| WANG Shu-na,FU Pei-lin,LI Jia-wei,ZHANG Xu,KAN Qian-hua.Reverse Analysis of Elasto-plastic Constitutive Parameters of Strengthening Layer for Laser Shock Processing TC4 Titanium Alloys[J],52(10):411-421 |
| Reverse Analysis of Elasto-plastic Constitutive Parameters of Strengthening Layer for Laser Shock Processing TC4 Titanium Alloys |
| Received:September 02, 2022 Revised:March 10, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.10.037 |
| KeyWord:TC4 titanium alloy laser shock processing nano-indentation dimensionless analysis reverse analysis finite element simulation |
| Author | Institution |
| WANG Shu-na |
Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu , China |
| FU Pei-lin |
Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu , China |
| LI Jia-wei |
Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu , China |
| ZHANG Xu |
Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu , China |
| KAN Qian-hua |
Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu , China |
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| Abstract: |
| Laser shock processing (LSP) can form a strengthening layer with a gradient structure on the surface of parts, and thus improves the fatigue life. It is of great significance to obtain the elasto-plastic parameters of TC4 titanium alloy after LSP for the fatigue life prediction. However, there are few reports on the determination of elasto-plastic parameters of LSP TC4 titanium alloy. The reverse algorithm combining the nano-indentation experiments with finite element simulation is an effective method to obtain the constitutive parameters of the thin strengthening layer. Therefore, employing the nano-indentation experiments and finite element simulation, the reverse analysis of the LSP TC4 titanium alloy was conducted to determine the elasto-plastic parameters. First, the nano-indentation experiments of the LSP TC4 titanium alloy specimen were carried out based on the Nano indenter G200 nano-indentation experimental apparatus with the Berkovich diamond indenter, and the indentation depth of 1 000 nm was set by the displacement-controlled method. Then the nano-indentation experiments were carried out on a single side of specimen along the depth direction of the strengthening layer, and the corresponding load-displacement curves at different distances from the surface were obtained. Subsequently, the distributions of elastic modulus and nano-hardness along the depth direction of the strengthening layer were obtained after using the Oliver-Pharr method to determine the unloading stiffness and the reduced modulus from the unloading curves. Then, following the power-law strain hardening assumption, the yield stress and strain hardening index of the surface strengthening layer were determined by numerically solvingthe dimensionless equations of the representative stress, the ratio of plastic work to total work, and the ratio of residual depth to pressing depth, respectively. Therefore, the elasto-plastic parameters of the surface strengthening layer of LSP TC4 titanium alloy were obtained. Finally, the elasto-plastic parameters obtained by the reverse analysis were introduced to a two-dimensional axisymmetric nano-indentation finite element model. The effectiveness of the reverse analysis was verified by comparing the simulated results with the corresponding experimental results, which took into account the load-displacement curves as well as the variations of elastic modulus and nano-hardness with the distance from the surface. The obtained results showed that the elastic modulus, nano-hardness, yield stress and hardening index possessed a varying distribution along the thickness direction of the strengthening layer (about 300 μm). The surface elastic modulus, nano-hardness and yield stress of the strengthening layer reached 121.2 GPa, 5.0 GPa and 1 396.4 MPa, which were 11%, 30% and 55% higher than that of the substrate, respectively. However, the strain hardening index increased gradually along the depth direction, and the index at the substrate and the surface of the strengthening layer were 0.252 and 0.167, respectively. Additionally, the simulated load- displacement curves agreed with the experimental curves well, and the relative errors of the maximum load, elastic modulus and nano-hardness were less than 1%, 7% and 3%, respectively, demonstrating the effectiveness of the reverse analysis. The calculated results could be great helpful to the fatigue life prediction and the further optimization of LSP process parameters. |
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