Calculation of Stresses and Strains in Four‐Point Bending Creep Tests

Abstract

An analysis of strains and stresses in four-point bending creep tests in the limit of small beam deflections resulted in a general equation which relates the load-point deflection, the applied load, the creep exponent (N), and the geometrical parameters of the loading system. Measurements of load-point deflection rates, which are experimentally easy to accomplish in ceramic systems, vs the applied load lead to the direct determination of the creep exponent and the creep compliance in a steadystate creep test. The creep compliance is a function of the temperature, grain size, and all other factors except stress. The elastic equation relating the load-point deflection and the outer fiber strain is strictly valid for viscous creep and a p proximately valid for nonviscous creep (i.e. N>1) if the ratio of the distance between the support points to the distance between the load points is not very large.

Creep behavior of a carbon-derived Si3N4/SiC nanocomposite

“…The sample deflection was recorded continuously during the creep test. From the deflection data, the outer fibre strain was calculated as a function of time, t, by the method of Hollenberg et al 26 and taken as the creep strain, ". The creep rate was calculated from the slope of the " versus t curve.…”

High temperature fracture of boron carbide: experiments and simple theoretical models

“…The crosshead speed of the testing machinet was 0.1mmmin -1 throughout. This corresponded to a strain rate of about 2 • 10 -4 sec -1 [5]. In the calculated Klc value the compliance factor as given by Brown and Srawley [6] was used.…”

The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

“…Following binder burnout, the specimens were sintered using a two stage gas pressure sintering technique. The pre-sintering stage, were computed for the four-point bend specimen from the load-displacement data using the procedure developed by Hollenberg et al [27], Scanning electron micrographs were taken from both the polished and etched tensile surfaces and the fracture surfaces of the creep tested samples. Transmission electron microscopy samples were taken from the as-received material and the tensile face of partially deformed creep specimens.…”