(10.3)--3拉（压）变形杆件内部的神奇世界——横截面的正应力.ppt

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1、拉（压）变形杆件内部的神奇世界 横截面的正应力ReviewFFFFTension and Compression 强度问题strength刚度问题stiffness问题的提出3 小明和小红，两个人用力相等，这是杆件受力平衡处于静止状态时的情况。用力过大杆件本身就会坏掉。你们认为此时杆件的内部是什么状态呢？4在这里用“假想截面”就会很方便！Stress in an Axially Loaded Bars1.The concept of Stress+The strength of axially loaded baraxial forcesproperties of the cross sect

2、ionsstrength of materialsGeneral casep:Internal force intensity Normal stressShear stressSign ConventionsNormal stress;Positive when it is a pulling(or tensile);Negative when it is a pressure(or compressive);Positive when it tends to rotae clockwise relative to the center of the free-body;Otherwise

3、it is negative.acdb Shear stresssFFN(x)Assume:stress on the cross-section is uniform.FF2.Stress on the cross-section of axially loaded bar103.Phenomena for the deformation and plane assumptionPlane assumption：all cross sections remain plane after deformation。d ac babcdFF stress on the cross-section

4、is uniform.ExampleDetermine the maximum working stress of the square brick column under the loads.It is known that F=50kN.FFFSolution Find the internal force first FN1=-50kNFN2=-150kNWe get the axial-force diagram as shown on the left.-50kN-150kN10001000370370240240FFF-50kN-150kNThe normal stress over the cross section of column I is(compression)For column II:(compression)10001000370370240240