Optical and analytical investigation of overloads in biaxial fatigue cracks

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ABSTRACT.A study on the approximation of the stress field in the vicinity of crack tip in a compact tension specimen made from Al 2024-T351 is presented. Crack tip stress tensor components are expressed using the linear elastic fracture mechanics (LEFM) theory in this work, more precisely via its multi-parameter formulation, i.e. by Williams power series (WPS). Determination of coefficients of terms of this series is performed using a least squares-based regression technique known as over deterministic method (ODM) for which displacements data obtained experimentally via optical measurements are taken as inputs. The stress fields reconstructed based on the displacement data obtained experimentally by means of optical measurements are verified by means of the stress field approximations derived for the normalized CT specimen via hybrid elements.

Section: Materials Al 2024 and Methods Of Measurementmentioning

confidence: 99%

Williams expansion-based approximation of the stress field in an Al 2024 body with a crack from optical measurements

Seitl¹,

Malíková²,

Sobek³

et al. 2017

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“…The chemical composition for this steel is: 0.17% C, 1.235% Mn, 0.225% Si, 0.010% P, 0.0006% S, 0.032% Al, 0.072% Cr, 0.058% Ni and 0.016% Mo. This is a low carbon steel, and has been widely used in the structural applications in the construction, manufacturing, ship building and offshore industries [21] that combines good fatigue resistance with low environmental impact for applications where no energy is consumed during the use phase of the component [22]. Monotonic tension, compression and torsion tests were conducted to evaluate the monotonic properties of the St52-3N steel (Tab.…”

Section: Methodsmentioning

confidence: 99%

Evaluation of new multiaxial damage parameters on low carbon steel

Cruces¹,

López-Crespo²,

Moreno³

et al. 2017

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Most mechanical components are subjected to the complex fatigue loading conditions, where both amplitude and direction of loading cycles change over the time. The estimation of damage caused by these complex loading scenarios are often done by simplified uniaxial fatigue theories, which ultimately leads to higher factor of safety during the final design considerations. Critical plane-based fatigue theories have been considered more accurate for computing the fatigue damage for multiaxial loading conditions in comparison to energy-based and equivalent stress-based theories. Two recently developed fatigue theories have been evaluated in this work for the available test data. Test data includes significant amount of biaxial load paths.

“…The camera was positioned so that the crack propagation direction was parallel to the positive x coordinate. The crack opening direction was parallel to the y coordinate [17]. Such pre-arranging simplifies the post-processing of the results [18], in particular for non pure mode I cracks (i.e.…”

Section: Full-field Experimental Measurement Of Displacementsmentioning

confidence: 99%

“…Understanding the evolution of higher order terms for different geometries is key to predict the constraint of elastic-plastic crack tip fields [9]. Consequently, a large effort has been devoted in recent times to develop algorithms for fast determination of higher order terms and to improve the accuracy in the estimation of higher order terms [10][11][12][13] both quasi-statically [14] and in dynamic situations [15]. Digital Image Correlation technique (DIC) was applied successfully on NiTi pseudoelastic alloy for evaluation of fracture toughness and another fracture properties [16].…”

Section: Introductionmentioning

confidence: 99%

“…Digital Image Correlation technique (DIC) was applied successfully on NiTi pseudoelastic alloy for evaluation of fracture toughness and another fracture properties [16]. In the papers [17,18,[23][24][25][26][27], the displacement field in the surrounding of a crack tip of single edge geometry specimens was employed in conjunction with Williams power series to estimate the stress intensity factor (SIF). The higher-order terms effects were analysed by using Williams expansion (focusing of T-stress) for various sizes of the crack tip distance of applied region for fitting data.…”

Section: Introductionmentioning

confidence: 99%

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Approximation of the crack-tip field in fatigue cracks in bridge steel specimens: DIC analysis of different constraint levels

Seitl¹,

Miarka

Ruzicka

et al. 2019

A study on the accuracy of the approximation of the displacement field around of crack tip in a sample made from bridge steel (S355) is main objective of contribution. Linear elastic fracture mechanics (LEFM) theory in framework of multi-parameter formulation, i.e. postulated by Williams is used to determine of coefficients of Williams power series terms. Over deterministic method was used to calculate the terms based on the least squares regression technique, applied on data from numerical simulation and experiment on S355 steel grades. Comparison between the stress fields (by principal stress  1 and von Mises stress  HMH) obtain from experimental measurement DIC, Hybrid method and obtain from reconstruction by using various number of Williams power terms are quantified in order to get key information around the crack tip region on bridge steel specimens.