Fracture Behavior of a Dual Phase Sheet Steel in Hole Expansion

2007 ◽  
Author(s):  
Yuxiu Zhang ◽  
Yi Liu ◽  
Xin Wu
Keyword(s):  
Crack Initiation ◽  
Sheet Steel ◽  
High Strength Steels ◽  
Forming Limit ◽  
Dual Phase ◽  
Crack Initiation And Propagation ◽  
Forming Process ◽  
Hole Expansion ◽  
Initiation And Propagation ◽  
Strain Paths

It is commonly recognized that for Advanced High Strength Steels (AHSS) the forming limit is mainly controlled by fracture, rather then by localized necking. To date a reliable fracture limit for forming AHSS is not well defined, especially when a practical forming process is under complex strain paths. Hole expansion test has been used by auto industry for assessing fracture-controlled material forming limit. Understanding of crack mechanisms involved in crack initiation and propagation is important for prediction of fracture failure. A dual phase steel with a fine grain and 20–40vol% martensite particles of ∼1μm mean size was used for this study. The results indicate that the hole piercing and blank placement during hole expansion has sensitive impact to the evaluation of edge crack initiation and propagation. Through the comparative study on the “burr up” and “burr down” blank settings the fracture process and the effect of blank preparation, hole expansion, burr geometry effect on crack initiation, and the crack propagation direction and local interaction with microstructure are investigated.

Study on Micro-Mechanism of Crack Initiation and Propagation Induced by Inclusion in Ultra-High Strength Steel

2007 ◽  
Vol 353-358 ◽  
pp. 1185-1190 ◽  
Author(s):  
Yan Ping Zeng ◽  
Hong Mei Fan ◽  
Xi Shu Wang ◽  
Xi Shan Xie
Keyword(s):  
Crack Initiation ◽  
High Strength Steel ◽  
Harmful Effect ◽  
High Strength Steels ◽  
High Strength ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Ultra High Strength Steel

Specially designed SEM in-situ tensile and fatigue tests have been conducted to trace the entire process of crack initiation and propagation till fracture in an ultra-high strength steel MA250. TiN is a typical inclusion and its average size is in the range of 8~10μm in MA250 steel. The micro-mechanism of the effect of TiN inclusion on crack initiation and propagation at tensile and fatigue tests both have been studied in detail. Experimental results show the harmful effect of TiN on tensile and fatigue properties both. This work is helpful to establish the practical life prediction model for the characteristic inclusion parameters in ultra-high strength steel components. It also enlightens us to eliminate TiN in the further development of ultra-high strength steels.

Modeling of Damage and Failure of Dual Phase Steel in Nakajima Test

2012 ◽  
Vol 525-526 ◽  
pp. 69-72 ◽  
Author(s):  
Jun He Lian ◽  
Peng Fei Liu ◽  
Sebastian Münstermann
Keyword(s):  
Damage Evolution ◽  
High Strength Steels ◽  
High Strength ◽  
Forming Limit ◽  
Dual Phase ◽  
Forming Process ◽  
Damage And Failure ◽  
Final Failure ◽  
Key Factor ◽  
Nakajima Test

For modern high strength steels, instead of metal instability, ductile damage triggered by the formation of microvoids or microcracks resulting from the complex material microstructure, has become the key factor responsible for the final failure in the forming process of such steels. The target of this study is to describe the initiation and evolution of damage in a dual-phase (DP) steel (DP600). By applying a newly proposed approach that is able to indicate the onset of damage in an engineering sense and quantify the subsequent damage evolution, to predict the forming limits for DP600 are predicted by simulating Nakajima test. Accordingly, two forming limit curves (FLC) are numerically computed to characterize two moments: when damage becomes pronounced and when the final failure is triggered by the accumulation of damage. Comparing with the conventional experimentally calibrated FLC at necking, the limit at crack initiation predicted by modeling gives a lower but defect-free forming boundary. The forming limit at final fracture is well captured by allowing the subsequent damage evolution to a critical value.

On the Influence of Strain-Path in Multiaxial Fatigue Failure

1987 ◽  
Vol 109 (2) ◽  
pp. 107-113 ◽  
Author(s):  
Han C. Wu ◽  
C. C. Yang
Keyword(s):  
Crack Initiation ◽  
Strain Path ◽  
Path Dependence ◽  
Fatigue Tests ◽  
Multiaxial Fatigue ◽  
Crack Initiation And Propagation ◽  
Torsional Fatigue ◽  
Initiation And Propagation ◽  
Strain Paths ◽  
Tubular Specimens

A set of strain-controlled experiments has been performed on tubular specimens of annealed stainless steel. The strain-paths are designed to highlight the characteristics of path-dependence in the axial-torsional fatigue tests. Fatigue life, directions of crack initiation, and propagation are the subjects of interest in this investigation. They have been observed to be strongly influenced by the strain-path. For all the specimens tested, crack initiation was in the tensile mode.

Sign in / Sign up

Export Citation Format

Share Document