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在線亞洲日產一區二區: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)關物理量

   物(wu)體沿直線(xian)或曲(qu)線(xian)在(zai)某(mou)一平衡位置(zhi)(zhi)附近做(zuo)周期性往復運動(dong)(dong)，稱為(wei)機械振(zhen)(zhen)動(dong)(dong)。日(ri)常生活中隨處可見(jian)振(zhen)(zhen)動(dong)(dong)現象，如鐘擺的(de)(de)往復運動(dong)(dong)、旗幟的(de)(de)擺動(dong)(dong)、聲帶的(de)(de)振(zhen)(zhen)動(dong)(dong)等。常見(jian)的(de)(de)表(biao)征振(zhen)(zhen)動(dong)(dong)的(de)(de)參(can)數(shu)有：波(bo)(bo)長，任一質(zhi)點經歷一次(ci)完整振(zhen)(zhen)動(dong)(dong)時波(bo)(bo)所(suo)(suo)傳(chuan)播的(de)(de)距離，通(tong)常用(yong)(yong)(yong)符號λ表(biao)示(shi)，單位為(wei)m（米）；波(bo)(bo)速，波(bo)(bo)在(zai)單位時間內所(suo)(suo)傳(chuan)播的(de)(de)距離，通(tong)常用(yong)(yong)(yong)符號c表(biao)示(shi)，單位為(wei)m/s（米/秒）；頻率(lv)，質(zhi)點在(zai)1s內進行全振(zhen)(zhen)動(dong)(dong)的(de)(de)次(ci)數(shu)，通(tong)常用(yong)(yong)(yong)f表(biao)示(shi)，單位為(wei)Hz（赫茲）；周期，質(zhi)點次(ci)全振(zhen)(zhen)動(dong)(dong)所(suo)(suo)需的(de)(de)時間，通(tong)常用(yong)(yong)(yong)T表(biao)示(shi)，單位為(wei)s（秒）；振(zhen)(zhen)幅，質(zhi)點離開平位置(zhi)(zhi)的(de)(de)最大距離，通(tong)常用(yong)(yong)(yong)A表(biao)示(shi)。

  上(shang)述波(bo)(bo)長(chang)(chang)(chang)、波(bo)(bo)速(su)、頻率(lv)(lv)三者(zhe)之間關系為：λ= c/f 由上(shang)式可知，頻率(lv)(lv)一定(ding)時，波(bo)(bo)速(su)越(yue)(yue)(yue)大(da)(da)，波(bo)(bo)長(chang)(chang)(chang)就越(yue)(yue)(yue)長(chang)(chang)(chang)；而波(bo)(bo)速(su)一定(ding)時，率(lv)(lv)越(yue)(yue)(yue)低，波(bo)(bo)長(chang)(chang)(chang)就越(yue)(yue)(yue)長(chang)(chang)(chang)。周期(qi)和頻率(lv)(lv)描(miao)述的是(shi)振動的快(kuai)慢，兩者(zhe)大(da)(da)小與周期(qi)互為倒(dao)數。振幅描(miao)述的是(shi)振動的強弱(ruo)。

2. 機械波(bo)

  振動(dong)在(zai)介(jie)質(zhi)或空(kong)間中的傳(chuan)播過程叫作(zuo)波(bo)(bo)(bo)動(dong)，簡稱(cheng)(cheng)波(bo)(bo)(bo)，可(ke)分為(wei)機(ji)械(xie)波(bo)(bo)(bo)與(yu)電磁波(bo)(bo)(bo)兩種。本書(shu)中僅涉及機(ji)械(xie)波(bo)(bo)(bo)。振動(dong)在(zai)彈(dan)性介(jie)質(zhi)中的傳(chuan)播稱(cheng)(cheng)為(wei)機(ji)械(xie)波(bo)(bo)(bo)，如固體(ti)(ti)、液(ye)體(ti)(ti)、氣體(ti)(ti)均可(ke)視為(wei)彈(dan)性介(jie)質(zhi)。機(ji)械(xie)波(bo)(bo)(bo)的頻(pin)率范(fan)圍(wei)很寬，從10-4Hz到102Hz，跨越16個數量級其中人(ren)類聽(ting)覺所(suo)能感知(zhi)的范(fan)圍(wei)在(zai)20~20000Hz。人(ren)們把能牽動(dong)聽(ting)覺神經(jing)的機(ji)械(xie)波(bo)(bo)(bo)稱(cheng)(cheng)為(wei)聲波(bo)(bo)(bo)，當(dang)(dang)聲波(bo)(bo)(bo)頻(pin)率低于(yu)20Hz時，稱(cheng)(cheng)為(wei)次聲波(bo)(bo)(bo)；當(dang)(dang)聲波(bo)(bo)(bo)頻(pin)率于(yu)20000Hz時，稱(cheng)(cheng)為(wei)超聲波(bo)(bo)(bo)。

  為(wei)簡單(dan)闡述機械波是(shi)如何(he)產(chan)生(sheng)和傳播(bo)的(de)(de)，建立如圖所彈性(xing)介質(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間以(yi)小(xiao)彈簧(huang)連(lian)接(jie)(jie)在(zai)(zai)(zai)一起(qi)，這(zhe)(zhe)種質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)間以(yi)彈性(xing)力(li)(li)連(lian)接(jie)(jie)在(zai)(zai)(zai)起(qi)的(de)(de)介質(zhi)(zhi)稱為(wei)彈性(xing)介質(zhi)(zhi)。外力(li)(li)F首先對質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A產(chan)生(sheng)作(zuo)用(yong)，A偏離均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，此(ci)時附(fu)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)將對A產(chan)生(sheng)力(li)(li)的(de)(de)作(zuo)用(yong)，迫使(shi)其(qi)(qi)回(hui)到(dao)(dao)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)。而當A回(hui)到(dao)(dao)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)時，其(qi)(qi)他(ta)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對其(qi)(qi)不產(chan)生(sheng)作(zuo)用(yong)，但(dan)是(shi)由于慣(guan)性(xing)的(de)(de)存在(zai)(zai)(zai)，A具有一定的(de)(de)速(su)度，不會停留在(zai)(zai)(zai)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，反而繼續(xu)向前方(fang)運(yun)(yun)動(dong)(dong)，并沿相反方(fang)向離開均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)。一旦離開均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，A又(you)會受到(dao)(dao)附(fu)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)對它(ta)(ta)相反的(de)(de)彈性(xing)力(li)(li)，使(shi)A再次(ci)回(hui)到(dao)(dao)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)。導致(zhi)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)A在(zai)(zai)(zai)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)來(lai)回(hui)往復產(chan)生(sheng)振(zhen)動(dong)(dong)。與此(ci)同時，A附(fu)近(jin)(jin)的(de)(de)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)也會受到(dao)(dao)同樣(yang)力(li)(li)的(de)(de)作(zuo)用(yong)使(shi)它(ta)(ta)們離開均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)，并在(zai)(zai)(zai)各自的(de)(de)均(jun)(jun)衡(heng)點(dian)(dian)(dian)(dian)(dian)附(fu)近(jin)(jin)運(yun)(yun)動(dong)(dong)。這(zhe)(zhe)樣(yang)彈性(xing)介質(zhi)(zhi)中單(dan)一質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)引起(qi)鄰(lin)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)，鄰(lin)近(jin)(jin)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)又(you)會引起(qi)更(geng)遠(yuan)質(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)的(de)(de)振(zhen)動(dong)(dong)最終由近(jin)(jin)及遠(yuan)地向各個方(fang)向傳播(bo)，從而形成機械波。

  超(chao)聲波(bo)(bo)是(shi)一種以波(bo)(bo)動(dong)(dong)(dong)(dong)形式在(zai)介(jie)質(zhi)(zhi)中(zhong)(zhong)傳(chuan)播(bo)的機(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)，提到(dao)了機(ji)械波(bo)(bo)傳(chuan)播(bo)所必需(xu)的兩個條(tiao)件：做(zuo)機(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)的波(bo)(bo)源和能(neng)夠傳(chuan)播(bo)機(ji)械振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)的介(jie)質(zhi)(zhi)。振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)與波(bo)(bo)動(dong)(dong)(dong)(dong)是(shi)相互關聯的，振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)產生波(bo)(bo)動(dong)(dong)(dong)(dong)，而波(bo)(bo)動(dong)(dong)(dong)(dong)是(shi)振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)的傳(chuan)播(bo)。波(bo)(bo)動(dong)(dong)(dong)(dong)時介(jie)質(zhi)(zhi)中(zhong)(zhong)的質(zhi)(zhi)點(dian)會在(zai)各自的平衡位置(zhi)附近做(zuo)往(wang)復(fu)運動(dong)(dong)(dong)(dong)，并不(bu)隨波(bo)(bo)前進，在(zai)波(bo)(bo)動(dong)(dong)(dong)(dong)中(zhong)(zhong)由各質(zhi)(zhi)點(dian)的位移(yi)連續變化將(jiang)振(zhen)(zhen)(zhen)動(dong)(dong)(dong)(dong)能(neng)量傳(chuan)播(bo)出去。