Compliance calibration of the short rod chevron-notch specimen for fracture toughness testing of brittle materials

Abstract

The short rod chevron-notch specimen has the advantages of (1) crack development at the chevron tip during the early stage of test loading and (2) convenient calculation of Ktc from the maximum test load and a calibration factor which depends only on the specimen geometry and manner of loading. For generalized application, calibration of the specimen over a range of specimen proportions and chevron-notch configurations is necessary. Such was the objective of this investigation, wherein calibration of the short rod specimen was made by means of experimental compliance measurements converted into dimensionless stress intensity factor coefficients. List of symbolsa crack length a0 initial crack length (distance from line of load application to tip of chevron) al length of chevron notch at the surface (distance from line of load application to point of chevron emergence at specimen surface) a,~ crack length at minimum of Y* A constant of proportionality between Kit and Pmx used by Barker and Guest [4] C specimen compliance (load line displacement divided by load) C' = E' DC Ct, compliance of specimen with trapezoidal crack C~, = E'DC,, D specimen diameter E Young's modulus E' = E for plane stress, = E/(I -v 2) for plane strain KI mode I stress intensity factor Ktc plane-strain fracture toughness P load Pmax maximum load Y dimensionless stress intensity factor coefficient for a straight-through crack, = KDX/-W/P stress intensity factor for a trapezoidal crack, = KDX/-W/P,= y(~)l,2--y* dimensionless Y* minimum of Y* a = a/W ao = ao/ W al = adW am = am/W v Poisson's ratio

Three-Dimensional Finite-Element Analysis of Chevron-Notched Fracture Specimens

“…In the second method, an "average" stress-intensity factor along the The dU/da in equation ( 5 ) was determined from the values of U evaluated at different crack lengths, a. Consider three crack lengths (ai < a < ak) and their corresponding total strain energies, Ui, Uj, and uk.…”

A 3-D finite element analysis of a chevron-notched, three-point bend fracture specimen for ceramic materials

“…Additionally, the geometry of the chevron notch presents an in6reasingly larger crack front to the advancing crack, thus forcing the crack to extend in a stable manner over the complete area of the chevron notch. Therefore energy principles, numerical methods, or empirical techniques may be applied to solve for the stress intensity factors of the various chevronnotched, short bar [4,5], short rod [6,7], or three/four-point bend [8][9][10][11] specimens. These solutions may be readily applied to develop complete crack growth resistance curves (R-curves).…”

A Review of Chevron-Notched Fracture Specimens

“…Based on a convergence study [20], the analytical results are expected to lie about 1. proposed by Bubsey et al [18] for the rod specimens. The equation they used was equation (5) [7], it was recognized that equation (5) proposed by Munz et ale [7] for bar specimens.…”

“…Second, the experimental [13,15,18,19) and the recent analytical [20,21) 1). This specimen was designed in such a way that the same minimum stress-intensity factor was obtained as for his rod specimen [5).…”