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(de)相(xiang)關物理量


   物體沿直線或曲線在某一平(ping)衡位置(zhi)附近做周期性往復(fu)運(yun)動，稱(cheng)為(wei)機械振(zhen)(zhen)動。日常(chang)生(sheng)活中隨處(chu)可見振(zhen)(zhen)動現象，如鐘(zhong)擺的(de)(de)往復(fu)運(yun)動、旗(qi)幟的(de)(de)擺動、聲帶的(de)(de)振(zhen)(zhen)動等(deng)。常(chang)見的(de)(de)表征(zheng)振(zhen)(zhen)動的(de)(de)參(can)數(shu)有：波(bo)長，任一質(zhi)(zhi)點(dian)經(jing)歷一次(ci)完整振(zhen)(zhen)動時(shi)波(bo)所傳播的(de)(de)距離，通常(chang)用(yong)符(fu)號λ表示，單(dan)位為(wei)m（米）；波(bo)速，波(bo)在單(dan)位時(shi)間(jian)內所傳播的(de)(de)距離，通常(chang)用(yong)符(fu)號c表示，單(dan)位為(wei)m/s（米/秒）；頻率(lv)，質(zhi)(zhi)點(dian)在1s內進行(xing)全振(zhen)(zhen)動的(de)(de)次(ci)數(shu)，通常(chang)用(yong)f表示，單(dan)位為(wei)Hz（赫茲）；周期，質(zhi)(zhi)點(dian)次(ci)全振(zhen)(zhen)動所需的(de)(de)時(shi)間(jian)，通常(chang)用(yong)T表示，單(dan)位為(wei)s（秒）；振(zhen)(zhen)幅(fu)，質(zhi)(zhi)點(dian)離開平(ping)位置(zhi)的(de)(de)最大(da)距離，通常(chang)用(yong)A表示。


  上(shang)述波長(chang)(chang)、波速、頻率(lv)三(san)者(zhe)之(zhi)間關系為(wei)：λ= c/f 由上(shang)式(shi)可知，頻率(lv)一(yi)(yi)定時，波速越(yue)大(da)，波長(chang)(chang)就(jiu)越(yue)長(chang)(chang)；而(er)波速一(yi)(yi)定時，率(lv)越(yue)低(di)，波長(chang)(chang)就(jiu)越(yue)長(chang)(chang)。周(zhou)期和頻率(lv)描(miao)述的是振動的快(kuai)慢，兩者(zhe)大(da)小與周(zhou)期互為(wei)倒數。振幅描(miao)述的是振動的強弱。


2. 機械波(bo)


  振動(dong)在介質(zhi)或空間中(zhong)(zhong)的傳播過程(cheng)叫作(zuo)波(bo)(bo)動(dong)，簡稱(cheng)波(bo)(bo)，可分(fen)為(wei)機(ji)(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)與電磁波(bo)(bo)兩種。本書(shu)中(zhong)(zhong)僅涉及機(ji)(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)。振動(dong)在彈性(xing)介質(zhi)中(zhong)(zhong)的傳播稱(cheng)為(wei)機(ji)(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)，如固體(ti)、液體(ti)、氣體(ti)均(jun)可視為(wei)彈性(xing)介質(zhi)。機(ji)(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)的頻率(lv)范(fan)圍很寬，從10-4Hz到102Hz，跨(kua)越16個數量級其中(zhong)(zhong)人(ren)類(lei)聽覺(jue)所能感知的范(fan)圍在20~20000Hz。人(ren)們把能牽動(dong)聽覺(jue)神經的機(ji)(ji)(ji)(ji)械(xie)(xie)波(bo)(bo)稱(cheng)為(wei)聲波(bo)(bo)，當聲波(bo)(bo)頻率(lv)低(di)于20Hz時(shi)，稱(cheng)為(wei)次(ci)聲波(bo)(bo)；當聲波(bo)(bo)頻率(lv)于20000Hz時(shi)，稱(cheng)為(wei)超聲波(bo)(bo)。


圖 1.jpg


  為簡(jian)單闡(chan)述機械(xie)波是(shi)如何產(chan)(chan)生(sheng)(sheng)和傳(chuan)播的，建立如圖所彈(dan)(dan)性介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)模型。圖2-1中質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)間(jian)以小(xiao)彈(dan)(dan)簧(huang)連接在一(yi)(yi)(yi)起(qi)，這種質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)間(jian)以彈(dan)(dan)性力(li)(li)連接在起(qi)的介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)稱為彈(dan)(dan)性介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)。外力(li)(li)F首先對質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)A產(chan)(chan)生(sheng)(sheng)作用，A偏離均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)，此時附(fu)近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)將對A產(chan)(chan)生(sheng)(sheng)力(li)(li)的作用，迫使(shi)其(qi)回到(dao)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)。而當A回到(dao)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)時，其(qi)他質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)對其(qi)不(bu)(bu)產(chan)(chan)生(sheng)(sheng)作用，但是(shi)由于慣性的存在，A具有(you)一(yi)(yi)(yi)定的速度，不(bu)(bu)會停(ting)留在均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)，反(fan)而繼續向前方(fang)運(yun)動(dong)，并沿(yan)相反(fan)方(fang)向離開(kai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)。一(yi)(yi)(yi)旦離開(kai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)，A又(you)會受到(dao)附(fu)近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)對它(ta)相反(fan)的彈(dan)(dan)性力(li)(li)，使(shi)A再次回到(dao)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)。導致(zhi)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)A在均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)來(lai)回往復產(chan)(chan)生(sheng)(sheng)振(zhen)動(dong)。與此同(tong)(tong)時，A附(fu)近(jin)(jin)的質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)也會受到(dao)同(tong)(tong)樣(yang)力(li)(li)的作用使(shi)它(ta)們離開(kai)均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)，并在各自的均(jun)(jun)(jun)衡(heng)點(dian)(dian)(dian)附(fu)近(jin)(jin)運(yun)動(dong)。這樣(yang)彈(dan)(dan)性介(jie)(jie)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)中單一(yi)(yi)(yi)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)的振(zhen)動(dong)引起(qi)鄰近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)的振(zhen)動(dong)，鄰近(jin)(jin)質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)的振(zhen)動(dong)又(you)會引起(qi)更遠質(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)(zhi)點(dian)(dian)(dian)的振(zhen)動(dong)最終由近(jin)(jin)及(ji)遠地向各個方(fang)向傳(chuan)播，從(cong)而形成機械(xie)波。


  超聲波是(shi)一種以波動(dong)(dong)形式在(zai)介質(zhi)中(zhong)(zhong)傳(chuan)(chuan)播(bo)(bo)的(de)(de)(de)(de)機(ji)械(xie)振(zhen)動(dong)(dong)，提到了機(ji)械(xie)波傳(chuan)(chuan)播(bo)(bo)所必需的(de)(de)(de)(de)兩個(ge)條件：做(zuo)機(ji)械(xie)振(zhen)動(dong)(dong)的(de)(de)(de)(de)波源和(he)能夠傳(chuan)(chuan)播(bo)(bo)機(ji)械(xie)振(zhen)動(dong)(dong)的(de)(de)(de)(de)介質(zhi)。振(zhen)動(dong)(dong)與波動(dong)(dong)是(shi)相互關聯的(de)(de)(de)(de)，振(zhen)動(dong)(dong)產(chan)生波動(dong)(dong)，而波動(dong)(dong)是(shi)振(zhen)動(dong)(dong)的(de)(de)(de)(de)傳(chuan)(chuan)播(bo)(bo)。波動(dong)(dong)時介質(zhi)中(zhong)(zhong)的(de)(de)(de)(de)質(zhi)點會在(zai)各自的(de)(de)(de)(de)平衡位(wei)置附(fu)近做(zuo)往復運動(dong)(dong)，并不(bu)隨(sui)波前進(jin)，在(zai)波動(dong)(dong)中(zhong)(zhong)由各質(zhi)點的(de)(de)(de)(de)位(wei)移連續變(bian)化將振(zhen)動(dong)(dong)能量傳(chuan)(chuan)播(bo)(bo)出去。