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. 振動及波的相關物(wu)理量
物體沿(yan)直(zhi)線(xian)或(huo)曲線(xian)在某一平衡位(wei)(wei)置附(fu)近做周期性(xing)往復運動(dong)(dong)，稱(cheng)為機械振動(dong)(dong)。日常(chang)(chang)生(sheng)活中(zhong)隨處可見(jian)振動(dong)(dong)現象，如鐘擺的(de)(de)(de)往復運動(dong)(dong)、旗幟的(de)(de)(de)擺動(dong)(dong)、聲帶的(de)(de)(de)振動(dong)(dong)等。常(chang)(chang)見(jian)的(de)(de)(de)表(biao)征振動(dong)(dong)的(de)(de)(de)參數有：波(bo)(bo)長(chang)，任一質點(dian)經歷一次完整振動(dong)(dong)時波(bo)(bo)所傳播的(de)(de)(de)距離(li)，通(tong)(tong)常(chang)(chang)用符(fu)(fu)號(hao)(hao)λ表(biao)示(shi)，單(dan)(dan)位(wei)(wei)為m（米）；波(bo)(bo)速，波(bo)(bo)在單(dan)(dan)位(wei)(wei)時間內(nei)所傳播的(de)(de)(de)距離(li)，通(tong)(tong)常(chang)(chang)用符(fu)(fu)號(hao)(hao)c表(biao)示(shi)，單(dan)(dan)位(wei)(wei)為m/s（米/秒(miao)）；頻率，質點(dian)在1s內(nei)進行全(quan)振動(dong)(dong)的(de)(de)(de)次數，通(tong)(tong)常(chang)(chang)用f表(biao)示(shi)，單(dan)(dan)位(wei)(wei)為Hz（赫茲(zi)）；周期，質點(dian)次全(quan)振動(dong)(dong)所需的(de)(de)(de)時間，通(tong)(tong)常(chang)(chang)用T表(biao)示(shi)，單(dan)(dan)位(wei)(wei)為s（秒(miao)）；振幅，質點(dian)離(li)開平位(wei)(wei)置的(de)(de)(de)最大距離(li)，通(tong)(tong)常(chang)(chang)用A表(biao)示(shi)。
上述(shu)波長(chang)(chang)、波速、頻(pin)率三者之(zhi)間關(guan)系為(wei)：λ= c/f 由上式可(ke)知(zhi)，頻(pin)率一定(ding)時，波速越大，波長(chang)(chang)就(jiu)越長(chang)(chang)；而波速一定(ding)時，率越低，波長(chang)(chang)就(jiu)越長(chang)(chang)。周期和頻(pin)率描述(shu)的(de)是振(zhen)動的(de)快慢(man)，兩者大小與周期互為(wei)倒數。振(zhen)幅描述(shu)的(de)是振(zhen)動的(de)強弱。
2. 機(ji)械波
振(zhen)動(dong)在介質或空間中(zhong)的傳播過程叫作波(bo)(bo)(bo)動(dong)，簡稱(cheng)波(bo)(bo)(bo)，可分為(wei)機械(xie)(xie)波(bo)(bo)(bo)與電磁波(bo)(bo)(bo)兩種(zhong)。本書中(zhong)僅(jin)涉及機械(xie)(xie)波(bo)(bo)(bo)。振(zhen)動(dong)在彈性介質中(zhong)的傳播稱(cheng)為(wei)機械(xie)(xie)波(bo)(bo)(bo)，如固體(ti)、液體(ti)、氣(qi)體(ti)均(jun)可視為(wei)彈性介質。機械(xie)(xie)波(bo)(bo)(bo)的頻(pin)(pin)率(lv)范圍很寬(kuan)，從10-4Hz到(dao)102Hz，跨(kua)越16個數量級其中(zhong)人(ren)類聽覺所能(neng)感知的范圍在20~20000Hz。人(ren)們(men)把能(neng)牽(qian)動(dong)聽覺神經的機械(xie)(xie)波(bo)(bo)(bo)稱(cheng)為(wei)聲(sheng)波(bo)(bo)(bo)，當(dang)聲(sheng)波(bo)(bo)(bo)頻(pin)(pin)率(lv)低于20Hz時，稱(cheng)為(wei)次聲(sheng)波(bo)(bo)(bo)；當(dang)聲(sheng)波(bo)(bo)(bo)頻(pin)(pin)率(lv)于20000Hz時，稱(cheng)為(wei)超聲(sheng)波(bo)(bo)(bo)。
為簡單闡述機械(xie)波是如(ru)何產(chan)(chan)(chan)生和傳(chuan)播的(de)(de)(de)(de)，建立(li)如(ru)圖(tu)所彈性(xing)介質(zhi)(zhi)(zhi)(zhi)(zhi)模型(xing)。圖(tu)2-1中(zhong)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間(jian)以小(xiao)彈簧連接在(zai)(zai)(zai)一起，這種質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)間(jian)以彈性(xing)力(li)(li)連接在(zai)(zai)(zai)起的(de)(de)(de)(de)介質(zhi)(zhi)(zhi)(zhi)(zhi)稱為彈性(xing)介質(zhi)(zhi)(zhi)(zhi)(zhi)。外力(li)(li)F首(shou)先對(dui)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A產(chan)(chan)(chan)生作用，A偏離(li)(li)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，此時(shi)(shi)附近(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)將對(dui)A產(chan)(chan)(chan)生力(li)(li)的(de)(de)(de)(de)作用，迫使(shi)其回(hui)(hui)到(dao)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。而當A回(hui)(hui)到(dao)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，其他質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對(dui)其不產(chan)(chan)(chan)生作用，但(dan)是由于(yu)慣(guan)性(xing)的(de)(de)(de)(de)存在(zai)(zai)(zai)，A具有一定的(de)(de)(de)(de)速度，不會(hui)(hui)停留在(zai)(zai)(zai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，反(fan)而繼續向(xiang)前方運動(dong)(dong)，并(bing)沿相反(fan)方向(xiang)離(li)(li)開(kai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。一旦(dan)離(li)(li)開(kai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，A又會(hui)(hui)受到(dao)附近(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)對(dui)它(ta)相反(fan)的(de)(de)(de)(de)彈性(xing)力(li)(li)，使(shi)A再次回(hui)(hui)到(dao)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)。導致質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)A在(zai)(zai)(zai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)來回(hui)(hui)往(wang)復產(chan)(chan)(chan)生振(zhen)(zhen)動(dong)(dong)。與此同時(shi)(shi)，A附近(jin)的(de)(de)(de)(de)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)也(ye)會(hui)(hui)受到(dao)同樣力(li)(li)的(de)(de)(de)(de)作用使(shi)它(ta)們離(li)(li)開(kai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)，并(bing)在(zai)(zai)(zai)各自的(de)(de)(de)(de)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)(dian)附近(jin)運動(dong)(dong)。這樣彈性(xing)介質(zhi)(zhi)(zhi)(zhi)(zhi)中(zhong)單一質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)引(yin)起鄰近(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)，鄰近(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)又會(hui)(hui)引(yin)起更遠(yuan)質(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)最終(zhong)由近(jin)及遠(yuan)地向(xiang)各個(ge)方向(xiang)傳(chuan)播，從(cong)而形成機械(xie)波。
超聲波是一種(zhong)以(yi)波動(dong)形式在介質(zhi)中傳(chuan)(chuan)播(bo)(bo)的(de)(de)(de)(de)(de)機械振動(dong)，提到了機械波傳(chuan)(chuan)播(bo)(bo)所必需的(de)(de)(de)(de)(de)兩(liang)個條件(jian)：做(zuo)機械振動(dong)的(de)(de)(de)(de)(de)波源和能夠傳(chuan)(chuan)播(bo)(bo)機械振動(dong)的(de)(de)(de)(de)(de)介質(zhi)。振動(dong)與波動(dong)是相互(hu)關聯的(de)(de)(de)(de)(de)，振動(dong)產(chan)生波動(dong)，而波動(dong)是振動(dong)的(de)(de)(de)(de)(de)傳(chuan)(chuan)播(bo)(bo)。波動(dong)時介質(zhi)中的(de)(de)(de)(de)(de)質(zhi)點會(hui)在各(ge)自的(de)(de)(de)(de)(de)平衡位(wei)置附近做(zuo)往復運動(dong)，并(bing)不隨波前進，在波動(dong)中由各(ge)質(zhi)點的(de)(de)(de)(de)(de)位(wei)移連續變化將振動(dong)能量(liang)傳(chuan)(chuan)播(bo)(bo)出去。
