Evaluation of fatigue crack propagation in surface modification layer by a load-controlled plate bending fatigue tester

Abstract

The objective of this study is to evaluate fatigue crack propagating behavior in surface modification layer treated by peening. A load-controlled plate bending fatigue tester has been developed in this study. This makes possible to evaluate relation between stress intensity factor range and fatigue crack growth rate, i.e., da/dN-K diagram, in the surface modification layer, since the tester keeps the load constant differently from a displacement-controlled tester. Although the displacement-controlled fatigue tester which keeps displacement constant has been widely used to evaluate the fatigue crack propagating behavior, an applied load, i.e., stress ratio, changes along with crack propagating. In this study, the fatigue crack propagation test was conducted on specimens treated by cavitation peening, which is one of the surface modification techniques, and mechanical properties were also evaluated, including residual stress, yield stress and Vickers hardness, so as to reveal the effect of such mechanical properties varied by the peeing on the fatigue crack propagating behavior. It was concluded that the da/dN-K diagram determined by the tester follows the Paris law and K at da/dN = 10-9 ~ 10-8 was increased more than twice by cavitation peening. The increment has a relation with the mechanical properties varied by the peening.

Comparison between Shot Peening, Cavitation Peening, and Laser Peening by Observation of Crack Initiation and Crack Growth in Stainless Steel

“…The length of the crack 2a was measured by a digital microscope at 1000× magnification. Under the present conditions, the relationships between 2a and b for the peened and non-peened specimens were the same [30]. The following relationship between 2a and b was obtained by observation of the crack shape, enabling b to be estimated by measuring 2a on the surface (see Figure 7 in the reference [30]).…”

“…The test frequency was 5 Hz and the stress ratio R was −1. The details of the bending fatigue test were shown in the references [29,30,32]. At the surface.…”

“…For the present experiments, 2a0, b0, C1 and C2 were At the surface. Specimens were tested at certain number of cycles, and put into the furnace to oxidize the crack propagation area, i.e., half elliptic region, and fractured (see Figure 6 in the reference [30]). The length of the crack 2a was measured by a digital microscope at 1000× magnification.…”

“…With a displacement controlled plane bending fatigue tester, the applied stress decreases as the crack area increases. Thus, a load controlled plane bending fatigue tester was developed [29], and using this, it was demonstrated that the threshold stress intensity factor range ∆K th and the stress intensity factor range increment ∆(∆K) were improved by cavitation peening [30]. The load controlled plane bending fatigue tester was used in these experiments to evaluate crack initiation and growth in surface layers treated by shot peening, cavitation peening, and laser peening.…”

Influence of vacuum carburizing treatment on fatigue crack growth characteristic in DSG2

“…It is a disposal method in which surface modification processing hardens the neighborhood of the surface of material, and an inside holds toughness. [1][2][3]. The surface modification processing methods include many processing methods including carburizing and a nitriding, such as a fine particle peening.…”