The constitutive behavior of laser welds in 304L stainless steel determined by digital image correlation

Boyce, Brad Lee; Reu, Phillip L.; Robino, C. V.

doi:10.1007/bf02586221

Cited by 62 publications

(40 citation statements)

References 17 publications

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“…However, since delta-ferrite is an unstable phase, it partially transforms to austenite at the heat treatment temperature of 1050°C. Decreasing ferrite content is generally known to result in a decrease in roomtemperature strength [30]. The decrease in 0.2% proof stress of the base metal in specimens C0-HT, C10-HT and C20-HT is similar to the decrease in the proof stress of plain specimens B0-HT, B10-HT and B20-HT.…”

Section: Heat Treatmentmentioning

confidence: 69%

Experimental and numerical study of strength mismatch in cross-weld tensile testing

Acar

Güngör

2015

The Journal of Strain Analysis for Engineering Design

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The mechanical properties of welded boiler tubes used in power plants can be significantly altered as a result of the fabrication history, such as pre-straining and heat treatment. The primary aim of the study was to determine the effect of fabrication history on local tensile properties across the welds. This was achieved by testing cross-weld specimens machined from welded thin-walled tubes (with unstrained or pre-strained base metal) before and after heat treatment. Digital image correlation (DIC), which is a full-field strain measurement technique, was implemented in order to obtain the local stress-strain curves and to extract the corresponding local tensile properties such as offset proof stress. Evidence of strain hardening due to the constraint and thermo-mechanical cycles during the welding process was found in the heat-affected-zone (HAZ) and evidence of softening was observed in the pre-strained base metal. It was found that the heat treatment process removed the effect of pre-straining and welding on the proof stress and the strength along the specimen was nearly homogenized. However, mapping the local stress-strain curves in the as-welded crossweld specimens with pre-strained base metal has revealed abnormal strain-relaxation with increase in load in the weld-affected region. For a better understanding of this behaviour, a tensile test of a cross-weld specimen with a large strength mismatch between the weld metal and the base metal was simulated using the finite element method. It was found that the strength mismatch in the specimen causes the development of bi-axial stresses in the HAZ once local yielding begins and the use of global axial stress to construct the local stress-strain 2 curve results in an apparent "reduced-strain" anomaly. Nevertheless, for the strength mismatch ratios studied, this anomalous behaviour did not seem to significantly affect the determination of the local proof stress in the specimens.

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Section: Heat Treatmentmentioning

confidence: 69%

Experimental and numerical study of strength mismatch in cross-weld tensile testing

Acar

Güngör

2015

The Journal of Strain Analysis for Engineering Design

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“…Microscale DIC is based on a standard optical-image-based DIC [6], which has been employed in our labs for numerous studies including the examination of deformation behavior in sub-millimeter weldments [7]. The two-dimensional variant of DIC compares images from a field of speckle contrast viewed from a single camera to determine the planar deformation field.…”

Section: Digital Image Correlationmentioning

confidence: 99%

Quantifying uncertainty from material inhomogeneity.

Battaile¹,

Emery²,

Brewer³

et al. 2009

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Most engineering materials are inherently inhomogeneous in their processing, internal structure, properties, and performance. Their properties are therefore statistical rather than deterministic. These inhomogeneities manifest across multiple length and time scales, leading to variabilities, i.e. statistical distributions, that are necessary to accurately describe each stage in the process-structure-properties hierarchy, and are ultimately the primary source of uncertainty in performance of the material and component. When localized events are responsible for component failure, or when component dimensions are on the order of microstructural features, this uncertainty is particularly important. For ultra-high reliability applications, the uncertainty is compounded by a lack of data describing the extremely rare events. Hands-on testing alone cannot supply sufficient data for this purpose.To date, there is no robust or coherent method to quantify this uncertainty so that it can be used in a predictive manner at the component length scale. The research presented in this report begins to address this lack of capability through a systematic study of the effects of microstructure on the strain concentration at a hole. To achieve the strain concentration, small circular holes (approximately 100 µm in diameter) were machined into brass tensile specimens using a femto-second laser. The brass was annealed at 450 ℃, 600 ℃, and 800 ℃ to produce three hole-to-grain size ratios of approximately 7, 1, and 1/7. Electron backscatter diffraction experiments were used to guide the construction of digital microstructures for finite element simulations of uniaxial tension. Digital image correlation experiments were used to qualitatively validate the numerical simulations. The simulations were performed iteratively to generate statistics describing the distribution of plastic strain at the hole in varying microstructural environments. In both the experiments and simulations, the deformation behavior was found to depend strongly on the character of the nearby microstructure.3 Acknowledgment

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“…Laser welds are no exception to this trend. As such, common engineering practice for the qualification and interrogation of welds are generally carried out by post-mortem failure investigations, [1] radiography, [2] and in some cases ultrasonic scans [3] . In practice, these techniques have primarily yielded failure strength values, planar evaluations or two-dimensional projections, of a threedimensional space.…”

Section: Introductionmentioning

confidence: 99%

Porosity in millimeter-scale welds of stainless steel : three-dimensional characterization.

Aagesen

Madison²

2012

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A variety of edge joints utilizing a continuous wave Nd:YAG laser have been produced and examined in a 304-L stainless steel to advance fundamental understanding of the linkage between processing and resultant microstructure in high-rate solidification events. Acquisition of three-dimensional reconstructions via micro-computed tomography combined with traditional metallography has allowed for qualitative and quantitative characterization of weld joints in a material system of wide use and broad applicability. The presence, variability and distribution of porosity, has been examined for average values, spatial distributions and morphology and then related back to fundamental processing parameters such as weld speed, weld power and laser focal length.4

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The constitutive behavior of laser welds in 304L stainless steel determined by digital image correlation

Cited by 62 publications

References 17 publications

Experimental and numerical study of strength mismatch in cross-weld tensile testing

Experimental and numerical study of strength mismatch in cross-weld tensile testing

Quantifying uncertainty from material inhomogeneity.

Porosity in millimeter-scale welds of stainless steel : three-dimensional characterization.

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