Depth-sensing spherical indentation tests (SITs) have been widely used in tensile property calculations, but the accuracy and reproducibility of calculations may be significantly influenced by displacement measurement errors. Taking two representative tensile property calculation methods as examples, namely the analytical and numerical methods, the rationale as to why accurate and reproducible tensile property calculations cannot be expected from the depth-sensing SITs was discussed in detail. Subsequently, the proportional limit σ0 calculation from plastic zone radius rp measurements, which was analytically developed in the expanding cavity model (ECM) and experimentally measured by digital image correlation (DIC), was introduced to enhance the accuracy and reproducibility of the two representative methods. Principles for setting the strain threshold εth were established, and factors influencing the σ0 calculation from rp measurements were investigated through the optical system, the friction condition, the hardening behaviors of specimen materials, and the indentation depth. Through finite element calculations, it was proven that tensile property calculations at the existence of displacement measurement errors, particularly the constant error from the origin correction, can be significantly improved with the introduction of rp measurements. Similar findings were also observed in experiments on four metals that exhibited different hardening behaviors.

No abstract

No abstract

We examined the fatigue properties in very high cycle regime of large FV520B-I specimens in an ultrasonic fatigue test. The fatigue mechanism in very high cycle regime didn't change and the fatigue properties obviously degraded as the specimen size enlarged. The fatigue life decreased and the S-N curve moved downward due to the increase of inclusion size in large specimens. The maximum inclusion sizes in specimens were predicted by the method of statistics of extreme value. The prediction of fatigue strength using the modified Murakami model was closer to the test result, and the fitting of fatigue life using the corrosion fatigue crack initiation life model was less effective compared with the fitting of small specimen test results

This study focuses on the development of effective yield surface of porous metals, which is characterized with the two constitutive parameters (i.e., q1 and q2) in the widely used Gurson–Tvergaard–Needleman (GTN) model. It was found that the influence of q1 and q2 on the mechanical responses may be masked by adjusting the two failure parameters (fc and fF), yielding a set of GTN parameters deviated from the actual situation and leading to the errors in failure predictions. Therefore, the two constitutive parameters should be carefully calibrated according to the hardening behavior of matrix. Further investigations on the void density and distributions proved that cubic cells containing 100 randomly distributed non‐intersecting spherical voids are sufficient in characterizing the homogenization. On this basis, effective yield surface of porous metals with a wide range of void volume fractions (from 0.4% to 20%) was investigated, and a correlation between the constitutive parameters and the power‐law hardening behavior of matrix was established. Finally, experimental verifications were conducted on low alloy steel SA508, indicating the q1 and q2 from this study can yield more accurate mechanical response predictions then the previously suggested values.