刚度与挠度(国外英文资料).doc

刚度与挠度(国外英文资料) stiffness The material according to the national standard tensile samples made of GB6397-86 standards, and then load the tensile testing machine, tensile load, slowly specimen gradually, until the sample fracture. In the process of tensile test, the automatic recording device can give force P and axial elongation sample Δ L relation curve of tensile curve. Were going to divide the tension F by the original cross sectional area A0, the stress sigma equals F over A0, the unit MPa. Speak elongation Δ L divided by the length of the original sample L0, quick strain epsilon (epsilon = Δ L/L0). In terms of sigma, epsilon is the x-coordinate, and then the stress-strain curve, as shown in figure 1, is low carbon steel stress-strain curve. The curve has eliminated the influence of sample size, which can directly reflect the performance of the material. In figure 1, the OP is the line segment, and the stress should be proportional to the response, such as unloading the load, and the elongating sample immediately responds to the original, which is called elastic deformation. The ratio of stress and strain in this phase, E = sigma/epsilon, is called the elastic modulus of the material, also known as stiffness, which is a measure of material resistance to elastic deformation. The greater the E, the greater the stiffness of the material. More than point P, such as loading, unloading elongation of the sample cant completely disappear, will retain part of the residual deformation, this cant restore the residual deformation is called plastic deformation. The curve shows a platform at the point S, indicating that stress is constant, and strain is still increasing, a phenomenon known as yield. After the material yield to the uniform plastic deformation stage, the stress increases, the strain gradually increases, the stress reaches the maximum. At this time, the sample area of the sample is thinner, and the necking phenomenon occurs. After that, the stress begins to fall,