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久久99國產精品久久99果凍傳媒: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. 振動及波的相關物(wu)理量(liang)

   物體(ti)沿(yan)直線或曲線在(zai)某一(yi)(yi)平(ping)衡(heng)位(wei)(wei)置附近做周期性往復運動(dong)，稱為(wei)機械振(zhen)(zhen)動(dong)。日常(chang)(chang)(chang)生活中隨處可見振(zhen)(zhen)動(dong)現象，如鐘擺的(de)(de)(de)往復運動(dong)、旗幟的(de)(de)(de)擺動(dong)、聲帶的(de)(de)(de)振(zhen)(zhen)動(dong)等。常(chang)(chang)(chang)見的(de)(de)(de)表征振(zhen)(zhen)動(dong)的(de)(de)(de)參數(shu)有：波(bo)長，任(ren)一(yi)(yi)質(zhi)點經歷一(yi)(yi)次(ci)(ci)完整振(zhen)(zhen)動(dong)時(shi)(shi)波(bo)所傳(chuan)(chuan)播(bo)的(de)(de)(de)距離(li)，通常(chang)(chang)(chang)用符(fu)(fu)號(hao)λ表示(shi)(shi)，單(dan)位(wei)(wei)為(wei)m（米(mi)(mi)）；波(bo)速，波(bo)在(zai)單(dan)位(wei)(wei)時(shi)(shi)間內所傳(chuan)(chuan)播(bo)的(de)(de)(de)距離(li)，通常(chang)(chang)(chang)用符(fu)(fu)號(hao)c表示(shi)(shi)，單(dan)位(wei)(wei)為(wei)m/s（米(mi)(mi)/秒）；頻率，質(zhi)點在(zai)1s內進行全(quan)振(zhen)(zhen)動(dong)的(de)(de)(de)次(ci)(ci)數(shu)，通常(chang)(chang)(chang)用f表示(shi)(shi)，單(dan)位(wei)(wei)為(wei)Hz（赫茲）；周期，質(zhi)點次(ci)(ci)全(quan)振(zhen)(zhen)動(dong)所需的(de)(de)(de)時(shi)(shi)間，通常(chang)(chang)(chang)用T表示(shi)(shi)，單(dan)位(wei)(wei)為(wei)s（秒）；振(zhen)(zhen)幅，質(zhi)點離(li)開(kai)平(ping)位(wei)(wei)置的(de)(de)(de)最大距離(li)，通常(chang)(chang)(chang)用A表示(shi)(shi)。

  上述(shu)波(bo)長、波(bo)速、頻(pin)率(lv)(lv)三者之間關系為：λ= c/f 由上式可(ke)知，頻(pin)率(lv)(lv)一(yi)定時，波(bo)速越(yue)(yue)大，波(bo)長就越(yue)(yue)長；而波(bo)速一(yi)定時，率(lv)(lv)越(yue)(yue)低，波(bo)長就越(yue)(yue)長。周(zhou)(zhou)期和頻(pin)率(lv)(lv)描述(shu)的(de)是振(zhen)動的(de)快慢，兩(liang)者大小與(yu)周(zhou)(zhou)期互為倒數(shu)。振(zhen)幅描述(shu)的(de)是振(zhen)動的(de)強弱。

2. 機械波

  振(zhen)動(dong)(dong)在(zai)介(jie)質或空間中(zhong)(zhong)的傳播過程叫作波(bo)(bo)(bo)動(dong)(dong)，簡稱(cheng)波(bo)(bo)(bo)，可分為(wei)機(ji)械(xie)(xie)波(bo)(bo)(bo)與(yu)電磁波(bo)(bo)(bo)兩種。本書中(zhong)(zhong)僅涉及機(ji)械(xie)(xie)波(bo)(bo)(bo)。振(zhen)動(dong)(dong)在(zai)彈性介(jie)質中(zhong)(zhong)的傳播稱(cheng)為(wei)機(ji)械(xie)(xie)波(bo)(bo)(bo)，如固體(ti)、液體(ti)、氣體(ti)均(jun)可視為(wei)彈性介(jie)質。機(ji)械(xie)(xie)波(bo)(bo)(bo)的頻(pin)率范圍(wei)很寬，從10-4Hz到(dao)102Hz，跨越16個數(shu)量級其中(zhong)(zhong)人類聽覺所能(neng)感知的范圍(wei)在(zai)20~20000Hz。人們把能(neng)牽動(dong)(dong)聽覺神經(jing)的機(ji)械(xie)(xie)波(bo)(bo)(bo)稱(cheng)為(wei)聲(sheng)波(bo)(bo)(bo)，當(dang)(dang)聲(sheng)波(bo)(bo)(bo)頻(pin)率低于20Hz時(shi)，稱(cheng)為(wei)次聲(sheng)波(bo)(bo)(bo)；當(dang)(dang)聲(sheng)波(bo)(bo)(bo)頻(pin)率于20000Hz時(shi)，稱(cheng)為(wei)超聲(sheng)波(bo)(bo)(bo)。

  為簡單(dan)闡(chan)述機(ji)(ji)械波是如何產生(sheng)和(he)傳播的(de)(de)(de)(de)，建立(li)如圖(tu)所彈性(xing)介(jie)質(zhi)(zhi)模型。圖(tu)2-1中質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間以小彈簧連(lian)接在(zai)一(yi)起(qi)，這種質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間以彈性(xing)力(li)連(lian)接在(zai)起(qi)的(de)(de)(de)(de)介(jie)質(zhi)(zhi)稱為彈性(xing)介(jie)質(zhi)(zhi)。外力(li)F首先對質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A產生(sheng)作(zuo)(zuo)用(yong)，A偏離(li)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，此時(shi)附(fu)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)將對A產生(sheng)力(li)的(de)(de)(de)(de)作(zuo)(zuo)用(yong)，迫使(shi)其回(hui)(hui)到(dao)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。而當A回(hui)(hui)到(dao)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)時(shi)，其他質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對其不產生(sheng)作(zuo)(zuo)用(yong)，但是由于慣性(xing)的(de)(de)(de)(de)存在(zai)，A具有一(yi)定的(de)(de)(de)(de)速度，不會停(ting)留在(zai)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，反(fan)而繼續向前方(fang)(fang)運動(dong)(dong)，并沿相反(fan)方(fang)(fang)向離(li)開(kai)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。一(yi)旦離(li)開(kai)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，A又(you)會受到(dao)附(fu)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對它相反(fan)的(de)(de)(de)(de)彈性(xing)力(li)，使(shi)A再次(ci)回(hui)(hui)到(dao)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。導致質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A在(zai)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)來回(hui)(hui)往復產生(sheng)振動(dong)(dong)。與(yu)此同時(shi)，A附(fu)近(jin)(jin)的(de)(de)(de)(de)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)也會受到(dao)同樣(yang)力(li)的(de)(de)(de)(de)作(zuo)(zuo)用(yong)使(shi)它們離(li)開(kai)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，并在(zai)各自的(de)(de)(de)(de)均(jun)衡(heng)(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)附(fu)近(jin)(jin)運動(dong)(dong)。這樣(yang)彈性(xing)介(jie)質(zhi)(zhi)中單(dan)一(yi)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振動(dong)(dong)引(yin)起(qi)鄰(lin)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振動(dong)(dong)，鄰(lin)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振動(dong)(dong)又(you)會引(yin)起(qi)更遠(yuan)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振動(dong)(dong)最終由近(jin)(jin)及遠(yuan)地向各個方(fang)(fang)向傳播，從而形成機(ji)(ji)械波。

  超聲波(bo)(bo)(bo)是一(yi)種以波(bo)(bo)(bo)動(dong)(dong)(dong)形式(shi)在介(jie)質(zhi)(zhi)(zhi)中傳(chuan)播(bo)(bo)的(de)(de)(de)機械(xie)振動(dong)(dong)(dong)，提到了機械(xie)波(bo)(bo)(bo)傳(chuan)播(bo)(bo)所(suo)必需的(de)(de)(de)兩(liang)個(ge)條(tiao)件(jian)：做機械(xie)振動(dong)(dong)(dong)的(de)(de)(de)波(bo)(bo)(bo)源和(he)能(neng)夠傳(chuan)播(bo)(bo)機械(xie)振動(dong)(dong)(dong)的(de)(de)(de)介(jie)質(zhi)(zhi)(zhi)。振動(dong)(dong)(dong)與波(bo)(bo)(bo)動(dong)(dong)(dong)是相互關聯的(de)(de)(de)，振動(dong)(dong)(dong)產生波(bo)(bo)(bo)動(dong)(dong)(dong)，而波(bo)(bo)(bo)動(dong)(dong)(dong)是振動(dong)(dong)(dong)的(de)(de)(de)傳(chuan)播(bo)(bo)。波(bo)(bo)(bo)動(dong)(dong)(dong)時介(jie)質(zhi)(zhi)(zhi)中的(de)(de)(de)質(zhi)(zhi)(zhi)點(dian)會(hui)在各(ge)(ge)自的(de)(de)(de)平衡位(wei)置附近做往復(fu)運動(dong)(dong)(dong)，并不隨波(bo)(bo)(bo)前進，在波(bo)(bo)(bo)動(dong)(dong)(dong)中由(you)各(ge)(ge)質(zhi)(zhi)(zhi)點(dian)的(de)(de)(de)位(wei)移連續變化將振動(dong)(dong)(dong)能(neng)量傳(chuan)播(bo)(bo)出去(qu)。