性能Ch2_NonaxialMechanicalProperties辩析.ppt

Stress states generalized Hookes Law for three dimensional stress (triaxial loading). Soft coefficient of stress应力状态软性系数 According the above-mentioned strength theory： σmax= σ1-υ(σ2+σ3) τ max=(σ 1-σ3)/2 Then, Torsional deformation * Chapter 2 Nonaxial Mechanical Properties 材料在其它静载下的力学性能 6 Note: compressive structure member (s 0 here). (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) OTHER COMMON STRESS STATES we presume the majority of material strength data is based on uniaxial tensile test results. Usually, all that you have to work with is the yield strength Sy and/or the ultimate tensile strength Su . This is fine if you only have the one normal stress component present! In this case, failure (defined as the onset of plastic deformation) occurs when σx = σ1 =Sy/n ‘n’ is the factor of safety. In many loading cases, we have more than just one normal stress component. So far, However in reality, Nonaxial loading/stress E.g. in torsion, we have a single shear stress component: Or, combined bending and torsion in a shaft: Such as: 5 ? Simple tension: cable ? Simple shear: drive shaft Note: t = M/AcR here. Ski lift (photo courtesy P.M. Anderson) COMMON STATES OF STRESS Even more complex, for instance: ? Bi-axial tension: ? Hydrostatic compression: Pressurized tank s 0 h (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) OTHER STRESS STATES For simplicity, these cases can all be reduced to a simple biaxial case by finding the principal stresses, σ1 and σ2, for realistic analysis and convenience! principal stress 主应力: 即主平面上的正应力。 Now when does failure occur? Strength theories Least representative units 8 ? Tensile strain: ? Lateral strain: ? Shear strain: Strain is always dimensionless. ENGINEERING STRAIN ? Hookes Law: s = E ε ? Poissons ratio, n: metals: n ~ 0.33 ceramics: ~0.25 polymers: ~0.40 Units: E: [GPa] or [psi] n: dimensionless For ductile materials there are two commonl