化机基础(力学)_第二章轴向拉伸压缩

1、ABP1 1AP1形状、尺寸、形状、尺寸、取向相同取向相同BP2P2 2AP1 1AP1形状、尺形状、尺寸相同寸相同P2P2 2(3) 小变形小变形PLLPPMA)()(L PLPPPmmmmACFF二力杆二力杆DABCPmABPBAPPPP第二节第二节 轴向拉伸或压缩时横截面上的内力轴向拉伸或压缩时横截面上的内力FNxyPmmPP由平衡方程由平衡方程 0XF FN P = 0FN = PPFNxyP F N= 0F N = P mmPPPFNxYPFN 30KN30KNmmPPPFNxY6kN10kN8kN4kNDABCIIIIIIIIIIII6kN10kN8kN4kNDABCIIIIIII

2、IIIII6kN10kN8kN4kNDABCIIIIIIIIIIII6kNAFN1II06 , 01NXFFkN61NF6kNAN1II6kN10kN8kN4kNDABCIIIIIIIIIIII6kNAFN1FN26kN10kNIIII0610 , 02NxFFkN42NFFN26kN10kNIIII6kN10kN8kN4kNDABCIIIIIIIIIIII6kNAFN1FN2FN36kN10kN4kNIIIIIIkNFN43N34kNIIIIIIFN66kN10kN8kN4kNDABCIIIIIIIIIIII+44+_x(kN)AaAPKApPApAP P0limAaAPAaKpK: : 正

3、应力正应力 法向应力，垂直于截面法向应力，垂直于截面剪应力剪应力 切向应力，平行于截面切向应力，平行于截面AaKp2长度力PamN112ApAP P0limPPPAFNP40003000CIIIBPAP240370P50kN150kN40003000CIIIBPAP 240370(b)(a)NP40003000CIIIBPAP240370 61111024024050000AFN261087. 0mN)(87. 0压应力MPa61037037050000IIIINIIAF26101 . 1mN)(1 . 1压应力MPaL1LL1b1bb1PPPP绝对变形：纵向变形量绝对变形：纵向变形量=变形后

4、的长度变形后的长度 变形前的长度变形前的长度 L=L1 LLLL1LPP相对变形：纵向应变，简称应变相对变形：纵向应变，简称应变无量纲量，即没有单位无量纲量，即没有单位p ELLALFLN EAFNniiiiNiAELFL1总bbbbb1b1bbbb1|ABCDP1P2100100100+ABCDP1P210010010020kN10kNFNMPaPaAFABNABAB401040105001020663MPaPaAFBCNBCBC201020105001010663MPaPaAFCDNCDCD501050102001010663AB、BC、CD 段上，段上，任意横截面上的应力分别为：任意横截

5、面上的应力分别为：+ABCDP1P210010010020kN10kNFNCDBCABLLLL总CDCDNCDBCBCNBCABABNABALFALFALF6933693369331020010200101001010 10500102001010010101050010200101001020mmm015. 010015. 03LdABCDEFFLOCabcdefbO csepabcdefbO csepabcdefbO csepabcdefbO csepabcdefbO csep%1001LLL%1001AAAbLdhn0sssnorn2 . 0 bbcCbbLTnorn maxmaxAFN

6、maxmaxCCTTmaxmaxAFNmaxmaxAFN%5%100maxmaxNFAAPFN)(max30kN40kNDABC31122320kN1m1m1m30kN40kNDABC31122320kN1m1m1mFN20+50+x(kN)10)(501050104001020663111压MPaPaAFN)(25102510400101066322-2拉MPaPaAFN)(1251012510400105066333-3拉MPaPaAFNmm5 . 0m105 . 0)501020(10400102001013693EALFEALFEALFLLLLCDNCDBCNBCABNABCDBCABACBG30030cos 0BCABxFFF030sin 0GFFBCy30GxyFABFBCB)(230sin压GGFBC)(330cos拉GFFBCAB杆安全压BCMPaPaAFBCBCNBC,)(83.311083.31)1040(4102026233杆安全拉ACMPaPaAFABABNAB,)(26.1101026.110)1020(4102036233(2)校核强度校核强度045cos30cos0045sin30sin0PFFFFFFACBCyACBCxPFPFBCAC) 13(226111226A