The split Hopkinson pressure bar(SHPB)tests are often conducted to obtain the dynamic compressive strengths of concrete-like materials which need to be interpreted or analyzed correctly as these data are very importan...The split Hopkinson pressure bar(SHPB)tests are often conducted to obtain the dynamic compressive strengths of concrete-like materials which need to be interpreted or analyzed correctly as these data are very important for the construction of reliable constitutive equations used in numerical simulations.In the present work,a numerical study is performed on the influence of specimen size on concrete in SHPB tests using a rate-independent material model.A new empirical equation for the dynamic increase factor due to inertia(confinement)effect is also proposed which took account of specimen size effect through its volume.It is shown that the empirical formula agrees well with the numerical results for the SHPB tests on concrete with different specimen sizes,and the dynamic increase factor due to inertia(confinement)effect increases with the increase of specimen size.展开更多
In the simulation of rupture processes of seismic sources by using either numerical method or rock mechanics experiments, improper setting of the specimen size will influence the stress field near the faults. In this ...In the simulation of rupture processes of seismic sources by using either numerical method or rock mechanics experiments, improper setting of the specimen size will influence the stress field near the faults. In this study, 2D finite element method (FEM) was used to calculate the stress field of rock specimens in different sizes with fixed-size elliptic holes. The calculated stress field was compared with analytic solution for elliptic-hole problem in an infinite medium. Numerical results showed that boundary effect of a rock specimen with an elliptic hole on stress field under uniaxial compression cannot be neglected. Critical aspect ratio of the specimen is about 3:2, and critical ratio of distance between the tip of the hole and the border of specimen (d) to the major axis of the elliptic hole (l) is about 7.3. Numerical analysis on rock specimen size can provide theoretical reference for rock specimen experiments, and it is also helpful for setting of model sizes in numerical simulations of fault movement.展开更多
This overview firstly introduces the state-of-the-art research progress in length scale-related fatigue performance of conventionally-fabricated metals evaluated by miniature specimens. Some key factors for size effec...This overview firstly introduces the state-of-the-art research progress in length scale-related fatigue performance of conventionally-fabricated metals evaluated by miniature specimens. Some key factors for size effects sensitive to microstructures including the specimen thickness, grain size and a ratio between them are highlighted to summarize some general rules for size effects. Then, ongoing research progress and new challenges in evaluating the fatigue performance of additive manufactured parts controlled by location-specific defects, microstructure heterogeneities as well as mechanical anisotropy using miniature specimen testing technique are discussed and addressed. Finally, a potential roadmap to establish a data-driven evaluation platform based on a large number of miniature specimen-based experiment data,theoretical computations and the ’big data’ analysis with machine learning is proposed. It is expected that this overview would provide a novel strategy for the realistic evaluation and fast qualification of fatigue properties of additive manufactured parts we have been facing to.展开更多
基金National Natural Science Foundation of China(11572317)
文摘The split Hopkinson pressure bar(SHPB)tests are often conducted to obtain the dynamic compressive strengths of concrete-like materials which need to be interpreted or analyzed correctly as these data are very important for the construction of reliable constitutive equations used in numerical simulations.In the present work,a numerical study is performed on the influence of specimen size on concrete in SHPB tests using a rate-independent material model.A new empirical equation for the dynamic increase factor due to inertia(confinement)effect is also proposed which took account of specimen size effect through its volume.It is shown that the empirical formula agrees well with the numerical results for the SHPB tests on concrete with different specimen sizes,and the dynamic increase factor due to inertia(confinement)effect increases with the increase of specimen size.
基金National Natural Science Foundation of China (40234042).
文摘In the simulation of rupture processes of seismic sources by using either numerical method or rock mechanics experiments, improper setting of the specimen size will influence the stress field near the faults. In this study, 2D finite element method (FEM) was used to calculate the stress field of rock specimens in different sizes with fixed-size elliptic holes. The calculated stress field was compared with analytic solution for elliptic-hole problem in an infinite medium. Numerical results showed that boundary effect of a rock specimen with an elliptic hole on stress field under uniaxial compression cannot be neglected. Critical aspect ratio of the specimen is about 3:2, and critical ratio of distance between the tip of the hole and the border of specimen (d) to the major axis of the elliptic hole (l) is about 7.3. Numerical analysis on rock specimen size can provide theoretical reference for rock specimen experiments, and it is also helpful for setting of model sizes in numerical simulations of fault movement.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.51771207 and 51571199)
文摘This overview firstly introduces the state-of-the-art research progress in length scale-related fatigue performance of conventionally-fabricated metals evaluated by miniature specimens. Some key factors for size effects sensitive to microstructures including the specimen thickness, grain size and a ratio between them are highlighted to summarize some general rules for size effects. Then, ongoing research progress and new challenges in evaluating the fatigue performance of additive manufactured parts controlled by location-specific defects, microstructure heterogeneities as well as mechanical anisotropy using miniature specimen testing technique are discussed and addressed. Finally, a potential roadmap to establish a data-driven evaluation platform based on a large number of miniature specimen-based experiment data,theoretical computations and the ’big data’ analysis with machine learning is proposed. It is expected that this overview would provide a novel strategy for the realistic evaluation and fast qualification of fatigue properties of additive manufactured parts we have been facing to.
