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破解碼: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)及波的相關物理(li)量


   物體沿直(zhi)線(xian)或曲(qu)線(xian)在(zai)某一平(ping)衡位(wei)(wei)(wei)(wei)置(zhi)附(fu)近(jin)做周(zhou)期性往復(fu)運(yun)動(dong)(dong)，稱為(wei)機械振(zhen)(zhen)動(dong)(dong)。日常(chang)(chang)生(sheng)活(huo)中(zhong)隨處(chu)可見振(zhen)(zhen)動(dong)(dong)現象，如(ru)鐘擺(bai)的往復(fu)運(yun)動(dong)(dong)、旗(qi)幟的擺(bai)動(dong)(dong)、聲帶的振(zhen)(zhen)動(dong)(dong)等。常(chang)(chang)見的表(biao)征振(zhen)(zhen)動(dong)(dong)的參數有：波(bo)長，任(ren)一質(zhi)點(dian)經(jing)歷一次完整振(zhen)(zhen)動(dong)(dong)時波(bo)所傳播的距(ju)離(li)，通(tong)常(chang)(chang)用(yong)(yong)符號(hao)λ表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)m（米）；波(bo)速，波(bo)在(zai)單位(wei)(wei)(wei)(wei)時間內所傳播的距(ju)離(li)，通(tong)常(chang)(chang)用(yong)(yong)符號(hao)c表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)m/s（米/秒）；頻率，質(zhi)點(dian)在(zai)1s內進(jin)行全振(zhen)(zhen)動(dong)(dong)的次數，通(tong)常(chang)(chang)用(yong)(yong)f表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)Hz（赫茲）；周(zhou)期，質(zhi)點(dian)次全振(zhen)(zhen)動(dong)(dong)所需(xu)的時間，通(tong)常(chang)(chang)用(yong)(yong)T表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)s（秒）；振(zhen)(zhen)幅，質(zhi)點(dian)離(li)開平(ping)位(wei)(wei)(wei)(wei)置(zhi)的最大距(ju)離(li)，通(tong)常(chang)(chang)用(yong)(yong)A表(biao)示。


  上述(shu)波(bo)(bo)長、波(bo)(bo)速、頻(pin)率(lv)三者之間(jian)關系為(wei)：λ= c/f 由上式(shi)可知，頻(pin)率(lv)一(yi)定(ding)時，波(bo)(bo)速越大，波(bo)(bo)長就(jiu)越長；而波(bo)(bo)速一(yi)定(ding)時，率(lv)越低，波(bo)(bo)長就(jiu)越長。周期和頻(pin)率(lv)描(miao)述(shu)的是振動(dong)的快慢，兩(liang)者大小與周期互為(wei)倒數。振幅描(miao)述(shu)的是振動(dong)的強弱(ruo)。


2. 機械波


  振(zhen)動在介質(zhi)或空間中(zhong)的(de)傳播過程叫(jiao)作波(bo)動，簡(jian)稱(cheng)波(bo)，可分為(wei)(wei)機(ji)械(xie)波(bo)與電磁波(bo)兩種(zhong)。本書中(zhong)僅涉及機(ji)械(xie)波(bo)。振(zhen)動在彈(dan)性(xing)(xing)介質(zhi)中(zhong)的(de)傳播稱(cheng)為(wei)(wei)機(ji)械(xie)波(bo)，如(ru)固體、液體、氣體均(jun)可視(shi)為(wei)(wei)彈(dan)性(xing)(xing)介質(zhi)。機(ji)械(xie)波(bo)的(de)頻(pin)率范(fan)圍很寬(kuan)，從10-4Hz到102Hz，跨越16個數量級其中(zhong)人類聽覺所能感知的(de)范(fan)圍在20~20000Hz。人們把能牽(qian)動聽覺神經的(de)機(ji)械(xie)波(bo)稱(cheng)為(wei)(wei)聲波(bo)，當聲波(bo)頻(pin)率低于20Hz時(shi)，稱(cheng)為(wei)(wei)次聲波(bo)；當聲波(bo)頻(pin)率于20000Hz時(shi)，稱(cheng)為(wei)(wei)超(chao)聲波(bo)。


圖 1.jpg


  為簡單(dan)闡述機械波是如(ru)何(he)產(chan)生和傳(chuan)(chuan)播的(de)，建立如(ru)圖所彈性(xing)(xing)介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間以(yi)小彈簧連接在(zai)一起，這種質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間以(yi)彈性(xing)(xing)力連接在(zai)起的(de)介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)稱為彈性(xing)(xing)介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)。外力F首先對質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A產(chan)生作(zuo)用(yong)，A偏(pian)離均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，此時(shi)附(fu)(fu)近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)將對A產(chan)生力的(de)作(zuo)用(yong)，迫使(shi)其回到(dao)(dao)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)。而(er)當A回到(dao)(dao)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)時(shi)，其他質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對其不產(chan)生作(zuo)用(yong)，但是由(you)于慣性(xing)(xing)的(de)存在(zai)，A具有一定的(de)速度，不會停留在(zai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，反(fan)而(er)繼續(xu)向(xiang)前方運動(dong)(dong)(dong)(dong)，并(bing)(bing)沿相反(fan)方向(xiang)離開(kai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)。一旦離開(kai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，A又會受到(dao)(dao)附(fu)(fu)近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對它相反(fan)的(de)彈性(xing)(xing)力，使(shi)A再次(ci)回到(dao)(dao)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)。導(dao)致質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A在(zai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)來(lai)回往復產(chan)生振動(dong)(dong)(dong)(dong)。與此同時(shi)，A附(fu)(fu)近(jin)的(de)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)也會受到(dao)(dao)同樣力的(de)作(zuo)用(yong)使(shi)它們離開(kai)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，并(bing)(bing)在(zai)各自(zi)的(de)均(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)附(fu)(fu)近(jin)運動(dong)(dong)(dong)(dong)。這樣彈性(xing)(xing)介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)中單(dan)一質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)振動(dong)(dong)(dong)(dong)引起鄰近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)振動(dong)(dong)(dong)(dong)，鄰近(jin)質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)振動(dong)(dong)(dong)(dong)又會引起更(geng)遠質(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)振動(dong)(dong)(dong)(dong)最終由(you)近(jin)及遠地向(xiang)各個方向(xiang)傳(chuan)(chuan)播，從而(er)形成(cheng)機械波。


  超(chao)聲(sheng)波(bo)是(shi)一種(zhong)以波(bo)動(dong)(dong)(dong)(dong)形(xing)式(shi)在(zai)介質(zhi)中(zhong)傳播(bo)(bo)的(de)(de)機械振(zhen)動(dong)(dong)(dong)(dong)，提到(dao)了機械波(bo)傳播(bo)(bo)所(suo)必(bi)需的(de)(de)兩個條(tiao)件：做(zuo)機械振(zhen)動(dong)(dong)(dong)(dong)的(de)(de)波(bo)源(yuan)和能(neng)夠傳播(bo)(bo)機械振(zhen)動(dong)(dong)(dong)(dong)的(de)(de)介質(zhi)。振(zhen)動(dong)(dong)(dong)(dong)與波(bo)動(dong)(dong)(dong)(dong)是(shi)相互(hu)關(guan)聯的(de)(de)，振(zhen)動(dong)(dong)(dong)(dong)產生波(bo)動(dong)(dong)(dong)(dong)，而波(bo)動(dong)(dong)(dong)(dong)是(shi)振(zhen)動(dong)(dong)(dong)(dong)的(de)(de)傳播(bo)(bo)。波(bo)動(dong)(dong)(dong)(dong)時介質(zhi)中(zhong)的(de)(de)質(zhi)點會在(zai)各(ge)自的(de)(de)平衡位(wei)(wei)置附近做(zuo)往(wang)復運動(dong)(dong)(dong)(dong)，并不隨波(bo)前進，在(zai)波(bo)動(dong)(dong)(dong)(dong)中(zhong)由各(ge)質(zhi)點的(de)(de)位(wei)(wei)移連續(xu)變化將振(zhen)動(dong)(dong)(dong)(dong)能(neng)量傳播(bo)(bo)出(chu)去。