Initiation and propagation behaviors of small fatigue. Corrosion fatigue may be reduced by alloy additions, inhibition and cathodic protection, all of which reduce pitting. Figure 2 shows that specimen thickness has no significant influence in the crack growth behavior of this alloy except for r0 and for. Crack initiation and early growth behavior of tc4 titanium. C, 1978 influence of metallurgical factors on the fatigue crack growth rate in alpha beta titanium alloys, afmltr7868, air force materials laboratory, may. High cycle fatigue and fatigue crack propagation behaviors of. The results suggest that for crack growth rates above 10. Environments were aqueous solutions of sodium chloride nacl, sodium hydroxide naoh. Salama, fellow asme senior research fellow, conoco inc. In the absence of residual stresses, fatigue crack propagation depends on the materials microstructural features. Investigation of fatigue crack initiation in ti6al4v during tensile. Effect of hip treatment on fatigue crack growth behavior. Results showed that surface cracks initiated from the interfaces between. Effects of microstructure on the fatigue crack growth.
Fatigue crack growth rate fcgr tests were conducted on titanium alloy ti5111 weld metal in air, artificial seawater, and artificial seawater with an applied cathodic potential. Compression fatigue behavior and failure mechanism of porous. Beachmarking and scanning electron microscopy sem techniques are used to study fatigue crack growth rates and crack shape evolution in the short and long crack regimes. Mar 16, 2020 it is known that the ra region is the characteristic zone of crack initiation for titanium alloys with em failed in hcf and. Fatigue crack growth of beta21s titanium alloy under. Random loading fatigue crack growth behavior of some aluminum. A schematic is shown of the fatigue crack growth rate behavior in the nearthreshold and paris regimes. The corrosion fatigue crack growth fcg behavior, the effect of applied potential on corrosion fcg rates, and the fracture surfaces of vt20 near. The results indicate that the fatigue crack growth rate of the hiped samples is higher than that of the asfabricated one under certain stress intensity factor. It has been shown in the past that the presence of residual stresses, introduced during processing, dictates the fatigue performance 14. Fatigue crack growth behavior is a crucial factor for the design and performance of modern structural materials. The crack growth rate dadn generally increases with the stress ratio r.
Random loading fatigue crack growth behavior of some. Fatigue crack growth characteristics of thin sheet. Fatigue crack growth rate behavior in the threshold and nearthreshold regimes is very important for the growth of small cracks for highcycle propeller and engine components. The effect of hot isostatic pressing treatment on the fatigue crack growth behavior of ti6al4v alloy fabricated by electron beam melting was investigated. Effects of microstructure on fatigue behavior of alphabeta. Fatigue crack growth behavior of titanium alloy ti6al4v and weldment article in journal of offshore mechanics and arctic engineering 1233 august 2001 with 81 reads how we measure reads. Porous titanium possesses higher normalized fatigue strength which is in the range of 0. This article investigated the fatigue crack growth behaviors in the novel tc32 titanium alloy with bimodal and basketweave microstructures, which were respectively obtained by the convectional. Fatigue crack growth and fracture behavior of ascast ti43. With increased attention given to high cycle fatigue 12 as one of the potential failure modes in military aircraft engine disks and blades made of titanium alloys.
On the fatigue behavior of gbased titanium aluminides. Results showed that at the same level of tensile performance, the basketweave microstructure had a lower fatigue crack growth rate than the. Small fatigue crack growth behavior of titanium alloy tc4. Corrosion fatigue crack growth behavior of titanium alloys. Fatigue and crackgrowth behavior in a titanium alloy. Since corrosion fatigue cracks initiate at a metals surface, surface treatments like plating. Since titanium alloys have high strength to weight ratio, reasonable strength at the moderately high temperature, good fracture and fatigue crack growth resistance, good corrosion resistance and biocompatibility. Effects of microstructure on fatigue behavior of alpha. In many cases, their behavior under the cyclic loading becomes the critical factor on which the. Nearthreshold fatigue crack growth behavior of finegrain. Introduction in cases where fatigue lives primarily depend on the early stages of crack growth, it is critical to understand the fatigue crack growth fcg characteristics in the nearthreshold regime. Effect of hip treatment on fatigue crack growth behavior of. Additionally, a strong sensitivity of fatigue crack growth to mean stress was also found with the omega precipitation. The btitanium alloys achieve their high strengths through the precipitation of fine aparticles in a bmatrix.
Fatigue crack growth behavior of titanium alloys is examined using the unified approach developed by the authors. This requirement manifests as two fracture mechanics parameters. The rate of fatigue crack propagation for ti6al6v2sn and ti6 a14v in aqueous environments has been measured as a function of solution chemistry, frequency, and stress wave form. Corrosion fatigue crack growth of titanium alloys in aqueous.
Lawless ge aircraft engines one neumann way cincinnati, oh 45215 m. Environments were aqueous solutions of sodium chloride nacl, sodium hydroxide naoh, potassium hydroxide koh, ferric chloride fecl 3, and. Prediction of cold dwellfatigue crack growth of titanium. Fracturemechanics concepts are applied in correlating and comparing the.
Based upon nominal deltak values, constant amplitude fatigue crack growth behavior at 175 c was either similar to r 0. Region i is the fatigue threshold region where the dk is too low to propagate a crack. Threshold conditions for fodinduced hcf failures in both ti6246 and ti6al4v titanium alloys were proposed based on a modified kitagawatakahashi diagram, where the limiting conditions are described in terms of the smoothbar fatigue limit at small crack sizes and the worstcase largecrack fatiguecrack growth threshold. Teng hu jiangsu province key laboratory of aerospace power system, college of energy and power engineering, nanjing university of aeronautics and astronautics, nanjing, jiangsu, china. Abstract in this paper, the small fatigue crack behavior of titanium alloy tc4 at different stress ratios was investigated. It is known that the ra region is the characteristic zone of crack initiation for titanium alloys with em failed in hcf and. Region ii encompasses data where the rate of crack growth changes roughly linearly with a change in stress intensity fluctuation. Fatigue crack growth behavior of titanium alloys request pdf. Compression fatigue behavior and failure mechanism of. Corrosion fatigue crack growth of titanium alloys in. Uniform tensiontension loadings were applied to centrally cracked panels, and the fatigue crack growth behavior was observed. The corrosion fatigue crack growth fcg behavior, the effect of applied potential on corrosion fcg rates, and the fracture surfaces of vt20 nearalpha and ts6 nearbeta titanium alloys were studied. Residual stress analysis and fatigue behavior of mechanically. In terms of fatigue crack growth response, omega phase increased the resistance to crack growth.
Fatigue crack initiation in ti6al4v has been investigated in high cycle fatigue. Fatigue crack growth behavior of titanium alloy ti6al4v. Relationships among the microstructure, mechanical properties. Prediction of cold dwellfatigue crack growth of titanium alloys. Crack growth rates increase with decreasing frequency in. The current paper is another demonstration of using the principles of fracture mechanics to predict the fatigue behavior of notched specimens made of a titanium alloy. Although the stress ratio has a significant effect on the total fatigue life and crack initiation life at constant. K fatigue crack growth behavior of titanium alloys is examined using the unified approach developed by the authors. Accelerated nearthreshold fatigue crack growth behavior of. Crack initiation and early growth behavior of tc4 titanium alloy under high cycle fatigue and very high cycle fatigue volume 33 issue 8 wei li, ning gao, hongqiao zhao, xinxin xing.
As the stress ratio r is increased, a pronounced increase in fatigue crack growth rate is typically observed in the. Fatigue crack growth rate rir2r3 paris regime near threshold regime crack tip stress intensity factor range figure 1. Fatigue crack growth behavior of titanium alloy ti6al4v and weldment mamdouh m. Fatigue crack growth behavior of titanium alloys sciencedirect. Small fatigue crack growth behavior of titanium alloy tc4 at. Small fatigue crack growth behavior of titanium alloy tc4 at different. An investigation of the effects of microstructure on. The initiation and propagation behaviors of small fatigue crack in tc4 were investigated in the present work. The b titanium alloys achieve their high strengths through the precipitation of fine aparticles in a bmatrix. An evaluation of fatigue behavior of various titanium alloys was also made. Internal crack characteristics in veryhighcycle fatigue of. Fatigue crack growth resistance and crack closure behavior in.
Fatigue crack growth resistance and crack closure behavior. Fractures are initiated either by pitting or persistent slip bands. The microstructures of ti6al4v are complex and strongly affect its mechanical properties and fatigue behavior. On the mechanical behaviour of titanium alloy tial6v4. Fatigue crack growth behavior in gradient microstructure of hardened. The approach is based on the realization that fatigue requires two load parameters for unambiguous description. Relationships among the microstructure, mechanical. Fatigue crack growth behaviors in novel tc32 titanium alloy. Fatigue crack growth behavior of ti6al4v alloy forging. Fatigue crack growth mechanisms of long and small cracks were investigated in cast and wrought aluminum and titanium alloys with various microstructures ascast a535, 6061t61, and milland beta annealed ti6al4v.
The studies reveal that surface crack growth rate data are generally comparable to the throughcrack growth rate data in the long crack growth regime. Fatigue crack growth behavior of titanium alloy ti6al4v and. Surface replication on the basis of a twopart silicon mixture and confocal laser scanning microscope were used to record and observe the small crack initiation and growth processes at room temperature in air. Several of the referenced studies have been conducted to evaluate the effect of microstructure andor heat treatment on crack growth behavior of ti6al4v alloy. Therefore, comparison of the fatigue crack growth behavior for only tl and lt oriented mechanical test specimens is not adequate to evaluate the effect of texture on the fatigue crack growth behavior for the cross rolled ti 62222 sheet product. These limited data, however, suggest that the crack growth. It is validated by comparing prediction results with the experimental data of several titanium alloys with different microstructures, dwell time, hydrogen contents, stress ratios and stress levels. Internal crack characteristics in veryhighcycle fatigue. The studies reveal that surface crack growth rate data are generally comparable to the through crack growth rate data in the long crack growth regime. Fatigue crack growth behavior and microstructural mechanisms in ti. Accelerated nearthreshold fatigue crack growth behavior. K fatigue in aqueous media is an electrochemical behavior. The approach is based on the realization that fatigue requires two load parameters.
Alloys studied include 7075t6 bare aluminum alloy, 2024t3 bare aluminum alloy, ti8al1mo1v duplex and mill anneal, and ti6al4v mill anneal. Effect of stress ratio and specimen thickness on fatigue crack growth rate for alloy 2017t4. Initiation and propagation behaviors of small fatigue crack. Fatigue crack growth characteristics of thin sheet titanium. Depending on the specific encironment, three types of fatigue crack growth rate behavior have been observed as a function of frequency. The crack growth behavior in tialloys is complicated by several factors such as microstructure and its dependent flow properties, planarity and heterogeneity of. Corrosion fatigue crack growth behavior of titanium alloys in.
Aug 29, 2018 small fatigue crack growth behavior of titanium alloy tc4 at different stress ratios xu. Both cyclic ratcheting and fatigue crack growth contribute to the fatigue failure mechanism, while the cyclic ratcheting is the dominant one. A limited number of studies are reported on the sn fatigue or fatigue crack growth behavior of ti10v2fe3al alloy, which is used in the aircraft structures. The fatigue crack propagation behavior of many materials can be divided into three regions as shown in the image. Oct 01, 2005 fatigue crack growth behavior of titanium alloys is examined using the unified approach developed by the authors.
944 1290 1081 1401 943 1539 900 459 257 300 718 172 420 205 1109 1586 1061 1277 153 1487 1448 224 16 102 333 590 1406 1212 159 478 320 1135 1261 1242 1556 15 37 374 275 1087 263 1060 287 44 541 56 778 858 1398