The understanding of the mechanisms of ductile fracture has been the subject of many studies due to the possibilities of application in the various fields of industry. In critical engineering structures such as pipelines, pressure vessels, ships, and aircraft, the ductile fracture is an important failure mode to be verified in the design and life phases. In the past, models based only on experimental results were used to predict ductile failure of structural components. However, performing numerous tests made the procedures complex and expensive. The development of computational models has allowed obtaining results with good precision at a lower cost, requiring few experimental tests for parameter calibration. Currently, the engineering community has a wide variety of computational models to study the ductile fracture problem in which their differences include the number of parameters to calibrate and the required computational cost. Among the available models, there is one group that uncouple the constitutive equations with the damage evolution. These uncoupled models present a simpler approach, where the failure will occur based on instantaneous local stress and strain values at the material points. Thus, uncoupled models generally require less computational power because of their fewer complex formulations and fewer constants to calibrate. This paper evaluates the tensile strain capacity in misaligned welded joints using a failure initiation locus combined with a softening law after initiation to decrease the material strength. Tensile Strain Capacity (TSC) is defined as an amount of deformation allowed to prevent material rupture. Studies based on Finite Element Analysis (FEA) have shown that misalignments have a significant influence on the tensile strain capacity of welded pipelines, and may also cause local bending and reduction in the effective weld cross-section. The failure locus is constructed based upon the growth and coalescence of voids in the material matrix under macroscopic stress and strain.  The initiation of ductile fracture is defined by a relation between the equivalent plastic deformation at the time of failure as a function of stress triaxiality and Lode stress parameter. The calibration of the material parameters of the model for an ASTM A285 steel is performed through experimental and computational tests of a cylindrical specimen with notches under uniaxial tension and fracture toughness tests using SE(B) specimens. Nonlinear FEA is conducted in three-dimensional models to investigate the effects of misalignment on strain capacity in welded joints with A285 steel. Several joint geometries were investigated, changing the welded plate thicknesses, weld misalignment, length, and depth of the planar elliptical flaw. The study will show the capability of the adopted model to investigate the TSC of welded plates when compared to available analytical formulations.


Prediction of Tensile Strain Capacity of Misaligned Welded Plates Using a Damage Model Depended on the Stress Triaxiality and the Lode Stress Parameter

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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