Study on Full-range True Stress-strain Relationship of High-strength Bolt Material
The true stress-strain relationship of bolt material should be considered in the simulation analysis on high-strength bolted joints with large deformation in the bolt shank under the limit state.For this reason,the M20,M24 and M30 high-strength bolts in grade 10.9 are taken as the study objects,and the full-range true stress-strain relationship of the bolt material is discussed.Firstly,the bolt material tensile specimens are fabricated and the material full-range engineering stress-strain curves are obtained by conducting uniaxial tensile tests.Then,the finite element method is used to simulate the tensile tests.The applicability of Ludwik,Hollomon,Voce and Swift expressions for describing material true stress-strain relationship is discussed by comparing the finite element analysis and the measured engineering stress-strain curves.Finally,based on the normalizing pre-necking true stress-strain and the normalizing true stress-strain in strain-hardening stage,2 improved Ramberg-Osgood expressions are proposed for describing the full-range true stress-strain relationship of bolt material.The result shows that(1)in the fitted Ludwik,Hollomon,Voce and Swift expressions based on the pre-necking strain-hardening stage true stress-strain curves,Ludwik,Hollomon and Swift expressions would overestimate the post-necking true stress of bolt material,while Voce expression would underestimate the post-necking true stress of bolt material;(2)the proposed Ramberg-Osgood expression based on the normalizing pre-necking true stress-strain relationship would accurately describe the true stress-strain relationship of the full-range of high-strength bolt material,and slightly overestimate the true stress of the bolt material in the strengthening stage;(3)the proposed Ramberg-Osgood expression based on the true stress-strain relationship at the normalized hardening stage could describe the true stress-strain relationship in the full-range of high strength bolt materials more accurately.
NETL
NSTL
万方数据
