Study on Intrinsic Influence Law of Specimen Size and Loading Speed on Charpy Impact Test

Abstract

Charpy impact energy/impact toughness is closely related to external factors such as specimen size. However, when the sample size is small, the linear conversion relationship between the Charpy impact energy of the sub-size and full-size Charpy specimens does not hold; the Charpy impact toughness varies with the size of the specimen and other factors. This indicates that studying the internal influence of external factors on impact energy or impact toughness is the key to accurately understanding and evaluating the toughness and brittleness of materials. In this paper, the effects of strain rate on the flow behavior and the effects of stress triaxiality on the fracture behavior of 30CrMnSiNi2A high-strength steel were investigated using quasi-static smooth bar and notched bar uniaxial tensile tests and Split Hopkinson Tensile Bar (SHTP). Based on the flow behavior and strain rate dependences of the yield behavior, a modified JC model was established to describe the flow behavior and strain rate behavior. Charpy impact tests were simulated using the modified JC model and JC failure model with the determined parameters. Reasonable agreements between the simulation and experimental results have been achieved, and the validity of the model was proved. According to the simulation results, the impact energy was divided into crack initiation energy, crack stability propagation energy and crack instability propagation energy. On this basis, the effects of striker velocity and specimen width on the energy and characteristic load of each part were studied. The results show that each part of the impact energy has a negligible dependence on the hammer velocity, but there is a significantly different positive linear relationship with the width of the sample. The energy increment of each part also showed an inverse correlation with the increase in the sample width. The findings reveal that the internal mechanism of Charpy impact toughness decreases with the increase in sample width; to a certain extent, it also reveals the internal reason why the linear transformation relationship of Charpy impact energy between sub-size specimens and standard specimens is not established when the specimens are small. The analytical method and results presented in this paper can provide a reference for the study of the dynamic behavior of high-strength steel, the relationship between material properties and sample size, and the elastic–plastic impact dynamic design.

Qualification of welded joints used in the sugar and alcohol sector of ASTM A335 P22 steel pipes welded by GTAW and SMAW processes

“…This severe drop in impact toughness in the weld metal was also observed by Júnior (2014), where BM absorbed about 180 J, HAZ absorbed about 140 J and WM absorbed between 12 and 16 J of energy in the Charpy impact test. According to Jia et. al.…”

Mechanics of structural size effect in impact brittle fracture of steels and consequent scaling laws for fracture

“…Although the crack layer is confined to be coplanar with the notch in Charpy impact experiments (due to the natural restriction in bending, imposed by the maximum moment occurring in crack [29][30][31]. Therefore, one is forced to use an average height to represent the crack layer thickness to quantify fracture energy dissipation.…”