Studying on the Propagation Behavior of Bent Crack Bending from Slant Pre-Crack with Compressive Residual Stress

2012 ◽  
Vol 433-440 ◽  
pp. 6558-6564
Author(s):  
You Li Ma
Keyword(s):  
Residual Stress ◽  
Mixed Mode ◽  
Compressive Residual Stress ◽  
Intensity Factors ◽  
Slant Angle ◽  
Fracture Angle ◽  
Bending Fatigue ◽  
Stress Criterion ◽  
Propagation Behavior ◽  
Discontinuous Displacement

For a slant pre-crack under mixed-mode conditions, a method is proposed in which mode Ⅰ and mode Ⅱ stress intensity factors ‹KI›mes and ‹KII›mes can be directly evaluated from the discontinuous displacement along it. The effect on fatigue pre-crack deformation behavior was discussed by comparing fatigue and annealed cracks. In general, using the biggest tangential stress criterion the direction propagating from the pre-cracks can be predicted by ‹KI›mes and ‹KII›mes calculated above. So testing for bending fatigue crack propagation under mixed-mode conditions was carried out using fatigue and annealed slant pre-cracks with slant angle β=450 defined as the angle between loading and pre-crack direction in a rectangular plate. As a result, for annealed pre-crack, the estimated fracture angle θestcorresponded to the measured oneθmes ; On the other hand, for fatigue pre-crack,θmes is bigger than θest because of the compressive residual stress around the pre-crack .

Studying on the Propagation Behavior of Bent Crack Bending from Slant Pre-Crack with Compressive Residual Stress

2011 ◽  
Vol 383-390 ◽  
pp. 3086-3091
Author(s):  
You Li Ma
Keyword(s):  
Residual Stress ◽  
Mixed Mode ◽  
Compressive Residual Stress ◽  
Intensity Factors ◽  
Slant Angle ◽  
Fracture Angle ◽  
Bending Fatigue ◽  
Stress Criterion ◽  
Propagation Behavior ◽  
Discontinuous Displacement

For a slant pre-crack under mixed-mode conditions, a method is proposed in which mode Ⅰ and mode Ⅱ stress intensity factors(KI)mes and (KII)mes can be directly evaluated from the discontinuous displacement along it. The effect on fatigue pre-crack deformation behavior was discussed by comparing fatigue and annealed cracks. In general, using the biggest tangential stress criterion the direction propagating from the pre-cracks can be predicted by (KI)mes and (KII)mes calculated above. So testing for bending fatigue crack propagation under mixed-mode conditions was carried out using fatigue and annealed slant pre-cracks with slant angle β=450 defined as the angle between loading and pre-crack direction in a rectangular plate. As a result, for annealed pre-crack, the estimated fracture angle θest corresponded to the measured one θmes; On the other hand, for fatigue pre-crack,θmes is bigger than θest because of the compressive residual stress around the pre-crack.

Effect of Residual Stress Field in Front of the Slant Precrack Tip on Bent Fatigue Crack Propagation

2007 ◽  
Vol 353-358 ◽  
pp. 1207-1210 ◽  
Author(s):  
Kenichi Shimizu ◽  
Tashiyuki Torii ◽  
J. Nyuya ◽  
Y. Ma
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Stress Field ◽  
Mixed Mode ◽  
Compressive Residual Stress ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Residual Stress Field ◽  
Method Analysis ◽  
Crack Sliding Displacement

Fatigue crack bending and propagation behaviors were studied under mixed-mode conditions using annealed and fatigue slant precracks. The bent fatigue crack initiated from the fatigue slant precrack propagated under mixed-mode conditions with mode II stress intensity factor evaluated from the crack sliding displacement measured along the crack. On the other hand, bent fatigue cracks propagated under the mode I condition for an annealed slant precrack specimen. The forces which suppress the crack opening/sliding were calculated along the slant precrack and the bent crack by FEM (Finite Element Method) analysis. As a result, the crack opening suppress forces were generated by the compressive residual stress around the fatigue slant precrack, while the forces which promote the crack sliding were caused by the residual stress field in front of the fatigue slant precrack.

Mode I and Mode II Stress Intensity Factors Based on Crack Opening and Sliding Displacements

2011 ◽  
Vol 179-180 ◽  
pp. 1417-1422
Author(s):  
You Li Ma
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Stress Ratio ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Intensity Factors ◽  
Slant Angle ◽  
Measured Stress ◽  
Discontinuous Displacement ◽  
Made In

It is necessary to study crack opening and sliding discontinuous displacement behavior under mixed-mode conditions because parts or structures of a machine with a crack maybe subject to stress from various directions. In this study ,therefore, using the cracks with different slant angle, which are made in circle stress of modeⅠwith stress ratio of R=0, the opening and sliding discontinuous displacements are measured ,so that modeⅠand mode Ⅱ stress intensity factors (KⅠ)mes and (KⅡ)mes at the crack tip are calculated. As a result, the measured stress intensity factors value of (KⅠ)mes from the fatigue crack with the slant angle β=60 deg. is smaller than the theoretical one (KⅠ). But for mode Ⅱ,(KⅡ)mes is about the same with (KⅡ). On the other hand, for the fatigue cracks with smaller slant angle β=45 deg.,(KⅡ)mes declined because of the crack-surface contact while (KⅠ)mes reduced.

Improvement of Fatigue Properties in a Cast Aluminum Alloy by Roller Burnishing and Friction Stir Processing

2014 ◽  
Vol 891-892 ◽  
pp. 662-667 ◽  
Author(s):  
Yuki Nakamura ◽  
Masaki Nakajima ◽  
Hiroaki Masuda ◽  
Toshifumi Kakiuchi ◽  
Yoshihiko Uematsu
Keyword(s):  
Residual Stress ◽  
Aluminum Alloy ◽  
Friction Stir Processing ◽  
Compressive Residual Stress ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cast Aluminum Alloy ◽  
Cast Aluminum ◽  
Bending Fatigue ◽  
Friction Stir

Roller burnishing (RB) and friction stir processing (FSP) were applied to a cast aluminum alloy, AC4CH-T6 (equivalent to A356-T6), to improve the fatigue properties. In roller burnished specimens, Vickers hardness was increased until the depth of 60μm compared with that of the as-cast specimens, resulting in work-hardening by RB. The compressive residual stress on the surface of the roller burnished specimens was also increased from 35MPa to 132MPa. In order to investigate the effect of RB on the fatigue properties, rotary bending fatigue tests have been performed using the roller burnished and the as-cast specimens. The roller burnished specimens exhibited higher fatigue strength than the untreated specimens. It is due to the increase in hardness and compressive residual stress by RB. In addition, plane bending fatigue tests have been performed using the friction stir processed and untreated specimens. Fatigue strengths of the friction stir processed specimens were highly improved compared with untreated specimens as the results of the elimination of casting defects by FSP. However, the crack growth rates of the friction stir processed specimens were faster than those of untreated specimens. It is due to the softening of the material by heat input during the FSP.

Sign in / Sign up

Export Citation Format

Share Document