Željko Domazet

Comparison of fatigue crack retardation methods

Abstract The efficiency of several fatigue crack retarding methods are examined. Al-alloy flat specimens with a central “key hole” starter notch were tested in a closed-loop servo hydraulic test machine. After the cracks had propagated to a predefined value, the following crack retarding methods were undertaken: repair welding, welded metal reinforcements, adhesively bonded CFRP patches, single peak tensile overloads and fatigue crack arrest holes. Fatigue test programmes were performed with constant load amplitudes and spectrum tensile loads. The results show that expanded and filled crack arrest holes, and CFRP patches applied to both sides, are the best fatigue crack retarding methods with all load conditions.

Application of gradient based IR thermography to the GRP structures inspection

The article presents application of non destructive testing method based on the pulse heating infrared thermography used to detect material anomalies for the case of glass reinforced polymer structures. The goal of presented research, based on the thermal gradient approach, is to establish the procedure capable of filtering out anomalies from other thermal influences caused by thermal reflections of surrounding objects, geometry influences and heat flows for observed object.

Life extension of fatigue damaged components

The complete procedure for the repair of fatigue damaged metal components is suggested and explained in this paper. All necessary steps are described and the most important one - the choice of the adequate fatigue crack retarding method - is supported with the fatigue test results of several fatigue crack repair methods. One group of fatigue tests deals with welding repairs as the most frequent repair procedure. The measures for fatigue strength improvements of repair weldments are described as well. Another group of specimens was tested with next fatigue crack retarding methods: metal reinforcement, CFRP patches, different crack arrest holes and tensile overloads. Structural stress factor was introduced as a crucial for the behavior of the repaired component.

The influence of rolling speed on the fatigue life of rolls with grooves

In the hot rolling process, rolls with grooves are used for the production of various simple and complex profiles. Main factors influencing the fatigue life of these rolls result from the technological process of the rolling. Rolling speed is an important parameter of technological process which has great influence on overall production. In order to increase rolling production, an analysis of the rolling speed influence on the fatigue life of the rolls has been carried out. The fatigue life estimation is carried out according to the fatigue life stress concept based on the local stress. Stress spectra in critical areas are determined for three different roll speeds. The analysis shows that although increasing the rolling speed causes decrease of the fatigue life of the roll, the stresses caused by the rolling at the highest speed should not lead to roll fracture.

Fatigue Strength of the Rolls with Grooves

In Steelworks Split failures of the rolls with grooves on the 3-high-roughing mill stand occurred four times. Detailed analysis of all the elements which influenced the failure was carried out. Stress analysis shownthatthe most critical area of the roll is the 7.a caliber what is corresponding with fracture positions. The fatigue strength of the material in the caliber groove for fatigue life prediction was missing and fatigue strength is determined by experimental testing.