)機(ji)(ji)械(xie)(xie)振(zhen)動的(de)(de)介質(zhi)。振(zhen)動與(yu)波(bo)動是相(xiang)互關聯的(de)(de)，振(zhen)動產生波(bo)動，而波(bo)動是振(zhen)動的(de)(de)傳播(bo)。波(bo)動時介質(zhi)中的(de)(de)質(zhi)點會(hui)在(zai)各(ge)自的(de)(de)平衡位置附近做往復(fu)運動，并不隨波(bo)前進(jin)，在(zai)波(bo)動中由各(ge)質(zhi)點的(de)(de)位移連續變化將振(zhen)動能量傳播(bo)出(chu)去。