Mechanisms and Mechanics of Fatigue Crack Propagation in Zr-Based Bulk Metallic Glass

2008 ◽  
Vol 378-379 ◽  
pp. 317-328 ◽  
Author(s):  
Yoshikazu Nakai ◽  
Makoto Seki
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Metallic Glass ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Loading Frequency ◽  
Stress Intensity Range ◽  
Intensity Range

In the present study, the fatigue crack propagation tests of Zr-based metallic glass were conducted in laboratory air, and the fracture surface was observed to clarify the effects of loading frequency and the stress ratio. In spite of being brittle material, the metallic glass showed stable fatigue crack propagation behaviour, and the relationship between the crack propagation rate, da/dN, and the stress intensity range, K, can be divided into three regions as well as conventional crystalline metals. The crack propagation rate can be expressed as a function of the stress intensity range by Paris law in the middle region. The power in Paris law was 1.4, and it is considerably smaller than the value for conventional crystalline metals. The threshold stress intensity range, Kth, was 1.8 MPam1/2. The effects of the stress ratio and the loading frequency were not observed on the relationships, da/dN-K and da/dN-Keff. Then, the fatigue crack propagation of the metallic glass is cycle dependent in laboratory air.

scholarly journals Effect of TiB Orientation on Near-Threshold Fatigue Crack Propagation in TiB-Reinforced Ti-3Al-2.5V Matrix Composites Treated with Heat Extrusion

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3685 ◽  
Author(s):  
Shoichi Kikuchi ◽  
Shunsuke Tamai ◽  
Takao Kawai ◽  
Yoshikazu Nakai ◽  
Hiroki Kurita ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Threshold Stress ◽  
Matrix Composites ◽  
Threshold Stress Intensity ◽  
Stress Intensity Range ◽  
Intensity Range

TiB-reinforced Ti-3Al-2.5V matrix composites, in which TiB whiskers are oriented parallel to the direction of heat extrusion, were fabricated via mechanical alloying and hot isostatic pressing (HIP). To investigate the near-threshold fatigue crack propagation in TiB-reinforced Ti-3Al-2.5V matrix composites, stress intensity factor K-decreasing tests were conducted for disk-shaped compact specimens having two different orientations of TiB whiskers at force ratios from 0.1 to 0.8 under ambient conditions. The crack growth rates, da/dN, for the composites incorporating TiB whiskers oriented perpendicular to the direction of crack growth were constantly lower than those obtained in the case where the orientation was parallel at the same stress intensity range ΔK, while the threshold stress intensity range, ΔKth, was higher. This effect can be explained by the increase in the degree of roughness-induced crack closure resulting from the perpendicular TiB, because fatigue cracks preferentially propagated across the boundaries between the matrix and the TiB in certain regions. In contrast, the effective threshold stress intensity range, ΔKeff,th, for composites was unaffected by the TiB orientation at low force ratios.

Elastic-Plastic Fracture of Cylindrical Shells Containing a Part-Through Circumferential Crack

1982 ◽  
Vol 104 (4) ◽  
pp. 323-330 ◽  
Author(s):  
H. Ezzat ◽  
F. Erdogan
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Propagation ◽  
Ductile Fracture ◽  
Fatigue Crack Propagation ◽  
Mouth Opening ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Crack Mouth Opening Displacement ◽  
Fracture Instability

In this paper the problem of fatigue crack propagation and ductile fracture of a cylindrical shell containing a macroscopic circumferential flaw is considered. The main interest in the study is in applications to line pipes and other cylindrical containers under secondary axial stresses in addition to the primary stresses coming from the internal pressure. The stress intensity factor for the part-through crack used in analyzing and correlating the fatigue crack propagation rate is obtained by using a line spring model in conjunction with Reissner’s shell theory. To analyze the ductile fracture instability and to correlate the experimental and theoretical results, the crack mouth opening displacement is used as the parameter. The experiments were performed on 20-in-dia (o.d.) and 0.34-in-thick X60 steel pipes. A 0.025-in-wide part-through circumferential flaw was introduced into the pipes as a crack starter which were then tested under four-point bending. The limited data on fatigue crack propagation give the expected result, namely that the crack propagation rate in pipes may be predicted from the fatigue results performed on simpler geometries provided the stress intensity factors in pipes are calculated with sufficient accuracy. The ductile fracture results show that the technique based on the asymptotic behavior of COD may be quite useful to determine a conservative estimate of the fracture instability load.

A Damage Accumulation Model for Fatigue Crack Propagation

1981 ◽  
Vol 103 (4) ◽  
pp. 293-297 ◽  
Author(s):  
C. Ihara ◽  
A. Igarashi
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Crack Propagation Rate ◽  
Stress Intensity Range ◽  
Dimensional Version ◽  
Damage Accumulation Model ◽  
Dislocation Multiplication

The fatigue crack propagation rate is investigated on the basis of a dislocation multiplication model which was used previously in evaluation of the fatigue life up to crack initiation. The expression for fatigue crack propagation rate is derived from a two-dimensional version of a stochastic model proposed by Tsurui and one of the authors (A.I.), and a distribution function of the life of material elements in this expression is calculated on the dislocation multiplication model. On these theoretical bases, it is shown that the fatigue crack propagation rate is proportional to some power of the stress intensity range. Our results are compared with the experimental data.

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