Experimental determination of the failure surface for DP980 high-strength metal sheets considering stress triaxiality and Lode angle

Abstract

To meet requirements for reduced fuel consumption of cars, the use of components made of sheets of high-strength steel instead of conventional steel has been on the rise. However, low ultimate elongation of high-strength steel often causes problems during plastic deformation and more research is needed to improve failure predictability. Ductile failure models available in commercial finite element analysis (FEA) packages require the material's tensile strength and failure strain for failure prediction. For stress states that are more complex than the uniaxial case, accurate prediction of the how, when, and where failure occurs has been become problematic and it has been investigated by numerous researchers. In this study, we investigate the prediction of failure in DP980 sheets under triaxle stress states. We first determine the shapes of specimens using certain triaxial stress states, such as pure shear, uniaxial tension, biaxial deformation, which are induced by corresponding tensile tests. When failure occurs, equivalent strain at the failure locus is obtained by means of digital image correlation (DIC) and then plotted against triaxiality and Lode angle, based on which the triaxiality failure diagram (TFD) is established to implement in the FEA program of LS-DYNA. Validation is made by comparing the numerical results with burring test data. Good agreement was found for failure locus and strain distribution at the time of failure.

A New Fracture Detection Algorithm of Low Amplitude Acoustic Emission Signal Based on Kalman Filter-Ripple Voltage

“…The strain values are measured by DIC (Digital Image Correlation). For more details of strain measurement, please refer to our previous study [ 38 ]. The difference is caused by various factors, such as minuscule differences in the thickness of the test specimens, as well as the hole-processing precision and alignment.…”

Determination of post-necking stress-strain relationship for zirconium low-oxidation based on actual cross-section measurements by DIC

“…Recently, DIC technology has been developed to address these limitations. When using DIC, displacement and strain fields are calculated by comparing the intensities of the individual pixels in a speckled pattern sprayed onto the specimen surface prior to the test [18][19][20]. When employing a charge-coupled device (CCD) camera, the intensity of a pixel is divided into 256 levels [21].…”

Determination of the Forming Limit for a ZIRLO™ Sheet with High Anisotropy

“…The same 0.48 mm-RD plate made of ZIRLO™ was used as previously used to obtain the FLD. Specimens representing specific η theoretical values were referenced from previous studies [ 33 , 34 ]. At this time, the η theoretical values represented by each specimen are 0.33, 0.46, 0.53, and 0.55, respectively.…”