Single-edge Bend Research Articles

Application of two parameter elastic-plastic fracture mechanics to analysis of structures

J-integral resistance curves are developed for single edge bend [SE(B)] specimens of HY80 over a range of crack length ratios from 0.13 to 0.83. The wide range of constraint present over this range of crack length ratios results in J-integral resistance curves with nearly constant initiation toughnesses as measured by J Ic, but with widely varying J- R curve slopes beyond J Ic. A nearly linear relationship is shown to exist between the slope of the material J-resistance curve after 1 mm of crack extension and the Q parameter introduced by O'Dowd and Shih (Family of crack-tip fields characterized by a triaxiality parameter: Part I—Structure of fields. Journal of Mechanics and Physics of Solids, 1991, 39(8), 989–1015) to quantify elastic-plastic constraint. The constancy of J Ic and the linear dependence of the tearing resistance on Q is used to develop an interpolation scheme to evaluate the J-integral resistance curve applicable to a specific structural application when the Q parameter can be estimated for the flaw geometry and loading present in the application.

A Modified Normalization Method for Developing J-R and CTOD-R Curves with the LMN Function

Abstract A direct method for obtaining J-R curves and δ-R curves from load-crack mouth opening displacement data is proposed. The method uses the direct method proposed by Landes, Herrera, Zhou, and Lee, based on the geometric normalization suggested by Ernst for deeply cracked bend specimens, to develop calibration curves that relate load, crack mouth opening displacement, and crack length. Given two of these parameters, the third can be calculated from the calibration curves. These curves are developed by assuming a power law plus a straight line functional form with unknown L, M, and N constants and evaluating the unknowns at three calibration points in the test. The method is studied for a HY-80 steel for four test temperatures and 50 mm-width, 25 mm-thickness side-notched single-edge bend specimens.

Inelastic Response of a Deep Crack Single-Edge Notch Specimen Under Impact Loading

Abstract Three-dimensional dynamic analyses are performed for a single-edge bend, SE(B), fracture specimen (a/W = 0.5) subjected to impact loading. Loading rates obtained in routine drop tower tests (terminal load-line velocity of 100 in./s or 2.54 m/s) are applied in the analyses. Explicit time integration coupled with an efficient element integration scheme is used to compute the dynamic response of the specimen. Strainrate sensitivity is introduced via a new, efficient implementation of the Bodner-Partom viscoplastic constitutive model. Material properties for A533B steel (a medium strength pressure vessel steel) are used in the analyses. Static analyses of the same SE(B) specimens provide baseline results from which inertial effects are assessed. Similarly, dynamic analyses using a strain-rate insensitive material provide a reference for the assessment of strain rate effects. Strains at key locations and the support reactions are extracted from the analyses to assess the accuracy of static formulas commonly used to estimate applied J values. In ertial effects on the applied J are quantified by examining the acceleration component of J. Results show that dynamic effects for the steel analyzed are negligible after twice a characteristic time that can be defined in terms of the first elastic period of the specimen.

CRACK CLOSURE AND FATIGUE CRACK GROWTH RATE IN THREE POINT BEND SPECIMENS OF DIFFERENT WIDTHS

Abstract— The crack closure stress intensity factor values and fatigue crack growth rates were determined in Three Point Single Edge Bend, SE(B), specimens prepared from rails manufactured using two different grades of rail steels. The width, and correspondingly the span, of the SE(B) specimens were varied eight fold; the thickness of all the specimens being the same. It is observed that the crack closure stress intensity factor values decrease with an increase in the width of SE(B) specimens. At a given value of ΔKeff, the fatigue crack growth rate (FCGR) is independent of the width. However, at a given value of ΔKeff, the FCGR is observed to decrease with increasing width. In view of the above results, the scope of application of the FCGR laws based on an effective stress intensity factor to the life prediction of components, requires careful examination.