scholarly journals Effect of Residual Stresses on the Fatigue Behaviour of Torsion Bars

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1056 ◽  
Author(s):  
Vinko Močilnik ◽  
Nenad Gubeljak ◽  
Jožef Predan

This article deals with the effect of residual stresses on the fatigue behaviour of torsion bars exposed to cyclic torsional loading with different effective loading ratios, R. The residual compressive stresses on the surface were induced during technological processes by cold surface rolling and torsional overloading (presetting) into the plastic region due to the increase in the elastic linear range for torque. In the paper, we consider two different technological processes for introducing compressive residual stress on the surface of same material. We analysed the stress states affected by different residual and applied stress using the Drucker-Prager criterion in order to determine the actual stress state. Results show that the fatigue limit can be achieved if the maximum principal stresses (combined from residual and applied stresses) do not overcome the safe stress zone. As soon as the maximum principal stress reaches the edge of the safe zone, the number of cycles to failure rapidly reduces. Experimental results show that the effective loading ratio Reff, and consequently the stress amplitude, varies through the cross section of the bar. This initiates the fatigue crack under the surface, in the highest amplitude stress zone, independent of the effective loading ratio Reff. Consequently, increasing the compressive residual stresses on the surface by a second technological process has no significant effect on fatigue crack initiation in situ far from the surface. Increasing the plastic torsional prestress can shift the maximum stress amplitude far from the surface, but a significant volume of material should remain elastically loaded in order to ensure balance with compressive stresses from the surface of the solid bar section.

2021 ◽  
Vol 31 ◽  
pp. 3-7
Author(s):  
M. Mlikota ◽  
S. Schmauder ◽  
K. Dogahe ◽  
Ž. Božić

2019 ◽  
Vol 51 (3) ◽  
pp. 1208-1220
Author(s):  
J. B. Lévesque ◽  
J. Lanteigne ◽  
H. Champliaud ◽  
D. Paquet

AbstractFatigue damage is commonly encountered by operators of Francis type hydraulic turbine runners made of 13Cr-4Ni soft martensitic stainless steel. These large and complex welded casting assemblies are subjected to fatigue crack initiation and growth in the vicinity of their welded regions. It is well known that fatigue behavior is influenced by residual stresses and the microstructure. By including solid-state phase transformation models in welding simulations, phase distribution can be evaluated along with their respective volumetric change and their effect on residual stresses. Thus, it enables the assessment of welding process on fatigue crack behavior by numerical methods. This paper focuses on modeling solid-state phase transformations of 13Cr-4Ni soft martensitic stainless steel, used for manufacturing hydraulic turbine runners, occurring upon welding. It proposes to determine the material parameters of the models for both the austenitic and the martensitic transformation by nonisothermal dilatometry tests. The experiments are conducted in a quenching dilatometer with applied thermal conditions as experienced in the heat-affected zone of homogeneous welds. The activation energy and the kinetic parameters of the austenitic transformation from fully martensitic state are measured from the experimental results. The martensitic transformation modeling from a fully austenitic domain is also presented.


1989 ◽  
Vol 60 (8) ◽  
pp. 370-374
Author(s):  
Jacky Lesage ◽  
Didier Chicot ◽  
Mohamed Al Karaishi

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1200
Author(s):  
Bache ◽  
Davies ◽  
Davey ◽  
Thomas ◽  
Berment-Parr

The novel titanium alloy TIMETAL® 407 (Ti-407) has been developed as an alternative to Ti-6Al-4V (Ti-6-4), for applications that demand relatively high ductility and energy absorption. Demonstrating a combination of lower strength and greater ductility, the alloy introduces a variety of cost reduction opportunities, including improved machinability. Thermo-mechanical processing and its effects on microstructure and subsequent mechanical performance are characterised, including a detailed assessment of the fatigue and crack propagation properties. Demonstrating relatively strong behaviour under high-cycle fatigue loading, Ti-407 is nevertheless susceptible to time-dependent fatigue effects. Its sensitivity to dwell loading is quantified, and the associated deformation and fracture mechanisms responsible for controlling fatigue life are explored. The intimate relationship between thermo-mechanical processing, micro-texture and fatigue crack initiation through the generation of quasi-cleavage facets is highlighted. Consistent fatigue crack growth kinetics are demonstrated, independent of local microstructure.


2002 ◽  
Vol 16 (01n02) ◽  
pp. 181-188 ◽  
Author(s):  
CHANG-MIN SUH ◽  
BYUNG-WON HWANG ◽  
KYUNG-RYUL KIM

To evaluate the effect of coatings on the fatigue behaviors of turbine rotor steel, TiN and TiAlN films were deposited on the 1Cr-1Mo-0.25V steels by arc-ion plating (AIP) method with and wihtout screen ion filter. The coating thickness were varied with 2.5 μm, 3.5 μm, and 5.0 μm. A Cu-K α beam source was used as a characteristic X-ray and the crystal plane of (422) was selected to evaluate the residual stresses. In order to clear the relationship between fatigue behavior and residual stress of specimen coated with TiN and TiAlN films, the fatigue tests of specimens with and without coating were carried out at room temperatures respectively. It is shown that the fatigue life of the coated specimen was longer than that of uncoated specimen. The compressive residual stresses on the coatings were higher, and the fatigue crack initiated at an inclusion in the substrate near bond interface. It is known that compressive residual stress caused by hard coating would retard the fatigue crack initiation on the specimen surface, and then led to fatigue strength and fatigue life increasing.


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