Authors: Wun Chet Davy Cheong, W.Z. Zhuang, Liang Chi Zhang
871
Authors: Imke Weich, Thomas Ummenhofer
Abstract: Research has been initiated on the effects of high frequency peening methods on the
fatigue strength. These methods combine an improvement of weld toe profile with an initiation of
compressive residual stresses and surface hardening. The effects of two techniques, High Frequency
Impact Treatment (HiFIT) and Ultrasonic Impact Treatemnt (UIT) are compared. Laser
measurements of the weld seam prove that both methods increase the overall weld toe radii.
Further, residual stress measurements verify the introduction of compressive residual stresses at
least up to a depth of 1 mm. The values meet the yield strength combined with an increase of the
surface hardness. These material mechanical effects cause an increased crack resistance. Crack
detection methods prove that the material mechanical effects yield to a retarded crack initiation.
Experimental results show that these effects lead to a significant increase of the fatigue strength and
reduced slopes of the SN-curves.
429
Authors: Muhammed Sohel Rana, Md. Shafiul Ferdous, Chobin Makabe, Masaki Fujikawa
Abstract: The enhancement method of fatigue life and the crack initiate and growth behavior of a holed specimen was investigated by using the 2024 Aluminum alloy and 0.45% Carbon steel. The purpose of present study is to propose a simple technical method for enhancement of fatigue life in a notched specimen. Also, the effect of local plastic deformation by cold work on fatigue crack initiation behavior was examined. This paper presents a basic experimental kinematic cold expansion method by inserting and removing a pin through the specimen hole. The shape of cross-section of pin was a circle or an ellipse. It was shown that the fatigue life of the specimen with the cold-worked hole was longer than that of the specimen with non-cold-worked hole for the case of same stress level in aluminum alloy and carbon steel. Also, the fatigue strength was higher in the case of the cold expanded hole. In this study, a methodology of lengthening of fatigue life of holed specimen is shown. Also, the improvement conditions of fatigue life were significantly affected by shape of pin, local hardening and residual stress conditions. The fatigue life improvement of the damaged component of structures was studied.
601
Authors: Shabnam Hosseini, Mohammad Bagher Limooei
Abstract: In this research, fatigue behaviour of Ti-6Al-4V alloy was investigated for smooth and notched specimens with stress concentration factor(Kt) 3.6 and 4.1. This investigation was conducted for various diameter bars having different ultimate strength.Rotating bending fatigue test at R= -1 was emploied for this research. Notch sensitivity data was compared with those of steels. The result indicated that the presence of notch in this alloy has a different amount of sensitivity when the notch specimens were subjected to high cycle fatigue (HCF) and low cycle fatigue(LCF) tests.The notch sensitivity of this alloy was shown generally to be much lower than steel alloys with similar ultimate strength values. Therefore,considering the low sensitivity to notch of this alloy, can be recommended for applications with the presence of notch such as biomedical application
7
Authors: Yu E Ma, Bao Qi Liu, Zhen Qiang Zhao
Abstract: Al-Li alloy 2198-T8 was used in the fuselage application. Integral fuselage panels were joined by double friction stir welds. Fatigue tests were conducted in the R=0.1. Notch was made between two welds. Residual stresses were measured and analyzed in the test samples with double welds. Cracks grew from the centre of two welds and across the two welds were observed, and crack growth rates were measured and compared with parent material. It is shown that crack growth rates are lower between double welds, and it is close to parent material after cross the two welds. The virtual crack closure technique (VCCT) method was used to calculate stress intensity factor from residual stress (Kres) in aim to explain the experimental findings.
651