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. 振動及波的相關(guan)物理量


   物體沿(yan)直線或曲線在(zai)(zai)某一平(ping)衡位(wei)置附近做周期性(xing)往復運(yun)動(dong)，稱為(wei)機(ji)械振(zhen)(zhen)動(dong)。日常生活中隨處可見振(zhen)(zhen)動(dong)現象，如鐘擺(bai)的(de)(de)(de)往復運(yun)動(dong)、旗幟(zhi)的(de)(de)(de)擺(bai)動(dong)、聲帶的(de)(de)(de)振(zhen)(zhen)動(dong)等。常見的(de)(de)(de)表征振(zhen)(zhen)動(dong)的(de)(de)(de)參(can)數有：波(bo)(bo)長，任(ren)一質點經(jing)歷一次(ci)完(wan)整振(zhen)(zhen)動(dong)時波(bo)(bo)所傳播的(de)(de)(de)距(ju)離，通(tong)常用符號λ表示(shi)(shi)(shi)(shi)，單位(wei)為(wei)m（米）；波(bo)(bo)速，波(bo)(bo)在(zai)(zai)單位(wei)時間內(nei)(nei)所傳播的(de)(de)(de)距(ju)離，通(tong)常用符號c表示(shi)(shi)(shi)(shi)，單位(wei)為(wei)m/s（米/秒）；頻(pin)率，質點在(zai)(zai)1s內(nei)(nei)進行全振(zhen)(zhen)動(dong)的(de)(de)(de)次(ci)數，通(tong)常用f表示(shi)(shi)(shi)(shi)，單位(wei)為(wei)Hz（赫茲）；周期，質點次(ci)全振(zhen)(zhen)動(dong)所需的(de)(de)(de)時間，通(tong)常用T表示(shi)(shi)(shi)(shi)，單位(wei)為(wei)s（秒）；振(zhen)(zhen)幅，質點離開平(ping)位(wei)置的(de)(de)(de)最大距(ju)離，通(tong)常用A表示(shi)(shi)(shi)(shi)。


  上述(shu)(shu)波(bo)(bo)長、波(bo)(bo)速、頻(pin)率(lv)三者(zhe)之間關系為：λ= c/f 由上式可知，頻(pin)率(lv)一定時(shi)，波(bo)(bo)速越大，波(bo)(bo)長就越長；而波(bo)(bo)速一定時(shi)，率(lv)越低，波(bo)(bo)長就越長。周期(qi)和頻(pin)率(lv)描述(shu)(shu)的(de)是振(zhen)動的(de)快慢，兩者(zhe)大小與周期(qi)互(hu)為倒(dao)數。振(zhen)幅描述(shu)(shu)的(de)是振(zhen)動的(de)強弱。


2. 機械波


  振動(dong)在介質或空間中(zhong)的傳播(bo)(bo)過程叫作波(bo)(bo)動(dong)，簡稱波(bo)(bo)，可(ke)分為(wei)機械(xie)波(bo)(bo)與(yu)電磁波(bo)(bo)兩種。本書中(zhong)僅涉及機械(xie)波(bo)(bo)。振動(dong)在彈性(xing)介質中(zhong)的傳播(bo)(bo)稱為(wei)機械(xie)波(bo)(bo)，如固體、液體、氣體均可(ke)視為(wei)彈性(xing)介質。機械(xie)波(bo)(bo)的頻率(lv)范圍很寬，從10-4Hz到102Hz，跨越16個數(shu)量(liang)級其中(zhong)人(ren)類聽(ting)(ting)覺(jue)所能(neng)感知的范圍在20~20000Hz。人(ren)們(men)把能(neng)牽動(dong)聽(ting)(ting)覺(jue)神(shen)經的機械(xie)波(bo)(bo)稱為(wei)聲(sheng)波(bo)(bo)，當(dang)聲(sheng)波(bo)(bo)頻率(lv)低于(yu)20Hz時，稱為(wei)次聲(sheng)波(bo)(bo)；當(dang)聲(sheng)波(bo)(bo)頻率(lv)于(yu)20000Hz時，稱為(wei)超(chao)聲(sheng)波(bo)(bo)。


圖 1.jpg


  為簡單闡述機械(xie)波(bo)是如何(he)產(chan)(chan)生和傳播的(de)(de)(de)(de)，建立如圖所(suo)彈(dan)(dan)(dan)性(xing)介(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)間(jian)以小彈(dan)(dan)(dan)簧(huang)連(lian)接在(zai)(zai)(zai)一起(qi)，這種質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)間(jian)以彈(dan)(dan)(dan)性(xing)力(li)連(lian)接在(zai)(zai)(zai)起(qi)的(de)(de)(de)(de)介(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)稱(cheng)為彈(dan)(dan)(dan)性(xing)介(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)。外力(li)F首先對(dui)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)A產(chan)(chan)生作(zuo)用，A偏(pian)離均(jun)(jun)衡(heng)點(dian)(dian)，此(ci)時附(fu)(fu)近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)將對(dui)A產(chan)(chan)生力(li)的(de)(de)(de)(de)作(zuo)用，迫使其(qi)回到(dao)均(jun)(jun)衡(heng)點(dian)(dian)。而(er)當A回到(dao)均(jun)(jun)衡(heng)點(dian)(dian)時，其(qi)他質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)對(dui)其(qi)不(bu)產(chan)(chan)生作(zuo)用，但是由于(yu)慣性(xing)的(de)(de)(de)(de)存(cun)在(zai)(zai)(zai)，A具(ju)有一定的(de)(de)(de)(de)速度，不(bu)會(hui)停留(liu)在(zai)(zai)(zai)均(jun)(jun)衡(heng)點(dian)(dian)，反而(er)繼(ji)續向前方(fang)運動(dong)，并沿相(xiang)反方(fang)向離開(kai)均(jun)(jun)衡(heng)點(dian)(dian)。一旦離開(kai)均(jun)(jun)衡(heng)點(dian)(dian)，A又會(hui)受到(dao)附(fu)(fu)近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)對(dui)它(ta)相(xiang)反的(de)(de)(de)(de)彈(dan)(dan)(dan)性(xing)力(li)，使A再次回到(dao)均(jun)(jun)衡(heng)點(dian)(dian)。導(dao)致質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)A在(zai)(zai)(zai)均(jun)(jun)衡(heng)點(dian)(dian)來回往復產(chan)(chan)生振動(dong)。與此(ci)同時，A附(fu)(fu)近(jin)(jin)的(de)(de)(de)(de)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)也(ye)會(hui)受到(dao)同樣(yang)(yang)力(li)的(de)(de)(de)(de)作(zuo)用使它(ta)們離開(kai)均(jun)(jun)衡(heng)點(dian)(dian)，并在(zai)(zai)(zai)各(ge)自的(de)(de)(de)(de)均(jun)(jun)衡(heng)點(dian)(dian)附(fu)(fu)近(jin)(jin)運動(dong)。這樣(yang)(yang)彈(dan)(dan)(dan)性(xing)介(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)中單一質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振動(dong)引起(qi)鄰近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振動(dong)，鄰近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振動(dong)又會(hui)引起(qi)更(geng)遠質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)的(de)(de)(de)(de)振動(dong)最終(zhong)由近(jin)(jin)及遠地向各(ge)個方(fang)向傳播，從而(er)形成機械(xie)波(bo)。


  超(chao)聲波是一種(zhong)以波動(dong)(dong)(dong)(dong)形(xing)式在介(jie)質中傳(chuan)播(bo)(bo)的(de)(de)機(ji)(ji)械(xie)振(zhen)(zhen)動(dong)(dong)(dong)(dong)，提到了機(ji)(ji)械(xie)波傳(chuan)播(bo)(bo)所(suo)必(bi)需的(de)(de)兩個(ge)條(tiao)件：做機(ji)(ji)械(xie)振(zhen)(zhen)動(dong)(dong)(dong)(dong)的(de)(de)波源和能(neng)夠傳(chuan)播(bo)(bo)機(ji)(ji)械(xie)振(zhen)(zhen)動(dong)(dong)(dong)(dong)的(de)(de)介(jie)質。振(zhen)(zhen)動(dong)(dong)(dong)(dong)與波動(dong)(dong)(dong)(dong)是相互關聯的(de)(de)，振(zhen)(zhen)動(dong)(dong)(dong)(dong)產(chan)生(sheng)波動(dong)(dong)(dong)(dong)，而波動(dong)(dong)(dong)(dong)是振(zhen)(zhen)動(dong)(dong)(dong)(dong)的(de)(de)傳(chuan)播(bo)(bo)。波動(dong)(dong)(dong)(dong)時(shi)介(jie)質中的(de)(de)質點會(hui)在各(ge)自的(de)(de)平衡位置(zhi)附(fu)近做往復運動(dong)(dong)(dong)(dong)，并不隨波前進，在波動(dong)(dong)(dong)(dong)中由各(ge)質點的(de)(de)位移連續(xu)變化將(jiang)振(zhen)(zhen)動(dong)(dong)(dong)(dong)能(neng)量傳(chuan)播(bo)(bo)出去。