Two measurement techniques for determining effective stress intensity factors

Abstract

Two methods were studied for determining crack closure and locking effects under combinations of mixed mode I and II loading, namely the strain gauge and the surface replica methods. They demonstrated that strain gauges are able to detect the mode I crack closure but not mode II crack locking. As an alternative, the surface replica method is suggested as a practical technique for measuring mode II crack locking effects. The effective mode II stress intensity factor range can be estimated by comparison of the actual measured sliding range between a pair of crack faces and the theoretical sliding range.

Fatigue crack growth rates under sequential mixed‐mode I and II loading cycles

“…For Δ K IInom /Δ K Inom equal to 2, the test was performed with the exact degree of overlap, without the 10° incremental step after precracking. Figures 4 and 5 show the crack closure and locking ratios measured at various loading conditions 15 …”

“…We used here two concepts of (a) changing compliance and (b) comparison of displacements to estimate the crack closure and locking effects. For crack locking assessment, measured sliding displacements near the crack tip were compared to theoretical sliding displacements calculated by fracture mechanics, to determine the attenuation of the crack sliding motion 15 . Both strain gauge (mode I) and surface replica (mode II) methods were used in all tests.…”

“…where U I and U II are defined as the mode I crack closure ratio and the mode II crack locking ratio, respectively 15 . The formulae used to calculate the nominal values of mode I and mode II stress intensities 8 are expressed as:…”

Fatigue Crack Growth under Non-Proportional Mixed Mode Loading in Rail and Wheel Steel Part 1: Sequential Mode I and Mode II Loading

“…The crack length (a) was measured with a traveling microscope at the resolution of 1 µm. In addition, ∆K Ieff and ∆K IIeff were defined by the ratios of crack closure (U I )and locking (U II ), respectively [18] ∆K Ieff = U I ∆K I (3)…”

Modelado de grieta y estimación de vida en Fretting Fatiga mediante el Método de los Elementos Finitos Extendido X-FEM

“…Sus análisis mediante el método de los elementos finitos, mostraron una reducción del valor del ratio efectivo R eff con la disminución del valor de R. Wong et al (2000) estudiaron dos métodos para determinar el cierre de grieta y sus efectos bajo condiciones de carga en modo mixto:…”