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連接: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(dong)及(ji)波的相關(guan)物理量


   物(wu)體沿直線或曲線在(zai)某(mou)一平衡位置(zhi)附(fu)近做周(zhou)期性往復運動，稱為機(ji)械振(zhen)(zhen)動。日(ri)常(chang)(chang)(chang)生活中隨處可見振(zhen)(zhen)動現象，如鐘(zhong)擺的往復運動、旗幟的擺動、聲帶的振(zhen)(zhen)動等。常(chang)(chang)(chang)見的表征(zheng)振(zhen)(zhen)動的參數有：波長，任一質(zhi)點經(jing)歷一次完整振(zhen)(zhen)動時(shi)(shi)波所(suo)傳(chuan)播的距(ju)離(li)(li)，通(tong)常(chang)(chang)(chang)用符號λ表示(shi)(shi)，單(dan)(dan)位為m（米）；波速，波在(zai)單(dan)(dan)位時(shi)(shi)間內所(suo)傳(chuan)播的距(ju)離(li)(li)，通(tong)常(chang)(chang)(chang)用符號c表示(shi)(shi)，單(dan)(dan)位為m/s（米/秒(miao)）；頻率，質(zhi)點在(zai)1s內進行全(quan)振(zhen)(zhen)動的次數，通(tong)常(chang)(chang)(chang)用f表示(shi)(shi)，單(dan)(dan)位為Hz（赫茲）；周(zhou)期，質(zhi)點次全(quan)振(zhen)(zhen)動所(suo)需的時(shi)(shi)間，通(tong)常(chang)(chang)(chang)用T表示(shi)(shi)，單(dan)(dan)位為s（秒(miao)）；振(zhen)(zhen)幅(fu)，質(zhi)點離(li)(li)開平位置(zhi)的最(zui)大距(ju)離(li)(li)，通(tong)常(chang)(chang)(chang)用A表示(shi)(shi)。


  上(shang)述(shu)波(bo)長、波(bo)速(su)、頻率(lv)三者之間關(guan)系為：λ= c/f 由上(shang)式可(ke)知，頻率(lv)一(yi)定(ding)時(shi)，波(bo)速(su)越(yue)大，波(bo)長就(jiu)越(yue)長；而波(bo)速(su)一(yi)定(ding)時(shi)，率(lv)越(yue)低，波(bo)長就(jiu)越(yue)長。周期(qi)和頻率(lv)描述(shu)的(de)是振(zhen)動的(de)快慢，兩者大小與周期(qi)互為倒數。振(zhen)幅描述(shu)的(de)是振(zhen)動的(de)強弱。


2. 機械波


  振(zhen)動在介質或(huo)空間中的傳(chuan)播(bo)過程(cheng)叫作波(bo)(bo)(bo)動，簡稱(cheng)(cheng)波(bo)(bo)(bo)，可分(fen)為(wei)機(ji)(ji)械(xie)(xie)(xie)(xie)波(bo)(bo)(bo)與電磁波(bo)(bo)(bo)兩(liang)種。本書(shu)中僅涉及(ji)機(ji)(ji)械(xie)(xie)(xie)(xie)波(bo)(bo)(bo)。振(zhen)動在彈性(xing)介質中的傳(chuan)播(bo)稱(cheng)(cheng)為(wei)機(ji)(ji)械(xie)(xie)(xie)(xie)波(bo)(bo)(bo)，如固(gu)體、液(ye)體、氣體均(jun)可視為(wei)彈性(xing)介質。機(ji)(ji)械(xie)(xie)(xie)(xie)波(bo)(bo)(bo)的頻率(lv)范(fan)圍(wei)(wei)很寬(kuan)，從10-4Hz到102Hz，跨越16個數量(liang)級其(qi)中人(ren)類聽(ting)(ting)覺(jue)所能(neng)感知的范(fan)圍(wei)(wei)在20~20000Hz。人(ren)們把能(neng)牽動聽(ting)(ting)覺(jue)神經的機(ji)(ji)械(xie)(xie)(xie)(xie)波(bo)(bo)(bo)稱(cheng)(cheng)為(wei)聲(sheng)(sheng)波(bo)(bo)(bo)，當聲(sheng)(sheng)波(bo)(bo)(bo)頻率(lv)低于(yu)20Hz時(shi)，稱(cheng)(cheng)為(wei)次聲(sheng)(sheng)波(bo)(bo)(bo)；當聲(sheng)(sheng)波(bo)(bo)(bo)頻率(lv)于(yu)20000Hz時(shi)，稱(cheng)(cheng)為(wei)超聲(sheng)(sheng)波(bo)(bo)(bo)。


圖 1.jpg


  為(wei)簡單(dan)闡述機械(xie)(xie)波(bo)是如(ru)何產生(sheng)和傳(chuan)播(bo)的(de)(de)，建立如(ru)圖(tu)所彈(dan)性(xing)介質(zhi)模(mo)型。圖(tu)2-1中質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間以(yi)小(xiao)彈(dan)簧連(lian)接(jie)在(zai)(zai)一(yi)(yi)起(qi)，這種質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間以(yi)彈(dan)性(xing)力(li)(li)連(lian)接(jie)在(zai)(zai)起(qi)的(de)(de)介質(zhi)稱(cheng)為(wei)彈(dan)性(xing)介質(zhi)。外力(li)(li)F首先對質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A產生(sheng)作(zuo)(zuo)用(yong)(yong)，A偏離(li)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，此(ci)時(shi)附近(jin)(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)將對A產生(sheng)力(li)(li)的(de)(de)作(zuo)(zuo)用(yong)(yong)，迫(po)使其(qi)(qi)回(hui)(hui)到(dao)(dao)(dao)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。而當A回(hui)(hui)到(dao)(dao)(dao)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)時(shi)，其(qi)(qi)他(ta)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對其(qi)(qi)不產生(sheng)作(zuo)(zuo)用(yong)(yong)，但是由于(yu)慣性(xing)的(de)(de)存在(zai)(zai)，A具有一(yi)(yi)定的(de)(de)速(su)度，不會(hui)(hui)(hui)停留在(zai)(zai)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，反而繼(ji)續(xu)向(xiang)前方(fang)運(yun)(yun)動(dong)(dong)，并(bing)沿(yan)相反方(fang)向(xiang)離(li)開(kai)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。一(yi)(yi)旦離(li)開(kai)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，A又(you)會(hui)(hui)(hui)受到(dao)(dao)(dao)附近(jin)(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對它(ta)相反的(de)(de)彈(dan)性(xing)力(li)(li)，使A再次回(hui)(hui)到(dao)(dao)(dao)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。導致質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A在(zai)(zai)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)來(lai)回(hui)(hui)往復(fu)產生(sheng)振(zhen)(zhen)動(dong)(dong)。與此(ci)同(tong)時(shi)，A附近(jin)(jin)的(de)(de)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)也會(hui)(hui)(hui)受到(dao)(dao)(dao)同(tong)樣力(li)(li)的(de)(de)作(zuo)(zuo)用(yong)(yong)使它(ta)們離(li)開(kai)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，并(bing)在(zai)(zai)各自(zi)的(de)(de)均(jun)衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)(dian)附近(jin)(jin)運(yun)(yun)動(dong)(dong)。這樣彈(dan)性(xing)介質(zhi)中單(dan)一(yi)(yi)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)引起(qi)鄰近(jin)(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)，鄰近(jin)(jin)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)又(you)會(hui)(hui)(hui)引起(qi)更遠(yuan)質(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)最終由近(jin)(jin)及(ji)遠(yuan)地向(xiang)各個方(fang)向(xiang)傳(chuan)播(bo)，從而形成機械(xie)(xie)波(bo)。


  超聲波(bo)(bo)是一(yi)種以波(bo)(bo)動(dong)(dong)(dong)形式(shi)在介質(zhi)(zhi)中傳(chuan)播(bo)(bo)的(de)(de)機(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)，提(ti)到了機(ji)械波(bo)(bo)傳(chuan)播(bo)(bo)所必(bi)需的(de)(de)兩個條(tiao)件(jian)：做(zuo)機(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)的(de)(de)波(bo)(bo)源和能夠傳(chuan)播(bo)(bo)機(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)的(de)(de)介質(zhi)(zhi)。振(zhen)(zhen)(zhen)動(dong)(dong)(dong)與波(bo)(bo)動(dong)(dong)(dong)是相互(hu)關聯的(de)(de)，振(zhen)(zhen)(zhen)動(dong)(dong)(dong)產生波(bo)(bo)動(dong)(dong)(dong)，而(er)波(bo)(bo)動(dong)(dong)(dong)是振(zhen)(zhen)(zhen)動(dong)(dong)(dong)的(de)(de)傳(chuan)播(bo)(bo)。波(bo)(bo)動(dong)(dong)(dong)時介質(zhi)(zhi)中的(de)(de)質(zhi)(zhi)點會(hui)在各自的(de)(de)平衡位置附近做(zuo)往復運動(dong)(dong)(dong)，并不隨波(bo)(bo)前進，在波(bo)(bo)動(dong)(dong)(dong)中由各質(zhi)(zhi)點的(de)(de)位移連續變化將振(zhen)(zhen)(zhen)動(dong)(dong)(dong)能量傳(chuan)播(bo)(bo)出去。