Determination of the Dynamic Stress Intensity Factor for the Four-Point Bend Impact Test

Abstract

A simple method for determination of the dynamic stress intensity factor (DSIF) variation with time during a four-point impact bend test has been proposed. A formula for DSIF calculation from the recorded loading has been obtained using modal superposition method. Results of calculations for different specimens have been compared with the experimental data and the results of the direct finite element analysis.Keywords: four-point impact bend test, modal superposition method, dynamic stress intensity factor 1. Introduction. Four-point bend (4PB) impact test can be used as an alternative to the conventional three-point bend (3PB) impact test for determination of the dynamic fracture toughness of brittle materials. Sometimes, this test has advantages over the 3PB one. First, in a 4PB test, the contact zone between the striker and the specimen is moved away from the crack tip. Thus, the stress field near the crack tip is less affected by this contact zone. Second, in a 4PB test the central part of the specimen is in pure bending. Therefore, this test can be more suitable if a crack-like defect in the modelled structure is loaded by pure bending too. Additionally, pure bending means that the crack in a 4PB test is loaded in a simpler way than in a 3PB one.To evaluate the dynamic fracture toughness, the dynamic stress intensity factor (DSIF) variation with time need to be either determined directly during the test or calculated from the test results.A mixed experimental-numerical DSIF determination was used previously by Rokach (1998) for one-point bending (1PB) and 3PB tests. This paper extends this approach to the 4PB impact test results.

Current challenges in modelling vibrational fatigue and fracture of structures: a review

“…In many situations, the stress intensity factor (SIF) is used to predict the stress state near the crack tip [122][123][124][125]. In dynamic loading, SIF is reinstated by the dynamic stress intensity factor (DSIF) [126][127][128][129][130][131][132][133]. In thermal loading condition, several literatures [123,[134][135][136][137][138][139][140][141][142][143][144][145][146][147][148] used thermal stress intensity factor (TSIF) to determine the thermal stress state.…”

“…The total value of K through time is expressed as Kabayashi and Ramulu [131] evaluated DSIF for unsymmetrical dynamic. Rokach and Łabędzki [128] proposed the method to determine the dynamic stress intensity factor for a four-point bend impact test. Wang et al [129] established a dynamic stress intensity factor applying the interaction integral method.…”

Crack initiation at high loading rates applying the four-point bending split Hopkinson pressure bar technique

“…During force equilibrium, F 1 and F 2 can be used to calculate K stat I and U p . Due to possible bending vibrations of the specimen, the dynamic stress intensity factor K dyn I was calculated according to Rokach [16][17][18]. The calculation of K dyn I (t) involves both the force in the incident bar and in the transmission bar.…”

“…The static calibration of the near-field strain gauge enabled the additional force measurement directly by the 01028-p.3 as calculated according to Rokach [16][17][18]. Material: 42CrMo4.…”