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)動及波的(de)相關物理(li)量


   物體沿直線(xian)或(huo)曲線(xian)在某一(yi)平衡位(wei)置附近做周(zhou)期性往(wang)復運動(dong)(dong)(dong)(dong)(dong)，稱為(wei)機械振(zhen)動(dong)(dong)(dong)(dong)(dong)。日常(chang)生(sheng)活中隨(sui)處可見振(zhen)動(dong)(dong)(dong)(dong)(dong)現象，如鐘擺(bai)的(de)(de)(de)(de)往(wang)復運動(dong)(dong)(dong)(dong)(dong)、旗(qi)幟的(de)(de)(de)(de)擺(bai)動(dong)(dong)(dong)(dong)(dong)、聲帶的(de)(de)(de)(de)振(zhen)動(dong)(dong)(dong)(dong)(dong)等(deng)。常(chang)見的(de)(de)(de)(de)表(biao)征振(zhen)動(dong)(dong)(dong)(dong)(dong)的(de)(de)(de)(de)參數有(you)：波(bo)(bo)長，任(ren)一(yi)質(zhi)點(dian)(dian)經(jing)歷一(yi)次完整(zheng)振(zhen)動(dong)(dong)(dong)(dong)(dong)時波(bo)(bo)所(suo)傳播的(de)(de)(de)(de)距離(li)，通常(chang)用(yong)符(fu)號λ表(biao)示(shi)(shi)，單(dan)位(wei)為(wei)m（米）；波(bo)(bo)速，波(bo)(bo)在單(dan)位(wei)時間(jian)內所(suo)傳播的(de)(de)(de)(de)距離(li)，通常(chang)用(yong)符(fu)號c表(biao)示(shi)(shi)，單(dan)位(wei)為(wei)m/s（米/秒）；頻(pin)率，質(zhi)點(dian)(dian)在1s內進行全振(zhen)動(dong)(dong)(dong)(dong)(dong)的(de)(de)(de)(de)次數，通常(chang)用(yong)f表(biao)示(shi)(shi)，單(dan)位(wei)為(wei)Hz（赫茲）；周(zhou)期，質(zhi)點(dian)(dian)次全振(zhen)動(dong)(dong)(dong)(dong)(dong)所(suo)需的(de)(de)(de)(de)時間(jian)，通常(chang)用(yong)T表(biao)示(shi)(shi)，單(dan)位(wei)為(wei)s（秒）；振(zhen)幅，質(zhi)點(dian)(dian)離(li)開平位(wei)置的(de)(de)(de)(de)最(zui)大距離(li)，通常(chang)用(yong)A表(biao)示(shi)(shi)。


  上(shang)(shang)述(shu)波長、波速、頻率三(san)者之間關系(xi)為：λ= c/f 由上(shang)(shang)式(shi)可(ke)知，頻率一(yi)定時(shi)，波速越大，波長就越長；而波速一(yi)定時(shi)，率越低，波長就越長。周(zhou)期和(he)頻率描述(shu)的(de)是振(zhen)動的(de)快慢，兩(liang)者大小與(yu)周(zhou)期互為倒數。振(zhen)幅描述(shu)的(de)是振(zhen)動的(de)強弱(ruo)。


2. 機械波


  振(zhen)動在介質(zhi)或空間中的(de)傳播過(guo)程叫作(zuo)波(bo)(bo)(bo)動，簡稱(cheng)波(bo)(bo)(bo)，可(ke)分為機(ji)械(xie)波(bo)(bo)(bo)與電磁波(bo)(bo)(bo)兩種(zhong)。本(ben)書(shu)中僅涉(she)及機(ji)械(xie)波(bo)(bo)(bo)。振(zhen)動在彈性(xing)介質(zhi)中的(de)傳播稱(cheng)為機(ji)械(xie)波(bo)(bo)(bo)，如固體(ti)(ti)、液(ye)體(ti)(ti)、氣(qi)體(ti)(ti)均可(ke)視為彈性(xing)介質(zhi)。機(ji)械(xie)波(bo)(bo)(bo)的(de)頻(pin)(pin)率范(fan)圍很寬(kuan)，從(cong)10-4Hz到102Hz，跨越16個數量級(ji)其中人(ren)類(lei)聽覺所能(neng)感知的(de)范(fan)圍在20~20000Hz。人(ren)們(men)把能(neng)牽動聽覺神經的(de)機(ji)械(xie)波(bo)(bo)(bo)稱(cheng)為聲波(bo)(bo)(bo)，當聲波(bo)(bo)(bo)頻(pin)(pin)率低于20Hz時(shi)，稱(cheng)為次聲波(bo)(bo)(bo)；當聲波(bo)(bo)(bo)頻(pin)(pin)率于20000Hz時(shi)，稱(cheng)為超聲波(bo)(bo)(bo)。


圖 1.jpg


  為簡單闡述(shu)機械波(bo)是(shi)如何產(chan)(chan)生(sheng)(sheng)(sheng)和傳播的(de)(de)(de)(de)，建立如圖所彈(dan)(dan)性(xing)(xing)介(jie)質(zhi)(zhi)(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間(jian)以小(xiao)彈(dan)(dan)簧連(lian)接在(zai)(zai)(zai)(zai)一起(qi)，這(zhe)種(zhong)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間(jian)以彈(dan)(dan)性(xing)(xing)力連(lian)接在(zai)(zai)(zai)(zai)起(qi)的(de)(de)(de)(de)介(jie)質(zhi)(zhi)(zhi)(zhi)稱為彈(dan)(dan)性(xing)(xing)介(jie)質(zhi)(zhi)(zhi)(zhi)。外(wai)力F首先對(dui)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A產(chan)(chan)生(sheng)(sheng)(sheng)作(zuo)用(yong)，A偏離(li)(li)均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，此時(shi)(shi)附近質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)將(jiang)對(dui)A產(chan)(chan)生(sheng)(sheng)(sheng)力的(de)(de)(de)(de)作(zuo)用(yong)，迫使其(qi)回到均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。而當A回到均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，其(qi)他質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對(dui)其(qi)不(bu)產(chan)(chan)生(sheng)(sheng)(sheng)作(zuo)用(yong)，但是(shi)由于慣性(xing)(xing)的(de)(de)(de)(de)存在(zai)(zai)(zai)(zai)，A具有一定的(de)(de)(de)(de)速度，不(bu)會停(ting)留在(zai)(zai)(zai)(zai)均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，反而繼續向(xiang)前方(fang)運動(dong)(dong)，并沿相(xiang)反方(fang)向(xiang)離(li)(li)開均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。一旦離(li)(li)開均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，A又會受(shou)到附近質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對(dui)它(ta)相(xiang)反的(de)(de)(de)(de)彈(dan)(dan)性(xing)(xing)力，使A再次回到均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)。導(dao)致(zhi)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A在(zai)(zai)(zai)(zai)均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)來回往(wang)復產(chan)(chan)生(sheng)(sheng)(sheng)振(zhen)動(dong)(dong)。與此同(tong)時(shi)(shi)，A附近的(de)(de)(de)(de)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)也會受(shou)到同(tong)樣力的(de)(de)(de)(de)作(zuo)用(yong)使它(ta)們離(li)(li)開均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)，并在(zai)(zai)(zai)(zai)各自的(de)(de)(de)(de)均衡(heng)(heng)(heng)點(dian)(dian)(dian)(dian)(dian)附近運動(dong)(dong)。這(zhe)樣彈(dan)(dan)性(xing)(xing)介(jie)質(zhi)(zhi)(zhi)(zhi)中單一質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)引(yin)起(qi)鄰(lin)近質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)，鄰(lin)近質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)又會引(yin)起(qi)更遠質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)動(dong)(dong)最終(zhong)由近及(ji)遠地向(xiang)各個方(fang)向(xiang)傳播，從(cong)而形成(cheng)機械波(bo)。


  超聲波(bo)(bo)(bo)是(shi)(shi)一種以波(bo)(bo)(bo)動(dong)形式在(zai)介質(zhi)(zhi)中傳(chuan)播(bo)(bo)的(de)(de)(de)(de)機(ji)械(xie)振動(dong)，提到(dao)了機(ji)械(xie)波(bo)(bo)(bo)傳(chuan)播(bo)(bo)所必需的(de)(de)(de)(de)兩(liang)個條(tiao)件(jian)：做機(ji)械(xie)振動(dong)的(de)(de)(de)(de)波(bo)(bo)(bo)源和(he)能(neng)夠傳(chuan)播(bo)(bo)機(ji)械(xie)振動(dong)的(de)(de)(de)(de)介質(zhi)(zhi)。振動(dong)與波(bo)(bo)(bo)動(dong)是(shi)(shi)相互(hu)關聯(lian)的(de)(de)(de)(de)，振動(dong)產生波(bo)(bo)(bo)動(dong)，而(er)波(bo)(bo)(bo)動(dong)是(shi)(shi)振動(dong)的(de)(de)(de)(de)傳(chuan)播(bo)(bo)。波(bo)(bo)(bo)動(dong)時介質(zhi)(zhi)中的(de)(de)(de)(de)質(zhi)(zhi)點會在(zai)各自的(de)(de)(de)(de)平衡(heng)位置(zhi)附近(jin)做往(wang)復運(yun)動(dong)，并不隨(sui)波(bo)(bo)(bo)前進(jin)，在(zai)波(bo)(bo)(bo)動(dong)中由各質(zhi)(zhi)點的(de)(de)(de)(de)位移(yi)連續變化將振動(dong)能(neng)量(liang)傳(chuan)播(bo)(bo)出去。