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高清下載香蕉視頻app蘋果: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)及波的相關物理量(liang)

   物體沿直線(xian)或曲線(xian)在(zai)某一平衡(heng)位(wei)(wei)(wei)(wei)置附(fu)近(jin)做周(zhou)期性往復運動，稱(cheng)為(wei)(wei)(wei)機(ji)械振(zhen)動。日(ri)常(chang)(chang)生活中隨處可見振(zhen)動現象(xiang)，如鐘擺(bai)的(de)(de)往復運動、旗幟(zhi)的(de)(de)擺(bai)動、聲帶(dai)的(de)(de)振(zhen)動等。常(chang)(chang)見的(de)(de)表(biao)征振(zhen)動的(de)(de)參數有(you)：波長(chang)，任一質點(dian)(dian)經歷一次完整(zheng)振(zhen)動時波所傳播的(de)(de)距(ju)離(li)，通(tong)(tong)常(chang)(chang)用(yong)(yong)符號λ表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)(wei)(wei)m（米(mi)）；波速，波在(zai)單位(wei)(wei)(wei)(wei)時間內所傳播的(de)(de)距(ju)離(li)，通(tong)(tong)常(chang)(chang)用(yong)(yong)符號c表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)(wei)(wei)m/s（米(mi)/秒）；頻率(lv)，質點(dian)(dian)在(zai)1s內進行全(quan)振(zhen)動的(de)(de)次數，通(tong)(tong)常(chang)(chang)用(yong)(yong)f表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)(wei)(wei)Hz（赫(he)茲）；周(zhou)期，質點(dian)(dian)次全(quan)振(zhen)動所需的(de)(de)時間，通(tong)(tong)常(chang)(chang)用(yong)(yong)T表(biao)示，單位(wei)(wei)(wei)(wei)為(wei)(wei)(wei)s（秒）；振(zhen)幅，質點(dian)(dian)離(li)開平位(wei)(wei)(wei)(wei)置的(de)(de)最(zui)大距(ju)離(li)，通(tong)(tong)常(chang)(chang)用(yong)(yong)A表(biao)示。

  上述(shu)波(bo)(bo)(bo)長、波(bo)(bo)(bo)速、頻率三者之間關系為：λ= c/f 由上式可知(zhi)，頻率一定時，波(bo)(bo)(bo)速越(yue)(yue)大，波(bo)(bo)(bo)長就越(yue)(yue)長；而波(bo)(bo)(bo)速一定時，率越(yue)(yue)低，波(bo)(bo)(bo)長就越(yue)(yue)長。周期和頻率描述(shu)的是(shi)振(zhen)動(dong)的快慢，兩者大小與(yu)周期互為倒數。振(zhen)幅描述(shu)的是(shi)振(zhen)動(dong)的強弱。

2. 機械(xie)波

  振(zhen)動(dong)(dong)在介(jie)質或空間中(zhong)的(de)(de)傳播(bo)過程叫作波(bo)(bo)(bo)(bo)動(dong)(dong)，簡(jian)稱(cheng)(cheng)波(bo)(bo)(bo)(bo)，可(ke)分為機(ji)(ji)(ji)械(xie)波(bo)(bo)(bo)(bo)與電磁波(bo)(bo)(bo)(bo)兩種。本(ben)書中(zhong)僅(jin)涉及機(ji)(ji)(ji)械(xie)波(bo)(bo)(bo)(bo)。振(zhen)動(dong)(dong)在彈性介(jie)質中(zhong)的(de)(de)傳播(bo)稱(cheng)(cheng)為機(ji)(ji)(ji)械(xie)波(bo)(bo)(bo)(bo)，如固體、液(ye)體、氣體均可(ke)視(shi)為彈性介(jie)質。機(ji)(ji)(ji)械(xie)波(bo)(bo)(bo)(bo)的(de)(de)頻(pin)率范圍(wei)很寬，從(cong)10-4Hz到102Hz，跨越16個數量級(ji)其(qi)中(zhong)人(ren)類聽覺所(suo)能感(gan)知(zhi)的(de)(de)范圍(wei)在20~20000Hz。人(ren)們把能牽動(dong)(dong)聽覺神經的(de)(de)機(ji)(ji)(ji)械(xie)波(bo)(bo)(bo)(bo)稱(cheng)(cheng)為聲波(bo)(bo)(bo)(bo)，當(dang)聲波(bo)(bo)(bo)(bo)頻(pin)率低于20Hz時(shi)，稱(cheng)(cheng)為次聲波(bo)(bo)(bo)(bo)；當(dang)聲波(bo)(bo)(bo)(bo)頻(pin)率于20000Hz時(shi)，稱(cheng)(cheng)為超聲波(bo)(bo)(bo)(bo)。

  為簡(jian)單(dan)闡述機械波(bo)是(shi)如(ru)(ru)何產生(sheng)和傳播的(de)(de)，建立如(ru)(ru)圖所彈(dan)(dan)性(xing)介(jie)(jie)質(zhi)(zhi)(zhi)模型。圖2-1中(zhong)(zhong)質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)間以小(xiao)彈(dan)(dan)簧連(lian)接在(zai)一(yi)起(qi)，這(zhe)(zhe)種(zhong)質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)間以彈(dan)(dan)性(xing)力(li)連(lian)接在(zai)起(qi)的(de)(de)介(jie)(jie)質(zhi)(zhi)(zhi)稱為彈(dan)(dan)性(xing)介(jie)(jie)質(zhi)(zhi)(zhi)。外(wai)力(li)F首先對質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)A產生(sheng)作(zuo)(zuo)用(yong)，A偏離均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)，此(ci)時(shi)附近質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)將(jiang)對A產生(sheng)力(li)的(de)(de)作(zuo)(zuo)用(yong)，迫(po)使其回(hui)(hui)到均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)。而(er)(er)(er)當A回(hui)(hui)到均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)，其他質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)對其不產生(sheng)作(zuo)(zuo)用(yong)，但是(shi)由于慣性(xing)的(de)(de)存(cun)在(zai)，A具(ju)有一(yi)定的(de)(de)速度，不會停留在(zai)均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)，反(fan)而(er)(er)(er)繼續向(xiang)前方(fang)運動(dong)，并沿(yan)相反(fan)方(fang)向(xiang)離開均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)。一(yi)旦離開均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)，A又(you)會受到附近質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)對它(ta)相反(fan)的(de)(de)彈(dan)(dan)性(xing)力(li)，使A再(zai)次(ci)回(hui)(hui)到均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)。導致(zhi)質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)A在(zai)均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)來回(hui)(hui)往復產生(sheng)振動(dong)。與此(ci)同(tong)(tong)時(shi)，A附近的(de)(de)質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)也會受到同(tong)(tong)樣力(li)的(de)(de)作(zuo)(zuo)用(yong)使它(ta)們離開均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)，并在(zai)各(ge)自的(de)(de)均衡點(dian)(dian)(dian)(dian)(dian)(dian)(dian)附近運動(dong)。這(zhe)(zhe)樣彈(dan)(dan)性(xing)介(jie)(jie)質(zhi)(zhi)(zhi)中(zhong)(zhong)單(dan)一(yi)質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振動(dong)引起(qi)鄰近質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振動(dong)，鄰近質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振動(dong)又(you)會引起(qi)更遠質(zhi)(zhi)(zhi)點(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)振動(dong)最終由近及遠地向(xiang)各(ge)個方(fang)向(xiang)傳播，從而(er)(er)(er)形成(cheng)機械波(bo)。

  超聲波(bo)(bo)是(shi)一種以(yi)波(bo)(bo)動(dong)(dong)(dong)(dong)形式在介(jie)質中(zhong)傳(chuan)(chuan)播的(de)機(ji)械振動(dong)(dong)(dong)(dong)，提到了機(ji)械波(bo)(bo)傳(chuan)(chuan)播所必需(xu)的(de)兩個條件：做機(ji)械振動(dong)(dong)(dong)(dong)的(de)波(bo)(bo)源和能夠傳(chuan)(chuan)播機(ji)械振動(dong)(dong)(dong)(dong)的(de)介(jie)質。振動(dong)(dong)(dong)(dong)與波(bo)(bo)動(dong)(dong)(dong)(dong)是(shi)相互關聯的(de)，振動(dong)(dong)(dong)(dong)產(chan)生(sheng)波(bo)(bo)動(dong)(dong)(dong)(dong)，而(er)波(bo)(bo)動(dong)(dong)(dong)(dong)是(shi)振動(dong)(dong)(dong)(dong)的(de)傳(chuan)(chuan)播。波(bo)(bo)動(dong)(dong)(dong)(dong)時介(jie)質中(zhong)的(de)質點會在各自的(de)平衡(heng)位置附(fu)近(jin)做往復運動(dong)(dong)(dong)(dong)，并不(bu)隨波(bo)(bo)前進，在波(bo)(bo)動(dong)(dong)(dong)(dong)中(zhong)由(you)各質點的(de)位移連續變化將振動(dong)(dong)(dong)(dong)能量(liang)傳(chuan)(chuan)播出(chu)去。