Shear-mode Fatigue Crack Growth Research Articles

OS0711 せん断モード疲労き裂進展試験について(OS7-2 解析・評価・き裂I,OS-7 多軸応力下における疲労損傷および疲労き裂進展1)

It is recognized that flaking-type failure due to contact fatigue is closely related to the growth of the shear-mode (Modes II and III) fatigue crack. In our research group, it is demonstrated that a shear mode fatigue crack can be reproduced for the cylindrical specimens by applying the cyclic torsion in the presence of the static axial compressive stress. However, a biaxial servo-hydraulic fatigue testing machine used is quite expensive to purchase and costly to maintain. Low testing speed (〜10 Hz) of the testing machine further aggravates the situation. As a result, study on shear mode fatigue crack growth is still in nascent stage. To overcome those difficulties, we have developed a high performance and cost-effective testing machine to reproduce the shear mode fatigue crack growth by improving the available resonance-type torsion fatigue testing machine. The primary advantage of using the resonance-type torsion fatigue testing machine is cost-efficiency. In addition, the testing speed can be effectively improved in comparison with that of a biaxial servo-hydraulic fatigue testing machine.

3D shear-mode fatigue crack growth in maraging steel and Ti-6Al-4V

Fatigue crack growth tests in mixed-mode II + III were performed on maraging steel and Ti-6Al- 4V. The 3D evolutions of the crack fronts -measured by SEM after interrupted tests- were analyzed, taking into account the reduction in effective crack driving force by the interlocking and friction of the asperities of the crack surface. Under small-scale yielding conditions, the mixed-mode crack growth rates were found to correlate best with Keff2 II + 1.2Keff2 III in maraging steel, while for Ti-6Al-4V, Keff2 II + 0.9Keff2 III appeared suitable. For extended plasticity, a crack growth prediction method is proposed and validated for Ti-6Al-4V. This method is based on elastic-plastic F.E. computations and application, ahead of each node of the crack front, of a shear-dominated fatigue criterion.

A15 SUJ2におけるせん断型疲労き裂進展下限界におよぼすき裂面間摩擦の影響(OS5 材料の変形・破壊の計測・解析と損傷評価IV)

A15 SUJ2におけるせん断型疲労き裂進展下限界におよぼすき裂面間摩擦の影響(OS5 材料の変形・破壊の計測・解析と損傷評価IV)

214 SUJ2におけるせん断型疲労き裂の進展挙動と進展下限界(GS 材料力学(その3))

214 SUJ2におけるせん断型疲労き裂の進展挙動と進展下限界(GS 材料力学(その3))

Mechanism of Shear Mode Fatigue Crack Growth in Pure Aluminium

The mechanism of shear mode fatigue crack growth in pure aluminum was investigated using pre-cracked specimen. The crack propagation tests were carried out by the cyclic torsion with a static axial load and the push-pull, respectively. In the case of the cyclic torsion, the fatigue crack grew by shear mode. The micro-cracks initiated perpendicular and parallel to the direction of main crack growth during the cyclic torsion. However, the interactions were not observed between the main crack and the micro-cracks, which directed perpendicular to the direction of main crack growth. The behavior of micro-cracks on pure aluminum was different from that of 4340 steel in which the pure shear mode crack growth hard to occurred. The crack growth behavior is related to the slip systems of the materials. The number of slip plane and the friction resistance between molecules of aluminum are smaller than those of steel. These and the loading conditions are related to the mechanism of the shear mode crack growth in aluminum. Under condition in the prenent study, the relation between the crack propagation rate and the stress intensity factor range was almost the same in the cases of the push-pull and the cyclic torsion with tension. However, the effects of friction between the crack surfaces on the crack propagation in a shear mode were not exactly evaluated.

Fractographic Investigation of Shear Mode Fatigue Crack Growth in Mild Steel by Etch Pits

Fractographic Investigation of Shear Mode Fatigue Crack Growth in Mild Steel by Etch Pits

Dislocation structure associated with fracture surface of fatigued copper single crystals

Abstract By special technique of transmission electron microscopy a dislocation structure associated with shear mode fatigue crack growth is shown.