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. 振動及波的相(xiang)關(guan)物(wu)理量


   物體沿直線或曲線在(zai)(zai)某一(yi)平衡位(wei)(wei)置(zhi)附近做周(zhou)期性往復(fu)運(yun)動(dong)(dong)(dong)，稱為(wei)(wei)機械振動(dong)(dong)(dong)。日常(chang)(chang)生活中隨(sui)處可見振動(dong)(dong)(dong)現(xian)象，如鐘擺(bai)(bai)的往復(fu)運(yun)動(dong)(dong)(dong)、旗幟的擺(bai)(bai)動(dong)(dong)(dong)、聲帶的振動(dong)(dong)(dong)等。常(chang)(chang)見的表(biao)征振動(dong)(dong)(dong)的參數有：波長，任一(yi)質點(dian)經歷一(yi)次(ci)完(wan)整振動(dong)(dong)(dong)時波所(suo)傳(chuan)播的距(ju)離(li)，通常(chang)(chang)用(yong)符(fu)號(hao)λ表(biao)示(shi)(shi)，單位(wei)(wei)為(wei)(wei)m（米(mi)）；波速，波在(zai)(zai)單位(wei)(wei)時間內所(suo)傳(chuan)播的距(ju)離(li)，通常(chang)(chang)用(yong)符(fu)號(hao)c表(biao)示(shi)(shi)，單位(wei)(wei)為(wei)(wei)m/s（米(mi)/秒）；頻率，質點(dian)在(zai)(zai)1s內進(jin)行全振動(dong)(dong)(dong)的次(ci)數，通常(chang)(chang)用(yong)f表(biao)示(shi)(shi)，單位(wei)(wei)為(wei)(wei)Hz（赫茲）；周(zhou)期，質點(dian)次(ci)全振動(dong)(dong)(dong)所(suo)需的時間，通常(chang)(chang)用(yong)T表(biao)示(shi)(shi)，單位(wei)(wei)為(wei)(wei)s（秒）；振幅，質點(dian)離(li)開平位(wei)(wei)置(zhi)的最大距(ju)離(li)，通常(chang)(chang)用(yong)A表(biao)示(shi)(shi)。


  上(shang)述波(bo)(bo)長(chang)、波(bo)(bo)速(su)、頻率(lv)(lv)(lv)三者之間關系為：λ= c/f 由上(shang)式可知(zhi)，頻率(lv)(lv)(lv)一定時(shi)(shi)，波(bo)(bo)速(su)越(yue)(yue)大，波(bo)(bo)長(chang)就越(yue)(yue)長(chang)；而(er)波(bo)(bo)速(su)一定時(shi)(shi)，率(lv)(lv)(lv)越(yue)(yue)低，波(bo)(bo)長(chang)就越(yue)(yue)長(chang)。周期和頻率(lv)(lv)(lv)描述的是振動的快慢，兩(liang)者大小與周期互為倒數(shu)。振幅(fu)描述的是振動的強弱。


2. 機械波


  振(zhen)動在介質(zhi)或空間中的(de)傳(chuan)播(bo)過程叫作(zuo)波(bo)(bo)(bo)(bo)動，簡稱波(bo)(bo)(bo)(bo)，可(ke)分為(wei)機(ji)械(xie)波(bo)(bo)(bo)(bo)與電磁(ci)波(bo)(bo)(bo)(bo)兩種。本(ben)書中僅涉及機(ji)械(xie)波(bo)(bo)(bo)(bo)。振(zhen)動在彈性介質(zhi)中的(de)傳(chuan)播(bo)稱為(wei)機(ji)械(xie)波(bo)(bo)(bo)(bo)，如固體、液體、氣體均可(ke)視為(wei)彈性介質(zhi)。機(ji)械(xie)波(bo)(bo)(bo)(bo)的(de)頻(pin)率范圍(wei)很寬(kuan)，從10-4Hz到102Hz，跨越16個(ge)數(shu)量級其(qi)中人類(lei)聽(ting)覺所能(neng)(neng)感知(zhi)的(de)范圍(wei)在20~20000Hz。人們把能(neng)(neng)牽動聽(ting)覺神經(jing)的(de)機(ji)械(xie)波(bo)(bo)(bo)(bo)稱為(wei)聲(sheng)(sheng)波(bo)(bo)(bo)(bo)，當聲(sheng)(sheng)波(bo)(bo)(bo)(bo)頻(pin)率低(di)于20Hz時(shi)，稱為(wei)次(ci)聲(sheng)(sheng)波(bo)(bo)(bo)(bo)；當聲(sheng)(sheng)波(bo)(bo)(bo)(bo)頻(pin)率于20000Hz時(shi)，稱為(wei)超(chao)聲(sheng)(sheng)波(bo)(bo)(bo)(bo)。


圖 1.jpg


  為(wei)簡單闡(chan)述機械波是(shi)如何產(chan)生(sheng)和傳(chuan)播的(de)(de)，建立如圖所彈(dan)性(xing)(xing)介質(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)點(dian)(dian)(dian)間以小彈(dan)簧連接在(zai)一起(qi)(qi)，這種質(zhi)(zhi)點(dian)(dian)(dian)間以彈(dan)性(xing)(xing)力(li)(li)連接在(zai)起(qi)(qi)的(de)(de)介質(zhi)(zhi)稱為(wei)彈(dan)性(xing)(xing)介質(zhi)(zhi)。外力(li)(li)F首先對(dui)質(zhi)(zhi)點(dian)(dian)(dian)A產(chan)生(sheng)作用，A偏離均衡(heng)(heng)(heng)點(dian)(dian)(dian)，此(ci)時(shi)(shi)附近(jin)(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)將對(dui)A產(chan)生(sheng)力(li)(li)的(de)(de)作用，迫使其回到(dao)(dao)均衡(heng)(heng)(heng)點(dian)(dian)(dian)。而當(dang)A回到(dao)(dao)均衡(heng)(heng)(heng)點(dian)(dian)(dian)時(shi)(shi)，其他質(zhi)(zhi)點(dian)(dian)(dian)對(dui)其不產(chan)生(sheng)作用，但是(shi)由于慣性(xing)(xing)的(de)(de)存在(zai)，A具有(you)一定(ding)的(de)(de)速(su)度，不會(hui)停(ting)留在(zai)均衡(heng)(heng)(heng)點(dian)(dian)(dian)，反而繼續向(xiang)前方(fang)運(yun)動(dong)(dong)，并沿相(xiang)反方(fang)向(xiang)離開均衡(heng)(heng)(heng)點(dian)(dian)(dian)。一旦離開均衡(heng)(heng)(heng)點(dian)(dian)(dian)，A又會(hui)受到(dao)(dao)附近(jin)(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)對(dui)它相(xiang)反的(de)(de)彈(dan)性(xing)(xing)力(li)(li)，使A再次(ci)回到(dao)(dao)均衡(heng)(heng)(heng)點(dian)(dian)(dian)。導致質(zhi)(zhi)點(dian)(dian)(dian)A在(zai)均衡(heng)(heng)(heng)點(dian)(dian)(dian)來回往(wang)復產(chan)生(sheng)振(zhen)(zhen)動(dong)(dong)。與此(ci)同(tong)(tong)時(shi)(shi)，A附近(jin)(jin)(jin)的(de)(de)質(zhi)(zhi)點(dian)(dian)(dian)也會(hui)受到(dao)(dao)同(tong)(tong)樣力(li)(li)的(de)(de)作用使它們離開均衡(heng)(heng)(heng)點(dian)(dian)(dian)，并在(zai)各(ge)自的(de)(de)均衡(heng)(heng)(heng)點(dian)(dian)(dian)附近(jin)(jin)(jin)運(yun)動(dong)(dong)。這樣彈(dan)性(xing)(xing)介質(zhi)(zhi)中單一質(zhi)(zhi)點(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)引起(qi)(qi)鄰近(jin)(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)，鄰近(jin)(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)又會(hui)引起(qi)(qi)更遠質(zhi)(zhi)點(dian)(dian)(dian)的(de)(de)振(zhen)(zhen)動(dong)(dong)最(zui)終由近(jin)(jin)(jin)及遠地向(xiang)各(ge)個方(fang)向(xiang)傳(chuan)播，從而形成機械波。


  超聲波(bo)(bo)是(shi)一種以波(bo)(bo)動(dong)(dong)(dong)形式在介(jie)質(zhi)中(zhong)傳播(bo)(bo)的(de)(de)(de)機(ji)械(xie)振動(dong)(dong)(dong)，提到了(le)機(ji)械(xie)波(bo)(bo)傳播(bo)(bo)所必需(xu)的(de)(de)(de)兩個(ge)條件：做機(ji)械(xie)振動(dong)(dong)(dong)的(de)(de)(de)波(bo)(bo)源(yuan)和能夠傳播(bo)(bo)機(ji)械(xie)振動(dong)(dong)(dong)的(de)(de)(de)介(jie)質(zhi)。振動(dong)(dong)(dong)與(yu)波(bo)(bo)動(dong)(dong)(dong)是(shi)相互(hu)關聯的(de)(de)(de)，振動(dong)(dong)(dong)產生波(bo)(bo)動(dong)(dong)(dong)，而波(bo)(bo)動(dong)(dong)(dong)是(shi)振動(dong)(dong)(dong)的(de)(de)(de)傳播(bo)(bo)。波(bo)(bo)動(dong)(dong)(dong)時介(jie)質(zhi)中(zhong)的(de)(de)(de)質(zhi)點會在各(ge)自(zi)的(de)(de)(de)平衡位置附近做往(wang)復運動(dong)(dong)(dong)，并不隨波(bo)(bo)前進，在波(bo)(bo)動(dong)(dong)(dong)中(zhong)由各(ge)質(zhi)點的(de)(de)(de)位移連(lian)續(xu)變化(hua)將振動(dong)(dong)(dong)能量傳播(bo)(bo)出去。